[llvm-commits] CVS: llvm-www/releases/1.3/docs/AliasAnalysis.html Bugpoint.html BytecodeFormat.html CFEBuildInstrs.html CodeGenerator.html CodingStandards.html CommandLine.html ExtendingLLVM.html FAQ.html GarbageCollection.html GettingStarted.html HowToSubmitABug.html index.html LangRef.html LLVMVsTheWorld.html ObjectFiles.html OpenProjects.html ProgrammersManual.html Projects.html ReleaseNotes.html SourceLevelDebugging.html Stacker.html SystemLibrary.html TableGenFundamentals.html TestingGuide.html WritingAnLLVMPass.html
John Criswell
criswell at cs.uiuc.edu
Fri Aug 13 15:03:15 PDT 2004
Changes in directory llvm-www/releases/1.3/docs:
AliasAnalysis.html added (r1.1)
Bugpoint.html added (r1.1)
BytecodeFormat.html added (r1.1)
CFEBuildInstrs.html added (r1.1)
CodeGenerator.html added (r1.1)
CodingStandards.html added (r1.1)
CommandLine.html added (r1.1)
ExtendingLLVM.html added (r1.1)
FAQ.html added (r1.1)
GarbageCollection.html added (r1.1)
GettingStarted.html added (r1.1)
HowToSubmitABug.html added (r1.1)
index.html added (r1.1)
LangRef.html added (r1.1)
LLVMVsTheWorld.html added (r1.1)
ObjectFiles.html added (r1.1)
OpenProjects.html added (r1.1)
ProgrammersManual.html added (r1.1)
Projects.html added (r1.1)
ReleaseNotes.html added (r1.1)
SourceLevelDebugging.html added (r1.1)
Stacker.html added (r1.1)
SystemLibrary.html added (r1.1)
TableGenFundamentals.html added (r1.1)
TestingGuide.html added (r1.1)
WritingAnLLVMPass.html added (r1.1)
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+ <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"
+ "http://www.w3.org/TR/html4/strict.dtd">
+ <html>
+ <head>
+ <title>LLVM Alias Analysis Infrastructure</title>
+ <link rel="stylesheet" href="llvm.css" type="text/css">
+ </head>
+ <body>
+
+ <div class="doc_title">
+ LLVM Alias Analysis Infrastructure
+ </div>
+
+ <ol>
+ <li><a href="#introduction">Introduction</a></li>
+
+ <li><a href="#overview"><tt>AliasAnalysis</tt> Class Overview</a>
+ <ul>
+ <li><a href="#pointers">Representation of Pointers</a></li>
+ <li><a href="#alias">The <tt>alias</tt> method</a></li>
+ <li><a href="#ModRefInfo">The <tt>getModRefInfo</tt> methods</a></li>
+ <li><a href="#OtherItfs">Other useful <tt>AliasAnalysis</tt> methods</a></li>
+ </ul>
+ </li>
+
+ <li><a href="#writingnew">Writing a new <tt>AliasAnalysis</tt> Implementation</a>
+ <ul>
+ <li><a href="#passsubclasses">Different Pass styles</a></li>
+ <li><a href="#requiredcalls">Required initialization calls</a></li>
+ <li><a href="#interfaces">Interfaces which may be specified</a></li>
+ <li><a href="#chaining"><tt>AliasAnalysis</tt> chaining behavior</a></li>
+ <li><a href="#updating">Updating analysis results for transformations</a></li>
+ <li><a href="#implefficiency">Efficiency Issues</a></li>
+ </ul>
+ </li>
+
+ <li><a href="#using">Using alias analysis results</a>
+ <ul>
+ <li><a href="#loadvn">Using the <tt>-load-vn</tt> Pass</a></li>
+ <li><a href="#ast">Using the <tt>AliasSetTracker</tt> class</a></li>
+ <li><a href="#direct">Using the <tt>AliasAnalysis</tt> interface directly</a></li>
+ </ul>
+ </li>
+
+ <li><a href="#exist">Existing alias analysis implementations and clients</a>
+ <ul>
+ <li><a href="#impls">Available <tt>AliasAnalysis</tt> implementations</a></li>
+ <li><a href="#aliasanalysis-xforms">Alias analysis driven transformations</a></li>
+ <li><a href="#aliasanalysis-debug">Clients for debugging and evaluation of
+ implementations</a></li>
+ </ul>
+ </li>
+ </ol>
+
+ <div class="doc_author">
+ <p>Written by <a href="mailto:sabre at nondot.org">Chris Lattner</a></p>
+ </div>
+
+ <!-- *********************************************************************** -->
+ <div class="doc_section">
+ <a name="introduction">Introduction</a>
+ </div>
+ <!-- *********************************************************************** -->
+
+ <div class="doc_text">
+
+ <p>Alias Analysis (aka Pointer Analysis) is a class of techniques which attempt
+ to determine whether or not two pointers ever can point to the same object in
+ memory. There are many different algorithms for alias analysis and many
+ different ways of classifying them: flow-sensitive vs flow-insensitive,
+ context-sensitive vs context-insensitive, field-sensitive vs field-insensitive,
+ unification-based vs subset-based, etc. Traditionally, alias analyses respond
+ to a query with a <a href="#MustNoMay">Must, May, or No</a> alias response,
+ indicating that two pointers always point to the same object, might point to the
+ same object, or are known to never point to the same object.</p>
+
+ <p>The LLVM <a
+ href="http://llvm.cs.uiuc.edu/doxygen/classllvm_1_1AliasAnalysis.html"><tt>AliasAnalysis</tt></a>
+ class is the primary interface used by clients and implementations of alias
+ analyses in the LLVM system. This class is the common interface between clients
+ of alias analysis information and the implementations providing it, and is
+ designed to support a wide range of implementations and clients (but currently
+ all clients are assumed to be flow-insensitive). In addition to simple alias
+ analysis information, this class exposes Mod/Ref information from those
+ implementations which can provide it, allowing for powerful analyses and
+ transformations to work well together.</p>
+
+ <p>This document contains information necessary to successfully implement this
+ interface, use it, and to test both sides. It also explains some of the finer
+ points about what exactly results mean. If you feel that something is unclear
+ or should be added, please <a href="mailto:sabre at nondot.org">let me
+ know</a>.</p>
+
+ </div>
+
+ <!-- *********************************************************************** -->
+ <div class="doc_section">
+ <a name="overview"><tt>AliasAnalysis</tt> Class Overview</a>
+ </div>
+ <!-- *********************************************************************** -->
+
+ <div class="doc_text">
+
+ <p>The <a
+ href="http://llvm.cs.uiuc.edu/doxygen/classllvm_1_1AliasAnalysis.html"><tt>AliasAnalysis</tt></a>
+ class defines the interface that the various alias analysis implementations
+ should support. This class exports two important enums: <tt>AliasResult</tt>
+ and <tt>ModRefResult</tt> which represent the result of an alias query or a
+ mod/ref query, respectively.</p>
+
+ <p>The <tt>AliasAnalysis</tt> interface exposes information about memory,
+ represented in several different ways. In particular, memory objects are
+ represented as a starting address and size, and function calls are represented
+ as the actual <tt>call</tt> or <tt>invoke</tt> instructions that performs the
+ call. The <tt>AliasAnalysis</tt> interface also exposes some helper methods
+ which allow you to get mod/ref information for arbitrary instructions.</p>
+
+ </div>
+
+ <!-- ======================================================================= -->
+ <div class="doc_subsection">
+ <a name="pointers">Representation of Pointers</a>
+ </div>
+
+ <div class="doc_text">
+
+ <p>Most importantly, the <tt>AliasAnalysis</tt> class provides several methods
+ which are used to query whether or not two memory objects alias, whether
+ function calls can modify or read a memory object, etc. For all of these
+ queries, memory objects are represented as a pair of their starting address (a
+ symbolic LLVM <tt>Value*</tt>) and a static size.</p>
+
+ <p>Representing memory objects as a starting address and a size is critically
+ important for correct Alias Analyses. For example, consider this (silly, but
+ possible) C code:</p>
+
+ <div class="doc_code">
+ <pre>
+ int i;
+ char C[2];
+ char A[10];
+ /* ... */
+ for (i = 0; i != 10; ++i) {
+ C[0] = A[i]; /* One byte store */
+ C[1] = A[9-i]; /* One byte store */
+ }
+ </pre>
+ </div>
+
+ <p>In this case, the <tt>basicaa</tt> pass will disambiguate the stores to
+ <tt>C[0]</tt> and <tt>C[1]</tt> because they are accesses to two distinct
+ locations one byte apart, and the accesses are each one byte. In this case, the
+ LICM pass can use store motion to remove the stores from the loop. In
+ constrast, the following code:</p>
+
+ <div class="doc_code">
+ <pre>
+ int i;
+ char C[2];
+ char A[10];
+ /* ... */
+ for (i = 0; i != 10; ++i) {
+ ((short*)C)[0] = A[i]; /* Two byte store! */
+ C[1] = A[9-i]; /* One byte store */
+ }
+ </pre>
+ </div>
+
+ <p>In this case, the two stores to C do alias each other, because the access to
+ the <tt>&C[0]</tt> element is a two byte access. If size information wasn't
+ available in the query, even the first case would have to conservatively assume
+ that the accesses alias.</p>
+
+ </div>
+
+ <!-- ======================================================================= -->
+ <div class="doc_subsection">
+ <a name="alias">The <tt>alias</tt> method</a>
+ </div>
+
+ <div class="doc_text">
+ The <tt>alias</tt> method is the primary interface used to determine whether or
+ not two memory objects alias each other. It takes two memory objects as input
+ and returns MustAlias, MayAlias, or NoAlias as appropriate.
+ </div>
+
+ <!-- _______________________________________________________________________ -->
+ <div class="doc_subsubsection">
+ <a name="MustMayNo">Must, May, and No Alias Responses</a>
+ </div>
+
+ <div class="doc_text">
+
+ <p>An Alias Analysis implementation can return one of three responses:
+ MustAlias, MayAlias, and NoAlias. The No and May alias results are obvious: if
+ the two pointers can never equal each other, return NoAlias, if they might,
+ return MayAlias.</p>
+
+ <p>The MustAlias response is trickier though. In LLVM, the Must Alias response
+ may only be returned if the two memory objects are guaranteed to always start at
+ exactly the same location. If two memory objects overlap, but do not start at
+ the same location, return MayAlias.</p>
+
+ </div>
+
+ <!-- ======================================================================= -->
+ <div class="doc_subsection">
+ <a name="ModRefInfo">The <tt>getModRefInfo</tt> methods</a>
+ </div>
+
+ <div class="doc_text">
+
+ <p>The <tt>getModRefInfo</tt> methods return information about whether the
+ execution of an instruction can read or modify a memory location. Mod/Ref
+ information is always conservative: if an instruction <b>might</b> read or write
+ a location, ModRef is returned.</p>
+
+ <p>The <tt>AliasAnalysis</tt> class also provides a <tt>getModRefInfo</tt>
+ method for testing dependencies between function calls. This method takes two
+ call sites (CS1 & CS2), returns NoModRef if the two calls refer to disjoint
+ memory locations, Ref if CS1 reads memory written by CS2, Mod if CS1 writes to
+ memory read or written by CS2, or ModRef if CS1 might read or write memory
+ accessed by CS2. Note that this relation is not commutative. Clients that use
+ this method should be predicated on the <tt>hasNoModRefInfoForCalls()</tt>
+ method, which indicates whether or not an analysis can provide mod/ref
+ information for function call pairs (most can not). If this predicate is false,
+ the client shouldn't waste analysis time querying the <tt>getModRefInfo</tt>
+ method many times.</p>
+
+ </div>
+
+
+ <!-- ======================================================================= -->
+ <div class="doc_subsection">
+ <a name="OtherItfs">Other useful <tt>AliasAnalysis</tt> methods</a>
+ </div>
+
+ <div class="doc_text">
+
+ <p>
+ Several other tidbits of information are often collected by various alias
+ analysis implementations and can be put to good use by various clients.
+ </p>
+
+ </div>
+
+ <!-- _______________________________________________________________________ -->
+ <div class="doc_subsubsection">
+ The <tt>getMustAliases</tt> method
+ </div>
+
+ <div class="doc_text">
+
+ <p>The <tt>getMustAliases</tt> method returns all values that are known to
+ always must alias a pointer. This information can be provided in some cases for
+ important objects like the null pointer and global values. Knowing that a
+ pointer always points to a particular function allows indirect calls to be
+ turned into direct calls, for example.</p>
+
+ </div>
+
+ <!-- _______________________________________________________________________ -->
+ <div class="doc_subsubsection">
+ The <tt>pointsToConstantMemory</tt> method
+ </div>
+
+ <div class="doc_text">
+
+ <p>The <tt>pointsToConstantMemory</tt> method returns true if and only if the
+ analysis can prove that the pointer only points to unchanging memory locations
+ (functions, constant global variables, and the null pointer). This information
+ can be used to refine mod/ref information: it is impossible for an unchanging
+ memory location to be modified.</p>
+
+ </div>
+
+
+ <!-- _______________________________________________________________________ -->
+ <div class="doc_subsubsection">
+ <a name="simplemodref">The <tt>doesNotAccessMemory</tt> and
+ <tt>onlyReadsMemory</tt> methods</a>
+ </div>
+
+ <div class="doc_text">
+
+ <p>These methods are used to provide very simple mod/ref information for
+ function calls. The <tt>doesNotAccessMemory</tt> method returns true for a
+ function if the analysis can prove that the function never reads or writes to
+ memory, or if the function only reads from constant memory. Functions with this
+ property are side-effect free and only depend on their input arguments, allowing
+ them to be eliminated if they form common subexpressions or be hoisted out of
+ loops. Many common functions behave this way (e.g., <tt>sin</tt> and
+ <tt>cos</tt>) but many others do not (e.g., <tt>acos</tt>, which modifies the
+ <tt>errno</tt> variable).</p>
+
+ <p>The <tt>onlyReadsMemory</tt> method returns true for a function if analysis
+ can prove that (at most) the function only reads from non-volatile memory.
+ Functions with this property are side-effect free, only depending on their input
+ arguments and the state of memory when they are called. This property allows
+ calls to these functions to be eliminated and moved around, as long as there is
+ no store instruction that changes the contents of memory. Note that all
+ functions that satisfy the <tt>doesNotAccessMemory</tt> method also satisfies
+ <tt>onlyReadsMemory</tt>.</p>
+
+ </div>
+
+
+
+ <!-- *********************************************************************** -->
+ <div class="doc_section">
+ <a name="writingnew">Writing a new <tt>AliasAnalysis</tt> Implementation</a>
+ </div>
+ <!-- *********************************************************************** -->
+
+ <div class="doc_text">
+
+ <p>Writing a new alias analysis implementation for LLVM is quite
+ straight-forward. There are already several implementations that you can use
+ for examples, and the following information should help fill in any details.
+ For a examples, take a look at the <a href="#impls">various alias analysis
+ implementations</a> included with LLVM.</p>
+
+ </div>
+
+ <!-- ======================================================================= -->
+ <div class="doc_subsection">
+ <a name="passsubclasses">Different Pass styles</a>
+ </div>
+
+ <div class="doc_text">
+
+ <p>The first step to determining what type of <a
+ href="WritingAnLLVMPass.html">LLVM pass</a> you need to use for your Alias
+ Analysis. As is the case with most other analyses and transformations, the
+ answer should be fairly obvious from what type of problem you are trying to
+ solve:</p>
+
+ <ol>
+ <li>If you require interprocedural analysis, it should be a
+ <tt>Pass</tt>.</li>
+ <li>If you are a function-local analysis, subclass <tt>FunctionPass</tt>.</li>
+ <li>If you don't need to look at the program at all, subclass
+ <tt>ImmutablePass</tt>.</li>
+ </ol>
+
+ <p>In addition to the pass that you subclass, you should also inherit from the
+ <tt>AliasAnalysis</tt> interface, of course, and use the
+ <tt>RegisterAnalysisGroup</tt> template to register as an implementation of
+ <tt>AliasAnalysis</tt>.</p>
+
+ </div>
+
+ <!-- ======================================================================= -->
+ <div class="doc_subsection">
+ <a name="requiredcalls">Required initialization calls</a>
+ </div>
+
+ <div class="doc_text">
+
+ <p>Your subclass of <tt>AliasAnalysis</tt> is required to invoke two methods on
+ the <tt>AliasAnalysis</tt> base class: <tt>getAnalysisUsage</tt> and
+ <tt>InitializeAliasAnalysis</tt>. In particular, your implementation of
+ <tt>getAnalysisUsage</tt> should explicitly call into the
+ <tt>AliasAnalysis::getAnalysisUsage</tt> method in addition to doing any
+ declaring any pass dependencies your pass has. Thus you should have something
+ like this:</p>
+
+ <div class="doc_code">
+ <pre>
+ void getAnalysisUsage(AnalysisUsage &AU) const {
+ AliasAnalysis::getAnalysisUsage(AU);
+ <i>// declare your dependencies here.</i>
+ }
+ </pre>
+ </div>
+
+ <p>Additionally, your must invoke the <tt>InitializeAliasAnalysis</tt> method
+ from your analysis run method (<tt>run</tt> for a <tt>Pass</tt>,
+ <tt>runOnFunction</tt> for a <tt>FunctionPass</tt>, or <tt>InitializePass</tt>
+ for an <tt>ImmutablePass</tt>). For example (as part of a <tt>Pass</tt>):</p>
+
+ <div class="doc_code">
+ <pre>
+ bool run(Module &M) {
+ InitializeAliasAnalysis(this);
+ <i>// Perform analysis here...</i>
+ return false;
+ }
+ </pre>
+ </div>
+
+ </div>
+
+ <!-- ======================================================================= -->
+ <div class="doc_subsection">
+ <a name="interfaces">Interfaces which may be specified</a>
+ </div>
+
+ <div class="doc_text">
+
+ <p>All of the <a
+ href="/doxygen/classllvm_1_1AliasAnalysis.html"><tt>AliasAnalysis</tt></a>
+ virtual methods default to providing <a href="#chaining">chaining</a> to another
+ alias analysis implementation, which ends up returning conservatively correct
+ information (returning "May" Alias and "Mod/Ref" for alias and mod/ref queries
+ respectively). Depending on the capabilities of the analysis you are
+ implementing, you just override the interfaces you can improve.</p>
+
+ </div>
+
+
+
+ <!-- ======================================================================= -->
+ <div class="doc_subsection">
+ <a name="chaining"><tt>AliasAnalysis</tt> chaining behavior</a>
+ </div>
+
+ <div class="doc_text">
+
+ <p>With only two special exceptions (the <tt><a
+ href="#basic-aa">basicaa</a></tt> and <a href="#no-aa"><tt>no-aa</tt></a>
+ passes) every alias analysis pass chains to another alias analysis
+ implementation (for example, the user can specify "<tt>-basicaa -ds-aa
+ -anders-aa -licm</tt>" to get the maximum benefit from the three alias
+ analyses). The alias analysis class automatically takes care of most of this
+ for methods that you don't override. For methods that you do override, in code
+ paths that return a conservative MayAlias or Mod/Ref result, simply return
+ whatever the superclass computes. For example:</p>
+
+ <div class="doc_code">
+ <pre>
+ AliasAnalysis::AliasResult alias(const Value *V1, unsigned V1Size,
+ const Value *V2, unsigned V2Size) {
+ if (...)
+ return NoAlias;
+ ...
+
+ <i>// Couldn't determine a must or no-alias result.</i>
+ return AliasAnalysis::alias(V1, V1Size, V2, V2Size);
+ }
+ </pre>
+ </div>
+
+ <p>In addition to analysis queries, you must make sure to unconditionally pass
+ LLVM <a href="#updating">update notification</a> methods to the superclass as
+ well if you override them, which allows all alias analyses in a change to be
+ updated.</p>
+
+ </div>
+
+
+ <!-- ======================================================================= -->
+ <div class="doc_subsection">
+ <a name="updating">Updating analysis results for transformations</a>
+ </div>
+
+ <div class="doc_text">
+ <p>
+ Alias analysis information is initially computed for a static snapshot of the
+ program, but clients will use this information to make transformations to the
+ code. All but the most trivial forms of alias analysis will need to have their
+ analysis results updated to reflect the changes made by these transformations.
+ </p>
+
+ <p>
+ The <tt>AliasAnalysis</tt> interface exposes two methods which are used to
+ communicate program changes from the clients to the analysis implementations.
+ Various alias analysis implementations should use these methods to ensure that
+ their internal data structures are kept up-to-date as the program changes (for
+ example, when an instruction is deleted), and clients of alias analysis must be
+ sure to call these interfaces appropriately.
+ </p>
+ </div>
+
+ <!-- _______________________________________________________________________ -->
+ <div class="doc_subsubsection">The <tt>deleteValue</tt> method</div>
+
+ <div class="doc_text">
+ The <tt>deleteValue</tt> method is called by transformations when they remove an
+ instruction or any other value from the program (including values that do not
+ use pointers). Typically alias analyses keep data structures that have entries
+ for each value in the program. When this method is called, they should remove
+ any entries for the specified value, if they exist.
+ </div>
+
+ <!-- _______________________________________________________________________ -->
+ <div class="doc_subsubsection">The <tt>copyValue</tt> method</div>
+
+ <div class="doc_text">
+ The <tt>copyValue</tt> method is used when a new value is introduced into the
+ program. There is no way to introduce a value into the program that did not
+ exist before (this doesn't make sense for a safe compiler transformation), so
+ this is the only way to introduce a new value. This method indicates that the
+ new value has exactly the same properties as the value being copied.
+ </div>
+
+ <!-- _______________________________________________________________________ -->
+ <div class="doc_subsubsection">The <tt>replaceWithNewValue</tt> method</div>
+
+ <div class="doc_text">
+ This method is a simple helper method that is provided to make clients easier to
+ use. It is implemented by copying the old analysis information to the new
+ value, then deleting the old value. This method cannot be overridden by alias
+ analysis implementations.
+ </div>
+
+ <!-- ======================================================================= -->
+ <div class="doc_subsection">
+ <a name="implefficiency">Efficiency Issues</a>
+ </div>
+
+ <div class="doc_text">
+
+ <p>From the LLVM perspective, the only thing you need to do to provide an
+ efficient alias analysis is to make sure that alias analysis <b>queries</b> are
+ serviced quickly. The actual calculation of the alias analysis results (the
+ "run" method) is only performed once, but many (perhaps duplicate) queries may
+ be performed. Because of this, try to move as much computation to the run
+ method as possible (within reason).</p>
+
+ </div>
+
+ <!-- *********************************************************************** -->
+ <div class="doc_section">
+ <a name="using">Using alias analysis results</a>
+ </div>
+ <!-- *********************************************************************** -->
+
+ <div class="doc_text">
+
+ <p>There are several different ways to use alias analysis results. In order of
+ preference, these are...</p>
+
+ </div>
+
+ <!-- ======================================================================= -->
+ <div class="doc_subsection">
+ <a name="loadvn">Using the <tt>-load-vn</tt> Pass</a>
+ </div>
+
+ <div class="doc_text">
+
+ <p>The <tt>load-vn</tt> pass uses alias analysis to provide value numbering
+ information for <tt>load</tt> instructions and pointer values. If your analysis
+ or transformation can be modeled in a form that uses value numbering
+ information, you don't have to do anything special to handle load instructions:
+ just use the <tt>load-vn</tt> pass, which uses alias analysis.</p>
+
+ </div>
+
+ <!-- ======================================================================= -->
+ <div class="doc_subsection">
+ <a name="ast">Using the <tt>AliasSetTracker</tt> class</a>
+ </div>
+
+ <div class="doc_text">
+
+ <p>Many transformations need information about alias <b>sets</b> that are active
+ in some scope, rather than information about pairwise aliasing. The <tt><a
+ href="/doxygen/classllvm_1_1AliasSetTracker.html">AliasSetTracker</a></tt> class
+ is used to efficiently build these Alias Sets from the pairwise alias analysis
+ information provided by the <tt>AliasAnalysis</tt> interface.</p>
+
+ <p>First you initialize the AliasSetTracker by using the "<tt>add</tt>" methods
+ to add information about various potentially aliasing instructions in the scope
+ you are interested in. Once all of the alias sets are completed, your pass
+ should simply iterate through the constructed alias sets, using the
+ <tt>AliasSetTracker</tt> <tt>begin()</tt>/<tt>end()</tt> methods.</p>
+
+ <p>The <tt>AliasSet</tt>s formed by the <tt>AliasSetTracker</tt> are guaranteed
+ to be disjoint, calculate mod/ref information and volatility for the set, and
+ keep track of whether or not all of the pointers in the set are Must aliases.
+ The AliasSetTracker also makes sure that sets are properly folded due to call
+ instructions, and can provide a list of pointers in each set.</p>
+
+ <p>As an example user of this, the <a href="/doxygen/structLICM.html">Loop
+ Invariant Code Motion</a> pass uses <tt>AliasSetTracker</tt>s to calculate alias
+ sets for each loop nest. If an <tt>AliasSet</tt> in a loop is not modified,
+ then all load instructions from that set may be hoisted out of the loop. If any
+ alias sets are stored to <b>and</b> are must alias sets, then the stores may be
+ sunk to outside of the loop, promoting the memory location to a register for the
+ duration of the loop nest. Both of these transformations only apply if the
+ pointer argument is loop-invariant.</p>
+
+ </div>
+
+ <!-- _______________________________________________________________________ -->
+ <div class="doc_subsubsection">
+ The AliasSetTracker implementation
+ </div>
+
+ <div class="doc_text">
+
+ <p>The AliasSetTracker class is implemented to be as efficient as possible. It
+ uses the union-find algorithm to efficiently merge AliasSets when a pointer is
+ inserted into the AliasSetTracker that aliases multiple sets. The primary data
+ structure is a hash table mapping pointers to the AliasSet they are in.</p>
+
+ <p>The AliasSetTracker class must maintain a list of all of the LLVM Value*'s
+ that are in each AliasSet. Since the hash table already has entries for each
+ LLVM Value* of interest, the AliasesSets thread the linked list through these
+ hash-table nodes to avoid having to allocate memory unnecessarily, and to make
+ merging alias sets extremely efficient (the linked list merge is constant time).
+ </p>
+
+ <p>You shouldn't need to understand these details if you are just a client of
+ the AliasSetTracker, but if you look at the code, hopefully this brief
+ description will help make sense of why things are designed the way they
+ are.</p>
+
+ </div>
+
+ <!-- ======================================================================= -->
+ <div class="doc_subsection">
+ <a name="direct">Using the <tt>AliasAnalysis</tt> interface directly</a>
+ </div>
+
+ <div class="doc_text">
+
+ <p>If neither of these utility class are what your pass needs, you should use
+ the interfaces exposed by the <tt>AliasAnalysis</tt> class directly. Try to use
+ the higher-level methods when possible (e.g., use mod/ref information instead of
+ the <a href="#alias"><tt>alias</tt></a> method directly if possible) to get the
+ best precision and efficiency.</p>
+
+ </div>
+
+ <!-- *********************************************************************** -->
+ <div class="doc_section">
+ <a name="exist">Existing alias analysis implementations and clients</a>
+ </div>
+ <!-- *********************************************************************** -->
+
+ <div class="doc_text">
+
+ <p>If you're going to be working with the LLVM alias analysis infrastructure,
+ you should know what clients and implementations of alias analysis are
+ available. In particular, if you are implementing an alias analysis, you should
+ be aware of the <a href="#aliasanalysis-debug">the clients</a> that are useful
+ for monitoring and evaluating different implementations.</p>
+
+ </div>
+
+ <!-- ======================================================================= -->
+ <div class="doc_subsection">
+ <a name="impls">Available <tt>AliasAnalysis</tt> implementations</a>
+ </div>
+
+ <div class="doc_text">
+
+ <p>This section lists the various implementations of the <tt>AliasAnalysis</tt>
+ interface. With the exception of the <a href="#no-aa"><tt>-no-aa</tt></a> and
+ <a href="#basic-aa"><tt>-basicaa</tt></a> implementations, all of these <a
+ href="#chaining">chain</a> to other alias analysis implementations.</p>
+
+ </div>
+
+ <!-- _______________________________________________________________________ -->
+ <div class="doc_subsubsection">
+ <a name="no-aa">The <tt>-no-aa</tt> pass</a>
+ </div>
+
+ <div class="doc_text">
+
+ <p>The <tt>-no-aa</tt> pass is just like what it sounds: an alias analysis that
+ never returns any useful information. This pass can be useful if you think that
+ alias analysis is doing something wrong and are trying to narrow down a
+ problem.</p>
+
+ </div>
+
+ <!-- _______________________________________________________________________ -->
+ <div class="doc_subsubsection">
+ <a name="basic-aa">The <tt>-basicaa</tt> pass</a>
+ </div>
+
+ <div class="doc_text">
+
+ <p>The <tt>-basicaa</tt> pass is the default LLVM alias analysis. It is an
+ aggressive local analysis that "knows" many important facts:</p>
+
+ <ul>
+ <li>Distinct globals, stack allocations, and heap allocations can never
+ alias.</li>
+ <li>Globals, stack allocations, and heap allocations never alias the null
+ pointer.</li>
+ <li>Different fields of a structure do not alias.</li>
+ <li>Indexes into arrays with statically differing subscripts cannot alias.</li>
+ <li>Many common standard C library functions <a
+ href="#simplemodref">never access memory or only read memory</a>.</li>
+ <li>Pointers that obviously point to constant globals
+ "<tt>pointToConstantMemory</tt>".</li>
+ <li>Function calls can not modify or references stack allocations if they never
+ escape from the function that allocates them (a common case for automatic
+ arrays).</li>
+ </ul>
+
+ </div>
+
+ <!-- _______________________________________________________________________ -->
+ <div class="doc_subsubsection">
+ <a name="globalsmodref">The <tt>-globalsmodref-aa</tt> pass</a>
+ </div>
+
+ <div class="doc_text">
+
+ <p>This pass implements a simple context-sensitive mod/ref and alias analysis
+ for internal global variables that don't "have their address taken". If a
+ global does not have its address taken, the pass knows that no pointers alias
+ the global. This pass also keeps track of functions that it knows never access
+ memory or never read memory. This allows certain optimizations (e.g. GCSE) to
+ eliminate call instructions entirely.
+ </p>
+
+ <p>The real power of this pass is that it provides context-sensitive mod/ref
+ information for call instructions. This allows the optimizer to know that
+ calls to a function do not clobber or read the value of the global, allowing
+ loads and stores to be eliminated.</p>
+
+ <p>Note that this pass is somewhat limited in its scope (only support
+ non-address taken globals), but is very quick analysis.</p>
+ </div>
+
+ <!-- _______________________________________________________________________ -->
+ <div class="doc_subsubsection">
+ <a name="anders-aa">The <tt>-anders-aa</tt> pass</a>
+ </div>
+
+ <div class="doc_text">
+
+ <p>The <tt>-anders-aa</tt> pass implements the well-known "Andersen's algorithm"
+ for interprocedural alias analysis. This algorithm is a subset-based,
+ flow-insensitive, context-insensitive, and field-insensitive alias analysis that
+ is widely believed to be fairly precise. Unfortunately, this algorithm is also
+ O(N<sup>3</sup>). The LLVM implementation currently does not implement any of
+ the refinements (such as "online cycle elimination" or "offline variable
+ substitution") to improve its efficiency, so it can be quite slow in common
+ cases.
+ </p>
+
+ </div>
+
+ <!-- _______________________________________________________________________ -->
+ <div class="doc_subsubsection">
+ <a name="steens-aa">The <tt>-steens-aa</tt> pass</a>
+ </div>
+
+ <div class="doc_text">
+
+ <p>The <tt>-steens-aa</tt> pass implements a variation on the well-known
+ "Steensgaard's algorithm" for interprocedural alias analysis. Steensgaard's
+ algorithm is a unification-based, flow-insensitive, context-insensitive, and
+ field-insensitive alias analysis that is also very scalable (effectively linear
+ time).</p>
+
+ <p>The LLVM <tt>-steens-aa</tt> pass implements a "speculatively
+ field-<b>sensitive</b>" version of Steensgaard's algorithm using the Data
+ Structure Analysis framework. This gives it substantially more precision than
+ the standard algorithm while maintaining excellent analysis scalability.</p>
+
+ </div>
+
+ <!-- _______________________________________________________________________ -->
+ <div class="doc_subsubsection">
+ <a name="ds-aa">The <tt>-ds-aa</tt> pass</a>
+ </div>
+
+ <div class="doc_text">
+
+ <p>The <tt>-ds-aa</tt> pass implements the full Data Structure Analysis
+ algorithm. Data Structure Analysis is a modular unification-based,
+ flow-insensitive, context-<b>sensitive</b>, and speculatively
+ field-<b>sensitive</b> alias analysis that is also quite scalable, usually at
+ O(n*log(n)).</p>
+
+ <p>This algorithm is capable of responding to a full variety of alias analysis
+ queries, and can provide context-sensitive mod/ref information as well. The
+ only major facility not implemented so far is support for must-alias
+ information.</p>
+
+ </div>
+
+
+ <!-- ======================================================================= -->
+ <div class="doc_subsection">
+ <a name="aliasanalysis-xforms">Alias analysis driven transformations</a>
+ </div>
+
+ <div class="doc_text">
+ LLVM includes several alias-analysis driven transformations which can be used
+ with any of the implementations above.
+ </div>
+
+ <!-- _______________________________________________________________________ -->
+ <div class="doc_subsubsection">
+ <a name="adce">The <tt>-adce</tt> pass</a>
+ </div>
+
+ <div class="doc_text">
+
+ <p>The <tt>-adce</tt> pass, which implements Aggressive Dead Code Elimination
+ uses the <tt>AliasAnalysis</tt> interface to delete calls to functions that do
+ not have side-effects and are not used.</p>
+
+ </div>
+
+
+ <!-- _______________________________________________________________________ -->
+ <div class="doc_subsubsection">
+ <a name="licm">The <tt>-licm</tt> pass</a>
+ </div>
+
+ <div class="doc_text">
+
+ <p>The <tt>-licm</tt> pass implements various Loop Invariant Code Motion related
+ transformations. It uses the <tt>AliasAnalysis</tt> interface for several
+ different transformations:</p>
+
+ <ul>
+ <li>It uses mod/ref information to hoist or sink load instructions out of loops
+ if there are no instructions in the loop that modifies the memory loaded.</li>
+
+ <li>It uses mod/ref information to hoist function calls out of loops that do not
+ write to memory and are loop-invariant.</li>
+
+ <li>If uses alias information to promote memory objects that are loaded and
+ stored to in loops to live in a register instead. It can do this if there are
+ no may aliases to the loaded/stored memory location.</li>
+ </ul>
+
+ </div>
+
+ <!-- _______________________________________________________________________ -->
+ <div class="doc_subsubsection">
+ <a name="argpromotion">The <tt>-argpromotion</tt> pass</a>
+ </div>
+
+ <div class="doc_text">
+ <p>
+ The <tt>-argpromotion</tt> pass promotes by-reference arguments to be passed in
+ by-value instead. In particular, if pointer arguments are only loaded from it
+ passes in the value loaded instead of the address to the function. This pass
+ uses alias information to make sure that the value loaded from the argument
+ pointer is not modified between the entry of the function and any load of the
+ pointer.</p>
+ </div>
+
+ <!-- _______________________________________________________________________ -->
+ <div class="doc_subsubsection">
+ <a name="gcseloadvn">The <tt>-load-vn</tt> & <tt>-gcse</tt> passes</a>
+ </div>
+
+ <div class="doc_text">
+
+ <p>The <tt>-load-vn</tt> pass uses alias analysis to "<a href="#loadvn">value
+ number</a>" loads and pointers values, which is used by the GCSE pass to
+ eliminate instructions. The <tt>-load-vn</tt> pass relies on alias information
+ and must-alias information. This combination of passes can make the following
+ transformations:</p>
+
+ <ul>
+ <li>Redundant load instructions are eliminated.</li>
+ <li>Load instructions that follow a store to the same location are replaced with
+ the stored value ("store forwarding").</li>
+ <li>Pointers values (e.g. formal arguments) that must-alias simpler expressions
+ (e.g. global variables or the null pointer) are replaced. Note that this
+ implements transformations like "virtual method resolution", turning indirect
+ calls into direct calls.</li>
+ </ul>
+
+ </div>
+
+ <!-- ======================================================================= -->
+ <div class="doc_subsection">
+ <a name="aliasanalysis-debug">Clients for debugging and evaluation of
+ implementations</a>
+ </div>
+
+ <div class="doc_text">
+
+ <p>These passes are useful for evaluating the various alias analysis
+ implementations. You can use them with commands like '<tt>opt -anders-aa -ds-aa
+ -aa-eval foo.bc -disable-output -stats</tt>'.</p>
+
+ </div>
+
+ <!-- _______________________________________________________________________ -->
+ <div class="doc_subsubsection">
+ <a name="print-alias-sets">The <tt>-print-alias-sets</tt> pass</a>
+ </div>
+
+ <div class="doc_text">
+
+ <p>The <tt>-print-alias-sets</tt> pass is exposed as part of the
+ <tt>analyze</tt> tool to print out the Alias Sets formed by the <a
+ href="#ast"><tt>AliasSetTracker</tt></a> class. This is useful if you're using
+ the <tt>AliasSetTracker</tt> class.</p>
+
+ </div>
+
+
+ <!-- _______________________________________________________________________ -->
+ <div class="doc_subsubsection">
+ <a name="count-aa">The <tt>-count-aa</tt> pass</a>
+ </div>
+
+ <div class="doc_text">
+
+ <p>The <tt>-count-aa</tt> pass is useful to see how many queries a particular
+ pass is making and what responses are returned by the alias analysis. As an
+ example,</p>
+
+ <div class="doc_code">
+ <pre>
+ % opt -basicaa -count-aa -ds-aa -count-aa -licm
+ </pre>
+ </div>
+
+ <p>will print out how many queries (and what responses are returned) by the
+ <tt>-licm</tt> pass (of the <tt>-ds-aa</tt> pass) and how many queries are made
+ of the <tt>-basicaa</tt> pass by the <tt>-ds-aa</tt> pass. This can be useful
+ when debugging a transformation or an alias analysis implementation.</p>
+
+ </div>
+
+ <!-- _______________________________________________________________________ -->
+ <div class="doc_subsubsection">
+ <a name="aa-eval">The <tt>-aa-eval</tt> pass</a>
+ </div>
+
+ <div class="doc_text">
+
+ <p>The <tt>-aa-eval</tt> pass simply iterates through all pairs of pointers in a
+ function and asks an alias analysis whether or not the pointers alias. This
+ gives an indication of the precision of the alias analysis. Statistics are
+ printed indicating the percent of no/may/must aliases found (a more precise
+ algorithm will have a lower number of may aliases).</p>
+
+ </div>
+
+ <!-- *********************************************************************** -->
+
+ <hr>
+ <address>
+ <a href="http://jigsaw.w3.org/css-validator/check/referer"><img
+ src="http://jigsaw.w3.org/css-validator/images/vcss" alt="Valid CSS!"></a>
+ <a href="http://validator.w3.org/check/referer"><img
+ src="http://www.w3.org/Icons/valid-html401" alt="Valid HTML 4.01!"></a>
+
+ <a href="mailto:sabre at nondot.org">Chris Lattner</a><br>
+ <a href="http://llvm.cs.uiuc.edu">LLVM Compiler Infrastructure</a><br>
+ Last modified: $Date: 2004/08/13 22:03:03 $
+ </address>
+
+ </body>
+ </html>
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+ <html>
+ <title>LLVM: bugpoint tool</title>
+
+ <body bgcolor=white>
+
+ <center><h1>LLVM: <tt>bugpoint</tt> tool</h1></center>
+ <HR>
+
+ <h3>NAME</h3>
+ <tt>bugpoint</tt>
+
+ <h3>SYNOPSIS</h3>
+ <tt>bugpoint [options] [input LLVM ll/bc files] [LLVM passes] --args <program arguments>...</tt>
+
+ <img src="img/Debugging.gif" width=444 height=314 align=right>
+ <h3>DESCRIPTION</h3>
+
+ The <tt>bugpoint</tt> tool narrows down the source of
+ problems in LLVM tools and passes. It can be used to debug three types of
+ failures: optimizer crashes, miscompilations by optimizers, or bad native
+ code generation (including problems in the static and JIT compilers). It aims
+ to reduce large test cases to small, useful ones. For example,
+ if <tt><a href="CommandGuide/gccas.html">gccas</a></tt> crashes while optimizing a file, it
+ will identify the optimization (or combination of optimizations) that causes the
+ crash, and reduce the file down to a small example which triggers the crash.<p>
+
+ <a name="designphilosophy">
+ <h4>Design Philosophy</h4>
+
+ <tt>bugpoint</tt> is designed to be a useful tool without requiring any
+ hooks into the LLVM infrastructure at all. It works with any and all LLVM
+ passes and code generators, and does not need to "know" how they work. Because
+ of this, it may appear to do stupid things or miss obvious
+ simplifications. <tt>bugpoint</tt> is also designed to trade off programmer
+ time for computer time in the compiler-debugging process; consequently, it may
+ take a long period of (unattended) time to reduce a test case, but we feel it
+ is still worth it. Note that <tt>bugpoint</tt> is generally very quick unless
+ debugging a miscompilation where each test of the program (which requires
+ executing it) takes a long time.<p>
+
+ <a name="automaticdebuggerselection">
+ <h4>Automatic Debugger Selection</h4>
+
+ <tt>bugpoint</tt> reads each <tt>.bc</tt> or <tt>.ll</tt> file
+ specified on the command line and links them together into a single module,
+ called the test program. If any LLVM passes are
+ specified on the command line, it runs these passes on the test program. If
+ any of the passes crash, or if they produce malformed output (which causes the
+ verifier to abort),
+ <tt>bugpoint</tt> starts the <a href="#crashdebug">crash debugger</a>.<p>
+
+ Otherwise, if the <a href="#opt_output"><tt>-output</tt></a> option was not
+ specified, <tt>bugpoint</tt> runs the test program with the C backend (which is
+ assumed to generate good code) to generate a reference output. Once
+ <tt>bugpoint</tt> has a reference output for the test program, it tries
+ executing it with the <a href="#opt_run-">selected</a> code generator. If the
+ selected code generator crashes, <tt>bugpoint</tt> starts the <a
+ href="#crashdebug">crash debugger</a> on the code generator. Otherwise, if the
+ resulting output differs from the reference output, it assumes the difference
+ resulted from a code generator failure, and starts the <a
+ href="#codegendebug">code generator debugger</a>.<p>
+
+ Finally, if the output of the selected code generator matches the reference
+ output, <tt>bugpoint</tt> runs the test program after all of the LLVM passes
+ have been applied to it. If its output differs from the reference output, it
+ assumes the difference resulted from a failure in one of the LLVM passes, and
+ enters the <a href="#miscompilationdebug">miscompilation
+ debugger</a>. Otherwise, there is no problem <tt>bugpoint</tt> can debug.<p>
+
+ <a name="crashdebug">
+ <h4>Crash debugger</h4>
+
+ If an optimizer or code generator crashes, <tt>bugpoint</tt> will try as hard as
+ it can to reduce the list of passes (for optimizer crashes) and the size of the
+ test program. First, <tt>bugpoint</tt> figures out which combination of
+ optimizer passes triggers the bug. This is useful when debugging a problem
+ exposed by <tt>gccas</tt>, for example, because it runs over 38 passes.<p>
+
+ Next, <tt>bugpoint</tt> tries removing functions from the test program, to
+ reduce its size. Usually it is able to reduce a test program to a single
+ function, when debugging intraprocedural optimizations. Once the number of
+ functions has been reduced, it attempts to delete various edges in the control
+ flow graph, to reduce the size of the function as much as possible. Finally,
+ <tt>bugpoint</tt> deletes any individual LLVM instructions whose absence does
+ not eliminate the failure. At the end, <tt>bugpoint</tt> should tell you what
+ passes crash, give you a bytecode file, and give you instructions on how to
+ reproduce the failure with <tt><a href="CommandGuide/opt.html">opt</a></tt>, <tt><a
+ href="CommandGuide/analyze.html">analyze</a></tt>, or <tt><a href="CommandGuide/llc.html">llc</a></tt>.<p>
+
+ <a name="codegendebug">
+ <h4>Code generator debugger</h4>
+
+ <p>The code generator debugger attempts to narrow down the amount of code that
+ is being miscompiled by the <a href="#opt_run-">selected</a> code generator. To
+ do this, it takes the test program and partitions it into two pieces: one piece
+ which it compiles with the C backend (into a shared object), and one piece which
+ it runs with either the JIT or the static LLC compiler. It uses several
+ techniques to reduce the amount of code pushed through the LLVM code generator,
+ to reduce the potential scope of the problem. After it is finished, it emits
+ two bytecode files (called "test" [to be compiled with the code generator] and
+ "safe" [to be compiled with the C backend], respectively), and instructions for
+ reproducing the problem. The code generator debugger assumes that the C backend
+ produces good code.</p>
+
+ <a name="miscompilationdebug">
+ <h4>Miscompilation debugger</h4>
+
+ The miscompilation debugger works similarly to the code generator
+ debugger. It works by splitting the test program into two pieces, running the
+ optimizations specified on one piece, linking the two pieces back together,
+ and then executing the result.
+ It attempts to narrow down the list of passes to the one (or few) which are
+ causing the miscompilation, then reduce the portion of the test program which is
+ being miscompiled. The miscompilation debugger assumes that the selected
+ code generator is working properly.<p>
+
+ <a name="bugpoint notes">
+ <h4>Advice for using <tt>bugpoint</tt></h4>
+
+ <tt>bugpoint</tt> can be a remarkably useful tool, but it sometimes works in
+ non-obvious ways. Here are some hints and tips:<p>
+
+ <ol>
+ <li>In the code generator and miscompilation debuggers, <tt>bugpoint</tt> only
+ works with programs that have deterministic output. Thus, if the program
+ outputs <tt>argv[0]</tt>, the date, time, or any other "random" data, <tt>bugpoint</tt> may
+ misinterpret differences in these data, when output, as the result of a
+ miscompilation. Programs should be temporarily modified to disable
+ outputs that are likely to vary from run to run.
+
+ <li>In the code generator and miscompilation debuggers, debugging will go
+ faster if you manually modify the program or its inputs to reduce the
+ runtime, but still exhibit the problem.
+
+ <li><tt>bugpoint</tt> is extremely useful when working on a new optimization:
+ it helps track down regressions quickly. To avoid having to relink
+ <tt>bugpoint</tt> every time you change your optimization however, have
+ <tt>bugpoint</tt> dynamically load your optimization with the <a
+ href="#opt_load"><tt>-load</tt></a> option.
+
+ <li><tt>bugpoint</tt> can generate a lot of output and run for a long period of
+ time. It is often useful to capture the output of the program to file. For
+ example, in the C shell, you can type:<br>
+ <tt>bugpoint ..... |& tee bugpoint.log</tt>
+ <br>to get a copy of <tt>bugpoint</tt>'s output in the file
+ <tt>bugpoint.log</tt>, as well as on your terminal.
+
+ <li><tt>bugpoint</tt> cannot debug problems with the LLVM linker. If
+ <tt>bugpoint</tt> crashes before you see its "All input ok" message,
+ you might try <tt>llvm-link -v</tt> on the same set of input files. If
+ that also crashes, you may be experiencing a linker bug.
+
+ <li>If your program is <b>supposed</b> to crash, <tt>bugpoint</tt> will be
+ confused. One way to deal with this is to cause bugpoint to ignore the exit
+ code from your program, by giving it the <tt>-check-exit-code=false</tt>
+ option.
+
+ </ol>
+
+ <h3>OPTIONS</h3>
+
+ <ul>
+ <li><tt>-additional-so <library></tt><br>
+ Load <tt><library></tt> into the test program whenever it is run.
+ This is useful if you are debugging programs which depend on non-LLVM
+ libraries (such as the X or curses libraries) to run.<p>
+
+ <li><tt>-args <program args></tt><br>
+ Pass all arguments specified after <tt>-args</tt> to the
+ test program whenever it runs. Note that if any of
+ the <tt><program args></tt> start with a '-', you should use:
+ <p>
+ <tt>bugpoint <bugpoint args> -args -- <program args></tt>
+ <p>
+ The "<tt>--</tt>" right after the <tt>-args</tt> option tells
+ <tt>bugpoint</tt> to consider any options starting with <tt>-</tt> to be
+ part of the <tt>-args</tt> option, not as options to <tt>bugpoint</tt>
+ itself.<p>
+
+ <li><tt>-tool-args <tool args></tt><br>
+ Pass all arguments specified after <tt>-tool-args</tt> to the
+ LLVM tool under test (llc, lli, etc.) whenever it runs.
+ You should use this option in the following way:
+ <p>
+ <tt>bugpoint <bugpoint args> -tool-args -- <tool args></tt>
+ <p>
+ The "<tt>--</tt>" right after the <tt>-tool-args</tt> option tells
+ <tt>bugpoint</tt> to consider any options starting with <tt>-</tt> to be
+ part of the <tt>-tool-args</tt> option, not as options to
+ <tt>bugpoint</tt> itself. (See <tt>-args</tt>, above.)<p>
+
+ <li><tt>-check-exit-code={true,false}</tt><br>
+ Assume a non-zero exit code or core dump from the test program is
+ a failure. Defaults to true.<p>
+
+ <li><tt>-disable-{dce,simplifycfg}</tt><br>
+ Do not run the specified passes to clean up and reduce the size of the
+ test program. By default, <tt>bugpoint</tt> uses these passes internally
+ when attempting to reduce test programs. If you're trying to find
+ a bug in one of these passes, <tt>bugpoint</tt> may crash.<p>
+
+ <li> <tt>-help</tt><br>
+ Print a summary of command line options.<p>
+
+ <a name="opt_input"><li><tt>-input <filename></tt><br>
+ Open <tt><filename></tt> and redirect the standard input of the
+ test program, whenever it runs, to come from that file.
+ <p>
+
+ <a name="opt_load"><li> <tt>-load <plugin></tt><br>
+ Load the dynamic object <tt><plugin></tt> into <tt>bugpoint</tt>
+ itself. This object should register new
+ optimization passes. Once loaded, the object will add new command line
+ options to enable various optimizations. To see the new complete list
+ of optimizations, use the -help and -load options together:
+ <p>
+ <tt>bugpoint -load <plugin> -help</tt>
+ <p>
+
+ <a name="opt_output"><li><tt>-output <filename></tt><br>
+ Whenever the test program produces output on its standard output
+ stream, it should match the contents of <tt><filename></tt>
+ (the "reference output"). If you do not use this option,
+ <tt>bugpoint</tt> will attempt to generate a reference output by
+ compiling the program with the C backend and running it.<p>
+
+ <li><tt>-profile-info-file <filename></tt><br>
+ Profile file loaded by -profile-loader.<p>
+
+ <a name="opt_run-"><li><tt>-run-{int,jit,llc,cbe}</tt><br>
+ Whenever the test program is compiled, <tt>bugpoint</tt> should generate
+ code for it using the specified code generator. These options allow
+ you to choose the interpreter, the JIT compiler, the static native
+ code compiler, or the C backend, respectively.<p>
+ </ul>
+
+ <h3>EXIT STATUS</h3>
+
+ If <tt>bugpoint</tt> succeeds in finding a problem, it will exit with 0.
+ Otherwise, if an error occurs, it will exit with a non-zero value.
+
+ <HR>
+ Maintained by the <a href="http://llvm.cs.uiuc.edu">LLVM Team</a>.
+ </body>
+ </html>
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+ <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" "http://www.w3.org/TR/html4/strict.dtd">
+ <html>
+ <head>
+ <title>LLVM Bytecode File Format</title>
+ <link rel="stylesheet" href="llvm.css" type="text/css">
+ <style type="text/css">
+ TR, TD { border: 2px solid gray; padding-left: 4pt; padding-right: 4pt;
+ padding-top: 2pt; padding-bottom: 2pt; }
+ TH { border: 2px solid gray; font-weight: bold; font-size: 105%; }
+ TABLE { text-align: center; border: 2px solid black;
+ border-collapse: collapse; margin-top: 1em; margin-left: 1em;
+ margin-right: 1em; margin-bottom: 1em; }
+ .td_left { border: 2px solid gray; text-align: left; }
+ </style>
+ </head>
+ <body>
+ <div class="doc_title"> LLVM Bytecode File Format </div>
+ <ol>
+ <li><a href="#abstract">Abstract</a></li>
+ <li><a href="#concepts">Concepts</a>
+ <ol>
+ <li><a href="#blocks">Blocks</a></li>
+ <li><a href="#lists">Lists</a></li>
+ <li><a href="#fields">Fields</a></li>
+ <li><a href="#align">Alignment</a></li>
+ <li><a href="#vbr">Variable Bit-Rate Encoding</a></li>
+ <li><a href="#encoding">Encoding Primitives</a></li>
+ <li><a href="#slots">Slots</a></li>
+ </ol>
+ </li>
+ <li><a href="#general">General Structure</a> </li>
+ <li><a href="#blockdefs">Block Definitions</a>
+ <ol>
+ <li><a href="#signature">Signature Block</a></li>
+ <li><a href="#module">Module Block</a></li>
+ <li><a href="#globaltypes">Global Type Pool</a></li>
+ <li><a href="#globalinfo">Module Info Block</a></li>
+ <li><a href="#constantpool">Global Constant Pool</a></li>
+ <li><a href="#functiondefs">Function Definition</a></li>
+ <li><a href="#compactiontable">Compaction Table</a></li>
+ <li><a href="#instructionlist">Instruction List</a></li>
+ <li><a href="#symtab">Symbol Table</a></li>
+ </ol>
+ </li>
+ <li><a href="#versiondiffs">Version Differences</a>
+ <ol>
+ <li><a href="#vers12">Version 1.2 Differences From 1.3</a></li>
+ <li><a href="#vers11">Version 1.1 Differences From 1.2</a></li>
+ <li><a href="#vers10">Version 1.0 Differences From 1.1</a></li>
+ </ol>
+ </li>
+ </ol>
+ <div class="doc_author">
+ <p>Written by <a href="mailto:rspencer at x10sys.com">Reid Spencer</a>
+ </p>
+ </div>
+ <!-- *********************************************************************** -->
+ <div class="doc_section"> <a name="abstract">Abstract </a></div>
+ <!-- *********************************************************************** -->
+ <div class="doc_text">
+ <p>This document describes the LLVM bytecode file format. It specifies
+ the binary encoding rules of the bytecode file format so that
+ equivalent systems can encode bytecode files correctly. The LLVM
+ bytecode representation is used to store the intermediate
+ representation on disk in compacted form.</p>
+ <p>The LLVM bytecode format may change in the future, but LLVM will
+ always be backwards compatible with older formats. This document will
+ only describe the most current version of the bytecode format. See <a
+ href="#versiondiffs">Version Differences</a> for the details on how
+ the current version is different from previous versions.</p>
+ </div>
+ <!-- *********************************************************************** -->
+ <div class="doc_section"> <a name="concepts">Concepts</a> </div>
+ <!-- *********************************************************************** -->
+ <div class="doc_text">
+ <p>This section describes the general concepts of the bytecode file
+ format without getting into specific layout details. It is recommended
+ that you read this section thoroughly before interpreting the detailed
+ descriptions.</p>
+ </div>
+ <!-- _______________________________________________________________________ -->
+ <div class="doc_subsection"><a name="blocks">Blocks</a> </div>
+ <div class="doc_text">
+ <p>LLVM bytecode files consist simply of a sequence of blocks of bytes
+ using a binary encoding Each block begins with an header of two
+ unsigned integers. The first value identifies the type of block and the
+ second value provides the size of the block in bytes. The block
+ identifier is used because it is possible for entire blocks to be
+ omitted from the file if they are empty. The block identifier helps the
+ reader determine which kind of block is next in the file. Note that
+ blocks can be nested within other blocks.</p>
+ <p> All blocks are variable length, and the block header specifies the
+ size of the block. All blocks begin on a byte index that is aligned to
+ an even 32-bit boundary. That is, the first block is 32-bit aligned
+ because it starts at offset 0. Each block is padded with zero fill
+ bytes to ensure that the next block also starts on a 32-bit boundary.</p>
+ </div>
+ <!-- _______________________________________________________________________ -->
+ <div class="doc_subsection"><a name="lists">Lists</a> </div>
+ <div class="doc_text">
+ <p>LLVM Bytecode blocks often contain lists of things of a similar
+ type. For example, a function contains a list of instructions and a
+ function type contains a list of argument types. There are two basic
+ types of lists: length lists (<a href="#llist">llist</a>), and null
+ terminated lists (<a href="#zlist">zlist</a>), as described below in
+ the <a href="#encoding">Encoding Primitives</a>.</p>
+ </div>
+ <!-- _______________________________________________________________________ -->
+ <div class="doc_subsection"><a name="fields">Fields</a> </div>
+ <div class="doc_text">
+ <p>Fields are units of information that LLVM knows how to write atomically. Most
+ fields have a uniform length or some kind of length indication built into their
+ encoding. For example, a constant string (array of bytes) is written simply as
+ the length followed by the characters. Although this is similar to a list,
+ constant strings are treated atomically and are thus fields.</p>
+ <p>Fields use a condensed bit format specific to the type of information
+ they must contain. As few bits as possible are written for each field. The
+ sections that follow will provide the details on how these fields are
+ written and how the bits are to be interpreted.</p>
+ </div>
+ <!-- _______________________________________________________________________ -->
+ <div class="doc_subsection"><a name="align">Alignment</a> </div>
+ <div class="doc_text">
+ <p>To support cross-platform differences, the bytecode file is aligned on
+ certain boundaries. This means that a small amount of padding (at most 3
+ bytes) will be added to ensure that the next entry is aligned to a 32-bit
+ boundary.</p>
+ </div>
+ <!-- _______________________________________________________________________ -->
+ <div class="doc_subsection"><a name="vbr">Variable Bit-Rate Encoding</a>
+ </div>
+ <div class="doc_text">
+ <p>Most of the values written to LLVM bytecode files are small integers. To
+ minimize the number of bytes written for these quantities, an encoding scheme
+ similar to UTF-8 is used to write integer data. The scheme is known as
+ variable bit rate (vbr) encoding. In this encoding, the high bit of
+ each byte is used to indicate if more bytes follow. If (byte &
+ 0x80) is non-zero in any given byte, it means there is another byte
+ immediately following that also contributes to the value. For the final
+ byte (byte & 0x80) is false (the high bit is not set). In each byte
+ only the low seven bits contribute to the value. Consequently 32-bit
+ quantities can take from one to <em>five</em> bytes to encode. In
+ general, smaller quantities will encode in fewer bytes, as follows:</p>
+ <table>
+ <tbody>
+ <tr>
+ <th>Byte #</th>
+ <th>Significant Bits</th>
+ <th>Maximum Value</th>
+ </tr>
+ <tr>
+ <td>1</td>
+ <td>0-6</td>
+ <td>127</td>
+ </tr>
+ <tr>
+ <td>2</td>
+ <td>7-13</td>
+ <td>16,383</td>
+ </tr>
+ <tr>
+ <td>3</td>
+ <td>14-20</td>
+ <td>2,097,151</td>
+ </tr>
+ <tr>
+ <td>4</td>
+ <td>21-27</td>
+ <td>268,435,455</td>
+ </tr>
+ <tr>
+ <td>5</td>
+ <td>28-34</td>
+ <td>34,359,738,367</td>
+ </tr>
+ <tr>
+ <td>6</td>
+ <td>35-41</td>
+ <td>4,398,046,511,103</td>
+ </tr>
+ <tr>
+ <td>7</td>
+ <td>42-48</td>
+ <td>562,949,953,421,311</td>
+ </tr>
+ <tr>
+ <td>8</td>
+ <td>49-55</td>
+ <td>72,057,594,037,927,935</td>
+ </tr>
+ <tr>
+ <td>9</td>
+ <td>56-62</td>
+ <td>9,223,372,036,854,775,807</td>
+ </tr>
+ <tr>
+ <td>10</td>
+ <td>63-69</td>
+ <td>1,180,591,620,717,411,303,423</td>
+ </tr>
+ </tbody>
+ </table>
+ <p>Note that in practice, the tenth byte could only encode bit 63 since
+ the maximum quantity to use this encoding is a 64-bit integer.</p>
+ <p><em>Signed</em> VBR values are encoded with the standard vbr
+ encoding, but with the sign bit as the low order bit instead of the
+ high order bit. This allows small negative quantities to be encoded
+ efficiently. For example, -3
+ is encoded as "((3 << 1) | 1)" and 3 is encoded as "(3 <<
+ 1) | 0)", emitted with the standard vbr encoding above.</p>
+ </div>
+ <!-- _______________________________________________________________________ -->
+ <div class="doc_subsection"><a name="encoding">Encoding Primitives</a> </div>
+ <div class="doc_text">
+ <p>Each field in the bytecode format is encoded into the file using a
+ small set of primitive formats. The table below defines the encoding
+ rules for the various primitives used and gives them each a type name.
+ The type names used in the descriptions of blocks and fields in the <a
+ href="#details">Detailed Layout</a>next section. Any type name with
+ the suffix <em>_vbr</em> indicates a quantity that is encoded using
+ variable bit rate encoding as described above.</p>
+ <table class="doc_table">
+ <tbody>
+ <tr>
+ <th><b>Type</b></th>
+ <th class="td_left"><b>Rule</b></th>
+ </tr>
+ <tr>
+ <td><a name="unsigned"><b>unsigned</b></a></td>
+ <td class="td_left">A 32-bit unsigned integer that always occupies four
+ consecutive bytes. The unsigned integer is encoded using LSB first
+ ordering. That is bits 2<sup>0</sup> through 2<sup>7</sup> are in the
+ byte with the lowest file offset (little endian).</td>
+ </tr>
+ <tr>
+ <td style="vertical-align: top;"><a name="uint24_vbr">
+ <b>uint24_vbr</b></a></td>
+ <td style="vertical-align: top; text-align: left;">A 24-bit unsigned
+ integer that occupies from one to four bytes using variable bit rate
+ encoding.</td>
+ </tr>
+ <tr>
+ <td><a name="uint32_vbr"><b>uint32_vbr</b></a></td>
+ <td class="td_left">A 32-bit unsigned integer that occupies from one to
+ five bytes using variable bit rate encoding.</td>
+ </tr>
+ <tr>
+ <td><a name="uint64_vbr"><b>uint64_vbr</b></a></td>
+ <td class="td_left">A 64-bit unsigned integer that occupies from one to ten
+ bytes using variable bit rate encoding.</td>
+ </tr>
+ <tr>
+ <td><a name="int64_vbr"><b>int64_vbr</b></a></td>
+ <td class="td_left">A 64-bit signed integer that occupies from one to ten
+ bytes using the signed variable bit rate encoding.</td>
+ </tr>
+ <tr>
+ <td><a name="char"><b>char</b></a></td>
+ <td class="td_left">A single unsigned character encoded into one byte</td>
+ </tr>
+ <tr>
+ <td><a name="bit"><b>bit(n-m)</b></a></td>
+ <td class="td_left">A set of bit within some larger integer field. The values
+ of <code>n</code> and <code>m</code> specify the inclusive range of bits
+ that define the subfield. The value for <code>m</code> may be omitted if
+ its the same as <code>n</code>.</td>
+ </tr>
+ <tr>
+ <td style="vertical-align: top;"><b><a name="float"><b>float</b></a></b></td>
+ <td style="vertical-align: top; text-align: left;">A floating point value encoded
+ as a 32-bit IEEE value written in little-endian form.<br>
+ </td>
+ </tr>
+ <tr>
+ <td style="vertical-align: top;"><b><b><a name="double"><b>double</b></a></b></b></td>
+ <td style="vertical-align: top; text-align: left;">A floating point value encoded
+ as a64-bit IEEE value written in little-endian form</td>
+ </tr>
+ <tr>
+ <td><a name="string"><b>string</b></a></td>
+ <td class="td_left">A uint32_vbr indicating the type of the
+ constant string which also includes its length, immediately followed by
+ the characters of the string. There is no terminating null byte in the
+ string.</td>
+ </tr>
+ <tr>
+ <td><a name="data"><b>data</b></a></td>
+ <td class="td_left">An arbitrarily long segment of data to which
+ no interpretation is implied. This is used for constant initializers.<br>
+ </td>
+ </tr>
+ <tr>
+ <td><a name="llist"><b>llist(x)</b></a></td>
+ <td class="td_left">A length list of x. This means the list is
+ encoded as an <a href="#uint32_vbr">uint32_vbr</a> providing the
+ length of the list, followed by a sequence of that many "x" items. This
+ implies that the reader should iterate the number of times provided by
+ the length.</td>
+ </tr>
+ <tr>
+ <td><a name="zlist"><b>zlist(x)</b></a></td>
+ <td class="td_left">A zero-terminated list of x. This means the
+ list is encoded as a sequence of an indeterminate number of "x" items,
+ followed by an <a href="#uint32_vbr">uint32_vbr</a> terminating value.
+ This implies that none of the "x" items can have a zero value (or else
+ the list terminates).</td>
+ </tr>
+ <tr>
+ <td><a name="block"><b>block</b></a></td>
+ <td class="td_left">A block of data that is logically related. A
+ block is an unsigned 32-bit integer that encodes the type of the block
+ in the low 5 bits and the size of the block in the high 27 bits. The
+ length does not include the block header or any alignment bytes at the
+ end of the block. Blocks may compose other blocks. </td>
+ </tr>
+ </tbody>
+ </table>
+ </div>
+ <!-- _______________________________________________________________________ -->
+ <div class="doc_subsection"><a name="notation">Field Notation</a> </div>
+ <div class="doc_text">
+ <p>In the detailed block and field descriptions that follow, a regex
+ like notation is used to describe optional and repeated fields. A very
+ limited subset of regex is used to describe these, as given in the
+ following table: </p>
+ <table class="doc_table">
+ <tbody>
+ <tr>
+ <th><b>Character</b></th>
+ <th class="td_left"><b>Meaning</b></th>
+ </tr>
+ <tr>
+ <td><b><code>?</code></b></td>
+ <td class="td_left">The question mark indicates 0 or 1
+ occurrences of the thing preceding it.</td>
+ </tr>
+ <tr>
+ <td><b><code>*</code></b></td>
+ <td class="td_left">The asterisk indicates 0 or more occurrences
+ of the thing preceding it.</td>
+ </tr>
+ <tr>
+ <td><b><code>+</code></b></td>
+ <td class="td_left">The plus sign indicates 1 or more occurrences
+ of the thing preceding it.</td>
+ </tr>
+ <tr>
+ <td><b><code>()</code></b></td>
+ <td class="td_left">Parentheses are used for grouping.</td>
+ </tr>
+ <tr>
+ <td><b><code>,</code></b></td>
+ <td class="td_left">The comma separates sequential fields.</td>
+ </tr>
+ </tbody>
+ </table>
+ <p>So, for example, consider the following specifications:</p>
+ <div class="doc_code">
+ <ol>
+ <li><code>string?</code></li>
+ <li><code>(uint32_vbr,uin32_vbr)+</code></li>
+ <li><code>(unsigned?,uint32_vbr)*</code></li>
+ <li><code>(llist(unsigned))?</code></li>
+ </ol>
+ </div>
+ <p>with the following interpretations:</p>
+ <ol>
+ <li>An optional string. Matches either nothing or a single string</li>
+ <li>One or more pairs of uint32_vbr.</li>
+ <li>Zero or more occurrences of either an unsigned followed by a
+ uint32_vbr or just a uint32_vbr.</li>
+ <li>An optional length list of unsigned values.</li>
+ </ol>
+ </div>
+ <!-- _______________________________________________________________________ -->
+ <div class="doc_subsection"><a name="slots">Slots</a> </div>
+ <div class="doc_text">
+ <p>The bytecode format uses the notion of a "slot" to reference Types
+ and Values. Since the bytecode file is a <em>direct</em> representation of
+ LLVM's intermediate representation, there is a need to represent pointers in
+ the file. Slots are used for this purpose. For example, if one has the following
+ assembly:
+ </p>
+ <div class="doc_code"><code> %MyType = type { int, sbyte }<br>
+ %MyVar = external global %MyType
+ </code></div>
+ <p>there are two definitions. The definition of <tt>%MyVar</tt> uses <tt>%MyType</tt>.
+ In the C++ IR this linkage between <tt>%MyVar</tt> and <tt>%MyType</tt>
+ is explicit through the use of C++ pointers. In bytecode, however, there's no
+ ability to store memory addresses. Instead, we compute and write out
+ slot numbers for every Type and Value written to the file.</p>
+ <p>A slot number is simply an unsigned 32-bit integer encoded in the variable
+ bit rate scheme (see <a href="#encoding">encoding</a>). This ensures that
+ low slot numbers are encoded in one byte. Through various bits of magic LLVM
+ attempts to always keep the slot numbers low. The first attempt is to associate
+ slot numbers with their "type plane". That is, Values of the same type
+ are written to the bytecode file in a list (sequentially). Their order in
+ that list determines their slot number. This means that slot #1 doesn't mean
+ anything unless you also specify for which type you want slot #1. Types are
+ handled specially and are always written to the file first (in the <a
+ href="#globaltypes">Global Type Pool</a>) and in such a way that both forward
+ and backward references of the types can often be resolved with a single pass
+ through the type pool. </p>
+ <p>Slot numbers are also kept small by rearranging their order. Because
+ of the structure of LLVM, certain values are much more likely to be used
+ frequently in the body of a function. For this reason, a compaction table is
+ provided in the body of a function if its use would make the function body
+ smaller. Suppose you have a function body that uses just the types "int*" and
+ "{double}" but uses them thousands of time. Its worthwhile to ensure that the
+ slot number for these types are low so they can be encoded in a single byte
+ (via vbr). This is exactly what the compaction table does.</p>
+ </div>
+ <!-- *********************************************************************** -->
+ <div class="doc_section"> <a name="general">General Structure</a> </div>
+ <!-- *********************************************************************** -->
+ <div class="doc_text">
+ <p>This section provides the general structure of the LLVM bytecode
+ file format. The bytecode file format requires blocks to be in a
+ certain order and nested in a particular way so that an LLVM module can
+ be constructed efficiently from the contents of the file. This ordering
+ defines a general structure for bytecode files as shown below. The
+ table below shows the order in which all block types may appear. Please
+ note that some of the blocks are optional and some may be repeated. The
+ structure is fairly loose because optional blocks, if empty, are
+ completely omitted from the file.</p>
+ <table>
+ <tbody>
+ <tr>
+ <th>ID</th>
+ <th>Parent</th>
+ <th>Optional?</th>
+ <th>Repeated?</th>
+ <th>Level</th>
+ <th>Block Type</th>
+ <th>Description</th>
+ </tr>
+ <tr>
+ <td>N/A</td>
+ <td>File</td>
+ <td>No</td>
+ <td>No</td>
+ <td>0</td>
+ <td class="td_left"><a href="#signature">Signature</a></td>
+ <td class="td_left">This contains the file signature (magic
+ number) that identifies the file as LLVM bytecode.</td>
+ </tr>
+ <tr>
+ <td>0x01</td>
+ <td>File</td>
+ <td>No</td>
+ <td>No</td>
+ <td>0</td>
+ <td class="td_left"><a href="#module">Module</a></td>
+ <td class="td_left">This is the top level block in a bytecode
+ file. It contains all the other blocks. </td>
+ </tr>
+ <tr>
+ <td>0x06</td>
+ <td>Module</td>
+ <td>No</td>
+ <td>No</td>
+ <td>1</td>
+ <td class="td_left"> <a href="#globaltypes">Global Type Pool</a></td>
+ <td class="td_left">This block contains all the global (module)
+ level types.</td>
+ </tr>
+ <tr>
+ <td>0x05</td>
+ <td>Module</td>
+ <td>No</td>
+ <td>No</td>
+ <td>1</td>
+ <td class="td_left"> <a href="#globalinfo">Module Globals Info</a></td>
+ <td class="td_left">This block contains the type, constness, and
+ linkage for each of the global variables in the module. It also
+ contains the type of the functions and the constant initializers.</td>
+ </tr>
+ <tr>
+ <td>0x03</td>
+ <td>Module</td>
+ <td>Yes</td>
+ <td>No</td>
+ <td>1</td>
+ <td class="td_left"> <a href="#constantpool">Module Constant Pool</a></td>
+ <td class="td_left">This block contains all the global constants
+ except function arguments, global values and constant strings.</td>
+ </tr>
+ <tr>
+ <td>0x02</td>
+ <td>Module</td>
+ <td>Yes</td>
+ <td>Yes</td>
+ <td>1</td>
+ <td class="td_left"> <a href="#functiondefs">Function Definitions</a>*</td>
+ <td class="td_left">One function block is written for each
+ function in the module. The function block contains the instructions,
+ compaction table, type constant pool, and symbol table for the function.</td>
+ </tr>
+ <tr>
+ <td>0x03</td>
+ <td>Function</td>
+ <td>Yes</td>
+ <td>No</td>
+ <td>2</td>
+ <td class="td_left"> <a
+ href="#constantpool">Function Constant Pool</a></td>
+ <td class="td_left">Any constants (including types) used solely
+ within the function are emitted here in the function constant pool. </td>
+ </tr>
+ <tr>
+ <td>0x08</td>
+ <td>Function</td>
+ <td>Yes</td>
+ <td>No</td>
+ <td>2</td>
+ <td class="td_left"> <a
+ href="#compactiontable">Compaction Table</a></td>
+ <td class="td_left">This table reduces bytecode size by providing
+ a funtion-local mapping of type and value slot numbers to their global
+ slot numbers</td>
+ </tr>
+ <tr>
+ <td>0x07</td>
+ <td>Function</td>
+ <td>No</td>
+ <td>No</td>
+ <td>2</td>
+ <td class="td_left"> <a
+ href="#instructionlist">Instruction List</a></td>
+ <td class="td_left">This block contains all the instructions of
+ the function. The basic blocks are inferred by terminating
+ instructions. </td>
+ </tr>
+ <tr>
+ <td>0x04</td>
+ <td>Function</td>
+ <td>Yes</td>
+ <td>No</td>
+ <td>2</td>
+ <td class="td_left"> <a
+ href="#symtab">Function Symbol Table</a></td>
+ <td class="td_left">This symbol table provides the names for the
+ function specific values used (basic block labels mostly).</td>
+ </tr>
+ <tr>
+ <td>0x04</td>
+ <td>Module</td>
+ <td>Yes</td>
+ <td>No</td>
+ <td>1</td>
+ <td class="td_left"> <a href="#symtab">Module Symbol Table</a></td>
+ <td class="td_left">This symbol table provides the names for the
+ various entries in the file that are not function specific (global
+ vars, and functions mostly).</td>
+ </tr>
+ </tbody>
+ </table>
+ <p>Use the links in the table for details about the contents of each of
+ the block types.</p>
+ </div>
+ <!-- *********************************************************************** -->
+ <div class="doc_section"> <a name="blockdefs">Block Definitions</a> </div>
+ <!-- *********************************************************************** -->
+ <div class="doc_text">
+ <p>This section provides the detailed layout of the individual block
+ types in the LLVM bytecode file format. </p>
+ </div>
+ <!-- _______________________________________________________________________ -->
+ <div class="doc_subsection"><a name="signature">Signature Block</a> </div>
+ <div class="doc_text">
+ <p>The signature occurs in every LLVM bytecode file and is always first.
+ It simply provides a few bytes of data to identify the file as being an LLVM
+ bytecode file. This block is always four bytes in length and differs from the
+ other blocks because there is no identifier and no block length at the start
+ of the block. Essentially, this block is just the "magic number" for the file.
+ </p>
+ <table>
+ <tbody>
+ <tr>
+ <th><b>Type</b></th>
+ <th class="td_left"><b>Field Description</b></th>
+ </tr>
+ <tr>
+ <td><a href="#char">char</a></td>
+ <td class="td_left">Constant "l" (0x6C)</td>
+ </tr>
+ <tr>
+ <td><a href="#char">char</a></td>
+ <td class="td_left">Constant "l" (0x6C)</td>
+ </tr>
+ <tr>
+ <td><a href="#char">char</a></td>
+ <td class="td_left">Constant "v" (0x76)</td>
+ </tr>
+ <tr>
+ <td><a href="#char">char</a></td>
+ <td class="td_left">Constant "m" (0x6D)</td>
+ </tr>
+ </tbody>
+ </table>
+ </div>
+ <!-- _______________________________________________________________________ -->
+ <div class="doc_subsection"><a name="module">Module Block</a> </div>
+ <div class="doc_text">
+ <p>The module block contains a small pre-amble and all the other blocks in
+ the file. The table below shows the structure of the module block. Note that it
+ only provides the module identifier, size of the module block, and the format
+ information. Everything else is contained in other blocks, described in other
+ sections.</p>
+ <table>
+ <tbody>
+ <tr>
+ <th><b>Type</b></th>
+ <th class="td_left"><b>Field Description</b></th>
+ </tr>
+ <tr>
+ <td><a href="#block">block</a><br>
+ </td>
+ <td class="td_left">Module Block Identifier (0x01) and Size<br>
+ </td>
+ </tr>
+ <tr>
+ <td><a href="#uint32_vbr">uint32_vbr</a></td>
+ <td class="td_left"><a href="#format">Format Information</a></td>
+ </tr>
+ <tr>
+ <td><a href="#block">block</a></td>
+ <td class="td_left"><a href="#globaltypes">Global Type Pool</a></td>
+ </tr>
+ <tr>
+ <td><a href="#block">block</a></td>
+ <td class="td_left"><a href="#globalinfo">Module Globals Info</a></td>
+ </tr>
+ <tr>
+ <td><a href="#block">block</a></td>
+ <td class="td_left"><a href="#constantpool">Module Constant Pool</a></td>
+ </tr>
+ <tr>
+ <td><a href="#block">block</a>*</td>
+ <td class="td_left"><a href="#functiondefs">Function Definitions</a></td>
+ </tr>
+ <tr>
+ <td><a href="#block">block</a></td>
+ <td class="td_left"><a href="#symboltable">Module Symbol Table</a></td>
+ </tr>
+ </tbody>
+ </table>
+ </div>
+ <!-- _______________________________________________________________________ -->
+ <div class="doc_subsubsection"><a name="format">Format Information</a></div>
+ <div class="doc_text">
+ <p>The format information field is encoded into a <a href="#uint32_vbr">uint32_vbr</a>
+ as shown in the following table.</p>
+ <table>
+ <tbody>
+ <tr>
+ <th><b>Type</b></th>
+ <th class="td_left"><b>Description</b></th>
+ </tr>
+ <tr>
+ <td><a href="#bit">bit(0)</a></td>
+ <td class="td_left">Target is big endian?</td>
+ </tr>
+ <tr>
+ <td><a href="#bit">bit(1)</a></td>
+ <td class="td_left">On target pointers are 64-bit?</td>
+ </tr>
+ <tr>
+ <td><a href="#bit">bit(2)</a></td>
+ <td class="td_left">Target has no endianess?</td>
+ </tr>
+ <tr>
+ <td><a href="#bit">bit(3)</a></td>
+ <td class="td_left">Target has no pointer size?</td>
+ </tr>
+ <tr>
+ <td><a href="#bit">bit(4-31)</a></td>
+ <td class="td_left">Bytecode format version</td>
+ </tr>
+ </tbody>
+ </table>
+ <p>
+ Of particular note, the bytecode format number is simply a 28-bit
+ monotonically increase integer that identifies the version of the bytecode
+ format (which is not directly related to the LLVM release number). The
+ bytecode versions defined so far are (note that this document only
+ describes the latest version, 1.3):</p>
+ <ul>
+ <li>#0: LLVM 1.0 & 1.1</li>
+ <li>#1: LLVM 1.2</li>
+ <li>#2: LLVM 1.2.5 (not released)</li>
+ <li>#3: LLVM 1.3<br>
+ </li>
+ </ul>
+ <p>Note that we plan to eventually expand the target description
+ capabilities
+ of bytecode files to <a href="http://llvm.cs.uiuc.edu/PR263">target
+ triples</a>.
+ </p>
+ </div>
+ <!-- _______________________________________________________________________ -->
+ <div class="doc_subsection"><a name="globaltypes">Global Type Pool</a> </div>
+ <div class="doc_text">
+ <p>The global type pool consists of type definitions. Their order of appearance
+ in the file determines their slot number (0 based). Slot numbers are
+ used to replace pointers in the intermediate representation. Each slot number
+ uniquely identifies one entry in a type plane (a collection of values of the
+ same type). Since all values have types and are associated with the order in
+ which the type pool is written, the global type pool <em>must</em> be written
+ as the first block of a module. If it is not, attempts to read the file will
+ fail because both forward and backward type resolution will not be possible.</p>
+ <p>The type pool is simply a list of type definitions, as shown in the
+ table below.</p>
+ <table>
+ <tbody>
+ <tr>
+ <th><b>Type</b></th>
+ <th class="td_left"><b>Field Description</b></th>
+ </tr>
+ <tr>
+ <td><a href="#unsigned">block</a></td>
+ <td class="td_left">Type Pool Identifier (0x06) + Size<br>
+ </td>
+ </tr>
+ <tr>
+ <td><a href="#llist">llist</a>(<a href="#type">type</a>)</td>
+ <td class="td_left">A length list of type definitions.</td>
+ </tr>
+ </tbody>
+ </table>
+ </div>
+ <!-- _______________________________________________________________________ -->
+ <div class="doc_subsubsection"><a name="type">Type Definitions</a></div>
+ <div class="doc_text">
+ <p>Types in the type pool are defined using a different format for each kind
+ of type, as given in the following sections.</p>
+ <h3>Primitive Types</h3>
+ <p>The primitive types encompass the basic integer and floating point
+ types</p>
+ <table>
+ <tbody>
+ <tr>
+ <th><b>Type</b></th>
+ <th class="td_left"><b>Description</b></th>
+ </tr>
+ <tr>
+ <td><a href="#uint24_vbr">uint24_vbr</a></td>
+ <td class="td_left">Type ID for the primitive types (values 1 to
+ 11) <sup>1</sup></td>
+ </tr>
+ </tbody>
+ </table>
+ Notes:
+ <ol>
+ <li>The values for the Type IDs for the primitive types are provided
+ by the definition of the <code>llvm::Type::TypeID</code> enumeration
+ in <code>include/llvm/Type.h</code>. The enumeration gives the
+ following mapping:
+ <ol>
+ <li>bool</li>
+ <li>ubyte</li>
+ <li>sbyte</li>
+ <li>ushort</li>
+ <li>short</li>
+ <li>uint</li>
+ <li>int</li>
+ <li>ulong</li>
+ <li>long</li>
+ <li>float</li>
+ <li>double</li>
+ </ol>
+ </li>
+ </ol>
+ <h3>Function Types</h3>
+ <table>
+ <tbody>
+ <tr>
+ <th><b>Type</b></th>
+ <th class="td_left"><b>Description</b></th>
+ </tr>
+ <tr>
+ <td><a href="#uint24_vbr">uint24_vbr</a></td>
+ <td class="td_left">Type ID for function types (13)</td>
+ </tr>
+ <tr>
+ <td><a href="#uint24_vbr">uint24_vbr</a></td>
+ <td class="td_left">Slot number of function's return type.</td>
+ </tr>
+ <tr>
+ <td><a href="#llist">llist</a>(<a href="#uint24_vbr">uint24_vbr</a>)</td>
+ <td class="td_left">Slot number of each argument's type.</td>
+ </tr>
+ <tr>
+ <td><a href="#uint32_vbr">uint32_vbr</a>?</td>
+ <td class="td_left">Value 0 if this is a varargs function,
+ missing otherwise.</td>
+ </tr>
+ </tbody>
+ </table>
+ <h3>Structure Types</h3>
+ <table>
+ <tbody>
+ <tr>
+ <th><b>Type</b></th>
+ <th class="td_left"><b>Description</b></th>
+ </tr>
+ <tr>
+ <td><a href="#uint24_vbr">uint24_vbr</a></td>
+ <td class="td_left">Type ID for structure types (14)</td>
+ </tr>
+ <tr>
+ <td><a href="#zlist">zlist</a>(<a href="#uint24_vbr">uint24_vbr</a>)</td>
+ <td class="td_left">Slot number of each of the element's fields.</td>
+ </tr>
+ </tbody>
+ </table>
+ <h3>Array Types</h3>
+ <table>
+ <tbody>
+ <tr>
+ <th><b>Type</b></th>
+ <th class="td_left"><b>Description</b></th>
+ </tr>
+ <tr>
+ <td><a href="#uint24_vbr">uint24_vbr</a></td>
+ <td class="td_left">Type ID for Array Types (15)</td>
+ </tr>
+ <tr>
+ <td><a href="#uint24_vbr">uint24_vbr</a></td>
+ <td class="td_left">Slot number of array's element type.</td>
+ </tr>
+ <tr>
+ <td><a href="#uint32_vbr">uint32_vbr</a></td>
+ <td class="td_left">The number of elements in the array.</td>
+ </tr>
+ </tbody>
+ </table>
+ <h3>Pointer Types</h3>
+ <table>
+ <tbody>
+ <tr>
+ <th><b>Type</b></th>
+ <th class="td_left"><b>Description</b></th>
+ </tr>
+ <tr>
+ <td><a href="#uint24_vbr">uint24_vbr</a></td>
+ <td class="td_left">Type ID For Pointer Types (16)</td>
+ </tr>
+ <tr>
+ <td><a href="#uint24_vbr">uint24_vbr</a></td>
+ <td class="td_left">Slot number of pointer's element type.</td>
+ </tr>
+ </tbody>
+ </table>
+ <h3>Opaque Types</h3>
+ <table>
+ <tbody>
+ <tr>
+ <th><b>Type</b></th>
+ <th class="td_left"><b>Description</b></th>
+ </tr>
+ <tr>
+ <td><a href="#uint24_vbr">uint24_vbr</a></td>
+ <td class="td_left">Type ID For Opaque Types (17)</td>
+ </tr>
+ </tbody>
+ </table>
+ </div>
+ <!-- _______________________________________________________________________ -->
+ <div class="doc_subsection"><a name="globalinfo">Module Global Info</a>
+ </div>
+ <div class="doc_text">
+ <p>The module global info block contains the definitions of all global
+ variables including their initializers and the <em>declaration</em> of
+ all functions. The format is shown in the table below:</p>
+ <table>
+ <tbody>
+ <tr>
+ <th><b>Type</b></th>
+ <th class="td_left"><b>Field Description</b></th>
+ </tr>
+ <tr>
+ <td><a href="#block">block</a></td>
+ <td class="td_left">Module global info identifier (0x05) + size<br>
+ </td>
+ </tr>
+ <tr>
+ <td><a href="#zlist">zlist</a>(<a href="#globalvar">globalvar</a>)</td>
+ <td class="td_left">A zero terminated list of global var
+ definitions occuring in the module.</td>
+ </tr>
+ <tr>
+ <td><a href="#zlist">zlist</a>(<a href="#uint24_vbr">uint24_vbr</a>)</td>
+ <td class="td_left">A zero terminated list of function types
+ occuring in the module.</td>
+ </tr>
+ <tr>
+ <td style="vertical-align: top;"><a href="#llist">llist</a>(<a
+ href="#string">string</a>)<br>
+ </td>
+ <td style="vertical-align: top; text-align: left;">A length list
+ of strings that specify the names of the libraries that this module
+ depends upon.<br>
+ </td>
+ </tr>
+ <tr>
+ <td style="vertical-align: top;"><a href="#string">string</a><br>
+ </td>
+ <td style="vertical-align: top; text-align: left;">The target
+ triple for the module (blank means no target triple specified, i.e. a
+ platform independent module).<br>
+ </td>
+ </tr>
+ </tbody>
+ </table>
+ </div>
+ <!-- _______________________________________________________________________ -->
+ <div class="doc_subsubsection"><a name="globalvar">Global Variable Field</a>
+ </div>
+ <div class="doc_text">
+ <p>Global variables are written using an <a href="#uint32_vbr">uint32_vbr</a>
+ that encodes information about the global variable and a list of the
+ constant initializers for the global var, if any.</p>
+ <p>The table below provides the bit layout of the first <a
+ href="#uint32_vbr">uint32_vbr</a> that describes the global variable.</p>
+ <table>
+ <tbody>
+ <tr>
+ <th><b>Type</b></th>
+ <th class="td_left"><b>Description</b></th>
+ </tr>
+ <tr>
+ <td><a href="#bit">bit(0)</a></td>
+ <td class="td_left">Is constant?</td>
+ </tr>
+ <tr>
+ <td><a href="#bit">bit(1)</a></td>
+ <td class="td_left">Has initializer? Note that this bit
+ determines whether the constant initializer field (described below)
+ follows. </td>
+ </tr>
+ <tr>
+ <td><a href="#bit">bit(2-4)</a></td>
+ <td class="td_left">Linkage type: 0=External, 1=Weak,
+ 2=Appending, 3=Internal, 4=LinkOnce</td>
+ </tr>
+ <tr>
+ <td><a href="#bit">bit(5-31)</a></td>
+ <td class="td_left">Slot number of type for the global variable.</td>
+ </tr>
+ </tbody>
+ </table>
+ <p>The table below provides the format of the constant initializers for
+ the global variable field, if it has one.</p>
+ <table>
+ <tbody>
+ <tr>
+ <th><b>Type</b></th>
+ <th class="td_left"><b>Description</b></th>
+ </tr>
+ <tr>
+ <td>(<a href="#zlist">zlist</a>(<a href="#uint32_vbr">uint32_vbr</a>))?
+ </td>
+ <td class="td_left">An optional zero-terminated list of slot
+ numbers of the global variable's constant initializer.</td>
+ </tr>
+ </tbody>
+ </table>
+ </div>
+ <!-- _______________________________________________________________________ -->
+ <div class="doc_subsection"><a name="constantpool">Constant Pool</a> </div>
+ <div class="doc_text">
+ <p>A constant pool defines as set of constant values. There are
+ actually two types of constant pool blocks: one for modules and one for
+ functions. For modules, the block begins with the constant strings
+ encountered anywhere in the module. For functions, the block begins
+ with types only encountered in the function. In both cases the header
+ is identical. The tables that follow, show the header, module constant
+ pool preamble, function constant pool preamble, and the part common to
+ both function and module constant pools.</p>
+ <p><b>Common Block Header</b></p>
+ <table>
+ <tbody>
+ <tr>
+ <th><b>Type</b></th>
+ <th class="td_left"><b>Field Description</b></th>
+ </tr>
+ <tr>
+ <td><a href="#block">block</a></td>
+ <td class="td_left">Constant pool identifier (0x03) + size<br>
+ </td>
+ </tr>
+ </tbody>
+ </table>
+ <p><b>Module Constant Pool Preamble (constant strings)</b></p>
+ <table>
+ <tbody>
+ <tr>
+ <th><b>Type</b></th>
+ <th class="td_left"><b>Field Description</b></th>
+ </tr>
+ <tr>
+ <td><a href="#uint32_vbr">uint32_vbr</a></td>
+ <td class="td_left">The number of constant strings that follow.</td>
+ </tr>
+ <tr>
+ <td><a href="#uint32_vbr">uint32_vbr</a></td>
+ <td class="td_left">Zero. This identifies the following "plane"
+ as containing the constant strings. This is needed to identify it
+ uniquely from other constant planes that follow. </td>
+ </tr>
+ <tr>
+ <td><a href="#uint24_vbr">uint24_vbr</a>+</td>
+ <td class="td_left">Slot number of the constant string's type.
+ Note that the constant string's type implicitly defines the length of
+ the string. </td>
+ </tr>
+ </tbody>
+ </table>
+ <p><b>Function Constant Pool Preamble (function types)</b></p>
+ <p>The structure of the types for functions is identical to the <a
+ href="#globaltypes">Global Type Pool</a>. Please refer to that section
+ for the details. </p>
+ <p><b>Common Part (other constants)</b></p>
+ <table>
+ <tbody>
+ <tr>
+ <th><b>Type</b></th>
+ <th class="td_left"><b>Field Description</b></th>
+ </tr>
+ <tr>
+ <td><a href="#uint32_vbr">uint32_vbr</a></td>
+ <td class="td_left">Number of entries in this type plane.</td>
+ </tr>
+ <tr>
+ <td><a href="#uint24_vbr">uint24_vbr</a></td>
+ <td class="td_left">Type slot number of this plane.</td>
+ </tr>
+ <tr>
+ <td><a href="#constant">constant</a>+</td>
+ <td class="td_left">The definition of a constant (see below).</td>
+ </tr>
+ </tbody>
+ </table>
+ </div>
+ <!-- _______________________________________________________________________ -->
+ <div class="doc_subsubsection"><a name="constant">Constant Field</a></div>
+ <div class="doc_text">
+ <p>Constants come in many shapes and flavors. The sections that followe
+ define the format for each of them. All constants start with a <a
+ href="#uint32_vbr">uint32_vbr</a> encoded integer that provides the
+ number of operands for the constant. For primitive, structure, and
+ array constants, this will always be zero since those types of
+ constants have no operands. In this case, we have the following field
+ definitions:</p>
+ <ul>
+ <li><b>Bool</b>. This is written as an <a href="#uint32_vbr">uint32_vbr</a>
+ of value 1U or 0U.</li>
+ <li><b>Signed Integers (sbyte,short,int,long)</b>. These are written
+ as an <a href="#int64_vbr">int64_vbr</a> with the corresponding value.</li>
+ <li><b>Unsigned Integers (ubyte,ushort,uint,ulong)</b>. These are
+ written as an <a href="#uint64_vbr">uint64_vbr</a> with the
+ corresponding value. </li>
+ <li><b>Floating Point</b>. Both the float and double types are
+ written literally in binary format.</li>
+ <li><b>Arrays</b>. Arrays are written simply as a list of <a
+ href="#uint32_vbr">uint32_vbr</a> encoded slot numbers to the constant
+ element values.</li>
+ <li><b>Structures</b>. Structures are written simply as a list of <a
+ href="#uint32_vbr">uint32_vbr</a> encoded slot numbers to the constant
+ field values of the structure.</li>
+ </ul>
+ <p>When the number of operands to the constant is non-zero, we have a
+ constant expression and its field format is provided in the table below.</p>
+ <table>
+ <tbody>
+ <tr>
+ <th><b>Type</b></th>
+ <th class="td_left"><b>Field Description</b></th>
+ </tr>
+ <tr>
+ <td><a href="#uint32_vbr">uint32_vbr</a></td>
+ <td class="td_left">Op code of the instruction for the constant
+ expression.</td>
+ </tr>
+ <tr>
+ <td><a href="#uint32_vbr">uint32_vbr</a></td>
+ <td class="td_left">The slot number of the constant value for an
+ operand.<sup>1</sup></td>
+ </tr>
+ <tr>
+ <td><a href="#uint24_vbr">uint24_vbr</a></td>
+ <td class="td_left">The slot number for the type of the constant
+ value for an operand.<sup>1</sup></td>
+ </tr>
+ </tbody>
+ </table>
+ Notes:
+ <ol>
+ <li>Both these fields are repeatable but only in pairs.</li>
+ </ol>
+ </div>
+ <!-- _______________________________________________________________________ -->
+ <div class="doc_subsection"><a name="functiondefs">Function Definition</a></div>
+ <div class="doc_text">
+ <p>Function definitions contain the linkage, constant pool or
+ compaction table, instruction list, and symbol table for a function.
+ The following table shows the structure of a function definition.</p>
+ <table>
+ <tbody>
+ <tr>
+ <th><b>Type</b></th>
+ <th class="td_left"><b>Field Description</b></th>
+ </tr>
+ <tr>
+ <td><a href="#block">block</a><br>
+ </td>
+ <td class="td_left">Function definition block identifier (0x02) +
+ size<br>
+ </td>
+ </tr>
+ <tr>
+ <td><a href="#uint32_vbr">uint32_vbr</a></td>
+ <td class="td_left">The linkage type of the function: 0=External,
+ 1=Weak, 2=Appending, 3=Internal, 4=LinkOnce<sup>1</sup></td>
+ </tr>
+ <tr>
+ <td><a href="#block">block</a></td>
+ <td class="td_left">The <a href="#constantpool">constant pool</a>
+ block for this function.<sup>2</sup></td>
+ </tr>
+ <tr>
+ <td><a href="#block">block</a></td>
+ <td class="td_left">The <a href="#compactiontable">compaction
+ table</a> block for the function.<sup>2</sup></td>
+ </tr>
+ <tr>
+ <td><a href="#block">block</a></td>
+ <td class="td_left">The <a href="#instructionlist">instruction
+ list</a> for the function.</td>
+ </tr>
+ <tr>
+ <td><a href="#block">block</a></td>
+ <td class="td_left">The function's <a href="#symboltable">symbol
+ table</a> containing only those symbols pertinent to the function
+ (mostly block labels).</td>
+ </tr>
+ </tbody>
+ </table>
+ Notes:
+ <ol>
+ <li>Note that if the linkage type is "External" then none of the
+ other fields will be present as the function is defined elsewhere.</li>
+ <li>Note that only one of the constant pool or compaction table will
+ be written. Compaction tables are only written if they will actually
+ save bytecode space. If not, then a regular constant pool is written.</li>
+ </ol>
+ </div>
+ <!-- _______________________________________________________________________ -->
+ <div class="doc_subsection"><a name="compactiontable">Compaction Table</a>
+ </div>
+ <div class="doc_text">
+ <p>Compaction tables are part of a function definition. They are merely
+ a device for reducing the size of bytecode files. The size of a
+ bytecode file is dependent on the <em>value</em> of the slot numbers
+ used because larger values use more bytes in the variable bit rate
+ encoding scheme. Furthermore, the compressed instruction format
+ reserves only six bits for the type of the instruction. In large
+ modules, declaring hundreds or thousands of types, the values of the
+ slot numbers can be quite large. However, functions may use only a
+ small fraction of the global types. In such cases a compaction table is
+ created that maps the global type and value slot numbers to smaller
+ values used by a function. Functions will contain either a
+ function-specific constant pool <em>or</em> a compaction table but not
+ both. Compaction tables have the format shown in the table below.</p>
+ <table>
+ <tbody>
+ <tr>
+ <th><b>Type</b></th>
+ <th class="td_left"><b>Field Description</b></th>
+ </tr>
+ <tr>
+ <td><a href="#uint32_vbr">uint32_vbr</a></td>
+ <td class="td_left">The number of types that follow</td>
+ </tr>
+ <tr>
+ <td><a href="#uint24_vbr">uint24_vbr</a>+</td>
+ <td class="td_left">The slot number in the global type plane of
+ the type that will be referenced in the function with the index of this
+ entry in the compaction table.</td>
+ </tr>
+ <tr>
+ <td><a href="#type_len">type_len</a></td>
+ <td class="td_left">An encoding of the type and number of values
+ that follow. This field's encoding varies depending on the size of the
+ type plane. See <a href="#type_len">Type and Length</a> for further
+ details.</td>
+ </tr>
+ <tr>
+ <td><a href="#uint32_vbr">uint32_vbr</a>+</td>
+ <td class="td_left">The slot number in the globals of the value
+ that will be referenced in the function with the index of this entry in
+ the compaction table</td>
+ </tr>
+ </tbody>
+ </table>
+ </div>
+ <!-- _______________________________________________________________________ -->
+ <div class="doc_subsubsection"><a name="type_len">Type and Length</a></div>
+ <div class="doc_text">
+ <p>The type and length of a compaction table type plane is encoded
+ differently depending on the length of the plane. For planes of length
+ 1 or 2, the length is encoded into bits 0 and 1 of a <a
+ href="#uint32_vbr">uint32_vbr</a> and the type is encoded into bits
+ 2-31. Because type numbers are often small, this often saves an extra
+ byte per plane. If the length of the plane is greater than 2 then the
+ encoding uses a <a href="#uint32_vbr">uint32_vbr</a> for each of the
+ length and type, in that order.</p>
+ </div>
+ <!-- _______________________________________________________________________ -->
+ <div class="doc_subsection"><a name="instructionlist">Instruction List</a>
+ </div>
+ <div class="doc_text">
+ <p>The instructions in a function are written as a simple list. Basic
+ blocks are inferred by the terminating instruction types. The format of
+ the block is given in the following table.</p>
+ <table>
+ <tbody>
+ <tr>
+ <th><b>Type</b></th>
+ <th class="td_left"><b>Field Description</b></th>
+ </tr>
+ <tr>
+ <td><a href="#block">block</a><br>
+ </td>
+ <td class="td_left">Instruction list identifier (0x07) + size<br>
+ </td>
+ </tr>
+ <tr>
+ <td><a href="#instruction">instruction</a>+</td>
+ <td class="td_left">An instruction. Instructions have a variety
+ of formats. See <a href="#instruction">Instructions</a> for details.</td>
+ </tr>
+ </tbody>
+ </table>
+ </div>
+ <!-- _______________________________________________________________________ -->
+ <div class="doc_subsubsection"><a name="instruction">Instructions</a></div>
+ <div class="doc_text">
+ <p>For brevity, instructions are written in one of four formats,
+ depending on the number of operands to the instruction. Each
+ instruction begins with a <a href="#uint32_vbr">uint32_vbr</a> that
+ encodes the type of the instruction as well as other things. The tables
+ that follow describe the format of this first word of each instruction.</p>
+ <p><b>Instruction Format 0</b></p>
+ <p>This format is used for a few instructions that can't easily be
+ optimized because they have large numbers of operands (e.g. PHI Node or
+ getelementptr). Each of the opcode, type, and operand fields is as
+ successive fields.</p>
+ <table>
+ <tbody>
+ <tr>
+ <th><b>Type</b></th>
+ <th class="td_left"><b>Field Description</b></th>
+ </tr>
+ <tr>
+ <td><a href="#uint32_vbr">uint32_vbr</a></td>
+ <td class="td_left">Specifies the opcode of the instruction. Note
+ that for compatibility with the other instruction formats, the opcode
+ is shifted left by 2 bits. Bits 0 and 1 must have value zero for this
+ format.</td>
+ </tr>
+ <tr>
+ <td><a href="#uint24_vbr">uint24_vbr</a></td>
+ <td class="td_left">Provides the slot number of the result type
+ of the instruction</td>
+ </tr>
+ <tr>
+ <td><a href="#uint32_vbr">uint32_vbr</a></td>
+ <td class="td_left">The number of operands that follow.</td>
+ </tr>
+ <tr>
+ <td><a href="#uint32_vbr">uint32_vbr</a>+</td>
+ <td class="td_left">The slot number of the value(s) for the
+ operand(s). <sup>1</sup></td>
+ </tr>
+ </tbody>
+ </table>
+ Notes:
+ <ol>
+ <li>Note that if the instruction is a getelementptr and the type of
+ the operand is a sequential type (array or pointer) then the slot
+ number is shifted up two bits and the low order bits will encode the
+ type of index used, as follows: 0=uint, 1=int, 2=ulong, 3=long.</li>
+ </ol>
+ <p><b>Instruction Format 1</b></p>
+ <p>This format encodes the opcode, type and a single operand into a
+ single <a href="#uint32_vbr">uint32_vbr</a> as follows:</p>
+ <table>
+ <tbody>
+ <tr>
+ <th><b>Bits</b></th>
+ <th><b>Type</b></th>
+ <th class="td_left"><b>Field Description</b></th>
+ </tr>
+ <tr>
+ <td>0-1</td>
+ <td>constant "1"</td>
+ <td class="td_left">These two bits must be the value 1 which
+ identifies this as an instruction of format 1.</td>
+ </tr>
+ <tr>
+ <td>2-7</td>
+ <td><a href="#opcodes">opcode</a></td>
+ <td class="td_left">Specifies the opcode of the instruction. Note
+ that the maximum opcode value is 63.</td>
+ </tr>
+ <tr>
+ <td>8-19</td>
+ <td><a href="#unsigned">unsigned</a></td>
+ <td class="td_left">Specifies the slot number of the type for
+ this instruction. Maximum slot number is 2<sup>12</sup>-1=4095.</td>
+ </tr>
+ <tr>
+ <td>20-31</td>
+ <td><a href="#unsigned">unsigned</a></td>
+ <td class="td_left">Specifies the slot number of the value for
+ the first operand. Maximum slot number is 2<sup>12</sup>-1=4095. Note
+ that the value 2<sup>12</sup>-1 denotes zero operands.</td>
+ </tr>
+ </tbody>
+ </table>
+ <p><b>Instruction Format 2</b></p>
+ <p>This format encodes the opcode, type and two operands into a single <a
+ href="#uint32_vbr">uint32_vbr</a> as follows:</p>
+ <table>
+ <tbody>
+ <tr>
+ <th><b>Bits</b></th>
+ <th><b>Type</b></th>
+ <th class="td_left"><b>Field Description</b></th>
+ </tr>
+ <tr>
+ <td>0-1</td>
+ <td>constant "2"</td>
+ <td class="td_left">These two bits must be the value 2 which
+ identifies this as an instruction of format 2.</td>
+ </tr>
+ <tr>
+ <td>2-7</td>
+ <td><a href="#opcodes">opcode</a></td>
+ <td class="td_left">Specifies the opcode of the instruction. Note
+ that the maximum opcode value is 63.</td>
+ </tr>
+ <tr>
+ <td>8-15</td>
+ <td><a href="#unsigned">unsigned</a></td>
+ <td class="td_left">Specifies the slot number of the type for
+ this instruction. Maximum slot number is 2<sup>8</sup>-1=255.</td>
+ </tr>
+ <tr>
+ <td>16-23</td>
+ <td><a href="#unsigned">unsigned</a></td>
+ <td class="td_left">Specifies the slot number of the value for
+ the first operand. Maximum slot number is 2<sup>8</sup>-1=255.</td>
+ </tr>
+ <tr>
+ <td>24-31</td>
+ <td><a href="#unsigned">unsigned</a></td>
+ <td class="td_left">Specifies the slot number of the value for
+ the second operand. Maximum slot number is 2<sup>8</sup>-1=255.</td>
+ </tr>
+ </tbody>
+ </table>
+ <p><b>Instruction Format 3</b></p>
+ <p>This format encodes the opcode, type and three operands into a
+ single <a href="#uint32_vbr">uint32_vbr</a> as follows:</p>
+ <table>
+ <tbody>
+ <tr>
+ <th><b>Bits</b></th>
+ <th><b>Type</b></th>
+ <th class="td_left"><b>Field Description</b></th>
+ </tr>
+ <tr>
+ <td>0-1</td>
+ <td>constant "3"</td>
+ <td class="td_left">These two bits must be the value 3 which
+ identifies this as an instruction of format 3.</td>
+ </tr>
+ <tr>
+ <td>2-7</td>
+ <td><a href="#opcodes">opcode</a></td>
+ <td class="td_left">Specifies the opcode of the instruction. Note
+ that the maximum opcode value is 63.</td>
+ </tr>
+ <tr>
+ <td>8-13</td>
+ <td><a href="#unsigned">unsigned</a></td>
+ <td class="td_left">Specifies the slot number of the type for
+ this instruction. Maximum slot number is 2<sup>6</sup>-1=63.</td>
+ </tr>
+ <tr>
+ <td>14-19</td>
+ <td><a href="#unsigned">unsigned</a></td>
+ <td class="td_left">Specifies the slot number of the value for
+ the first operand. Maximum slot number is 2<sup>6</sup>-1=63.</td>
+ </tr>
+ <tr>
+ <td>20-25</td>
+ <td><a href="#unsigned">unsigned</a></td>
+ <td class="td_left">Specifies the slot number of the value for
+ the second operand. Maximum slot number is 2<sup>6</sup>-1=63.</td>
+ </tr>
+ <tr>
+ <td>26-31</td>
+ <td><a href="#unsigned">unsigned</a></td>
+ <td class="td_left">Specifies the slot number of the value for
+ the third operand. Maximum slot number is 2<sup>6</sup>-1=63.</td>
+ </tr>
+ </tbody>
+ </table>
+ </div>
+ <!-- _______________________________________________________________________ -->
+ <div class="doc_subsection"><a name="symtab">Symbol Table</a> </div>
+ <div class="doc_text">
+ <p>A symbol table can be put out in conjunction with a module or a function.
+ A symbol table is a list of type planes. Each type plane starts with the number
+ of entries in the plane and the type plane's slot number (so the type
+ can be looked up in the global type pool). For each entry in a type
+ plane, the slot number of the value and the name associated with that
+ value are written. The format is given in the table below. </p>
+ <table>
+ <tbody>
+ <tr>
+ <th><b>Type</b></th>
+ <th class="td_left"><b>Field Description</b></th>
+ </tr>
+ <tr>
+ <td><a href="#block">block</a><br>
+ </td>
+ <td class="td_left">Symbol Table Identifier (0x04)</td>
+ </tr>
+ <tr>
+ <td><a href="#uint32_vbr">uint32_vbr</a></td>
+ <td class="td_left">Number of entries in type plane</td>
+ </tr>
+ <tr>
+ <td><a href="#symtab_entry">symtab_entry</a>*</td>
+ <td class="td_left">Provides the slot number of the type and its
+ name.</td>
+ </tr>
+ <tr>
+ <td><a href="#symtab_plane">symtab_plane</a>*</td>
+ <td class="td_left">A type plane containing value slot number and
+ name for all values of the same type.</td>
+ </tr>
+ </tbody>
+ </table>
+ </div>
+ <!-- _______________________________________________________________________ -->
+ <div class="doc_subsubsection"> <a name="symtab_plane">Symbol Table
+ Plane</a>
+ </div>
+ <div class="doc_text">
+ <p>A symbol table plane provides the symbol table entries for all
+ values of a common type. The encoding is given in the following table:</p>
+ <table>
+ <tbody>
+ <tr>
+ <th><b>Type</b></th>
+ <th class="td_left"><b>Field Description</b></th>
+ </tr>
+ <tr>
+ <td><a href="#uint32_vbr">uint32_vbr</a></td>
+ <td class="td_left">Number of entries in this plane.</td>
+ </tr>
+ <tr>
+ <td><a href="#uint32_vbr">uint32_vbr</a></td>
+ <td class="td_left">Slot number of type for this plane.</td>
+ </tr>
+ <tr>
+ <td><a href="#symtab_entry">symtab_entry</a>+</td>
+ <td class="td_left">The symbol table entries for this plane.</td>
+ </tr>
+ </tbody>
+ </table>
+ </div>
+ <!-- _______________________________________________________________________ -->
+ <div class="doc_subsubsection"> <a name="symtab_entry">Symbol Table
+ Entry</a>
+ </div>
+ <div class="doc_text">
+ <p>A symbol table entry provides the assocation between a type or
+ value's slot number and the name given to that type or value. The
+ format is given in the following table:</p>
+ <table>
+ <tbody>
+ <tr>
+ <th><b>Type</b></th>
+ <th class="td_left"><b>Field Description</b></th>
+ </tr>
+ <tr>
+ <td><a href="#uint32_vbr">uint24_vbr</a></td>
+ <td class="td_left">Slot number of the type or value being given
+ a name. </td>
+ </tr>
+ <tr>
+ <td><a href="#uint32_vbr">uint32_vbr</a></td>
+ <td class="td_left">Length of the character array that follows.</td>
+ </tr>
+ <tr>
+ <td><a href="#char">char</a>+</td>
+ <td class="td_left">The characters of the name.</td>
+ </tr>
+ </tbody>
+ </table>
+ </div>
+ <!-- *********************************************************************** -->
+ <div class="doc_section"> <a name="versiondiffs">Version Differences</a>
+ </div>
+ <!-- *********************************************************************** -->
+ <div class="doc_text">
+ <p>This section describes the differences in the Bytecode Format across
+ LLVM
+ versions. The versions are listed in reverse order because it assumes
+ the current version is as documented in the previous sections. Each
+ section here
+ describes the differences between that version and the one that <i>follows</i>.
+ </p>
+ </div>
+ <!-- _______________________________________________________________________ -->
+ <div class="doc_subsection"><a name="vers12">Version 1.2 Differences
+ From 1.3</a></div>
+ <!-- _______________________________________________________________________ -->
+ <div class="doc_subsubsection">Type Derives From Value</div>
+ <div class="doc_text">
+ <p>In version 1.2, the Type class in the LLVM IR derives from the Value
+ class. This is not the case in version 1.3. Consequently, in version
+ 1.2 the notion of a "Type Type" was used to write out values that were
+ Types. The types always occuped plane 12 (corresponding to the
+ TypeTyID) of any type planed set of values. In 1.3 this representation
+ is not convenient because the TypeTyID (12) is not present and its
+ value is now used for LabelTyID. Consequently, the data structures
+ written that involve types do so by writing all the types first and
+ then each of the value planes according to those types. In version 1.2,
+ the types would have been written intermingled with the values.</p>
+ </div>
+ <!-- _______________________________________________________________________ -->
+ <div class="doc_subsubsection">Restricted getelementptr Types</div>
+ <div class="doc_text">
+ <p>In version 1.2, the getelementptr instruction required a ubyte type
+ index for accessing a structure field and a long type index for
+ accessing an array element. Consequently, it was only possible to
+ access structures of 255 or fewer elements. Starting in version 1.3,
+ this restriction was lifted. Structures must now be indexed with uint
+ constants. Arrays may now be indexed with int, uint, long, or ulong
+ typed values. The consequence of this was that the bytecode format had
+ to change in order to accommodate the larger range of structure indices.</p>
+ </div>
+ <!-- _______________________________________________________________________ -->
+ <div class="doc_subsubsection">Short Block Headers</div>
+ <div class="doc_text">
+ <p>In version 1.2, block headers were always 8 bytes being comprised of
+ both an unsigned integer type and an unsigned integer size. For very
+ small modules, these block headers turn out to be a large fraction of
+ the total bytecode file size. In an attempt to make these small files
+ smaller, the type and size information was encoded into a single
+ unsigned integer (4 bytes) comprised of 5 bits for the block type
+ (maximum 31 block types) and 27 bits for the block size (max
+ ~134MBytes). These limits seemed sufficient for any blocks or sizes
+ forseen in the future. Note that the module block, which encloses all
+ the other blocks is still written as 8 bytes since bytecode files
+ larger than 134MBytes might be possible.</p>
+ </div>
+ <!-- _______________________________________________________________________ -->
+ <div class="doc_subsubsection">Dependent Libraries and Target Triples</div>
+ <div class="doc_text">
+ <p>In version 1.2, the bytecode format does not store module's target
+ triple or dependent. These fields have been added to the end of the <a
+ href="#globalinfo">module global info block</a>. The purpose of these
+ fields is to allow a front end compiler to specifiy that the generated
+ module is specific to a particular target triple (operating
+ system/manufacturer/processor) which makes it non-portable; and to
+ allow front end compilers to specify the list of libraries that the
+ module depends on for successful linking.</p>
+ </div>
+ <!-- _______________________________________________________________________ -->
+ <div class="doc_subsubsection">Types Restricted to 24-bits</div>
+ <div class="doc_text">
+ <p>In version 1.2, type slot identifiers were written as 32-bit VBR
+ quantities. In 1.3 this has been reduced to 24-bits in order to ensure
+ that it is not possible to overflow the type field of a global variable
+ definition. 24-bits for type slot numbers is deemed sufficient for any
+ practical use of LLVM.</p>
+ </div>
+ <!-- _______________________________________________________________________ -->
+ <!-- _______________________________________________________________________ -->
+ <div class="doc_subsection"><a name="vers11">Version 1.1 Differences
+ From 1.2 </a></div>
+ <!-- _______________________________________________________________________ -->
+ <div class="doc_subsubsection">Explicit Primitive Zeros</div>
+ <div class="doc_text">
+ <p>In version 1.1, the zero value for primitives was explicitly encoded
+ into the bytecode format. Since these zero values are constant values
+ in the LLVM IR and never change, there is no reason to explicitly
+ encode them. This explicit encoding was removed in version 1.2.</p>
+ </div>
+ <!-- _______________________________________________________________________ -->
+ <div class="doc_subsubsection">Inconsistent Module Global Info</div>
+ <div class="doc_text">
+ <p>In version 1.1, the Module Global Info block was not aligned causing
+ the next block to be read in on an unaligned boundary. This problem was
+ corrected in version 1.2.<br>
+ <br>
+ </p>
+ </div>
+ <!-- _______________________________________________________________________ -->
+ <div class="doc_subsection"><a name="vers10">Version 1.0 Differences
+ From 1.1</a></div>
+ <div class="doc_text">
+ <p>None. Version 1.0 and 1.1 bytecode formats are identical.</p>
+ </div>
+ <!-- *********************************************************************** -->
+ <hr>
+ <address> <a href="http://jigsaw.w3.org/css-validator/check/referer"><img
+ src="http://jigsaw.w3.org/css-validator/images/vcss" alt="Valid CSS!"></a>
+ <a href="http://validator.w3.org/check/referer"><img
+ src="http://www.w3.org/Icons/valid-html401" alt="Valid HTML 4.01!"></a>
+ <a href="mailto:rspencer at x10sys.com">Reid Spencer</a> and <a
+ href="mailto:sabre at nondot.org">Chris Lattner</a><br>
+ <a href="http://llvm.cs.uiuc.edu">The LLVM Compiler Infrastructure</a><br>
+ Last modified: $Date: 2004/08/13 22:03:03 $
+ </address>
+ <!-- vim: sw=2
+ -->
+ </body>
+ </html>
Index: llvm-www/releases/1.3/docs/CFEBuildInstrs.html
diff -c /dev/null llvm-www/releases/1.3/docs/CFEBuildInstrs.html:1.1
*** /dev/null Fri Aug 13 17:03:14 2004
--- llvm-www/releases/1.3/docs/CFEBuildInstrs.html Fri Aug 13 17:03:03 2004
***************
*** 0 ****
--- 1,309 ----
+ <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"
+ "http://www.w3.org/TR/html4/strict.dtd">
+ <html>
+ <head>
+ <meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
+ <link rel="stylesheet" href="llvm.css" type="text/css" media="screen">
+ <title>Bootstrapping the LLVM C/C++ Front-End</title>
+ </head>
+ <body>
+
+ <div class="doc_title">
+ Bootstrapping the LLVM C/C++ Front-End
+ </div>
+
+ <ol>
+ <li><a href="#cautionarynote">A Cautionary Note</a>
+ <ul>
+ <li><a href="#cygwin">Building under Cygwin</a></li>
+ </ul>
+ </li>
+ <li><a href="#instructions">Instructions</a></li>
+ <li><a href="#license">License Information</a></li>
+ </ol>
+
+ <div class="doc_author">
+ <p>Written by Brian R. Gaeke and
+ <a href="http://nondot.org/sabre">Chris Lattner</a></p>
+ </div>
+
+ <!-- *********************************************************************** -->
+ <div class="doc_section">
+ <a name="cautionarynote">A Cautionary Note</a>
+ </div>
+ <!-- *********************************************************************** -->
+
+ <div class="doc_text">
+ <p>This document is intended to explain the process of building the
+ LLVM C/C++ front-end, based on GCC 3.4, from its source code. You
+ would have to do this, for example, if you are porting LLVM to a new
+ architecture or operating system.</p>
+
+ <p><b>NOTE:</b> This is currently a somewhat fragile, error-prone
+ process, and you should <b>only</b> try to do it if:</p>
+
+ <ol>
+ <li>you really, really, really can't use the binaries we distribute</li>
+ <li>you need GCC to fix some of the header files on your system</li>
+ <li>you are an elite GCC hacker.</li>
+ </ol>
+
+ <p>We welcome patches to help make this process simpler.</p>
+ </div>
+
+ <!--=========================================================================-->
+ <div class="doc_subsection">
+ <a name="cygwin">Building under Cygwin</a>
+ </div>
+ <!--=========================================================================-->
+
+ <div class="doc_text">
+ <p>If you are building LLVM and the C front-end under Cygwin, please note that
+ the LLVM and GCC makefiles do not correctly handle spaces in paths. To deal
+ with this issue, make sure that your LLVM and GCC source and build trees are
+ located in a top-level directory (like <tt>/cygdrive/c/llvm</tt> and
+ <tt>/cygdrive/c/llvm-cfrontend</tt>), not in a directory that contains a space
+ (which includes your "home directory", because it lives under the "Documents
+ and Settings" directory). We welcome patches to fix this issue.
+ </p>
+ </div>
+
+ <!-- *********************************************************************** -->
+ <div class="doc_section">
+ <a name="instructions">Instructions</a>
+ </div>
+ <!-- *********************************************************************** -->
+
+ <div class="doc_text">
+ <p>
+ <ol>
+ <li><p>Configure and build the LLVM libraries and tools using:</p>
+ <pre>
+ % cd llvm
+ % ./configure [options...]
+ % gmake
+ </pre>
+ <p>This will build all of the LLVM tools and libraries, but you will see
+ warnings about missing the C front-end (certain runtime libraries can't
+ be built without it). Ignore these warnings for now.</p></li>
+
+ <li><p>Add the directory containing the tools to your PATH.</p>
+ <pre>
+ % set path = ( `cd llvm/tools/Debug && pwd` $path )
+ </pre></li>
+
+ <li><p>Unpack the C/C++ front-end source into cfrontend/src.</p></li>
+
+ <li><p>Make "build" and "install" directories as siblings of the "src"
+ tree.</p>
+ <pre>
+ % pwd
+ /usr/local/example/cfrontend/src
+ % cd ..
+ % mkdir build install
+ % set CFEINSTALL = `pwd`/install
+ </pre></li>
+
+
+ <li><p>Configure, build, and install the C front-end:</p>
+
+ <p>
+ <b>Linux/x86:</b><br>
+ <b>MacOS X/PowerPC</b> (requires dlcompat library):
+ </p>
+
+ <pre>
+ % cd build
+ % ../src/configure --prefix=$CFEINSTALL --disable-threads --disable-nls --disable-shared \
+ --enable-languages=c,c++
+ % gmake
+ % setenv LLVM_LIB_SEARCH_PATH `pwd`/gcc
+ % gmake all; gmake install
+ </pre>
+
+ <p><b>Cygwin/x86:</b></p>
+
+ <pre>
+ % cd build
+ % ../src/configure --prefix=$CFEINSTALL --disable-threads --disable-nls --disable-shared \
+ --enable-languages=c,c++ --disable-c-mbchar
+ % gmake
+ % setenv LLVM_LIB_SEARCH_PATH `pwd`/gcc
+ % gmake all; gmake install
+ </pre>
+
+ <p><b>Solaris/SPARC:</b></p>
+
+ <p>
+ For Solaris/SPARC, LLVM only supports the SPARC V9. Therefore, the
+ configure command line should specify sparcv9, as shown below. Also,
+ note that Solaris has trouble with various wide (multibyte) character
+ functions from C as referenced from C++, so we typically configure with
+ --disable-c-mbchar (cf. <a href="http://llvm.cs.uiuc.edu/PR206">Bug 206</a>).
+ </p>
+
+ <pre>
+ % cd build
+ % ../src/configure --prefix=$CFEINSTALL --disable-threads --disable-nls \
+ --disable-shared --enable-languages=c,c++ --host=sparcv9-sun-solaris2.8 \
+ --disable-c-mbchar
+ % gmake
+ % setenv LLVM_LIB_SEARCH_PATH `pwd`/gcc
+ % gmake all; gmake install
+ </pre>
+
+ <p><b>Common Problem:</b> You may get error messages regarding the fact
+ that LLVM does not support inline assembly. Here are two common
+ fixes:</p>
+
+ <ul>
+ <li><p><b>Fix 1:</b> If you have system header files that include
+ inline assembly, you may have to modify them to remove the inline
+ assembly, and install the modified versions in
+ <code>$CFEINSTALL/<i>target-triplet</i>/sys-include</code>.</li>
+
+ <li><b>Fix 2:</b> If you are building the C++ front-end on a CPU we
+ haven't tried yet, you will probably have to edit the appropriate
+ version of atomicity.h under
+ <code>src/libstdc++-v3/config/cpu/<i>name-of-cpu</i>/atomicity.h</code>
+ and apply a patch so that it does not use inline assembly.</li>
+ </ul>
+
+ <p><b>Porting to a new architecture:</b> If you are porting the new front-end
+ to a new architecture, or compiling in a different configuration that we have
+ previously, there are probably several changes you will have to make to the GCC
+ target to get it to work correctly. These include:<p>
+
+ <ul>
+ <li>Often targets include special or assembler linker flags which
+ <tt>gccas</tt>/<tt>gccld</tt> does not understand. In general, these can
+ just be removed.</li>
+ <li>LLVM currently does not support any floating point values other than
+ 32-bit and 64-bit IEEE floating point. The primary effect of this is
+ that you may have to map "long double" onto "double".</li>
+ <li>The profiling hooks in GCC do not apply at all to the LLVM front-end.
+ These may need to be disabled.</li>
+ <li>No inline assembly for position independent code. At the LLVM level,
+ everything is position independent.</li>
+ <li>We handle <tt>.init</tt> and <tt>.fini</tt> differently.</li>
+ <li>You may have to disable multilib support in your target. Using multilib
+ support causes the GCC compiler driver to add a lot of "<tt>-L</tt>"
+ options to the link line, which do not relate to LLVM and confuse
+ <tt>gccld</tt>. To disable multilibs, delete any
+ <tt>MULTILIB_OPTIONS</tt> lines from your target files.</li>
+ <li>Did we mention that we don't support inline assembly? You'll probably
+ have to add some fixinclude hacks to disable it in the system
+ headers.</li>
+ </ul>
+ </li>
+
+ <li><p>Go back into the LLVM source tree proper. Rerun configure, using
+ the <code>--with-llvmgccdir=$CFEINSTALL</code> option to specify the path
+ to the newly built C front-end.</p></li>
+
+ <li><p>If you edited header files during the C/C++ front-end build as
+ described in "Fix 1" above, you must now copy those header files from
+ <code>$CFEINSTALL/<i>target-triplet</i>/sys-include</code> to
+ <code>$CFEINSTALL/lib/gcc/<i>target-triplet</i>/3.4-llvm/include</code>.
+ (This should be the "include" directory in the same directory as the
+ libgcc.a library, which you can find by running
+ <code>$CFEINSTALL/bin/gcc --print-libgcc-file-name</code>.)</p></li>
+
+ <li><p>Rebuild your CVS tree. This shouldn't cause the whole thing to be
+ rebuilt, but it should build the runtime libraries. After the tree is
+ built, install the runtime libraries into your C front-end build tree.
+ These are the commands you need.</p>
+ <pre>
+ % gmake
+ % mkdir $CFEINSTALL/bytecode-libs
+ % gmake -C runtime install-bytecode
+ % setenv LLVM_LIB_SEARCH_PATH $CFEINSTALL/bytecode-libs
+ </pre></li>
+
+ <li><p>Test the newly-installed C frontend by one or more of the
+ following means:</p>
+ <ul>
+ <li> compiling and running a "hello, LLVM" program in C and C++.</li>
+ <li> running the tests under <tt>test/Programs</tt> using <code>gmake -C
+ test/Programs</code></li>
+ </ul></li>
+ </ol>
+ </div>
+
+ <!-- *********************************************************************** -->
+ <div class="doc_section">
+ <a name="license">License Information</a>
+ </div>
+
+ <div class="doc_text">
+ <p>
+ The LLVM GCC frontend is licensed to you under the GNU General Public License
+ and the GNU Lesser General Public License. Please see the files COPYING and
+ COPYING.LIB for more details.
+ </p>
+
+ <p>
+ The software also has the following additional copyrights:
+ </p>
+
+ <pre>
+
+ Copyright (c) 2003, 2004 University of Illinois at Urbana-Champaign.
+ All rights reserved.
+
+ Developed by:
+
+ LLVM Team
+
+ University of Illinois at Urbana-Champaign
+
+ http://llvm.cs.uiuc.edu
+
+ THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS
+ FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ CONTRIBUTORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS WITH THE
+ SOFTWARE.
+
+ Copyright (c) 1994
+ Hewlett-Packard Company
+
+ Permission to use, copy, modify, distribute and sell this software
+ and its documentation for any purpose is hereby granted without fee,
+ provided that the above copyright notice appear in all copies and
+ that both that copyright notice and this permission notice appear
+ in supporting documentation. Hewlett-Packard Company makes no
+ representations about the suitability of this software for any
+ purpose. It is provided "as is" without express or implied warranty.
+
+ Copyright (c) 1996, 1997, 1998, 1999
+ Silicon Graphics Computer Systems, Inc.
+
+ Permission to use, copy, modify, distribute and sell this software
+ and its documentation for any purpose is hereby granted without fee,
+ provided that the above copyright notice appear in all copies and
+ that both that copyright notice and this permission notice appear
+ in supporting documentation. Silicon Graphics makes no
+ representations about the suitability of this software for any
+ purpose. It is provided "as is" without express or implied warranty.
+ </pre>
+ </div>
+
+ <!-- *********************************************************************** -->
+
+ <hr>
+ <address>
+ <a href="http://jigsaw.w3.org/css-validator/check/referer"><img
+ src="http://jigsaw.w3.org/css-validator/images/vcss" alt="Valid CSS!"></a>
+ <a href="http://validator.w3.org/check/referer"><img
+ src="http://www.w3.org/Icons/valid-html401" alt="Valid HTML 4.01!"></a>
+
+ Brian Gaeke<br>
+ <a href="http://llvm.cs.uiuc.edu">LLVM Compiler Infrastructure</a><br>
+ Last modified: $Date: 2004/08/13 22:03:03 $
+ </address>
+
+ </body>
+ </html>
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+ <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"
+ "http://www.w3.org/TR/html4/strict.dtd">
+ <html>
+ <head>
+ <title>The LLVM Target-Independent Code Generator</title>
+ <link rel="stylesheet" href="llvm.css" type="text/css">
+ </head>
+ <body>
+
+ <div class="doc_title">
+ The LLVM Target-Independent Code Generator
+ </div>
+
+ <ol>
+ <li><a href="#introduction">Introduction</a>
+ <ul>
+ <li><a href="#required">Required components in the code generator</a></li>
+ <li><a href="#high-level-design">The high-level design of the code generator</a></li>
+ <li><a href="#tablegen">Using TableGen for target description</a></li>
+ </ul>
+ </li>
+ <li><a href="#targetdesc">Target description classes</a>
+ <ul>
+ <li><a href="#targetmachine">The <tt>TargetMachine</tt> class</a></li>
+ <li><a href="#targetdata">The <tt>TargetData</tt> class</a></li>
+ <li><a href="#mregisterinfo">The <tt>MRegisterInfo</tt> class</a></li>
+ <li><a href="#targetinstrinfo">The <tt>TargetInstrInfo</tt> class</a></li>
+ <li><a href="#targetframeinfo">The <tt>TargetFrameInfo</tt> class</a></li>
+ <li><a href="#targetjitinfo">The <tt>TargetJITInfo</tt> class</a></li>
+ </ul>
+ </li>
+ <li><a href="#codegendesc">Machine code description classes</a>
+ <ul>
+ <li><a href="#machineinstr">The <tt>MachineInstr</tt> class</a></li>
+ </ul>
+ </li>
+ <li><a href="#codegenalgs">Target-independent code generation algorithms</a>
+ </li>
+ <li><a href="#targetimpls">Target description implementations</a>
+ <ul>
+ <li><a href="#x86">The X86 backend</a></li>
+ </ul>
+ </li>
+
+ </ol>
+
+ <div class="doc_author">
+ <p>Written by <a href="mailto:sabre at nondot.org">Chris Lattner</a></p>
+ </div>
+
+ <div class="doc_warning">
+ <p>Warning: This is a work in progress.</p>
+ </div>
+
+ <!-- *********************************************************************** -->
+ <div class="doc_section">
+ <a name="introduction">Introduction</a>
+ </div>
+ <!-- *********************************************************************** -->
+
+ <div class="doc_text">
+
+ <p>The LLVM target-independent code generator is a framework that provides a
+ suite of reusable components for translating the LLVM internal representation to
+ the machine code for a specified target -- either in assembly form (suitable for
+ a static compiler) or in binary machine code format (usable for a JIT compiler).
+ The LLVM target-independent code generator consists of five main components:</p>
+
+ <ol>
+ <li><a href="#targetdesc">Abstract target description</a> interfaces which
+ capture important properties about various aspects of the machine, independently
+ of how they will be used. These interfaces are defined in
+ <tt>include/llvm/Target/</tt>.</li>
+
+ <li>Classes used to represent the <a href="#codegendesc">machine code</a> being
+ generated for a target. These classes are intended to be abstract enough to
+ represent the machine code for <i>any</i> target machine. These classes are
+ defined in <tt>include/llvm/CodeGen/</tt>.</li>
+
+ <li><a href="#codegenalgs">Target-independent algorithms</a> used to implement
+ various phases of native code generation (register allocation, scheduling, stack
+ frame representation, etc). This code lives in <tt>lib/CodeGen/</tt>.</li>
+
+ <li><a href="#targetimpls">Implementations of the abstract target description
+ interfaces</a> for particular targets. These machine descriptions make use of
+ the components provided by LLVM, and can optionally provide custom
+ target-specific passes, to build complete code generators for a specific target.
+ Target descriptions live in <tt>lib/Target/</tt>.</li>
+
+ <li><a href="#jit">The target-independent JIT components</a>. The LLVM JIT is
+ completely target independent (it uses the <tt>TargetJITInfo</tt> structure to
+ interface for target-specific issues. The code for the target-independent
+ JIT lives in <tt>lib/ExecutionEngine/JIT</tt>.</li>
+
+ </ol>
+
+ <p>
+ Depending on which part of the code generator you are interested in working on,
+ different pieces of this will be useful to you. In any case, you should be
+ familiar with the <a href="#targetdesc">target description</a> and <a
+ href="#codegendesc">machine code representation</a> classes. If you want to add
+ a backend for a new target, you will need to <a href="#targetimpls">implement the
+ target description</a> classes for your new target and understand the <a
+ href="LangRef.html">LLVM code representation</a>. If you are interested in
+ implementing a new <a href="#codegenalgs">code generation algorithm</a>, it
+ should only depend on the target-description and machine code representation
+ classes, ensuring that it is portable.
+ </p>
+
+ </div>
+
+ <!-- ======================================================================= -->
+ <div class="doc_subsection">
+ <a name="required">Required components in the code generator</a>
+ </div>
+
+ <div class="doc_text">
+
+ <p>The two pieces of the LLVM code generator are the high-level interface to the
+ code generator and the set of reusable components that can be used to build
+ target-specific backends. The two most important interfaces (<a
+ href="#targetmachine"><tt>TargetMachine</tt></a> and <a
+ href="#targetdata"><tt>TargetData</tt></a> classes) are the only ones that are
+ required to be defined for a backend to fit into the LLVM system, but the others
+ must be defined if the reusable code generator components are going to be
+ used.</p>
+
+ <p>This design has two important implications. The first is that LLVM can
+ support completely non-traditional code generation targets. For example, the C
+ backend does not require register allocation, instruction selection, or any of
+ the other standard components provided by the system. As such, it only
+ implements these two interfaces, and does its own thing. Another example of a
+ code generator like this is a (purely hypothetical) backend that converts LLVM
+ to the GCC RTL form and uses GCC to emit machine code for a target.</p>
+
+ <p>This design also implies that it is possible to design and
+ implement radically different code generators in the LLVM system that do not
+ make use of any of the built-in components. Doing so is not recommended at all,
+ but could be required for radically different targets that do not fit into the
+ LLVM machine description model: programmable FPGAs for example.</p>
+
+ <p><b>Important Note:</b> For historical reasons, the LLVM SparcV9 code
+ generator uses almost entirely different code paths than described in this
+ document. For this reason, there are some deprecated interfaces (such as
+ <tt>TargetRegInfo</tt> and <tt>TargetSchedInfo</tt>), which are only used by the
+ V9 backend and should not be used by any other targets. Also, all code in the
+ <tt>lib/Target/SparcV9</tt> directory and subdirectories should be considered
+ deprecated, and should not be used as the basis for future code generator work.
+ The SparcV9 backend is slowly being merged into the rest of the
+ target-independent code generators, but this is a low-priority process with no
+ predictable completion date.</p>
+
+ </div>
+
+ <!-- ======================================================================= -->
+ <div class="doc_subsection">
+ <a name="high-level-design">The high-level design of the code generator</a>
+ </div>
+
+ <div class="doc_text">
+
+ <p>The LLVM target-indendent code generator is designed to support efficient and
+ quality code generation for standard register-based microprocessors. Code
+ generation in this model is divided into the following stages:</p>
+
+ <ol>
+ <li><b>Instruction Selection</b> - Determining an efficient implementation of the
+ input LLVM code in the target instruction set. This stage produces the initial
+ code for the program in the target instruction set, then makes use of virtual
+ registers in SSA form and physical registers that represent any required
+ register assignments due to target constraints or calling conventions.</li>
+
+ <li><b>SSA-based Machine Code Optimizations</b> - This (optional) stage consists
+ of a series of machine-code optimizations that operate on the SSA-form produced
+ by the instruction selector. Optimizations like modulo-scheduling, normal
+ scheduling, or peephole optimization work here.</li>
+
+ <li><b>Register Allocation</b> - The target code is transformed from an infinite
+ virtual register file in SSA form to the concrete register file used by the
+ target. This phase introduces spill code and eliminates all virtual register
+ references from the program.</li>
+
+ <li><b>Prolog/Epilog Code Insertion</b> - Once the machine code has been
+ generated for the function and the amount of stack space required is known (used
+ for LLVM alloca's and spill slots), the prolog and epilog code for the function
+ can be inserted and "abstract stack location references" can be eliminated.
+ This stage is responsible for implementing optimizations like frame-pointer
+ elimination and stack packing.</li>
+
+ <li><b>Late Machine Code Optimizations</b> - Optimizations that operate on
+ "final" machine code can go here, such as spill code scheduling and peephole
+ optimizations.</li>
+
+ <li><b>Code Emission</b> - The final stage actually outputs the code for
+ the current function, either in the target assembler format or in machine
+ code.</li>
+
+ </ol>
+
+ <p>
+ The code generator is based on the assumption that the instruction selector will
+ use an optimal pattern matching selector to create high-quality sequences of
+ native instructions. Alternative code generator designs based on pattern
+ expansion and
+ aggressive iterative peephole optimization are much slower. This design
+ permits efficient compilation (important for JIT environments) and
+ aggressive optimization (used when generating code offline) by allowing
+ components of varying levels of sophisication to be used for any step of
+ compilation.</p>
+
+ <p>
+ In addition to these stages, target implementations can insert arbitrary
+ target-specific passes into the flow. For example, the X86 target uses a
+ special pass to handle the 80x87 floating point stack architecture. Other
+ targets with unusual requirements can be supported with custom passes as needed.
+ </p>
+
+ </div>
+
+
+ <!-- ======================================================================= -->
+ <div class="doc_subsection">
+ <a name="tablegen">Using TableGen for target description</a>
+ </div>
+
+ <div class="doc_text">
+
+ <p>The target description classes require a detailed description of the target
+ architecture. These target descriptions often have a large amount of common
+ information (e.g., an add instruction is almost identical to a sub instruction).
+ In order to allow the maximum amount of commonality to be factored out, the LLVM
+ code generator uses the <a href="TableGenFundamentals.html">TableGen</a> tool to
+ describe big chunks of the target machine, which allows the use of domain- and
+ target-specific abstractions to reduce the amount of repetition.
+ </p>
+
+ </div>
+
+ <!-- *********************************************************************** -->
+ <div class="doc_section">
+ <a name="targetdesc">Target description classes</a>
+ </div>
+ <!-- *********************************************************************** -->
+
+ <div class="doc_text">
+
+ <p>The LLVM target description classes (which are located in the
+ <tt>include/llvm/Target</tt> directory) provide an abstract description of the
+ target machine, independent of any particular client. These classes are
+ designed to capture the <i>abstract</i> properties of the target (such as what
+ instruction and registers it has), and do not incorporate any particular pieces
+ of code generation algorithms (these interfaces do not take interference graphs
+ as inputs or other algorithm-specific data structures).</p>
+
+ <p>All of the target description classes (except the <tt><a
+ href="#targetdata">TargetData</a></tt> class) are designed to be subclassed by
+ the concrete target implementation, and have virtual methods implemented. To
+ get to these implementations, the <tt><a
+ href="#targetmachine">TargetMachine</a></tt> class provides accessors that
+ should be implemented by the target.</p>
+
+ </div>
+
+ <!-- ======================================================================= -->
+ <div class="doc_subsection">
+ <a name="targetmachine">The <tt>TargetMachine</tt> class</a>
+ </div>
+
+ <div class="doc_text">
+
+ <p>The <tt>TargetMachine</tt> class provides virtual methods that are used to
+ access the target-specific implementations of the various target description
+ classes (with the <tt>getInstrInfo</tt>, <tt>getRegisterInfo</tt>,
+ <tt>getFrameInfo</tt>, ... methods). This class is designed to be specialized by
+ a concrete target implementation (e.g., <tt>X86TargetMachine</tt>) which
+ implements the various virtual methods. The only required target description
+ class is the <a href="#targetdata"><tt>TargetData</tt></a> class, but if the
+ code generator components are to be used, the other interfaces should be
+ implemented as well.</p>
+
+ </div>
+
+
+ <!-- ======================================================================= -->
+ <div class="doc_subsection">
+ <a name="targetdata">The <tt>TargetData</tt> class</a>
+ </div>
+
+ <div class="doc_text">
+
+ <p>The <tt>TargetData</tt> class is the only required target description class,
+ and it is the only class that is not extensible (it cannot be derived from). It
+ specifies information about how the target lays out memory for structures, the
+ alignment requirements for various data types, the size of pointers in the
+ target, and whether the target is little- or big-endian.</p>
+
+ </div>
+
+
+ <!-- ======================================================================= -->
+ <div class="doc_subsection">
+ <a name="mregisterinfo">The <tt>MRegisterInfo</tt> class</a>
+ </div>
+
+ <div class="doc_text">
+
+ <p>The <tt>MRegisterInfo</tt> class (which will eventually be renamed to
+ <tt>TargetRegisterInfo</tt>) is used to describe the register file of the
+ target and any interactions between the registers.</p>
+
+ <p>Registers in the code generator are represented in the code generator by
+ unsigned numbers. Physical registers (those that actually exist in the target
+ description) are unique small numbers, and virtual registers are generally
+ large.</p>
+
+ <p>Each register in the processor description has an associated
+ <tt>MRegisterDesc</tt> entry, which provides a textual name for the register
+ (used for assembly output and debugging dumps), a set of aliases (used to
+ indicate that one register overlaps with another), and some flag bits.
+ </p>
+
+ <p>In addition to the per-register description, the <tt>MRegisterInfo</tt> class
+ exposes a set of processor specific register classes (instances of the
+ <tt>TargetRegisterClass</tt> class). Each register class contains sets of
+ registers that have the same properties (for example, they are all 32-bit
+ integer registers). Each SSA virtual register created by the instruction
+ selector has an associated register class. When the register allocator runs, it
+ replaces virtual registers with a physical register in the set.</p>
+
+ <p>
+ The target-specific implementations of these classes is auto-generated from a <a
+ href="TableGenFundamentals.html">TableGen</a> description of the register file.
+ </p>
+
+ </div>
+
+ <!-- ======================================================================= -->
+ <div class="doc_subsection">
+ <a name="targetinstrinfo">The <tt>TargetInstrInfo</tt> class</a>
+ </div>
+
+ <!-- ======================================================================= -->
+ <div class="doc_subsection">
+ <a name="targetframeinfo">The <tt>TargetFrameInfo</tt> class</a>
+ </div>
+
+ <!-- ======================================================================= -->
+ <div class="doc_subsection">
+ <a name="targetjitinfo">The <tt>TargetJITInfo</tt> class</a>
+ </div>
+
+ <!-- *********************************************************************** -->
+ <div class="doc_section">
+ <a name="codegendesc">Machine code description classes</a>
+ </div>
+ <!-- *********************************************************************** -->
+
+ <div class="doc_text">
+
+ <p>
+ At the high-level, LLVM code is translated to a machine specific representation
+ formed out of MachineFunction, MachineBasicBlock, and <a
+ href="#machineinstr"><tt>MachineInstr</tt></a> instances
+ (defined in include/llvm/CodeGen). This representation is completely target
+ agnostic, representing instructions in their most abstract form: an opcode and a
+ series of operands. This representation is designed to support both SSA
+ representation for machine code, as well as a register allocated, non-SSA form.
+ </p>
+
+ </div>
+
+ <!-- ======================================================================= -->
+ <div class="doc_subsection">
+ <a name="machineinstr">The <tt>MachineInstr</tt> class</a>
+ </div>
+
+ <div class="doc_text">
+
+ <p>Target machine instructions are represented as instances of the
+ <tt>MachineInstr</tt> class. This class is an extremely abstract way of
+ representing machine instructions. In particular, all it keeps track of is
+ an opcode number and some number of operands.</p>
+
+ <p>The opcode number is an simple unsigned number that only has meaning to a
+ specific backend. All of the instructions for a target should be defined in
+ the <tt>*InstrInfo.td</tt> file for the target, and the opcode enum values
+ are autogenerated from this description. The <tt>MachineInstr</tt> class does
+ not have any information about how to intepret the instruction (i.e., what the
+ semantics of the instruction are): for that you must refer to the
+ <tt><a href="#targetinstrinfo">TargetInstrInfo</a></tt> class.</p>
+
+ <p>The operands of a machine instruction can be of several different types:
+ they can be a register reference, constant integer, basic block reference, etc.
+ In addition, a machine operand should be marked as a def or a use of the value
+ (though only registers are allowed to be defs).</p>
+
+ <p>By convention, the LLVM code generator orders instruction operands so that
+ all register definitions come before the register uses, even on architectures
+ that are normally printed in other orders. For example, the sparc add
+ instruction: "<tt>add %i1, %i2, %i3</tt>" adds the "%i1", and "%i2" registers
+ and stores the result into the "%i3" register. In the LLVM code generator,
+ the operands should be stored as "<tt>%i3, %i1, %i2</tt>": with the destination
+ first.</p>
+
+ <p>Keeping destination operands at the beginning of the operand list has several
+ advantages. In particular, the debugging printer will print the instruction
+ like this:</p>
+
+ <pre>
+ %r3 = add %i1, %i2
+ </pre>
+
+ <p>If the first operand is a def, and it is also easier to <a
+ href="#buildmi">create instructions</a> whose only def is the first
+ operand.</p>
+
+ </div>
+
+ <!-- _______________________________________________________________________ -->
+ <div class="doc_subsubsection">
+ <a name="buildmi">Using the <tt>MachineInstrBuilder.h</tt> functions</a>
+ </div>
+
+ <div class="doc_text">
+
+ <p>Machine instructions are created by using the <tt>BuildMI</tt> functions,
+ located in the <tt>include/llvm/CodeGen/MachineInstrBuilder.h</tt> file. The
+ <tt>BuildMI</tt> functions make it easy to build arbitrary machine
+ instructions. Usage of the <tt>BuildMI</tt> functions look like this:
+ </p>
+
+ <pre>
+ // Create a 'DestReg = mov 42' (rendered in X86 assembly as 'mov DestReg, 42')
+ // instruction. The '1' specifies how many operands will be added.
+ MachineInstr *MI = BuildMI(X86::MOV32ri, 1, DestReg).addImm(42);
+
+ // Create the same instr, but insert it at the end of a basic block.
+ MachineBasicBlock &MBB = ...
+ BuildMI(MBB, X86::MOV32ri, 1, DestReg).addImm(42);
+
+ // Create the same instr, but insert it before a specified iterator point.
+ MachineBasicBlock::iterator MBBI = ...
+ BuildMI(MBB, MBBI, X86::MOV32ri, 1, DestReg).addImm(42);
+
+ // Create a 'cmp Reg, 0' instruction, no destination reg.
+ MI = BuildMI(X86::CMP32ri, 2).addReg(Reg).addImm(0);
+ // Create an 'sahf' instruction which takes no operands and stores nothing.
+ MI = BuildMI(X86::SAHF, 0);
+
+ // Create a self looping branch instruction.
+ BuildMI(MBB, X86::JNE, 1).addMBB(&MBB);
+ </pre>
+
+ <p>
+ The key thing to remember with the <tt>BuildMI</tt> functions is that you have
+ to specify the number of operands that the machine instruction will take
+ (allowing efficient memory allocation). Also, if operands default to be uses
+ of values, not definitions. If you need to add a definition operand (other
+ than the optional destination register), you must explicitly mark it as such.
+ </p>
+
+ </div>
+
+ <!-- _______________________________________________________________________ -->
+ <div class="doc_subsubsection">
+ <a name="fixedregs">Fixed (aka preassigned) registers</a>
+ </div>
+
+ <div class="doc_text">
+
+ <p>One important issue that the code generator needs to be aware of is the
+ presence of fixed registers. In particular, there are often places in the
+ instruction stream where the register allocator <em>must</em> arrange for a
+ particular value to be in a particular register. This can occur due to
+ limitations in the instruction set (e.g., the X86 can only do a 32-bit divide
+ with the <tt>EAX</tt>/<tt>EDX</tt> registers), or external factors like calling
+ conventions. In any case, the instruction selector should emit code that
+ copies a virtual register into or out of a physical register when needed.</p>
+
+ <p>For example, consider this simple LLVM example:</p>
+
+ <pre>
+ int %test(int %X, int %Y) {
+ %Z = div int %X, %Y
+ ret int %Z
+ }
+ </pre>
+
+ <p>The X86 instruction selector produces this machine code for the div
+ and ret (use
+ "<tt>llc X.bc -march=x86 -print-machineinstrs</tt>" to get this):</p>
+
+ <pre>
+ ;; Start of div
+ %EAX = mov %reg1024 ;; Copy X (in reg1024) into EAX
+ %reg1027 = sar %reg1024, 31
+ %EDX = mov %reg1027 ;; Sign extend X into EDX
+ idiv %reg1025 ;; Divide by Y (in reg1025)
+ %reg1026 = mov %EAX ;; Read the result (Z) out of EAX
+
+ ;; Start of ret
+ %EAX = mov %reg1026 ;; 32-bit return value goes in EAX
+ ret
+ </pre>
+
+ <p>By the end of code generation, the register allocator has coallesced
+ the registers and deleted the resultant identity moves, producing the
+ following code:</p>
+
+ <pre>
+ ;; X is in EAX, Y is in ECX
+ mov %EAX, %EDX
+ sar %EDX, 31
+ idiv %ECX
+ ret
+ </pre>
+
+ <p>This approach is extremely general (if it can handle the X86 architecture,
+ it can handle anything!) and allows all of the target specific
+ knowledge about the instruction stream to be isolated in the instruction
+ selector. Note that physical registers should have a short lifetime for good
+ code generation, and all physical registers are assumed dead on entry and
+ exit of basic blocks (before register allocation). Thus if you need a value
+ to be live across basic block boundaries, it <em>must</em> live in a virtual
+ register.</p>
+
+ </div>
+
+ <!-- _______________________________________________________________________ -->
+ <div class="doc_subsubsection">
+ <a name="ssa">Machine code SSA form</a>
+ </div>
+
+ <div class="doc_text">
+
+ <p><tt>MachineInstr</tt>'s are initially instruction selected in SSA-form, and
+ are maintained in SSA-form until register allocation happens. For the most
+ part, this is trivially simple since LLVM is already in SSA form: LLVM PHI nodes
+ become machine code PHI nodes, and virtual registers are only allowed to have a
+ single definition.</p>
+
+ <p>After register allocation, machine code is no longer in SSA-form, as there
+ are no virtual registers left in the code.</p>
+
+ </div>
+
+ <!-- *********************************************************************** -->
+ <div class="doc_section">
+ <a name="targetimpls">Target description implementations</a>
+ </div>
+ <!-- *********************************************************************** -->
+
+ <div class="doc_text">
+
+ <p>This section of the document explains any features or design decisions that
+ are specific to the code generator for a particular target.</p>
+
+ </div>
+
+
+ <!-- ======================================================================= -->
+ <div class="doc_subsection">
+ <a name="x86">The X86 backend</a>
+ </div>
+
+ <div class="doc_text">
+
+ <p>
+ The X86 code generator lives in the <tt>lib/Target/X86</tt> directory. This
+ code generator currently targets a generic P6-like processor. As such, it
+ produces a few P6-and-above instructions (like conditional moves), but it does
+ not make use of newer features like MMX or SSE. In the future, the X86 backend
+ will have subtarget support added for specific processor families and
+ implementations.</p>
+
+ </div>
+
+ <!-- _______________________________________________________________________ -->
+ <div class="doc_subsubsection">
+ <a name="x86_memory">Representing X86 addressing modes in MachineInstrs</a>
+ </div>
+
+ <div class="doc_text">
+
+ <p>
+ The x86 has a very, uhm, flexible, way of accessing memory. It is capable of
+ forming memory addresses of the following expression directly in integer
+ instructions (which use ModR/M addressing):</p>
+
+ <pre>
+ Base+[1,2,4,8]*IndexReg+Disp32
+ </pre>
+
+ <p>Wow, that's crazy. In order to represent this, LLVM tracks no less that 4
+ operands for each memory operand of this form. This means that the "load" form
+ of 'mov' has the following "Operands" in this order:</p>
+
+ <pre>
+ Index: 0 | 1 2 3 4
+ Meaning: DestReg, | BaseReg, Scale, IndexReg, Displacement
+ OperandTy: VirtReg, | VirtReg, UnsImm, VirtReg, SignExtImm
+ </pre>
+
+ <p>Stores and all other instructions treat the four memory operands in the same
+ way, in the same order.</p>
+
+ </div>
+
+ <!-- _______________________________________________________________________ -->
+ <div class="doc_subsubsection">
+ <a name="x86_names">Instruction naming</a>
+ </div>
+
+ <div class="doc_text">
+
+ <p>
+ An instruction name consists of the base name, a default operand size
+ followed by a character per operand with an optional special size. For
+ example:</p>
+
+ <p>
+ <tt>ADD8rr</tt> -> add, 8-bit register, 8-bit register<br>
+ <tt>IMUL16rmi</tt> -> imul, 16-bit register, 16-bit memory, 16-bit immediate<br>
+ <tt>IMUL16rmi8</tt> -> imul, 16-bit register, 16-bit memory, 8-bit immediate<br>
+ <tt>MOVSX32rm16</tt> -> movsx, 32-bit register, 16-bit memory
+ </p>
+
+ </div>
+
+ <!-- *********************************************************************** -->
+ <hr>
+ <address>
+ <a href="http://jigsaw.w3.org/css-validator/check/referer"><img
+ src="http://jigsaw.w3.org/css-validator/images/vcss" alt="Valid CSS!"></a>
+ <a href="http://validator.w3.org/check/referer"><img
+ src="http://www.w3.org/Icons/valid-html401" alt="Valid HTML 4.01!" /></a>
+
+ <a href="mailto:sabre at nondot.org">Chris Lattner</a><br>
+ <a href="http://llvm.cs.uiuc.edu">The LLVM Compiler Infrastructure</a><br>
+ Last modified: $Date: 2004/08/13 22:03:03 $
+ </address>
+
+ </body>
+ </html>
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+ <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"
+ "http://www.w3.org/TR/html4/strict.dtd">
+ <html>
+ <head>
+ <link rel="stylesheet" href="llvm.css" type="text/css">
+ <title>A Few Coding Standards</title>
+ </head>
+ <body>
+
+ <div class="doc_title">
+ A Few Coding Standards
+ </div>
+
+ <ol>
+ <li><a href="#introduction">Introduction</a></li>
+ <li><a href="#mechanicalissues">Mechanical Source Issues</a>
+ <ol>
+ <li><a href="#sourceformating">Source Code Formatting</a>
+ <ol>
+ <li><a href="#scf_commenting">Commenting</a></li>
+ <li><a href="#scf_commentformat">Comment Formatting</a></li>
+ <li><a href="#scf_includes">#include Style</a></li>
+ <li><a href="#scf_codewidth">Source Code Width</a></li>
+ <li><a href="#scf_spacestabs">Use Spaces Instead of Tabs</a></li>
+ <li><a href="#scf_indentation">Indent Code Consistently</a></li>
+ </ol></li>
+ <li><a href="#compilerissues">Compiler Issues</a>
+ <ol>
+ <li><a href="#ci_warningerrors">Treat Compiler Warnings Like
+ Errors</a></li>
+ <li><a href="#ci_portable_code">Write Portable Code</a></li>
+ </ol></li>
+ </ol></li>
+ <li><a href="#styleissues">Style Issues</a>
+ <ol>
+ <li><a href="#macro">The High Level Issues</a>
+ <ol>
+ <li><a href="#hl_module">A Public Header File <b>is</b> a
+ Module</a></li>
+ <li><a href="#hl_dontinclude">#include as Little as Possible</a></li>
+ <li><a href="#hl_privateheaders">Keep "internal" Headers
+ Private</a></li>
+ </ol></li>
+ <li><a href="#micro">The Low Level Issues</a>
+ <ol>
+ <li><a href="#hl_assert">Assert Liberally</a></li>
+ <li><a href="#hl_preincrement">Prefer Preincrement</a></li>
+ <li><a href="#hl_avoidendl">Avoid std::endl</a></li>
+ <li><a href="#hl_exploitcpp">Exploit C++ to its Fullest</a></li>
+ </ol></li>
+ </ol></li>
+ <li><a href="#seealso">See Also</a></li>
+ </ol>
+
+ <div class="doc_author">
+ <p>Written by <a href="mailto:sabre at nondot.org">Chris Lattner</a></p>
+ </div>
+
+
+ <!-- *********************************************************************** -->
+ <div class="doc_section">
+ <a name="introduction">Introduction</a>
+ </div>
+ <!-- *********************************************************************** -->
+
+ <div class="doc_text">
+
+ <p>This document attempts to describe a few coding standards that are being used
+ in the LLVM source tree. Although no coding standards should be regarded as
+ absolute requirements to be followed in all instances, coding standards can be
+ useful.</p>
+
+ <p>This document intentionally does not prescribe fixed standards for religious
+ issues such as brace placement and space usage. For issues like this, follow
+ the golden rule:</p>
+
+ <blockquote>
+
+ <p><b><a name="goldenrule">If you are adding a significant body of source to a
+ project, feel free to use whatever style you are most comfortable with. If you
+ are extending, enhancing, or bug fixing already implemented code, use the style
+ that is already being used so that the source is uniform and easy to
+ follow.</a></b></p>
+
+ </blockquote>
+
+ <p>The ultimate goal of these guidelines is the increase readability and
+ maintainability of our common source base. If you have suggestions for topics to
+ be included, please mail them to <a
+ href="mailto:sabre at nondot.org">Chris</a>.</p>
+
+ </div>
+
+ <!-- *********************************************************************** -->
+ <div class="doc_section">
+ <a name="mechanicalissues">Mechanical Source Issues</a>
+ </div>
+ <!-- *********************************************************************** -->
+
+ <!-- ======================================================================= -->
+ <div class="doc_subsection">
+ <a name="sourceformating">Source Code Formatting</a>
+ </div>
+
+ <!-- _______________________________________________________________________ -->
+ <div class="doc_subsubsection">
+ <a name="scf_commenting">Commenting</a>
+ </div>
+
+ <div class="doc_text">
+
+ <p>Comments are one critical part of readability and maintainability. Everyone
+ knows they should comment, so should you. :) Although we all should probably
+ comment our code more than we do, there are a few very critical places that
+ documentation is very useful:</p>
+
+ <b>File Headers</b>
+
+ <p>Every source file should have a header on it that
+ describes the basic purpose of the file. If a file does not have a header, it
+ should not be checked into CVS. Most source trees will probably have a standard
+ file header format. The standard format for the LLVM source tree looks like
+ this:</p>
+
+ <div class="doc_code">
+ <pre>
+ //===-- llvm/Instruction.h - Instruction class definition -------*- C++ -*-===//
+ //
+ // The LLVM Compiler Infrastructure
+ //
+ // This file was developed by the LLVM research group and is distributed under
+ // the University of Illinois Open Source License. See LICENSE.TXT for details.
+ //
+ //===----------------------------------------------------------------------===//
+ //
+ // This file contains the declaration of the Instruction class, which is the
+ // base class for all of the VM instructions.
+ //
+ //===----------------------------------------------------------------------===//
+ </pre>
+ </div>
+
+ <p>A few things to note about this particular format: The "<tt>-*- C++
+ -*-</tt>" string on the first line is there to tell Emacs that the source file
+ is a C++ file, not a C file (Emacs assumes .h files are C files by default).
+ Note that this tag is not necessary in .cpp files. The name of the file is also
+ on the first line, along with a very short description of the purpose of the
+ file. This is important when printing out code and flipping though lots of
+ pages.</p>
+
+ <p>The next section in the file is a concise note that defines the license that
+ the file is released under. This makes it perfectly clear what terms the source
+ code can be distributed under.</p>
+
+ <p>The main body of the description does not have to be very long in most cases.
+ Here it's only two lines. If an algorithm is being implemented or something
+ tricky is going on, a reference to the paper where it is published should be
+ included, as well as any notes or "gotchas" in the code to watch out for.</p>
+
+ <b>Class overviews</b>
+
+ <p>Classes are one fundemental part of a good object oriented design. As such,
+ a class definition should have a comment block that explains what the class is
+ used for... if it's not obvious. If it's so completely obvious your grandma
+ could figure it out, it's probably safe to leave it out. Naming classes
+ something sane goes a long ways towards avoiding writing documentation. :)</p>
+
+
+ <b>Method information</b>
+
+ <p>Methods defined in a class (as well as any global functions) should also be
+ documented properly. A quick note about what it does any a description of the
+ borderline behaviour is all that is necessary here (unless something
+ particularly tricky or insideous is going on). The hope is that people can
+ figure out how to use your interfaces without reading the code itself... that is
+ the goal metric.</p>
+
+ <p>Good things to talk about here are what happens when something unexpected
+ happens: does the method return null? Abort? Format your hard disk?</p>
+
+ </div>
+
+ <!-- _______________________________________________________________________ -->
+ <div class="doc_subsubsection">
+ <a name="scf_commentformat">Comment Formatting</a>
+ </div>
+
+ <div class="doc_text">
+
+ <p>In general, prefer C++ style (<tt>//</tt>) comments. They take less space,
+ require less typing, don't have nesting problems, etc. There are a few cases
+ when it is useful to use C style (<tt>/* */</tt>) comments however:</p>
+
+ <ol>
+ <li>When writing a C code: Obviously if you are writing C code, use C style
+ comments. :)</li>
+ <li>When writing a header file that may be #included by a C source file.</li>
+ <li>When writing a source file that is used by a tool that only accepts C
+ style comments.</li>
+ </ol>
+
+ <p>To comment out a large block of code, use <tt>#if 0</tt> and <tt>#endif</tt>.
+ These nest properly and are better behaved in general than C style comments.</p>
+
+ </div>
+
+ <!-- _______________________________________________________________________ -->
+ <div class="doc_subsubsection">
+ <a name="scf_includes">#include Style</a>
+ </div>
+
+ <div class="doc_text">
+
+ <p>Immediately after the <a href="#scf_commenting">header file comment</a> (and
+ include guards if working on a header file), the <a
+ href="#hl_dontinclude">minimal</a> list of <tt>#include</tt>s required by the
+ file should be listed. We prefer these <tt>#include</tt>s to be listed in this
+ order:</p>
+
+ <ol>
+ <li><a href="#mmheader">Main Module header</a></li>
+ <li><a href="#hl_privateheaders">Local/Private Headers</a></li>
+ <li><tt>llvm/*</tt></li>
+ <li><tt>llvm/Analysis/*</tt></li>
+ <li><tt>llvm/Assembly/*</tt></li>
+ <li><tt>llvm/Bytecode/*</tt></li>
+ <li><tt>llvm/CodeGen/*</tt></li>
+ <li>...</li>
+ <li><tt>Support/*</tt></li>
+ <li><tt>Config/*</tt></li>
+ <li>System <tt>#includes</tt></li>
+ </ol>
+
+ <p>... and each catagory should be sorted by name.</p>
+
+ <p><a name="mmheader">The "Main Module Header"</a> file applies to .cpp file
+ which implement an interface defined by a .h file. This #include should always
+ be included <b>first</b> regardless of where it lives on the file system. By
+ including a header file first in the .cpp files that implement the interfaces,
+ we ensure that the header does not have any hidden dependencies which are not
+ explicitly #included in the header, but should be. It is also a form of
+ documentation in the .cpp file to indicate where the interfaces it implements
+ are defined.</p>
+
+ </div>
+
+ <!-- _______________________________________________________________________ -->
+ <div class="doc_subsubsection">
+ <a name="scf_codewidth">Source Code Width</a>
+ </div>
+
+ <div class="doc_text">
+
+ <p>Write your code to fit within 80 columns of text. This helps those of us who
+ like to print out code and look at your code in an xterm without resizing
+ it.</p>
+
+ </div>
+
+ <!-- _______________________________________________________________________ -->
+ <div class="doc_subsubsection">
+ <a name="scf_spacestabs">Use Spaces Instead of Tabs</a>
+ </div>
+
+ <div class="doc_text">
+
+ <p>In all cases, prefer spaces to tabs in source files. People have different
+ prefered indentation levels, and different styles of indentation that they
+ like... this is fine. What isn't is that different editors/viewers expand tabs
+ out to different tab stops. This can cause your code to look completely
+ unreadable, and it is not worth dealing with.</p>
+
+ <p>As always, follow the <a href="#goldenrule">Golden Rule</a> above: follow the
+ style of existing code if your are modifying and extending it. If you like four
+ spaces of indentation, <b>DO NOT</b> do that in the middle of a chunk of code
+ with two spaces of indentation. Also, do not reindent a whole source file: it
+ makes for incredible diffs that are absolutely worthless.</p>
+
+ </div>
+
+ <!-- _______________________________________________________________________ -->
+ <div class="doc_subsubsection">
+ <a name="scf_indentation">Indent Code Consistently</a>
+ </div>
+
+ <div class="doc_text">
+
+ <p>Okay, your first year of programming you were told that indentation is
+ important. If you didn't believe and internalize this then, now is the time.
+ Just do it.</p>
+
+ </div>
+
+
+ <!-- ======================================================================= -->
+ <div class="doc_subsection">
+ <a name="compilerissues">Compiler Issues</a>
+ </div>
+
+
+ <!-- _______________________________________________________________________ -->
+ <div class="doc_subsubsection">
+ <a name="ci_warningerrors">Treat Compiler Warnings Like Errors</a>
+ </div>
+
+ <div class="doc_text">
+
+ <p>If your code has compiler warnings in it, something is wrong: you aren't
+ casting values correctly, your have "questionable" constructs in your code, or
+ you are doing something legitimately wrong. Compiler warnings can cover up
+ legitimate errors in output and make dealing with a translation unit
+ difficult.</p>
+
+ <p>It is not possible to prevent all warnings from all compilers, nor is it
+ desirable. Instead, pick a standard compiler (like <tt>gcc</tt>) that provides
+ a good thorough set of warnings, and stick to them. At least in the case of
+ <tt>gcc</tt>, it is possible to work around any spurious errors by changing the
+ syntax of the code slightly. For example, an warning that annoys me occurs when
+ I write code like this:</p>
+
+ <div class="doc_code">
+ <pre>
+ if (V = getValue()) {
+ ...
+ }
+ </pre>
+ </div>
+
+ <p><tt>gcc</tt> will warn me that I probably want to use the <tt>==</tt>
+ operator, and that I probably mistyped it. In most cases, I haven't, and I
+ really don't want the spurious errors. To fix this particular problem, I
+ rewrite the code like this:</p>
+
+ <div class="doc_code">
+ <pre>
+ if ((V = getValue())) {
+ ...
+ }
+ </pre>
+ </div>
+
+ <p>...which shuts <tt>gcc</tt> up. Any <tt>gcc</tt> warning that annoys you can
+ be fixed by massaging the code appropriately.</p>
+
+ <p>These are the <tt>gcc</tt> warnings that I prefer to enable: <tt>-Wall
+ -Winline -W -Wwrite-strings -Wno-unused</tt></p>
+
+ </div>
+
+ <!-- _______________________________________________________________________ -->
+ <div class="doc_subsubsection">
+ <a name="ci_portable_code">Write Portable Code</a>
+ </div>
+
+ <div class="doc_text">
+
+ <p>In almost all cases, it is possible and within reason to write completely
+ portable code. If there are cases where it isn't possible to write portable
+ code, isolate it behind a well defined (and well documented) interface.</p>
+
+ <p>In practice, this means that you shouldn't assume much about the host
+ compiler, including its support for "high tech" features like partial
+ specialization of templates. In fact, Visual C++ 6 could be an important target
+ for our work in the future, and we don't want to have to rewrite all of our code
+ to support it.</p>
+
+ </div>
+
+ <!-- *********************************************************************** -->
+ <div class="doc_section">
+ <a name="styleissues">Style Issues</a>
+ </div>
+ <!-- *********************************************************************** -->
+
+
+ <!-- ======================================================================= -->
+ <div class="doc_subsection">
+ <a name="macro">The High Level Issues</a>
+ </div>
+
+
+ <!-- _______________________________________________________________________ -->
+ <div class="doc_subsubsection">
+ <a name="hl_module">A Public Header File <b>is</b> a Module</a>
+ </div>
+
+ <div class="doc_text">
+
+ <p>C++ doesn't do too well in the modularity department. There is no real
+ encapsulation or data hiding (unless you use expensive protocol classes), but it
+ is what we have to work with. When you write a public header file (in the LLVM
+ source tree, they live in the top level "include" directory), you are defining a
+ module of functionality.</p>
+
+ <p>Ideally, modules should be completely independent of each other, and their
+ header files should only include the absolute minimum number of headers
+ possible. A module is not just a class, a function, or a namespace: <a
+ href="http://www.cuj.com/articles/2000/0002/0002c/0002c.htm">it's a collection
+ of these</a> that defines an interface. This interface may be several
+ functions, classes or data structures, but the important issue is how they work
+ together.</p>
+
+ <p>In general, a module should be implemented with one or more <tt>.cpp</tt>
+ files. Each of these <tt>.cpp</tt> files should include the header that defines
+ their interface first. This ensure that all of the dependences of the module
+ header have been properly added to the module header itself, and are not
+ implicit. System headers should be included after user headers for a
+ translation unit.</p>
+
+ </div>
+
+ <!-- _______________________________________________________________________ -->
+ <div class="doc_subsubsection">
+ <a name="hl_dontinclude">#include as Little as Possible</a>
+ </div>
+
+ <div class="doc_text">
+
+ <p><tt>#include</tt> hurts compile time performance. Don't do it unless you
+ have to, especially in header files.</p>
+
+ <p>But wait, sometimes you need to have the definition of a class to use it, or
+ to inherit from it. In these cases go ahead and #include that header file. Be
+ aware however that there are many cases where you don't need to have the full
+ definition of a class. If you are using a pointer or reference to a class, you
+ don't need the header file. If you are simply returning a class instance from a
+ prototyped function or method, you don't need it. In fact, for most cases, you
+ simply don't need the definition of a class... and not <tt>#include</tt>'ing
+ speeds up compilation.</p>
+
+ <p>It is easy to try to go too overboard on this recommendation, however. You
+ <b>must</b> include all of the header files that you are using, either directly
+ or indirectly (through another header file). To make sure that you don't
+ accidently forget to include a header file in your module header, make sure to
+ include your module header <b>first</b> in the implementation file (as mentioned
+ above). This way there won't be any hidden dependencies that you'll find out
+ about later...</p>
+
+ </div>
+
+ <!-- _______________________________________________________________________ -->
+ <div class="doc_subsubsection">
+ <a name="hl_privateheaders">Keep "internal" Headers Private</a>
+ </div>
+
+ <div class="doc_text">
+
+ <p>Many modules have a complex implementation that causes them to use more than
+ one implementation (<tt>.cpp</tt>) file. It is often tempting to put the
+ internal communication interface (helper classes, extra functions, etc) in the
+ public module header file. Don't do this. :)</p>
+
+ <p>If you really need to do something like this, put a private header file in
+ the same directory as the source files, and include it locally. This ensures
+ that your private interface remains private and undisturbed by outsiders.</p>
+
+ <p>Note however, that it's okay to put extra implementation methods a public
+ class itself... just make them private (or protected), and all is well.</p>
+
+ </div>
+
+ <!-- ======================================================================= -->
+ <div class="doc_subsection">
+ <a name="micro">The Low Level Issues</a>
+ </div>
+
+
+ <!-- _______________________________________________________________________ -->
+ <div class="doc_subsubsection">
+ <a name="hl_assert">Assert Liberally</a>
+ </div>
+
+ <div class="doc_text">
+
+ <p>Use the "<tt>assert</tt>" function to its fullest. Check all of your
+ preconditions and assumptions, you never know when a bug (not neccesarily even
+ yours) might be caught early by an assertion, which reduces debugging time
+ dramatically. The "<tt><cassert></tt>" header file is probably already
+ included by the header files you are using, so it doesn't cost anything to use
+ it.</p>
+
+ <p>To further assist with debugging, make sure to put some kind of error message
+ in the assertion statement (which is printed if the assertion is tripped). This
+ helps the poor debugging make sense of why an assertion is being made and
+ enforced, and hopefully what to do about it. Here is one complete example:</p>
+
+ <div class="doc_code">
+ <pre>
+ inline Value *getOperand(unsigned i) {
+ assert(i < Operands.size() && "getOperand() out of range!");
+ return Operands[i];
+ }
+ </pre>
+ </div>
+
+ <p>Here are some examples:</p>
+
+ <div class="doc_code">
+ <pre>
+ assert(Ty->isPointerType() && "Can't allocate a non pointer type!");
+
+ assert((Opcode == Shl || Opcode == Shr) && "ShiftInst Opcode invalid!");
+
+ assert(idx < getNumSuccessors() && "Successor # out of range!");
+
+ assert(V1.getType() == V2.getType() && "Constant types must be identical!");
+
+ assert(isa<PHINode>(Succ->front()) && "Only works on PHId BBs!");
+ </pre>
+ </div>
+
+ <p>You get the idea...</p>
+
+ </div>
+
+
+ <!-- _______________________________________________________________________ -->
+ <div class="doc_subsubsection">
+ <a name="hl_preincrement">Prefer Preincrement</a>
+ </div>
+
+ <div class="doc_text">
+
+ <p>Hard fast rule: Preincrement (<tt>++X</tt>) may be no slower than
+ postincrement (<tt>X++</tt>) and could very well be a lot faster than it. Use
+ preincrementation whenever possible.</p>
+
+ <p>The semantics of postincrement include making a copy of the value being
+ incremented, returning it, and then preincrementing the "work value". For
+ primitive types, this isn't a big deal... but for iterators, it can be a huge
+ issue (for example, some iterators contains stack and set objects in them...
+ copying an iterator could invoke the copy ctor's of these as well). In general,
+ get in the habit of always using preincrement, and you won't have a problem.</p>
+
+ </div>
+
+ <!-- _______________________________________________________________________ -->
+ <div class="doc_subsubsection">
+ <a name="hl_avoidendl">Avoid std::endl</a>
+ </div>
+
+ <div class="doc_text">
+
+ <p>The <tt>std::endl</tt> modifier, when used with iostreams outputs a newline
+ to the output stream specified. In addition to doing this, however, it also
+ flushes the output stream. In other words, these are equivalent:</p>
+
+ <div class="doc_code">
+ <pre>
+ std::cout << std::endl;
+ std::cout << '\n' << std::flush;
+ </pre>
+ </div>
+
+ <p>Most of the time, you probably have no reason to flush the output stream, so
+ it's better to use a literal <tt>'\n'</tt>.</p>
+
+ </div>
+
+ <!-- _______________________________________________________________________ -->
+ <div class="doc_subsubsection">
+ <a name="hl_exploitcpp">Exploit C++ to its Fullest</a>
+ </div>
+
+ <div class="doc_text">
+
+ <p>C++ is a powerful language. With a firm grasp on its capabilities, you can
+ make write effective, consise, readable and maintainable code all at the same
+ time. By staying consistent, you reduce the amount of special cases that need
+ to be remembered. Reducing the total number of lines of code you write is a
+ good way to avoid documentation, and avoid giving bugs a place to hide.</p>
+
+ <p>For these reasons, come to know and love the contents of your local
+ <algorithm> header file. Know about <functional> and what it can do
+ for you. C++ is just a tool that wants you to master it. :)</p>
+
+ </div>
+
+ <!-- *********************************************************************** -->
+ <div class="doc_section">
+ <a name="seealso">See Also</a>
+ </div>
+ <!-- *********************************************************************** -->
+
+ <div class="doc_text">
+
+ <p>A lot of these comments and recommendations have been culled for other
+ sources. Two particularly important books for our work are:</p>
+
+ <ol>
+
+ <li><a href="http://www.aw-bc.com/catalog/academic/product/0,1144,0201310155,00.html">Effective
+ C++</a> by Scott Meyers. There is an online version of the book (only some
+ chapters though) <a
+ href="http://www.awlonline.com/cseng/meyerscddemo/">available as well</a>. Also
+ interesting and useful are "More Effective C++" and "Effective STL" by the same
+ author.</li>
+
+ <li><a href="http://cseng.aw.com/book/0,3828,0201633620,00.html">Large-Scale C++
+ Software Design</a> by John Lakos</li>
+
+ </ol>
+
+ <p>If you get some free time, and you haven't read them: do so, you might learn
+ something. :)</p>
+
+ </div>
+
+ <!-- *********************************************************************** -->
+
+ <hr>
+ <address>
+ <a href="http://jigsaw.w3.org/css-validator/check/referer"><img
+ src="http://jigsaw.w3.org/css-validator/images/vcss" alt="Valid CSS!"></a>
+ <a href="http://validator.w3.org/check/referer"><img
+ src="http://www.w3.org/Icons/valid-html401" alt="Valid HTML 4.01!"></a>
+
+ <a href="mailto:sabre at nondot.org">Chris Lattner</a><br>
+ <a href="http://llvm.cs.uiuc.edu">LLVM Compiler Infrastructure</a><br>
+ Last modified: $Date: 2004/08/13 22:03:03 $
+ </address>
+
+ </body>
+ </html>
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+ <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"
+ "http://www.w3.org/TR/html4/strict.dtd">
+ <html>
+ <head>
+ <title>CommandLine 2.0 Library Manual</title>
+ <link rel="stylesheet" href="llvm.css" type="text/css">
+ </head>
+ <body>
+
+ <div class="doc_title">
+ CommandLine 2.0 Library Manual
+ </div>
+
+ <ol>
+ <li><a href="#introduction">Introduction</a></li>
+
+ <li><a href="#quickstart">Quick Start Guide</a>
+ <ol>
+ <li><a href="#bool">Boolean Arguments</a></li>
+ <li><a href="#alias">Argument Aliases</a></li>
+ <li><a href="#onealternative">Selecting an alternative from a
+ set of possibilities</a></li>
+ <li><a href="#namedalternatives">Named alternatives</a></li>
+ <li><a href="#list">Parsing a list of options</a></li>
+ <li><a href="#description">Adding freeform text to help output</a></li>
+ </ol></li>
+
+ <li><a href="#referenceguide">Reference Guide</a>
+ <ol>
+ <li><a href="#positional">Positional Arguments</a>
+ <ul>
+ <li><a href="#--">Specifying positional options with hyphens</a></li>
+ <li><a href="#cl::ConsumeAfter">The <tt>cl::ConsumeAfter</tt>
+ modifier</a></li>
+ </ul></li>
+
+ <li><a href="#storage">Internal vs External Storage</a></li>
+
+ <li><a href="#attributes">Option Attributes</a></li>
+
+ <li><a href="#modifiers">Option Modifiers</a>
+ <ul>
+ <li><a href="#hiding">Hiding an option from <tt>--help</tt>
+ output</a></li>
+ <li><a href="#numoccurrences">Controlling the number of occurrences
+ required and allowed</a></li>
+ <li><a href="#valrequired">Controlling whether or not a value must be
+ specified</a></li>
+ <li><a href="#formatting">Controlling other formatting options</a></li>
+ <li><a href="#misc">Miscellaneous option modifiers</a></li>
+ </ul></li>
+
+ <li><a href="#toplevel">Top-Level Classes and Functions</a>
+ <ul>
+ <li><a href="#cl::ParseCommandLineOptions">The
+ <tt>cl::ParseCommandLineOptions</tt> function</a></li>
+ <li><a href="#cl::ParseEnvironmentOptions">The
+ <tt>cl::ParseEnvironmentOptions</tt> function</a></li>
+ <li><a href="#cl::opt">The <tt>cl::opt</tt> class</a></li>
+ <li><a href="#cl::list">The <tt>cl::list</tt> class</a></li>
+ <li><a href="#cl::alias">The <tt>cl::alias</tt> class</a></li>
+ </ul></li>
+
+ <li><a href="#builtinparsers">Builtin parsers</a>
+ <ul>
+ <li><a href="#genericparser">The Generic <tt>parser<t></tt>
+ parser</a></li>
+ <li><a href="#boolparser">The <tt>parser<bool></tt>
+ specialization</a></li>
+ <li><a href="#stringparser">The <tt>parser<string></tt>
+ specialization</a></li>
+ <li><a href="#intparser">The <tt>parser<int></tt>
+ specialization</a></li>
+ <li><a href="#doubleparser">The <tt>parser<double></tt> and
+ <tt>parser<float></tt> specializations</a></li>
+ </ul></li>
+ </ol></li>
+ <li><a href="#extensionguide">Extension Guide</a>
+ <ol>
+ <li><a href="#customparser">Writing a custom parser</a></li>
+ <li><a href="#explotingexternal">Exploiting external storage</a></li>
+ <li><a href="#dynamicopts">Dynamically adding command line
+ options</a></li>
+ </ol></li>
+ </ol>
+
+ <div class="doc_author">
+ <p>Written by <a href="mailto:sabre at nondot.org">Chris Lattner</a></p>
+ </div>
+
+ <!-- *********************************************************************** -->
+ <div class="doc_section">
+ <a name="introduction">Introduction</a>
+ </div>
+ <!-- *********************************************************************** -->
+
+ <div class="doc_text">
+
+ <p>This document describes the CommandLine argument processing library. It will
+ show you how to use it, and what it can do. The CommandLine library uses a
+ declarative approach to specifying the command line options that your program
+ takes. By default, these options declarations implicitly hold the value parsed
+ for the option declared (of course this <a href="#storage">can be
+ changed</a>).</p>
+
+ <p>Although there are a <b>lot</b> of command line argument parsing libraries
+ out there in many different languages, none of them fit well with what I needed.
+ By looking at the features and problems of other libraries, I designed the
+ CommandLine library to have the following features:</p>
+
+ <ol>
+ <li>Speed: The CommandLine library is very quick and uses little resources. The
+ parsing time of the library is directly proportional to the number of arguments
+ parsed, not the the number of options recognized. Additionally, command line
+ argument values are captured transparently into user defined global variables,
+ which can be accessed like any other variable (and with the same
+ performance).</li>
+
+ <li>Type Safe: As a user of CommandLine, you don't have to worry about
+ remembering the type of arguments that you want (is it an int? a string? a
+ bool? an enum?) and keep casting it around. Not only does this help prevent
+ error prone constructs, it also leads to dramatically cleaner source code.</li>
+
+ <li>No subclasses required: To use CommandLine, you instantiate variables that
+ correspond to the arguments that you would like to capture, you don't subclass a
+ parser. This means that you don't have to write <b>any</b> boilerplate
+ code.</li>
+
+ <li>Globally accessible: Libraries can specify command line arguments that are
+ automatically enabled in any tool that links to the library. This is possible
+ because the application doesn't have to keep a "list" of arguments to pass to
+ the parser. This also makes supporting <a href="#dynamicopts">dynamically
+ loaded options</a> trivial.</li>
+
+ <li>Cleaner: CommandLine supports enum and other types directly, meaning that
+ there is less error and more security built into the library. You don't have to
+ worry about whether your integral command line argument accidentally got
+ assigned a value that is not valid for your enum type.</li>
+
+ <li>Powerful: The CommandLine library supports many different types of
+ arguments, from simple <a href="#boolparser">boolean flags</a> to <a
+ href="#cl::opt">scalars arguments</a> (<a href="#stringparser">strings</a>, <a
+ href="#intparser">integers</a>, <a href="#genericparser">enums</a>, <a
+ href="#doubleparser">doubles</a>), to <a href="#cl::list">lists of
+ arguments</a>. This is possible because CommandLine is...</li>
+
+ <li>Extensible: It is very simple to add a new argument type to CommandLine.
+ Simply specify the parser that you want to use with the command line option when
+ you declare it. <a href="#customparser">Custom parsers</a> are no problem.</li>
+
+ <li>Labor Saving: The CommandLine library cuts down on the amount of grunt work
+ that you, the user, have to do. For example, it automatically provides a
+ <tt>--help</tt> option that shows the available command line options for your
+ tool. Additionally, it does most of the basic correctness checking for
+ you.</li>
+
+ <li>Capable: The CommandLine library can handle lots of different forms of
+ options often found in real programs. For example, <a
+ href="#positional">positional</a> arguments, <tt>ls</tt> style <a
+ href="#cl::Grouping">grouping</a> options (to allow processing '<tt>ls
+ -lad</tt>' naturally), <tt>ld</tt> style <a href="#cl::Prefix">prefix</a>
+ options (to parse '<tt>-lmalloc -L/usr/lib</tt>'), and <a
+ href="#cl::ConsumeAfter">interpreter style options</a>.</li>
+
+ </ol>
+
+ <p>This document will hopefully let you jump in and start using CommandLine in
+ your utility quickly and painlessly. Additionally it should be a simple
+ reference manual to figure out how stuff works. If it is failing in some area
+ (or you want an extension to the library), nag the author, <a
+ href="mailto:sabre at nondot.org">Chris Lattner</a>.</p>
+
+ </div>
+
+ <!-- *********************************************************************** -->
+ <div class="doc_section">
+ <a name="quickstart">Quick Start Guide</a>
+ </div>
+ <!-- *********************************************************************** -->
+
+ <div class="doc_text">
+
+ <p>This section of the manual runs through a simple CommandLine'ification of a
+ basic compiler tool. This is intended to show you how to jump into using the
+ CommandLine library in your own program, and show you some of the cool things it
+ can do.</p>
+
+ <p>To start out, you need to include the CommandLine header file into your
+ program:</p>
+
+ <pre>
+ #include "Support/CommandLine.h"
+ </pre>
+
+ <p>Additionally, you need to add this as the first line of your main
+ program:</p>
+
+ <pre>
+ int main(int argc, char **argv) {
+ <a href="#cl::ParseCommandLineOptions">cl::ParseCommandLineOptions</a>(argc, argv);
+ ...
+ }
+ </pre>
+
+ <p>... which actually parses the arguments and fills in the variable
+ declarations.</p>
+
+ <p>Now that you are ready to support command line arguments, we need to tell the
+ system which ones we want, and what type of argument they are. The CommandLine
+ library uses a declarative syntax to model command line arguments with the
+ global variable declarations that capture the parsed values. This means that
+ for every command line option that you would like to support, there should be a
+ global variable declaration to capture the result. For example, in a compiler,
+ we would like to support the unix standard '<tt>-o <filename></tt>' option
+ to specify where to put the output. With the CommandLine library, this is
+ represented like this:</p>
+
+ <a name="value_desc_example"></a>
+ <pre>
+ <a href="#cl::opt">cl::opt</a><string> OutputFilename("<i>o</i>", <a href="#cl::desc">cl::desc</a>("<i>Specify output filename</i>"), <a href="#cl::value_desc">cl::value_desc</a>("<i>filename</i>"));
+ </pre>
+
+ <p>This declares a global variable "<tt>OutputFilename</tt>" that is used to
+ capture the result of the "<tt>o</tt>" argument (first parameter). We specify
+ that this is a simple scalar option by using the "<tt><a
+ href="#cl::opt">cl::opt</a></tt>" template (as opposed to the <a
+ href="#list">"<tt>cl::list</tt> template</a>), and tell the CommandLine library
+ that the data type that we are parsing is a string.</p>
+
+ <p>The second and third parameters (which are optional) are used to specify what
+ to output for the "<tt>--help</tt>" option. In this case, we get a line that
+ looks like this:</p>
+
+ <pre>
+ USAGE: compiler [options]
+
+ OPTIONS:
+ -help - display available options (--help-hidden for more)
+ <b>-o <filename> - Specify output filename</b>
+ </pre>
+
+ <p>Because we specified that the command line option should parse using the
+ <tt>string</tt> data type, the variable declared is automatically usable as a
+ real string in all contexts that a normal C++ string object may be used. For
+ example:</p>
+
+ <pre>
+ ...
+ ofstream Output(OutputFilename.c_str());
+ if (Out.good()) ...
+ ...
+ </pre>
+
+ <p>There are many different options that you can use to customize the command
+ line option handling library, but the above example shows the general interface
+ to these options. The options can be specified in any order, and are specified
+ with helper functions like <a href="#cl::desc"><tt>cl::desc(...)</tt></a>, so
+ there are no positional dependencies to remember. The available options are
+ discussed in detail in the <a href="#referenceguide">Reference Guide</a>.</p>
+
+ <p>Continuing the example, we would like to have our compiler take an input
+ filename as well as an output filename, but we do not want the input filename to
+ be specified with a hyphen (ie, not <tt>-filename.c</tt>). To support this
+ style of argument, the CommandLine library allows for <a
+ href="#positional">positional</a> arguments to be specified for the program.
+ These positional arguments are filled with command line parameters that are not
+ in option form. We use this feature like this:</p>
+
+ <pre>
+ <a href="#cl::opt">cl::opt</a><string> InputFilename(<a href="#cl::Positional">cl::Positional</a>, <a href="#cl::desc">cl::desc</a>("<i><input file></i>"), <a href="#cl::init">cl::init</a>("<i>-</i>"));
+ </pre>
+
+ <p>This declaration indicates that the first positional argument should be
+ treated as the input filename. Here we use the <tt><a
+ href="#cl::init">cl::init</a></tt> option to specify an initial value for the
+ command line option, which is used if the option is not specified (if you do not
+ specify a <tt><a href="#cl::init">cl::init</a></tt> modifier for an option, then
+ the default constructor for the data type is used to initialize the value).
+ Command line options default to being optional, so if we would like to require
+ that the user always specify an input filename, we would add the <tt><a
+ href="#cl::Required">cl::Required</a></tt> flag, and we could eliminate the
+ <tt><a href="#cl::init">cl::init</a></tt> modifier, like this:</p>
+
+ <pre>
+ <a href="#cl::opt">cl::opt</a><string> InputFilename(<a href="#cl::Positional">cl::Positional</a>, <a href="#cl::desc">cl::desc</a>("<i><input file></i>"), <b><a href="#cl::Required">cl::Required</a></b>);
+ </pre>
+
+ <p>Again, the CommandLine library does not require the options to be specified
+ in any particular order, so the above declaration is equivalent to:</p>
+
+ <pre>
+ <a href="#cl::opt">cl::opt</a><string> InputFilename(<a href="#cl::Positional">cl::Positional</a>, <a href="#cl::Required">cl::Required</a>, <a href="#cl::desc">cl::desc</a>("<i><input file></i>"));
+ </pre>
+
+ <p>By simply adding the <tt><a href="#cl::Required">cl::Required</a></tt> flag,
+ the CommandLine library will automatically issue an error if the argument is not
+ specified, which shifts all of the command line option verification code out of
+ your application into the library. This is just one example of how using flags
+ can alter the default behaviour of the library, on a per-option basis. By
+ adding one of the declarations above, the <tt>--help</tt> option synopsis is now
+ extended to:</p>
+
+ <pre>
+ USAGE: compiler [options] <b><input file></b>
+
+ OPTIONS:
+ -help - display available options (--help-hidden for more)
+ -o <filename> - Specify output filename
+ </pre>
+
+ <p>... indicating that an input filename is expected.</p>
+
+ </div>
+
+ <!-- ======================================================================= -->
+ <div class="doc_subsection">
+ <a name="bool">Boolean Arguments</a>
+ </div>
+
+ <div class="doc_text">
+
+ <p>In addition to input and output filenames, we would like the compiler example
+ to support three boolean flags: "<tt>-f</tt>" to force overwriting of the output
+ file, "<tt>--quiet</tt>" to enable quiet mode, and "<tt>-q</tt>" for backwards
+ compatibility with some of our users. We can support these by declaring options
+ of boolean type like this:</p>
+
+ <pre>
+ <a href="#cl::opt">cl::opt</a><bool> Force ("<i>f</i>", <a href="#cl::desc">cl::desc</a>("<i>Overwrite output files</i>"));
+ <a href="#cl::opt">cl::opt</a><bool> Quiet ("<i>quiet</i>", <a href="#cl::desc">cl::desc</a>("<i>Don't print informational messages</i>"));
+ <a href="#cl::opt">cl::opt</a><bool> Quiet2("<i>q</i>", <a href="#cl::desc">cl::desc</a>("<i>Don't print informational messages</i>"), <a href="#cl::Hidden">cl::Hidden</a>);
+ </pre>
+
+ <p>This does what you would expect: it declares three boolean variables
+ ("<tt>Force</tt>", "<tt>Quiet</tt>", and "<tt>Quiet2</tt>") to recognize these
+ options. Note that the "<tt>-q</tt>" option is specified with the "<a
+ href="#cl::Hidden"><tt>cl::Hidden</tt></a>" flag. This modifier prevents it
+ from being shown by the standard "<tt>--help</tt>" output (note that it is still
+ shown in the "<tt>--help-hidden</tt>" output).</p>
+
+ <p>The CommandLine library uses a <a href="#builtinparsers">different parser</a>
+ for different data types. For example, in the string case, the argument passed
+ to the option is copied literally into the content of the string variable... we
+ obviously cannot do that in the boolean case, however, so we must use a smarter
+ parser. In the case of the boolean parser, it allows no options (in which case
+ it assigns the value of true to the variable), or it allows the values
+ "<tt>true</tt>" or "<tt>false</tt>" to be specified, allowing any of the
+ following inputs:</p>
+
+ <pre>
+ compiler -f # No value, 'Force' == true
+ compiler -f=true # Value specified, 'Force' == true
+ compiler -f=TRUE # Value specified, 'Force' == true
+ compiler -f=FALSE # Value specified, 'Force' == false
+ </pre>
+
+ <p>... you get the idea. The <a href="#boolparser">bool parser</a> just turns
+ the string values into boolean values, and rejects things like '<tt>compiler
+ -f=foo</tt>'. Similarly, the <a href="#doubleparser">float</a>, <a
+ href="#doubleparser">double</a>, and <a href="#intparser">int</a> parsers work
+ like you would expect, using the '<tt>strtol</tt>' and '<tt>strtod</tt>' C
+ library calls to parse the string value into the specified data type.</p>
+
+ <p>With the declarations above, "<tt>compiler --help</tt>" emits this:</p>
+
+ <pre>
+ USAGE: compiler [options] <input file>
+
+ OPTIONS:
+ <b>-f - Overwrite output files</b>
+ -o - Override output filename
+ <b>-quiet - Don't print informational messages</b>
+ -help - display available options (--help-hidden for more)
+ </pre>
+
+ <p>and "<tt>opt --help-hidden</tt>" prints this:</p>
+
+ <pre>
+ USAGE: compiler [options] <input file>
+
+ OPTIONS:
+ -f - Overwrite output files
+ -o - Override output filename
+ <b>-q - Don't print informational messages</b>
+ -quiet - Don't print informational messages
+ -help - display available options (--help-hidden for more)
+ </pre>
+
+ <p>This brief example has shown you how to use the '<tt><a
+ href="#cl::opt">cl::opt</a></tt>' class to parse simple scalar command line
+ arguments. In addition to simple scalar arguments, the CommandLine library also
+ provides primitives to support CommandLine option <a href="#alias">aliases</a>,
+ and <a href="#list">lists</a> of options.</p>
+
+ </div>
+
+ <!-- ======================================================================= -->
+ <div class="doc_subsection">
+ <a name="alias">Argument Aliases</a>
+ </div>
+
+ <div class="doc_text">
+
+ <p>So far, the example works well, except for the fact that we need to check the
+ quiet condition like this now:</p>
+
+ <pre>
+ ...
+ if (!Quiet && !Quiet2) printInformationalMessage(...);
+ ...
+ </pre>
+
+ <p>... which is a real pain! Instead of defining two values for the same
+ condition, we can use the "<tt><a href="#cl::alias">cl::alias</a></tt>" class to make the "<tt>-q</tt>"
+ option an <b>alias</b> for the "<tt>-quiet</tt>" option, instead of providing
+ a value itself:</p>
+
+ <pre>
+ <a href="#cl::opt">cl::opt</a><bool> Force ("<i>f</i>", <a href="#cl::desc">cl::desc</a>("<i>Overwrite output files</i>"));
+ <a href="#cl::opt">cl::opt</a><bool> Quiet ("<i>quiet</i>", <a href="#cl::desc">cl::desc</a>("<i>Don't print informational messages</i>"));
+ <a href="#cl::alias">cl::alias</a> QuietA("<i>q</i>", <a href="#cl::desc">cl::desc</a>("<i>Alias for -quiet</i>"), <a href="#cl::aliasopt">cl::aliasopt</a>(Quiet));
+ </pre>
+
+ <p>The third line (which is the only one we modified from above) defines a
+ "<tt>-q</tt> alias that updates the "<tt>Quiet</tt>" variable (as specified by
+ the <tt><a href="#cl::aliasopt">cl::aliasopt</a></tt> modifier) whenever it is
+ specified. Because aliases do not hold state, the only thing the program has to
+ query is the <tt>Quiet</tt> variable now. Another nice feature of aliases is
+ that they automatically hide themselves from the <tt>-help</tt> output
+ (although, again, they are still visible in the <tt>--help-hidden
+ output</tt>).</p>
+
+ <p>Now the application code can simply use:</p>
+
+ <pre>
+ ...
+ if (!Quiet) printInformationalMessage(...);
+ ...
+ </pre>
+
+ <p>... which is much nicer! The "<tt><a href="#cl::alias">cl::alias</a></tt>"
+ can be used to specify an alternative name for any variable type, and has many
+ uses.</p>
+
+ </div>
+
+ <!-- ======================================================================= -->
+ <div class="doc_subsection">
+ <a name="onealternative">Selecting an alternative from a set of
+ possibilities</a>
+ </div>
+
+ <div class="doc_text">
+
+ <p>So far, we have seen how the CommandLine library handles builtin types like
+ <tt>std::string</tt>, <tt>bool</tt> and <tt>int</tt>, but how does it handle
+ things it doesn't know about, like enums or '<tt>int*</tt>'s?</p>
+
+ <p>The answer is that it uses a table driven generic parser (unless you specify
+ your own parser, as described in the <a href="#extensionguide">Extension
+ Guide</a>). This parser maps literal strings to whatever type is required, are
+ requires you to tell it what this mapping should be.</p>
+
+ <p>Lets say that we would like to add four optimizations levels to our
+ optimizer, using the standard flags "<tt>-g</tt>", "<tt>-O0</tt>",
+ "<tt>-O1</tt>", and "<tt>-O2</tt>". We could easily implement this with boolean
+ options like above, but there are several problems with this strategy:</p>
+
+ <ol>
+ <li>A user could specify more than one of the options at a time, for example,
+ "<tt>opt -O3 -O2</tt>". The CommandLine library would not be able to catch this
+ erroneous input for us.</li>
+
+ <li>We would have to test 4 different variables to see which ones are set.</li>
+
+ <li>This doesn't map to the numeric levels that we want... so we cannot easily
+ see if some level >= "<tt>-O1</tt>" is enabled.</li>
+
+ </ol>
+
+ <p>To cope with these problems, we can use an enum value, and have the
+ CommandLine library fill it in with the appropriate level directly, which is
+ used like this:</p>
+
+ <pre>
+ enum OptLevel {
+ g, O1, O2, O3
+ };
+
+ <a href="#cl::opt">cl::opt</a><OptLevel> OptimizationLevel(<a href="#cl::desc">cl::desc</a>("<i>Choose optimization level:</i>"),
+ <a href="#cl::values">cl::values</a>(
+ clEnumVal(g , "<i>No optimizations, enable debugging</i>"),
+ clEnumVal(O1, "<i>Enable trivial optimizations</i>"),
+ clEnumVal(O2, "<i>Enable default optimizations</i>"),
+ clEnumVal(O3, "<i>Enable expensive optimizations</i>"),
+ clEnumValEnd));
+
+ ...
+ if (OptimizationLevel >= O2) doPartialRedundancyElimination(...);
+ ...
+ </pre>
+
+ <p>This declaration defines a variable "<tt>OptimizationLevel</tt>" of the
+ "<tt>OptLevel</tt>" enum type. This variable can be assigned any of the values
+ that are listed in the declaration (Note that the declaration list must be
+ terminated with the "<tt>clEnumValEnd</tt>" argument!). The CommandLine
+ library enforces
+ that the user can only specify one of the options, and it ensure that only valid
+ enum values can be specified. The "<tt>clEnumVal</tt>" macros ensure that the
+ command line arguments matched the enum values. With this option added, our
+ help output now is:</p>
+
+ <pre>
+ USAGE: compiler [options] <input file>
+
+ OPTIONS:
+ <b>Choose optimization level:
+ -g - No optimizations, enable debugging
+ -O1 - Enable trivial optimizations
+ -O2 - Enable default optimizations
+ -O3 - Enable expensive optimizations</b>
+ -f - Overwrite output files
+ -help - display available options (--help-hidden for more)
+ -o <filename> - Specify output filename
+ -quiet - Don't print informational messages
+ </pre>
+
+ <p>In this case, it is sort of awkward that flag names correspond directly to
+ enum names, because we probably don't want a enum definition named "<tt>g</tt>"
+ in our program. Because of this, we can alternatively write this example like
+ this:</p>
+
+ <pre>
+ enum OptLevel {
+ Debug, O1, O2, O3
+ };
+
+ <a href="#cl::opt">cl::opt</a><OptLevel> OptimizationLevel(<a href="#cl::desc">cl::desc</a>("<i>Choose optimization level:</i>"),
+ <a href="#cl::values">cl::values</a>(
+ clEnumValN(Debug, "g", "<i>No optimizations, enable debugging</i>"),
+ clEnumVal(O1 , "<i>Enable trivial optimizations</i>"),
+ clEnumVal(O2 , "<i>Enable default optimizations</i>"),
+ clEnumVal(O3 , "<i>Enable expensive optimizations</i>"),
+ clEnumValEnd));
+
+ ...
+ if (OptimizationLevel == Debug) outputDebugInfo(...);
+ ...
+ </pre>
+
+ <p>By using the "<tt>clEnumValN</tt>" macro instead of "<tt>clEnumVal</tt>", we
+ can directly specify the name that the flag should get. In general a direct
+ mapping is nice, but sometimes you can't or don't want to preserve the mapping,
+ which is when you would use it.</p>
+
+ </div>
+
+ <!-- ======================================================================= -->
+ <div class="doc_subsection">
+ <a name="namedalternatives">Named Alternatives</a>
+ </div>
+
+ <div class="doc_text">
+
+ <p>Another useful argument form is a named alternative style. We shall use this
+ style in our compiler to specify different debug levels that can be used.
+ Instead of each debug level being its own switch, we want to support the
+ following options, of which only one can be specified at a time:
+ "<tt>--debug-level=none</tt>", "<tt>--debug-level=quick</tt>",
+ "<tt>--debug-level=detailed</tt>". To do this, we use the exact same format as
+ our optimization level flags, but we also specify an option name. For this
+ case, the code looks like this:</p>
+
+ <pre>
+ enum DebugLev {
+ nodebuginfo, quick, detailed
+ };
+
+ // Enable Debug Options to be specified on the command line
+ <a href="#cl::opt">cl::opt</a><DebugLev> DebugLevel("<i>debug_level</i>", <a href="#cl::desc">cl::desc</a>("<i>Set the debugging level:</i>"),
+ <a href="#cl::values">cl::values</a>(
+ clEnumValN(nodebuginfo, "none", "<i>disable debug information</i>"),
+ clEnumVal(quick, "<i>enable quick debug information</i>"),
+ clEnumVal(detailed, "<i>enable detailed debug information</i>"),
+ clEnumValEnd));
+ </pre>
+
+ <p>This definition defines an enumerated command line variable of type "<tt>enum
+ DebugLev</tt>", which works exactly the same way as before. The difference here
+ is just the interface exposed to the user of your program and the help output by
+ the "<tt>--help</tt>" option:</p>
+
+ <pre>
+ USAGE: compiler [options] <input file>
+
+ OPTIONS:
+ Choose optimization level:
+ -g - No optimizations, enable debugging
+ -O1 - Enable trivial optimizations
+ -O2 - Enable default optimizations
+ -O3 - Enable expensive optimizations
+ <b>-debug_level - Set the debugging level:
+ =none - disable debug information
+ =quick - enable quick debug information
+ =detailed - enable detailed debug information</b>
+ -f - Overwrite output files
+ -help - display available options (--help-hidden for more)
+ -o <filename> - Specify output filename
+ -quiet - Don't print informational messages
+ </pre>
+
+ <p>Again, the only structural difference between the debug level declaration and
+ the optimiation level declaration is that the debug level declaration includes
+ an option name (<tt>"debug_level"</tt>), which automatically changes how the
+ library processes the argument. The CommandLine library supports both forms so
+ that you can choose the form most appropriate for your application.</p>
+
+ </div>
+
+ <!-- ======================================================================= -->
+ <div class="doc_subsection">
+ <a name="list">Parsing a list of options</a>
+ </div>
+
+ <div class="doc_text">
+
+ <p>Now that we have the standard run of the mill argument types out of the way,
+ lets get a little wild and crazy. Lets say that we want our optimizer to accept
+ a <b>list</b> of optimizations to perform, allowing duplicates. For example, we
+ might want to run: "<tt>compiler -dce -constprop -inline -dce -strip</tt>". In
+ this case, the order of the arguments and the number of appearances is very
+ important. This is what the "<tt><a href="#cl::list">cl::list</a></tt>"
+ template is for. First, start by defining an enum of the optimizations that you
+ would like to perform:</p>
+
+ <pre>
+ enum Opts {
+ // 'inline' is a C++ keyword, so name it 'inlining'
+ dce, constprop, inlining, strip
+ };
+ </pre>
+
+ <p>Then define your "<tt><a href="#cl::list">cl::list</a></tt>" variable:</p>
+
+ <pre>
+ <a href="#cl::list">cl::list</a><Opts> OptimizationList(<a href="#cl::desc">cl::desc</a>("<i>Available Optimizations:</i>"),
+ <a href="#cl::values">cl::values</a>(
+ clEnumVal(dce , "<i>Dead Code Elimination</i>"),
+ clEnumVal(constprop , "<i>Constant Propagation</i>"),
+ clEnumValN(inlining, "<i>inline</i>", "<i>Procedure Integration</i>"),
+ clEnumVal(strip , "<i>Strip Symbols</i>"),
+ clEnumValEnd));
+ </pre>
+
+ <p>This defines a variable that is conceptually of the type
+ "<tt>std::vector<enum Opts></tt>". Thus, you can access it with standard
+ vector methods:</p>
+
+ <pre>
+ for (unsigned i = 0; i != OptimizationList.size(); ++i)
+ switch (OptimizationList[i])
+ ...
+ </pre>
+
+ <p>... to iterate through the list of options specified.</p>
+
+ <p>Note that the "<tt><a href="#cl::list">cl::list</a></tt>" template is
+ completely general and may be used with any data types or other arguments that
+ you can use with the "<tt><a href="#cl::opt">cl::opt</a></tt>" template. One
+ especially useful way to use a list is to capture all of the positional
+ arguments together if there may be more than one specified. In the case of a
+ linker, for example, the linker takes several '<tt>.o</tt>' files, and needs to
+ capture them into a list. This is naturally specified as:</p>
+
+ <pre>
+ ...
+ <a href="#cl::list">cl::list</a><std::string> InputFilenames(<a href="#cl::Positional">cl::Positional</a>, <a href="#cl::desc">cl::desc</a>("<Input files>"), <a href="#cl::OneOrMore">cl::OneOrMore</a>);
+ ...
+ </pre>
+
+ <p>This variable works just like a "<tt>vector<string></tt>" object. As
+ such, accessing the list is simple, just like above. In this example, we used
+ the <tt><a href="#cl::OneOrMore">cl::OneOrMore</a></tt> modifier to inform the
+ CommandLine library that it is an error if the user does not specify any
+ <tt>.o</tt> files on our command line. Again, this just reduces the amount of
+ checking we have to do.</p>
+
+ </div>
+
+ <!-- ======================================================================= -->
+ <div class="doc_subsection">
+ <a name="description">Adding freeform text to help output</a>
+ </div>
+
+ <div class="doc_text">
+
+ <p>As our program grows and becomes more mature, we may decide to put summary
+ information about what it does into the help output. The help output is styled
+ to look similar to a Unix <tt>man</tt> page, providing concise information about
+ a program. Unix <tt>man</tt> pages, however often have a description about what
+ the program does. To add this to your CommandLine program, simply pass a third
+ argument to the <a
+ href="#cl::ParseCommandLineOptions"><tt>cl::ParseCommandLineOptions</tt></a>
+ call in main. This additional argument is then printed as the overview
+ information for your program, allowing you to include any additional information
+ that you want. For example:</p>
+
+ <pre>
+ int main(int argc, char **argv) {
+ <a href="#cl::ParseCommandLineOptions">cl::ParseCommandLineOptions</a>(argc, argv, " CommandLine compiler example\n\n"
+ " This program blah blah blah...\n");
+ ...
+ }
+ </pre>
+
+ <p>Would yield the help output:</p>
+
+ <pre>
+ <b>OVERVIEW: CommandLine compiler example
+
+ This program blah blah blah...</b>
+
+ USAGE: compiler [options] <input file>
+
+ OPTIONS:
+ ...
+ -help - display available options (--help-hidden for more)
+ -o <filename> - Specify output filename
+ </pre>
+
+ </div>
+
+
+ <!-- *********************************************************************** -->
+ <div class="doc_section">
+ <a name="referenceguide">Reference Guide</a>
+ </div>
+ <!-- *********************************************************************** -->
+
+ <div class="doc_text">
+
+ <p>Now that you know the basics of how to use the CommandLine library, this
+ section will give you the detailed information you need to tune how command line
+ options work, as well as information on more "advanced" command line option
+ processing capabilities.</p>
+
+ </div>
+
+ <!-- ======================================================================= -->
+ <div class="doc_subsection">
+ <a name="positional">Positional Arguments</a>
+ </div>
+
+ <div class="doc_text">
+
+ <p>Positional arguments are those arguments that are not named, and are not
+ specified with a hyphen. Positional arguments should be used when an option is
+ specified by its position alone. For example, the standard Unix <tt>grep</tt>
+ tool takes a regular expression argument, and an optional filename to search
+ through (which defaults to standard input if a filename is not specified).
+ Using the CommandLine library, this would be specified as:</p>
+
+ <pre>
+ <a href="#cl::opt">cl::opt</a><string> Regex (<a href="#cl::Positional">cl::Positional</a>, <a href="#cl::desc">cl::desc</a>("<i><regular expression></i>"), <a href="#cl::Required">cl::Required</a>);
+ <a href="#cl::opt">cl::opt</a><string> Filename(<a href="#cl::Positional">cl::Positional</a>, <a href="#cl::desc">cl::desc</a>("<i><input file></i>"), <a href="#cl::init">cl::init</a>("<i>-</i>"));
+ </pre>
+
+ <p>Given these two option declarations, the <tt>--help</tt> output for our grep
+ replacement would look like this:</p>
+
+ <pre>
+ USAGE: spiffygrep [options] <b><regular expression> <input file></b>
+
+ OPTIONS:
+ -help - display available options (--help-hidden for more)
+ </pre>
+
+ <p>... and the resultant program could be used just like the standard
+ <tt>grep</tt> tool.</p>
+
+ <p>Positional arguments are sorted by their order of construction. This means
+ that command line options will be ordered according to how they are listed in a
+ .cpp file, but will not have an ordering defined if they positional arguments
+ are defined in multiple .cpp files. The fix for this problem is simply to
+ define all of your positional arguments in one .cpp file.</p>
+
+ </div>
+
+
+ <!-- _______________________________________________________________________ -->
+ <div class="doc_subsubsection">
+ <a name="--">Specifying positional options with hyphens</a>
+ </div>
+
+ <div class="doc_text">
+
+ <p>Sometimes you may want to specify a value to your positional argument that
+ starts with a hyphen (for example, searching for '<tt>-foo</tt>' in a file). At
+ first, you will have trouble doing this, because it will try to find an argument
+ named '<tt>-foo</tt>', and will fail (and single quotes will not save you).
+ Note that the system <tt>grep</tt> has the same problem:</p>
+
+ <pre>
+ $ spiffygrep '-foo' test.txt
+ Unknown command line argument '-foo'. Try: spiffygrep --help'
+
+ $ grep '-foo' test.txt
+ grep: illegal option -- f
+ grep: illegal option -- o
+ grep: illegal option -- o
+ Usage: grep -hblcnsviw pattern file . . .
+ </pre>
+
+ <p>The solution for this problem is the same for both your tool and the system
+ version: use the '<tt>--</tt>' marker. When the user specifies '<tt>--</tt>' on
+ the command line, it is telling the program that all options after the
+ '<tt>--</tt>' should be treated as positional arguments, not options. Thus, we
+ can use it like this:</p>
+
+ <pre>
+ $ spiffygrep -- -foo test.txt
+ ...output...
+ </pre>
+
+ </div>
+
+ <!-- _______________________________________________________________________ -->
+ <div class="doc_subsubsection">
+ <a name="cl::ConsumeAfter">The <tt>cl::ConsumeAfter</tt> modifier</a>
+ </div>
+
+ <div class="doc_text">
+
+ <p>The <tt>cl::ConsumeAfter</tt> <a href="#formatting">formatting option</a> is
+ used to construct programs that use "interpreter style" option processing. With
+ this style of option processing, all arguments specified after the last
+ positional argument are treated as special interpreter arguments that are not
+ interpreted by the command line argument.</p>
+
+ <p>As a concrete example, lets say we are developing a replacement for the
+ standard Unix Bourne shell (<tt>/bin/sh</tt>). To run <tt>/bin/sh</tt>, first
+ you specify options to the shell itself (like <tt>-x</tt> which turns on trace
+ output), then you specify the name of the script to run, then you specify
+ arguments to the script. These arguments to the script are parsed by the bourne
+ shell command line option processor, but are not interpreted as options to the
+ shell itself. Using the CommandLine library, we would specify this as:</p>
+
+ <pre>
+ <a href="#cl::opt">cl::opt</a><string> Script(<a href="#cl::Positional">cl::Positional</a>, <a href="#cl::desc">cl::desc</a>("<i><input script></i>"), <a href="#cl::init">cl::init</a>("-"));
+ <a href="#cl::list">cl::list</a><string> Argv(<a href="#cl::ConsumeAfter">cl::ConsumeAfter</a>, <a href="#cl::desc">cl::desc</a>("<i><program arguments>...</i>"));
+ <a href="#cl::opt">cl::opt</a><bool> Trace("<i>x</i>", <a href="#cl::desc">cl::desc</a>("<i>Enable trace output</i>"));
+ </pre>
+
+ <p>which automatically provides the help output:</p>
+
+ <pre>
+ USAGE: spiffysh [options] <b><input script> <program arguments>...</b>
+
+ OPTIONS:
+ -help - display available options (--help-hidden for more)
+ <b>-x - Enable trace output</b>
+ </pre>
+
+ <p>At runtime, if we run our new shell replacement as '<tt>spiffysh -x test.sh
+ -a -x -y bar</tt>', the <tt>Trace</tt> variable will be set to true, the
+ <tt>Script</tt> variable will be set to "<tt>test.sh</tt>", and the
+ <tt>Argv</tt> list will contain <tt>["-a", "-x", "-y", "bar"]</tt>, because they
+ were specified after the last positional argument (which is the script
+ name).</p>
+
+ <p>There are several limitations to when <tt>cl::ConsumeAfter</tt> options can
+ be specified. For example, only one <tt>cl::ConsumeAfter</tt> can be specified
+ per program, there must be at least one <a href="#positional">positional
+ argument</a> specified, there must not be any <a href="#cl::list">cl::list</a>
+ positional arguments, and the <tt>cl::ConsumeAfter</tt> option should be a <a
+ href="#cl::list">cl::list</a> option.</p>
+
+ </div>
+
+ <!-- ======================================================================= -->
+ <div class="doc_subsection">
+ <a name="storage">Internal vs External Storage</a>
+ </div>
+
+ <div class="doc_text">
+
+ <p>By default, all command line options automatically hold the value that they
+ parse from the command line. This is very convenient in the common case,
+ especially when combined with the ability to define command line options in the
+ files that use them. This is called the internal storage model.</p>
+
+ <p>Sometimes, however, it is nice to separate the command line option processing
+ code from the storage of the value parsed. For example, lets say that we have a
+ '<tt>-debug</tt>' option that we would like to use to enable debug information
+ across the entire body of our program. In this case, the boolean value
+ controlling the debug code should be globally accessable (in a header file, for
+ example) yet the command line option processing code should not be exposed to
+ all of these clients (requiring lots of .cpp files to #include
+ <tt>CommandLine.h</tt>).</p>
+
+ <p>To do this, set up your .h file with your option, like this for example:</p>
+
+ <pre>
+ <i>// DebugFlag.h - Get access to the '-debug' command line option
+ //
+
+ // DebugFlag - This boolean is set to true if the '-debug' command line option
+ // is specified. This should probably not be referenced directly, instead, use
+ // the DEBUG macro below.
+ //</i>
+ extern bool DebugFlag;
+
+ <i>// DEBUG macro - This macro should be used by code to emit debug information.
+ // In the '-debug' option is specified on the command line, and if this is a
+ // debug build, then the code specified as the option to the macro will be
+ // executed. Otherwise it will not be. Example:
+ //
+ // DEBUG(cerr << "Bitset contains: " << Bitset << "\n");
+ //</i>
+ <span class="doc_red">#ifdef NDEBUG
+ #define DEBUG(X)
+ #else
+ #define DEBUG(X)</span> \
+ do { if (DebugFlag) { X; } } while (0)
+ <span class="doc_red">#endif</span>
+ </pre>
+
+ <p>This allows clients to blissfully use the <tt>DEBUG()</tt> macro, or the
+ <tt>DebugFlag</tt> explicitly if they want to. Now we just need to be able to
+ set the <tt>DebugFlag</tt> boolean when the option is set. To do this, we pass
+ an additial argument to our command line argument processor, and we specify
+ where to fill in with the <a href="#cl::location">cl::location</a>
+ attribute:</p>
+
+ <pre>
+ bool DebugFlag; <i>// the actual value</i>
+ static <a href="#cl::opt">cl::opt</a><bool, true> <i>// The parser</i>
+ Debug("<i>debug</i>", <a href="#cl::desc">cl::desc</a>("<i>Enable debug output</i>"), <a href="#cl::Hidden">cl::Hidden</a>,
+ <a href="#cl::location">cl::location</a>(DebugFlag));
+ </pre>
+
+ <p>In the above example, we specify "<tt>true</tt>" as the second argument to
+ the <a href="#cl::opt">cl::opt</a> template, indicating that the template should
+ not maintain a copy of the value itself. In addition to this, we specify the <a
+ href="#cl::location">cl::location</a> attribute, so that <tt>DebugFlag</tt> is
+ automatically set.</p>
+
+ </div>
+
+ <!-- ======================================================================= -->
+ <div class="doc_subsection">
+ <a name="attributes">Option Attributes</a>
+ </div>
+
+ <div class="doc_text">
+
+ <p>This section describes the basic attributes that you can specify on
+ options.</p>
+
+ <ul>
+
+ <li>The option name attribute (which is required for all options, except <a
+ href="#positional">positional options</a>) specifies what the option name is.
+ This option is specified in simple double quotes:
+
+ <pre>
+ <a href="#cl::opt">cl::opt</a><<b>bool</b>> Quiet("<i>quiet</i>");
+ </pre>
+
+ </li>
+
+ <li><a name="cl::desc">The <b><tt>cl::desc</tt></b></a> attribute specifies a
+ description for the option to be shown in the <tt>--help</tt> output for the
+ program.</li>
+
+ <li><a name="cl::value_desc">The <b><tt>cl::value_desc</tt></b></a> attribute
+ specifies a string that can be used to fine tune the <tt>--help</tt> output for
+ a command line option. Look <a href="#value_desc_example">here</a> for an
+ example.</li>
+
+ <li><a name="cl::init">The <b><tt>cl::init</tt></b></a> attribute specifies an
+ inital value for a <a href="#cl::opt">scalar</a> option. If this attribute is
+ not specified then the command line option value defaults to the value created
+ by the default constructor for the type. <b>Warning</b>: If you specify both
+ <b><tt>cl::init</tt></b> and <b><tt>cl::location</tt></b> for an option,
+ you must specify <b><tt>cl::location</tt></b> first, so that when the
+ command-line parser sees <b><tt>cl::init</tt></b>, it knows where to put the
+ initial value. (You will get an error at runtime if you don't put them in
+ the right order.)</li>
+
+ <li><a name="cl::location">The <b><tt>cl::location</tt></b></a> attribute where to
+ store the value for a parsed command line option if using external storage. See
+ the section on <a href="#storage">Internal vs External Storage</a> for more
+ information.</li>
+
+ <li><a name="cl::aliasopt">The <b><tt>cl::aliasopt</tt></b></a> attribute
+ specifies which option a <a href="#cl::alias">cl::alias</a> option is an alias
+ for.</li>
+
+ <li><a name="cl::values">The <b><tt>cl::values</tt></b></a> attribute specifies
+ the string-to-value mapping to be used by the generic parser. It takes a
+ <b>clEnumValEnd terminated</b> list of (option, value, description) triplets
+ that
+ specify the option name, the value mapped to, and the description shown in the
+ <tt>--help</tt> for the tool. Because the generic parser is used most
+ frequently with enum values, two macros are often useful:
+
+ <ol>
+
+ <li><a name="clEnumVal">The <b><tt>clEnumVal</tt></b></a> macro is used as a
+ nice simple way to specify a triplet for an enum. This macro automatically
+ makes the option name be the same as the enum name. The first option to the
+ macro is the enum, the second is the description for the command line
+ option.</li>
+
+ <li><a name="clEnumValN">The <b><tt>clEnumValN</tt></b></a> macro is used to
+ specify macro options where the option name doesn't equal the enum name. For
+ this macro, the first argument is the enum value, the second is the flag name,
+ and the second is the description.</li>
+
+ </ol>
+
+ You will get a compile time error if you try to use cl::values with a parser
+ that does not support it.</li>
+
+ </ul>
+
+ </div>
+
+ <!-- ======================================================================= -->
+ <div class="doc_subsection">
+ <a name="modifiers">Option Modifiers</a>
+ </div>
+
+ <div class="doc_text">
+
+ <p>Option modifiers are the flags and expressions that you pass into the
+ constructors for <tt><a href="#cl::opt">cl::opt</a></tt> and <tt><a
+ href="#cl::list">cl::list</a></tt>. These modifiers give you the ability to
+ tweak how options are parsed and how <tt>--help</tt> output is generated to fit
+ your application well.</p>
+
+ <p>These options fall into five main catagories:</p>
+
+ <ol>
+ <li><a href="#hiding">Hiding an option from <tt>--help</tt> output</a></li>
+ <li><a href="#numoccurrences">Controlling the number of occurrences
+ required and allowed</a></li>
+ <li><a href="#valrequired">Controlling whether or not a value must be
+ specified</a></li>
+ <li><a href="#formatting">Controlling other formatting options</a></li>
+ <li><a href="#misc">Miscellaneous option modifiers</a></li>
+ </ol>
+
+ <p>It is not possible to specify two options from the same catagory (you'll get
+ a runtime error) to a single option, except for options in the miscellaneous
+ catagory. The CommandLine library specifies defaults for all of these settings
+ that are the most useful in practice and the most common, which mean that you
+ usually shouldn't have to worry about these.</p>
+
+ </div>
+
+ <!-- _______________________________________________________________________ -->
+ <div class="doc_subsubsection">
+ <a name="hiding">Hiding an option from <tt>--help</tt> output</a>
+ </div>
+
+ <div class="doc_text">
+
+ <p>The <tt>cl::NotHidden</tt>, <tt>cl::Hidden</tt>, and
+ <tt>cl::ReallyHidden</tt> modifiers are used to control whether or not an option
+ appears in the <tt>--help</tt> and <tt>--help-hidden</tt> output for the
+ compiled program:</p>
+
+ <ul>
+
+ <li><a name="cl::NotHidden">The <b><tt>cl::NotHidden</tt></b></a> modifier
+ (which is the default for <tt><a href="#cl::opt">cl::opt</a></tt> and <tt><a
+ href="#cl::list">cl::list</a></tt> options), indicates the option is to appear
+ in both help listings.</li>
+
+ <li><a name="cl::Hidden">The <b><tt>cl::Hidden</tt></b></a> modifier (which is the
+ default for <tt><a href="#cl::alias">cl::alias</a></tt> options), indicates that
+ the option should not appear in the <tt>--help</tt> output, but should appear in
+ the <tt>--help-hidden</tt> output.</li>
+
+ <li><a name="cl::ReallyHidden">The <b><tt>cl::ReallyHidden</tt></b></a> modifier,
+ indicates that the option should not appear in any help output.</li>
+
+ </ul>
+
+ </div>
+
+ <!-- _______________________________________________________________________ -->
+ <div class="doc_subsubsection">
+ <a name="numoccurrences">Controlling the number of occurrences required and
+ allowed</a>
+ </div>
+
+ <div class="doc_text">
+
+ <p>This group of options is used to control how many time an option is allowed
+ (or required) to be specified on the command line of your program. Specifying a
+ value for this setting allows the CommandLine library to do error checking for
+ you.</p>
+
+ <p>The allowed values for this option group are:</p>
+
+ <ul>
+
+ <li><a name="cl::Optional">The <b><tt>cl::Optional</tt></b></a> modifier (which
+ is the default for the <tt><a href="#cl::opt">cl::opt</a></tt> and <tt><a
+ href="#cl::alias">cl::alias</a></tt> classes) indicates that your program will
+ allow either zero or one occurrence of the option to be specified.</li>
+
+ <li><a name="cl::ZeroOrMore">The <b><tt>cl::ZeroOrMore</tt></b></a> modifier
+ (which is the default for the <tt><a href="#cl::list">cl::list</a></tt> class)
+ indicates that your program will allow the option to be specified zero or more
+ times.</li>
+
+ <li><a name="cl::Required">The <b><tt>cl::Required</tt></b></a> modifier
+ indicates that the specified option must be specified exactly one time.</li>
+
+ <li><a name="cl::OneOrMore">The <b><tt>cl::OneOrMore</tt></b></a> modifier
+ indicates that the option must be specified at least one time.</li>
+
+ <li>The <b><tt>cl::ConsumeAfter</tt></b> modifier is described in the <a
+ href="#positional">Positional arguments section</a></li>
+
+ </ul>
+
+ <p>If an option is not specified, then the value of the option is equal to the
+ value specified by the <tt><a href="#cl::init">cl::init</a></tt> attribute. If
+ the <tt><a href="#cl::init">cl::init</a></tt> attribute is not specified, the
+ option value is initialized with the default constructor for the data type.</p>
+
+ <p>If an option is specified multiple times for an option of the <tt><a
+ href="#cl::opt">cl::opt</a></tt> class, only the last value will be
+ retained.</p>
+
+ </div>
+
+ <!-- _______________________________________________________________________ -->
+ <div class="doc_subsubsection">
+ <a name="valrequired">Controlling whether or not a value must be specified</a>
+ </div>
+
+ <div class="doc_text">
+
+ <p>This group of options is used to control whether or not the option allows a
+ value to be present. In the case of the CommandLine library, a value is either
+ specified with an equal sign (e.g. '<tt>-index-depth=17</tt>') or as a trailing
+ string (e.g. '<tt>-o a.out</tt>').</p>
+
+ <p>The allowed values for this option group are:</p>
+
+ <ul>
+
+ <li><a name="cl::ValueOptional">The <b><tt>cl::ValueOptional</tt></b></a> modifier
+ (which is the default for <tt>bool</tt> typed options) specifies that it is
+ acceptable to have a value, or not. A boolean argument can be enabled just by
+ appearing on the command line, or it can have an explicit '<tt>-foo=true</tt>'.
+ If an option is specified with this mode, it is illegal for the value to be
+ provided without the equal sign. Therefore '<tt>-foo true</tt>' is illegal. To
+ get this behavior, you must use the <a
+ href="#cl::ValueRequired">cl::ValueRequired</a> modifier.</li>
+
+ <li><a name="cl::ValueRequired">The <b><tt>cl::ValueRequired</tt></b></a> modifier
+ (which is the default for all other types except for <a
+ href="#onealternative">unnamed alternatives using the generic parser</a>)
+ specifies that a value must be provided. This mode informs the command line
+ library that if an option is not provides with an equal sign, that the next
+ argument provided must be the value. This allows things like '<tt>-o
+ a.out</tt>' to work.</li>
+
+ <li><a name="cl::ValueDisallowed">The <b><tt>cl::ValueDisallowed</tt></b></a>
+ modifier (which is the default for <a href="#onealternative">unnamed
+ alternatives using the generic parser</a>) indicates that it is a runtime error
+ for the user to specify a value. This can be provided to disallow users from
+ providing options to boolean options (like '<tt>-foo=true</tt>').</li>
+
+ </ul>
+
+ <p>In general, the default values for this option group work just like you would
+ want them to. As mentioned above, you can specify the <a
+ href="#cl::ValueDisallowed">cl::ValueDisallowed</a> modifier to a boolean
+ argument to restrict your command line parser. These options are mostly useful
+ when <a href="#extensionguide">extending the library</a>.</p>
+
+ </div>
+
+ <!-- _______________________________________________________________________ -->
+ <div class="doc_subsubsection">
+ <a name="formatting">Controlling other formatting options</a>
+ </div>
+
+ <div class="doc_text">
+
+ <p>The formatting option group is used to specify that the command line option
+ has special abilities and is otherwise different from other command line
+ arguments. As usual, you can only specify at most one of these arguments.</p>
+
+ <ul>
+
+ <li><a name="cl::NormalFormatting">The <b><tt>cl::NormalFormatting</tt></b></a>
+ modifier (which is the default all options) specifies that this option is
+ "normal".</li>
+
+ <li><a name="cl::Positional">The <b><tt>cl::Positional</tt></b></a> modifier
+ specifies that this is a positional argument, that does not have a command line
+ option associated with it. See the <a href="#positional">Positional
+ Arguments</a> section for more information.</li>
+
+ <li>The <b><a href="#cl::ConsumeAfter"><tt>cl::ConsumeAfter</tt></a></b> modifier
+ specifies that this option is used to capture "interpreter style" arguments. See <a href="#cl::ConsumeAfter">this section for more information</a>.</li>
+
+ <li><a name="cl::Prefix">The <b><tt>cl::Prefix</tt></b></a> modifier specifies
+ that this option prefixes its value. With 'Prefix' options, there is no equal
+ sign that separates the value from the option name specified. This is useful
+ for processing odd arguments like '<tt>-lmalloc -L/usr/lib'</tt> in a linker
+ tool. Here, the '<tt>l</tt>' and '<tt>L</tt>' options are normal string (list)
+ options, that have the <a href="#cl::Prefix">cl::Prefix</a> modifier added to
+ allow the CommandLine library to recognize them. Note that <a
+ href="#cl::Prefix">cl::Prefix</a> options must not have the <a
+ href="#cl::ValueDisallowed">cl::ValueDisallowed</a> modifier specified.</li>
+
+ <li><a name="cl::Grouping">The <b><tt>cl::Grouping</tt></b></a> modifier is used
+ to implement unix style tools (like <tt>ls</tt>) that have lots of single letter
+ arguments, but only require a single dash. For example, the '<tt>ls -labF</tt>'
+ command actually enables four different options, all of which are single
+ letters. Note that <a href="#cl::Grouping">cl::Grouping</a> options cannot have
+ values.</li>
+
+ </ul>
+
+ <p>The CommandLine library does not restrict how you use the <a
+ href="#cl::Prefix">cl::Prefix</a> or <a href="#cl::Grouping">cl::Grouping</a>
+ modifiers, but it is possible to specify ambiguous argument settings. Thus, it
+ is possible to have multiple letter options that are prefix or grouping options,
+ and they will still work as designed.</p>
+
+ <p>To do this, the CommandLine library uses a greedy algorithm to parse the
+ input option into (potentially multiple) prefix and grouping options. The
+ strategy basically looks like this:</p>
+
+ <p><tt>parse(string OrigInput) {</tt>
+
+ <ol>
+ <li><tt>string input = OrigInput;</tt>
+ <li><tt>if (isOption(input)) return getOption(input).parse();</tt> <i>// Normal option</i>
+ <li><tt>while (!isOption(input) && !input.empty()) input.pop_back();</tt> <i>// Remove the last letter</i>
+ <li><tt>if (input.empty()) return error();</tt> <i>// No matching option</i>
+ <li><tt>if (getOption(input).isPrefix())<br>
+ return getOption(input).parse(input);</tt>
+ <li><tt>while (!input.empty()) { <i>// Must be grouping options</i><br>
+ getOption(input).parse();<br>
+ OrigInput.erase(OrigInput.begin(), OrigInput.begin()+input.length());<br>
+ input = OrigInput;<br>
+ while (!isOption(input) && !input.empty()) input.pop_back();<br>
+ }</tt>
+ <li><tt>if (!OrigInput.empty()) error();</tt></li>
+
+ </ol>
+
+ <p><tt>}</tt></p>
+
+ </div>
+
+ <!-- _______________________________________________________________________ -->
+ <div class="doc_subsubsection">
+ <a name="misc">Miscellaneous option modifiers</a>
+ </div>
+
+ <div class="doc_text">
+
+ <p>The miscellaneous option modifiers are the only flags where you can specify
+ more than one flag from the set: they are not mutually exclusive. These flags
+ specify boolean properties that modify the option.</p>
+
+ <ul>
+
+ <li><a name="cl::CommaSeparated">The <b><tt>cl::CommaSeparated</tt></b></a> modifier
+ indicates that any commas specified for an option's value should be used to
+ split the value up into multiple values for the option. For example, these two
+ options are equivalent when <tt>cl::CommaSeparated</tt> is specified:
+ "<tt>-foo=a -foo=b -foo=c</tt>" and "<tt>-foo=a,b,c</tt>". This option only
+ makes sense to be used in a case where the option is allowed to accept one or
+ more values (i.e. it is a <a href="#cl::list">cl::list</a> option).</li>
+
+ <li><a name="cl::PositionalEatsArgs">The
+ <b><tt>cl::PositionalEatsArgs</tt></b></a> modifier (which only applies to
+ positional arguments, and only makes sense for lists) indicates that positional
+ argument should consume any strings after it (including strings that start with
+ a "-") up until another recognized positional argument. For example, if you
+ have two "eating" positional arguments "<tt>pos1</tt>" and "<tt>pos2</tt>" the
+ string "<tt>-pos1 -foo -bar baz -pos2 -bork</tt>" would cause the "<tt>-foo -bar
+ -baz</tt>" strings to be applied to the "<tt>-pos1</tt>" option and the
+ "<tt>-bork</tt>" string to be applied to the "<tt>-pos2</tt>" option.</li>
+
+ </ul>
+
+ <p>So far, these are the only two miscellaneous option modifiers.</p>
+
+ </div>
+
+ <!-- ======================================================================= -->
+ <div class="doc_subsection">
+ <a name="toplevel">Top-Level Classes and Functions</a>
+ </div>
+
+ <div class="doc_text">
+
+ <p>Despite all of the built-in flexibility, the CommandLine option library
+ really only consists of one function (<a
+ href="#cl::ParseCommandLineOptions"><tt>cl::ParseCommandLineOptions</tt></a>)
+ and three main classes: <a href="#cl::opt"><tt>cl::opt</tt></a>, <a
+ href="#cl::list"><tt>cl::list</tt></a>, and <a
+ href="#cl::alias"><tt>cl::alias</tt></a>. This section describes these three
+ classes in detail.</p>
+
+ </div>
+
+ <!-- _______________________________________________________________________ -->
+ <div class="doc_subsubsection">
+ <a name="cl::ParseCommandLineOptions">The <tt>cl::ParseCommandLineOptions</tt>
+ function</a>
+ </div>
+
+ <div class="doc_text">
+
+ <p>The <tt>cl::ParseCommandLineOptions</tt> function is designed to be called
+ directly from <tt>main</tt>, and is used to fill in the values of all of the
+ command line option variables once <tt>argc</tt> and <tt>argv</tt> are
+ available.</p>
+
+ <p>The <tt>cl::ParseCommandLineOptions</tt> function requires two parameters
+ (<tt>argc</tt> and <tt>argv</tt>), but may also take an optional third parameter
+ which holds <a href="#description">additional extra text</a> to emit when the
+ <tt>--help</tt> option is invoked.</p>
+
+ </div>
+
+ <!-- _______________________________________________________________________ -->
+ <div class="doc_subsubsection">
+ <a name="cl::ParseEnvironmentOptions">The <tt>cl::ParseEnvironmentOptions</tt>
+ function</a>
+ </div>
+
+ <div class="doc_text">
+
+ <p>The <tt>cl::ParseEnvironmentOptions</tt> function has mostly the same effects
+ as <a
+ href="#cl::ParseCommandLineOptions"><tt>cl::ParseCommandLineOptions</tt></a>,
+ except that it is designed to take values for options from an environment
+ variable, for those cases in which reading the command line is not convenient or
+ not desired. It fills in the values of all the command line option variables
+ just like <a
+ href="#cl::ParseCommandLineOptions"><tt>cl::ParseCommandLineOptions</tt></a>
+ does.</p>
+
+ <p>It takes three parameters: first, the name of the program (since
+ <tt>argv</tt> may not be available, it can't just look in <tt>argv[0]</tt>),
+ second, the name of the environment variable to examine, and third, the optional
+ <a href="#description">additional extra text</a> to emit when the
+ <tt>--help</tt> option is invoked.</p>
+
+ <p><tt>cl::ParseEnvironmentOptions</tt> will break the environment
+ variable's value up into words and then process them using
+ <a href="#cl::ParseCommandLineOptions"><tt>cl::ParseCommandLineOptions</tt></a>.
+ <b>Note:</b> Currently <tt>cl::ParseEnvironmentOptions</tt> does not support
+ quoting, so an environment variable containing <tt>-option "foo bar"</tt> will
+ be parsed as three words, <tt>-option</tt>, <tt>"foo</tt>, and <tt>bar"</tt>,
+ which is different from what you would get from the shell with the same
+ input.</p>
+
+ </div>
+
+ <!-- _______________________________________________________________________ -->
+ <div class="doc_subsubsection">
+ <a name="cl::opt">The <tt>cl::opt</tt> class</a>
+ </div>
+
+ <div class="doc_text">
+
+ <p>The <tt>cl::opt</tt> class is the class used to represent scalar command line
+ options, and is the one used most of the time. It is a templated class which
+ can take up to three arguments (all except for the first have default values
+ though):</p>
+
+ <pre>
+ <b>namespace</b> cl {
+ <b>template</b> <<b>class</b> DataType, <b>bool</b> ExternalStorage = <b>false</b>,
+ <b>class</b> ParserClass = parser<DataType> >
+ <b>class</b> opt;
+ }
+ </pre>
+
+ <p>The first template argument specifies what underlying data type the command
+ line argument is, and is used to select a default parser implementation. The
+ second template argument is used to specify whether the option should contain
+ the storage for the option (the default) or whether external storage should be
+ used to contain the value parsed for the option (see <a href="#storage">Internal
+ vs External Storage</a> for more information).</p>
+
+ <p>The third template argument specifies which parser to use. The default value
+ selects an instantiation of the <tt>parser</tt> class based on the underlying
+ data type of the option. In general, this default works well for most
+ applications, so this option is only used when using a <a
+ href="#customparser">custom parser</a>.</p>
+
+ </div>
+
+ <!-- _______________________________________________________________________ -->
+ <div class="doc_subsubsection">
+ <a name="cl::list">The <tt>cl::list</tt> class</a>
+ </div>
+
+ <div class="doc_text">
+
+ <p>The <tt>cl::list</tt> class is the class used to represent a list of command
+ line options. It too is a templated class which can take up to three
+ arguments:</p>
+
+ <pre>
+ <b>namespace</b> cl {
+ <b>template</b> <<b>class</b> DataType, <b>class</b> Storage = <b>bool</b>,
+ <b>class</b> ParserClass = parser<DataType> >
+ <b>class</b> list;
+ }
+ </pre>
+
+ <p>This class works the exact same as the <a
+ href="#cl::opt"><tt>cl::opt</tt></a> class, except that the second argument is
+ the <b>type</b> of the external storage, not a boolean value. For this class,
+ the marker type '<tt>bool</tt>' is used to indicate that internal storage should
+ be used.</p>
+
+ </div>
+
+ <!-- _______________________________________________________________________ -->
+ <div class="doc_subsubsection">
+ <a name="cl::alias">The <tt>cl::alias</tt> class</a>
+ </div>
+
+ <div class="doc_text">
+
+ <p>The <tt>cl::alias</tt> class is a nontemplated class that is used to form
+ aliases for other arguments.</p>
+
+ <pre>
+ <b>namespace</b> cl {
+ <b>class</b> alias;
+ }
+ </pre>
+
+ <p>The <a href="#cl::aliasopt"><tt>cl::aliasopt</tt></a> attribute should be
+ used to specify which option this is an alias for. Alias arguments default to
+ being <a href="#cl::Hidden">Hidden</a>, and use the aliased options parser to do
+ the conversion from string to data.</p>
+
+ </div>
+
+ <!-- ======================================================================= -->
+ <div class="doc_subsection">
+ <a name="builtinparsers">Builtin parsers</a>
+ </div>
+
+ <div class="doc_text">
+
+ <p>Parsers control how the string value taken from the command line is
+ translated into a typed value, suitable for use in a C++ program. By default,
+ the CommandLine library uses an instance of <tt>parser<type></tt> if the
+ command line option specifies that it uses values of type '<tt>type</tt>'.
+ Because of this, custom option processing is specified with specializations of
+ the '<tt>parser</tt>' class.</p>
+
+ <p>The CommandLine library provides the following builtin parser
+ specializations, which are sufficient for most applications. It can, however,
+ also be extended to work with new data types and new ways of interpreting the
+ same data. See the <a href="#customparser">Writing a Custom Parser</a> for more
+ details on this type of library extension.</p>
+
+ <ul>
+
+ <li><a name="genericparser">The <b>generic <tt>parser<t></tt> parser</b></a>
+ can be used to map strings values to any data type, through the use of the <a
+ href="#cl::values">cl::values</a> property, which specifies the mapping
+ information. The most common use of this parser is for parsing enum values,
+ which allows you to use the CommandLine library for all of the error checking to
+ make sure that only valid enum values are specified (as opposed to accepting
+ arbitrary strings). Despite this, however, the generic parser class can be used
+ for any data type.</li>
+
+ <li><a name="boolparser">The <b><tt>parser<bool></tt> specialization</b></a>
+ is used to convert boolean strings to a boolean value. Currently accepted
+ strings are "<tt>true</tt>", "<tt>TRUE</tt>", "<tt>True</tt>", "<tt>1</tt>",
+ "<tt>false</tt>", "<tt>FALSE</tt>", "<tt>False</tt>", and "<tt>0</tt>".</li>
+
+ <li><a name="stringparser">The <b><tt>parser<string></tt>
+ specialization</b></a> simply stores the parsed string into the string value
+ specified. No conversion or modification of the data is performed.</li>
+
+ <li><a name="intparser">The <b><tt>parser<int></tt> specialization</b></a>
+ uses the C <tt>strtol</tt> function to parse the string input. As such, it will
+ accept a decimal number (with an optional '+' or '-' prefix) which must start
+ with a non-zero digit. It accepts octal numbers, which are identified with a
+ '<tt>0</tt>' prefix digit, and hexadecimal numbers with a prefix of
+ '<tt>0x</tt>' or '<tt>0X</tt>'.</li>
+
+ <li><a name="doubleparser">The <b><tt>parser<double></tt></b></a> and
+ <b><tt>parser<float></tt> specializations</b> use the standard C
+ <tt>strtod</tt> function to convert floating point strings into floating point
+ values. As such, a broad range of string formats is supported, including
+ exponential notation (ex: <tt>1.7e15</tt>) and properly supports locales.
+ </li>
+
+ </ul>
+
+ </div>
+
+ <!-- *********************************************************************** -->
+ <div class="doc_section">
+ <a name="extensionguide">Extension Guide</a>
+ </div>
+ <!-- *********************************************************************** -->
+
+ <div class="doc_text">
+
+ <p>Although the CommandLine library has a lot of functionality built into it
+ already (as discussed previously), one of its true strengths lie in its
+ extensibility. This section discusses how the CommandLine library works under
+ the covers and illustrates how to do some simple, common, extensions.</p>
+
+ </div>
+
+ <!-- ======================================================================= -->
+ <div class="doc_subsection">
+ <a name="customparser">Writing a custom parser</a>
+ </div>
+
+ <div class="doc_text">
+
+ <p>One of the simplest and most common extensions is the use of a custom parser.
+ As <a href="#builtinparsers">discussed previously</a>, parsers are the portion
+ of the CommandLine library that turns string input from the user into a
+ particular parsed data type, validating the input in the process.</p>
+
+ <p>There are two ways to use a new parser:</p>
+
+ <ol>
+
+ <li>
+
+ <p>Specialize the <a href="#genericparser"><tt>cl::parser</tt></a> template for
+ your custom data type.<p>
+
+ <p>This approach has the advantage that users of your custom data type will
+ automatically use your custom parser whenever they define an option with a value
+ type of your data type. The disadvantage of this approach is that it doesn't
+ work if your fundemental data type is something that is already supported.</p>
+
+ </li>
+
+ <li>
+
+ <p>Write an independent class, using it explicitly from options that need
+ it.</p>
+
+ <p>This approach works well in situations where you would line to parse an
+ option using special syntax for a not-very-special data-type. The drawback of
+ this approach is that users of your parser have to be aware that they are using
+ your parser, instead of the builtin ones.</p>
+
+ </li>
+
+ </ol>
+
+ <p>To guide the discussion, we will discuss a custom parser that accepts file
+ sizes, specified with an optional unit after the numeric size. For example, we
+ would like to parse "102kb", "41M", "1G" into the appropriate integer value. In
+ this case, the underlying data type we want to parse into is
+ '<tt>unsigned</tt>'. We choose approach #2 above because we don't want to make
+ this the default for all <tt>unsigned</tt> options.</p>
+
+ <p>To start out, we declare our new <tt>FileSizeParser</tt> class:</p>
+
+ <pre>
+ <b>struct</b> FileSizeParser : <b>public</b> cl::basic_parser<<b>unsigned</b>> {
+ <i>// parse - Return true on error.</i>
+ <b>bool</b> parse(cl::Option &O, <b>const char</b> *ArgName, <b>const</b> std::string &ArgValue,
+ <b>unsigned</b> &Val);
+ };
+ </pre>
+
+ <p>Our new class inherits from the <tt>cl::basic_parser</tt> template class to
+ fill in the default, boiler plate, code for us. We give it the data type that
+ we parse into (the last argument to the <tt>parse</tt> method so that clients of
+ our custom parser know what object type to pass in to the parse method (here we
+ declare that we parse into '<tt>unsigned</tt>' variables.</p>
+
+ <p>For most purposes, the only method that must be implemented in a custom
+ parser is the <tt>parse</tt> method. The <tt>parse</tt> method is called
+ whenever the option is invoked, passing in the option itself, the option name,
+ the string to parse, and a reference to a return value. If the string to parse
+ is not well formed, the parser should output an error message and return true.
+ Otherwise it should return false and set '<tt>Val</tt>' to the parsed value. In
+ our example, we implement <tt>parse</tt> as:</p>
+
+ <pre>
+ <b>bool</b> FileSizeParser::parse(cl::Option &O, <b>const char</b> *ArgName,
+ <b>const</b> std::string &Arg, <b>unsigned</b> &Val) {
+ <b>const char</b> *ArgStart = Arg.c_str();
+ <b>char</b> *End;
+
+ <i>// Parse integer part, leaving 'End' pointing to the first non-integer char</i>
+ Val = (unsigned)strtol(ArgStart, &End, 0);
+
+ <b>while</b> (1) {
+ <b>switch</b> (*End++) {
+ <b>case</b> 0: <b>return</b> false; <i>// No error</i>
+ <b>case</b> 'i': <i>// Ignore the 'i' in KiB if people use that</i>
+ <b>case</b> 'b': <b>case</b> 'B': <i>// Ignore B suffix</i>
+ <b>break</b>;
+
+ <b>case</b> 'g': <b>case</b> 'G': Val *= 1024*1024*1024; <b>break</b>;
+ <b>case</b> 'm': <b>case</b> 'M': Val *= 1024*1024; <b>break</b>;
+ <b>case</b> 'k': <b>case</b> 'K': Val *= 1024; <b>break</b>;
+
+ default:
+ <i>// Print an error message if unrecognized character!</i>
+ <b>return</b> O.error(": '" + Arg + "' value invalid for file size argument!");
+ }
+ }
+ }
+ </pre>
+
+ <p>This function implements a very simple parser for the kinds of strings we are
+ interested in. Although it has some holes (it allows "<tt>123KKK</tt>" for
+ example), it is good enough for this example. Note that we use the option
+ itself to print out the error message (the <tt>error</tt> method always returns
+ true) in order to get a nice error message (shown below). Now that we have our
+ parser class, we can use it like this:</p>
+
+ <pre>
+ <b>static</b> <a href="#cl::opt">cl::opt</a><<b>unsigned</b>, <b>false</b>, FileSizeParser>
+ MFS(<i>"max-file-size"</i>, <a href="#cl::desc">cl::desc</a>(<i>"Maximum file size to accept"</i>),
+ <a href="#cl::value_desc">cl::value_desc</a>("<i>size</i>"));
+ </pre>
+
+ <p>Which adds this to the output of our program:</p>
+
+ <pre>
+ OPTIONS:
+ -help - display available options (--help-hidden for more)
+ ...
+ <b>-max-file-size=<size> - Maximum file size to accept</b>
+ </pre>
+
+ <p>And we can test that our parse works correctly now (the test program just
+ prints out the max-file-size argument value):</p>
+
+ <pre>
+ $ ./test
+ MFS: 0
+ $ ./test -max-file-size=123MB
+ MFS: 128974848
+ $ ./test -max-file-size=3G
+ MFS: 3221225472
+ $ ./test -max-file-size=dog
+ -max-file-size option: 'dog' value invalid for file size argument!
+ </pre>
+
+ <p>It looks like it works. The error message that we get is nice and helpful,
+ and we seem to accept reasonable file sizes. This wraps up the "custom parser"
+ tutorial.</p>
+
+ </div>
+
+ <!-- ======================================================================= -->
+ <div class="doc_subsection">
+ <a name="explotingexternal">Exploiting external storage</a>
+ </div>
+
+ <div class="doc_text">
+
+ <p>TODO: fill in this section</p>
+
+ </div>
+
+ <!-- ======================================================================= -->
+ <div class="doc_subsection">
+ <a name="dynamicopts">Dynamically adding command line options</a>
+ </div>
+
+ <div class="doc_text">
+
+ <p>TODO: fill in this section</p>
+
+ </div>
+
+ <!-- *********************************************************************** -->
+
+ <hr>
+ <address>
+ <a href="http://jigsaw.w3.org/css-validator/check/referer"><img
+ src="http://jigsaw.w3.org/css-validator/images/vcss" alt="Valid CSS!"></a>
+ <a href="http://validator.w3.org/check/referer"><img
+ src="http://www.w3.org/Icons/valid-html401" alt="Valid HTML 4.01!"></a>
+
+ <a href="mailto:sabre at nondot.org">Chris Lattner</a><br>
+ <a href="http://llvm.cs.uiuc.edu">LLVM Compiler Infrastructure</a><br>
+ Last modified: $Date: 2004/08/13 22:03:03 $
+ </address>
+
+ </body>
+ </html>
Index: llvm-www/releases/1.3/docs/ExtendingLLVM.html
diff -c /dev/null llvm-www/releases/1.3/docs/ExtendingLLVM.html:1.1
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--- 1,238 ----
+ <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"
+ "http://www.w3.org/TR/html4/strict.dtd">
+ <html>
+ <head>
+ <title>Extending LLVM: Adding instructions, intrinsics, types, etc.</title>
+ <link rel="stylesheet" href="llvm.css" type="text/css">
+ </head>
+
+ <body>
+
+ <div class="doc_title">
+ Extending LLVM: Adding instructions, intrinsics, types, etc.
+ </div>
+
+ <ol>
+ <li><a href="#introduction">Introduction and Warning</a></li>
+ <li><a href="#intrinsic">Adding a new intrinsic function</a></li>
+ <li><a href="#instruction">Adding a new instruction</a></li>
+ <li><a href="#type">Adding a new type</a>
+ <ol>
+ <li><a href="#fund_type">Adding a new fundamental type</a></li>
+ <li><a href="#derived_type">Adding a new derived type</a></li>
+ </ol></li>
+ </ol>
+
+ <div class="doc_author">
+ <p>Written by <a href="http://misha.brukman.net">Misha Brukman</a></p>
+ </div>
+
+ <!-- *********************************************************************** -->
+ <div class="doc_section">
+ <a name="introduction">Introduction and Warning</a>
+ </div>
+ <!-- *********************************************************************** -->
+
+ <div class="doc_text">
+
+ <p>During the course of using LLVM, you may wish to customize it for your
+ research project or for experimentation. At this point, you may realize that
+ you need to add something to LLVM, whether it be a new fundamental type, a new
+ intrinsic function, or a whole new instruction.</p>
+
+ <p>When you come to this realization, stop and think. Do you really need to
+ extend LLVM? Is it a new fundamental capability that LLVM does not support at
+ its current incarnation or can it be synthesized from already pre-existing LLVM
+ elements? If you are not sure, ask on the <a
+ href="http://mail.cs.uiuc.edu/mailman/listinfo/llvmdev">LLVM-dev</a> list. The
+ reason is that extending LLVM will get involved as you need to update all the
+ different passes that you intend to use with your extension, and there are
+ <em>many</em> LLVM analyses and transformations, so it may be quite a bit of
+ work.</p>
+
+ <p>Adding an <a href="#intrinsic">intrinsic function</a> is easier than adding
+ an instruction, and is transparent to optimization passes which treat it as an
+ unanalyzable function. If your added functionality can be expressed as a
+ function call, an intrinsic function is the method of choice for LLVM
+ extension.</p>
+
+ <p>Before you invest a significant amount of effort into a non-trivial
+ extension, <span class="doc_warning">ask on the list</span> if what you are
+ looking to do can be done with already-existing infrastructure, or if maybe
+ someone else is already working on it. You will save yourself a lot of time and
+ effort by doing so.</p>
+
+ <p>Finally, these are my notes, and since my extensions are not complete, I may
+ be missing steps. If you find some omissions, please let me know <a
+ href="http://misha.brukman.net/contact.html">directly</a> or post on <a
+ href="http://mail.cs.uiuc.edu/mailman/listinfo/llvmdev">LLVM-dev</a>.</p>
+
+ </div>
+
+ <!-- *********************************************************************** -->
+ <div class="doc_section">
+ <a name="intrinsic">Adding a new intrinsic function</a>
+ </div>
+ <!-- *********************************************************************** -->
+
+ <div class="doc_text">
+
+ <p>Adding a new intrinsic function to LLVM is much easier than adding a new
+ instruction. Almost all extensions to LLVM should start as an intrinsic
+ function and then be turned into an instruction if warranted.</p>
+
+ <ol>
+ <li><tt>llvm/docs/LangRef.html</tt>:
+ Document the intrinsic. Decide whether it is code generator specific and
+ what the restrictions are. Talk to other people about it so that you are
+ sure it's a good idea.</li>
+
+ <li><tt>llvm/include/llvm/Intrinsics.h</tt>:
+ add an enum in the <tt>llvm::Intrinsic</tt> namespace</li>
+
+ <li><tt>llvm/lib/CodeGen/IntrinsicLowering.cpp</tt>:
+ implement the lowering for this intrinsic</li>
+
+ <li><tt>llvm/lib/VMCore/Verifier.cpp</tt>:
+ Add code to check the invariants of the intrinsic are respected.</li>
+
+ <li><tt>llvm/lib/VMCore/Function.cpp (<tt>Function::getIntrinsicID()</tt>)</tt>:
+ Identify the new intrinsic function, returning the enum for the intrinsic
+ that you added.</li>
+
+ <li><tt>llvm/lib/Analysis/BasicAliasAnalysis.cpp</tt>: If the new intrinsic does
+ not access memory or does not write to memory, add it to the relevant list
+ of functions.</li>
+
+ <li><tt>llvm/lib/Transforms/Utils/Local.cpp</tt>: If it is possible to constant
+ propagate your intrinsic, add support to it in the
+ <tt>canConstantFoldCallTo</tt> and <tt>ConstantFoldCall</tt> functions.</li>
+
+ <li>Test your intrinsic</li>
+ <li><tt>llvm/test/Regression/*</tt>: add your test cases to the test suite.</li>
+ </ol>
+
+ <p>If this intrinsic requires code generator support (ie, it cannot be lowered).
+ You should also add support to the code generator in question.</p>
+
+ </div>
+
+ <!-- *********************************************************************** -->
+ <div class="doc_section">
+ <a name="instruction">Adding a new instruction</a>
+ </div>
+ <!-- *********************************************************************** -->
+
+ <div class="doc_text">
+
+ <p><span class="doc_warning">WARNING: adding instructions changes the bytecode
+ format, and it will take some effort to maintain compatibility with
+ the previous version.</span> Only add an instruction if it is absolutely
+ necessary.</p>
+
+ <ol>
+
+ <li><tt>llvm/include/llvm/Instruction.def</tt>:
+ add a number for your instruction and an enum name</li>
+
+ <li><tt>llvm/include/llvm/Instructions.h</tt>:
+ add a definition for the class that will represent your instruction</li>
+
+ <li><tt>llvm/include/llvm/Support/InstVisitor.h</tt>:
+ add a prototype for a visitor to your new instruction type</li>
+
+ <li><tt>llvm/lib/AsmParser/Lexer.l</tt>:
+ add a new token to parse your instruction from assembly text file</li>
+
+ <li><tt>llvm/lib/AsmParser/llvmAsmParser.y</tt>:
+ add the grammar on how your instruction can be read and what it will
+ construct as a result</li>
+
+ <li><tt>llvm/lib/Bytecode/Reader/InstructionReader.cpp</tt>:
+ add a case for your instruction and how it will be parsed from bytecode</li>
+
+ <li><tt>llvm/lib/VMCore/Instruction.cpp</tt>:
+ add a case for how your instruction will be printed out to assembly</li>
+
+ <li><tt>llvm/lib/VMCore/Instructions.cpp</tt>:
+ implement the class you defined in <tt>llvm/include/llvm/Instructions.h</tt></li>
+
+ </ol>
+
+ <p>Also, you need to implement (or modify) any analyses or passes that you want
+ to understand this new instruction.</p>
+
+ </div>
+
+
+ <!-- *********************************************************************** -->
+ <div class="doc_section">
+ <a name="type">Adding a new type</a>
+ </div>
+ <!-- *********************************************************************** -->
+
+ <div class="doc_text">
+
+ <p><span class="doc_warning">WARNING: adding new types changes the bytecode
+ format, and will break compatibility with currently-existing LLVM
+ installations.</span> Only add new types if it is absolutely necessary.</p>
+
+ </div>
+
+ <!-- ======================================================================= -->
+ <div class="doc_subsection">
+ <a name="fund_type">Adding a fundamental type</a>
+ </div>
+
+ <div class="doc_text">
+
+ <ol>
+
+ <li><tt>llvm/include/llvm/Type.def</tt>:
+ add enum for the type</li>
+
+ <li><tt>llvm/include/llvm/Type.h</tt>:
+ add ID number for the new type; add static <tt>Type*</tt> for this type</li>
+
+ <li><tt>llvm/lib/VMCore/Type.cpp</tt>:
+ add mapping from <tt>TypeID</tt> => <tt>Type*</tt>;
+ initialize the static <tt>Type*</tt></li>
+
+ <li><tt>llvm/lib/AsmReader/Lexer.l</tt>:
+ add ability to parse in the type from text assembly</li>
+
+ <li><tt>llvm/lib/AsmReader/llvmAsmParser.y</tt>:
+ add a token for that type</li>
+
+ </ol>
+
+ </div>
+
+ <!-- ======================================================================= -->
+ <div class="doc_subsection">
+ <a name="derived_type">Adding a derived type</a>
+ </div>
+
+ <div class="doc_text">
+
+ <p>TODO</p>
+
+ </div>
+
+ <!-- *********************************************************************** -->
+
+ <hr>
+ <address>
+ <a href="http://jigsaw.w3.org/css-validator/check/referer"><img
+ src="http://jigsaw.w3.org/css-validator/images/vcss" alt="Valid CSS!"></a>
+ <a href="http://validator.w3.org/check/referer"><img
+ src="http://www.w3.org/Icons/valid-html401" alt="Valid HTML 4.01!" /></a>
+
+ <a href="http://misha.brukman.net">Misha Brukman</a><br>
+ <a href="http://llvm.cs.uiuc.edu">The LLVM Compiler Infrastructure</a>
+ <br>
+ Last modified: $Date: 2004/08/13 22:03:03 $
+ </address>
+
+ </body>
+ </html>
Index: llvm-www/releases/1.3/docs/FAQ.html
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*** 0 ****
--- 1,533 ----
+ <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"
+ "http://www.w3.org/TR/html4/strict.dtd">
+ <html>
+ <head>
+ <title>LLVM: Frequently Asked Questions</title>
+ <style type="text/css">
+ @import url("llvm.css");
+ .question { font-weight: bold }
+ .answer { margin-left: 2em }
+ </style>
+ </head>
+ <body>
+
+ <div class="doc_title">
+ LLVM: Frequently Asked Questions
+ </div>
+
+ <ol>
+ <li><a href="#license">License</a>
+ <ol>
+ <li>Why are the LLVM source code and the front-end distributed under different
+ licenses?</li>
+ <li>Does the University of Illinois Open Source License really qualify as an
+ "open source" license?</li>
+ <li>Can I modify LLVM source code and redistribute the modified source?</li>
+ <li>Can I modify LLVM source code and redistribute binaries or other tools
+ based on it, without redistributing the source?</li>
+ </ol></li>
+
+ <li><a href="#source">Source code</a>
+ <ol>
+ <li>In what language is LLVM written?</li>
+ <li>How portable is the LLVM source code?</li>
+ </ol></li>
+
+ <li><a href="#build">Build Problems</a>
+ <ol>
+ <li>When I run configure, it finds the wrong C compiler.</li>
+ <li>I compile the code, and I get some error about <tt>/localhome</tt>.</li>
+ <li>The <tt>configure</tt> script finds the right C compiler, but it uses the
+ LLVM linker from a previous build. What do I do?</li>
+ <li>When creating a dynamic library, I get a strange GLIBC error.</li>
+ <li>I've updated my source tree from CVS, and now my build is trying to use a
+ file/directory that doesn't exist.</li>
+ <li>I've modified a Makefile in my source tree, but my build tree keeps using
+ the old version. What do I do?</li>
+ <li>I've upgraded to a new version of LLVM, and I get strange build
+ errors.</li>
+ <li>I've built LLVM and am testing it, but the tests freeze.</li>
+ <li>Why do test results differ when I perform different types of builds?</li>
+ <li>Compiling LLVM with GCC 3.3.2 fails, what should I do?</li>
+ <li>When I use the test suite, all of the C Backend tests fail. What is
+ wrong?</li>
+ </ol></li>
+
+ <li><a href="#cfe">Using the GCC Front End</a>
+ <ol>
+ <li>
+ When I compile software that uses a configure script, the configure script
+ thinks my system has all of the header files and libraries it is testing
+ for. How do I get configure to work correctly?
+ </li>
+
+ <li>
+ When I compile code using the LLVM GCC front end, it complains that it
+ cannot find libcrtend.a.
+ </li>
+ </ol>
+ </li>
+
+ <li><a href="#cfe_code">Questions about code generated by the GCC front-end</a>
+ <ol>
+ <li>What is this <tt>__main()</tt> call that gets inserted into
+ <tt>main()</tt>?</li>
+ <li>Where did all of my code go??</li>
+ <li>What is this <tt>llvm.global_ctors</tt> and
+ <tt>_GLOBAL__I__tmp_webcompile...</tt> stuff that happens when I
+ #include <iostream>?</li>
+ </ol>
+ </li>
+ </ol>
+
+ <div class="doc_author">
+ <p>Written by <a href="http://llvm.cs.uiuc.edu">The LLVM Team</a></p>
+ </div>
+
+
+ <!-- *********************************************************************** -->
+ <div class="doc_section">
+ <a name="license">License</a>
+ </div>
+ <!-- *********************************************************************** -->
+
+ <div class="question">
+ <p>Why are the LLVM source code and the front-end distributed under different
+ licenses?</p>
+ </div>
+
+ <div class="answer">
+ <p>The C/C++ front-ends are based on GCC and must be distributed under the GPL.
+ Our aim is to distribute LLVM source code under a <em>much less restrictive</em>
+ license, in particular one that does not compel users who distribute tools based
+ on modifying the source to redistribute the modified source code as well.</p>
+ </div>
+
+ <div class="question">
+ <p>Does the University of Illinois Open Source License really qualify as an
+ "open source" license?</p>
+ </div>
+
+ <div class="answer">
+ <p>Yes, the license is <a
+ href="http://www.opensource.org/licenses/UoI-NCSA.php">certified</a> by the Open
+ Source Initiative (OSI).</p>
+ </div>
+
+ <div class="question">
+ <p>Can I modify LLVM source code and redistribute the modified source?</p>
+ </div>
+
+ <div class="answer">
+ <p>Yes. The modified source distribution must retain the copyright notice and
+ follow the three bulletted conditions listed in the <a
+ href="http://llvm.cs.uiuc.edu/releases/1.2/LICENSE.TXT">LLVM license</a>.</p>
+ </div>
+
+ <div class="question">
+ <p>Can I modify LLVM source code and redistribute binaries or other tools based
+ on it, without redistributing the source?</p>
+ </div>
+
+ <div class="answer">
+ <p>Yes, this is why we distribute LLVM under a less restrictive license than
+ GPL, as explained in the first question above.</p>
+ </div>
+
+ <!-- *********************************************************************** -->
+ <div class="doc_section">
+ <a name="source">Source Code</a>
+ </div>
+ <!-- *********************************************************************** -->
+
+ <div class="question">
+ <p>In what language is LLVM written?</p>
+ </div>
+
+ <div class="answer">
+ <p>All of the LLVM tools and libraries are written in C++ with extensive use of
+ the STL.</p>
+ </div>
+
+ <div class="question">
+ <p>How portable is the LLVM source code?</p>
+ </div>
+
+ <div class="answer">
+ <p>The LLVM source code should be portable to most modern UNIX-like operating
+ systems. Most of the code is written in standard C++ with operating system
+ services abstracted to a support library. The tools required to build and test
+ LLVM have been ported to a plethora of platforms.</p>
+
+ <p>Some porting problems may exist in the following areas:</p>
+
+ <ul>
+
+ <li>The GCC front end code is not as portable as the LLVM suite, so it may not
+ compile as well on unsupported platforms.</li>
+
+ <li>The Python test classes are more UNIX-centric than they should be, so
+ porting to non-UNIX like platforms (i.e. Windows, MacOS 9) will require some
+ effort.</li>
+
+ <li>The LLVM build system relies heavily on UNIX shell tools, like the Bourne
+ Shell and sed. Porting to systems without these tools (MacOS 9, Plan 9) will
+ require more effort.</li>
+
+ </ul>
+
+ </div>
+
+ <!-- *********************************************************************** -->
+ <div class="doc_section">
+ <a name="build">Build Problems</a>
+ </div>
+ <!-- *********************************************************************** -->
+
+ <div class="question">
+ <p>When I run configure, it finds the wrong C compiler.</p>
+ </div>
+
+ <div class="answer">
+
+ <p>The <tt>configure</tt> script attempts to locate first <tt>gcc</tt> and then
+ <tt>cc</tt>, unless it finds compiler paths set in <tt>CC</tt> and <tt>CXX</tt>
+ for the C and C++ compiler, respectively.</p>
+
+ <p>If <tt>configure</tt> finds the wrong compiler, either adjust your
+ <tt>PATH</tt> environment variable or set <tt>CC</tt> and <tt>CXX</tt>
+ explicitly.</p>
+
+ </div>
+
+ <div class="question">
+ <p>I compile the code, and I get some error about <tt>/localhome</tt>.</p>
+ </div>
+
+ <div class="answer">
+
+ <p>There are several possible causes for this. The first is that you didn't set
+ a pathname properly when using <tt>configure</tt>, and it defaulted to a
+ pathname that we use on our research machines.</p>
+
+ <p>Another possibility is that we hardcoded a path in our Makefiles. If you see
+ this, please email the LLVM bug mailing list with the name of the offending
+ Makefile and a description of what is wrong with it.</p>
+
+ </div>
+
+ <div class="question">
+ <p>The <tt>configure</tt> script finds the right C compiler, but it uses the
+ LLVM linker from a previous build. What do I do?</p>
+ </div>
+
+ <div class="answer">
+ <p>The <tt>configure</tt> script uses the <tt>PATH</tt> to find executables, so
+ if it's grabbing the wrong linker/assembler/etc, there are two ways to fix
+ it:</p>
+
+ <ol>
+
+ <li><p>Adjust your <tt>PATH</tt> environment variable so that the correct
+ program appears first in the <tt>PATH</tt>. This may work, but may not be
+ convenient when you want them <i>first</i> in your path for other
+ work.</p></li>
+
+ <li><p>Run <tt>configure</tt> with an alternative <tt>PATH</tt> that is
+ correct. In a Borne compatible shell, the syntax would be:</p>
+
+ <p><tt>PATH=[the path without the bad program] ./configure ...</tt></p>
+
+ <p>This is still somewhat inconvenient, but it allows <tt>configure</tt>
+ to do its work without having to adjust your <tt>PATH</tt>
+ permanently.</p></li>
+
+ </ol>
+
+ </div>
+
+ <div class="question">
+ <p>When creating a dynamic library, I get a strange GLIBC error.</p>
+ </div>
+
+ <div class="answer">
+ <p>Under some operating systems (i.e. Linux), libtool does not work correctly if
+ GCC was compiled with the --disable-shared option. To work around this, install
+ your own version of GCC that has shared libraries enabled by default.</p>
+ </div>
+
+ <div class="question">
+ <p>I've updated my source tree from CVS, and now my build is trying to use a
+ file/directory that doesn't exist.</p>
+ </div>
+
+ <div class="answer">
+ <p>You need to re-run configure in your object directory. When new Makefiles
+ are added to the source tree, they have to be copied over to the object tree in
+ order to be used by the build.</p>
+ </div>
+
+ <div class="question">
+ <p>I've modified a Makefile in my source tree, but my build tree keeps using the
+ old version. What do I do?</p>
+ </div>
+
+ <div class="answer">
+
+ <p>If the Makefile already exists in your object tree, you
+ can just run the following command in the top level directory of your object
+ tree:</p>
+
+ <p><tt>./config.status <relative path to Makefile></tt><p>
+
+ <p>If the Makefile is new, you will have to modify the configure script to copy
+ it over.</p>
+
+ </div>
+
+ <div class="question">
+ <p>I've upgraded to a new version of LLVM, and I get strange build errors.</p>
+ </div>
+
+ <div class="answer">
+
+ <p>Sometimes, changes to the LLVM source code alters how the build system works.
+ Changes in libtool, autoconf, or header file dependencies are especially prone
+ to this sort of problem.</p>
+
+ <p>The best thing to try is to remove the old files and re-build. In most
+ cases, this takes care of the problem. To do this, just type <tt>make
+ clean</tt> and then <tt>make</tt> in the directory that fails to build.</p>
+
+ </div>
+
+ <div class="question">
+ <p>I've built LLVM and am testing it, but the tests freeze.</p>
+ </div>
+
+ <div class="answer">
+
+ <p>This is most likely occurring because you built a profile or release
+ (optimized) build of LLVM and have not specified the same information on the
+ <tt>gmake</tt> command line.</p>
+
+ <p>For example, if you built LLVM with the command:</p>
+
+ <p><tt>gmake ENABLE_PROFILING=1</tt>
+
+ <p>...then you must run the tests with the following commands:</p>
+
+ <p><tt>cd llvm/test<br>gmake ENABLE_PROFILING=1</tt></p>
+
+ </div>
+
+ <div class="question">
+ <p>Why do test results differ when I perform different types of builds?</p>
+ </div>
+
+ <div class="answer">
+
+ <p>The LLVM test suite is dependent upon several features of the LLVM tools and
+ libraries.</p>
+
+ <p>First, the debugging assertions in code are not enabled in optimized or
+ profiling builds. Hence, tests that used to fail may pass.</p>
+
+ <p>Second, some tests may rely upon debugging options or behavior that is only
+ available in the debug build. These tests will fail in an optimized or profile
+ build.</p>
+
+ </div>
+
+ <div class="question">
+ <p>Compiling LLVM with GCC 3.3.2 fails, what should I do?</p>
+ </div>
+
+ <div class="answer">
+ <p>This is <a href="http://gcc.gnu.org/PR?13392">a bug in GCC</a>, and
+ affects projects other than LLVM. Try upgrading or downgrading your GCC.</p>
+ </div>
+
+ <div class="question">
+ <p>
+ When I use the test suite, all of the C Backend tests fail. What is
+ wrong?
+ </p>
+ </div>
+
+ <div class="answer">
+ <p>
+ If you build LLVM and the C Backend tests fail in <tt>llvm/test/Programs</tt>,
+ then chances are good that the directory pointed to by the LLVM_LIB_SEARCH_PATH
+ environment variable does not contain the libcrtend.a library.
+ </p>
+
+ <p>
+ To fix it, verify that LLVM_LIB_SEARCH_PATH points to the correct directory
+ and that libcrtend.a is inside. For pre-built LLVM GCC front ends, this
+ should be the absolute path to
+ <tt>cfrontend/<<i>platform</i>>/llvm-gcc/bytecode-libs</tt>. If you've
+ built your own LLVM GCC front end, then ensure that you've built and installed
+ the libraries in <tt>llvm/runtime</tt> and have LLVM_LIB_SEARCH_PATH pointing
+ to the <tt>LLVMGCCDIR/bytecode-libs</tt> subdirectory.
+ </p>
+ </div>
+
+ <!-- *********************************************************************** -->
+ <div class="doc_section">
+ <a name="cfe">Using the GCC Front End</a>
+ </div>
+
+ <div class="question">
+ <p>
+ When I compile software that uses a configure script, the configure script
+ thinks my system has all of the header files and libraries it is testing for.
+ How do I get configure to work correctly?
+ </p>
+ </div>
+
+ <div class="answer">
+ <p>
+ The configure script is getting things wrong because the LLVM linker allows
+ symbols to be undefined at link time (so that they can be resolved during JIT
+ or translation to the C back end). That is why configure thinks your system
+ "has everything."
+ </p>
+ <p>
+ To work around this, perform the following steps:
+ </p>
+
+ <ol>
+ <li>
+ Make sure the CC and CXX environment variables contains the full path to the
+ LLVM GCC front end.
+ </li>
+
+ <li>
+ Make sure that the regular C compiler is first in your PATH.
+ </li>
+
+ <li>
+ Add the string "-Wl,-native" to your CFLAGS environment variable.
+ </li>
+ </ol>
+
+ <p>
+ This will allow the gccld linker to create a native code executable instead of
+ a shell script that runs the JIT. Creating native code requires standard
+ linkage, which in turn will allow the configure script to find out if code is
+ not linking on your system because the feature isn't available on your system.
+ </p>
+ </div>
+
+ <div class="question">
+ <p>
+ When I compile code using the LLVM GCC front end, it complains that it cannot
+ find libcrtend.a.
+ </p>
+ </div>
+
+ <div class="answer">
+ <p>
+ In order to find libcrtend.a, you must have the directory in which it lives in
+ your LLVM_LIB_SEARCH_PATH environment variable. For the binary distribution of
+ the LLVM GCC front end, this will be the full path of the bytecode-libs
+ directory inside of the LLVM GCC distribution.
+ </p>
+ </div>
+
+
+ <!-- *********************************************************************** -->
+ <div class="doc_section">
+ <a name="cfe_code">Questions about code generated by the GCC front-end</a>
+ </div>
+
+ <div class="question"><p>
+ What is this <tt>__main()</tt> call that gets inserted into <tt>main()</tt>?
+ </p></div>
+
+ <div class="answer">
+ <p>
+ The <tt>__main</tt> call is inserted by the C/C++ compiler in order to guarantee
+ that static constructors and destructors are called when the program starts up
+ and shuts down. In C, you can create static constructors and destructors by
+ using GCC extensions, and in C++ you can do so by creating a global variable
+ whose class has a ctor or dtor.
+ </p>
+
+ <p>
+ The actual implementation of <tt>__main</tt> lives in the
+ <tt>llvm/runtime/GCCLibraries/crtend/</tt> directory in the source-base, and is
+ linked in automatically when you link the program.
+ </p>
+ </div>
+
+ <!--=========================================================================-->
+
+ <div class="question"><p>
+ Where did all of my code go??
+ </p></div>
+
+ <div class="answer">
+ <p>
+ If you are using the LLVM demo page, you may often wonder what happened to all
+ of the code that you typed in. Remember that the demo script is running the
+ code through the LLVM optimizers, so if your code doesn't actually do anything
+ useful, it might all be deleted.
+ </p>
+
+ <p>
+ To prevent this, make sure that the code is actually needed. For example, if
+ you are computing some expression, return the value from the function instead of
+ leaving it in a local variable. If you really want to constrain the optimizer,
+ you can read from and assign to <tt>volatile</tt> global variables.
+ </p>
+ </div>
+
+ <!--=========================================================================-->
+
+ <div class="question"><p>
+ What is this <tt>llvm.global_ctors</tt> and <tt>_GLOBAL__I__tmp_webcompile...</tt> stuff that happens when I #include <iostream>?
+ </p></div>
+
+ <div class="answer">
+ <p>
+ If you #include the <iostream> header into a C++ translation unit, the
+ file will probably use the <tt>std::cin</tt>/<tt>std::cout</tt>/... global
+ objects. However, C++ does not guarantee an order of initialization between
+ static objects in different translation units, so if a static ctor/dtor in your
+ .cpp file used <tt>std::cout</tt>, for example, the object would not necessarily
+ be automatically initialized before your use.
+ </p>
+
+ <p>
+ To make <tt>std::cout</tt> and friends work correctly in these scenarios, the
+ STL that we use declares a static object that gets created in every translation
+ unit that includes <iostream>. This object has a static constructor and
+ destructor that initializes and destroys the global iostream objects before they
+ could possibly be used in the file. The code that you see in the .ll file
+ corresponds to the constructor and destructor registration code.
+ </p>
+
+ <p>
+ If you would like to make it easier to <b>understand</b> the LLVM code generated
+ by the compiler in the demo page, consider using printf instead of iostreams to
+ print values.
+ </p>
+ </div>
+
+ <!-- *********************************************************************** -->
+
+ <hr>
+ <address>
+ <a href="http://jigsaw.w3.org/css-validator/check/referer"><img
+ src="http://jigsaw.w3.org/css-validator/images/vcss" alt="Valid CSS!"></a>
+ <a href="http://validator.w3.org/check/referer"><img
+ src="http://www.w3.org/Icons/valid-html401" alt="Valid HTML 4.01!"></a>
+
+ <a href="http://llvm.cs.uiuc.edu">LLVM Compiler Infrastructure</a><br>
+ Last modified: $Date: 2004/08/13 22:03:03 $
+ </address>
+
+ </body>
+ </html>
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+ <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"
+ "http://www.w3.org/TR/html4/strict.dtd">
+ <html>
+ <head>
+ <title>Accurate Garbage Collection with LLVM</title>
+ <link rel="stylesheet" href="llvm.css" type="text/css">
+ </head>
+ <body>
+
+ <div class="doc_title">
+ Accurate Garbage Collection with LLVM
+ </div>
+
+ <ol>
+ <li><a href="#introduction">Introduction</a>
+ <ul>
+ <li><a href="#feature">GC features provided and algorithms supported</a></li>
+ </ul>
+ </li>
+
+ <li><a href="#interfaces">Interfaces for user programs</a>
+ <ul>
+ <li><a href="#roots">Identifying GC roots on the stack: <tt>llvm.gcroot</tt></a></li>
+ <li><a href="#allocate">Allocating memory from the GC</a></li>
+ <li><a href="#barriers">Reading and writing references to the heap</a></li>
+ <li><a href="#explicit">Explicit invocation of the garbage collector</a></li>
+ </ul>
+ </li>
+
+ <li><a href="#gcimpl">Implementing a garbage collector</a>
+ <ul>
+ <li><a href="#llvm_gc_readwrite">Implementing <tt>llvm_gc_read</tt> and <tt>llvm_gc_write</tt></a></li>
+ <li><a href="#callbacks">Callback functions used to implement the garbage collector</a></li>
+ </ul>
+ </li>
+ <li><a href="#gcimpls">GC implementations available</a>
+ <ul>
+ <li><a href="#semispace">SemiSpace - A simple copying garbage collector</a></li>
+ </ul>
+ </li>
+
+ <!--
+ <li><a href="#codegen">Implementing GC support in a code generator</a></li>
+ -->
+ </ol>
+
+ <div class="doc_author">
+ <p>Written by <a href="mailto:sabre at nondot.org">Chris Lattner</a></p>
+ </div>
+
+ <!-- *********************************************************************** -->
+ <div class="doc_section">
+ <a name="introduction">Introduction</a>
+ </div>
+ <!-- *********************************************************************** -->
+
+ <div class="doc_text">
+
+ <p>Garbage collection is a widely used technique that frees the programmer from
+ having to know the life-times of heap objects, making software easier to produce
+ and maintain. Many programming languages rely on garbage collection for
+ automatic memory management. There are two primary forms of garbage collection:
+ conservative and accurate.</p>
+
+ <p>Conservative garbage collection often does not require any special support
+ from either the language or the compiler: it can handle non-type-safe
+ programming languages (such as C/C++) and does not require any special
+ information from the compiler. The [LINK] Boehm collector is an example of a
+ state-of-the-art conservative collector.</p>
+
+ <p>Accurate garbage collection requires the ability to identify all pointers in
+ the program at run-time (which requires that the source-language be type-safe in
+ most cases). Identifying pointers at run-time requires compiler support to
+ locate all places that hold live pointer variables at run-time, including the
+ <a href="#roots">processor stack and registers</a>.</p>
+
+ <p>
+ Conservative garbage collection is attractive because it does not require any
+ special compiler support, but it does have problems. In particular, because the
+ conservative garbage collector cannot <i>know</i> that a particular word in the
+ machine is a pointer, it cannot move live objects in the heap (preventing the
+ use of compacting and generational GC algorithms) and it can occasionally suffer
+ from memory leaks due to integer values that happen to point to objects in the
+ program. In addition, some aggressive compiler transformations can break
+ conservative garbage collectors (though these seem rare in practice).
+ </p>
+
+ <p>
+ Accurate garbage collectors do not suffer from any of these problems, but they
+ can suffer from degraded scalar optimization of the program. In particular,
+ because the runtime must be able to identify and update all pointers active in
+ the program, some optimizations are less effective. In practice, however, the
+ locality and performance benefits of using aggressive garbage allocation
+ techniques dominates any low-level losses.
+ </p>
+
+ <p>
+ This document describes the mechanisms and interfaces provided by LLVM to
+ support accurate garbage collection.
+ </p>
+
+ </div>
+
+ <!-- ======================================================================= -->
+ <div class="doc_subsection">
+ <a name="feature">GC features provided and algorithms supported</a>
+ </div>
+
+ <div class="doc_text">
+
+ <p>
+ LLVM provides support for a broad class of garbage collection algorithms,
+ including compacting semi-space collectors, mark-sweep collectors, generational
+ collectors, and even reference counting implementations. It includes support
+ for <a href="#barriers">read and write barriers</a>, and associating <a
+ href="#roots">meta-data with stack objects</a> (used for tagless garbage
+ collection). All LLVM code generators support garbage collection, including the
+ C backend.
+ </p>
+
+ <p>
+ We hope that the primitive support built into LLVM is sufficient to support a
+ broad class of garbage collected languages, including Scheme, ML, scripting
+ languages, Java, C#, etc. That said, the implemented garbage collectors may
+ need to be extended to support language-specific features such as finalization,
+ weak references, or other features. As these needs are identified and
+ implemented, they should be added to this specification.
+ </p>
+
+ <p>
+ LLVM does not currently support garbage collection of multi-threaded programs or
+ GC-safe points other than function calls, but these will be added in the future
+ as there is interest.
+ </p>
+
+ </div>
+
+ <!-- *********************************************************************** -->
+ <div class="doc_section">
+ <a name="interfaces">Interfaces for user programs</a>
+ </div>
+ <!-- *********************************************************************** -->
+
+ <div class="doc_text">
+
+ <p>This section describes the interfaces provided by LLVM and by the garbage
+ collector run-time that should be used by user programs. As such, this is the
+ interface that front-end authors should generate code for.
+ </p>
+
+ </div>
+
+ <!-- ======================================================================= -->
+ <div class="doc_subsection">
+ <a name="roots">Identifying GC roots on the stack: <tt>llvm.gcroot</tt></a>
+ </div>
+
+ <div class="doc_text">
+
+ <div class="doc_code"><tt>
+ void %llvm.gcroot(<ty>** %ptrloc, <ty2>* %metadata)
+ </tt></div>
+
+ <p>
+ The <tt>llvm.gcroot</tt> intrinsic is used to inform LLVM of a pointer variable
+ on the stack. The first argument contains the address of the variable on the
+ stack, and the second contains a pointer to metadata that should be associated
+ with the pointer (which <b>must</b> be a constant or global value address). At
+ runtime, the <tt>llvm.gcroot</tt> intrinsic stores a null pointer into the
+ specified location to initialize the pointer.</p>
+
+ <p>
+ Consider the following fragment of Java code:
+ </p>
+
+ <pre>
+ {
+ Object X; // A null-initialized reference to an object
+ ...
+ }
+ </pre>
+
+ <p>
+ This block (which may be located in the middle of a function or in a loop nest),
+ could be compiled to this LLVM code:
+ </p>
+
+ <pre>
+ Entry:
+ ;; In the entry block for the function, allocate the
+ ;; stack space for X, which is an LLVM pointer.
+ %X = alloca %Object*
+ ...
+
+ ;; "CodeBlock" is the block corresponding to the start
+ ;; of the scope above.
+ CodeBlock:
+ ;; Initialize the object, telling LLVM that it is now live.
+ ;; Java has type-tags on objects, so it doesn't need any
+ ;; metadata.
+ call void %llvm.gcroot(%Object** %X, sbyte* null)
+ ...
+
+ ;; As the pointer goes out of scope, store a null value into
+ ;; it, to indicate that the value is no longer live.
+ store %Object* null, %Object** %X
+ ...
+ </pre>
+
+ </div>
+
+ <!-- ======================================================================= -->
+ <div class="doc_subsection">
+ <a name="allocate">Allocating memory from the GC</a>
+ </div>
+
+ <div class="doc_text">
+
+ <div class="doc_code"><tt>
+ sbyte *%llvm_gc_allocate(unsigned %Size)
+ </tt></div>
+
+ <p>The <tt>llvm_gc_allocate</tt> function is a global function defined by the
+ garbage collector implementation to allocate memory. It returns a
+ zeroed-out block of memory of the appropriate size.</p>
+
+ </div>
+
+ <!-- ======================================================================= -->
+ <div class="doc_subsection">
+ <a name="barriers">Reading and writing references to the heap</a>
+ </div>
+
+ <div class="doc_text">
+
+ <div class="doc_code"><tt>
+ sbyte *%llvm.gcread(sbyte *, sbyte **)<br>
+ void %llvm.gcwrite(sbyte*, sbyte*, sbyte**)
+ </tt></div>
+
+ <p>Several of the more interesting garbage collectors (e.g., generational
+ collectors) need to be informed when the mutator (the program that needs garbage
+ collection) reads or writes object references into the heap. In the case of a
+ generational collector, it needs to keep track of which "old" generation objects
+ have references stored into them. The amount of code that typically needs to be
+ executed is usually quite small (and not on the critical path of any
+ computation), so the overall performance impact of the inserted code is
+ tolerable.</p>
+
+ <p>To support garbage collectors that use read or write barriers, LLVM provides
+ the <tt>llvm.gcread</tt> and <tt>llvm.gcwrite</tt> intrinsics. The first
+ intrinsic has exactly the same semantics as a non-volatile LLVM load and the
+ second has the same semantics as a non-volatile LLVM store, with the
+ additions that they also take a pointer to the start of the memory
+ object as an argument. At code generation
+ time, these intrinsics are replaced with calls into the garbage collector
+ (<tt><a href="#llvm_gc_readwrite">llvm_gc_read</a></tt> and <tt><a
+ href="#llvm_gc_readwrite">llvm_gc_write</a></tt> respectively), which are then
+ inlined into the code.
+ </p>
+
+ <p>
+ If you are writing a front-end for a garbage collected language, every load or
+ store of a reference from or to the heap should use these intrinsics instead of
+ normal LLVM loads/stores.</p>
+
+ </div>
+
+ <!-- ======================================================================= -->
+ <div class="doc_subsection">
+ <a name="initialize">Garbage collector startup and initialization</a>
+ </div>
+
+ <div class="doc_text">
+
+ <div class="doc_code"><tt>
+ void %llvm_gc_initialize(unsigned %InitialHeapSize)
+ </tt></div>
+
+ <p>
+ The <tt>llvm_gc_initialize</tt> function should be called once before any other
+ garbage collection functions are called. This gives the garbage collector the
+ chance to initialize itself and allocate the heap spaces. The initial heap size
+ to allocate should be specified as an argument.
+ </p>
+
+ </div>
+
+ <!-- ======================================================================= -->
+ <div class="doc_subsection">
+ <a name="explicit">Explicit invocation of the garbage collector</a>
+ </div>
+
+ <div class="doc_text">
+
+ <div class="doc_code"><tt>
+ void %llvm_gc_collect()
+ </tt></div>
+
+ <p>
+ The <tt>llvm_gc_collect</tt> function is exported by the garbage collector
+ implementations to provide a full collection, even when the heap is not
+ exhausted. This can be used by end-user code as a hint, and may be ignored by
+ the garbage collector.
+ </p>
+
+ </div>
+
+
+ <!-- *********************************************************************** -->
+ <div class="doc_section">
+ <a name="gcimpl">Implementing a garbage collector</a>
+ </div>
+ <!-- *********************************************************************** -->
+
+ <div class="doc_text">
+
+ <p>
+ Implementing a garbage collector for LLVM is fairly straight-forward. The LLVM
+ garbage collectors are provided in a form that makes them easy to link into the
+ language-specific runtime that a language front-end would use. They require
+ functionality from the language-specific runtime to get information about <a
+ href="#gcdescriptors">where pointers are located in heap objects</a>.
+ </p>
+
+ <p>The
+ implementation must include the <a
+ href="#allocate"><tt>llvm_gc_allocate</tt></a> and <a
+ href="#explicit"><tt>llvm_gc_collect</tt></a> functions, and it must implement
+ the <a href="#llvm_gc_readwrite">read/write barrier</a> functions as well. To
+ do this, it will probably have to <a href="#traceroots">trace through the roots
+ from the stack</a> and understand the <a href="#gcdescriptors">GC descriptors
+ for heap objects</a>. Luckily, there are some <a href="#gcimpls">example
+ implementations</a> available.
+ </p>
+ </div>
+
+
+ <!-- ======================================================================= -->
+ <div class="doc_subsection">
+ <a name="llvm_gc_readwrite">Implementing <tt>llvm_gc_read</tt> and <tt>llvm_gc_write</tt></a>
+ </div>
+
+ <div class="doc_text">
+ <div class="doc_code"><tt>
+ void *llvm_gc_read(void*, void **)<br>
+ void llvm_gc_write(void*, void *, void**)
+ </tt></div>
+
+ <p>
+ These functions <i>must</i> be implemented in every garbage collector, even if
+ they do not need read/write barriers. In this case, just load or store the
+ pointer, then return.
+ </p>
+
+ <p>
+ If an actual read or write barrier is needed, it should be straight-forward to
+ implement it.
+ </p>
+
+ </div>
+
+ <!-- ======================================================================= -->
+ <div class="doc_subsection">
+ <a name="callbacks">Callback functions used to implement the garbage collector</a>
+ </div>
+
+ <div class="doc_text">
+ <p>
+ Garbage collector implementations make use of call-back functions that are
+ implemented by other parts of the LLVM system.
+ </p>
+ </div>
+
+ <!--_________________________________________________________________________-->
+ <div class="doc_subsubsection">
+ <a name="traceroots">Tracing GC pointers from the program stack</a>
+ </div>
+
+ <div class="doc_text">
+ <div class="doc_code"><tt>
+ void llvm_cg_walk_gcroots(void (*FP)(void **Root, void *Meta));
+ </tt></div>
+
+ <p>
+ The <tt>llvm_cg_walk_gcroots</tt> function is a function provided by the code
+ generator that iterates through all of the GC roots on the stack, calling the
+ specified function pointer with each record. For each GC root, the address of
+ the pointer and the meta-data (from the <a
+ href="#gcroot"><tt>llvm.gcroot</tt></a> intrinsic) are provided.
+ </p>
+ </div>
+
+ <!--_________________________________________________________________________-->
+ <div class="doc_subsubsection">
+ <a name="staticroots">Tracing GC pointers from static roots</a>
+ </div>
+
+ <div class="doc_text">
+ TODO
+ </div>
+
+
+ <!--_________________________________________________________________________-->
+ <div class="doc_subsubsection">
+ <a name="gcdescriptors">Tracing GC pointers from heap objects</a>
+ </div>
+
+ <div class="doc_text">
+ <p>
+ The three most common ways to keep track of where pointers live in heap objects
+ are (listed in order of space overhead required):</p>
+
+ <ol>
+ <li>In languages with polymorphic objects, pointers from an object header are
+ usually used to identify the GC pointers in the heap object. This is common for
+ object-oriented languages like Self, Smalltalk, Java, or C#.</li>
+
+ <li>If heap objects are not polymorphic, often the "shape" of the heap can be
+ determined from the roots of the heap or from some other meta-data [<a
+ href="#appel89">Appel89</a>, <a href="#goldberg91">Goldberg91</a>, <a
+ href="#tolmach94">Tolmach94</a>]. In this case, the garbage collector can
+ propagate the information around from meta data stored with the roots. This
+ often eliminates the need to have a header on objects in the heap. This is
+ common in the ML family.</li>
+
+ <li>If all heap objects have pointers in the same locations, or pointers can be
+ distinguished just by looking at them (e.g., the low order bit is clear), no
+ book-keeping is needed at all. This is common for Lisp-like languages.</li>
+ </ol>
+
+ <p>The LLVM garbage collectors are capable of supporting all of these styles of
+ language, including ones that mix various implementations. To do this, it
+ allows the source-language to associate meta-data with the <a
+ href="#roots">stack roots</a>, and the heap tracing routines can propagate the
+ information. In addition, LLVM allows the front-end to extract GC information
+ from in any form from a specific object pointer (this supports situations #1 and
+ #3).
+ </p>
+
+ <p><b>Making this efficient</b></p>
+
+
+
+ </div>
+
+
+
+ <!-- *********************************************************************** -->
+ <div class="doc_section">
+ <a name="gcimpls">GC implementations available</a>
+ </div>
+ <!-- *********************************************************************** -->
+
+ <div class="doc_text">
+
+ <p>
+ To make this more concrete, the currently implemented LLVM garbage collectors
+ all live in the <tt>llvm/runtime/GC/*</tt> directories in the LLVM source-base.
+ If you are interested in implementing an algorithm, there are many interesting
+ possibilities (mark/sweep, a generational collector, a reference counting
+ collector, etc), or you could choose to improve one of the existing algorithms.
+ </p>
+
+ </div>
+
+ <!-- ======================================================================= -->
+ <div class="doc_subsection">
+ <a name="semispace">SemiSpace - A simple copying garbage collector</a>
+ </div>
+
+ <div class="doc_text">
+ <p>
+ SemiSpace is a very simple copying collector. When it starts up, it allocates
+ two blocks of memory for the heap. It uses a simple bump-pointer allocator to
+ allocate memory from the first block until it runs out of space. When it runs
+ out of space, it traces through all of the roots of the program, copying blocks
+ to the other half of the memory space.
+ </p>
+
+ </div>
+
+ <!--_________________________________________________________________________-->
+ <div class="doc_subsubsection">
+ Possible Improvements
+ </div>
+
+ <div class="doc_text">
+
+ <p>
+ If a collection cycle happens and the heap is not compacted very much (say less
+ than 25% of the allocated memory was freed), the memory regions should be
+ doubled in size.</p>
+
+ </div>
+
+ <!-- *********************************************************************** -->
+ <div class="doc_section">
+ <a name="references">References</a>
+ </div>
+ <!-- *********************************************************************** -->
+
+ <div class="doc_text">
+
+ <p><a name="appel89">[Appel89]</a> Runtime Tags Aren't Necessary. Andrew
+ W. Appel. Lisp and Symbolic Computation 19(7):703-705, July 1989.</p>
+
+ <p><a name="goldberg91">[Goldberg91]</a> Tag-free garbage collection for
+ strongly typed programming languages. Benjamin Goldberg. ACM SIGPLAN
+ PLDI'91.</p>
+
+ <p><a name="tolmach94">[Tolmach94]</a> Tag-free garbage collection using
+ explicit type parameters. Andrew Tolmach. Proceedings of the 1994 ACM
+ conference on LISP and functional programming.</p>
+
+ </div>
+
+ <!-- *********************************************************************** -->
+
+ <hr>
+ <address>
+ <a href="http://jigsaw.w3.org/css-validator/check/referer"><img
+ src="http://jigsaw.w3.org/css-validator/images/vcss" alt="Valid CSS!"></a>
+ <a href="http://validator.w3.org/check/referer"><img
+ src="http://www.w3.org/Icons/valid-html401" alt="Valid HTML 4.01!"></a>
+
+ <a href="mailto:sabre at nondot.org">Chris Lattner</a><br>
+ <a href="http://llvm.cs.uiuc.edu">LLVM Compiler Infrastructure</a><br>
+ Last modified: $Date: 2004/08/13 22:03:03 $
+ </address>
+
+ </body>
+ </html>
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+ <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"
+ "http://www.w3.org/TR/html4/strict.dtd">
+ <html>
+ <head>
+ <title>Getting Started with LLVM System</title>
+ <link rel="stylesheet" href="llvm.css" type="text/css">
+ </head>
+ <body>
+
+ <div class="doc_title">
+ Getting Started with the LLVM System
+ </div>
+
+ <ul>
+ <li><a href="#overview">Overview</a>
+ <li><a href="#quickstart">Getting Started Quickly (A Summary)</a>
+ <li><a href="#requirements">Requirements</a>
+ <ol>
+ <li><a href="#hardware">Hardware</a>
+ <li><a href="#software">Software</a>
+ <li><a href="#brokengcc">Broken versions of GCC</a>
+ </ol></li>
+
+ <li><a href="#starting">Getting Started with LLVM</a>
+ <ol>
+ <li><a href="#terminology">Terminology and Notation</a>
+ <li><a href="#environment">Setting Up Your Environment</a>
+ <li><a href="#unpack">Unpacking the LLVM Archives</a>
+ <li><a href="#checkout">Checkout LLVM from CVS</a>
+ <li><a href="#installcf">Install the GCC Front End</a>
+ <li><a href="#config">Local LLVM Configuration</a>
+ <li><a href="#compile">Compiling the LLVM Suite Source Code</a>
+ <li><a href="#objfiles">The Location of LLVM Object Files</a>
+ <li><a href="#optionalconfig">Optional Configuration Items</a>
+ </ol></li>
+
+ <li><a href="#layout">Program layout</a>
+ <ol>
+ <li><a href="#cvsdir"><tt>CVS</tt> directories</a>
+ <li><a href="#include"><tt>llvm/include</tt></a>
+ <li><a href="#lib"><tt>llvm/lib</tt></a>
+ <li><a href="#runtime"><tt>llvm/runtime</tt></a>
+ <li><a href="#test"><tt>llvm/test</tt></a>
+ <li><a href="#tools"><tt>llvm/tools</tt></a>
+ <li><a href="#utils"><tt>llvm/utils</tt></a>
+ </ol></li>
+
+ <li><a href="#tutorial">An Example Using the LLVM Tool Chain</a>
+ <li><a href="#problems">Common Problems</a>
+ <li><a href="#links">Links</a>
+ </ul>
+
+ <div class="doc_author">
+ <p>Written by:
+ <a href="mailto:criswell at uiuc.edu">John Criswell</a>,
+ <a href="mailto:sabre at nondot.org">Chris Lattner</a>,
+ <a href="http://misha.brukman.net">Misha Brukman</a>,
+ <a href="http://www.cs.uiuc.edu/~vadve">Vikram Adve</a>, and
+ <a href="mailto:gshi1 at uiuc.edu">Guochun Shi</a>.
+ </p>
+ </div>
+
+
+ <!-- *********************************************************************** -->
+ <div class="doc_section">
+ <a name="overview"><b>Overview</b></a>
+ </div>
+ <!-- *********************************************************************** -->
+
+ <div class="doc_text">
+
+ <p>Welcome to LLVM! In order to get started, you first need to know some
+ basic information.</p>
+
+ <p>First, LLVM comes in two pieces. The first piece is the LLVM suite. This
+ contains all of the tools, libraries, and header files needed to use the low
+ level virtual machine. It contains an assembler, disassembler, bytecode
+ analyzer, and bytecode optimizer. It also contains a test suite that can be
+ used to test the LLVM tools and the GCC front end.</p>
+
+ <p>The second piece is the GCC front end. This component provides a version of
+ GCC that compiles C and C++ code into LLVM bytecode. Currently, the GCC front
+ end is a modified version of GCC 3.4 (we track the GCC 3.4 development). Once
+ compiled into LLVM bytecode, a program can be manipulated with the LLVM tools
+ from the LLVM suite.</p>
+
+ </div>
+
+ <!-- *********************************************************************** -->
+ <div class="doc_section">
+ <a name="quickstart"><b>Getting Started Quickly (A Summary)</b></a>
+ </div>
+ <!-- *********************************************************************** -->
+
+ <div class="doc_text">
+
+ <p>Here's the short story for getting up and running quickly with LLVM:</p>
+
+ <ol>
+ <li>Install the GCC front end:
+ <ol>
+ <li><tt>cd <i>where-you-want-the-C-front-end-to-live</i></tt>
+ <li><tt>gunzip --stdout cfrontend.<i>platform</i>.tar.gz | tar -xvf -</tt>
+ <li><b>Sparc and MacOS X Only:</b><br>
+ <tt>cd cfrontend/<i>platform</i><br>
+ ./fixheaders</tt>
+ </ol></li>
+
+ <li>Get the Source Code
+ <ul>
+ <li>With the distributed files:
+ <ol>
+ <li><tt>cd <i>where-you-want-llvm-to-live</i></tt>
+ <li><tt>gunzip --stdout llvm-<i>version</i>.tar.gz | tar -xvf -</tt>
+ <li><tt>cd llvm</tt>
+ </ol></li>
+
+ <li>With anonymous CVS access (or use a <a href="#mirror">mirror</a>):
+ <ol>
+ <li><tt>cd <i>where-you-want-llvm-to-live</i></tt></li>
+ <li><tt>cvs -d
+ :pserver:anon at llvm-cvs.cs.uiuc.edu:/var/cvs/llvm login</tt></li>
+ <li>Hit the return key when prompted for the password.
+ <li><tt>cvs -z3 -d :pserver:anon at llvm-cvs.cs.uiuc.edu:/var/cvs/llvm
+ co llvm</tt></li>
+ <li><tt>cd llvm</tt></li>
+ </ol></li>
+ </ul></li>
+
+ <li>Configure the LLVM Build Environment
+ <ol>
+ <li>Change directory to where you want to store the LLVM object
+ files and run <tt>configure</tt> to configure the Makefiles and
+ header files for the default platform. Useful options include:
+ <ul>
+ <li><tt>--with-llvmgccdir=<i>directory</i></tt>
+ <p>Specify the full pathname of where the LLVM GCC frontend is
+ installed.</p></li>
+ <li><tt>--enable-spec2000=<i>directory</i></tt>
+ <p>Enable the SPEC2000 benchmarks for testing. The SPEC2000
+ benchmarks should be available in
+ <tt><i>directory</i></tt>.</p></li>
+ </ul>
+ </ol></li>
+
+ <li>Build the LLVM Suite:
+ <ol>
+ <li>Set your LLVM_LIB_SEARCH_PATH environment variable.</li>
+ <li><tt>gmake -k |& tee gnumake.out
+ # this is csh or tcsh syntax</tt></li>
+ <li>If you get an "internal compiler error (ICE)" see <a href="#brokengcc">below</a>.</li>
+ </ol>
+
+ </ol>
+
+ <p>Consult the <a href="#starting">Getting Started with LLVM</a> section for
+ detailed information on configuring and compiling LLVM. See <a
+ href="#environment">Setting Up Your Environment</a> for tips that simplify
+ working with the GCC front end and LLVM tools. Go to <a href="#layout">Program
+ Layout</a> to learn about the layout of the source code tree.</p>
+
+ </div>
+
+ <!-- *********************************************************************** -->
+ <div class="doc_section">
+ <a name="requirements"><b>Requirements</b></a>
+ </div>
+ <!-- *********************************************************************** -->
+
+ <div class="doc_text">
+
+ <p>Before you begin to use the LLVM system, review the requirements given below.
+ This may save you some trouble by knowing ahead of time what hardware and
+ software you will need.</p>
+
+ </div>
+
+ <!-- ======================================================================= -->
+ <div class="doc_subsection">
+ <a name="hardware"><b>Hardware</b></a>
+ </div>
+
+ <div class="doc_text">
+
+ <p>LLVM is known to work on the following platforms:</p>
+
+ <ul>
+
+ <li>Linux on x86 (Pentium and above)
+ <ul>
+ <li>Approximately 2.6 GB of Free Disk Space
+ <ul>
+ <li>Source code: 57 MB</li>
+ <li>Object code: 2.5 GB</li>
+ <li>GCC front end: 30 MB</li>
+ </ul></li>
+ </ul>
+ </li>
+
+ <li>Solaris on SparcV9 (Ultrasparc)
+ <ul>
+ <li>Approximately 2.6 GB of Free Disk Space
+ <ul>
+ <li>Source code: 57 MB</li>
+ <li>Object code: 2.5 GB</li>
+ <li>GCC front end: 46 MB</li>
+ </ul></li>
+ </ul>
+ </li>
+
+ <li>FreeBSD on x86 (Pentium and above)
+ <ul>
+ <li>Approximately 1 GB of Free Disk Space
+ <ul>
+ <li>Source code: 57 MB</li>
+ <li>Object code: 850 MB</li>
+ <li>GCC front end: 40 MB</li>
+ </ul></li>
+ </ul>
+ </li>
+
+ <li>MacOS X on PowerPC
+ <ul>
+ <li>Experimental support for static native code generation
+ <li>Approximately 1.6 GB of Free Disk Space
+ <ul>
+ <li>Source code: 57 MB</li>
+ <li>Object code: 1.5 GB</li>
+ <li>GCC front end: 36 MB</li>
+ </ul></li>
+ </ul>
+
+ </li>
+ </ul>
+
+ <p>The LLVM suite <i>may</i> compile on other platforms, but it is not
+ guaranteed to do so. If compilation is successful, the LLVM utilities should be
+ able to assemble, disassemble, analyze, and optimize LLVM bytecode. Code
+ generation should work as well, although the generated native code may not work
+ on your platform.</p>
+
+ <p>The GCC front end is not very portable at the moment. If you want to get it
+ to work on another platform, you can download a copy of the source and <a href="CFEBuildInstrs.html">try to compile it</a> on your platform.</p>
+
+ </div>
+
+ <!-- ======================================================================= -->
+ <div class="doc_subsection">
+ <a name="software"><b>Software</b></a>
+ </div>
+
+ <div class="doc_text">
+
+ <p>Compiling LLVM requires that you have several software packages
+ installed:</p>
+
+ <ul>
+ <li><a href="http://gcc.gnu.org">GCC 3.x with C and C++ language
+ support</a> (See <a href="#brokengcc">below</a> for specific version info)</li>
+
+ <li><a href="http://savannah.gnu.org/projects/make">GNU Make</a></li>
+
+ <li><a href="http://www.gnu.org/software/flex">Flex</a></li>
+
+ <li><a href="http://www.gnu.org/software/bison/bison.html">Bison</a></li>
+ </ul>
+
+ <p>There are some additional tools that you may want to have when working with
+ LLVM:</p>
+
+ <ul>
+ <li><A href="http://www.gnu.org/software/automake">GNU Automake</A></li>
+ <li><A href="http://www.gnu.org/software/autoconf">GNU Autoconf</A></li>
+ <li><A href="http://savannah.gnu.org/projects/m4">GNU M4</A>
+
+ <p>If you want to make changes to the configure scripts, you will need GNU
+ autoconf (2.57 or higher), and consequently, GNU M4 (version 1.4 or
+ higher). You will also need automake. Any old version of
+ automake from 1.4p5 on should work; we only use aclocal from that
+ package.</p></li>
+
+ <li><A href="http://www.codesourcery.com/qm/qmtest">QMTest 2.0.3</A></li>
+ <li><A href="http://www.python.org">Python</A>
+
+ <p>
+ These are needed to use the LLVM test suite. Please note that newer
+ versions of QMTest may not work with the LLVM test suite. QMTest 2.0.3
+ can be retrieved from the QMTest CVS repository using the following
+ commands:</p>
+ <ul>
+ <li><tt>cvs -d :pserver:anoncvs at cvs.codesourcery.com:/home/qm/Repository login</tt>
+ </li>
+ <li>When prompted, use <tt>anoncvs</tt> as the password.
+ </li>
+ <li><tt>cvs -d :pserver:anoncvs at cvs.codesourcery.com:/home/qm/Repository co -r release-2-0-3 qm</tt>
+ </li>
+ </ul>
+ </li>
+
+ </ul>
+ </div>
+
+ <!-- ======================================================================= -->
+ <div class="doc_subsection">
+ <a name="brokengcc">Broken versions of GCC</a>
+ </div>
+
+ <div class="doc_text">
+
+ <p>LLVM is very demanding of the host C++ compiler, and as such tends to expose
+ bugs in the compiler. In particular, several versions of GCC crash when trying
+ to compile LLVM. We routinely use GCC 3.3.3 and GCC 3.4.0 and have had success
+ with them. Other versions of GCC will probably work as well. GCC versions listed
+ here are known to not work. If you are using one of these versions, please try
+ to upgrade your GCC to something more recent. If you run into a problem with a
+ version of GCC not listed here, please <a href="mailto:llvmdev at cs.uiuc.edu">let
+ us know</a>. Please use the "<tt>gcc -v</tt>" command to find out which version
+ of GCC you are using.
+ </p>
+
+ <p><b>GCC versions prior to 3.0</b>: GCC 2.96.x and before had several
+ problems in the STL that effectively prevent it from compiling LLVM.
+ </p>
+
+ <p><b>GCC 3.3.2</b>: This version of GCC suffered from a <a
+ href="http://gcc.gnu.org/PR13392">serious bug</a> which causes it to crash in
+ the "<tt>convert_from_eh_region_ranges_1</tt>" GCC function.</p>
+
+ </div>
+
+
+
+ <!-- *********************************************************************** -->
+ <div class="doc_section">
+ <a name="starting"><b>Getting Started with LLVM</b></a>
+ </div>
+ <!-- *********************************************************************** -->
+
+ <div class="doc_text">
+
+ <p>The remainder of this guide is meant to get you up and running with
+ LLVM and to give you some basic information about the LLVM environment.</p>
+
+ <p>The later sections of this guide describe the <a
+ href="#layout">general layout</a> of the the LLVM source tree, a <a
+ href="#tutorial">simple example</a> using the LLVM tool chain, and <a
+ href="#links">links</a> to find more information about LLVM or to get
+ help via e-mail.</p>
+ </div>
+
+ <!-- ======================================================================= -->
+ <div class="doc_subsection">
+ <a name="terminology">Terminology and Notation</a>
+ </div>
+
+ <div class="doc_text">
+
+ <p>Throughout this manual, the following names are used to denote paths
+ specific to the local system and working environment. <i>These are not
+ environment variables you need to set but just strings used in the rest
+ of this document below</i>. In any of the examples below, simply replace
+ each of these names with the appropriate pathname on your local system.
+ All these paths are absolute:</p>
+
+ <dl>
+ <dt>SRC_ROOT
+ <dd>
+ This is the top level directory of the LLVM source tree.
+ <p>
+
+ <dt>OBJ_ROOT
+ <dd>
+ This is the top level directory of the LLVM object tree (i.e. the
+ tree where object files and compiled programs will be placed. It
+ can be the same as SRC_ROOT).
+ <p>
+
+ <dt>LLVMGCCDIR
+ <dd>
+ This is the where the LLVM GCC Front End is installed.
+ <p>
+ For the pre-built GCC front end binaries, the LLVMGCCDIR is
+ <tt>cfrontend/<i>platform</i>/llvm-gcc</tt>.
+ </dl>
+
+ </div>
+
+ <!-- ======================================================================= -->
+ <div class="doc_subsection">
+ <a name="environment">Setting Up Your Environment</a>
+ </div>
+
+ <div class="doc_text">
+
+ <p>
+ In order to compile and use LLVM, you will need to set some environment
+ variables. There are also some shell aliases which you may find useful.
+ You can set these on the command line, or better yet, set them in your
+ <tt>.cshrc</tt> or <tt>.profile</tt>.
+
+ <dl>
+ <dt><tt>LLVM_LIB_SEARCH_PATH</tt>=<tt><i>LLVMGCCDIR</i>/bytecode-libs</tt>
+ <dd>
+ This environment variable helps the LLVM GCC front end find bytecode
+ libraries that it will need for compilation.
+ <p>
+
+ <dt>alias llvmgcc <i>LLVMGCCDIR</i><tt>/bin/gcc</tt>
+ <dt>alias llvmg++ <i>LLVMGCCDIR</i><tt>/bin/g++</tt>
+ <dd>
+ This alias allows you to use the LLVM C and C++ front ends without putting
+ them in your <tt>PATH</tt> or typing in their complete pathnames.
+ </dl>
+
+ </div>
+
+ <!-- ======================================================================= -->
+ <div class="doc_subsection">
+ <a name="unpack">Unpacking the LLVM Archives</a>
+ </div>
+
+ <div class="doc_text">
+
+ <p>
+ If you have the LLVM distribution, you will need to unpack it before you
+ can begin to compile it. LLVM is distributed as a set of two files: the LLVM
+ suite and the LLVM GCC front end compiled for your platform. Each
+ file is a TAR archive that is compressed with the gzip program.
+ </p>
+
+ <p> The files are as follows:
+ <dl>
+ <dt>llvm-1.3.tar.gz
+ <dd>This is the source code to the LLVM suite.
+ <p>
+
+ <dt>cfrontend-1.3.sparc-sun-solaris2.8.tar.gz
+ <dd>This is the binary release of the GCC front end for Solaris/Sparc.
+ <p>
+
+ <dt>cfrontend-1.3.i686-redhat-linux-gnu.tar.gz
+ <dd>This is the binary release of the GCC front end for Linux/x86.
+ <p>
+
+ <dt>cfrontend-1.3.i386-unknown-freebsd5.1.tar.gz
+ <dd>This is the binary release of the GCC front end for FreeBSD/x86.
+ <p>
+
+ <dt>cfrontend-1.3.powerpc-apple-darwin7.0.0.tar.gz
+ <dd>This is the binary release of the GCC front end for MacOS X/PPC.
+ </dl>
+
+ </div>
+
+ <!-- ======================================================================= -->
+ <div class="doc_subsection">
+ <a name="checkout">Checkout LLVM from CVS</a>
+ </div>
+
+ <div class="doc_text">
+
+ <p>If you have access to our CVS repository, you can get a fresh copy of
+ the entire source code. All you need to do is check it out from CVS as
+ follows:</p>
+
+ <ul>
+ <li><tt>cd <i>where-you-want-llvm-to-live</i></tt>
+ <li><tt>cvs -d :pserver:anon at llvm-cvs.cs.uiuc.edu:/var/cvs/llvm login</tt>
+ <li>Hit the return key when prompted for the password.
+ <li><tt>cvs -z3 -d :pserver:anon at llvm-cvs.cs.uiuc.edu:/var/cvs/llvm co
+ llvm</tt>
+ </ul>
+
+ <p>This will create an '<tt>llvm</tt>' directory in the current
+ directory and fully populate it with the LLVM source code, Makefiles,
+ test directories, and local copies of documentation files.</p>
+
+ <p>If you want to get a specific release (as opposed to the most recent
+ revision), you can specify a label. The following releases have the following
+ label:</p>
+
+ <ul>
+ <li>Release 1.3: <b>RELEASE_13</b></li>
+ <li>Release 1.2: <b>RELEASE_12</b></li>
+ <li>Release 1.1: <b>RELEASE_11</b></li>
+ <li>Release 1.0: <b>RELEASE_1</b></li>
+ </ul>
+
+ <p>If you would like to get the GCC front end source code, you can also get it
+ from the CVS repository:</p>
+
+ <pre>
+ cvs -z3 -d :pserver:anon at llvm-cvs.cs.uiuc.edu:/var/cvs/llvm co llvm-gcc
+ </pre>
+
+ <p>Please note that you must follow <a href="CFEBuildInstrs.html">these
+ instructions</a> to successfully build the LLVM C front-end.</p>
+
+ </div>
+
+ <!-- ======================================================================= -->
+ <div class="doc_subsubsection">
+ <a name="mirrors">LLVM CVS Mirrors</a>
+ </div>
+
+ <div class="doc_text">
+
+ <p>If the main CVS server is overloaded or inaccessible, you can try one of
+ these user-hosted mirrors:</p>
+
+ <ul>
+ <li><a href="http://llvm.x10sys.com/">Mirror hosted by eXtensible Systems
+ Inc.</a></li>
+ </ul>
+ </div>
+
+ <!-- ======================================================================= -->
+ <div class="doc_subsection">
+ <a name="installcf">Install the GCC Front End</a>
+ </div>
+
+ <div class="doc_text">
+
+ <p>Before configuring and compiling the LLVM suite, you need to extract the LLVM
+ GCC front end from the binary distribution. It is used for building the
+ bytecode libraries later used by the GCC front end for linking programs, and its
+ location must be specified when the LLVM suite is configured.</p>
+
+ <p>To install the GCC front end, do the following:</p>
+
+ <ol>
+ <li><tt>cd <i>where-you-want-the-front-end-to-live</i></tt></li>
+ <li><tt>gunzip --stdout cfrontend-<i>version</i>.<i>platform</i>.tar.gz | tar -xvf
+ -</tt></li>
+ </ol>
+
+ <p>If you are using Solaris/Sparc or MacOS X/PPC, you will need to fix the
+ header files:</p>
+
+ <p><tt>cd cfrontend/<i>platform</i><br>
+ ./fixheaders</tt></p>
+
+ <p>The binary versions of the GCC front end may not suit all of your needs. For
+ example, the binary distribution may include an old version of a system header
+ file, not "fix" a header file that needs to be fixed for GCC, or it may be
+ linked with libraries not available on your system.</p>
+
+ <p>In cases like these, you may want to try <a
+ href="CFEBuildInstrs.html">building the GCC front end from source.</a> This is
+ not for the faint of heart, so be forewarned.</p>
+
+ </div>
+
+ <!-- ======================================================================= -->
+ <div class="doc_subsection">
+ <a name="config">Local LLVM Configuration</a>
+ </div>
+
+ <div class="doc_text">
+
+ <p>Once checked out from the CVS repository, the LLVM suite source code must be
+ configured via the <tt>configure</tt> script. This script sets variables in
+ <tt>llvm/Makefile.config</tt> and <tt>llvm/include/Config/config.h</tt>. It
+ also populates <i>OBJ_ROOT</i> with the Makefiles needed to begin building
+ LLVM.</p>
+
+ <p>The following environment variables are used by the <tt>configure</tt>
+ script to configure the build system:</p>
+
+ <table border=1>
+ <tr>
+ <th>Variable</th>
+ <th>Purpose</th>
+ </tr>
+
+ <tr>
+ <td>CC</td>
+ <td>Tells <tt>configure</tt> which C compiler to use. By default,
+ <tt>configure</tt> will look for the first GCC C compiler in
+ <tt>PATH</tt>. Use this variable to override
+ <tt>configure</tt>'s default behavior.</td>
+ </tr>
+
+ <tr>
+ <td>CXX</td>
+ <td>Tells <tt>configure</tt> which C++ compiler to use. By default,
+ <tt>configure</tt> will look for the first GCC C++ compiler in
+ <tt>PATH</tt>. Use this variable to override
+ <tt>configure</tt>'s default behavior.</td>
+ </tr>
+ </table>
+
+ <p>The following options can be used to set or enable LLVM specific options:</p>
+
+ <dl>
+ <dt><i>--with-llvmgccdir=LLVMGCCDIR</i>
+ <dd>
+ Path to the location where the LLVM GCC front end binaries and
+ associated libraries were installed. This must be specified as an
+ absolute pathname.
+ <p>
+ <dt><i>--enable-optimized</i>
+ <dd>
+ Enables optimized compilation by default (debugging symbols are removed
+ and GCC optimization flags are enabled). The default is to use an
+ unoptimized build (also known as a debug build).
+ <p>
+ <dt><i>--enable-jit</i>
+ <dd>
+ Compile the Just In Time (JIT) compiler functionality. This is not
+ available
+ on all platforms. The default is dependent on platform, so it is best
+ to explicitly enable it if you want it.
+ <p>
+ <dt><i>--enable-spec2000</i>
+ <dt><i>--enable-spec2000=<<tt>directory</tt>></i>
+ <dd>
+ Enable the use of SPEC2000 when testing LLVM. This is disabled by default
+ (unless <tt>configure</tt> finds SPEC2000 installed). By specifying
+ <tt>directory</tt>, you can tell configure where to find the SPEC2000
+ benchmarks. If <tt>directory</tt> is left unspecified, <tt>configure</tt>
+ uses the default value
+ <tt>/home/vadve/shared/benchmarks/speccpu2000/benchspec</tt>.
+ <p>
+ <dt><i>--enable-spec95</i>
+ <dt><i>--enable-spec95=<<tt>directory</tt>></i>
+ <dd>
+ Enable the use of SPEC95 when testing LLVM. It is similar to the
+ <i>--enable-spec2000</i> option.
+ <p>
+ <dt><i>--enable-povray</i>
+ <dt><i>--enable-povray=<<tt>directory</tt>></i>
+ <dd>
+ Enable the use of Povray as an external test. Versions of Povray written
+ in C should work. This option is similar to the <i>--enable-spec2000</i>
+ option.
+ </dl>
+
+ <p>To configure LLVM, follow these steps:</p>
+
+ <ol>
+ <li>Change directory into the object root directory:
+ <br>
+ <tt>cd <i>OBJ_ROOT</i></tt>
+ <p>
+
+ <li>Run the <tt>configure</tt> script located in the LLVM source tree:
+ <br>
+ <tt><i>SRC_ROOT</i>/configure</tt>
+ <p>
+ </ol>
+
+ <p>In addition to running <tt>configure</tt>, you must set the
+ <tt>LLVM_LIB_SEARCH_PATH</tt> environment variable in your startup scripts.
+ This environment variable is used to locate "system" libraries like
+ "<tt>-lc</tt>" and "<tt>-lm</tt>" when linking. This variable should be set to
+ the absolute path of the <tt>bytecode-libs</tt> subdirectory of the GCC front
+ end, or <i>LLVMGCCDIR</i>/<tt>bytecode-libs</tt>. For example, one might set
+ <tt>LLVM_LIB_SEARCH_PATH</tt> to
+ <tt>/home/vadve/lattner/local/x86/llvm-gcc/bytecode-libs</tt> for the x86
+ version of the GCC front end on our research machines.</p>
+
+ </div>
+
+ <!-- ======================================================================= -->
+ <div class="doc_subsection">
+ <a name="compile">Compiling the LLVM Suite Source Code</a>
+ </div>
+
+ <div class="doc_text">
+
+ <p>Once you have configured LLVM, you can build it. There are three types of
+ builds:</p>
+
+ <dl>
+ <dt>Debug Builds
+ <dd>
+ These builds are the default when one types <tt>gmake</tt> (unless the
+ <tt>--enable-optimized</tt> option was used during configuration). The
+ build system will compile the tools and libraries with debugging
+ information.
+ <p>
+
+ <dt>Release (Optimized) Builds
+ <dd>
+ These builds are enabled with the <tt>--enable-optimized</tt> option to
+ <tt>configure</tt> or by specifying <tt>ENABLE_OPTIMIZED=1</tt> on the
+ <tt>gmake</tt> command line. For these builds, the build system will
+ compile the tools and libraries with GCC optimizations enabled and strip
+ debugging information from the libraries and executables it generates.
+ <p>
+
+ <dt>Profile Builds
+ <dd>
+ These builds are for use with profiling. They compile profiling
+ information into the code for use with programs like <tt>gprof</tt>.
+ Profile builds must be started by specifying <tt>ENABLE_PROFILING=1</tt>
+ on the <tt>gmake</tt> command line.
+ </dl>
+
+ <p>Once you have LLVM configured, you can build it by entering the
+ <i>OBJ_ROOT</i> directory and issuing the following command:</p>
+
+ <p><tt>gmake</tt></p>
+
+ <p>If the build fails, please <a href="#brokengcc">check here</a> to see if you
+ are using a known broken version of GCC to compile LLVM with.</p>
+
+ <p>
+ If you have multiple processors in your machine, you may wish to use some of
+ the parallel build options provided by GNU Make. For example, you could use the
+ command:</p>
+
+ <p><tt>gmake -j2</tt></p>
+
+ <p>There are several special targets which are useful when working with the LLVM
+ source code:</p>
+
+ <dl>
+ <dt><tt>gmake clean</tt>
+ <dd>
+ Removes all files generated by the build. This includes object files,
+ generated C/C++ files, libraries, and executables.
+ <p>
+
+ <dt><tt>gmake distclean</tt>
+ <dd>
+ Removes everything that <tt>gmake clean</tt> does, but also removes
+ files generated by <tt>configure</tt>. It attempts to return the
+ source tree to the original state in which it was shipped.
+ <p>
+
+ <dt><tt>gmake install</tt>
+ <dd>
+ Installs LLVM files into the proper location. For the most part,
+ this does nothing, but it does install bytecode libraries into the
+ GCC front end's bytecode library directory. If you need to update
+ your bytecode libraries, this is the target to use once you've built
+ them.
+ <p>
+ </dl>
+
+ <p>It is also possible to override default values from <tt>configure</tt> by
+ declaring variables on the command line. The following are some examples:</p>
+
+ <dl>
+ <dt><tt>gmake ENABLE_OPTIMIZED=1</tt>
+ <dd>
+ Perform a Release (Optimized) build.
+ <p>
+
+ <dt><tt>gmake ENABLE_PROFILING=1</tt>
+ <dd>
+ Perform a Profiling build.
+ <p>
+
+ <dt><tt>gmake VERBOSE=1</tt>
+ <dd>
+ Print what <tt>gmake</tt> is doing on standard output.
+ <p>
+ </dl>
+
+ <p>Every directory in the LLVM object tree includes a <tt>Makefile</tt> to build
+ it and any subdirectories that it contains. Entering any directory inside the
+ LLVM object tree and typing <tt>gmake</tt> should rebuild anything in or below
+ that directory that is out of date.</p>
+
+ </div>
+
+ <!-- ======================================================================= -->
+ <div class="doc_subsection">
+ <a name="objfiles">The Location of LLVM Object Files</a>
+ </div>
+
+ <div class="doc_text">
+
+ <p>The LLVM build system is capable of sharing a single LLVM source tree among
+ several LLVM builds. Hence, it is possible to build LLVM for several different
+ platforms or configurations using the same source tree.</p>
+
+ <p>This is accomplished in the typical autoconf manner:</p>
+
+ <ul>
+ <li><p>Change directory to where the LLVM object files should live:</p>
+
+ <p><tt>cd <i>OBJ_ROOT</i></tt></p></li>
+
+ <li><p>Run the <tt>configure</tt> script found in the LLVM source
+ directory:</p>
+
+ <p><tt><i>SRC_ROOT</i>/configure</tt></p></li>
+ </ul>
+
+ <p>The LLVM build will place files underneath <i>OBJ_ROOT</i> in directories
+ named after the build type:</p>
+
+ <dl>
+ <dt>Debug Builds
+ <dd>
+ <dl>
+ <dt>Tools
+ <dd><tt><i>OBJ_ROOT</i>/tools/Debug</tt>
+ <dt>Libraries
+ <dd><tt><i>OBJ_ROOT</i>/lib/Debug</tt>
+ </dl>
+ <p>
+
+ <dt>Release Builds
+ <dd>
+ <dl>
+ <dt>Tools
+ <dd><tt><i>OBJ_ROOT</i>/tools/Release</tt>
+ <dt>Libraries
+ <dd><tt><i>OBJ_ROOT</i>/lib/Release</tt>
+ </dl>
+ <p>
+
+ <dt>Profile Builds
+ <dd>
+ <dl>
+ <dt>Tools
+ <dd><tt><i>OBJ_ROOT</i>/tools/Profile</tt>
+ <dt>Libraries
+ <dd><tt><i>OBJ_ROOT</i>/lib/Profile</tt>
+ </dl>
+ </dl>
+
+ </div>
+
+ <!-- ======================================================================= -->
+ <div class="doc_subsection">
+ <a name="optionalconfig">Optional Configuration Items</a>
+ </div>
+
+ <div class="doc_text">
+
+ <p>
+ If you're running on a linux system that supports the "<a
+ href="http://www.tat.physik.uni-tuebingen.de/~rguenth/linux/binfmt_misc.html">binfmt_misc</a>"
+ module, and you have root access on the system, you can set your system up to
+ execute LLVM bytecode files directly. To do this, use commands like this (the
+ first command may not be required if you are already using the module):</p>
+
+ <pre>
+ $ mount -t binfmt_misc none /proc/sys/fs/binfmt_misc
+ $ echo ':llvm:M::llvm::/path/to/lli:' > /proc/sys/fs/binfmt_misc/register
+ $ chmod u+x hello.bc (if needed)
+ $ ./hello.bc
+ </pre>
+
+ <p>
+ This allows you to execute LLVM bytecode files directly. Thanks to Jack
+ Cummings for pointing this out!
+ </p>
+
+ </div>
+
+
+ <!-- *********************************************************************** -->
+ <div class="doc_section">
+ <a name="layout"><b>Program Layout</b></a>
+ </div>
+ <!-- *********************************************************************** -->
+
+ <div class="doc_text">
+
+ <p>One useful source of information about the LLVM source base is the LLVM <a
+ href="http://www.doxygen.org">doxygen</a> documentation available at <tt><a
+ href="http://llvm.cs.uiuc.edu/doxygen/">http://llvm.cs.uiuc.edu/doxygen/</a></tt>.
+ The following is a brief introduction to code layout:</p>
+
+ </div>
+
+ <!-- ======================================================================= -->
+ <div class="doc_subsection">
+ <a name="cvsdir"><tt>CVS</tt> directories</a>
+ </div>
+
+ <div class="doc_text">
+
+ <p>Every directory checked out of CVS will contain a <tt>CVS</tt> directory; for
+ the most part these can just be ignored.</p>
+
+ </div>
+
+ <!-- ======================================================================= -->
+ <div class="doc_subsection">
+ <a name="include"><tt>llvm/include</tt></a>
+ </div>
+
+ <div class="doc_text">
+
+ <p>This directory contains public header files exported from the LLVM
+ library. The three main subdirectories of this directory are:</p>
+
+ <ol>
+ <li><tt>llvm/include/llvm</tt> - This directory contains all of the LLVM
+ specific header files. This directory also has subdirectories for
+ different portions of LLVM: <tt>Analysis</tt>, <tt>CodeGen</tt>,
+ <tt>Target</tt>, <tt>Transforms</tt>, etc...</li>
+
+ <li><tt>llvm/include/Support</tt> - This directory contains generic
+ support libraries that are independent of LLVM, but are used by LLVM.
+ For example, some C++ STL utilities and a Command Line option processing
+ library store their header files here.</li>
+
+ <li><tt>llvm/include/Config</tt> - This directory contains header files
+ configured by the <tt>configure</tt> script. They wrap "standard" UNIX
+ and C header files. Source code can include these header files which
+ automatically take care of the conditional #includes that the
+ <tt>configure</tt> script generates.</li>
+ </ol>
+
+ </div>
+
+ <!-- ======================================================================= -->
+ <div class="doc_subsection">
+ <a name="lib"><tt>llvm/lib</tt></a>
+ </div>
+
+ <div class="doc_text">
+
+ <p>This directory contains most of the source files of the LLVM system. In LLVM,
+ almost all code exists in libraries, making it very easy to share code among the
+ different <a href="#tools">tools</a>.</p>
+
+ <dl>
+ <dt><tt>llvm/lib/VMCore/</tt><dd> This directory holds the core LLVM
+ source files that implement core classes like Instruction and BasicBlock.
+
+ <dt><tt>llvm/lib/AsmParser/</tt><dd> This directory holds the source code
+ for the LLVM assembly language parser library.
+
+ <dt><tt>llvm/lib/ByteCode/</tt><dd> This directory holds code for reading
+ and write LLVM bytecode.
+
+ <dt><tt>llvm/lib/CWriter/</tt><dd> This directory implements the LLVM to C
+ converter.
+
+ <dt><tt>llvm/lib/Analysis/</tt><dd> This directory contains a variety of
+ different program analyses, such as Dominator Information, Call Graphs,
+ Induction Variables, Interval Identification, Natural Loop Identification,
+ etc...
+
+ <dt><tt>llvm/lib/Transforms/</tt><dd> This directory contains the source
+ code for the LLVM to LLVM program transformations, such as Aggressive Dead
+ Code Elimination, Sparse Conditional Constant Propagation, Inlining, Loop
+ Invariant Code Motion, Dead Global Elimination, and many others...
+
+ <dt><tt>llvm/lib/Target/</tt><dd> This directory contains files that
+ describe various target architectures for code generation. For example,
+ the llvm/lib/Target/SparcV9 directory holds the Sparc machine
+ description.<br>
+
+ <dt><tt>llvm/lib/CodeGen/</tt><dd> This directory contains the major parts
+ of the code generator: Instruction Selector, Instruction Scheduling, and
+ Register Allocation.
+
+ <dt><tt>llvm/lib/Support/</tt><dd> This directory contains the source code
+ that corresponds to the header files located in
+ <tt>llvm/include/Support/</tt>.
+ </dl>
+
+ </div>
+
+ <!-- ======================================================================= -->
+ <div class="doc_subsection">
+ <a name="runtime"><tt>llvm/runtime</tt></a>
+ </div>
+
+ <div class="doc_text">
+
+ <p>This directory contains libraries which are compiled into LLVM bytecode and
+ used when linking programs with the GCC front end. Most of these libraries are
+ skeleton versions of real libraries; for example, libc is a stripped down
+ version of glibc.</p>
+
+ <p>Unlike the rest of the LLVM suite, this directory needs the LLVM GCC front
+ end to compile.</p>
+
+ </div>
+
+ <!-- ======================================================================= -->
+ <div class="doc_subsection">
+ <a name="test"><tt>llvm/test</tt></a>
+ </div>
+
+ <div class="doc_text">
+
+ <p>This directory contains regression tests and source code that is used to test
+ the LLVM infrastructure.</p>
+
+ </div>
+
+ <!-- ======================================================================= -->
+ <div class="doc_subsection">
+ <a name="tools"><tt>llvm/tools</tt></a>
+ </div>
+
+ <div class="doc_text">
+
+ <p>The <b>tools</b> directory contains the executables built out of the
+ libraries above, which form the main part of the user interface. You can
+ always get help for a tool by typing <tt>tool_name --help</tt>. The
+ following is a brief introduction to the most important tools:</p>
+
+ <dl>
+ <dt><tt><b>analyze</b></tt> <dd><tt>analyze</tt> is used to run a specific
+ analysis on an input LLVM bytecode file and print out the results. It is
+ primarily useful for debugging analyses, or familiarizing yourself with
+ what an analysis does.<p>
+
+ <dt><tt><b>bugpoint</b></tt> <dd><tt>bugpoint</tt> is used to debug
+ optimization passes or code generation backends by narrowing down the
+ given test case to the minimum number of passes and/or instructions that
+ still cause a problem, whether it is a crash or miscompilation. See <a
+ href="HowToSubmitABug.html">HowToSubmitABug.html</a> for more information
+ on using <tt>bugpoint</tt>.<p>
+
+ <dt><tt><b>llvm-ar</b></tt> <dd>The archiver produces an archive containing
+ the given LLVM bytecode files, optionally with an index for faster
+ lookup.<p>
+
+ <dt><tt><b>llvm-as</b></tt> <dd>The assembler transforms the human readable
+ LLVM assembly to LLVM bytecode.<p>
+
+ <dt><tt><b>llvm-dis</b></tt><dd>The disassembler transforms the LLVM
+ bytecode to human readable LLVM assembly.<p>
+
+ <dt><tt><b>llvm-link</b></tt><dd> <tt>llvm-link</tt>, not surprisingly,
+ links multiple LLVM modules into a single program.<p>
+
+ <dt><tt><b>lli</b></tt><dd> <tt>lli</tt> is the LLVM interpreter, which
+ can directly execute LLVM bytecode (although very slowly...). In addition
+ to a simple interpreter, <tt>lli</tt> also has a tracing mode (entered by
+ specifying <tt>-trace</tt> on the command line). Finally, for
+ architectures that support it (currently only x86 and Sparc), by default,
+ <tt>lli</tt> will function as a Just-In-Time compiler (if the
+ functionality was compiled in), and will execute the code <i>much</i>
+ faster than the interpreter.<p>
+
+ <dt><tt><b>llc</b></tt><dd> <tt>llc</tt> is the LLVM backend compiler, which
+ translates LLVM bytecode to a SPARC or x86 assembly file, or to C code (with
+ the -march=c option).<p>
+
+ <dt><tt><b>llvmgcc</b></tt><dd> <tt>llvmgcc</tt> is a GCC-based C frontend
+ that has been retargeted to emit LLVM code as the machine code output. It
+ works just like any other GCC compiler, taking the typical <tt>-c, -S, -E,
+ -o</tt> options that are typically used. The source code for the
+ <tt>llvmgcc</tt> tool is currently not included in the LLVM CVS tree
+ because it is quite large and not very interesting.<p>
+
+ <blockquote>
+ <dl>
+ <dt><tt><b>gccas</b></tt> <dd>This tool is invoked by the
+ <tt>llvmgcc</tt> frontend as the "assembler" part of the compiler. This
+ tool actually assembles LLVM assembly to LLVM bytecode,
+ performs a variety of optimizations, and outputs LLVM bytecode. Thus
+ when you invoke <tt>llvmgcc -c x.c -o x.o</tt>, you are causing
+ <tt>gccas</tt> to be run, which writes the <tt>x.o</tt> file (which is
+ an LLVM bytecode file that can be disassembled or manipulated just like
+ any other bytecode file). The command line interface to <tt>gccas</tt>
+ is designed to be as close as possible to the <b>system</b>
+ `<tt>as</tt>' utility so that the gcc frontend itself did not have to be
+ modified to interface to a "weird" assembler.<p>
+
+ <dt><tt><b>gccld</b></tt> <dd><tt>gccld</tt> links together several LLVM
+ bytecode files into one bytecode file and does some optimization. It is
+ the linker invoked by the GCC frontend when multiple .o files need to be
+ linked together. Like <tt>gccas</tt>, the command line interface of
+ <tt>gccld</tt> is designed to match the system linker, to aid
+ interfacing with the GCC frontend.</dl><p>
+ </blockquote>
+
+ <dt><tt><b>opt</b></tt><dd> <tt>opt</tt> reads LLVM bytecode, applies a
+ series of LLVM to LLVM transformations (which are specified on the command
+ line), and then outputs the resultant bytecode. The '<tt>opt --help</tt>'
+ command is a good way to get a list of the program transformations
+ available in LLVM.
+
+ </dl>
+
+ </div>
+
+ <!-- ======================================================================= -->
+ <div class="doc_subsection">
+ <a name="utils"><tt>llvm/utils</tt></a>
+ </div>
+
+ <div class="doc_text">
+
+ <p>This directory contains utilities for working with LLVM source code, and some
+ of the utilities are actually required as part of the build process because they
+ are code generators for parts of LLVM infrastructure.</p>
+
+ <dl>
+ <dt><tt><b>Burg/</b></tt> <dd><tt>Burg</tt> is an instruction selector
+ generator -- it builds trees on which it then performs pattern-matching to
+ select instructions according to the patterns the user has specified. Burg
+ is currently used in the Sparc V9 backend.<p>
+
+ <dt><tt><b>codegen-diff</b></tt> <dd><tt>codegen-diff</tt> is a script
+ that finds differences between code that LLC generates and code that LLI
+ generates. This is a useful tool if you are debugging one of them,
+ assuming that the other generates correct output. For the full user
+ manual, run <tt>`perldoc codegen-diff'</tt>.<p>
+
+ <dt><tt><b>cvsupdate</b></tt> <dd><tt>cvsupdate</tt> is a script that will
+ update your CVS tree, but produce a much cleaner and more organized output
+ than simply running <tt>`cvs -z3 up -dP'</tt> will. For example, it will group
+ together all the new and updated files and modified files in separate
+ sections, so you can see at a glance what has changed. If you are at the
+ top of your LLVM CVS tree, running <tt>utils/cvsupdate</tt> is the
+ preferred way of updating the tree.<p>
+
+ <dt><tt><b>emacs/</b></tt> <dd>The <tt>emacs</tt> directory contains
+ syntax-highlighting files which will work with Emacs and XEmacs editors,
+ providing syntax highlighting support for LLVM assembly files and TableGen
+ description files. For information on how to use the syntax files, consult
+ the <tt>README</tt> file in that directory.<p>
+
+ <dt><tt><b>getsrcs.sh</b></tt> <dd>The <tt>getsrcs.sh</tt> script finds
+ and outputs all non-generated source files, which is useful if one wishes
+ to do a lot of development across directories and does not want to
+ individually find each file. One way to use it is to run, for example:
+ <tt>xemacs `utils/getsources.sh`</tt> from the top of your LLVM source
+ tree.<p>
+
+ <dt><tt><b>makellvm</b></tt> <dd>The <tt>makellvm</tt> script compiles all
+ files in the current directory and then compiles and links the tool that
+ is the first argument. For example, assuming you are in the directory
+ <tt>llvm/lib/Target/Sparc</tt>, if <tt>makellvm</tt> is in your path,
+ simply running <tt>makellvm llc</tt> will make a build of the current
+ directory, switch to directory <tt>llvm/tools/llc</tt> and build it,
+ causing a re-linking of LLC.<p>
+
+ <dt><tt><b>NightlyTest.pl</b></tt> and
+ <tt><b>NightlyTestTemplate.html</b></tt> <dd>These files are used in a
+ cron script to generate nightly status reports of the functionality of
+ tools, and the results can be seen by following the appropriate link on
+ the <a href="http://llvm.cs.uiuc.edu/">LLVM homepage</a>.<p>
+
+ <dt><tt><b>TableGen/</b></tt> <dd>The <tt>TableGen</tt> directory contains
+ the tool used to generate register descriptions, instruction set
+ descriptions, and even assemblers from common TableGen description
+ files.<p>
+
+ <dt><tt><b>vim/</b></tt> <dd>The <tt>vim</tt> directory contains
+ syntax-highlighting files which will work with the VIM editor, providing
+ syntax highlighting support for LLVM assembly files and TableGen
+ description files. For information on how to use the syntax files, consult
+ the <tt>README</tt> file in that directory.<p>
+
+ </dl>
+
+ </div>
+
+ <!-- *********************************************************************** -->
+ <div class="doc_section">
+ <a name="tutorial">An Example Using the LLVM Tool Chain</a>
+ </div>
+ <!-- *********************************************************************** -->
+
+ <div class="doc_text">
+
+ <ol>
+ <li>First, create a simple C file, name it 'hello.c':
+ <pre>
+ #include <stdio.h>
+ int main() {
+ printf("hello world\n");
+ return 0;
+ }
+ </pre></li>
+
+ <li><p>Next, compile the C file into a LLVM bytecode file:</p>
+ <p><tt>% llvmgcc hello.c -o hello</tt></p>
+
+ <p>Note that you should have already built the tools and they have to be
+ in your path, at least <tt>gccas</tt> and <tt>gccld</tt>.</p>
+
+ <p>This will create two result files: <tt>hello</tt> and
+ <tt>hello.bc</tt>. The <tt>hello.bc</tt> is the LLVM bytecode that
+ corresponds the the compiled program and the library facilities that it
+ required. <tt>hello</tt> is a simple shell script that runs the bytecode
+ file with <tt>lli</tt>, making the result directly executable. Note that
+ all LLVM optimizations are enabled by default, so there is no need for a
+ "-O3" switch.</p></li>
+
+ <li><p>Run the program. To make sure the program ran, execute one of the
+ following commands:</p>
+
+ <p><tt>% ./hello</tt></p>
+
+ <p>or</p>
+
+ <p><tt>% lli hello.bc</tt></p></li>
+
+ <li><p>Use the <tt>llvm-dis</tt> utility to take a look at the LLVM assembly
+ code:</p>
+
+ <p><tt>% llvm-dis < hello.bc | less</tt><p></li>
+
+ <li><p>Compile the program to native assembly using the LLC code
+ generator:</p>
+
+ <p><tt>% llc hello.bc -o hello.s</tt></p>
+
+ <li><p>Assemble the native assembly language file into a program:</p>
+
+ <p><b>Solaris:</b><tt>% /opt/SUNWspro/bin/cc -xarch=v9 hello.s -o hello.native</tt></p>
+ <p><b>Others:</b><tt>% gcc hello.s -o hello.native</tt></p>
+
+ <li><p>Execute the native code program:</p>
+
+ <p><tt>% ./hello.native</tt></p></li>
+
+ </ol>
+
+ </div>
+
+ <!-- *********************************************************************** -->
+ <div class="doc_section">
+ <a name="problems">Common Problems</a>
+ </div>
+ <!-- *********************************************************************** -->
+
+ <div class="doc_text">
+
+ <p>If you are having problems building or using LLVM, or if you have any other
+ general questions about LLVM, please consult the <a href="FAQ.html">Frequently
+ Asked Questions</a> page.</p>
+
+ </div>
+
+ <!-- *********************************************************************** -->
+ <div class="doc_section">
+ <a name="links">Links</a>
+ </div>
+ <!-- *********************************************************************** -->
+
+ <div class="doc_text">
+
+ <p>This document is just an <b>introduction</b> to how to use LLVM to do
+ some simple things... there are many more interesting and complicated things
+ that you can do that aren't documented here (but we'll gladly accept a patch
+ if you want to write something up!). For more information about LLVM, check
+ out:</p>
+
+ <ul>
+ <li><a href="http://llvm.cs.uiuc.edu/">LLVM homepage</a></li>
+ <li><a href="http://llvm.cs.uiuc.edu/doxygen/">LLVM doxygen tree</a></li>
+ <li><a href="http://llvm.cs.uiuc.edu/docs/Projects.html">Starting a Project
+ that Uses LLVM</a></li>
+ </ul>
+
+ </div>
+
+ <!-- *********************************************************************** -->
+
+ <hr>
+ <address>
+ <a href="http://jigsaw.w3.org/css-validator/check/referer"><img
+ src="http://jigsaw.w3.org/css-validator/images/vcss" alt="Valid CSS!"></a>
+ <a href="http://validator.w3.org/check/referer"><img
+ src="http://www.w3.org/Icons/valid-html401" alt="Valid HTML 4.01!" /></a>
+
+ <a href="mailto:sabre at nondot.org">Chris Lattner</a><br>
+ <a href="http://llvm.cs.uiuc.edu">The LLVM Compiler Infrastructure</a><br>
+ Last modified: $Date: 2004/08/13 22:03:03 $
+ </address>
+
+ </body>
+ </html>
Index: llvm-www/releases/1.3/docs/HowToSubmitABug.html
diff -c /dev/null llvm-www/releases/1.3/docs/HowToSubmitABug.html:1.1
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--- 1,360 ----
+ <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"
+ "http://www.w3.org/TR/html4/strict.dtd">
+ <html>
+ <head>
+ <title>How to submit an LLVM bug report</title>
+ <link rel="stylesheet" href="llvm.css" type="text/css">
+ </head>
+ <body>
+
+ <div class="doc_title">
+ How to submit an LLVM bug report
+ </div>
+
+ <table border="0" width="100%">
+ <tr>
+ <td valign="top">
+
+ <ol>
+ <li><a href="#introduction">Introduction - Got bugs?</a></li>
+ <li><a href="#crashers">Crashing Bugs</a>
+ <ul>
+ <li><a href="#front-end">Front-end bugs</a>
+ <li><a href="#gccas">GCCAS bugs</a>
+ <li><a href="#gccld">GCCLD bugs</a>
+ <li><a href="#passes">Bugs in LLVM passes</a>
+ </ul></li>
+ <li><a href="#miscompilations">Miscompilations</a></li>
+ <li><a href="#codegen">Incorrect code generation (JIT and LLC)</a></li>
+
+ </ol>
+
+ <div class="doc_author">
+ <p>Written by <a href="mailto:sabre at nondot.org">Chris Lattner</a> and
+ <a href="http://misha.brukman.net">Misha Brukman</a></p>
+ </div>
+
+ </td>
+ <td align="right">
+ <img src="img/Debugging.gif" alt="Debugging" width="444" height="314">
+ </td>
+ </tr>
+ </table>
+
+ <!-- *********************************************************************** -->
+ <div class="doc_section">
+ <a name="introduction">Introduction - Got bugs?</a>
+ </div>
+ <!-- *********************************************************************** -->
+
+ <div class="doc_text">
+
+ <p>If you're working with LLVM and run into a bug, we definitely want to know
+ about it. This document describes what you can do to increase the odds of
+ getting it fixed quickly.</p>
+
+ <p>Basically you have to do two things at a minimum. First, decide whether the
+ bug <a href="#crashers">crashes the compiler</a> (or an LLVM pass), or if the
+ compiler is <a href="#miscompilations">miscompiling</a> the program. Based on
+ what type of bug it is, follow the instructions in the linked section to narrow
+ down the bug so that the person who fixes it will be able to find the problem
+ more easily.</p>
+
+ <p>Once you have a reduced test-case, go to <a
+ href="http://llvm.cs.uiuc.edu/bugs/enter_bug.cgi">the LLVM Bug Tracking
+ System</a>, select the category in which the bug falls, and fill out the form
+ with the necessary details. The bug description should contain the following
+ information:</p>
+
+ <ul>
+ <li>All information necessary to reproduce the problem.</li>
+ <li>The reduced test-case that triggers the bug.</li>
+ <li>The location where you obtained LLVM (if not from our CVS
+ repository).</li>
+ </ul>
+
+ <p>Thanks for helping us make LLVM better!</p>
+
+ </div>
+
+ <!-- *********************************************************************** -->
+ <div class="doc_section">
+ <a name="crashers">Crashing Bugs</a>
+ </div>
+ <!-- *********************************************************************** -->
+
+ <div class="doc_text">
+
+ <p>More often than not, bugs in the compiler cause it to crash - often due to an
+ assertion failure of some sort. If you are running <tt><b>opt</b></tt> or
+ <tt><b>analyze</b></tt> directly, and something crashes, jump to the section on
+ <a href="#passes">bugs in LLVM passes</a>. Otherwise, the most important
+ piece of the puzzle is to figure out if it is the GCC-based front-end that is
+ buggy or if it's one of the LLVM tools that has problems.</p>
+
+ <p>To figure out which program is crashing (the front-end,
+ <tt><b>gccas</b></tt>, or <tt><b>gccld</b></tt>), run the
+ <tt><b>llvm-gcc</b></tt> command line as you were when the crash occurred, but
+ add a <tt>-v</tt> option to the command line. The compiler will print out a
+ bunch of stuff, and should end with telling you that one of
+ <tt><b>cc1</b>/<b>cc1plus</b></tt>, <tt><b>gccas</b></tt>, or
+ <tt><b>gccld</b></tt> crashed.</p>
+
+ <ul>
+
+ <li>If <tt><b>cc1</b></tt> or <tt><b>cc1plus</b></tt> crashed, you found a
+ problem with the front-end.
+ Jump ahead to the section on <a href="#front-end">front-end bugs</a>.</li>
+
+ <li>If <tt><b>gccas</b></tt> crashed, you found a bug in <a href="#gccas">one
+ of the passes in <tt><b>gccas</b></tt></a>.</li>
+
+ <li>If <tt><b>gccld</b></tt> crashed, you found a bug in <a href="#gccld">one
+ of the passes in <tt><b>gccld</b></tt></a>.</li>
+
+ <li>Otherwise, something really weird happened. Email the list with what you
+ have at this point.</li>
+
+ </ul>
+
+ </div>
+
+ <!-- ======================================================================= -->
+ <div class="doc_subsection">
+ <a name="front-end">Front-end bugs</a>
+ </div>
+
+ <div class="doc_text">
+
+ <p>If the problem is in the front-end, you should re-run the same
+ <tt>llvm-gcc</tt> command that resulted in the crash, but add the
+ <tt>-save-temps</tt> option. The compiler will crash again, but it will leave
+ behind a <tt><i>foo</i>.i</tt> file (containing preprocessed C source code) and
+ possibly <tt><i>foo</i>.s</tt> (containing LLVM assembly code), for each
+ compiled <tt><i>foo</i>.c</tt> file. Send us the <tt><i>foo</i>.i</tt> file,
+ along with a brief description of the error it caused.</p>
+
+ </div>
+
+ <!-- ======================================================================= -->
+ <div class="doc_subsection">
+ <a name="gccas">GCCAS bugs</a>
+ </div>
+
+ <div class="doc_text">
+
+ <p>If you find that a bug crashes in the <tt><b>gccas</b></tt> stage of
+ compilation, compile your test-case to a <tt>.s</tt> file with the
+ <tt>-save-temps</tt> option to <tt><b>llvm-gcc</b></tt>. Then run:</p>
+
+ <div class="doc_code">
+ <p><tt><b>gccas</b> -debug-pass=Arguments < /dev/null -o - > /dev/null</tt></p>
+ </div>
+
+ <p>... which will print a list of arguments, indicating the list of passes that
+ <tt><b>gccas</b></tt> runs. Once you have the input file and the list of
+ passes, go to the section on <a href="#passes">debugging bugs in LLVM
+ passes</a>.</p>
+
+ </div>
+
+ <!-- ======================================================================= -->
+ <div class="doc_subsection">
+ <a name="gccld">GCCLD bugs</a>
+ </div>
+
+ <div class="doc_text">
+
+ <p>If you find that a bug crashes in the <tt><b>gccld</b></tt> stage of
+ compilation, gather all of the <tt>.o</tt> bytecode files and libraries that are
+ being linked together (the "<tt><b>llvm-gcc</b> -v</tt>" output should include
+ the full list of objects linked). Then run:</p>
+
+ <div class="doc_code">
+ <p><tt><b>llvm-as</b> < /dev/null > null.bc<br>
+ <b>gccld</b> -debug-pass=Arguments null.bc</tt>
+ </p>
+ </div>
+
+ <p>... which will print a list of arguments, indicating the list of passes that
+ <tt><b>gccld</b></tt> runs. Once you have the input files and the list of
+ passes, go to the section on <a href="#passes">debugging bugs in LLVM
+ passes</a>.</p>
+
+ </div>
+
+ <!-- ======================================================================= -->
+ <div class="doc_subsection">
+ <a name="passes">Bugs in LLVM passes</a>
+ </div>
+
+ <div class="doc_text">
+
+ <p>At this point, you should have some number of LLVM assembly files or bytecode
+ files and a list of passes which crash when run on the specified input. In
+ order to reduce the list of passes (which is probably large) and the input to
+ something tractable, use the <tt><b>bugpoint</b></tt> tool as follows:</p>
+
+ <div class="doc_code">
+ <p><tt><b>bugpoint</b> <input files> <list of passes></tt></p>
+ </div>
+
+ <p><tt><b>bugpoint</b></tt> will print a bunch of output as it reduces the
+ test-case, but it should eventually print something like this:</p>
+
+ <div class="doc_code">
+ <p><tt>
+ ...<br>
+ Emitted bytecode to 'bugpoint-reduced-simplified.bc'<br>
+ <br>
+ *** You can reproduce the problem with: opt bugpoint-reduced-simplified.bc -licm<br>
+ </tt></p>
+ </div>
+
+ <p>Once you complete this, please send the LLVM bytecode file and the command
+ line to reproduce the problem to the llvmbugs mailing list.</p>
+
+ </div>
+
+ <!-- *********************************************************************** -->
+ <div class="doc_section">
+ <a name="miscompilations">Miscompilations</a>
+ </div>
+ <!-- *********************************************************************** -->
+
+ <div class="doc_text">
+
+ <p>A miscompilation occurs when a pass does not correctly transform a program,
+ thus producing errors that are only noticed during execution. This is different
+ from producing invalid LLVM code (i.e., code not in SSA form, using values
+ before defining them, etc.) which the verifier will check for after a pass
+ finishes its run.</p>
+
+ <p>If it looks like the LLVM compiler is miscompiling a program, the very first
+ thing to check is to make sure it is not using undefined behavior. In
+ particular, check to see if the program <a
+ href="http://valgrind.kde.org/">valgrind</a>s clean, passes purify, or some
+ other memory checker tool. Many of the "LLVM bugs" that we have chased down
+ ended up being bugs in the program being compiled, not LLVM.</p>
+
+ <p>Once you determine that the program itself is not buggy, you should choose
+ which code generator you wish to compile the program with (e.g. C backend, the
+ JIT, or LLC) and optionally a series of LLVM passes to run. For example:</p>
+
+ <div class="doc_code">
+ <p><tt>
+ <b>bugpoint</b> -run-cbe [... optzn passes ...] file-to-test.bc --args -- [program arguments]</tt></p>
+ </div>
+
+ <p><tt>bugpoint</tt> will try to narrow down your list of passes to the one pass
+ that causes an error, and simplify the bytecode file as much as it can to assist
+ you. It will print a message letting you know how to reproduce the resulting
+ error.</p>
+
+ </div>
+
+ <!-- *********************************************************************** -->
+ <div class="doc_section">
+ <a name="codegen">Incorrect code generation</a>
+ </div>
+ <!-- *********************************************************************** -->
+
+ <div class="doc_text">
+
+ <p>Similarly to debugging incorrect compilation by mis-behaving passes, you can
+ debug incorrect code generation by either LLC or the JIT, using
+ <tt>bugpoint</tt>. The process <tt>bugpoint</tt> follows in this case is to try
+ to narrow the code down to a function that is miscompiled by one or the other
+ method, but since for correctness, the entire program must be run,
+ <tt>bugpoint</tt> will compile the code it deems to not be affected with the C
+ Backend, and then link in the shared object it generates.</p>
+
+ <p>To debug the JIT:</p>
+
+ <div class="doc_code">
+ <pre>
+ bugpoint -run-jit -output=[correct output file] [bytecode file] \
+ --tool-args -- [arguments to pass to lli] \
+ --args -- [program arguments]
+ </pre>
+ </div>
+
+ <p>Similarly, to debug the LLC, one would run:</p>
+
+ <div class="doc_code">
+ <pre>
+ bugpoint -run-llc -output=[correct output file] [bytecode file] \
+ --tool-args -- [arguments to pass to llc] \
+ --args -- [program arguments]
+ </pre>
+ </div>
+
+ <p><b>Special note:</b> if you are debugging MultiSource or SPEC tests that
+ already exist in the <tt>llvm/test</tt> hierarchy, there is an easier way to
+ debug the JIT, LLC, and CBE, using the pre-written Makefile targets, which
+ will pass the program options specified in the Makefiles:</p>
+
+ <div class="doc_code">
+ <p><tt>
+ cd llvm/test/../../program<br>
+ make bugpoint-jit
+ </tt></p>
+ </div>
+
+ <p>At the end of a successful <tt>bugpoint</tt> run, you will be presented
+ with two bytecode files: a <em>safe</em> file which can be compiled with the C
+ backend and the <em>test</em> file which either LLC or the JIT
+ mis-codegenerates, and thus causes the error.</p>
+
+ <p>To reproduce the error that <tt>bugpoint</tt> found, it is sufficient to do
+ the following:</p>
+
+ <ol>
+
+ <li><p>Regenerate the shared object from the safe bytecode file:</p>
+
+ <div class="doc_code">
+ <p><tt>
+ <b>llc</b> -march=c safe.bc -o safe.c<br>
+ <b>gcc</b> -shared safe.c -o safe.so
+ </tt></p>
+ </div></li>
+
+ <li><p>If debugging LLC, compile test bytecode native and link with the shared
+ object:</p>
+
+ <div class="doc_code">
+ <p><tt>
+ <b>llc</b> test.bc -o test.s -f<br>
+ <b>gcc</b> test.s safe.so -o test.llc<br>
+ ./test.llc [program options]
+ </tt></p>
+ </div></li>
+
+ <li><p>If debugging the JIT, load the shared object and supply the test
+ bytecode:</p>
+
+ <div class="doc_code">
+ <p><tt><b>lli</b> -load=safe.so test.bc [program options]</tt></p>
+ </div></li>
+
+ </ol>
+
+ </div>
+
+ <!-- *********************************************************************** -->
+ <hr>
+ <address>
+ <a href="http://jigsaw.w3.org/css-validator/check/referer"><img
+ src="http://jigsaw.w3.org/css-validator/images/vcss" alt="Valid CSS!"></a>
+ <a href="http://validator.w3.org/check/referer"><img
+ src="http://www.w3.org/Icons/valid-html401" alt="Valid HTML 4.01!" /></a>
+
+ <a href="mailto:sabre at nondot.org">Chris Lattner</a><br>
+ <a href="http://llvm.cs.uiuc.edu">The LLVM Compiler Infrastructure</a>
+ <br>
+ Last modified: $Date: 2004/08/13 22:03:03 $
+ </address>
+
+ </body>
+ </html>
Index: llvm-www/releases/1.3/docs/index.html
diff -c /dev/null llvm-www/releases/1.3/docs/index.html:1.1
*** /dev/null Fri Aug 13 17:03:14 2004
--- llvm-www/releases/1.3/docs/index.html Fri Aug 13 17:03:03 2004
***************
*** 0 ****
--- 1,200 ----
+ <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"
+ "http://www.w3.org/TR/html4/strict.dtd">
+ <html>
+ <head>
+ <title>Documentation for the LLVM System</title>
+ <link rel="stylesheet" href="llvm.css" type="text/css">
+ </head>
+ <body>
+
+ <div class="doc_title">Documentation for the LLVM System</div>
+
+ <div class="doc_text">
+ <ul>
+ <li><a href="#llvmdesign">LLVM Design</a></li>
+ <li><a href="#userguide">LLVM User Guides</a></li>
+ <li><a href="#llvmprog">General LLVM Programming Documentation</a></li>
+ <li><a href="#subsystems">LLVM Subsystem Documentation</a></li>
+ <li><a href="#maillist">LLVM Mailing Lists</a></li>
+ </ul>
+ </div>
+
+ <div class="doc_author">
+ <p>Written by <a href="http://llvm.cs.uiuc.edu">The LLVM Team</a></p>
+ </div>
+
+ <!--=======================================================================-->
+ <div class="doc_section"><a name="llvmdesign">LLVM Design</a></div>
+ <!--=======================================================================-->
+
+ <ul>
+ <li><a href="pubs/2004-01-30-CGO-LLVM.html"> LLVM: A Compilation Framework for
+ Lifelong Program Analysis & Transformation</a>: - Describes
+ the LLVM instruction set and compilation strategy. This should be the first
+ document you read to get an overview of LLVM.</li>
+
+ <li><a href="LangRef.html">LLVM Reference Manual</a> - Defines the LLVM
+ intermediate representation, the assembly form of the different nodes, and
+ provides reference information about the different tools in LLVM.</li>
+
+ <li><a href="BytecodeFormat.html">LLVM Bytecode File Format</a></li>
+
+ </ul>
+
+ <!--=======================================================================-->
+ <div class="doc_section"><a name="userguide">LLVM User Guides</a></div>
+ <!--=======================================================================-->
+
+ <ul>
+ <li><a href="GettingStarted.html">The LLVM Getting Started Guide</a> -
+ Discusses how to get up and running quickly with the LLVM infrastructure.
+ Everything from unpacking and compilation of the distribution to execution of
+ some tools.</li>
+
+ <li><a href="CommandGuide/index.html">LLVM Command Guide</a> - A reference
+ manual for the LLVM command line utilities ("man" pages for LLVM tools).</li>
+
+ <li><a href="FAQ.html">Frequently Asked Questions</a> - A list of common
+ questions and problems and their solutions.</li>
+
+ <li><a href="ReleaseNotes.html">Release notes for the current release</a>
+ - This describes new features, known bugs, and other limitations.</li>
+
+ <li><a href="HowToSubmitABug.html">How to Submit A Bug Report</a> -
+ Instructions for properly submitting information about any bugs you run into in
+ the LLVM system.</li>
+
+ <li><a href="TestingGuide.html">LLVM Test Suite Guide</a> - A reference
+ manual for using the LLVM test suite.</li>
+
+ <li><a href="CFEBuildInstrs.html">How to build the C/C++ front-end</a> -
+ Instructions for building the front-end from source.</li>
+
+ <li><a name="irc">You can probably find help on the unofficial LLVM IRC
+ channel</a>. We often are on irc.oftc.net in the #llvm channel. If you are
+ using the mozilla browser, and have chatzilla installed, you can join by <a
+ href="irc://irc.oftc.net/llvm">clicking here</a>.</li>
+
+ </ul>
+
+
+ <!--=======================================================================-->
+ <div class="doc_section"><a name="llvmprog">General LLVM Programming Documentation</a></div>
+ <!--=======================================================================-->
+
+ <ul>
+ <li><a href="ProgrammersManual.html">The LLVM Programmers Manual</a> -
+ Introduction to the general layout of the LLVM sourcebase, important classes
+ and APIs, and some tips & tricks.</li>
+
+ <li><a href="Projects.html">LLVM Project Guide</a> - How-to guide and
+ templates for new projects that <em>use</em> the LLVM infrastructure. The
+ templates (directory organization, Makefiles, and test tree) allow the project
+ code to be located outside (or inside) the <tt>llvm/</tt> tree, while using LLVM
+ header files and libraries.</li>
+
+ <li><a href="CommandLine.html">CommandLine library Reference Manual</a> -
+ Provides information on using the command line parsing library.</li>
+
+ <li><a href="CodingStandards.html">Recommended LLVM Coding standards</a> -
+ Details the LLVM coding standards and provides useful information on writing
+ efficient C++ code.</li>
+
+ <li><a href="OpenProjects.html">Open Projects</a> - Look here if you are
+ interested in doing something with LLVM but aren't sure what needs to be
+ done.</li>
+
+ <li><a href="ExtendingLLVM.html">Extending LLVM</a> - Look here to see how
+ to add instructions and intrinsics to LLVM.</li>
+
+ <li><a href="CodingStandards.html">Coding Standards</a> - Guidelines for
+ hacking LLVM source.</li>
+
+ <li><a href="http://llvm.cs.uiuc.edu/doxygen/">Doxygen generated
+ documentation</a> (<a href="http://llvm.cs.uiuc.edu/doxygen/inherits.html">
+ classes</a>)</li>
+
+ <li><a href="http://llvm.cs.uiuc.edu/cvsweb/cvsweb.cgi/llvm">CVSWeb CVS Tree
+ Browser</a></li>
+
+ </ul>
+
+ <!--=======================================================================-->
+ <div class="doc_section"><a name="subsystems">LLVM Subsystem Documentation</a></div>
+ <!--=======================================================================-->
+
+ <ul>
+
+ <li><a href="WritingAnLLVMPass.html">Writing an LLVM Pass</a> - Information
+ on how to write LLVM transformations and analyses.</li>
+
+ <li><a href="CodeGenerator.html">The LLVM Target-Independent Code
+ Generator</a> - The design and implementation of the LLVM code generator.
+ Useful if you are working on retargetting LLVM to a new architecture, designing
+ a new codegen pass, or enhancing existing components.</li>
+
+ <li><a href="TableGenFundamentals.html">TableGen Fundamentals</a> -
+ Describes the TableGen tool, which is used heavily by the LLVM code
+ generator.</li>
+
+ <li><a href="AliasAnalysis.html">Alias Analysis in LLVM</a> - Information
+ on how to write a new alias analysis implementation or how to use existing
+ analyses.</li>
+
+ <li><a href="Stacker.html">The Stacker Cronicles</a> - This document
+ describes both the Stacker language and LLVM frontend, but also some details
+ about LLVM useful for those writing front-ends.</li>
+
+ <li><a href="GarbageCollection.html">Accurate Garbage Collection with
+ LLVM</a> - The interfaces source-language compilers should use for compiling
+ GC'd programs.</li>
+
+ <li><a href="SourceLevelDebugging.html">Source Level Debugging with
+ LLVM</a> - This document describes the design and philosophy behind the LLVM
+ source-level debugger.</li>
+
+ <li><a href="Bugpoint.html">Bugpoint</a> automatic bug finder and
+ test-case reducer description and usage information.</li>
+
+ </ul>
+
+ <!--=======================================================================-->
+ <div class="doc_section"><a name="maillist">LLVM Mailing Lists</a></div>
+ <!--=======================================================================-->
+
+ <ul>
+ <li>The <a href="http://mail.cs.uiuc.edu/mailman/listinfo/llvm-announce">
+ LLVM Announcements List</a>: This is a low volume list that provides important
+ announcements regarding LLVM. It gets email about once a month.</li>
+
+ <li>The <a href="http://mail.cs.uiuc.edu/mailman/listinfo/llvmdev">Developer's
+ List</a>: This list is for people who want to be included in technical
+ discussions of LLVM. People post to this list when they have questions about
+ writing code for or using the LLVM tools. It is relatively low volume.</li>
+
+ <li>The <a href="http://mail.cs.uiuc.edu/pipermail/llvmbugs/">Bugs &
+ Patches Archive</a>: This list gets emailed every time a bug is opened and
+ closed, and when people submit patches to be included in LLVM. It is higher
+ volume than the LLVMdev list.</li>
+
+ <li>The <a href="http://mail.cs.uiuc.edu/pipermail/llvm-commits/">CVS Commits
+ Archive</a>: This list contains all commit messages that are made when LLVM
+ developers commit code changes to the CVS archive. It is useful for those who
+ want to stay on the bleeding edge of LLVM development. This list is very high
+ volume.</li>
+
+ </ul>
+
+ <!-- *********************************************************************** -->
+
+ <hr>
+ <address>
+ <a href="http://jigsaw.w3.org/css-validator/check/referer"><img
+ src="http://jigsaw.w3.org/css-validator/images/vcss" alt="Valid CSS!"></a>
+ <a href="http://validator.w3.org/check/referer"><img
+ src="http://www.w3.org/Icons/valid-html401" alt="Valid HTML 4.01!"></a>
+
+ <a href="http://llvm.cs.uiuc.edu">LLVM Compiler Infrastructure</a><br>
+ Last modified: $Date: 2004/08/13 22:03:03 $
+ </address>
+
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+ <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"
+ "http://www.w3.org/TR/html4/strict.dtd">
+ <html>
+ <head>
+ <title>LLVM Assembly Language Reference Manual</title>
+ <link rel="stylesheet" href="llvm.css" type="text/css">
+ </head>
+
+ <body>
+
+ <div class="doc_title"> LLVM Language Reference Manual </div>
+ <ol>
+ <li><a href="#abstract">Abstract</a></li>
+ <li><a href="#introduction">Introduction</a></li>
+ <li><a href="#identifiers">Identifiers</a></li>
+ <li><a href="#typesystem">Type System</a>
+ <ol>
+ <li><a href="#t_primitive">Primitive Types</a>
+ <ol>
+ <li><a href="#t_classifications">Type Classifications</a></li>
+ </ol>
+ </li>
+ <li><a href="#t_derived">Derived Types</a>
+ <ol>
+ <li><a href="#t_array">Array Type</a></li>
+ <li><a href="#t_function">Function Type</a></li>
+ <li><a href="#t_pointer">Pointer Type</a></li>
+ <li><a href="#t_struct">Structure Type</a></li>
+ <!-- <li><a href="#t_packed" >Packed Type</a> -->
+ </ol>
+ </li>
+ </ol>
+ </li>
+ <li><a href="#highlevel">High Level Structure</a>
+ <ol>
+ <li><a href="#modulestructure">Module Structure</a></li>
+ <li><a href="#globalvars">Global Variables</a></li>
+ <li><a href="#functionstructure">Function Structure</a></li>
+ </ol>
+ </li>
+ <li><a href="#instref">Instruction Reference</a>
+ <ol>
+ <li><a href="#terminators">Terminator Instructions</a>
+ <ol>
+ <li><a href="#i_ret">'<tt>ret</tt>' Instruction</a></li>
+ <li><a href="#i_br">'<tt>br</tt>' Instruction</a></li>
+ <li><a href="#i_switch">'<tt>switch</tt>' Instruction</a></li>
+ <li><a href="#i_invoke">'<tt>invoke</tt>' Instruction</a></li>
+ <li><a href="#i_unwind">'<tt>unwind</tt>' Instruction</a></li>
+ </ol>
+ </li>
+ <li><a href="#binaryops">Binary Operations</a>
+ <ol>
+ <li><a href="#i_add">'<tt>add</tt>' Instruction</a></li>
+ <li><a href="#i_sub">'<tt>sub</tt>' Instruction</a></li>
+ <li><a href="#i_mul">'<tt>mul</tt>' Instruction</a></li>
+ <li><a href="#i_div">'<tt>div</tt>' Instruction</a></li>
+ <li><a href="#i_rem">'<tt>rem</tt>' Instruction</a></li>
+ <li><a href="#i_setcc">'<tt>set<i>cc</i></tt>' Instructions</a></li>
+ </ol>
+ </li>
+ <li><a href="#bitwiseops">Bitwise Binary Operations</a>
+ <ol>
+ <li><a href="#i_and">'<tt>and</tt>' Instruction</a></li>
+ <li><a href="#i_or">'<tt>or</tt>' Instruction</a></li>
+ <li><a href="#i_xor">'<tt>xor</tt>' Instruction</a></li>
+ <li><a href="#i_shl">'<tt>shl</tt>' Instruction</a></li>
+ <li><a href="#i_shr">'<tt>shr</tt>' Instruction</a></li>
+ </ol>
+ </li>
+ <li><a href="#memoryops">Memory Access Operations</a>
+ <ol>
+ <li><a href="#i_malloc">'<tt>malloc</tt>' Instruction</a></li>
+ <li><a href="#i_free">'<tt>free</tt>' Instruction</a></li>
+ <li><a href="#i_alloca">'<tt>alloca</tt>' Instruction</a></li>
+ <li><a href="#i_load">'<tt>load</tt>' Instruction</a></li>
+ <li><a href="#i_store">'<tt>store</tt>' Instruction</a></li>
+ <li><a href="#i_getelementptr">'<tt>getelementptr</tt>' Instruction</a></li>
+ </ol>
+ </li>
+ <li><a href="#otherops">Other Operations</a>
+ <ol>
+ <li><a href="#i_phi">'<tt>phi</tt>' Instruction</a></li>
+ <li><a href="#i_cast">'<tt>cast .. to</tt>' Instruction</a></li>
+ <li><a href="#i_select">'<tt>select</tt>' Instruction</a></li>
+ <li><a href="#i_call">'<tt>call</tt>' Instruction</a></li>
+ <li><a href="#i_vanext">'<tt>vanext</tt>' Instruction</a></li>
+ <li><a href="#i_vaarg">'<tt>vaarg</tt>' Instruction</a></li>
+ </ol>
+ </li>
+ </ol>
+ </li>
+ <li><a href="#intrinsics">Intrinsic Functions</a>
+ <ol>
+ <li><a href="#int_varargs">Variable Argument Handling Intrinsics</a>
+ <ol>
+ <li><a href="#i_va_start">'<tt>llvm.va_start</tt>' Intrinsic</a></li>
+ <li><a href="#i_va_end">'<tt>llvm.va_end</tt>' Intrinsic</a></li>
+ <li><a href="#i_va_copy">'<tt>llvm.va_copy</tt>' Intrinsic</a></li>
+ </ol>
+ </li>
+ <li><a href="#int_gc">Accurate Garbage Collection Intrinsics</a>
+ <ol>
+ <li><a href="#i_gcroot">'<tt>llvm.gcroot</tt>' Intrinsic</a></li>
+ <li><a href="#i_gcread">'<tt>llvm.gcread</tt>' Intrinsic</a></li>
+ <li><a href="#i_gcwrite">'<tt>llvm.gcwrite</tt>' Intrinsic</a></li>
+ </ol>
+ </li>
+ <li><a href="#int_codegen">Code Generator Intrinsics</a>
+ <ol>
+ <li><a href="#i_returnaddress">'<tt>llvm.returnaddress</tt>' Intrinsic</a></li>
+ <li><a href="#i_frameaddress">'<tt>llvm.frameaddress</tt>' Intrinsic</a></li>
+ </ol>
+ </li>
+ <li><a href="#int_os">Operating System Intrinsics</a>
+ <ol>
+ <li><a href="#i_readport">'<tt>llvm.readport</tt>' Intrinsic</a></li>
+ <li><a href="#i_writeport">'<tt>llvm.writeport</tt>' Intrinsic</a></li>
+ <li><a href="#i_readio">'<tt>llvm.readio</tt>' Intrinsic</a></li>
+ <li><a href="#i_writeio">'<tt>llvm.writeio</tt>' Intrinsic</a></li>
+ </ol>
+ <li><a href="#int_libc">Standard C Library Intrinsics</a>
+ <ol>
+ <li><a href="#i_memcpy">'<tt>llvm.memcpy</tt>' Intrinsic</a></li>
+ <li><a href="#i_memmove">'<tt>llvm.memmove</tt>' Intrinsic</a></li>
+ <li><a href="#i_memset">'<tt>llvm.memset</tt>' Intrinsic</a></li>
+ <li><a href="#i_isunordered">'<tt>llvm.isunordered</tt>' Intrinsic</a></li>
+ </ol>
+ </li>
+ <li><a href="#int_debugger">Debugger intrinsics</a></li>
+ </ol>
+ </li>
+ </ol>
+
+ <div class="doc_author">
+ <p>Written by <a href="mailto:sabre at nondot.org">Chris Lattner</a>
+ and <a href="mailto:vadve at cs.uiuc.edu">Vikram Adve</a></p>
+ </div>
+
+ <!-- *********************************************************************** -->
+ <div class="doc_section"> <a name="abstract">Abstract </a></div>
+ <!-- *********************************************************************** -->
+
+ <div class="doc_text">
+ <p>This document is a reference manual for the LLVM assembly language.
+ LLVM is an SSA based representation that provides type safety,
+ low-level operations, flexibility, and the capability of representing
+ 'all' high-level languages cleanly. It is the common code
+ representation used throughout all phases of the LLVM compilation
+ strategy.</p>
+ </div>
+
+ <!-- *********************************************************************** -->
+ <div class="doc_section"> <a name="introduction">Introduction</a> </div>
+ <!-- *********************************************************************** -->
+
+ <div class="doc_text">
+
+ <p>The LLVM code representation is designed to be used in three
+ different forms: as an in-memory compiler IR, as an on-disk bytecode
+ representation (suitable for fast loading by a Just-In-Time compiler),
+ and as a human readable assembly language representation. This allows
+ LLVM to provide a powerful intermediate representation for efficient
+ compiler transformations and analysis, while providing a natural means
+ to debug and visualize the transformations. The three different forms
+ of LLVM are all equivalent. This document describes the human readable
+ representation and notation.</p>
+
+ <p>The LLVM representation aims to be a light-weight and low-level
+ while being expressive, typed, and extensible at the same time. It
+ aims to be a "universal IR" of sorts, by being at a low enough level
+ that high-level ideas may be cleanly mapped to it (similar to how
+ microprocessors are "universal IR's", allowing many source languages to
+ be mapped to them). By providing type information, LLVM can be used as
+ the target of optimizations: for example, through pointer analysis, it
+ can be proven that a C automatic variable is never accessed outside of
+ the current function... allowing it to be promoted to a simple SSA
+ value instead of a memory location.</p>
+
+ </div>
+
+ <!-- _______________________________________________________________________ -->
+ <div class="doc_subsubsection"> <a name="wellformed">Well-Formedness</a> </div>
+
+ <div class="doc_text">
+
+ <p>It is important to note that this document describes 'well formed'
+ LLVM assembly language. There is a difference between what the parser
+ accepts and what is considered 'well formed'. For example, the
+ following instruction is syntactically okay, but not well formed:</p>
+
+ <pre>
+ %x = <a href="#i_add">add</a> int 1, %x
+ </pre>
+
+ <p>...because the definition of <tt>%x</tt> does not dominate all of
+ its uses. The LLVM infrastructure provides a verification pass that may
+ be used to verify that an LLVM module is well formed. This pass is
+ automatically run by the parser after parsing input assembly, and by
+ the optimizer before it outputs bytecode. The violations pointed out
+ by the verifier pass indicate bugs in transformation passes or input to
+ the parser.</p>
+
+ <!-- Describe the typesetting conventions here. --> </div>
+
+ <!-- *********************************************************************** -->
+ <div class="doc_section"> <a name="identifiers">Identifiers</a> </div>
+ <!-- *********************************************************************** -->
+
+ <div class="doc_text">
+
+ <p>LLVM uses three different forms of identifiers, for different
+ purposes:</p>
+
+ <ol>
+ <li>Numeric constants are represented as you would expect: 12, -3
+ 123.421, etc. Floating point constants have an optional hexadecimal
+ notation.</li>
+ <li>Named values are represented as a string of characters with a '%'
+ prefix. For example, %foo, %DivisionByZero,
+ %a.really.long.identifier. The actual regular expression used is '<tt>%[a-zA-Z$._][a-zA-Z$._0-9]*</tt>'.
+ Identifiers which require other characters in their names can be
+ surrounded with quotes. In this way, anything except a <tt>"</tt>
+ character can be used in a name.</li>
+ <li>Unnamed values are represented as an unsigned numeric value with
+ a '%' prefix. For example, %12, %2, %44.</li>
+ </ol>
+ <p>LLVM requires that values start with a '%' sign for two reasons:
+ Compilers don't need to worry about name clashes with reserved words,
+ and the set of reserved words may be expanded in the future without
+ penalty. Additionally, unnamed identifiers allow a compiler to quickly
+ come up with a temporary variable without having to avoid symbol table
+ conflicts.</p>
+ <p>Reserved words in LLVM are very similar to reserved words in other
+ languages. There are keywords for different opcodes ('<tt><a
+ href="#i_add">add</a></tt>', '<tt><a href="#i_cast">cast</a></tt>', '<tt><a
+ href="#i_ret">ret</a></tt>', etc...), for primitive type names ('<tt><a
+ href="#t_void">void</a></tt>', '<tt><a href="#t_uint">uint</a></tt>',
+ etc...), and others. These reserved words cannot conflict with
+ variable names, because none of them start with a '%' character.</p>
+ <p>Here is an example of LLVM code to multiply the integer variable '<tt>%X</tt>'
+ by 8:</p>
+ <p>The easy way:</p>
+ <pre> %result = <a href="#i_mul">mul</a> uint %X, 8<br></pre>
+ <p>After strength reduction:</p>
+ <pre> %result = <a href="#i_shl">shl</a> uint %X, ubyte 3<br></pre>
+ <p>And the hard way:</p>
+ <pre> <a href="#i_add">add</a> uint %X, %X <i>; yields {uint}:%0</i>
+ <a
+ href="#i_add">add</a> uint %0, %0 <i>; yields {uint}:%1</i>
+ %result = <a
+ href="#i_add">add</a> uint %1, %1<br></pre>
+ <p>This last way of multiplying <tt>%X</tt> by 8 illustrates several
+ important lexical features of LLVM:</p>
+ <ol>
+ <li>Comments are delimited with a '<tt>;</tt>' and go until the end
+ of line.</li>
+ <li>Unnamed temporaries are created when the result of a computation
+ is not assigned to a named value.</li>
+ <li>Unnamed temporaries are numbered sequentially</li>
+ </ol>
+ <p>...and it also show a convention that we follow in this document.
+ When demonstrating instructions, we will follow an instruction with a
+ comment that defines the type and name of value produced. Comments are
+ shown in italic text.</p>
+ <p>The one non-intuitive notation for constants is the optional
+ hexidecimal form of floating point constants. For example, the form '<tt>double
+ 0x432ff973cafa8000</tt>' is equivalent to (but harder to read than) '<tt>double
+ 4.5e+15</tt>' which is also supported by the parser. The only time
+ hexadecimal floating point constants are useful (and the only time that
+ they are generated by the disassembler) is when an FP constant has to
+ be emitted that is not representable as a decimal floating point number
+ exactly. For example, NaN's, infinities, and other special cases are
+ represented in their IEEE hexadecimal format so that assembly and
+ disassembly do not cause any bits to change in the constants.</p>
+ </div>
+ <!-- *********************************************************************** -->
+ <div class="doc_section"> <a name="typesystem">Type System</a> </div>
+ <!-- *********************************************************************** -->
+ <div class="doc_text">
+ <p>The LLVM type system is one of the most important features of the
+ intermediate representation. Being typed enables a number of
+ optimizations to be performed on the IR directly, without having to do
+ extra analyses on the side before the transformation. A strong type
+ system makes it easier to read the generated code and enables novel
+ analyses and transformations that are not feasible to perform on normal
+ three address code representations.</p>
+ <!-- The written form for the type system was heavily influenced by the
+ syntactic problems with types in the C language<sup><a
+ href="#rw_stroustrup">1</a></sup>.<p> --> </div>
+ <!-- ======================================================================= -->
+ <div class="doc_subsection"> <a name="t_primitive">Primitive Types</a> </div>
+ <div class="doc_text">
+ <p>The primitive types are the fundamental building blocks of the LLVM
+ system. The current set of primitive types are as follows:</p>
+
+ <table border="0" style="align: center">
+ <tbody>
+ <tr>
+ <td>
+ <table border="1" cellspacing="0" cellpadding="4" style="align: center">
+ <tbody>
+ <tr>
+ <td><tt>void</tt></td>
+ <td>No value</td>
+ </tr>
+ <tr>
+ <td><tt>ubyte</tt></td>
+ <td>Unsigned 8 bit value</td>
+ </tr>
+ <tr>
+ <td><tt>ushort</tt></td>
+ <td>Unsigned 16 bit value</td>
+ </tr>
+ <tr>
+ <td><tt>uint</tt></td>
+ <td>Unsigned 32 bit value</td>
+ </tr>
+ <tr>
+ <td><tt>ulong</tt></td>
+ <td>Unsigned 64 bit value</td>
+ </tr>
+ <tr>
+ <td><tt>float</tt></td>
+ <td>32 bit floating point value</td>
+ </tr>
+ <tr>
+ <td><tt>label</tt></td>
+ <td>Branch destination</td>
+ </tr>
+ </tbody>
+ </table>
+ </td>
+ <td valign="top">
+ <table border="1" cellspacing="0" cellpadding="4">
+ <tbody>
+ <tr>
+ <td><tt>bool</tt></td>
+ <td>True or False value</td>
+ </tr>
+ <tr>
+ <td><tt>sbyte</tt></td>
+ <td>Signed 8 bit value</td>
+ </tr>
+ <tr>
+ <td><tt>short</tt></td>
+ <td>Signed 16 bit value</td>
+ </tr>
+ <tr>
+ <td><tt>int</tt></td>
+ <td>Signed 32 bit value</td>
+ </tr>
+ <tr>
+ <td><tt>long</tt></td>
+ <td>Signed 64 bit value</td>
+ </tr>
+ <tr>
+ <td><tt>double</tt></td>
+ <td>64 bit floating point value</td>
+ </tr>
+ </tbody>
+ </table>
+ </td>
+ </tr>
+ </tbody>
+ </table>
+
+ </div>
+ <!-- _______________________________________________________________________ -->
+ <div class="doc_subsubsection"> <a name="t_classifications">Type
+ Classifications</a> </div>
+ <div class="doc_text">
+ <p>These different primitive types fall into a few useful
+ classifications:</p>
+
+ <table border="1" cellspacing="0" cellpadding="4">
+ <tbody>
+ <tr>
+ <td><a name="t_signed">signed</a></td>
+ <td><tt>sbyte, short, int, long, float, double</tt></td>
+ </tr>
+ <tr>
+ <td><a name="t_unsigned">unsigned</a></td>
+ <td><tt>ubyte, ushort, uint, ulong</tt></td>
+ </tr>
+ <tr>
+ <td><a name="t_integer">integer</a></td>
+ <td><tt>ubyte, sbyte, ushort, short, uint, int, ulong, long</tt></td>
+ </tr>
+ <tr>
+ <td><a name="t_integral">integral</a></td>
+ <td><tt>bool, ubyte, sbyte, ushort, short, uint, int, ulong, long</tt></td>
+ </tr>
+ <tr>
+ <td><a name="t_floating">floating point</a></td>
+ <td><tt>float, double</tt></td>
+ </tr>
+ <tr>
+ <td><a name="t_firstclass">first class</a></td>
+ <td><tt>bool, ubyte, sbyte, ushort, short,<br>
+ uint, int, ulong, long, float, double, <a href="#t_pointer">pointer</a></tt></td>
+ </tr>
+ </tbody>
+ </table>
+
+ <p>The <a href="#t_firstclass">first class</a> types are perhaps the
+ most important. Values of these types are the only ones which can be
+ produced by instructions, passed as arguments, or used as operands to
+ instructions. This means that all structures and arrays must be
+ manipulated either by pointer or by component.</p>
+ </div>
+ <!-- ======================================================================= -->
+ <div class="doc_subsection"> <a name="t_derived">Derived Types</a> </div>
+ <div class="doc_text">
+ <p>The real power in LLVM comes from the derived types in the system.
+ This is what allows a programmer to represent arrays, functions,
+ pointers, and other useful types. Note that these derived types may be
+ recursive: For example, it is possible to have a two dimensional array.</p>
+ </div>
+ <!-- _______________________________________________________________________ -->
+ <div class="doc_subsubsection"> <a name="t_array">Array Type</a> </div>
+ <div class="doc_text">
+ <h5>Overview:</h5>
+ <p>The array type is a very simple derived type that arranges elements
+ sequentially in memory. The array type requires a size (number of
+ elements) and an underlying data type.</p>
+ <h5>Syntax:</h5>
+ <pre> [<# elements> x <elementtype>]<br></pre>
+ <p>The number of elements is a constant integer value, elementtype may
+ be any type with a size.</p>
+ <h5>Examples:</h5>
+ <p> <tt>[40 x int ]</tt>: Array of 40 integer values.<br>
+ <tt>[41 x int ]</tt>: Array of 41 integer values.<br>
+ <tt>[40 x uint]</tt>: Array of 40 unsigned integer values.</p>
+ <p> </p>
+ <p>Here are some examples of multidimensional arrays:</p>
+
+ <table border="0" cellpadding="0" cellspacing="0">
+ <tbody>
+ <tr>
+ <td><tt>[3 x [4 x int]]</tt></td>
+ <td>: 3x4 array integer values.</td>
+ </tr>
+ <tr>
+ <td><tt>[12 x [10 x float]]</tt></td>
+ <td>: 12x10 array of single precision floating point values.</td>
+ </tr>
+ <tr>
+ <td><tt>[2 x [3 x [4 x uint]]]</tt></td>
+ <td>: 2x3x4 array of unsigned integer values.</td>
+ </tr>
+ </tbody>
+ </table>
+
+ </div>
+ <!-- _______________________________________________________________________ -->
+ <div class="doc_subsubsection"> <a name="t_function">Function Type</a> </div>
+ <div class="doc_text">
+ <h5>Overview:</h5>
+ <p>The function type can be thought of as a function signature. It
+ consists of a return type and a list of formal parameter types.
+ Function types are usually used to build virtual function tables
+ (which are structures of pointers to functions), for indirect function
+ calls, and when defining a function.</p>
+ <p>
+ The return type of a function type cannot be an aggregate type.
+ </p>
+ <h5>Syntax:</h5>
+ <pre> <returntype> (<parameter list>)<br></pre>
+ <p>Where '<tt><parameter list></tt>' is a comma-separated list of
+ type specifiers. Optionally, the parameter list may include a type <tt>...</tt>,
+ which indicates that the function takes a variable number of arguments.
+ Variable argument functions can access their arguments with the <a
+ href="#int_varargs">variable argument handling intrinsic</a> functions.</p>
+ <h5>Examples:</h5>
+
+ <table border="0" cellpadding="0" cellspacing="0">
+ <tbody>
+ <tr>
+ <td><tt>int (int)</tt></td>
+ <td>: function taking an <tt>int</tt>, returning an <tt>int</tt></td>
+ </tr>
+ <tr>
+ <td><tt>float (int, int *) *</tt></td>
+ <td>: <a href="#t_pointer">Pointer</a> to a function that takes
+ an <tt>int</tt> and a <a href="#t_pointer">pointer</a> to <tt>int</tt>,
+ returning <tt>float</tt>.</td>
+ </tr>
+ <tr>
+ <td><tt>int (sbyte *, ...)</tt></td>
+ <td>: A vararg function that takes at least one <a
+ href="#t_pointer">pointer</a> to <tt>sbyte</tt> (signed char in C),
+ which returns an integer. This is the signature for <tt>printf</tt>
+ in LLVM.</td>
+ </tr>
+ </tbody>
+ </table>
+
+ </div>
+ <!-- _______________________________________________________________________ -->
+ <div class="doc_subsubsection"> <a name="t_struct">Structure Type</a> </div>
+ <div class="doc_text">
+ <h5>Overview:</h5>
+ <p>The structure type is used to represent a collection of data members
+ together in memory. The packing of the field types is defined to match
+ the ABI of the underlying processor. The elements of a structure may
+ be any type that has a size.</p>
+ <p>Structures are accessed using '<tt><a href="#i_load">load</a></tt>
+ and '<tt><a href="#i_store">store</a></tt>' by getting a pointer to a
+ field with the '<tt><a href="#i_getelementptr">getelementptr</a></tt>'
+ instruction.</p>
+ <h5>Syntax:</h5>
+ <pre> { <type list> }<br></pre>
+ <h5>Examples:</h5>
+
+ <table border="0" cellpadding="0" cellspacing="0">
+ <tbody>
+ <tr>
+ <td><tt>{ int, int, int }</tt></td>
+ <td>: a triple of three <tt>int</tt> values</td>
+ </tr>
+ <tr>
+ <td><tt>{ float, int (int) * }</tt></td>
+ <td>: A pair, where the first element is a <tt>float</tt> and the
+ second element is a <a href="#t_pointer">pointer</a> to a <a
+ href="#t_function">function</a> that takes an <tt>int</tt>, returning
+ an <tt>int</tt>.</td>
+ </tr>
+ </tbody>
+ </table>
+
+ </div>
+ <!-- _______________________________________________________________________ -->
+ <div class="doc_subsubsection"> <a name="t_pointer">Pointer Type</a> </div>
+ <div class="doc_text">
+ <h5>Overview:</h5>
+ <p>As in many languages, the pointer type represents a pointer or
+ reference to another object, which must live in memory.</p>
+ <h5>Syntax:</h5>
+ <pre> <type> *<br></pre>
+ <h5>Examples:</h5>
+
+ <table border="0" cellpadding="0" cellspacing="0">
+ <tbody>
+ <tr>
+ <td><tt>[4x int]*</tt></td>
+ <td>: <a href="#t_pointer">pointer</a> to <a href="#t_array">array</a>
+ of four <tt>int</tt> values</td>
+ </tr>
+ <tr>
+ <td><tt>int (int *) *</tt></td>
+ <td>: A <a href="#t_pointer">pointer</a> to a <a
+ href="#t_function">function</a> that takes an <tt>int</tt>, returning
+ an <tt>int</tt>.</td>
+ </tr>
+ </tbody>
+ </table>
+
+ </div>
+ <!-- _______________________________________________________________________ --><!--
+ <div class="doc_subsubsection">
+ <a name="t_packed">Packed Type</a>
+ </div>
+
+ <div class="doc_text">
+
+ Mention/decide that packed types work with saturation or not. Maybe have a packed+saturated type in addition to just a packed type.<p>
+
+ Packed types should be 'nonsaturated' because standard data types are not saturated. Maybe have a saturated packed type?<p>
+
+ </div>
+
+ --><!-- *********************************************************************** -->
+ <div class="doc_section"> <a name="highlevel">High Level Structure</a> </div>
+ <!-- *********************************************************************** --><!-- ======================================================================= -->
+ <div class="doc_subsection"> <a name="modulestructure">Module Structure</a> </div>
+ <div class="doc_text">
+ <p>LLVM programs are composed of "Module"s, each of which is a
+ translation unit of the input programs. Each module consists of
+ functions, global variables, and symbol table entries. Modules may be
+ combined together with the LLVM linker, which merges function (and
+ global variable) definitions, resolves forward declarations, and merges
+ symbol table entries. Here is an example of the "hello world" module:</p>
+ <pre><i>; Declare the string constant as a global constant...</i>
+ <a href="#identifiers">%.LC0</a> = <a href="#linkage_internal">internal</a> <a
+ href="#globalvars">constant</a> <a href="#t_array">[13 x sbyte]</a> c"hello world\0A\00" <i>; [13 x sbyte]*</i>
+
+ <i>; External declaration of the puts function</i>
+ <a href="#functionstructure">declare</a> int %puts(sbyte*) <i>; int(sbyte*)* </i>
+
+ <i>; Definition of main function</i>
+ int %main() { <i>; int()* </i>
+ <i>; Convert [13x sbyte]* to sbyte *...</i>
+ %cast210 = <a
+ href="#i_getelementptr">getelementptr</a> [13 x sbyte]* %.LC0, long 0, long 0 <i>; sbyte*</i>
+
+ <i>; Call puts function to write out the string to stdout...</i>
+ <a
+ href="#i_call">call</a> int %puts(sbyte* %cast210) <i>; int</i>
+ <a
+ href="#i_ret">ret</a> int 0<br>}<br></pre>
+ <p>This example is made up of a <a href="#globalvars">global variable</a>
+ named "<tt>.LC0</tt>", an external declaration of the "<tt>puts</tt>"
+ function, and a <a href="#functionstructure">function definition</a>
+ for "<tt>main</tt>".</p>
+ <a name="linkage"> In general, a module is made up of a list of global
+ values, where both functions and global variables are global values.
+ Global values are represented by a pointer to a memory location (in
+ this case, a pointer to an array of char, and a pointer to a function),
+ and have one of the following linkage types:</a>
+ <p> </p>
+ <dl>
+ <dt><tt><b><a name="linkage_internal">internal</a></b></tt> </dt>
+ <dd>Global values with internal linkage are only directly accessible
+ by objects in the current module. In particular, linking code into a
+ module with an internal global value may cause the internal to be
+ renamed as necessary to avoid collisions. Because the symbol is
+ internal to the module, all references can be updated. This
+ corresponds to the notion of the '<tt>static</tt>' keyword in C, or the
+ idea of "anonymous namespaces" in C++.
+ <p> </p>
+ </dd>
+ <dt><tt><b><a name="linkage_linkonce">linkonce</a></b></tt>: </dt>
+ <dd>"<tt>linkonce</tt>" linkage is similar to <tt>internal</tt>
+ linkage, with the twist that linking together two modules defining the
+ same <tt>linkonce</tt> globals will cause one of the globals to be
+ discarded. This is typically used to implement inline functions.
+ Unreferenced <tt>linkonce</tt> globals are allowed to be discarded.
+ <p> </p>
+ </dd>
+ <dt><tt><b><a name="linkage_weak">weak</a></b></tt>: </dt>
+ <dd>"<tt>weak</tt>" linkage is exactly the same as <tt>linkonce</tt>
+ linkage, except that unreferenced <tt>weak</tt> globals may not be
+ discarded. This is used to implement constructs in C such as "<tt>int
+ X;</tt>" at global scope.
+ <p> </p>
+ </dd>
+ <dt><tt><b><a name="linkage_appending">appending</a></b></tt>: </dt>
+ <dd>"<tt>appending</tt>" linkage may only be applied to global
+ variables of pointer to array type. When two global variables with
+ appending linkage are linked together, the two global arrays are
+ appended together. This is the LLVM, typesafe, equivalent of having
+ the system linker append together "sections" with identical names when
+ .o files are linked.
+ <p> </p>
+ </dd>
+ <dt><tt><b><a name="linkage_external">externally visible</a></b></tt>:</dt>
+ <dd>If none of the above identifiers are used, the global is
+ externally visible, meaning that it participates in linkage and can be
+ used to resolve external symbol references.
+ <p> </p>
+ </dd>
+ </dl>
+ <p> </p>
+ <p><a name="linkage_external">For example, since the "<tt>.LC0</tt>"
+ variable is defined to be internal, if another module defined a "<tt>.LC0</tt>"
+ variable and was linked with this one, one of the two would be renamed,
+ preventing a collision. Since "<tt>main</tt>" and "<tt>puts</tt>" are
+ external (i.e., lacking any linkage declarations), they are accessible
+ outside of the current module. It is illegal for a function <i>declaration</i>
+ to have any linkage type other than "externally visible".</a></p>
+ </div>
+
+ <!-- ======================================================================= -->
+ <div class="doc_subsection">
+ <a name="globalvars">Global Variables</a>
+ </div>
+
+ <div class="doc_text">
+
+ <p>Global variables define regions of memory allocated at compilation
+ time instead of run-time. Global variables may optionally be
+ initialized. A variable may be defined as a global "constant", which
+ indicates that the contents of the variable will never be modified
+ (opening options for optimization).</p>
+
+ <p>As SSA values, global variables define pointer values that are in
+ scope (i.e. they dominate) for all basic blocks in the program. Global
+ variables always define a pointer to their "content" type because they
+ describe a region of memory, and all memory objects in LLVM are
+ accessed through pointers.</p>
+
+ </div>
+
+
+ <!-- ======================================================================= -->
+ <div class="doc_subsection">
+ <a name="functionstructure">Functions</a>
+ </div>
+
+ <div class="doc_text">
+
+ <p>LLVM function definitions are composed of a (possibly empty) argument list,
+ an opening curly brace, a list of basic blocks, and a closing curly brace. LLVM
+ function declarations are defined with the "<tt>declare</tt>" keyword, a
+ function name, and a function signature.</p>
+
+ <p>A function definition contains a list of basic blocks, forming the CFG for
+ the function. Each basic block may optionally start with a label (giving the
+ basic block a symbol table entry), contains a list of instructions, and ends
+ with a <a href="#terminators">terminator</a> instruction (such as a branch or
+ function return).</p>
+
+ <p>The first basic block in program is special in two ways: it is immediately
+ executed on entrance to the function, and it is not allowed to have predecessor
+ basic blocks (i.e. there can not be any branches to the entry block of a
+ function). Because the block can have no predecessors, it also cannot have any
+ <a href="#i_phi">PHI nodes</a>.</p>
+
+ <p>LLVM functions are identified by their name and type signature. Hence, two
+ functions with the same name but different parameter lists or return values are
+ considered different functions, and LLVM will resolves references to each
+ appropriately.</p>
+
+ </div>
+
+
+ <!-- *********************************************************************** -->
+ <div class="doc_section"> <a name="instref">Instruction Reference</a> </div>
+ <!-- *********************************************************************** -->
+ <div class="doc_text">
+ <p>The LLVM instruction set consists of several different
+ classifications of instructions: <a href="#terminators">terminator
+ instructions</a>, <a href="#binaryops">binary instructions</a>, <a
+ href="#memoryops">memory instructions</a>, and <a href="#otherops">other
+ instructions</a>.</p>
+ </div>
+ <!-- ======================================================================= -->
+ <div class="doc_subsection"> <a name="terminators">Terminator
+ Instructions</a> </div>
+ <div class="doc_text">
+ <p>As mentioned <a href="#functionstructure">previously</a>, every
+ basic block in a program ends with a "Terminator" instruction, which
+ indicates which block should be executed after the current block is
+ finished. These terminator instructions typically yield a '<tt>void</tt>'
+ value: they produce control flow, not values (the one exception being
+ the '<a href="#i_invoke"><tt>invoke</tt></a>' instruction).</p>
+ <p>There are five different terminator instructions: the '<a
+ href="#i_ret"><tt>ret</tt></a>' instruction, the '<a href="#i_br"><tt>br</tt></a>'
+ instruction, the '<a href="#i_switch"><tt>switch</tt></a>' instruction,
+ the '<a href="#i_invoke"><tt>invoke</tt></a>' instruction, and the '<a
+ href="#i_unwind"><tt>unwind</tt></a>' instruction.</p>
+ </div>
+ <!-- _______________________________________________________________________ -->
+ <div class="doc_subsubsection"> <a name="i_ret">'<tt>ret</tt>'
+ Instruction</a> </div>
+ <div class="doc_text">
+ <h5>Syntax:</h5>
+ <pre> ret <type> <value> <i>; Return a value from a non-void function</i>
+ ret void <i>; Return from void function</i>
+ </pre>
+ <h5>Overview:</h5>
+ <p>The '<tt>ret</tt>' instruction is used to return control flow (and a
+ value) from a function, back to the caller.</p>
+ <p>There are two forms of the '<tt>ret</tt>' instruction: one that
+ returns a value and then causes control flow, and one that just causes
+ control flow to occur.</p>
+ <h5>Arguments:</h5>
+ <p>The '<tt>ret</tt>' instruction may return any '<a
+ href="#t_firstclass">first class</a>' type. Notice that a function is
+ not <a href="#wellformed">well formed</a> if there exists a '<tt>ret</tt>'
+ instruction inside of the function that returns a value that does not
+ match the return type of the function.</p>
+ <h5>Semantics:</h5>
+ <p>When the '<tt>ret</tt>' instruction is executed, control flow
+ returns back to the calling function's context. If the caller is a "<a
+ href="#i_call"><tt>call</tt></a>" instruction, execution continues at
+ the instruction after the call. If the caller was an "<a
+ href="#i_invoke"><tt>invoke</tt></a>" instruction, execution continues
+ at the beginning "normal" of the destination block. If the instruction
+ returns a value, that value shall set the call or invoke instruction's
+ return value.</p>
+ <h5>Example:</h5>
+ <pre> ret int 5 <i>; Return an integer value of 5</i>
+ ret void <i>; Return from a void function</i>
+ </pre>
+ </div>
+ <!-- _______________________________________________________________________ -->
+ <div class="doc_subsubsection"> <a name="i_br">'<tt>br</tt>' Instruction</a> </div>
+ <div class="doc_text">
+ <h5>Syntax:</h5>
+ <pre> br bool <cond>, label <iftrue>, label <iffalse><br> br label <dest> <i>; Unconditional branch</i>
+ </pre>
+ <h5>Overview:</h5>
+ <p>The '<tt>br</tt>' instruction is used to cause control flow to
+ transfer to a different basic block in the current function. There are
+ two forms of this instruction, corresponding to a conditional branch
+ and an unconditional branch.</p>
+ <h5>Arguments:</h5>
+ <p>The conditional branch form of the '<tt>br</tt>' instruction takes a
+ single '<tt>bool</tt>' value and two '<tt>label</tt>' values. The
+ unconditional form of the '<tt>br</tt>' instruction takes a single '<tt>label</tt>'
+ value as a target.</p>
+ <h5>Semantics:</h5>
+ <p>Upon execution of a conditional '<tt>br</tt>' instruction, the '<tt>bool</tt>'
+ argument is evaluated. If the value is <tt>true</tt>, control flows
+ to the '<tt>iftrue</tt>' <tt>label</tt> argument. If "cond" is <tt>false</tt>,
+ control flows to the '<tt>iffalse</tt>' <tt>label</tt> argument.</p>
+ <h5>Example:</h5>
+ <pre>Test:<br> %cond = <a href="#i_setcc">seteq</a> int %a, %b<br> br bool %cond, label %IfEqual, label %IfUnequal<br>IfEqual:<br> <a
+ href="#i_ret">ret</a> int 1<br>IfUnequal:<br> <a href="#i_ret">ret</a> int 0<br></pre>
+ </div>
+ <!-- _______________________________________________________________________ -->
+ <div class="doc_subsubsection">
+ <a name="i_switch">'<tt>switch</tt>' Instruction</a>
+ </div>
+
+ <div class="doc_text">
+ <h5>Syntax:</h5>
+
+ <pre>
+ switch <intty> <value>, label <defaultdest> [ <intty> <val>, label <dest> ... ]
+ </pre>
+
+ <h5>Overview:</h5>
+
+ <p>The '<tt>switch</tt>' instruction is used to transfer control flow to one of
+ several different places. It is a generalization of the '<tt>br</tt>'
+ instruction, allowing a branch to occur to one of many possible
+ destinations.</p>
+
+
+ <h5>Arguments:</h5>
+
+ <p>The '<tt>switch</tt>' instruction uses three parameters: an integer
+ comparison value '<tt>value</tt>', a default '<tt>label</tt>' destination, and
+ an array of pairs of comparison value constants and '<tt>label</tt>'s. The
+ table is not allowed to contain duplicate constant entries.</p>
+
+ <h5>Semantics:</h5>
+
+ <p>The <tt>switch</tt> instruction specifies a table of values and
+ destinations. When the '<tt>switch</tt>' instruction is executed, this
+ table is searched for the given value. If the value is found, control flow is
+ transfered to the corresponding destination; otherwise, control flow is
+ transfered to the default destination.</p>
+
+ <h5>Implementation:</h5>
+
+ <p>Depending on properties of the target machine and the particular
+ <tt>switch</tt> instruction, this instruction may be code generated in different
+ ways. For example, it could be generated as a series of chained conditional
+ branches or with a lookup table.</p>
+
+ <h5>Example:</h5>
+
+ <pre>
+ <i>; Emulate a conditional br instruction</i>
+ %Val = <a href="#i_cast">cast</a> bool %value to int
+ switch int %Val, label %truedest [int 0, label %falsedest ]
+
+ <i>; Emulate an unconditional br instruction</i>
+ switch uint 0, label %dest [ ]
+
+ <i>; Implement a jump table:</i>
+ switch uint %val, label %otherwise [ uint 0, label %onzero
+ uint 1, label %onone
+ uint 2, label %ontwo ]
+ </pre>
+ </div>
+ <!-- _______________________________________________________________________ -->
+ <div class="doc_subsubsection"> <a name="i_invoke">'<tt>invoke</tt>'
+ Instruction</a> </div>
+ <div class="doc_text">
+ <h5>Syntax:</h5>
+ <pre> <result> = invoke <ptr to function ty> %<function ptr val>(<function args>)<br> to label <normal label> except label <exception label><br></pre>
+ <h5>Overview:</h5>
+ <p>The '<tt>invoke</tt>' instruction causes control to transfer to a
+ specified function, with the possibility of control flow transfer to
+ either the '<tt>normal</tt>' <tt>label</tt> label or the '<tt>exception</tt>'<tt>label</tt>.
+ If the callee function returns with the "<tt><a href="#i_ret">ret</a></tt>"
+ instruction, control flow will return to the "normal" label. If the
+ callee (or any indirect callees) returns with the "<a href="#i_unwind"><tt>unwind</tt></a>"
+ instruction, control is interrupted, and continued at the dynamically
+ nearest "except" label.</p>
+ <h5>Arguments:</h5>
+ <p>This instruction requires several arguments:</p>
+ <ol>
+ <li>'<tt>ptr to function ty</tt>': shall be the signature of the
+ pointer to function value being invoked. In most cases, this is a
+ direct function invocation, but indirect <tt>invoke</tt>s are just as
+ possible, branching off an arbitrary pointer to function value. </li>
+ <li>'<tt>function ptr val</tt>': An LLVM value containing a pointer
+ to a function to be invoked. </li>
+ <li>'<tt>function args</tt>': argument list whose types match the
+ function signature argument types. If the function signature indicates
+ the function accepts a variable number of arguments, the extra
+ arguments can be specified. </li>
+ <li>'<tt>normal label</tt>': the label reached when the called
+ function executes a '<tt><a href="#i_ret">ret</a></tt>' instruction. </li>
+ <li>'<tt>exception label</tt>': the label reached when a callee
+ returns with the <a href="#i_unwind"><tt>unwind</tt></a> instruction. </li>
+ </ol>
+ <h5>Semantics:</h5>
+ <p>This instruction is designed to operate as a standard '<tt><a
+ href="#i_call">call</a></tt>' instruction in most regards. The
+ primary difference is that it establishes an association with a label,
+ which is used by the runtime library to unwind the stack.</p>
+ <p>This instruction is used in languages with destructors to ensure
+ that proper cleanup is performed in the case of either a <tt>longjmp</tt>
+ or a thrown exception. Additionally, this is important for
+ implementation of '<tt>catch</tt>' clauses in high-level languages that
+ support them.</p>
+ <h5>Example:</h5>
+ <pre> %retval = invoke int %Test(int 15)<br> to label %Continue<br> except label %TestCleanup <i>; {int}:retval set</i>
+ </pre>
+ </div>
+ <!-- _______________________________________________________________________ -->
+ <div class="doc_subsubsection"> <a name="i_unwind">'<tt>unwind</tt>'
+ Instruction</a> </div>
+ <div class="doc_text">
+ <h5>Syntax:</h5>
+ <pre> unwind<br></pre>
+ <h5>Overview:</h5>
+ <p>The '<tt>unwind</tt>' instruction unwinds the stack, continuing
+ control flow at the first callee in the dynamic call stack which used
+ an <a href="#i_invoke"><tt>invoke</tt></a> instruction to perform the
+ call. This is primarily used to implement exception handling.</p>
+ <h5>Semantics:</h5>
+ <p>The '<tt>unwind</tt>' intrinsic causes execution of the current
+ function to immediately halt. The dynamic call stack is then searched
+ for the first <a href="#i_invoke"><tt>invoke</tt></a> instruction on
+ the call stack. Once found, execution continues at the "exceptional"
+ destination block specified by the <tt>invoke</tt> instruction. If
+ there is no <tt>invoke</tt> instruction in the dynamic call chain,
+ undefined behavior results.</p>
+ </div>
+ <!-- ======================================================================= -->
+ <div class="doc_subsection"> <a name="binaryops">Binary Operations</a> </div>
+ <div class="doc_text">
+ <p>Binary operators are used to do most of the computation in a
+ program. They require two operands, execute an operation on them, and
+ produce a single value. The result value of a binary operator is not
+ necessarily the same type as its operands.</p>
+ <p>There are several different binary operators:</p>
+ </div>
+ <!-- _______________________________________________________________________ -->
+ <div class="doc_subsubsection"> <a name="i_add">'<tt>add</tt>'
+ Instruction</a> </div>
+ <div class="doc_text">
+ <h5>Syntax:</h5>
+ <pre> <result> = add <ty> <var1>, <var2> <i>; yields {ty}:result</i>
+ </pre>
+ <h5>Overview:</h5>
+ <p>The '<tt>add</tt>' instruction returns the sum of its two operands.</p>
+ <h5>Arguments:</h5>
+ <p>The two arguments to the '<tt>add</tt>' instruction must be either <a
+ href="#t_integer">integer</a> or <a href="#t_floating">floating point</a>
+ values. Both arguments must have identical types.</p>
+ <h5>Semantics:</h5>
+ <p>The value produced is the integer or floating point sum of the two
+ operands.</p>
+ <h5>Example:</h5>
+ <pre> <result> = add int 4, %var <i>; yields {int}:result = 4 + %var</i>
+ </pre>
+ </div>
+ <!-- _______________________________________________________________________ -->
+ <div class="doc_subsubsection"> <a name="i_sub">'<tt>sub</tt>'
+ Instruction</a> </div>
+ <div class="doc_text">
+ <h5>Syntax:</h5>
+ <pre> <result> = sub <ty> <var1>, <var2> <i>; yields {ty}:result</i>
+ </pre>
+ <h5>Overview:</h5>
+ <p>The '<tt>sub</tt>' instruction returns the difference of its two
+ operands.</p>
+ <p>Note that the '<tt>sub</tt>' instruction is used to represent the '<tt>neg</tt>'
+ instruction present in most other intermediate representations.</p>
+ <h5>Arguments:</h5>
+ <p>The two arguments to the '<tt>sub</tt>' instruction must be either <a
+ href="#t_integer">integer</a> or <a href="#t_floating">floating point</a>
+ values. Both arguments must have identical types.</p>
+ <h5>Semantics:</h5>
+ <p>The value produced is the integer or floating point difference of
+ the two operands.</p>
+ <h5>Example:</h5>
+ <pre> <result> = sub int 4, %var <i>; yields {int}:result = 4 - %var</i>
+ <result> = sub int 0, %val <i>; yields {int}:result = -%var</i>
+ </pre>
+ </div>
+ <!-- _______________________________________________________________________ -->
+ <div class="doc_subsubsection"> <a name="i_mul">'<tt>mul</tt>'
+ Instruction</a> </div>
+ <div class="doc_text">
+ <h5>Syntax:</h5>
+ <pre> <result> = mul <ty> <var1>, <var2> <i>; yields {ty}:result</i>
+ </pre>
+ <h5>Overview:</h5>
+ <p>The '<tt>mul</tt>' instruction returns the product of its two
+ operands.</p>
+ <h5>Arguments:</h5>
+ <p>The two arguments to the '<tt>mul</tt>' instruction must be either <a
+ href="#t_integer">integer</a> or <a href="#t_floating">floating point</a>
+ values. Both arguments must have identical types.</p>
+ <h5>Semantics:</h5>
+ <p>The value produced is the integer or floating point product of the
+ two operands.</p>
+ <p>There is no signed vs unsigned multiplication. The appropriate
+ action is taken based on the type of the operand.</p>
+ <h5>Example:</h5>
+ <pre> <result> = mul int 4, %var <i>; yields {int}:result = 4 * %var</i>
+ </pre>
+ </div>
+ <!-- _______________________________________________________________________ -->
+ <div class="doc_subsubsection"> <a name="i_div">'<tt>div</tt>'
+ Instruction</a> </div>
+ <div class="doc_text">
+ <h5>Syntax:</h5>
+ <pre> <result> = div <ty> <var1>, <var2> <i>; yields {ty}:result</i>
+ </pre>
+ <h5>Overview:</h5>
+ <p>The '<tt>div</tt>' instruction returns the quotient of its two
+ operands.</p>
+ <h5>Arguments:</h5>
+ <p>The two arguments to the '<tt>div</tt>' instruction must be either <a
+ href="#t_integer">integer</a> or <a href="#t_floating">floating point</a>
+ values. Both arguments must have identical types.</p>
+ <h5>Semantics:</h5>
+ <p>The value produced is the integer or floating point quotient of the
+ two operands.</p>
+ <h5>Example:</h5>
+ <pre> <result> = div int 4, %var <i>; yields {int}:result = 4 / %var</i>
+ </pre>
+ </div>
+ <!-- _______________________________________________________________________ -->
+ <div class="doc_subsubsection"> <a name="i_rem">'<tt>rem</tt>'
+ Instruction</a> </div>
+ <div class="doc_text">
+ <h5>Syntax:</h5>
+ <pre> <result> = rem <ty> <var1>, <var2> <i>; yields {ty}:result</i>
+ </pre>
+ <h5>Overview:</h5>
+ <p>The '<tt>rem</tt>' instruction returns the remainder from the
+ division of its two operands.</p>
+ <h5>Arguments:</h5>
+ <p>The two arguments to the '<tt>rem</tt>' instruction must be either <a
+ href="#t_integer">integer</a> or <a href="#t_floating">floating point</a>
+ values. Both arguments must have identical types.</p>
+ <h5>Semantics:</h5>
+ <p>This returns the <i>remainder</i> of a division (where the result
+ has the same sign as the divisor), not the <i>modulus</i> (where the
+ result has the same sign as the dividend) of a value. For more
+ information about the difference, see: <a
+ href="http://mathforum.org/dr.math/problems/anne.4.28.99.html">The
+ Math Forum</a>.</p>
+ <h5>Example:</h5>
+ <pre> <result> = rem int 4, %var <i>; yields {int}:result = 4 % %var</i>
+ </pre>
+ </div>
+ <!-- _______________________________________________________________________ -->
+ <div class="doc_subsubsection"> <a name="i_setcc">'<tt>set<i>cc</i></tt>'
+ Instructions</a> </div>
+ <div class="doc_text">
+ <h5>Syntax:</h5>
+ <pre> <result> = seteq <ty> <var1>, <var2> <i>; yields {bool}:result</i>
+ <result> = setne <ty> <var1>, <var2> <i>; yields {bool}:result</i>
+ <result> = setlt <ty> <var1>, <var2> <i>; yields {bool}:result</i>
+ <result> = setgt <ty> <var1>, <var2> <i>; yields {bool}:result</i>
+ <result> = setle <ty> <var1>, <var2> <i>; yields {bool}:result</i>
+ <result> = setge <ty> <var1>, <var2> <i>; yields {bool}:result</i>
+ </pre>
+ <h5>Overview:</h5>
+ <p>The '<tt>set<i>cc</i></tt>' family of instructions returns a boolean
+ value based on a comparison of their two operands.</p>
+ <h5>Arguments:</h5>
+ <p>The two arguments to the '<tt>set<i>cc</i></tt>' instructions must
+ be of <a href="#t_firstclass">first class</a> type (it is not possible
+ to compare '<tt>label</tt>'s, '<tt>array</tt>'s, '<tt>structure</tt>'
+ or '<tt>void</tt>' values, etc...). Both arguments must have identical
+ types.</p>
+ <h5>Semantics:</h5>
+ <p>The '<tt>seteq</tt>' instruction yields a <tt>true</tt> '<tt>bool</tt>'
+ value if both operands are equal.<br>
+ The '<tt>setne</tt>' instruction yields a <tt>true</tt> '<tt>bool</tt>'
+ value if both operands are unequal.<br>
+ The '<tt>setlt</tt>' instruction yields a <tt>true</tt> '<tt>bool</tt>'
+ value if the first operand is less than the second operand.<br>
+ The '<tt>setgt</tt>' instruction yields a <tt>true</tt> '<tt>bool</tt>'
+ value if the first operand is greater than the second operand.<br>
+ The '<tt>setle</tt>' instruction yields a <tt>true</tt> '<tt>bool</tt>'
+ value if the first operand is less than or equal to the second operand.<br>
+ The '<tt>setge</tt>' instruction yields a <tt>true</tt> '<tt>bool</tt>'
+ value if the first operand is greater than or equal to the second
+ operand.</p>
+ <h5>Example:</h5>
+ <pre> <result> = seteq int 4, 5 <i>; yields {bool}:result = false</i>
+ <result> = setne float 4, 5 <i>; yields {bool}:result = true</i>
+ <result> = setlt uint 4, 5 <i>; yields {bool}:result = true</i>
+ <result> = setgt sbyte 4, 5 <i>; yields {bool}:result = false</i>
+ <result> = setle sbyte 4, 5 <i>; yields {bool}:result = true</i>
+ <result> = setge sbyte 4, 5 <i>; yields {bool}:result = false</i>
+ </pre>
+ </div>
+ <!-- ======================================================================= -->
+ <div class="doc_subsection"> <a name="bitwiseops">Bitwise Binary
+ Operations</a> </div>
+ <div class="doc_text">
+ <p>Bitwise binary operators are used to do various forms of
+ bit-twiddling in a program. They are generally very efficient
+ instructions, and can commonly be strength reduced from other
+ instructions. They require two operands, execute an operation on them,
+ and produce a single value. The resulting value of the bitwise binary
+ operators is always the same type as its first operand.</p>
+ </div>
+ <!-- _______________________________________________________________________ -->
+ <div class="doc_subsubsection"> <a name="i_and">'<tt>and</tt>'
+ Instruction</a> </div>
+ <div class="doc_text">
+ <h5>Syntax:</h5>
+ <pre> <result> = and <ty> <var1>, <var2> <i>; yields {ty}:result</i>
+ </pre>
+ <h5>Overview:</h5>
+ <p>The '<tt>and</tt>' instruction returns the bitwise logical and of
+ its two operands.</p>
+ <h5>Arguments:</h5>
+ <p>The two arguments to the '<tt>and</tt>' instruction must be <a
+ href="#t_integral">integral</a> values. Both arguments must have
+ identical types.</p>
+ <h5>Semantics:</h5>
+ <p>The truth table used for the '<tt>and</tt>' instruction is:</p>
+ <p> </p>
+ <div style="align: center">
+ <table border="1" cellspacing="0" cellpadding="4">
+ <tbody>
+ <tr>
+ <td>In0</td>
+ <td>In1</td>
+ <td>Out</td>
+ </tr>
+ <tr>
+ <td>0</td>
+ <td>0</td>
+ <td>0</td>
+ </tr>
+ <tr>
+ <td>0</td>
+ <td>1</td>
+ <td>0</td>
+ </tr>
+ <tr>
+ <td>1</td>
+ <td>0</td>
+ <td>0</td>
+ </tr>
+ <tr>
+ <td>1</td>
+ <td>1</td>
+ <td>1</td>
+ </tr>
+ </tbody>
+ </table>
+ </div>
+ <h5>Example:</h5>
+ <pre> <result> = and int 4, %var <i>; yields {int}:result = 4 & %var</i>
+ <result> = and int 15, 40 <i>; yields {int}:result = 8</i>
+ <result> = and int 4, 8 <i>; yields {int}:result = 0</i>
+ </pre>
+ </div>
+ <!-- _______________________________________________________________________ -->
+ <div class="doc_subsubsection"> <a name="i_or">'<tt>or</tt>' Instruction</a> </div>
+ <div class="doc_text">
+ <h5>Syntax:</h5>
+ <pre> <result> = or <ty> <var1>, <var2> <i>; yields {ty}:result</i>
+ </pre>
+ <h5>Overview:</h5>
+ <p>The '<tt>or</tt>' instruction returns the bitwise logical inclusive
+ or of its two operands.</p>
+ <h5>Arguments:</h5>
+ <p>The two arguments to the '<tt>or</tt>' instruction must be <a
+ href="#t_integral">integral</a> values. Both arguments must have
+ identical types.</p>
+ <h5>Semantics:</h5>
+ <p>The truth table used for the '<tt>or</tt>' instruction is:</p>
+ <p> </p>
+ <div style="align: center">
+ <table border="1" cellspacing="0" cellpadding="4">
+ <tbody>
+ <tr>
+ <td>In0</td>
+ <td>In1</td>
+ <td>Out</td>
+ </tr>
+ <tr>
+ <td>0</td>
+ <td>0</td>
+ <td>0</td>
+ </tr>
+ <tr>
+ <td>0</td>
+ <td>1</td>
+ <td>1</td>
+ </tr>
+ <tr>
+ <td>1</td>
+ <td>0</td>
+ <td>1</td>
+ </tr>
+ <tr>
+ <td>1</td>
+ <td>1</td>
+ <td>1</td>
+ </tr>
+ </tbody>
+ </table>
+ </div>
+ <h5>Example:</h5>
+ <pre> <result> = or int 4, %var <i>; yields {int}:result = 4 | %var</i>
+ <result> = or int 15, 40 <i>; yields {int}:result = 47</i>
+ <result> = or int 4, 8 <i>; yields {int}:result = 12</i>
+ </pre>
+ </div>
+ <!-- _______________________________________________________________________ -->
+ <div class="doc_subsubsection"> <a name="i_xor">'<tt>xor</tt>'
+ Instruction</a> </div>
+ <div class="doc_text">
+ <h5>Syntax:</h5>
+ <pre> <result> = xor <ty> <var1>, <var2> <i>; yields {ty}:result</i>
+ </pre>
+ <h5>Overview:</h5>
+ <p>The '<tt>xor</tt>' instruction returns the bitwise logical exclusive
+ or of its two operands. The <tt>xor</tt> is used to implement the
+ "one's complement" operation, which is the "~" operator in C.</p>
+ <h5>Arguments:</h5>
+ <p>The two arguments to the '<tt>xor</tt>' instruction must be <a
+ href="#t_integral">integral</a> values. Both arguments must have
+ identical types.</p>
+ <h5>Semantics:</h5>
+ <p>The truth table used for the '<tt>xor</tt>' instruction is:</p>
+ <p> </p>
+ <div style="align: center">
+ <table border="1" cellspacing="0" cellpadding="4">
+ <tbody>
+ <tr>
+ <td>In0</td>
+ <td>In1</td>
+ <td>Out</td>
+ </tr>
+ <tr>
+ <td>0</td>
+ <td>0</td>
+ <td>0</td>
+ </tr>
+ <tr>
+ <td>0</td>
+ <td>1</td>
+ <td>1</td>
+ </tr>
+ <tr>
+ <td>1</td>
+ <td>0</td>
+ <td>1</td>
+ </tr>
+ <tr>
+ <td>1</td>
+ <td>1</td>
+ <td>0</td>
+ </tr>
+ </tbody>
+ </table>
+ </div>
+ <p> </p>
+ <h5>Example:</h5>
+ <pre> <result> = xor int 4, %var <i>; yields {int}:result = 4 ^ %var</i>
+ <result> = xor int 15, 40 <i>; yields {int}:result = 39</i>
+ <result> = xor int 4, 8 <i>; yields {int}:result = 12</i>
+ <result> = xor int %V, -1 <i>; yields {int}:result = ~%V</i>
+ </pre>
+ </div>
+ <!-- _______________________________________________________________________ -->
+ <div class="doc_subsubsection"> <a name="i_shl">'<tt>shl</tt>'
+ Instruction</a> </div>
+ <div class="doc_text">
+ <h5>Syntax:</h5>
+ <pre> <result> = shl <ty> <var1>, ubyte <var2> <i>; yields {ty}:result</i>
+ </pre>
+ <h5>Overview:</h5>
+ <p>The '<tt>shl</tt>' instruction returns the first operand shifted to
+ the left a specified number of bits.</p>
+ <h5>Arguments:</h5>
+ <p>The first argument to the '<tt>shl</tt>' instruction must be an <a
+ href="#t_integer">integer</a> type. The second argument must be an '<tt>ubyte</tt>'
+ type.</p>
+ <h5>Semantics:</h5>
+ <p>The value produced is <tt>var1</tt> * 2<sup><tt>var2</tt></sup>.</p>
+ <h5>Example:</h5>
+ <pre> <result> = shl int 4, ubyte %var <i>; yields {int}:result = 4 << %var</i>
+ <result> = shl int 4, ubyte 2 <i>; yields {int}:result = 16</i>
+ <result> = shl int 1, ubyte 10 <i>; yields {int}:result = 1024</i>
+ </pre>
+ </div>
+ <!-- _______________________________________________________________________ -->
+ <div class="doc_subsubsection"> <a name="i_shr">'<tt>shr</tt>'
+ Instruction</a> </div>
+ <div class="doc_text">
+ <h5>Syntax:</h5>
+ <pre> <result> = shr <ty> <var1>, ubyte <var2> <i>; yields {ty}:result</i>
+ </pre>
+ <h5>Overview:</h5>
+ <p>The '<tt>shr</tt>' instruction returns the first operand shifted to
+ the right a specified number of bits.</p>
+ <h5>Arguments:</h5>
+ <p>The first argument to the '<tt>shr</tt>' instruction must be an <a
+ href="#t_integer">integer</a> type. The second argument must be an '<tt>ubyte</tt>'
+ type.</p>
+ <h5>Semantics:</h5>
+ <p>If the first argument is a <a href="#t_signed">signed</a> type, the
+ most significant bit is duplicated in the newly free'd bit positions.
+ If the first argument is unsigned, zero bits shall fill the empty
+ positions.</p>
+ <h5>Example:</h5>
+ <pre> <result> = shr int 4, ubyte %var <i>; yields {int}:result = 4 >> %var</i>
+ <result> = shr uint 4, ubyte 1 <i>; yields {uint}:result = 2</i>
+ <result> = shr int 4, ubyte 2 <i>; yields {int}:result = 1</i>
+ <result> = shr sbyte 4, ubyte 3 <i>; yields {sbyte}:result = 0</i>
+ <result> = shr sbyte -2, ubyte 1 <i>; yields {sbyte}:result = -1</i>
+ </pre>
+ </div>
+ <!-- ======================================================================= -->
+ <div class="doc_subsection"> <a name="memoryops">Memory Access
+ Operations</a></div>
+ <div class="doc_text">
+ <p>A key design point of an SSA-based representation is how it
+ represents memory. In LLVM, no memory locations are in SSA form, which
+ makes things very simple. This section describes how to read, write,
+ allocate and free memory in LLVM.</p>
+ </div>
+ <!-- _______________________________________________________________________ -->
+ <div class="doc_subsubsection"> <a name="i_malloc">'<tt>malloc</tt>'
+ Instruction</a> </div>
+ <div class="doc_text">
+ <h5>Syntax:</h5>
+ <pre> <result> = malloc <type>, uint <NumElements> <i>; yields {type*}:result</i>
+ <result> = malloc <type> <i>; yields {type*}:result</i>
+ </pre>
+ <h5>Overview:</h5>
+ <p>The '<tt>malloc</tt>' instruction allocates memory from the system
+ heap and returns a pointer to it.</p>
+ <h5>Arguments:</h5>
+ <p>The '<tt>malloc</tt>' instruction allocates <tt>sizeof(<type>)*NumElements</tt>
+ bytes of memory from the operating system and returns a pointer of the
+ appropriate type to the program. The second form of the instruction is
+ a shorter version of the first instruction that defaults to allocating
+ one element.</p>
+ <p>'<tt>type</tt>' must be a sized type.</p>
+ <h5>Semantics:</h5>
+ <p>Memory is allocated using the system "<tt>malloc</tt>" function, and
+ a pointer is returned.</p>
+ <h5>Example:</h5>
+ <pre> %array = malloc [4 x ubyte ] <i>; yields {[%4 x ubyte]*}:array</i>
+
+ %size = <a
+ href="#i_add">add</a> uint 2, 2 <i>; yields {uint}:size = uint 4</i>
+ %array1 = malloc ubyte, uint 4 <i>; yields {ubyte*}:array1</i>
+ %array2 = malloc [12 x ubyte], uint %size <i>; yields {[12 x ubyte]*}:array2</i>
+ </pre>
+ </div>
+ <!-- _______________________________________________________________________ -->
+ <div class="doc_subsubsection"> <a name="i_free">'<tt>free</tt>'
+ Instruction</a> </div>
+ <div class="doc_text">
+ <h5>Syntax:</h5>
+ <pre> free <type> <value> <i>; yields {void}</i>
+ </pre>
+ <h5>Overview:</h5>
+ <p>The '<tt>free</tt>' instruction returns memory back to the unused
+ memory heap, to be reallocated in the future.</p>
+ <p> </p>
+ <h5>Arguments:</h5>
+ <p>'<tt>value</tt>' shall be a pointer value that points to a value
+ that was allocated with the '<tt><a href="#i_malloc">malloc</a></tt>'
+ instruction.</p>
+ <h5>Semantics:</h5>
+ <p>Access to the memory pointed to by the pointer is not longer defined
+ after this instruction executes.</p>
+ <h5>Example:</h5>
+ <pre> %array = <a href="#i_malloc">malloc</a> [4 x ubyte] <i>; yields {[4 x ubyte]*}:array</i>
+ free [4 x ubyte]* %array
+ </pre>
+ </div>
+ <!-- _______________________________________________________________________ -->
+ <div class="doc_subsubsection"> <a name="i_alloca">'<tt>alloca</tt>'
+ Instruction</a> </div>
+ <div class="doc_text">
+ <h5>Syntax:</h5>
+ <pre> <result> = alloca <type>, uint <NumElements> <i>; yields {type*}:result</i>
+ <result> = alloca <type> <i>; yields {type*}:result</i>
+ </pre>
+ <h5>Overview:</h5>
+ <p>The '<tt>alloca</tt>' instruction allocates memory on the current
+ stack frame of the procedure that is live until the current function
+ returns to its caller.</p>
+ <h5>Arguments:</h5>
+ <p>The the '<tt>alloca</tt>' instruction allocates <tt>sizeof(<type>)*NumElements</tt>
+ bytes of memory on the runtime stack, returning a pointer of the
+ appropriate type to the program. The second form of the instruction is
+ a shorter version of the first that defaults to allocating one element.</p>
+ <p>'<tt>type</tt>' may be any sized type.</p>
+ <h5>Semantics:</h5>
+ <p>Memory is allocated, a pointer is returned. '<tt>alloca</tt>'d
+ memory is automatically released when the function returns. The '<tt>alloca</tt>'
+ instruction is commonly used to represent automatic variables that must
+ have an address available. When the function returns (either with the <tt><a
+ href="#i_ret">ret</a></tt> or <tt><a href="#i_invoke">invoke</a></tt>
+ instructions), the memory is reclaimed.</p>
+ <h5>Example:</h5>
+ <pre> %ptr = alloca int <i>; yields {int*}:ptr</i>
+ %ptr = alloca int, uint 4 <i>; yields {int*}:ptr</i>
+ </pre>
+ </div>
+ <!-- _______________________________________________________________________ -->
+ <div class="doc_subsubsection"> <a name="i_load">'<tt>load</tt>'
+ Instruction</a> </div>
+ <div class="doc_text">
+ <h5>Syntax:</h5>
+ <pre> <result> = load <ty>* <pointer><br> <result> = volatile load <ty>* <pointer><br></pre>
+ <h5>Overview:</h5>
+ <p>The '<tt>load</tt>' instruction is used to read from memory.</p>
+ <h5>Arguments:</h5>
+ <p>The argument to the '<tt>load</tt>' instruction specifies the memory
+ address to load from. The pointer must point to a <a
+ href="#t_firstclass">first class</a> type. If the <tt>load</tt> is
+ marked as <tt>volatile</tt> then the optimizer is not allowed to modify
+ the number or order of execution of this <tt>load</tt> with other
+ volatile <tt>load</tt> and <tt><a href="#i_store">store</a></tt>
+ instructions. </p>
+ <h5>Semantics:</h5>
+ <p>The location of memory pointed to is loaded.</p>
+ <h5>Examples:</h5>
+ <pre> %ptr = <a href="#i_alloca">alloca</a> int <i>; yields {int*}:ptr</i>
+ <a
+ href="#i_store">store</a> int 3, int* %ptr <i>; yields {void}</i>
+ %val = load int* %ptr <i>; yields {int}:val = int 3</i>
+ </pre>
+ </div>
+ <!-- _______________________________________________________________________ -->
+ <div class="doc_subsubsection"> <a name="i_store">'<tt>store</tt>'
+ Instruction</a> </div>
+ <h5>Syntax:</h5>
+ <pre> store <ty> <value>, <ty>* <pointer> <i>; yields {void}</i>
+ volatile store <ty> <value>, <ty>* <pointer> <i>; yields {void}</i>
+ </pre>
+ <h5>Overview:</h5>
+ <p>The '<tt>store</tt>' instruction is used to write to memory.</p>
+ <h5>Arguments:</h5>
+ <p>There are two arguments to the '<tt>store</tt>' instruction: a value
+ to store and an address to store it into. The type of the '<tt><pointer></tt>'
+ operand must be a pointer to the type of the '<tt><value></tt>'
+ operand. If the <tt>store</tt> is marked as <tt>volatile</tt> then the
+ optimizer is not allowed to modify the number or order of execution of
+ this <tt>store</tt> with other volatile <tt>load</tt> and <tt><a
+ href="#i_store">store</a></tt> instructions.</p>
+ <h5>Semantics:</h5>
+ <p>The contents of memory are updated to contain '<tt><value></tt>'
+ at the location specified by the '<tt><pointer></tt>' operand.</p>
+ <h5>Example:</h5>
+ <pre> %ptr = <a href="#i_alloca">alloca</a> int <i>; yields {int*}:ptr</i>
+ <a
+ href="#i_store">store</a> int 3, int* %ptr <i>; yields {void}</i>
+ %val = load int* %ptr <i>; yields {int}:val = int 3</i>
+ </pre>
+ <!-- _______________________________________________________________________ -->
+ <div class="doc_subsubsection">
+ <a name="i_getelementptr">'<tt>getelementptr</tt>' Instruction</a>
+ </div>
+
+ <div class="doc_text">
+ <h5>Syntax:</h5>
+ <pre>
+ <result> = getelementptr <ty>* <ptrval>{, <ty> <idx>}*
+ </pre>
+
+ <h5>Overview:</h5>
+
+ <p>
+ The '<tt>getelementptr</tt>' instruction is used to get the address of a
+ subelement of an aggregate data structure.</p>
+
+ <h5>Arguments:</h5>
+
+ <p>This instruction takes a list of integer constants that indicate what
+ elements of the aggregate object to index to. The actual types of the arguments
+ provided depend on the type of the first pointer argument. The
+ '<tt>getelementptr</tt>' instruction is used to index down through the type
+ levels of a structure. When indexing into a structure, only <tt>uint</tt>
+ integer constants are allowed. When indexing into an array or pointer
+ <tt>int</tt> and <tt>long</tt> indexes are allowed of any sign.</p>
+
+ <p>For example, let's consider a C code fragment and how it gets
+ compiled to LLVM:</p>
+
+ <pre>
+ struct RT {
+ char A;
+ int B[10][20];
+ char C;
+ };
+ struct ST {
+ int X;
+ double Y;
+ struct RT Z;
+ };
+
+ int *foo(struct ST *s) {
+ return &s[1].Z.B[5][13];
+ }
+ </pre>
+
+ <p>The LLVM code generated by the GCC frontend is:</p>
+
+ <pre>
+ %RT = type { sbyte, [10 x [20 x int]], sbyte }
+ %ST = type { int, double, %RT }
+
+ implementation
+
+ int* %foo(%ST* %s) {
+ entry:
+ %reg = getelementptr %ST* %s, int 1, uint 2, uint 1, int 5, int 13
+ ret int* %reg
+ }
+ </pre>
+
+ <h5>Semantics:</h5>
+
+ <p>The index types specified for the '<tt>getelementptr</tt>' instruction depend
+ on the pointer type that is being index into. <a href="#t_pointer">Pointer</a>
+ and <a href="#t_array">array</a> types require <tt>uint</tt>, <tt>int</tt>,
+ <tt>ulong</tt>, or <tt>long</tt> values, and <a href="#t_struct">structure</a>
+ types require <tt>uint</tt> <b>constants</b>.</p>
+
+ <p>In the example above, the first index is indexing into the '<tt>%ST*</tt>'
+ type, which is a pointer, yielding a '<tt>%ST</tt>' = '<tt>{ int, double, %RT
+ }</tt>' type, a structure. The second index indexes into the third element of
+ the structure, yielding a '<tt>%RT</tt>' = '<tt>{ sbyte, [10 x [20 x int]],
+ sbyte }</tt>' type, another structure. The third index indexes into the second
+ element of the structure, yielding a '<tt>[10 x [20 x int]]</tt>' type, an
+ array. The two dimensions of the array are subscripted into, yielding an
+ '<tt>int</tt>' type. The '<tt>getelementptr</tt>' instruction return a pointer
+ to this element, thus computing a value of '<tt>int*</tt>' type.</p>
+
+ <p>Note that it is perfectly legal to index partially through a
+ structure, returning a pointer to an inner element. Because of this,
+ the LLVM code for the given testcase is equivalent to:</p>
+
+ <pre>
+ int* "foo"(%ST* %s) {
+ %t1 = getelementptr %ST* %s, int 1 <i>; yields %ST*:%t1</i>
+ %t2 = getelementptr %ST* %t1, int 0, uint 2 <i>; yields %RT*:%t2</i>
+ %t3 = getelementptr %RT* %t2, int 0, uint 1 <i>; yields [10 x [20 x int]]*:%t3</i>
+ %t4 = getelementptr [10 x [20 x int]]* %t3, int 0, int 5 <i>; yields [20 x int]*:%t4</i>
+ %t5 = getelementptr [20 x int]* %t4, int 0, int 13 <i>; yields int*:%t5</i>
+ ret int* %t5
+ }
+ </pre>
+ <h5>Example:</h5>
+ <pre>
+ <i>; yields [12 x ubyte]*:aptr</i>
+ %aptr = getelementptr {int, [12 x ubyte]}* %sptr, long 0, uint 1
+ </pre>
+
+ </div>
+ <!-- ======================================================================= -->
+ <div class="doc_subsection"> <a name="otherops">Other Operations</a> </div>
+ <div class="doc_text">
+ <p>The instructions in this category are the "miscellaneous"
+ instructions, which defy better classification.</p>
+ </div>
+ <!-- _______________________________________________________________________ -->
+ <div class="doc_subsubsection"> <a name="i_phi">'<tt>phi</tt>'
+ Instruction</a> </div>
+ <div class="doc_text">
+ <h5>Syntax:</h5>
+ <pre> <result> = phi <ty> [ <val0>, <label0>], ...<br></pre>
+ <h5>Overview:</h5>
+ <p>The '<tt>phi</tt>' instruction is used to implement the φ node in
+ the SSA graph representing the function.</p>
+ <h5>Arguments:</h5>
+ <p>The type of the incoming values are specified with the first type
+ field. After this, the '<tt>phi</tt>' instruction takes a list of pairs
+ as arguments, with one pair for each predecessor basic block of the
+ current block. Only values of <a href="#t_firstclass">first class</a>
+ type may be used as the value arguments to the PHI node. Only labels
+ may be used as the label arguments.</p>
+ <p>There must be no non-phi instructions between the start of a basic
+ block and the PHI instructions: i.e. PHI instructions must be first in
+ a basic block.</p>
+ <h5>Semantics:</h5>
+ <p>At runtime, the '<tt>phi</tt>' instruction logically takes on the
+ value specified by the parameter, depending on which basic block we
+ came from in the last <a href="#terminators">terminator</a> instruction.</p>
+ <h5>Example:</h5>
+ <pre>Loop: ; Infinite loop that counts from 0 on up...<br> %indvar = phi uint [ 0, %LoopHeader ], [ %nextindvar, %Loop ]<br> %nextindvar = add uint %indvar, 1<br> br label %Loop<br></pre>
+ </div>
+
+ <!-- _______________________________________________________________________ -->
+ <div class="doc_subsubsection">
+ <a name="i_cast">'<tt>cast .. to</tt>' Instruction</a>
+ </div>
+
+ <div class="doc_text">
+
+ <h5>Syntax:</h5>
+
+ <pre>
+ <result> = cast <ty> <value> to <ty2> <i>; yields ty2</i>
+ </pre>
+
+ <h5>Overview:</h5>
+
+ <p>
+ The '<tt>cast</tt>' instruction is used as the primitive means to convert
+ integers to floating point, change data type sizes, and break type safety (by
+ casting pointers).
+ </p>
+
+
+ <h5>Arguments:</h5>
+
+ <p>
+ The '<tt>cast</tt>' instruction takes a value to cast, which must be a first
+ class value, and a type to cast it to, which must also be a <a
+ href="#t_firstclass">first class</a> type.
+ </p>
+
+ <h5>Semantics:</h5>
+
+ <p>
+ This instruction follows the C rules for explicit casts when determining how the
+ data being cast must change to fit in its new container.
+ </p>
+
+ <p>
+ When casting to bool, any value that would be considered true in the context of
+ a C '<tt>if</tt>' condition is converted to the boolean '<tt>true</tt>' values,
+ all else are '<tt>false</tt>'.
+ </p>
+
+ <p>
+ When extending an integral value from a type of one signness to another (for
+ example '<tt>sbyte</tt>' to '<tt>ulong</tt>'), the value is sign-extended if the
+ <b>source</b> value is signed, and zero-extended if the source value is
+ unsigned. <tt>bool</tt> values are always zero extended into either zero or
+ one.
+ </p>
+
+ <h5>Example:</h5>
+
+ <pre>
+ %X = cast int 257 to ubyte <i>; yields ubyte:1</i>
+ %Y = cast int 123 to bool <i>; yields bool:true</i>
+ </pre>
+ </div>
+
+ <!-- _______________________________________________________________________ -->
+ <div class="doc_subsubsection">
+ <a name="i_select">'<tt>select</tt>' Instruction</a>
+ </div>
+
+ <div class="doc_text">
+
+ <h5>Syntax:</h5>
+
+ <pre>
+ <result> = select bool <cond>, <ty> <val1>, <ty> <val2> <i>; yields ty</i>
+ </pre>
+
+ <h5>Overview:</h5>
+
+ <p>
+ The '<tt>select</tt>' instruction is used to choose one value based on a
+ condition, without branching.
+ </p>
+
+
+ <h5>Arguments:</h5>
+
+ <p>
+ The '<tt>select</tt>' instruction requires a boolean value indicating the condition, and two values of the same <a href="#t_firstclass">first class</a> type.
+ </p>
+
+ <h5>Semantics:</h5>
+
+ <p>
+ If the boolean condition evaluates to true, the instruction returns the first
+ value argument, otherwise it returns the second value argument.
+ </p>
+
+ <h5>Example:</h5>
+
+ <pre>
+ %X = select bool true, ubyte 17, ubyte 42 <i>; yields ubyte:17</i>
+ </pre>
+ </div>
+
+
+
+
+
+ <!-- _______________________________________________________________________ -->
+ <div class="doc_subsubsection"> <a name="i_call">'<tt>call</tt>'
+ Instruction</a> </div>
+ <div class="doc_text">
+ <h5>Syntax:</h5>
+ <pre> <result> = call <ty>* <fnptrval>(<param list>)<br></pre>
+ <h5>Overview:</h5>
+ <p>The '<tt>call</tt>' instruction represents a simple function call.</p>
+ <h5>Arguments:</h5>
+ <p>This instruction requires several arguments:</p>
+ <ol>
+ <li>
+ <p>'<tt>ty</tt>': shall be the signature of the pointer to function
+ value being invoked. The argument types must match the types implied
+ by this signature.</p>
+ </li>
+ <li>
+ <p>'<tt>fnptrval</tt>': An LLVM value containing a pointer to a
+ function to be invoked. In most cases, this is a direct function
+ invocation, but indirect <tt>call</tt>s are just as possible,
+ calling an arbitrary pointer to function values.</p>
+ </li>
+ <li>
+ <p>'<tt>function args</tt>': argument list whose types match the
+ function signature argument types. If the function signature
+ indicates the function accepts a variable number of arguments, the
+ extra arguments can be specified.</p>
+ </li>
+ </ol>
+ <h5>Semantics:</h5>
+ <p>The '<tt>call</tt>' instruction is used to cause control flow to
+ transfer to a specified function, with its incoming arguments bound to
+ the specified values. Upon a '<tt><a href="#i_ret">ret</a></tt>'
+ instruction in the called function, control flow continues with the
+ instruction after the function call, and the return value of the
+ function is bound to the result argument. This is a simpler case of
+ the <a href="#i_invoke">invoke</a> instruction.</p>
+ <h5>Example:</h5>
+ <pre> %retval = call int %test(int %argc)<br> call int(sbyte*, ...) *%printf(sbyte* %msg, int 12, sbyte 42);<br></pre>
+ </div>
+ <!-- _______________________________________________________________________ -->
+ <div class="doc_subsubsection"> <a name="i_vanext">'<tt>vanext</tt>'
+ Instruction</a> </div>
+ <div class="doc_text">
+ <h5>Syntax:</h5>
+ <pre> <resultarglist> = vanext <va_list> <arglist>, <argty><br></pre>
+ <h5>Overview:</h5>
+ <p>The '<tt>vanext</tt>' instruction is used to access arguments passed
+ through the "variable argument" area of a function call. It is used to
+ implement the <tt>va_arg</tt> macro in C.</p>
+ <h5>Arguments:</h5>
+ <p>This instruction takes a <tt>valist</tt> value and the type of the
+ argument. It returns another <tt>valist</tt>.</p>
+ <h5>Semantics:</h5>
+ <p>The '<tt>vanext</tt>' instruction advances the specified <tt>valist</tt>
+ past an argument of the specified type. In conjunction with the <a
+ href="#i_vaarg"><tt>vaarg</tt></a> instruction, it is used to implement
+ the <tt>va_arg</tt> macro available in C. For more information, see
+ the variable argument handling <a href="#int_varargs">Intrinsic
+ Functions</a>.</p>
+ <p>It is legal for this instruction to be called in a function which
+ does not take a variable number of arguments, for example, the <tt>vfprintf</tt>
+ function.</p>
+ <p><tt>vanext</tt> is an LLVM instruction instead of an <a
+ href="#intrinsics">intrinsic function</a> because it takes an type as
+ an argument.</p>
+ <h5>Example:</h5>
+ <p>See the <a href="#int_varargs">variable argument processing</a>
+ section.</p>
+ </div>
+ <!-- _______________________________________________________________________ -->
+ <div class="doc_subsubsection"> <a name="i_vaarg">'<tt>vaarg</tt>'
+ Instruction</a> </div>
+ <div class="doc_text">
+ <h5>Syntax:</h5>
+ <pre> <resultval> = vaarg <va_list> <arglist>, <argty><br></pre>
+ <h5>Overview:</h5>
+ <p>The '<tt>vaarg</tt>' instruction is used to access arguments passed
+ through the "variable argument" area of a function call. It is used to
+ implement the <tt>va_arg</tt> macro in C.</p>
+ <h5>Arguments:</h5>
+ <p>This instruction takes a <tt>valist</tt> value and the type of the
+ argument. It returns a value of the specified argument type.</p>
+ <h5>Semantics:</h5>
+ <p>The '<tt>vaarg</tt>' instruction loads an argument of the specified
+ type from the specified <tt>va_list</tt>. In conjunction with the <a
+ href="#i_vanext"><tt>vanext</tt></a> instruction, it is used to
+ implement the <tt>va_arg</tt> macro available in C. For more
+ information, see the variable argument handling <a href="#int_varargs">Intrinsic
+ Functions</a>.</p>
+ <p>It is legal for this instruction to be called in a function which
+ does not take a variable number of arguments, for example, the <tt>vfprintf</tt>
+ function.</p>
+ <p><tt>vaarg</tt> is an LLVM instruction instead of an <a
+ href="#intrinsics">intrinsic function</a> because it takes an type as
+ an argument.</p>
+ <h5>Example:</h5>
+ <p>See the <a href="#int_varargs">variable argument processing</a>
+ section.</p>
+ </div>
+
+ <!-- *********************************************************************** -->
+ <div class="doc_section"> <a name="intrinsics">Intrinsic Functions</a> </div>
+ <!-- *********************************************************************** -->
+
+ <div class="doc_text">
+
+ <p>LLVM supports the notion of an "intrinsic function". These functions have
+ well known names and semantics, and are required to follow certain
+ restrictions. Overall, these instructions represent an extension mechanism for
+ the LLVM language that does not require changing all of the transformations in
+ LLVM to add to the language (or the bytecode reader/writer, the parser,
+ etc...).</p>
+
+ <p>Intrinsic function names must all start with an "<tt>llvm.</tt>" prefix, this
+ prefix is reserved in LLVM for intrinsic names, thus functions may not be named
+ this. Intrinsic functions must always be external functions: you cannot define
+ the body of intrinsic functions. Intrinsic functions may only be used in call
+ or invoke instructions: it is illegal to take the address of an intrinsic
+ function. Additionally, because intrinsic functions are part of the LLVM
+ language, it is required that they all be documented here if any are added.</p>
+
+
+ <p>
+ Adding an intrinsic to LLVM is straight-forward if it is possible to express the
+ concept in LLVM directly (ie, code generator support is not _required_). To do
+ this, extend the default implementation of the IntrinsicLowering class to handle
+ the intrinsic. Code generators use this class to lower intrinsics they do not
+ understand to raw LLVM instructions that they do.
+ </p>
+
+ </div>
+
+ <!-- ======================================================================= -->
+ <div class="doc_subsection">
+ <a name="int_varargs">Variable Argument Handling Intrinsics</a>
+ </div>
+
+ <div class="doc_text">
+
+ <p>Variable argument support is defined in LLVM with the <a
+ href="#i_vanext"><tt>vanext</tt></a> instruction and these three
+ intrinsic functions. These functions are related to the similarly
+ named macros defined in the <tt><stdarg.h></tt> header file.</p>
+
+ <p>All of these functions operate on arguments that use a
+ target-specific value type "<tt>va_list</tt>". The LLVM assembly
+ language reference manual does not define what this type is, so all
+ transformations should be prepared to handle intrinsics with any type
+ used.</p>
+
+ <p>This example shows how the <a href="#i_vanext"><tt>vanext</tt></a>
+ instruction and the variable argument handling intrinsic functions are
+ used.</p>
+
+ <pre>
+ int %test(int %X, ...) {
+ ; Initialize variable argument processing
+ %ap = call sbyte* %<a href="#i_va_start">llvm.va_start</a>()
+
+ ; Read a single integer argument
+ %tmp = vaarg sbyte* %ap, int
+
+ ; Advance to the next argument
+ %ap2 = vanext sbyte* %ap, int
+
+ ; Demonstrate usage of llvm.va_copy and llvm.va_end
+ %aq = call sbyte* %<a href="#i_va_copy">llvm.va_copy</a>(sbyte* %ap2)
+ call void %<a href="#i_va_end">llvm.va_end</a>(sbyte* %aq)
+
+ ; Stop processing of arguments.
+ call void %<a href="#i_va_end">llvm.va_end</a>(sbyte* %ap2)
+ ret int %tmp
+ }
+ </pre>
+ </div>
+
+ <!-- _______________________________________________________________________ -->
+ <div class="doc_subsubsection">
+ <a name="i_va_start">'<tt>llvm.va_start</tt>' Intrinsic</a>
+ </div>
+
+
+ <div class="doc_text">
+ <h5>Syntax:</h5>
+ <pre> call va_list ()* %llvm.va_start()<br></pre>
+ <h5>Overview:</h5>
+ <p>The '<tt>llvm.va_start</tt>' intrinsic returns a new <tt><arglist></tt>
+ for subsequent use by the variable argument intrinsics.</p>
+ <h5>Semantics:</h5>
+ <p>The '<tt>llvm.va_start</tt>' intrinsic works just like the <tt>va_start</tt>
+ macro available in C. In a target-dependent way, it initializes and
+ returns a <tt>va_list</tt> element, so that the next <tt>vaarg</tt>
+ will produce the first variable argument passed to the function. Unlike
+ the C <tt>va_start</tt> macro, this intrinsic does not need to know the
+ last argument of the function, the compiler can figure that out.</p>
+ <p>Note that this intrinsic function is only legal to be called from
+ within the body of a variable argument function.</p>
+ </div>
+
+ <!-- _______________________________________________________________________ -->
+ <div class="doc_subsubsection">
+ <a name="i_va_end">'<tt>llvm.va_end</tt>' Intrinsic</a>
+ </div>
+
+ <div class="doc_text">
+ <h5>Syntax:</h5>
+ <pre> call void (va_list)* %llvm.va_end(va_list <arglist>)<br></pre>
+ <h5>Overview:</h5>
+ <p>The '<tt>llvm.va_end</tt>' intrinsic destroys <tt><arglist></tt>
+ which has been initialized previously with <tt><a href="#i_va_start">llvm.va_start</a></tt>
+ or <tt><a href="#i_va_copy">llvm.va_copy</a></tt>.</p>
+ <h5>Arguments:</h5>
+ <p>The argument is a <tt>va_list</tt> to destroy.</p>
+ <h5>Semantics:</h5>
+ <p>The '<tt>llvm.va_end</tt>' intrinsic works just like the <tt>va_end</tt>
+ macro available in C. In a target-dependent way, it destroys the <tt>va_list</tt>.
+ Calls to <a href="#i_va_start"><tt>llvm.va_start</tt></a> and <a
+ href="#i_va_copy"><tt>llvm.va_copy</tt></a> must be matched exactly
+ with calls to <tt>llvm.va_end</tt>.</p>
+ </div>
+
+ <!-- _______________________________________________________________________ -->
+ <div class="doc_subsubsection">
+ <a name="i_va_copy">'<tt>llvm.va_copy</tt>' Intrinsic</a>
+ </div>
+
+ <div class="doc_text">
+
+ <h5>Syntax:</h5>
+
+ <pre>
+ call va_list (va_list)* %llvm.va_copy(va_list <destarglist>)
+ </pre>
+
+ <h5>Overview:</h5>
+
+ <p>The '<tt>llvm.va_copy</tt>' intrinsic copies the current argument position
+ from the source argument list to the destination argument list.</p>
+
+ <h5>Arguments:</h5>
+
+ <p>The argument is the <tt>va_list</tt> to copy.</p>
+
+ <h5>Semantics:</h5>
+
+ <p>The '<tt>llvm.va_copy</tt>' intrinsic works just like the <tt>va_copy</tt>
+ macro available in C. In a target-dependent way, it copies the source
+ <tt>va_list</tt> element into the returned list. This intrinsic is necessary
+ because the <tt><a href="#i_va_start">llvm.va_start</a></tt> intrinsic may be
+ arbitrarily complex and require memory allocation, for example.</p>
+
+ </div>
+
+ <!-- ======================================================================= -->
+ <div class="doc_subsection">
+ <a name="int_gc">Accurate Garbage Collection Intrinsics</a>
+ </div>
+
+ <div class="doc_text">
+
+ <p>
+ LLVM support for <a href="GarbageCollection.html">Accurate Garbage
+ Collection</a> requires the implementation and generation of these intrinsics.
+ These intrinsics allow identification of <a href="#i_gcroot">GC roots on the
+ stack</a>, as well as garbage collector implementations that require <a
+ href="#i_gcread">read</a> and <a href="#i_gcwrite">write</a> barriers.
+ Front-ends for type-safe garbage collected languages should generate these
+ intrinsics to make use of the LLVM garbage collectors. For more details, see <a
+ href="GarbageCollection.html">Accurate Garbage Collection with LLVM</a>.
+ </p>
+ </div>
+
+ <!-- _______________________________________________________________________ -->
+ <div class="doc_subsubsection">
+ <a name="i_gcroot">'<tt>llvm.gcroot</tt>' Intrinsic</a>
+ </div>
+
+ <div class="doc_text">
+
+ <h5>Syntax:</h5>
+
+ <pre>
+ call void (<ty>**, <ty2>*)* %llvm.gcroot(<ty>** %ptrloc, <ty2>* %metadata)
+ </pre>
+
+ <h5>Overview:</h5>
+
+ <p>The '<tt>llvm.gcroot</tt>' intrinsic declares the existance of a GC root to
+ the code generator, and allows some metadata to be associated with it.</p>
+
+ <h5>Arguments:</h5>
+
+ <p>The first argument specifies the address of a stack object that contains the
+ root pointer. The second pointer (which must be either a constant or a global
+ value address) contains the meta-data to be associated with the root.</p>
+
+ <h5>Semantics:</h5>
+
+ <p>At runtime, a call to this intrinsics stores a null pointer into the "ptrloc"
+ location. At compile-time, the code generator generates information to allow
+ the runtime to find the pointer at GC safe points.
+ </p>
+
+ </div>
+
+
+ <!-- _______________________________________________________________________ -->
+ <div class="doc_subsubsection">
+ <a name="i_gcread">'<tt>llvm.gcread</tt>' Intrinsic</a>
+ </div>
+
+ <div class="doc_text">
+
+ <h5>Syntax:</h5>
+
+ <pre>
+ call sbyte* (sbyte**)* %llvm.gcread(sbyte** %Ptr)
+ </pre>
+
+ <h5>Overview:</h5>
+
+ <p>The '<tt>llvm.gcread</tt>' intrinsic identifies reads of references from heap
+ locations, allowing garbage collector implementations that require read
+ barriers.</p>
+
+ <h5>Arguments:</h5>
+
+ <p>The argument is the address to read from, which should be an address
+ allocated from the garbage collector.</p>
+
+ <h5>Semantics:</h5>
+
+ <p>The '<tt>llvm.gcread</tt>' intrinsic has the same semantics as a load
+ instruction, but may be replaced with substantially more complex code by the
+ garbage collector runtime, as needed.</p>
+
+ </div>
+
+
+ <!-- _______________________________________________________________________ -->
+ <div class="doc_subsubsection">
+ <a name="i_gcwrite">'<tt>llvm.gcwrite</tt>' Intrinsic</a>
+ </div>
+
+ <div class="doc_text">
+
+ <h5>Syntax:</h5>
+
+ <pre>
+ call void (sbyte*, sbyte**)* %llvm.gcwrite(sbyte* %P1, sbyte** %P2)
+ </pre>
+
+ <h5>Overview:</h5>
+
+ <p>The '<tt>llvm.gcwrite</tt>' intrinsic identifies writes of references to heap
+ locations, allowing garbage collector implementations that require write
+ barriers (such as generational or reference counting collectors).</p>
+
+ <h5>Arguments:</h5>
+
+ <p>The first argument is the reference to store, and the second is the heap
+ location to store to.</p>
+
+ <h5>Semantics:</h5>
+
+ <p>The '<tt>llvm.gcwrite</tt>' intrinsic has the same semantics as a store
+ instruction, but may be replaced with substantially more complex code by the
+ garbage collector runtime, as needed.</p>
+
+ </div>
+
+
+
+ <!-- ======================================================================= -->
+ <div class="doc_subsection">
+ <a name="int_codegen">Code Generator Intrinsics</a>
+ </div>
+
+ <div class="doc_text">
+ <p>
+ These intrinsics are provided by LLVM to expose special features that may only
+ be implemented with code generator support.
+ </p>
+
+ </div>
+
+ <!-- _______________________________________________________________________ -->
+ <div class="doc_subsubsection">
+ <a name="i_returnaddress">'<tt>llvm.returnaddress</tt>' Intrinsic</a>
+ </div>
+
+ <div class="doc_text">
+
+ <h5>Syntax:</h5>
+ <pre>
+ call void* ()* %llvm.returnaddress(uint <level>)
+ </pre>
+
+ <h5>Overview:</h5>
+
+ <p>
+ The '<tt>llvm.returnaddress</tt>' intrinsic returns a target-specific value
+ indicating the return address of the current function or one of its callers.
+ </p>
+
+ <h5>Arguments:</h5>
+
+ <p>
+ The argument to this intrinsic indicates which function to return the address
+ for. Zero indicates the calling function, one indicates its caller, etc. The
+ argument is <b>required</b> to be a constant integer value.
+ </p>
+
+ <h5>Semantics:</h5>
+
+ <p>
+ The '<tt>llvm.returnaddress</tt>' intrinsic either returns a pointer indicating
+ the return address of the specified call frame, or zero if it cannot be
+ identified. The value returned by this intrinsic is likely to be incorrect or 0
+ for arguments other than zero, so it should only be used for debugging purposes.
+ </p>
+
+ <p>
+ Note that calling this intrinsic does not prevent function inlining or other
+ aggressive transformations, so the value returned may not that of the obvious
+ source-language caller.
+ </p>
+ </div>
+
+
+ <!-- _______________________________________________________________________ -->
+ <div class="doc_subsubsection">
+ <a name="i_frameaddress">'<tt>llvm.frameaddress</tt>' Intrinsic</a>
+ </div>
+
+ <div class="doc_text">
+
+ <h5>Syntax:</h5>
+ <pre>
+ call void* ()* %llvm.frameaddress(uint <level>)
+ </pre>
+
+ <h5>Overview:</h5>
+
+ <p>
+ The '<tt>llvm.frameaddress</tt>' intrinsic returns the target-specific frame
+ pointer value for the specified stack frame.
+ </p>
+
+ <h5>Arguments:</h5>
+
+ <p>
+ The argument to this intrinsic indicates which function to return the frame
+ pointer for. Zero indicates the calling function, one indicates its caller,
+ etc. The argument is <b>required</b> to be a constant integer value.
+ </p>
+
+ <h5>Semantics:</h5>
+
+ <p>
+ The '<tt>llvm.frameaddress</tt>' intrinsic either returns a pointer indicating
+ the frame address of the specified call frame, or zero if it cannot be
+ identified. The value returned by this intrinsic is likely to be incorrect or 0
+ for arguments other than zero, so it should only be used for debugging purposes.
+ </p>
+
+ <p>
+ Note that calling this intrinsic does not prevent function inlining or other
+ aggressive transformations, so the value returned may not that of the obvious
+ source-language caller.
+ </p>
+ </div>
+
+ <!-- ======================================================================= -->
+ <div class="doc_subsection">
+ <a name="int_os">Operating System Intrinsics</a>
+ </div>
+
+ <div class="doc_text">
+ <p>
+ These intrinsics are provided by LLVM to support the implementation of
+ operating system level code.
+ </p>
+
+ </div>
+
+ <!-- _______________________________________________________________________ -->
+ <div class="doc_subsubsection">
+ <a name="i_readport">'<tt>llvm.readport</tt>' Intrinsic</a>
+ </div>
+
+ <div class="doc_text">
+
+ <h5>Syntax:</h5>
+ <pre>
+ call <integer type> (<integer type>)* %llvm.readport (<integer type> <address>)
+ </pre>
+
+ <h5>Overview:</h5>
+
+ <p>
+ The '<tt>llvm.readport</tt>' intrinsic reads data from the specified hardware
+ I/O port.
+ </p>
+
+ <h5>Arguments:</h5>
+
+ <p>
+ The argument to this intrinsic indicates the hardware I/O address from which
+ to read the data. The address is in the hardware I/O address namespace (as
+ opposed to being a memory location for memory mapped I/O).
+ </p>
+
+ <h5>Semantics:</h5>
+
+ <p>
+ The '<tt>llvm.readport</tt>' intrinsic reads data from the hardware I/O port
+ specified by <i>address</i> and returns the value. The address and return
+ value must be integers, but the size is dependent upon the platform upon which
+ the program is code generated. For example, on x86, the address must be an
+ unsigned 16 bit value, and the return value must be 8, 16, or 32 bits.
+ </p>
+
+ </div>
+
+ <!-- _______________________________________________________________________ -->
+ <div class="doc_subsubsection">
+ <a name="i_writeport">'<tt>llvm.writeport</tt>' Intrinsic</a>
+ </div>
+
+ <div class="doc_text">
+
+ <h5>Syntax:</h5>
+ <pre>
+ call void (<integer type>, <integer type>)* %llvm.writeport (<integer type> <value>, <integer type> <address>)
+ </pre>
+
+ <h5>Overview:</h5>
+
+ <p>
+ The '<tt>llvm.writeport</tt>' intrinsic writes data to the specified hardware
+ I/O port.
+ </p>
+
+ <h5>Arguments:</h5>
+
+ <p>
+ The first argument is the value to write to the I/O port.
+ </p>
+
+ <p>
+ The second argument indicates the hardware I/O address to which data should be
+ written. The address is in the hardware I/O address namespace (as opposed to
+ being a memory location for memory mapped I/O).
+ </p>
+
+ <h5>Semantics:</h5>
+
+ <p>
+ The '<tt>llvm.writeport</tt>' intrinsic writes <i>value</i> to the I/O port
+ specified by <i>address</i>. The address and value must be integers, but the
+ size is dependent upon the platform upon which the program is code generated.
+ For example, on x86, the address must be an unsigned 16 bit value, and the
+ value written must be 8, 16, or 32 bits in length.
+ </p>
+
+ </div>
+
+ <!-- _______________________________________________________________________ -->
+ <div class="doc_subsubsection">
+ <a name="i_readio">'<tt>llvm.readio</tt>' Intrinsic</a>
+ </div>
+
+ <div class="doc_text">
+
+ <h5>Syntax:</h5>
+ <pre>
+ call <result> (<ty>*)* %llvm.readio (<ty> * <pointer>)
+ </pre>
+
+ <h5>Overview:</h5>
+
+ <p>
+ The '<tt>llvm.readio</tt>' intrinsic reads data from a memory mapped I/O
+ address.
+ </p>
+
+ <h5>Arguments:</h5>
+
+ <p>
+ The argument to this intrinsic is a pointer indicating the memory address from
+ which to read the data. The data must be a
+ <a href="#t_firstclass">first class</a> type.
+ </p>
+
+ <h5>Semantics:</h5>
+
+ <p>
+ The '<tt>llvm.readio</tt>' intrinsic reads data from a memory mapped I/O
+ location specified by <i>pointer</i> and returns the value. The argument must
+ be a pointer, and the return value must be a
+ <a href="#t_firstclass">first class</a> type. However, certain architectures
+ may not support I/O on all first class types. For example, 32 bit processors
+ may only support I/O on data types that are 32 bits or less.
+ </p>
+
+ <p>
+ This intrinsic enforces an in-order memory model for llvm.readio and
+ llvm.writeio calls on machines that use dynamic scheduling. Dynamically
+ scheduled processors may execute loads and stores out of order, re-ordering at
+ run time accesses to memory mapped I/O registers. Using these intrinsics
+ ensures that accesses to memory mapped I/O registers occur in program order.
+ </p>
+
+ </div>
+
+ <!-- _______________________________________________________________________ -->
+ <div class="doc_subsubsection">
+ <a name="i_writeio">'<tt>llvm.writeio</tt>' Intrinsic</a>
+ </div>
+
+ <div class="doc_text">
+
+ <h5>Syntax:</h5>
+ <pre>
+ call void (<ty1>, <ty2>*)* %llvm.writeio (<ty1> <value>, <ty2> * <pointer>)
+ </pre>
+
+ <h5>Overview:</h5>
+
+ <p>
+ The '<tt>llvm.writeio</tt>' intrinsic writes data to the specified memory
+ mapped I/O address.
+ </p>
+
+ <h5>Arguments:</h5>
+
+ <p>
+ The first argument is the value to write to the memory mapped I/O location.
+ The second argument is a pointer indicating the memory address to which the
+ data should be written.
+ </p>
+
+ <h5>Semantics:</h5>
+
+ <p>
+ The '<tt>llvm.writeio</tt>' intrinsic writes <i>value</i> to the memory mapped
+ I/O address specified by <i>pointer</i>. The value must be a
+ <a href="#t_firstclass">first class</a> type. However, certain architectures
+ may not support I/O on all first class types. For example, 32 bit processors
+ may only support I/O on data types that are 32 bits or less.
+ </p>
+
+ <p>
+ This intrinsic enforces an in-order memory model for llvm.readio and
+ llvm.writeio calls on machines that use dynamic scheduling. Dynamically
+ scheduled processors may execute loads and stores out of order, re-ordering at
+ run time accesses to memory mapped I/O registers. Using these intrinsics
+ ensures that accesses to memory mapped I/O registers occur in program order.
+ </p>
+
+ </div>
+
+ <!-- ======================================================================= -->
+ <div class="doc_subsection">
+ <a name="int_libc">Standard C Library Intrinsics</a>
+ </div>
+
+ <div class="doc_text">
+ <p>
+ LLVM provides intrinsics for a few important standard C library functions.
+ These intrinsics allow source-language front-ends to pass information about the
+ alignment of the pointer arguments to the code generator, providing opportunity
+ for more efficient code generation.
+ </p>
+
+ </div>
+
+ <!-- _______________________________________________________________________ -->
+ <div class="doc_subsubsection">
+ <a name="i_memcpy">'<tt>llvm.memcpy</tt>' Intrinsic</a>
+ </div>
+
+ <div class="doc_text">
+
+ <h5>Syntax:</h5>
+ <pre>
+ call void (sbyte*, sbyte*, uint, uint)* %llvm.memcpy(sbyte* <dest>, sbyte* <src>,
+ uint <len>, uint <align>)
+ </pre>
+
+ <h5>Overview:</h5>
+
+ <p>
+ The '<tt>llvm.memcpy</tt>' intrinsic copies a block of memory from the source
+ location to the destination location.
+ </p>
+
+ <p>
+ Note that, unlike the standard libc function, the <tt>llvm.memcpy</tt> intrinsic
+ does not return a value, and takes an extra alignment argument.
+ </p>
+
+ <h5>Arguments:</h5>
+
+ <p>
+ The first argument is a pointer to the destination, the second is a pointer to
+ the source. The third argument is an (arbitrarily sized) integer argument
+ specifying the number of bytes to copy, and the fourth argument is the alignment
+ of the source and destination locations.
+ </p>
+
+ <p>
+ If the call to this intrinisic has an alignment value that is not 0 or 1, then
+ the caller guarantees that the size of the copy is a multiple of the alignment
+ and that both the source and destination pointers are aligned to that boundary.
+ </p>
+
+ <h5>Semantics:</h5>
+
+ <p>
+ The '<tt>llvm.memcpy</tt>' intrinsic copies a block of memory from the source
+ location to the destination location, which are not allowed to overlap. It
+ copies "len" bytes of memory over. If the argument is known to be aligned to
+ some boundary, this can be specified as the fourth argument, otherwise it should
+ be set to 0 or 1.
+ </p>
+ </div>
+
+
+ <!-- _______________________________________________________________________ -->
+ <div class="doc_subsubsection">
+ <a name="i_memmove">'<tt>llvm.memmove</tt>' Intrinsic</a>
+ </div>
+
+ <div class="doc_text">
+
+ <h5>Syntax:</h5>
+ <pre>
+ call void (sbyte*, sbyte*, uint, uint)* %llvm.memmove(sbyte* <dest>, sbyte* <src>,
+ uint <len>, uint <align>)
+ </pre>
+
+ <h5>Overview:</h5>
+
+ <p>
+ The '<tt>llvm.memmove</tt>' intrinsic moves a block of memory from the source
+ location to the destination location. It is similar to the '<tt>llvm.memcpy</tt>'
+ intrinsic but allows the two memory locations to overlap.
+ </p>
+
+ <p>
+ Note that, unlike the standard libc function, the <tt>llvm.memmove</tt> intrinsic
+ does not return a value, and takes an extra alignment argument.
+ </p>
+
+ <h5>Arguments:</h5>
+
+ <p>
+ The first argument is a pointer to the destination, the second is a pointer to
+ the source. The third argument is an (arbitrarily sized) integer argument
+ specifying the number of bytes to copy, and the fourth argument is the alignment
+ of the source and destination locations.
+ </p>
+
+ <p>
+ If the call to this intrinisic has an alignment value that is not 0 or 1, then
+ the caller guarantees that the size of the copy is a multiple of the alignment
+ and that both the source and destination pointers are aligned to that boundary.
+ </p>
+
+ <h5>Semantics:</h5>
+
+ <p>
+ The '<tt>llvm.memmove</tt>' intrinsic copies a block of memory from the source
+ location to the destination location, which may overlap. It
+ copies "len" bytes of memory over. If the argument is known to be aligned to
+ some boundary, this can be specified as the fourth argument, otherwise it should
+ be set to 0 or 1.
+ </p>
+ </div>
+
+
+ <!-- _______________________________________________________________________ -->
+ <div class="doc_subsubsection">
+ <a name="i_memset">'<tt>llvm.memset</tt>' Intrinsic</a>
+ </div>
+
+ <div class="doc_text">
+
+ <h5>Syntax:</h5>
+ <pre>
+ call void (sbyte*, ubyte, uint, uint)* %llvm.memset(sbyte* <dest>, ubyte <val>,
+ uint <len>, uint <align>)
+ </pre>
+
+ <h5>Overview:</h5>
+
+ <p>
+ The '<tt>llvm.memset</tt>' intrinsic fills a block of memory with a particular
+ byte value.
+ </p>
+
+ <p>
+ Note that, unlike the standard libc function, the <tt>llvm.memset</tt> intrinsic
+ does not return a value, and takes an extra alignment argument.
+ </p>
+
+ <h5>Arguments:</h5>
+
+ <p>
+ The first argument is a pointer to the destination to fill, the second is the
+ byte value to fill it with, the third argument is an (arbitrarily sized) integer
+ argument specifying the number of bytes to fill, and the fourth argument is the
+ known alignment of destination location.
+ </p>
+
+ <p>
+ If the call to this intrinisic has an alignment value that is not 0 or 1, then
+ the caller guarantees that the size of the copy is a multiple of the alignment
+ and that the destination pointer is aligned to that boundary.
+ </p>
+
+ <h5>Semantics:</h5>
+
+ <p>
+ The '<tt>llvm.memset</tt>' intrinsic fills "len" bytes of memory starting at the
+ destination location. If the argument is known to be aligned to some boundary,
+ this can be specified as the fourth argument, otherwise it should be set to 0 or
+ 1.
+ </p>
+ </div>
+
+
+ <!-- _______________________________________________________________________ -->
+ <div class="doc_subsubsection">
+ <a name="i_isunordered">'<tt>llvm.isunordered</tt>' Intrinsic</a>
+ </div>
+
+ <div class="doc_text">
+
+ <h5>Syntax:</h5>
+ <pre>
+ call bool (<float or double>, <float or double>)* %llvm.isunordered(<float or double> Val1,
+ <float or double> Val2)
+ </pre>
+
+ <h5>Overview:</h5>
+
+ <p>
+ The '<tt>llvm.isunordered</tt>' intrinsic returns true if either or both of the
+ specified floating point values is a NAN.
+ </p>
+
+ <h5>Arguments:</h5>
+
+ <p>
+ The arguments are floating point numbers of the same type.
+ </p>
+
+ <h5>Semantics:</h5>
+
+ <p>
+ If either or both of the arguments is a SNAN or QNAN, it returns true, otherwise
+ false.
+ </p>
+ </div>
+
+
+
+
+ <!-- ======================================================================= -->
+ <div class="doc_subsection">
+ <a name="int_debugger">Debugger Intrinsics</a>
+ </div>
+
+ <div class="doc_text">
+ <p>
+ The LLVM debugger intrinsics (which all start with <tt>llvm.dbg.</tt> prefix),
+ are described in the <a
+ href="SourceLevelDebugging.html#format_common_intrinsics">LLVM Source Level
+ Debugging</a> document.
+ </p>
+ </div>
+
+
+ <!-- *********************************************************************** -->
+ <hr>
+ <address>
+ <a href="http://jigsaw.w3.org/css-validator/check/referer"><img
+ src="http://jigsaw.w3.org/css-validator/images/vcss" alt="Valid CSS!"></a>
+ <a href="http://validator.w3.org/check/referer"><img
+ src="http://www.w3.org/Icons/valid-html401" alt="Valid HTML 4.01!" /></a>
+
+ <a href="mailto:sabre at nondot.org">Chris Lattner</a><br>
+ <a href="http://llvm.cs.uiuc.edu">The LLVM Compiler Infrastructure</a><br>
+ Last modified: $Date: 2004/08/13 22:03:03 $
+ </address>
+ </body>
+ </html>
Index: llvm-www/releases/1.3/docs/LLVMVsTheWorld.html
diff -c /dev/null llvm-www/releases/1.3/docs/LLVMVsTheWorld.html:1.1
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--- 1,180 ----
+ <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"
+ "http://www.w3.org/TR/html4/strict.dtd">
+ <html>
+ <head>
+ <link rel="stylesheet" href="llvm.css" type="text/css">
+ <title>LLVM vs. the World - Comparing Compilers to Compilers</title>
+ </head>
+
+ <body>
+
+ <div class="doc_title">
+ LLVM vs. the World - Comparing Compilers to Compilers
+ </div>
+
+ <ol>
+ <li><a href="#introduction">Introduction</a></li>
+ <li><a href="#generalapplicability">General Applicability</a></li>
+ <li><a href="#typesystem">Type System</a></li>
+ <li><a href="#dataflowinformation">Control-flow and Data-flow Information</a></li>
+ <li><a href="#registers">Registers</a></li>
+ <li><a href="#programmerinterface">Programmer Interface</a></li>
+ <li><a href="#codeemission">Machine Code Emission</a></li>
+ </ol>
+
+ <div class="doc_author">
+ <p>Written by Brian R. Gaeke</p>
+ </div>
+
+ <!-- *********************************************************************** -->
+ <div class="doc_section">
+ <a name="introduction">Introduction</a>
+ </div>
+ <!-- *********************************************************************** -->
+
+ <div class="doc_text">
+ <p>Whether you are a stranger to LLVM or not, and whether you are considering
+ using it for your projects or not, you may find it useful to understand how we
+ compare ourselves to other well-known compilers. The following list of points
+ should help you understand -- from our point of view -- some of the important
+ ways in which we see LLVM as different from other selected compilers and
+ code generation systems.</p>
+
+ <p>At the moment, we only compare ourselves below to <a
+ href="http://gcc.gnu.org/">GCC</a> and <a
+ href="http://www.gnu.org/software/lightning/">GNU lightning</a>, but we will try
+ to revise and expand it as our knowledge and experience permit. Contributions are
+ welcome.</p>
+ </div>
+
+ <!-- *********************************************************************** -->
+ <div class="doc_section">
+ <a name="generalapplicability">General Applicability</a>
+ </div>
+ <!-- *********************************************************************** -->
+
+ <div class="doc_text">
+ <p>GNU lightning: Only currently usable for dynamic runtime emission of binary
+ machine code to memory. Supports one backend at a time.</p>
+
+ <p>LLVM: Supports compilation of C and C++ (with more languages coming soon),
+ strong SSA-based optimization at compile-time, link-time, run-time, and
+ off-line, and multiple platform backends with Just-in-Time and ahead-of-time
+ compilation frameworks. (See our document on <a
+ href="http://llvm.cs.uiuc.edu/pubs/2004-01-30-CGO-LLVM.html">Lifelong
+ Code Optimization</a> for more.)</p>
+
+ <p>GCC: Many relatively mature platform backends support assembly-language code
+ generation from many source languages. No run-time compilation
+ support.</p>
+ </div>
+
+ <!-- *********************************************************************** -->
+ <div class="doc_section">
+ <a name="typesystem">Type System</a>
+ </div>
+ <!-- *********************************************************************** -->
+
+ <div class="doc_text">
+ <p>GNU lightning: C integer types and "void *" are supported. No type checking
+ is performed. Explicit type casts are not typically necessary unless the
+ underlying machine-specific types are distinct (e.g., sign- or zero-extension is
+ apparently necessary, but casting "int" to "void *" would not be.)
+ Floating-point support may not work on all platforms (it does not appear to be
+ documented in the latest release).</p>
+
+ <p>LLVM: Compositional type system based on C types, supporting structures,
+ opaque types, and C integer and floating point types. Explicit cast instructions
+ are required to transform a value from one type to another.</p>
+
+ <p>GCC: Union of high-level types including those used in Pascal, C, C++, Ada,
+ Java, and FORTRAN.</p>
+ </div>
+
+ <!-- *********************************************************************** -->
+ <div class="doc_section">
+ <a name="dataflowinformation">Control-flow and Data-flow Information</a>
+ </div>
+ <!-- *********************************************************************** -->
+
+ <div class="doc_text">
+ <p>GNU lightning: No data-flow information encoded in the generated program. No
+ support for calculating CFG or def-use chains over generated programs.</p>
+
+ <p>LLVM: Scalar values in Static Single-Assignment form; def-use chains and CFG
+ always implicitly available and automatically kept up to date.</p>
+
+ <p>GCC: Trees and RTL do not directly encode data-flow info; but def-use chains
+ and CFGs can be calculated on the side. They are not automatically kept up to
+ date.</p>
+ </div>
+
+ <!-- *********************************************************************** -->
+ <div class="doc_section">
+ <a name="registers">Registers</a>
+ </div>
+ <!-- *********************************************************************** -->
+
+ <div class="doc_text">
+ <p>GNU lightning: Very small fixed register set -- it takes the least common
+ denominator of supported platforms; basically it inherits its tiny register set
+ from IA-32, unnecessarily crippling targets like PowerPC with a large register
+ set.</p>
+
+ <p>LLVM: An infinite register set, reduced to a particular platform's finite
+ register set by register allocator.</p>
+
+ <p>GCC: Trees and RTL provide an arbitrarily large set of values. Reduced to a
+ particular platform's finite register set by register allocator.</p>
+ </div>
+
+ <!-- *********************************************************************** -->
+ <div class="doc_section">
+ <a name="programmerinterface">Programmer Interface</a>
+ </div>
+ <!-- *********************************************************************** -->
+
+ <div class="doc_text">
+ <p>GNU lightning: Library interface based on C preprocessor macros that emit
+ binary code for a particular instruction to memory. No support for manipulating
+ code before emission.</p>
+
+ <p>LLVM: Library interface based on classes representing platform-independent
+ intermediate code (Instruction) and platform-dependent code (MachineInstr) which
+ can be manipulated arbitrarily and then emitted to memory.</p>
+
+ <p>GCC: Internal header file interface (tree.h) to abstract syntax trees,
+ representing roughly the union of all possible supported source-language
+ constructs; also, an internal header file interface (rtl.h, rtl.def) to a
+ low-level IR called RTL which represents roughly the union of all possible
+ target machine instructions.</p>
+ </div>
+
+ <!-- *********************************************************************** -->
+ <div class="doc_section">
+ <a name="codeemission">Machine Code Emission</a>
+ </div>
+ <!-- *********************************************************************** -->
+
+ <div class="doc_text">
+ <p>GNU lightning: Only supports binary machine code emission to memory.</p>
+
+ <p>LLVM: Supports writing out assembly language to a file, and binary machine
+ code to memory, from the same back-end.</p>
+
+ <p>GCC: Supports writing out assembly language to a file. No support for
+ emitting machine code to memory.</p>
+ </div>
+
+ <!-- *********************************************************************** -->
+
+ <hr>
+ <div class="doc_footer">
+ <address>Brian R. Gaeke</address>
+ <a href="http://llvm.cs.uiuc.edu">The LLVM Compiler Infrastructure</a>
+ <br>
+ Last modified: $Date: 2004/08/13 22:03:03 $
+ </div>
+
+ </body>
+ </html>
Index: llvm-www/releases/1.3/docs/ObjectFiles.html
diff -c /dev/null llvm-www/releases/1.3/docs/ObjectFiles.html:1.1
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+ <!DOCTYPE HTML PUBLIC "-//W3C//DTD XHTML 1.1//EN" "http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd">
+ <html>
+ <head>
+ <title>Object Files: Understanding The Result Of LLVM Compilation</title>
+ <link rel="stylesheet" href="llvm.css" type="text/css">
+ </head>
+ <body>
+ <div class="doc_title">Object Files: Understanding The Result Of LLVM Compilation</div>
+ <hr>
+ <ol>
+ <li><a href="#abstract">Abstract</a></li>
+ <li><a href="#introduction">Introduction</a></li>
+ <li><a href="#files">File Contents</a></li>
+ <li><a href="#rot">Linkage Rules Of Thumb</a>
+ <ol>
+ <li><a href="#always">Always Link vmcore.o, support.a</a>
+ <li><a href="#placeholder">Placeholder</a>
+ </ol>
+ </li>
+ </ol>
+
+ <div class="doc_author">
+ <p>Written by <a href="mailto:rspencer at x10sys.com">Reid Spencer</a></p>
+ </div>
+
+ <hr>
+
+ <!-- ======================================================================= -->
+ <div class="doc_section"><a name="abstract">Abstract</a></div>
+ <div class="doc_text">
+ <p>This document describes the contents of the many objects files and libraries
+ that are produced by compiling LLVM. To make use of LLVM this information is
+ needed in order to understand what files should be linked into your program.
+ </p>
+ </div>
+ <!-- ======================================================================= -->
+ <div class="doc_section"> <a name="introduction">Introduction</a></div>
+ <div class="doc_text">
+ <p>If you're writing a compiler, virtual machine, or any other utility for
+ LLVM, you'll need to figure out which of the many .a (archive) and .o
+ (object) files you will need to link with to be successful. An
+ understanding of the contents of these files and their inter-relationships
+ will be useful in coming up with an optimal specification for the objects
+ and libraries to link with.
+ </p>
+ <p>The purpose of this document is to hopefully reduce some of the trial and
+ error that the author experienced in using LLVM.
+ </p>
+ </div>
+ <!-- ======================================================================= -->
+ <div class="doc_section"><a name="files"></a>File Contents</div>
+ <div class="doc_text">
+ <p>The table below provides a summary of the basic contents of each file.</p>
+ <table class="doc_table"
+ style="width:80%; text-align: left; border: 2px solid blue; border-collapse: collapse;">
+ <tr class="doc_table">
+ <td colspan="2" class="doc_section">Summary Of LLVM Library And Object Files
+ </td>
+ </tr>
+ <tr class="doc_table">
+ <td style="border: 2px solid blue"><h2><u>Library</u></h2></td>
+ <td style="border: 2px solid blue"><h2><u>Description</u></h2></td>
+ </tr>
+ <tr class="doc_table">
+ <td style="border: 2px solid blue">libipo.a</td>
+ <td style="border: 2px solid blue">
+ An archive of all inter-procedural optimizations.
+ </td>
+ </tr>
+ <tr class="doc_table">
+ <td style="border: 2px solid blue">libscalaropts.a</td>
+ <td style="border: 2px solid blue">
+ An archive of all scalar optimizations.
+ </td>
+ </tr>
+ <tr class="doc_table">
+ <td style="border: 2px solid blue">libtransforms.a</td>
+ <td style="border: 2px solid blue">
+ An archive of just the level raise pass.
+ </td>
+ </tr>
+ <tr class="doc_table">
+ <td style="border: 2px solid blue">libtarget.a</td>
+ <td style="border: 2px solid blue">
+ An archive containing code generator support for describing
+ target architectures.
+ </td>
+ </tr>
+ <tr class="doc_table">
+ <td style="border: 2px solid blue">libanalysis.a</td>
+ <td style="border: 2px solid blue">
+ An archive containing intra-procedural analyses.
+ </td>
+ </tr>
+ <tr class="doc_table">
+ <td style="border: 2px solid blue">libdatastructure.a</td>
+ <td style="border: 2px solid blue">
+ An archive containing optimizations for data structures.
+ </td>
+ </tr>
+ <tr class="doc_table">
+ <td style="border: 2px solid blue">libinstrument.a</td>
+ <td style="border: 2px solid blue">No idea.</td>
+ </tr>
+ <tr class="doc_table">
+ <td style="border: 2px solid blue">libregalloc.a</td>
+ <td style="border: 2px solid blue">Register Allocation code.</td>
+ </tr>
+ <tr class="doc_table">
+ <td style="border: 2px solid blue">libipa.a</td>
+ <td style="border: 2px solid blue">
+ An archive containing inter-procedural analyses</td>
+ </tr>
+ <tr class="doc_table">
+ <td style="border: 2px solid blue">libtransformutils.a</td>
+ <td style="border: 2px solid blue">
+ Utiltities for transformations?
+ </td>
+ </tr>
+ <tr class="doc_table">
+ <td style="border: 2px solid blue">libsupport.a</td>
+ <td style="border: 2px solid blue">General support utilities</td>
+ </tr>
+ <tr class="doc_table">
+ <td style="border: 2px solid blue">libevar.a</td>
+ <td style="border: 2px solid blue">Live variable analysis for SPARC</td>
+ </tr>
+ <tr class="doc_table">
+ <td style="border: 2px solid blue"><h2><u>Object File</u></h2></td>
+ <td style="border: 2px solid blue"><h2><u>Description</u></h2></td>
+ </tr>
+ <tr class="doc_table">
+ <td style="border: 2px solid blue">support.o</td>
+ <td style="border: 2px solid blue">General support utilities</td>
+ </tr>
+ <tr class="doc_table">
+ <td style="border: 2px solid blue">asmparser.o</td>
+ <td style="border: 2px solid blue">Assembler Parser</td>
+ </tr>
+ <tr class="doc_table">
+ <td style="border: 2px solid blue">bcreader.o</td>
+ <td style="border: 2px solid blue">Byte Code Reader</td>
+ </tr>
+ <tr class="doc_table">
+ <td style="border: 2px solid blue">bcwriter.o</td>
+ <td style="border: 2px solid blue">Byte Code Writer</td>
+ </tr>
+ <tr class="doc_table">
+ <td style="border: 2px solid blue">sched.o</td>
+ <td style="border: 2px solid blue">SPARC instruction scheduler</td>
+ </tr>
+ <tr class="doc_table">
+ <td style="border: 2px solid blue">selectiondag.o</td>
+ <td style="border: 2px solid blue">Aggressive instruction selector for Directed Acyclic Graphs</td>
+ </tr>
+ <tr class="doc_table">
+ <td style="border: 2px solid blue">transformutils.o</td>
+ <td style="border: 2px solid blue">Utilities for code transformations</td>
+ </tr>
+ <tr class="doc_table">
+ <td style="border: 2px solid blue">ipa.o</td>
+ <td style="border: 2px solid blue">Inter-Procedural Analysis Optimizations</td>
+ </tr>
+ <tr class="doc_table">
+ <td style="border: 2px solid blue">select.o</td>
+ <td style="border: 2px solid blue">SPARC instruction selector</td>
+ </tr>
+ <tr class="doc_table">
+ <td style="border: 2px solid blue">cwriter.o</td>
+ <td style="border: 2px solid blue">"C" Code Writer</td>
+ </tr>
+ <tr class="doc_table">
+ <td style="border: 2px solid blue">profpaths.o</td>
+ <td style="border: 2px solid blue">Path profiling instrumentation</td>
+ </tr>
+ <tr class="doc_table">
+ <td style="border: 2px solid blue">regalloc.o</td>
+ <td style="border: 2px solid blue">Register Allocation</td>
+ </tr>
+ <tr class="doc_table">
+ <td style="border: 2px solid blue">instrument.o</td>
+ <td style="border: 2px solid blue">Instrumentation? Of What?</td>
+ </tr>
+ <tr class="doc_table">
+ <td style="border: 2px solid blue">datastructure.o</td>
+ <td style="border: 2px solid blue">Data Structure Analysis</td>
+ </tr>
+ <tr class="doc_table">
+ <td style="border: 2px solid blue">codegen.o</td>
+ <td style="border: 2px solid blue">Native code generation</td>
+ </tr>
+ <tr class="doc_table">
+ <td style="border: 2px solid blue">livevar.o</td>
+ <td style="border: 2px solid blue">Live Variable Analysis</td>
+ </tr>
+ <tr class="doc_table">
+ <td style="border: 2px solid blue">vmcore.o</td>
+ <td style="border: 2px solid blue">Virtual Machine Core</td>
+ </tr>
+ <tr class="doc_table">
+ <td style="border: 2px solid blue">lli-interpreter.o</td>
+ <td style="border: 2px solid blue">Interpreter for LLVM ByteCode</td>
+ </tr>
+ <tr class="doc_table">
+ <td style="border: 2px solid blue">lli-jit.o</td>
+ <td style="border: 2px solid blue">
+ Just-In-Time Compiler For LLVM ByteCode
+ </td>
+ </tr>
+ <tr class="doc_table">
+ <td style="border: 2px solid blue">executionengine.o</td>
+ <td style="border: 2px solid blue">Engine for LLI</td>
+ </tr>
+ <tr class="doc_table">
+ <td style="border: 2px solid blue">debugger.o</td>
+ <td style="border: 2px solid blue">Source Level Debugging Support</td>
+ </tr>
+ <tr class="doc_table">
+ <td style="border: 2px solid blue">analysis.o</td>
+ <td style="border: 2px solid blue">General Framework For Analysis?</td>
+ </tr>
+ <tr class="doc_table">
+ <td style="border: 2px solid blue">sparc.o</td>
+ <td style="border: 2px solid blue">Sun SPARC Processor Specific</td>
+ </tr>
+ <tr class="doc_table">
+ <td style="border: 2px solid blue">target.o</td>
+ <td style="border: 2px solid blue">Target Machine Support?</td>
+ </tr>
+ <tr class="doc_table">
+ <td style="border: 2px solid blue">transforms.o</td>
+ <td style="border: 2px solid blue">Code Transformations</td>
+ </tr>
+ <tr class="doc_table">
+ <td style="border: 2px solid blue">x86.o</td>
+ <td style="border: 2px solid blue">Intel x86 Processor Specific</td>
+ </tr>
+ <tr class="doc_table">
+ <td style="border: 2px solid blue">powerpc.o</td>
+ <td style="border: 2px solid blue">PowerPC Processor Specific</td>
+ </tr>
+ <tr class="doc_table">
+ <td style="border: 2px solid blue">scalaropts.o</td>
+ <td style="border: 2px solid blue">Optimizations For Scalars</td>
+ </tr>
+ <tr class="doc_table">
+ <td style="border: 2px solid blue">ipo.o</td>
+ <td style="border: 2px solid blue">Inter-Procedural Optimization</td>
+ </tr>
+ <tr class="doc_table">
+ <td style="border: 2px solid blue">trace.o</td>
+ <td style="border: 2px solid blue">Support For Tracing/Debugging?</td>
+ </tr>
+ <tr class="doc_table">
+ <td style="border: 2px solid blue">profile_rt.o</td>
+ <td style="border: 2px solid blue">Runtime Library For Profiler</td>
+ </tr>
+ <tr class="doc_table">
+ <td style="border: 2px solid blue">sample.o</td>
+ <td style="border: 2px solid blue">Sample Program ?</td>
+ </tr>
+ <tr class="doc_table">
+ <td style="border: 2px solid blue">stkr_compiler.o</td>
+ <td style="border: 2px solid blue">Stacker Language Compiler Library</td>
+ </tr>
+ <tr class="doc_table">
+ <td style="border: 2px solid blue">stkr_runtime.o</td>
+ <td style="border: 2px solid blue">Stacker Language Runtime Library</td>
+ </tr>
+ </table>
+ </div>
+ <p></p>
+ <!-- ======================================================================= -->
+ <div class="doc_section"><a name="rot">Linkage Rules Of Thumb</a></div>
+ <div class="doc_text">
+ <p>This section contains various "rules of thumb" about what files you
+ should link into your programs.</p>
+ </div>
+ <!-- ======================================================================= -->
+ <div class="doc_subsection"><a name="always">Always Link vmcore.o support.a</a>
+ </div>
+ <div class="doc_text">
+ <p>No matter what you do with LLVM, you'll always need to link with vmcore.o
+ and support.a.</p>
+ </div>
+ <!-- ======================================================================= -->
+ <div class="doc_subsection"><a name="Placeholder">Placeholder</a></div>
+ <div class="doc_text">
+ <p>Need more rules of thumb here.</p>
+ </div>
+ <!-- ======================================================================= -->
+ <hr>
+ <div class="doc_footer">
+ <address><a href="mailto:rspencer at x10sys.com">Reid Spencer</a></address>
+ <a href="http://llvm.cs.uiuc.edu">The LLVM Compiler Infrastructure</a>
+ <br>Last modified: $Date: 2004/08/13 22:03:03 $ </div>
+ </body>
+ </html>
+ <!-- vim: sw=2 ts=2 ai
+ -->
Index: llvm-www/releases/1.3/docs/OpenProjects.html
diff -c /dev/null llvm-www/releases/1.3/docs/OpenProjects.html:1.1
*** /dev/null Fri Aug 13 17:03:14 2004
--- llvm-www/releases/1.3/docs/OpenProjects.html Fri Aug 13 17:03:04 2004
***************
*** 0 ****
--- 1,360 ----
+ <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"
+ "http://www.w3.org/TR/html4/strict.dtd">
+ <html>
+ <head>
+ <title>Open LLVM Projects</title>
+ <link rel="stylesheet" href="llvm.css" type="text/css">
+ </head>
+ <body>
+
+ <div class="doc_title">
+ Open LLVM Projects
+ </div>
+
+ <ul>
+ <li><a href="#what">What is this?</a></li>
+ <li><a href="#improving">Improving the current system</a>
+ <ol>
+ <li><a href="#code-cleanups">Implementing Code Cleanup bugs</a></li>
+ <li><a href="#glibc">Port glibc to LLVM</a></li>
+ <li><a href="#programs">Compile programs with the LLVM Compiler</a></li>
+ <li><a href="#llvm_ir">Extend the LLVM intermediate representation</a></li>
+ <li><a href="#misc_imp">Miscellaneous Improvements</a></li>
+ </ol></li>
+
+ <li><a href="#new">Adding new capabilities to LLVM</a>
+ <ol>
+ <li><a href="#newfeaturebugs">Implementing new feature PRs</a></li>
+ <li><a href="#pointeranalysis">Pointer and Alias Analysis</a></li>
+ <li><a href="#profileguided">Profile Guided Optimization</a></li>
+ <li><a href="#xforms">New Transformations and Analyses</a></li>
+ <li><a href="#x86be">X86 Back-end Improvements</a></li>
+ <li><a href="#misc_new">Miscellaneous Additions</a></li>
+ </ol></li>
+ </ul>
+
+ <div class="doc_author">
+ <p>Written by the <a href="http://llvm.cs.uiuc.edu/">LLVM Team</a></p>
+ </div>
+
+
+ <!-- *********************************************************************** -->
+ <div class="doc_section">
+ <a name="what">What is this?</a>
+ </div>
+ <!-- *********************************************************************** -->
+
+ <div class="doc_text">
+
+ <p>This document is meant to be a sort of "big TODO list" for LLVM. Each
+ project in this document is something that would be useful for LLVM to have, and
+ would also be a great way to get familiar with the system. Some of these
+ projects are small and self-contained, which may be implemented in a couple of
+ days, others are larger. Several of these projects may lead to interesting
+ research projects in their own right. In any case, we welcome all
+ contributions.</p>
+
+ <p>If you are thinking about tackling one of these projects, please send a mail
+ to the <a href="http://mail.cs.uiuc.edu/mailman/listinfo/llvmdev">LLVM
+ Developer's</a> mailing list, so that we know the project is being worked on.
+ Additionally this is a good way to get more information about a specific project
+ or to suggest other projects to add to this page.
+ </p>
+
+ <p>The projects in this page are open-ended. More specific projects are
+ filed as unassigned enhancements in the <a href="http://llvm.cs.uiuc.edu/bugs/">
+ LLVM bug tracker</a>. See the <a href="http://llvm.cs.uiuc.edu/bugs/buglist.cgi?keywords_type=allwords&keywords=&bug_status=NEW&bug_status=ASSIGNED&bug_status=REOPENED&bug_severity=enhancement&emailassigned_to1=1&emailtype1=substring&email1=unassigned">list of currently outstanding issues</a> if you wish to help improve LLVM.</p>
+
+ </div>
+
+ <!-- *********************************************************************** -->
+ <div class="doc_section">
+ <a name="improving">Improving the current system</a>
+ </div>
+ <!-- *********************************************************************** -->
+
+ <div class="doc_text">
+
+ <p>Improvements to the current infrastructure are always very welcome and tend
+ to be fairly straight-forward to implement. Here are some of the key areas that
+ can use improvement...</p>
+
+ </div>
+
+ <!-- ======================================================================= -->
+ <div class="doc_subsection">
+ <a name="code-cleanups">Implementing Code Cleanup bugs</a>
+ </div>
+
+ <div class="doc_text">
+
+ <p>
+ The <a href="http://llvm.cs.uiuc.edu/bugs/">LLVM bug tracker</a> occasionally
+ has <a href="http://llvm.cs.uiuc.edu/bugs/buglist.cgi?short_desc_type=allwordssubstr&short_desc=&long_desc_type=allwordssubstr&long_desc=&bug_file_loc_type=allwordssubstr&bug_file_loc=&status_whiteboard_type=allwordssubstr&status_whiteboard=&keywords_type=allwords&keywords=code-cleanup&bug_status=NEW&bug_status=ASSIGNED&bug_status=REOPENED&emailassigned_to1=1&emailtype1=substring&email1=&emailassigned_to2=1&emailreporter2=1&emailcc2=1&emailtype2=substring&email2=&bugidtype=include&bug_id=&votes=&changedin=&chfieldfrom=&chfieldto=Now&chfieldvalue=&cmdtype=doit&order=Bug+Number&field0-0-0=noop&type0-0-0=noop&value0-0-0=">"code-cleanup" bugs</a> filed in it. Taking one of these and fixing it is a good
+ way to get your feet wet in the LLVM code and discover how some of its components
+ work.
+ </p>
+
+ </div>
+
+ <!-- ======================================================================= -->
+ <div class="doc_subsection">
+ <a name="glibc">Port glibc to LLVM</a>
+ </div>
+
+ <div class="doc_text">
+
+ <p>It would be very useful to <a
+ href="http://www.gnu.org/software/libc/manual/html_node/Porting.html">port</a> <a
+ href="http://www.gnu.org/software/libc/">glibc</a> to LLVM. This would allow a
+ variety of interprocedural algorithms to be much more effective in the face of
+ library calls. The most important pieces to port are things like the string
+ library and the <tt>stdio</tt> related functions... low-level system calls like
+ '<tt>read</tt>' should stay unimplemented in LLVM.</p>
+
+ </div>
+
+ <!-- ======================================================================= -->
+ <div class="doc_subsection">
+ <a name="programs">Compile programs with the LLVM Compiler</a>
+ </div>
+
+ <div class="doc_text">
+
+ <p>We are always looking for new testcases and benchmarks for use with LLVM. In
+ particular, it is useful to try compiling your favorite C source code with LLVM.
+ If it doesn't compile, try to figure out why or report it to the <a
+ href="http://mail.cs.uiuc.edu/pipermail/llvmbugs/">llvm-bugs</a> list. If you
+ get the program to compile, it would be extremely useful to convert the build
+ system to be compatible with the LLVM Programs testsuite so that we can check it
+ into CVS and the automated tester can use it to track progress of the
+ compiler.</p>
+
+ <p>When testing a code, try running it with a variety of optimizations, and with
+ all the back-ends: CBE, llc, and lli.</p>
+
+ </div>
+
+ <!-- ======================================================================= -->
+ <div class="doc_subsection">
+ <a name="llvm_ir">Extend the LLVM intermediate representation</a>
+ </div>
+
+ <div class="doc_text">
+
+ <ol>
+ <li>Add support for platform-independent prefetch support. The GCC <a
+ href="http://gcc.gnu.org/projects/prefetch.html">prefetch project</a> page
+ has a good survey of the prefetching capabilities of a variety of modern
+ processors.</li>
+
+ </ol>
+
+ </div>
+
+ <!-- ======================================================================= -->
+ <div class="doc_subsection">
+ <a name="misc_imp">Miscellaneous Improvements</a>
+ </div>
+
+ <div class="doc_text">
+
+ <ol>
+ <li>Someone needs to look into getting the <tt>ranlib</tt> tool to index LLVM
+ bytecode files, so that linking in .a files is not hideously slow. They
+ would also then have to implement the reader for this index in
+ <tt>gccld</tt>.</li>
+
+ <li>Rework the PassManager to be more flexible</li>
+
+ <li>Some transformations and analyses only work on reducible flow graphs. It
+ would be nice to have a transformation which could be "required" by these passes
+ which makes irreducible graphs reducible. This can easily be accomplished
+ through code duplication. See <a
+ href="http://citeseer.nj.nec.com/janssen97making.html">Making Graphs Reducible
+ with Controlled Node Splitting</a> and perhaps <a
+ href="http://doi.acm.org/10.1145/262004.262005">Nesting of Reducible and
+ Irreducible Loops</a>.</li>
+
+ </ol>
+
+ </div>
+
+ <!-- *********************************************************************** -->
+ <div class="doc_section">
+ <a name="new">Adding new capabilities to LLVM</a>
+ </div>
+ <!-- *********************************************************************** -->
+
+ <div class="doc_text">
+
+ <p>Sometimes creating new things is more fun than improving existing things.
+ These projects tend to be more involved and perhaps require more work, but can
+ also be very rewarding.</p>
+
+ </div>
+
+
+ <!-- ======================================================================= -->
+ <div class="doc_subsection">
+ <a name="newfeaturebugs">Implementing new feature PRs</a>
+ </div>
+
+ <div class="doc_text">
+
+ <p>Many ideas for feature requests are stored in LLVM bugzilla. Just <a href="http://llvm.org/bugs/buglist.cgi?short_desc_type=allwordssubstr&short_desc=&long_desc_type=allwordssubstr&long_desc=&bug_file_loc_type=allwordssubstr&bug_file_loc=&status_whiteboard_type=allwordssubstr&status_whiteboard=&keywords_type=allwords&keywords=new-feature&bug_status=UNCONFIRMED&bug_status=NEW&bug_status=ASSIGNED&bug_status=REOPENED&emailassigned_to1=1&emailtype1=substring&email1=&emailassigned_to2=1&emailreporter2=1&emailcc2=1&emailtype2=substring&email2=&bugidtype=include&bug_id=&votes=&changedin=&chfieldfrom=&chfieldto=Now&chfieldvalue=&cmdtype=doit&namedcmd=All+PRs&newqueryname=&order=Bug+Number&field0-0-0=noop&type0-0-0=noop&value0-0-0=">search for bugs with a "new-feature" keyword</a>.</p>
+
+ </div>
+
+ <!-- ======================================================================= -->
+ <div class="doc_subsection">
+ <a name="pointeranalysis">Pointer and Alias Analysis</a>
+ </div>
+
+ <div class="doc_text">
+
+ <p>We have a <a href="AliasAnalysis.html">strong base for development</a> of
+ both pointer analysis based optimizations as well as pointer analyses
+ themselves. It seems natural to want to take advantage of this...</p>
+
+ <ol>
+ <li>Implement a flow-sensitive context-sensitive alias analysis algorithm<br>
+ - Pick one of the somewhat efficient algorithms, but strive for maximum
+ precision</li>
+
+ <li>Implement a flow-sensitive context-insensitive alias analysis algorithm<br>
+ - Just an efficient local algorithm perhaps?</li>
+
+ <li>Implement alias-analysis-based optimizations:
+ <ul>
+ <li>Dead store elimination</li>
+ <li>...</li>
+ </ul></li>
+ </ol>
+
+ </div>
+
+ <!-- ======================================================================= -->
+ <div class="doc_subsection">
+ <a name="profileguided">Profile Guided Optimization</a>
+ </div>
+
+ <div class="doc_text">
+
+ <p>We now have a unified infrastructure for writing profile-guided
+ transformations, which will work either at offline-compile-time or in the JIT,
+ but we don't have many transformations. We would welcome new profile-guided
+ transformations as well as improvements to the current profiling system.
+ </p>
+
+ <p>Ideas for profile guided transformations:</p>
+
+ <ol>
+ <li>Superblock formation (with many optimizations)</li>
+ <li>Loop unrolling/peeling</li>
+ <li>Profile directed inlining</li>
+ <li>Code layout</li>
+ <li>...</li>
+ </ol>
+
+ <p>Improvements to the existing support:</p>
+
+ <ol>
+ <li>The current block and edge profiling code that gets inserted is very simple
+ and inefficient. Through the use of control-dependence information, many fewer
+ counters could be inserted into the code. Also, if the execution count of a
+ loop is known to be a compile-time or runtime constant, all of the counters in
+ the loop could be avoided.</li>
+
+ <li>You could implement one of the "static profiling" algorithms which analyze a
+ piece of code an make educated guesses about the relative execution frequencies
+ of various parts of the code.</li>
+
+ <li>You could add path profiling support, or adapt the existing LLVM path
+ profiling code to work with the generic profiling interfaces.</li>
+ </ol>
+
+ </div>
+
+ <!-- ======================================================================= -->
+ <div class="doc_subsection">
+ <a name="xforms">New Transformations and Analyses</a>
+ </div>
+
+ <div class="doc_text">
+
+ <ol>
+ <li>Implement a Dependence Analysis Infrastructure<br>
+ - Design some way to represent and query dep analysis</li>
+ <li>Implement a strength reduction pass</li>
+ <li>Value range propagation pass</li>
+ </ol>
+
+ </div>
+
+ <!-- ======================================================================= -->
+ <div class="doc_section">
+ <a name="x86be">X86 Back-end Improvements</a>
+ </div>
+
+ <div class="doc_text">
+
+ <ol>
+ <li>Implement a better instruction selector</li>
+ <li>Implement support for the "switch" instruction without requiring the
+ lower-switches pass.</li>
+ <li>Implement interprocedural register allocation. The CallGraphSCCPass can be
+ used to implement a bottom-up analysis that will determine the *actual*
+ registers clobbered by a function. Use the pass to fine tune register usage
+ in callers based on *actual* registers used by the callee.</li>
+ </ol>
+
+ </div>
+
+ <!-- ======================================================================= -->
+ <div class="doc_section">
+ <a name="misc_new">Miscellaneous Additions</a>
+ </div>
+
+ <div class="doc_text">
+
+ <ol>
+ <li>Port the <a href="http://www-sop.inria.fr/mimosa/fp/Bigloo/">Bigloo</A>
+ Scheme compiler, from Manuel Serrano at INRIA Sophia-Antipolis, to
+ output LLVM bytecode. It seems that it can already output .NET
+ bytecode, JVM bytecode, and C, so LLVM would ostensibly be another good
+ candidate.</li>
+ <li>Write a new frontend for C/C++ <b>in</b> C++, giving us the ability to
+ directly use LLVM C++ classes from within a compiler rather than use
+ C-based wrapper functions a la llvm-gcc. One possible starting point is the <a
+ href="http://www.parashift.com/c++-faq-lite/compiler-dependencies.html#faq-37.11">C++
+ yacc grammar by Ed Willink</a>.</li>
+ <li>Write a new frontend for some other language (Java? OCaml? Forth?)</li>
+ <li>Write a new backend for a target (IA64? MIPS? MMIX?)</li>
+ <li>Write a disassembler for machine code that would use TableGen to output
+ <tt>MachineInstr</tt>s for transformations, optimizations, etc.</li>
+ <li>Random test vector generator: Use a C grammar to generate random C code;
+ run it through llvm-gcc, then run a random set of passes on it using opt.
+ Try to crash opt. When opt crashes, use bugpoint to reduce the test case and
+ mail the result to yourself. Repeat ad infinitum.</li>
+ <li>Design a simple, recognizable logo.</li>
+ </ol>
+
+ </div>
+
+ <!-- *********************************************************************** -->
+
+ <hr>
+ <address>
+ <a href="http://jigsaw.w3.org/css-validator/check/referer"><img
+ src="http://jigsaw.w3.org/css-validator/images/vcss" alt="Valid CSS!"></a>
+ <a href="http://validator.w3.org/check/referer"><img
+ src="http://www.w3.org/Icons/valid-html401" alt="Valid HTML 4.01!"></a>
+
+ <a href="mailto:sabre at nondot.org">Chris Lattner</a><br>
+ <a href="http://llvm.cs.uiuc.edu">LLVM Compiler Infrastructure</a><br>
+ Last modified: $Date: 2004/08/13 22:03:04 $
+ </address>
+
+ </body>
+ </html>
Index: llvm-www/releases/1.3/docs/ProgrammersManual.html
diff -c /dev/null llvm-www/releases/1.3/docs/ProgrammersManual.html:1.1
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*** 0 ****
--- 1,2053 ----
+ <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"
+ "http://www.w3.org/TR/html4/strict.dtd">
+ <html>
+ <head>
+ <title>LLVM Programmer's Manual</title>
+ <link rel="stylesheet" href="llvm.css" type="text/css">
+ </head>
+ <body>
+
+ <div class="doc_title">
+ LLVM Programmer's Manual
+ </div>
+
+ <ol>
+ <li><a href="#introduction">Introduction</a></li>
+ <li><a href="#general">General Information</a>
+ <ul>
+ <li><a href="#stl">The C++ Standard Template Library</a><!--
+ <li>The <tt>-time-passes</tt> option
+ <li>How to use the LLVM Makefile system
+ <li>How to write a regression test
+ --> </li>
+ </ul>
+ </li>
+ <li><a href="#apis">Important and useful LLVM APIs</a>
+ <ul>
+ <li><a href="#isa">The <tt>isa<></tt>, <tt>cast<></tt>
+ and <tt>dyn_cast<></tt> templates</a> </li>
+ <li><a href="#DEBUG">The <tt>DEBUG()</tt> macro & <tt>-debug</tt>
+ option</a>
+ <ul>
+ <li><a href="#DEBUG_TYPE">Fine grained debug info with <tt>DEBUG_TYPE</tt>
+ and the <tt>-debug-only</tt> option</a> </li>
+ </ul>
+ </li>
+ <li><a href="#Statistic">The <tt>Statistic</tt> template & <tt>-stats</tt>
+ option</a><!--
+ <li>The <tt>InstVisitor</tt> template
+ <li>The general graph API
+ --> </li>
+ </ul>
+ </li>
+ <li><a href="#common">Helpful Hints for Common Operations</a>
+ <ul>
+ <li><a href="#inspection">Basic Inspection and Traversal Routines</a>
+ <ul>
+ <li><a href="#iterate_function">Iterating over the <tt>BasicBlock</tt>s
+ in a <tt>Function</tt></a> </li>
+ <li><a href="#iterate_basicblock">Iterating over the <tt>Instruction</tt>s
+ in a <tt>BasicBlock</tt></a> </li>
+ <li><a href="#iterate_institer">Iterating over the <tt>Instruction</tt>s
+ in a <tt>Function</tt></a> </li>
+ <li><a href="#iterate_convert">Turning an iterator into a
+ class pointer</a> </li>
+ <li><a href="#iterate_complex">Finding call sites: a more
+ complex example</a> </li>
+ <li><a href="#calls_and_invokes">Treating calls and invokes
+ the same way</a> </li>
+ <li><a href="#iterate_chains">Iterating over def-use &
+ use-def chains</a> </li>
+ </ul>
+ </li>
+ <li><a href="#simplechanges">Making simple changes</a>
+ <ul>
+ <li><a href="#schanges_creating">Creating and inserting new
+ <tt>Instruction</tt>s</a> </li>
+ <li><a href="#schanges_deleting">Deleting <tt>Instruction</tt>s</a> </li>
+ <li><a href="#schanges_replacing">Replacing an <tt>Instruction</tt>
+ with another <tt>Value</tt></a> </li>
+ </ul>
+ <!--
+ <li>Working with the Control Flow Graph
+ <ul>
+ <li>Accessing predecessors and successors of a <tt>BasicBlock</tt>
+ <li>
+ <li>
+ </ul>
+ --> </li>
+ </ul>
+ </li>
+ <li><a href="#coreclasses">The Core LLVM Class Hierarchy Reference</a>
+ <ul>
+ <li><a href="#Value">The <tt>Value</tt> class</a>
+ <ul>
+ <li><a href="#User">The <tt>User</tt> class</a>
+ <ul>
+ <li><a href="#Instruction">The <tt>Instruction</tt> class</a>
+ <ul>
+ <li><a href="#GetElementPtrInst">The <tt>GetElementPtrInst</tt>
+ class</a></li>
+ </ul></li>
+ <li><a href="#Module">The <tt>Module</tt> class</a></li>
+ <li><a href="#Constant">The <tt>Constant</tt> class</a>
+ <ul>
+ <li><a href="#GlobalValue">The <tt>GlobalValue</tt> class</a>
+ <ul>
+ <li><a href="#BasicBlock">The <tt>BasicBlock</tt>class</a></li>
+ <li><a href="#Function">The <tt>Function</tt> class</a></li>
+ <li><a href="#GlobalVariable">The <tt>GlobalVariable</tt> class
+ </a></li>
+ </ul></li>
+ </ul>
+ </li>
+ <li><a href="#Type">The <tt>Type</tt> class</a> </li>
+ <li><a href="#Argument">The <tt>Argument</tt> class</a></li>
+ </ul></li>
+ </ul></li>
+ <li><a href="#SymbolTable">The <tt>SymbolTable</tt> class </a></li>
+ <li>The <tt>ilist</tt> and <tt>iplist</tt> classes
+ <ul>
+ <li>Creating, inserting, moving and deleting from LLVM lists </li>
+ </ul>
+ </li>
+ <li>Important iterator invalidation semantics to be aware of.</li>
+ </li>
+ </ol>
+
+ <div class="doc_author">
+ <p>Written by <a href="mailto:sabre at nondot.org">Chris Lattner</a>,
+ <a href="mailto:dhurjati at cs.uiuc.edu">Dinakar Dhurjati</a>,
+ <a href="mailto:jstanley at cs.uiuc.edu">Joel Stanley</a>, and
+ <a href="mailto:rspencer at x10sys.com">Reid Spencer</a></p>
+ </div>
+
+ <!-- *********************************************************************** -->
+ <div class="doc_section">
+ <a name="introduction">Introduction </a>
+ </div>
+ <!-- *********************************************************************** -->
+
+ <div class="doc_text">
+
+ <p>This document is meant to highlight some of the important classes and
+ interfaces available in the LLVM source-base. This manual is not
+ intended to explain what LLVM is, how it works, and what LLVM code looks
+ like. It assumes that you know the basics of LLVM and are interested
+ in writing transformations or otherwise analyzing or manipulating the
+ code.</p>
+
+ <p>This document should get you oriented so that you can find your
+ way in the continuously growing source code that makes up the LLVM
+ infrastructure. Note that this manual is not intended to serve as a
+ replacement for reading the source code, so if you think there should be
+ a method in one of these classes to do something, but it's not listed,
+ check the source. Links to the <a href="/doxygen/">doxygen</a> sources
+ are provided to make this as easy as possible.</p>
+
+ <p>The first section of this document describes general information that is
+ useful to know when working in the LLVM infrastructure, and the second describes
+ the Core LLVM classes. In the future this manual will be extended with
+ information describing how to use extension libraries, such as dominator
+ information, CFG traversal routines, and useful utilities like the <tt><a
+ href="/doxygen/InstVisitor_8h-source.html">InstVisitor</a></tt> template.</p>
+
+ </div>
+
+ <!-- *********************************************************************** -->
+ <div class="doc_section">
+ <a name="general">General Information</a>
+ </div>
+ <!-- *********************************************************************** -->
+
+ <div class="doc_text">
+
+ <p>This section contains general information that is useful if you are working
+ in the LLVM source-base, but that isn't specific to any particular API.</p>
+
+ </div>
+
+ <!-- ======================================================================= -->
+ <div class="doc_subsection">
+ <a name="stl">The C++ Standard Template Library</a>
+ </div>
+
+ <div class="doc_text">
+
+ <p>LLVM makes heavy use of the C++ Standard Template Library (STL),
+ perhaps much more than you are used to, or have seen before. Because of
+ this, you might want to do a little background reading in the
+ techniques used and capabilities of the library. There are many good
+ pages that discuss the STL, and several books on the subject that you
+ can get, so it will not be discussed in this document.</p>
+
+ <p>Here are some useful links:</p>
+
+ <ol>
+
+ <li><a href="http://www.dinkumware.com/refxcpp.html">Dinkumware C++ Library
+ reference</a> - an excellent reference for the STL and other parts of the
+ standard C++ library.</li>
+
+ <li><a href="http://www.tempest-sw.com/cpp/">C++ In a Nutshell</a> - This is an
+ O'Reilly book in the making. It has a decent
+ Standard Library
+ Reference that rivals Dinkumware's, and is unfortunately no longer free since the book has been
+ published.</li>
+
+ <li><a href="http://www.parashift.com/c++-faq-lite/">C++ Frequently Asked
+ Questions</a></li>
+
+ <li><a href="http://www.sgi.com/tech/stl/">SGI's STL Programmer's Guide</a> -
+ Contains a useful <a
+ href="http://www.sgi.com/tech/stl/stl_introduction.html">Introduction to the
+ STL</a>.</li>
+
+ <li><a href="http://www.research.att.com/%7Ebs/C++.html">Bjarne Stroustrup's C++
+ Page</a></li>
+
+ <li><a href="http://www.linux.com.cn/Bruce_Eckel/TICPPv2/Contents.htm">
+ Bruce Eckel's Thinking in C++, 2nd ed. Volume 2 Revision 4.0 (even better, get
+ the book).</a></li>
+
+ </ol>
+
+ <p>You are also encouraged to take a look at the <a
+ href="CodingStandards.html">LLVM Coding Standards</a> guide which focuses on how
+ to write maintainable code more than where to put your curly braces.</p>
+
+ </div>
+
+ <!-- ======================================================================= -->
+ <div class="doc_subsection">
+ <a name="stl">Other useful references</a>
+ </div>
+
+ <div class="doc_text">
+
+ <ol>
+ <li><a href="http://www.psc.edu/%7Esemke/cvs_branches.html">CVS
+ Branch and Tag Primer</a></li>
+ <li><a href="http://www.fortran-2000.com/ArnaudRecipes/sharedlib.html">Using
+ static and shared libraries across platforms</a></li>
+ </ol>
+
+ </div>
+
+ <!-- *********************************************************************** -->
+ <div class="doc_section">
+ <a name="apis">Important and useful LLVM APIs</a>
+ </div>
+ <!-- *********************************************************************** -->
+
+ <div class="doc_text">
+
+ <p>Here we highlight some LLVM APIs that are generally useful and good to
+ know about when writing transformations.</p>
+
+ </div>
+
+ <!-- ======================================================================= -->
+ <div class="doc_subsection">
+ <a name="isa">The isa<>, cast<> and dyn_cast<> templates</a>
+ </div>
+
+ <div class="doc_text">
+
+ <p>The LLVM source-base makes extensive use of a custom form of RTTI.
+ These templates have many similarities to the C++ <tt>dynamic_cast<></tt>
+ operator, but they don't have some drawbacks (primarily stemming from
+ the fact that <tt>dynamic_cast<></tt> only works on classes that
+ have a v-table). Because they are used so often, you must know what they
+ do and how they work. All of these templates are defined in the <a
+ href="/doxygen/Casting_8h-source.html"><tt>Support/Casting.h</tt></a>
+ file (note that you very rarely have to include this file directly).</p>
+
+ <dl>
+ <dt><tt>isa<></tt>: </dt>
+
+ <dd>The <tt>isa<></tt> operator works exactly like the Java
+ "<tt>instanceof</tt>" operator. It returns true or false depending on whether
+ a reference or pointer points to an instance of the specified class. This can
+ be very useful for constraint checking of various sorts (example below).</dd>
+
+ <dt><tt>cast<></tt>: </dt>
+
+ <dd>The <tt>cast<></tt> operator is a "checked cast" operation. It
+ converts a pointer or reference from a base class to a derived cast, causing
+ an assertion failure if it is not really an instance of the right type. This
+ should be used in cases where you have some information that makes you believe
+ that something is of the right type. An example of the <tt>isa<></tt>
+ and <tt>cast<></tt> template is:
+
+ <pre>
+ static bool isLoopInvariant(const <a href="#Value">Value</a> *V, const Loop *L) {
+ if (isa<<a href="#Constant">Constant</a>>(V) || isa<<a href="#Argument">Argument</a>>(V) || isa<<a href="#GlobalValue">GlobalValue</a>>(V))
+ return true;
+
+ <i>// Otherwise, it must be an instruction...</i>
+ return !L->contains(cast<<a href="#Instruction">Instruction</a>>(V)->getParent());
+ </pre>
+
+ <p>Note that you should <b>not</b> use an <tt>isa<></tt> test followed
+ by a <tt>cast<></tt>, for that use the <tt>dyn_cast<></tt>
+ operator.</p>
+
+ </dd>
+
+ <dt><tt>dyn_cast<></tt>:</dt>
+
+ <dd>The <tt>dyn_cast<></tt> operator is a "checking cast" operation. It
+ checks to see if the operand is of the specified type, and if so, returns a
+ pointer to it (this operator does not work with references). If the operand is
+ not of the correct type, a null pointer is returned. Thus, this works very
+ much like the <tt>dynamic_cast</tt> operator in C++, and should be used in the
+ same circumstances. Typically, the <tt>dyn_cast<></tt> operator is used
+ in an <tt>if</tt> statement or some other flow control statement like this:
+
+ <pre>
+ if (<a href="#AllocationInst">AllocationInst</a> *AI = dyn_cast<<a href="#AllocationInst">AllocationInst</a>>(Val)) {
+ ...
+ }
+ </pre>
+
+ <p> This form of the <tt>if</tt> statement effectively combines together a
+ call to <tt>isa<></tt> and a call to <tt>cast<></tt> into one
+ statement, which is very convenient.</p>
+
+ <p> Another common example is:</p>
+
+ <pre>
+ <i>// Loop over all of the phi nodes in a basic block</i>
+ BasicBlock::iterator BBI = BB->begin();
+ for (; <a href="#PhiNode">PHINode</a> *PN = dyn_cast<<a href="#PHINode">PHINode</a>>(BBI); ++BBI)
+ std::cerr << *PN;
+ </pre>
+
+ <p>Note that the <tt>dyn_cast<></tt> operator, like C++'s
+ <tt>dynamic_cast</tt> or Java's <tt>instanceof</tt> operator, can be abused.
+ In particular you should not use big chained <tt>if/then/else</tt> blocks to
+ check for lots of different variants of classes. If you find yourself
+ wanting to do this, it is much cleaner and more efficient to use the
+ InstVisitor class to dispatch over the instruction type directly.</p>
+
+ </dd>
+
+ <dt><tt>cast_or_null<></tt>: </dt>
+
+ <dd>The <tt>cast_or_null<></tt> operator works just like the
+ <tt>cast<></tt> operator, except that it allows for a null pointer as
+ an argument (which it then propagates). This can sometimes be useful,
+ allowing you to combine several null checks into one.</dd>
+
+ <dt><tt>dyn_cast_or_null<></tt>: </dt>
+
+ <dd>The <tt>dyn_cast_or_null<></tt> operator works just like the
+ <tt>dyn_cast<></tt> operator, except that it allows for a null pointer
+ as an argument (which it then propagates). This can sometimes be useful,
+ allowing you to combine several null checks into one.</dd>
+
+ </dl>
+
+ <p>These five templates can be used with any classes, whether they have a
+ v-table or not. To add support for these templates, you simply need to add
+ <tt>classof</tt> static methods to the class you are interested casting
+ to. Describing this is currently outside the scope of this document, but there
+ are lots of examples in the LLVM source base.</p>
+
+ </div>
+
+ <!-- ======================================================================= -->
+ <div class="doc_subsection">
+ <a name="DEBUG">The <tt>DEBUG()</tt> macro & <tt>-debug</tt> option</a>
+ </div>
+
+ <div class="doc_text">
+
+ <p>Often when working on your pass you will put a bunch of debugging printouts
+ and other code into your pass. After you get it working, you want to remove
+ it... but you may need it again in the future (to work out new bugs that you run
+ across).</p>
+
+ <p> Naturally, because of this, you don't want to delete the debug printouts,
+ but you don't want them to always be noisy. A standard compromise is to comment
+ them out, allowing you to enable them if you need them in the future.</p>
+
+ <p>The "<tt><a href="/doxygen/Debug_8h-source.html">Support/Debug.h</a></tt>"
+ file provides a macro named <tt>DEBUG()</tt> that is a much nicer solution to
+ this problem. Basically, you can put arbitrary code into the argument of the
+ <tt>DEBUG</tt> macro, and it is only executed if '<tt>opt</tt>' (or any other
+ tool) is run with the '<tt>-debug</tt>' command line argument:</p>
+
+ <pre> ... <br> DEBUG(std::cerr << "I am here!\n");<br> ...<br></pre>
+
+ <p>Then you can run your pass like this:</p>
+
+ <pre> $ opt < a.bc > /dev/null -mypass<br> <no output><br> $ opt < a.bc > /dev/null -mypass -debug<br> I am here!<br> $<br></pre>
+
+ <p>Using the <tt>DEBUG()</tt> macro instead of a home-brewed solution allows you
+ to not have to create "yet another" command line option for the debug output for
+ your pass. Note that <tt>DEBUG()</tt> macros are disabled for optimized builds,
+ so they do not cause a performance impact at all (for the same reason, they
+ should also not contain side-effects!).</p>
+
+ <p>One additional nice thing about the <tt>DEBUG()</tt> macro is that you can
+ enable or disable it directly in gdb. Just use "<tt>set DebugFlag=0</tt>" or
+ "<tt>set DebugFlag=1</tt>" from the gdb if the program is running. If the
+ program hasn't been started yet, you can always just run it with
+ <tt>-debug</tt>.</p>
+
+ </div>
+
+ <!-- _______________________________________________________________________ -->
+ <div class="doc_subsubsection">
+ <a name="DEBUG_TYPE">Fine grained debug info with <tt>DEBUG_TYPE()</tt> and
+ the <tt>-debug-only</tt> option</a>
+ </div>
+
+ <div class="doc_text">
+
+ <p>Sometimes you may find yourself in a situation where enabling <tt>-debug</tt>
+ just turns on <b>too much</b> information (such as when working on the code
+ generator). If you want to enable debug information with more fine-grained
+ control, you define the <tt>DEBUG_TYPE</tt> macro and the <tt>-debug</tt> only
+ option as follows:</p>
+
+ <pre> ...<br> DEBUG(std::cerr << "No debug type\n");<br> #undef DEBUG_TYPE<br> #define DEBUG_TYPE "foo"<br> DEBUG(std::cerr << "'foo' debug type\n");<br> #undef DEBUG_TYPE<br> #define DEBUG_TYPE "bar"<br> DEBUG(std::cerr << "'bar' debug type\n");<br> #undef DEBUG_TYPE<br> #define DEBUG_TYPE ""<br> DEBUG(std::cerr << "No debug type (2)\n");<br> ...<br></pre>
+
+ <p>Then you can run your pass like this:</p>
+
+ <pre> $ opt < a.bc > /dev/null -mypass<br> <no output><br> $ opt < a.bc > /dev/null -mypass -debug<br> No debug type<br> 'foo' debug type<br> 'bar' debug type<br> No debug type (2)<br> $ opt < a.bc > /dev/null -mypass -debug-only=foo<br> 'foo' debug type<br> $ opt < a.bc > /dev/null -mypass -debug-only=bar<br> 'bar' debug type<br> $<br></pre>
+
+ <p>Of course, in practice, you should only set <tt>DEBUG_TYPE</tt> at the top of
+ a file, to specify the debug type for the entire module (if you do this before
+ you <tt>#include "Support/Debug.h"</tt>, you don't have to insert the ugly
+ <tt>#undef</tt>'s). Also, you should use names more meaningful than "foo" and
+ "bar", because there is no system in place to ensure that names do not
+ conflict. If two different modules use the same string, they will all be turned
+ on when the name is specified. This allows, for example, all debug information
+ for instruction scheduling to be enabled with <tt>-debug-type=InstrSched</tt>,
+ even if the source lives in multiple files.</p>
+
+ </div>
+
+ <!-- ======================================================================= -->
+ <div class="doc_subsection">
+ <a name="Statistic">The <tt>Statistic</tt> template & <tt>-stats</tt>
+ option</a>
+ </div>
+
+ <div class="doc_text">
+
+ <p>The "<tt><a
+ href="/doxygen/Statistic_8h-source.html">Support/Statistic.h</a></tt>" file
+ provides a template named <tt>Statistic</tt> that is used as a unified way to
+ keep track of what the LLVM compiler is doing and how effective various
+ optimizations are. It is useful to see what optimizations are contributing to
+ making a particular program run faster.</p>
+
+ <p>Often you may run your pass on some big program, and you're interested to see
+ how many times it makes a certain transformation. Although you can do this with
+ hand inspection, or some ad-hoc method, this is a real pain and not very useful
+ for big programs. Using the <tt>Statistic</tt> template makes it very easy to
+ keep track of this information, and the calculated information is presented in a
+ uniform manner with the rest of the passes being executed.</p>
+
+ <p>There are many examples of <tt>Statistic</tt> uses, but the basics of using
+ it are as follows:</p>
+
+ <ol>
+ <li>Define your statistic like this:
+ <pre>static Statistic<> NumXForms("mypassname", "The # of times I did stuff");<br></pre>
+
+ <p>The <tt>Statistic</tt> template can emulate just about any data-type,
+ but if you do not specify a template argument, it defaults to acting like
+ an unsigned int counter (this is usually what you want).</p></li>
+
+ <li>Whenever you make a transformation, bump the counter:
+ <pre> ++NumXForms; // I did stuff<br></pre>
+ </li>
+ </ol>
+
+ <p>That's all you have to do. To get '<tt>opt</tt>' to print out the
+ statistics gathered, use the '<tt>-stats</tt>' option:</p>
+
+ <pre> $ opt -stats -mypassname < program.bc > /dev/null<br> ... statistic output ...<br></pre>
+
+ <p> When running <tt>gccas</tt> on a C file from the SPEC benchmark
+ suite, it gives a report that looks like this:</p>
+
+ <pre> 7646 bytecodewriter - Number of normal instructions<br> 725 bytecodewriter - Number of oversized instructions<br> 129996 bytecodewriter - Number of bytecode bytes written<br> 2817 raise - Number of insts DCEd or constprop'd<br> 3213 raise - Number of cast-of-self removed<br> 5046 raise - Number of expression trees converted<br> 75 raise - Number of other getelementptr's formed<br> 138 raise - Number of load/store peepholes<br> 42 deadtypeelim - Number of unused typenames removed from symtab<br> 392 funcresolve - Number of varargs functions resolved<br> 27 globaldce - Number of global variables removed<br> 2 adce - Number of basic blocks removed<br> 134 cee - Number of branches revectored<br> 49 cee - Number of setcc instruction eliminated<br> 532 gcse - Number of loads removed<br> 2919 gcse - Number!
of instructions removed<br> 86 indvars - Number of canonical indvars added<br> 87 indvars - Number of aux indvars removed<br> 25 instcombine - Number of dead inst eliminate<br> 434 instcombine - Number of insts combined<br> 248 licm - Number of load insts hoisted<br> 1298 licm - Number of insts hoisted to a loop pre-header<br> 3 licm - Number of insts hoisted to multiple loop preds (bad, no loop pre-header)<br> 75 mem2reg - Number of alloca's promoted<br> 1444 cfgsimplify - Number of blocks simplified<br></pre>
+
+ <p>Obviously, with so many optimizations, having a unified framework for this
+ stuff is very nice. Making your pass fit well into the framework makes it more
+ maintainable and useful.</p>
+
+ </div>
+
+ <!-- *********************************************************************** -->
+ <div class="doc_section">
+ <a name="common">Helpful Hints for Common Operations</a>
+ </div>
+ <!-- *********************************************************************** -->
+
+ <div class="doc_text">
+
+ <p>This section describes how to perform some very simple transformations of
+ LLVM code. This is meant to give examples of common idioms used, showing the
+ practical side of LLVM transformations. <p> Because this is a "how-to" section,
+ you should also read about the main classes that you will be working with. The
+ <a href="#coreclasses">Core LLVM Class Hierarchy Reference</a> contains details
+ and descriptions of the main classes that you should know about.</p>
+
+ </div>
+
+ <!-- NOTE: this section should be heavy on example code -->
+ <!-- ======================================================================= -->
+ <div class="doc_subsection">
+ <a name="inspection">Basic Inspection and Traversal Routines</a>
+ </div>
+
+ <div class="doc_text">
+
+ <p>The LLVM compiler infrastructure have many different data structures that may
+ be traversed. Following the example of the C++ standard template library, the
+ techniques used to traverse these various data structures are all basically the
+ same. For a enumerable sequence of values, the <tt>XXXbegin()</tt> function (or
+ method) returns an iterator to the start of the sequence, the <tt>XXXend()</tt>
+ function returns an iterator pointing to one past the last valid element of the
+ sequence, and there is some <tt>XXXiterator</tt> data type that is common
+ between the two operations.</p>
+
+ <p>Because the pattern for iteration is common across many different aspects of
+ the program representation, the standard template library algorithms may be used
+ on them, and it is easier to remember how to iterate. First we show a few common
+ examples of the data structures that need to be traversed. Other data
+ structures are traversed in very similar ways.</p>
+
+ </div>
+
+ <!-- _______________________________________________________________________ -->
+ <div class="doc_subsubsection">
+ <a name="iterate_function">Iterating over the </a><a
+ href="#BasicBlock"><tt>BasicBlock</tt></a>s in a <a
+ href="#Function"><tt>Function</tt></a>
+ </div>
+
+ <div class="doc_text">
+
+ <p>It's quite common to have a <tt>Function</tt> instance that you'd like to
+ transform in some way; in particular, you'd like to manipulate its
+ <tt>BasicBlock</tt>s. To facilitate this, you'll need to iterate over all of
+ the <tt>BasicBlock</tt>s that constitute the <tt>Function</tt>. The following is
+ an example that prints the name of a <tt>BasicBlock</tt> and the number of
+ <tt>Instruction</tt>s it contains:</p>
+
+ <pre> // func is a pointer to a Function instance<br> for (Function::iterator i = func->begin(), e = func->end(); i != e; ++i) {<br><br> // print out the name of the basic block if it has one, and then the<br> // number of instructions that it contains<br><br> cerr << "Basic block (name=" << i->getName() << ") has " <br> << i->size() << " instructions.\n";<br> }<br></pre>
+
+ <p>Note that i can be used as if it were a pointer for the purposes of
+ invoking member functions of the <tt>Instruction</tt> class. This is
+ because the indirection operator is overloaded for the iterator
+ classes. In the above code, the expression <tt>i->size()</tt> is
+ exactly equivalent to <tt>(*i).size()</tt> just like you'd expect.</p>
+
+ </div>
+
+ <!-- _______________________________________________________________________ -->
+ <div class="doc_subsubsection">
+ <a name="iterate_basicblock">Iterating over the </a><a
+ href="#Instruction"><tt>Instruction</tt></a>s in a <a
+ href="#BasicBlock"><tt>BasicBlock</tt></a>
+ </div>
+
+ <div class="doc_text">
+
+ <p>Just like when dealing with <tt>BasicBlock</tt>s in <tt>Function</tt>s, it's
+ easy to iterate over the individual instructions that make up
+ <tt>BasicBlock</tt>s. Here's a code snippet that prints out each instruction in
+ a <tt>BasicBlock</tt>:</p>
+
+ <pre> // blk is a pointer to a BasicBlock instance<br> for (BasicBlock::iterator i = blk->begin(), e = blk->end(); i != e; ++i)<br> // the next statement works since operator<<(ostream&,...) <br> // is overloaded for Instruction&<br> cerr << *i << "\n";<br></pre>
+
+ <p>However, this isn't really the best way to print out the contents of a
+ <tt>BasicBlock</tt>! Since the ostream operators are overloaded for virtually
+ anything you'll care about, you could have just invoked the print routine on the
+ basic block itself: <tt>cerr << *blk << "\n";</tt>.</p>
+
+ <p>Note that currently operator<< is implemented for <tt>Value*</tt>, so
+ it will print out the contents of the pointer, instead of the pointer value you
+ might expect. This is a deprecated interface that will be removed in the
+ future, so it's best not to depend on it. To print out the pointer value for
+ now, you must cast to <tt>void*</tt>.</p>
+
+ </div>
+
+ <!-- _______________________________________________________________________ -->
+ <div class="doc_subsubsection">
+ <a name="iterate_institer">Iterating over the </a><a
+ href="#Instruction"><tt>Instruction</tt></a>s in a <a
+ href="#Function"><tt>Function</tt></a>
+ </div>
+
+ <div class="doc_text">
+
+ <p>If you're finding that you commonly iterate over a <tt>Function</tt>'s
+ <tt>BasicBlock</tt>s and then that <tt>BasicBlock</tt>'s <tt>Instruction</tt>s,
+ <tt>InstIterator</tt> should be used instead. You'll need to include <a
+ href="/doxygen/InstIterator_8h-source.html"><tt>llvm/Support/InstIterator.h</tt></a>,
+ and then instantiate <tt>InstIterator</tt>s explicitly in your code. Here's a
+ small example that shows how to dump all instructions in a function to the standard error stream:<p>
+
+ <pre>#include "<a href="/doxygen/InstIterator_8h-source.html">llvm/Support/InstIterator.h</a>"<br>...<br>// Suppose F is a ptr to a function<br>for (inst_iterator i = inst_begin(F), e = inst_end(F); i != e; ++i)<br> cerr << *i << "\n";<br></pre>
+ Easy, isn't it? You can also use <tt>InstIterator</tt>s to fill a
+ worklist with its initial contents. For example, if you wanted to
+ initialize a worklist to contain all instructions in a <tt>Function</tt>
+ F, all you would need to do is something like:
+ <pre>std::set<Instruction*> worklist;<br>worklist.insert(inst_begin(F), inst_end(F));<br></pre>
+
+ <p>The STL set <tt>worklist</tt> would now contain all instructions in the
+ <tt>Function</tt> pointed to by F.</p>
+
+ </div>
+
+ <!-- _______________________________________________________________________ -->
+ <div class="doc_subsubsection">
+ <a name="iterate_convert">Turning an iterator into a class pointer (and
+ vice-versa)</a>
+ </div>
+
+ <div class="doc_text">
+
+ <p>Sometimes, it'll be useful to grab a reference (or pointer) to a class
+ instance when all you've got at hand is an iterator. Well, extracting
+ a reference or a pointer from an iterator is very straight-forward.
+ Assuming that <tt>i</tt> is a <tt>BasicBlock::iterator</tt> and <tt>j</tt>
+ is a <tt>BasicBlock::const_iterator</tt>:</p>
+
+ <pre> Instruction& inst = *i; // grab reference to instruction reference<br> Instruction* pinst = &*i; // grab pointer to instruction reference<br> const Instruction& inst = *j;<br></pre>
+
+ <p>However, the iterators you'll be working with in the LLVM framework are
+ special: they will automatically convert to a ptr-to-instance type whenever they
+ need to. Instead of dereferencing the iterator and then taking the address of
+ the result, you can simply assign the iterator to the proper pointer type and
+ you get the dereference and address-of operation as a result of the assignment
+ (behind the scenes, this is a result of overloading casting mechanisms). Thus
+ the last line of the last example,</p>
+
+ <pre>Instruction* pinst = &*i;</pre>
+
+ <p>is semantically equivalent to</p>
+
+ <pre>Instruction* pinst = i;</pre>
+
+ <p>It's also possible to turn a class pointer into the corresponding iterator,
+ and this is a constant time operation (very efficient). The following code
+ snippet illustrates use of the conversion constructors provided by LLVM
+ iterators. By using these, you can explicitly grab the iterator of something
+ without actually obtaining it via iteration over some structure:</p>
+
+ <pre>void printNextInstruction(Instruction* inst) {<br> BasicBlock::iterator it(inst);<br> ++it; // after this line, it refers to the instruction after *inst.<br> if (it != inst->getParent()->end()) cerr << *it << "\n";<br>}<br></pre>
+
+ </div>
+
+ <!--_______________________________________________________________________-->
+ <div class="doc_subsubsection">
+ <a name="iterate_complex">Finding call sites: a slightly more complex
+ example</a>
+ </div>
+
+ <div class="doc_text">
+
+ <p>Say that you're writing a FunctionPass and would like to count all the
+ locations in the entire module (that is, across every <tt>Function</tt>) where a
+ certain function (i.e., some <tt>Function</tt>*) is already in scope. As you'll
+ learn later, you may want to use an <tt>InstVisitor</tt> to accomplish this in a
+ much more straight-forward manner, but this example will allow us to explore how
+ you'd do it if you didn't have <tt>InstVisitor</tt> around. In pseudocode, this
+ is what we want to do:</p>
+
+ <pre>initialize callCounter to zero<br>for each Function f in the Module<br> for each BasicBlock b in f<br> for each Instruction i in b<br> if (i is a CallInst and calls the given function)<br> increment callCounter<br></pre>
+
+ <p>And the actual code is (remember, since we're writing a
+ <tt>FunctionPass</tt>, our <tt>FunctionPass</tt>-derived class simply has to
+ override the <tt>runOnFunction</tt> method...):</p>
+
+ <pre>Function* targetFunc = ...;<br><br>class OurFunctionPass : public FunctionPass {<br> public:<br> OurFunctionPass(): callCounter(0) { }<br><br> virtual runOnFunction(Function& F) {<br> for (Function::iterator b = F.begin(), be = F.end(); b != be; ++b) {<br> for (BasicBlock::iterator i = b->begin(); ie = b->end(); i != ie; ++i) {<br> if (<a
+ href="#CallInst">CallInst</a>* callInst = <a href="#isa">dyn_cast</a><<a
+ href="#CallInst">CallInst</a>>(&*i)) {<br> // we know we've encountered a call instruction, so we<br> // need to determine if it's a call to the<br> // function pointed to by m_func or not.<br> <br> if (callInst->getCalledFunction() == targetFunc)<br> ++callCounter;<br> }<br> }<br> }<br> <br> private:<br> unsigned callCounter;<br>};<br></pre>
+
+ </div>
+
+ <!--_______________________________________________________________________-->
+ <div class="doc_subsubsection">
+ <a name="calls_and_invokes">Treating calls and invokes the same way</a>
+ </div>
+
+ <div class="doc_text">
+
+ <p>You may have noticed that the previous example was a bit oversimplified in
+ that it did not deal with call sites generated by 'invoke' instructions. In
+ this, and in other situations, you may find that you want to treat
+ <tt>CallInst</tt>s and <tt>InvokeInst</tt>s the same way, even though their
+ most-specific common base class is <tt>Instruction</tt>, which includes lots of
+ less closely-related things. For these cases, LLVM provides a handy wrapper
+ class called <a
+ href="http://llvm.cs.uiuc.edu/doxygen/classllvm_1_1CallSite.html"><tt>CallSite</tt></a>.
+ It is essentially a wrapper around an <tt>Instruction</tt> pointer, with some
+ methods that provide functionality common to <tt>CallInst</tt>s and
+ <tt>InvokeInst</tt>s.</p>
+
+ <p>This class has "value semantics": it should be passed by value, not by
+ reference and it should not be dynamically allocated or deallocated using
+ <tt>operator new</tt> or <tt>operator delete</tt>. It is efficiently copyable,
+ assignable and constructable, with costs equivalents to that of a bare pointer.
+ If you look at its definition, it has only a single pointer member.</p>
+
+ </div>
+
+ <!--_______________________________________________________________________-->
+ <div class="doc_subsubsection">
+ <a name="iterate_chains">Iterating over def-use & use-def chains</a>
+ </div>
+
+ <div class="doc_text">
+
+ <p>Frequently, we might have an instance of the <a
+ href="/doxygen/structllvm_1_1Value.html">Value Class</a> and we want to
+ determine which <tt>User</tt>s use the <tt>Value</tt>. The list of all
+ <tt>User</tt>s of a particular <tt>Value</tt> is called a <i>def-use</i> chain.
+ For example, let's say we have a <tt>Function*</tt> named <tt>F</tt> to a
+ particular function <tt>foo</tt>. Finding all of the instructions that
+ <i>use</i> <tt>foo</tt> is as simple as iterating over the <i>def-use</i> chain
+ of <tt>F</tt>:</p>
+
+ <pre>Function* F = ...;<br><br>for (Value::use_iterator i = F->use_begin(), e = F->use_end(); i != e; ++i) {<br> if (Instruction *Inst = dyn_cast<Instruction>(*i)) {<br> cerr << "F is used in instruction:\n";<br> cerr << *Inst << "\n";<br> }<br>}<br></pre>
+
+ <p>Alternately, it's common to have an instance of the <a
+ href="/doxygen/classllvm_1_1User.html">User Class</a> and need to know what
+ <tt>Value</tt>s are used by it. The list of all <tt>Value</tt>s used by a
+ <tt>User</tt> is known as a <i>use-def</i> chain. Instances of class
+ <tt>Instruction</tt> are common <tt>User</tt>s, so we might want to iterate over
+ all of the values that a particular instruction uses (that is, the operands of
+ the particular <tt>Instruction</tt>):</p>
+
+ <pre>Instruction* pi = ...;<br><br>for (User::op_iterator i = pi->op_begin(), e = pi->op_end(); i != e; ++i) {<br> Value* v = *i;<br> ...<br>}<br></pre>
+
+ <!--
+ def-use chains ("finding all users of"): Value::use_begin/use_end
+ use-def chains ("finding all values used"): User::op_begin/op_end [op=operand]
+ -->
+
+ </div>
+
+ <!-- ======================================================================= -->
+ <div class="doc_subsection">
+ <a name="simplechanges">Making simple changes</a>
+ </div>
+
+ <div class="doc_text">
+
+ <p>There are some primitive transformation operations present in the LLVM
+ infrastructure that are worth knowing about. When performing
+ transformations, it's fairly common to manipulate the contents of basic
+ blocks. This section describes some of the common methods for doing so
+ and gives example code.</p>
+
+ </div>
+
+ <!--_______________________________________________________________________-->
+ <div class="doc_subsubsection">
+ <a name="schanges_creating">Creating and inserting new
+ <tt>Instruction</tt>s</a>
+ </div>
+
+ <div class="doc_text">
+
+ <p><i>Instantiating Instructions</i></p>
+
+ <p>Creation of <tt>Instruction</tt>s is straight-forward: simply call the
+ constructor for the kind of instruction to instantiate and provide the necessary
+ parameters. For example, an <tt>AllocaInst</tt> only <i>requires</i> a
+ (const-ptr-to) <tt>Type</tt>. Thus:</p>
+
+ <pre>AllocaInst* ai = new AllocaInst(Type::IntTy);</pre>
+
+ <p>will create an <tt>AllocaInst</tt> instance that represents the allocation of
+ one integer in the current stack frame, at runtime. Each <tt>Instruction</tt>
+ subclass is likely to have varying default parameters which change the semantics
+ of the instruction, so refer to the <a
+ href="/doxygen/classllvm_1_1Instruction.html">doxygen documentation for the subclass of
+ Instruction</a> that you're interested in instantiating.</p>
+
+ <p><i>Naming values</i></p>
+
+ <p>It is very useful to name the values of instructions when you're able to, as
+ this facilitates the debugging of your transformations. If you end up looking
+ at generated LLVM machine code, you definitely want to have logical names
+ associated with the results of instructions! By supplying a value for the
+ <tt>Name</tt> (default) parameter of the <tt>Instruction</tt> constructor, you
+ associate a logical name with the result of the instruction's execution at
+ runtime. For example, say that I'm writing a transformation that dynamically
+ allocates space for an integer on the stack, and that integer is going to be
+ used as some kind of index by some other code. To accomplish this, I place an
+ <tt>AllocaInst</tt> at the first point in the first <tt>BasicBlock</tt> of some
+ <tt>Function</tt>, and I'm intending to use it within the same
+ <tt>Function</tt>. I might do:</p>
+
+ <pre>AllocaInst* pa = new AllocaInst(Type::IntTy, 0, "indexLoc");</pre>
+
+ <p>where <tt>indexLoc</tt> is now the logical name of the instruction's
+ execution value, which is a pointer to an integer on the runtime stack.</p>
+
+ <p><i>Inserting instructions</i></p>
+
+ <p>There are essentially two ways to insert an <tt>Instruction</tt>
+ into an existing sequence of instructions that form a <tt>BasicBlock</tt>:</p>
+
+ <ul>
+ <li>Insertion into an explicit instruction list
+
+ <p>Given a <tt>BasicBlock* pb</tt>, an <tt>Instruction* pi</tt> within that
+ <tt>BasicBlock</tt>, and a newly-created instruction we wish to insert
+ before <tt>*pi</tt>, we do the following: </p>
+
+ <pre> BasicBlock *pb = ...;<br> Instruction *pi = ...;<br> Instruction *newInst = new Instruction(...);<br> pb->getInstList().insert(pi, newInst); // inserts newInst before pi in pb<br></pre>
+
+ <p>Appending to the end of a <tt>BasicBlock</tt> is so common that
+ the <tt>Instruction</tt> class and <tt>Instruction</tt>-derived
+ classes provide constructors which take a pointer to a
+ <tt>BasicBlock</tt> to be appended to. For example code that
+ looked like: </p>
+
+ <pre> BasicBlock *pb = ...;<br> Instruction *newInst = new Instruction(...);<br> pb->getInstList().push_back(newInst); // appends newInst to pb<br></pre>
+
+ <p>becomes: </p>
+
+ <pre> BasicBlock *pb = ...;<br> Instruction *newInst = new Instruction(..., pb);<br></pre>
+
+ <p>which is much cleaner, especially if you are creating
+ long instruction streams.</p></li>
+
+ <li>Insertion into an implicit instruction list
+
+ <p><tt>Instruction</tt> instances that are already in <tt>BasicBlock</tt>s
+ are implicitly associated with an existing instruction list: the instruction
+ list of the enclosing basic block. Thus, we could have accomplished the same
+ thing as the above code without being given a <tt>BasicBlock</tt> by doing:
+ </p>
+
+ <pre> Instruction *pi = ...;<br> Instruction *newInst = new Instruction(...);<br> pi->getParent()->getInstList().insert(pi, newInst);<br></pre>
+
+ <p>In fact, this sequence of steps occurs so frequently that the
+ <tt>Instruction</tt> class and <tt>Instruction</tt>-derived classes provide
+ constructors which take (as a default parameter) a pointer to an
+ <tt>Instruction</tt> which the newly-created <tt>Instruction</tt> should
+ precede. That is, <tt>Instruction</tt> constructors are capable of
+ inserting the newly-created instance into the <tt>BasicBlock</tt> of a
+ provided instruction, immediately before that instruction. Using an
+ <tt>Instruction</tt> constructor with a <tt>insertBefore</tt> (default)
+ parameter, the above code becomes:</p>
+
+ <pre>Instruction* pi = ...;<br>Instruction* newInst = new Instruction(..., pi);<br></pre>
+
+ <p>which is much cleaner, especially if you're creating a lot of
+ instructions and adding them to <tt>BasicBlock</tt>s.</p></li>
+ </ul>
+
+ </div>
+
+ <!--_______________________________________________________________________-->
+ <div class="doc_subsubsection">
+ <a name="schanges_deleting">Deleting <tt>Instruction</tt>s</a>
+ </div>
+
+ <div class="doc_text">
+
+ <p>Deleting an instruction from an existing sequence of instructions that form a
+ <a href="#BasicBlock"><tt>BasicBlock</tt></a> is very straight-forward. First,
+ you must have a pointer to the instruction that you wish to delete. Second, you
+ need to obtain the pointer to that instruction's basic block. You use the
+ pointer to the basic block to get its list of instructions and then use the
+ erase function to remove your instruction. For example:</p>
+
+ <pre> <a href="#Instruction">Instruction</a> *I = .. ;<br> <a
+ href="#BasicBlock">BasicBlock</a> *BB = I->getParent();<br> BB->getInstList().erase(I);<br></pre>
+
+ </div>
+
+ <!--_______________________________________________________________________-->
+ <div class="doc_subsubsection">
+ <a name="schanges_replacing">Replacing an <tt>Instruction</tt> with another
+ <tt>Value</tt></a>
+ </div>
+
+ <div class="doc_text">
+
+ <p><i>Replacing individual instructions</i></p>
+
+ <p>Including "<a href="/doxygen/BasicBlockUtils_8h-source.html">llvm/Transforms/Utils/BasicBlockUtils.h</a>"
+ permits use of two very useful replace functions: <tt>ReplaceInstWithValue</tt>
+ and <tt>ReplaceInstWithInst</tt>.</p>
+
+ <h4><a name="schanges_deleting">Deleting <tt>Instruction</tt>s</a></h4>
+
+ <ul>
+ <li><tt>ReplaceInstWithValue</tt>
+
+ <p>This function replaces all uses (within a basic block) of a given
+ instruction with a value, and then removes the original instruction. The
+ following example illustrates the replacement of the result of a particular
+ <tt>AllocaInst</tt> that allocates memory for a single integer with an null
+ pointer to an integer.</p>
+
+ <pre>AllocaInst* instToReplace = ...;<br>BasicBlock::iterator ii(instToReplace);<br>ReplaceInstWithValue(instToReplace->getParent()->getInstList(), ii,<br> Constant::getNullValue(PointerType::get(Type::IntTy)));<br></pre></li>
+
+ <li><tt>ReplaceInstWithInst</tt>
+
+ <p>This function replaces a particular instruction with another
+ instruction. The following example illustrates the replacement of one
+ <tt>AllocaInst</tt> with another.</p>
+
+ <pre>AllocaInst* instToReplace = ...;<br>BasicBlock::iterator ii(instToReplace);<br>ReplaceInstWithInst(instToReplace->getParent()->getInstList(), ii,<br> new AllocaInst(Type::IntTy, 0, "ptrToReplacedInt"));<br></pre></li>
+ </ul>
+
+ <p><i>Replacing multiple uses of <tt>User</tt>s and <tt>Value</tt>s</i></p>
+
+ <p>You can use <tt>Value::replaceAllUsesWith</tt> and
+ <tt>User::replaceUsesOfWith</tt> to change more than one use at a time. See the
+ doxygen documentation for the <a href="/doxygen/structllvm_1_1Value.html">Value Class</a>
+ and <a href="/doxygen/classllvm_1_1User.html">User Class</a>, respectively, for more
+ information.</p>
+
+ <!-- Value::replaceAllUsesWith User::replaceUsesOfWith Point out:
+ include/llvm/Transforms/Utils/ especially BasicBlockUtils.h with:
+ ReplaceInstWithValue, ReplaceInstWithInst -->
+
+ </div>
+
+ <!-- *********************************************************************** -->
+ <div class="doc_section">
+ <a name="coreclasses">The Core LLVM Class Hierarchy Reference </a>
+ </div>
+ <!-- *********************************************************************** -->
+
+ <div class="doc_text">
+
+ <p>The Core LLVM classes are the primary means of representing the program
+ being inspected or transformed. The core LLVM classes are defined in
+ header files in the <tt>include/llvm/</tt> directory, and implemented in
+ the <tt>lib/VMCore</tt> directory.</p>
+
+ </div>
+
+ <!-- ======================================================================= -->
+ <div class="doc_subsection">
+ <a name="Value">The <tt>Value</tt> class</a>
+ </div>
+
+ <div>
+
+ <p><tt>#include "<a href="/doxygen/Value_8h-source.html">llvm/Value.h</a>"</tt>
+ <br>
+ doxygen info: <a href="/doxygen/structllvm_1_1Value.html">Value Class</a></p>
+
+ <p>The <tt>Value</tt> class is the most important class in the LLVM Source
+ base. It represents a typed value that may be used (among other things) as an
+ operand to an instruction. There are many different types of <tt>Value</tt>s,
+ such as <a href="#Constant"><tt>Constant</tt></a>s,<a
+ href="#Argument"><tt>Argument</tt></a>s. Even <a
+ href="#Instruction"><tt>Instruction</tt></a>s and <a
+ href="#Function"><tt>Function</tt></a>s are <tt>Value</tt>s.</p>
+
+ <p>A particular <tt>Value</tt> may be used many times in the LLVM representation
+ for a program. For example, an incoming argument to a function (represented
+ with an instance of the <a href="#Argument">Argument</a> class) is "used" by
+ every instruction in the function that references the argument. To keep track
+ of this relationship, the <tt>Value</tt> class keeps a list of all of the <a
+ href="#User"><tt>User</tt></a>s that is using it (the <a
+ href="#User"><tt>User</tt></a> class is a base class for all nodes in the LLVM
+ graph that can refer to <tt>Value</tt>s). This use list is how LLVM represents
+ def-use information in the program, and is accessible through the <tt>use_</tt>*
+ methods, shown below.</p>
+
+ <p>Because LLVM is a typed representation, every LLVM <tt>Value</tt> is typed,
+ and this <a href="#Type">Type</a> is available through the <tt>getType()</tt>
+ method. In addition, all LLVM values can be named. The "name" of the
+ <tt>Value</tt> is a symbolic string printed in the LLVM code:</p>
+
+ <pre> %<b>foo</b> = add int 1, 2<br></pre>
+
+ <p><a name="#nameWarning">The name of this instruction is "foo".</a> <b>NOTE</b>
+ that the name of any value may be missing (an empty string), so names should
+ <b>ONLY</b> be used for debugging (making the source code easier to read,
+ debugging printouts), they should not be used to keep track of values or map
+ between them. For this purpose, use a <tt>std::map</tt> of pointers to the
+ <tt>Value</tt> itself instead.</p>
+
+ <p>One important aspect of LLVM is that there is no distinction between an SSA
+ variable and the operation that produces it. Because of this, any reference to
+ the value produced by an instruction (or the value available as an incoming
+ argument, for example) is represented as a direct pointer to the instance of
+ the class that
+ represents this value. Although this may take some getting used to, it
+ simplifies the representation and makes it easier to manipulate.</p>
+
+ </div>
+
+ <!-- _______________________________________________________________________ -->
+ <div class="doc_subsubsection">
+ <a name="m_Value">Important Public Members of the <tt>Value</tt> class</a>
+ </div>
+
+ <div class="doc_text">
+
+ <ul>
+ <li><tt>Value::use_iterator</tt> - Typedef for iterator over the
+ use-list<br>
+ <tt>Value::use_const_iterator</tt> - Typedef for const_iterator over
+ the use-list<br>
+ <tt>unsigned use_size()</tt> - Returns the number of users of the
+ value.<br>
+ <tt>bool use_empty()</tt> - Returns true if there are no users.<br>
+ <tt>use_iterator use_begin()</tt> - Get an iterator to the start of
+ the use-list.<br>
+ <tt>use_iterator use_end()</tt> - Get an iterator to the end of the
+ use-list.<br>
+ <tt><a href="#User">User</a> *use_back()</tt> - Returns the last
+ element in the list.
+ <p> These methods are the interface to access the def-use
+ information in LLVM. As with all other iterators in LLVM, the naming
+ conventions follow the conventions defined by the <a href="#stl">STL</a>.</p>
+ </li>
+ <li><tt><a href="#Type">Type</a> *getType() const</tt>
+ <p>This method returns the Type of the Value.</p>
+ </li>
+ <li><tt>bool hasName() const</tt><br>
+ <tt>std::string getName() const</tt><br>
+ <tt>void setName(const std::string &Name)</tt>
+ <p> This family of methods is used to access and assign a name to a <tt>Value</tt>,
+ be aware of the <a href="#nameWarning">precaution above</a>.</p>
+ </li>
+ <li><tt>void replaceAllUsesWith(Value *V)</tt>
+
+ <p>This method traverses the use list of a <tt>Value</tt> changing all <a
+ href="#User"><tt>User</tt>s</a> of the current value to refer to
+ "<tt>V</tt>" instead. For example, if you detect that an instruction always
+ produces a constant value (for example through constant folding), you can
+ replace all uses of the instruction with the constant like this:</p>
+
+ <pre> Inst->replaceAllUsesWith(ConstVal);<br></pre>
+ </ul>
+
+ </div>
+
+ <!-- ======================================================================= -->
+ <div class="doc_subsection">
+ <a name="User">The <tt>User</tt> class</a>
+ </div>
+
+ <div class="doc_text">
+
+ <p>
+ <tt>#include "<a href="/doxygen/User_8h-source.html">llvm/User.h</a>"</tt><br>
+ doxygen info: <a href="/doxygen/classllvm_1_1User.html">User Class</a><br>
+ Superclass: <a href="#Value"><tt>Value</tt></a></p>
+
+ <p>The <tt>User</tt> class is the common base class of all LLVM nodes that may
+ refer to <a href="#Value"><tt>Value</tt></a>s. It exposes a list of "Operands"
+ that are all of the <a href="#Value"><tt>Value</tt></a>s that the User is
+ referring to. The <tt>User</tt> class itself is a subclass of
+ <tt>Value</tt>.</p>
+
+ <p>The operands of a <tt>User</tt> point directly to the LLVM <a
+ href="#Value"><tt>Value</tt></a> that it refers to. Because LLVM uses Static
+ Single Assignment (SSA) form, there can only be one definition referred to,
+ allowing this direct connection. This connection provides the use-def
+ information in LLVM.</p>
+
+ </div>
+
+ <!-- _______________________________________________________________________ -->
+ <div class="doc_subsubsection">
+ <a name="m_User">Important Public Members of the <tt>User</tt> class</a>
+ </div>
+
+ <div class="doc_text">
+
+ <p>The <tt>User</tt> class exposes the operand list in two ways: through
+ an index access interface and through an iterator based interface.</p>
+
+ <ul>
+ <li><tt>Value *getOperand(unsigned i)</tt><br>
+ <tt>unsigned getNumOperands()</tt>
+ <p> These two methods expose the operands of the <tt>User</tt> in a
+ convenient form for direct access.</p></li>
+
+ <li><tt>User::op_iterator</tt> - Typedef for iterator over the operand
+ list<br>
+ <tt>User::op_const_iterator</tt> <tt>use_iterator op_begin()</tt> -
+ Get an iterator to the start of the operand list.<br>
+ <tt>use_iterator op_end()</tt> - Get an iterator to the end of the
+ operand list.
+ <p> Together, these methods make up the iterator based interface to
+ the operands of a <tt>User</tt>.</p></li>
+ </ul>
+
+ </div>
+
+ <!-- ======================================================================= -->
+ <div class="doc_subsection">
+ <a name="Instruction">The <tt>Instruction</tt> class</a>
+ </div>
+
+ <div class="doc_text">
+
+ <p><tt>#include "</tt><tt><a
+ href="/doxygen/Instruction_8h-source.html">llvm/Instruction.h</a>"</tt><br>
+ doxygen info: <a href="/doxygen/classllvm_1_1Instruction.html">Instruction Class</a><br>
+ Superclasses: <a href="#User"><tt>User</tt></a>, <a
+ href="#Value"><tt>Value</tt></a></p>
+
+ <p>The <tt>Instruction</tt> class is the common base class for all LLVM
+ instructions. It provides only a few methods, but is a very commonly used
+ class. The primary data tracked by the <tt>Instruction</tt> class itself is the
+ opcode (instruction type) and the parent <a
+ href="#BasicBlock"><tt>BasicBlock</tt></a> the <tt>Instruction</tt> is embedded
+ into. To represent a specific type of instruction, one of many subclasses of
+ <tt>Instruction</tt> are used.</p>
+
+ <p> Because the <tt>Instruction</tt> class subclasses the <a
+ href="#User"><tt>User</tt></a> class, its operands can be accessed in the same
+ way as for other <a href="#User"><tt>User</tt></a>s (with the
+ <tt>getOperand()</tt>/<tt>getNumOperands()</tt> and
+ <tt>op_begin()</tt>/<tt>op_end()</tt> methods).</p> <p> An important file for
+ the <tt>Instruction</tt> class is the <tt>llvm/Instruction.def</tt> file. This
+ file contains some meta-data about the various different types of instructions
+ in LLVM. It describes the enum values that are used as opcodes (for example
+ <tt>Instruction::Add</tt> and <tt>Instruction::SetLE</tt>), as well as the
+ concrete sub-classes of <tt>Instruction</tt> that implement the instruction (for
+ example <tt><a href="#BinaryOperator">BinaryOperator</a></tt> and <tt><a
+ href="#SetCondInst">SetCondInst</a></tt>). Unfortunately, the use of macros in
+ this file confuses doxygen, so these enum values don't show up correctly in the
+ <a href="/doxygen/classllvm_1_1Instruction.html">doxygen output</a>.</p>
+
+ </div>
+
+ <!-- _______________________________________________________________________ -->
+ <div class="doc_subsubsection">
+ <a name="m_Instruction">Important Public Members of the <tt>Instruction</tt>
+ class</a>
+ </div>
+
+ <div class="doc_text">
+
+ <ul>
+ <li><tt><a href="#BasicBlock">BasicBlock</a> *getParent()</tt>
+ <p>Returns the <a href="#BasicBlock"><tt>BasicBlock</tt></a> that
+ this <tt>Instruction</tt> is embedded into.</p></li>
+ <li><tt>bool mayWriteToMemory()</tt>
+ <p>Returns true if the instruction writes to memory, i.e. it is a
+ <tt>call</tt>,<tt>free</tt>,<tt>invoke</tt>, or <tt>store</tt>.</p></li>
+ <li><tt>unsigned getOpcode()</tt>
+ <p>Returns the opcode for the <tt>Instruction</tt>.</p></li>
+ <li><tt><a href="#Instruction">Instruction</a> *clone() const</tt>
+ <p>Returns another instance of the specified instruction, identical
+ in all ways to the original except that the instruction has no parent
+ (ie it's not embedded into a <a href="#BasicBlock"><tt>BasicBlock</tt></a>),
+ and it has no name</p></li>
+ </ul>
+
+ </div>
+
+ <!-- ======================================================================= -->
+ <div class="doc_subsection">
+ <a name="BasicBlock">The <tt>BasicBlock</tt> class</a>
+ </div>
+
+ <div class="doc_text">
+
+ <p><tt>#include "<a
+ href="/doxygen/BasicBlock_8h-source.html">llvm/BasicBlock.h</a>"</tt><br>
+ doxygen info: <a href="/doxygen/structllvm_1_1BasicBlock.html">BasicBlock
+ Class</a><br>
+ Superclass: <a href="#Value"><tt>Value</tt></a></p>
+
+ <p>This class represents a single entry multiple exit section of the code,
+ commonly known as a basic block by the compiler community. The
+ <tt>BasicBlock</tt> class maintains a list of <a
+ href="#Instruction"><tt>Instruction</tt></a>s, which form the body of the block.
+ Matching the language definition, the last element of this list of instructions
+ is always a terminator instruction (a subclass of the <a
+ href="#TerminatorInst"><tt>TerminatorInst</tt></a> class).</p>
+
+ <p>In addition to tracking the list of instructions that make up the block, the
+ <tt>BasicBlock</tt> class also keeps track of the <a
+ href="#Function"><tt>Function</tt></a> that it is embedded into.</p>
+
+ <p>Note that <tt>BasicBlock</tt>s themselves are <a
+ href="#Value"><tt>Value</tt></a>s, because they are referenced by instructions
+ like branches and can go in the switch tables. <tt>BasicBlock</tt>s have type
+ <tt>label</tt>.</p>
+
+ </div>
+
+ <!-- _______________________________________________________________________ -->
+ <div class="doc_subsubsection">
+ <a name="m_BasicBlock">Important Public Members of the <tt>BasicBlock</tt>
+ class</a>
+ </div>
+
+ <div class="doc_text">
+
+ <ul>
+ <li><tt>BasicBlock(const std::string &Name = "", </tt><tt><a
+ href="#Function">Function</a> *Parent = 0)</tt>
+ <p>The <tt>BasicBlock</tt> constructor is used to create new basic
+ blocks for insertion into a function. The constructor optionally takes
+ a name for the new block, and a <a href="#Function"><tt>Function</tt></a>
+ to insert it into. If the <tt>Parent</tt> parameter is specified, the
+ new <tt>BasicBlock</tt> is automatically inserted at the end of the
+ specified <a href="#Function"><tt>Function</tt></a>, if not specified,
+ the BasicBlock must be manually inserted into the <a href="#Function"><tt>Function</tt></a>.</p>
+ </li>
+ <li><tt>BasicBlock::iterator</tt> - Typedef for instruction list
+ iterator<br>
+ <tt>BasicBlock::const_iterator</tt> - Typedef for const_iterator.<br>
+ <tt>begin()</tt>, <tt>end()</tt>, <tt>front()</tt>, <tt>back()</tt>,<tt>size()</tt>,<tt>empty()</tt>,<tt>rbegin()</tt>,<tt>rend()
+ - </tt>STL style functions for accessing the instruction list.
+ <p> These methods and typedefs are forwarding functions that have
+ the same semantics as the standard library methods of the same names.
+ These methods expose the underlying instruction list of a basic block in
+ a way that is easy to manipulate. To get the full complement of
+ container operations (including operations to update the list), you must
+ use the <tt>getInstList()</tt> method.</p></li>
+ <li><tt>BasicBlock::InstListType &getInstList()</tt>
+ <p> This method is used to get access to the underlying container
+ that actually holds the Instructions. This method must be used when
+ there isn't a forwarding function in the <tt>BasicBlock</tt> class for
+ the operation that you would like to perform. Because there are no
+ forwarding functions for "updating" operations, you need to use this if
+ you want to update the contents of a <tt>BasicBlock</tt>.</p></li>
+ <li><tt><a href="#Function">Function</a> *getParent()</tt>
+ <p> Returns a pointer to <a href="#Function"><tt>Function</tt></a>
+ the block is embedded into, or a null pointer if it is homeless.</p></li>
+ <li><tt><a href="#TerminatorInst">TerminatorInst</a> *getTerminator()</tt>
+ <p> Returns a pointer to the terminator instruction that appears at
+ the end of the <tt>BasicBlock</tt>. If there is no terminator
+ instruction, or if the last instruction in the block is not a
+ terminator, then a null pointer is returned.</p></li>
+ </ul>
+
+ </div>
+
+ <!-- ======================================================================= -->
+ <div class="doc_subsection">
+ <a name="GlobalValue">The <tt>GlobalValue</tt> class</a>
+ </div>
+
+ <div class="doc_text">
+
+ <p><tt>#include "<a
+ href="/doxygen/GlobalValue_8h-source.html">llvm/GlobalValue.h</a>"</tt><br>
+ doxygen info: <a href="/doxygen/classllvm_1_1GlobalValue.html">GlobalValue
+ Class</a><br>
+ Superclasses: <a href="#User"><tt>User</tt></a>, <a
+ href="#Value"><tt>Value</tt></a></p>
+
+ <p>Global values (<a href="#GlobalVariable"><tt>GlobalVariable</tt></a>s or <a
+ href="#Function"><tt>Function</tt></a>s) are the only LLVM values that are
+ visible in the bodies of all <a href="#Function"><tt>Function</tt></a>s.
+ Because they are visible at global scope, they are also subject to linking with
+ other globals defined in different translation units. To control the linking
+ process, <tt>GlobalValue</tt>s know their linkage rules. Specifically,
+ <tt>GlobalValue</tt>s know whether they have internal or external linkage, as
+ defined by the <tt>LinkageTypes</tt> enumeration.</p>
+
+ <p>If a <tt>GlobalValue</tt> has internal linkage (equivalent to being
+ <tt>static</tt> in C), it is not visible to code outside the current translation
+ unit, and does not participate in linking. If it has external linkage, it is
+ visible to external code, and does participate in linking. In addition to
+ linkage information, <tt>GlobalValue</tt>s keep track of which <a
+ href="#Module"><tt>Module</tt></a> they are currently part of.</p>
+
+ <p>Because <tt>GlobalValue</tt>s are memory objects, they are always referred to
+ by their <b>address</b>. As such, the <a href="#Type"><tt>Type</tt></a> of a
+ global is always a pointer to its contents. It is important to remember this
+ when using the <tt>GetElementPtrInst</tt> instruction because this pointer must
+ be dereferenced first. For example, if you have a <tt>GlobalVariable</tt> (a
+ subclass of <tt>GlobalValue)</tt> that is an array of 24 ints, type <tt>[24 x
+ int]</tt>, then the <tt>GlobalVariable</tt> is a pointer to that array. Although
+ the address of the first element of this array and the value of the
+ <tt>GlobalVariable</tt> are the same, they have different types. The
+ <tt>GlobalVariable</tt>'s type is <tt>[24 x int]</tt>. The first element's type
+ is <tt>int.</tt> Because of this, accessing a global value requires you to
+ dereference the pointer with <tt>GetElementPtrInst</tt> first, then its elements
+ can be accessed. This is explained in the <a href="LangRef.html#globalvars">LLVM
+ Language Reference Manual</a>.</p>
+
+ </div>
+
+ <!-- _______________________________________________________________________ -->
+ <div class="doc_subsubsection">
+ <a name="m_GlobalValue">Important Public Members of the <tt>GlobalValue</tt>
+ class</a>
+ </div>
+
+ <div class="doc_text">
+
+ <ul>
+ <li><tt>bool hasInternalLinkage() const</tt><br>
+ <tt>bool hasExternalLinkage() const</tt><br>
+ <tt>void setInternalLinkage(bool HasInternalLinkage)</tt>
+ <p> These methods manipulate the linkage characteristics of the <tt>GlobalValue</tt>.</p>
+ <p> </p>
+ </li>
+ <li><tt><a href="#Module">Module</a> *getParent()</tt>
+ <p> This returns the <a href="#Module"><tt>Module</tt></a> that the
+ GlobalValue is currently embedded into.</p></li>
+ </ul>
+
+ </div>
+
+ <!-- ======================================================================= -->
+ <div class="doc_subsection">
+ <a name="Function">The <tt>Function</tt> class</a>
+ </div>
+
+ <div class="doc_text">
+
+ <p><tt>#include "<a
+ href="/doxygen/Function_8h-source.html">llvm/Function.h</a>"</tt><br> doxygen
+ info: <a href="/doxygen/classllvm_1_1Function.html">Function Class</a><br>
+ Superclasses: <a href="#GlobalValue"><tt>GlobalValue</tt></a>, <a
+ href="#User"><tt>User</tt></a>, <a href="#Value"><tt>Value</tt></a></p>
+
+ <p>The <tt>Function</tt> class represents a single procedure in LLVM. It is
+ actually one of the more complex classes in the LLVM heirarchy because it must
+ keep track of a large amount of data. The <tt>Function</tt> class keeps track
+ of a list of <a href="#BasicBlock"><tt>BasicBlock</tt></a>s, a list of formal <a
+ href="#Argument"><tt>Argument</tt></a>s, and a <a
+ href="#SymbolTable"><tt>SymbolTable</tt></a>.</p>
+
+ <p>The list of <a href="#BasicBlock"><tt>BasicBlock</tt></a>s is the most
+ commonly used part of <tt>Function</tt> objects. The list imposes an implicit
+ ordering of the blocks in the function, which indicate how the code will be
+ layed out by the backend. Additionally, the first <a
+ href="#BasicBlock"><tt>BasicBlock</tt></a> is the implicit entry node for the
+ <tt>Function</tt>. It is not legal in LLVM to explicitly branch to this initial
+ block. There are no implicit exit nodes, and in fact there may be multiple exit
+ nodes from a single <tt>Function</tt>. If the <a
+ href="#BasicBlock"><tt>BasicBlock</tt></a> list is empty, this indicates that
+ the <tt>Function</tt> is actually a function declaration: the actual body of the
+ function hasn't been linked in yet.</p>
+
+ <p>In addition to a list of <a href="#BasicBlock"><tt>BasicBlock</tt></a>s, the
+ <tt>Function</tt> class also keeps track of the list of formal <a
+ href="#Argument"><tt>Argument</tt></a>s that the function receives. This
+ container manages the lifetime of the <a href="#Argument"><tt>Argument</tt></a>
+ nodes, just like the <a href="#BasicBlock"><tt>BasicBlock</tt></a> list does for
+ the <a href="#BasicBlock"><tt>BasicBlock</tt></a>s.</p>
+
+ <p>The <a href="#SymbolTable"><tt>SymbolTable</tt></a> is a very rarely used
+ LLVM feature that is only used when you have to look up a value by name. Aside
+ from that, the <a href="#SymbolTable"><tt>SymbolTable</tt></a> is used
+ internally to make sure that there are not conflicts between the names of <a
+ href="#Instruction"><tt>Instruction</tt></a>s, <a
+ href="#BasicBlock"><tt>BasicBlock</tt></a>s, or <a
+ href="#Argument"><tt>Argument</tt></a>s in the function body.</p>
+
+ <p>Note that <tt>Function</tt> is a <a href="#GlobalValue">GlobalValue</a>
+ and therefore also a <a href="#Constant">Constant</a>. The value of the function
+ is its address (after linking) which is guaranteed to be constant.</p>
+ </div>
+
+ <!-- _______________________________________________________________________ -->
+ <div class="doc_subsubsection">
+ <a name="m_Function">Important Public Members of the <tt>Function</tt>
+ class</a>
+ </div>
+
+ <div class="doc_text">
+
+ <ul>
+ <li><tt>Function(const </tt><tt><a href="#FunctionType">FunctionType</a>
+ *Ty, LinkageTypes Linkage, const std::string &N = "", Module* Parent = 0)</tt>
+
+ <p>Constructor used when you need to create new <tt>Function</tt>s to add
+ the the program. The constructor must specify the type of the function to
+ create and what type of linkage the function should have. The <a
+ href="#FunctionType"><tt>FunctionType</tt></a> argument
+ specifies the formal arguments and return value for the function. The same
+ <a href="#FunctionTypel"><tt>FunctionType</tt></a> value can be used to
+ create multiple functions. The <tt>Parent</tt> argument specifies the Module
+ in which the function is defined. If this argument is provided, the function
+ will automatically be inserted into that module's list of
+ functions.</p></li>
+
+ <li><tt>bool isExternal()</tt>
+
+ <p>Return whether or not the <tt>Function</tt> has a body defined. If the
+ function is "external", it does not have a body, and thus must be resolved
+ by linking with a function defined in a different translation unit.</p></li>
+
+ <li><tt>Function::iterator</tt> - Typedef for basic block list iterator<br>
+ <tt>Function::const_iterator</tt> - Typedef for const_iterator.<br>
+
+ <tt>begin()</tt>, <tt>end()</tt>, <tt>front()</tt>, <tt>back()</tt>,
+ <tt>size()</tt>, <tt>empty()</tt>, <tt>rbegin()</tt>, <tt>rend()</tt>
+
+ <p>These are forwarding methods that make it easy to access the contents of
+ a <tt>Function</tt> object's <a href="#BasicBlock"><tt>BasicBlock</tt></a>
+ list.</p></li>
+
+ <li><tt>Function::BasicBlockListType &getBasicBlockList()</tt>
+
+ <p>Returns the list of <a href="#BasicBlock"><tt>BasicBlock</tt></a>s. This
+ is necessary to use when you need to update the list or perform a complex
+ action that doesn't have a forwarding method.</p></li>
+
+ <li><tt>Function::aiterator</tt> - Typedef for the argument list
+ iterator<br>
+ <tt>Function::const_aiterator</tt> - Typedef for const_iterator.<br>
+
+ <tt>abegin()</tt>, <tt>aend()</tt>, <tt>afront()</tt>, <tt>aback()</tt>,
+ <tt>asize()</tt>, <tt>aempty()</tt>, <tt>arbegin()</tt>, <tt>arend()</tt>
+
+ <p>These are forwarding methods that make it easy to access the contents of
+ a <tt>Function</tt> object's <a href="#Argument"><tt>Argument</tt></a>
+ list.</p></li>
+
+ <li><tt>Function::ArgumentListType &getArgumentList()</tt>
+
+ <p>Returns the list of <a href="#Argument"><tt>Argument</tt></a>s. This is
+ necessary to use when you need to update the list or perform a complex
+ action that doesn't have a forwarding method.</p></li>
+
+ <li><tt><a href="#BasicBlock">BasicBlock</a> &getEntryBlock()</tt>
+
+ <p>Returns the entry <a href="#BasicBlock"><tt>BasicBlock</tt></a> for the
+ function. Because the entry block for the function is always the first
+ block, this returns the first block of the <tt>Function</tt>.</p></li>
+
+ <li><tt><a href="#Type">Type</a> *getReturnType()</tt><br>
+ <tt><a href="#FunctionType">FunctionType</a> *getFunctionType()</tt>
+
+ <p>This traverses the <a href="#Type"><tt>Type</tt></a> of the
+ <tt>Function</tt> and returns the return type of the function, or the <a
+ href="#FunctionType"><tt>FunctionType</tt></a> of the actual
+ function.</p></li>
+
+ <li><tt><a href="#SymbolTable">SymbolTable</a> *getSymbolTable()</tt>
+
+ <p> Return a pointer to the <a href="#SymbolTable"><tt>SymbolTable</tt></a>
+ for this <tt>Function</tt>.</p></li>
+ </ul>
+
+ </div>
+
+ <!-- ======================================================================= -->
+ <div class="doc_subsection">
+ <a name="GlobalVariable">The <tt>GlobalVariable</tt> class</a>
+ </div>
+
+ <div class="doc_text">
+
+ <p><tt>#include "<a
+ href="/doxygen/GlobalVariable_8h-source.html">llvm/GlobalVariable.h</a>"</tt>
+ <br>
+ doxygen info: <a href="/doxygen/classllvm_1_1GlobalVariable.html">GlobalVariable
+ Class</a><br> Superclasses: <a href="#GlobalValue"><tt>GlobalValue</tt></a>, <a
+ href="#User"><tt>User</tt></a>, <a href="#Value"><tt>Value</tt></a></p>
+
+ <p>Global variables are represented with the (suprise suprise)
+ <tt>GlobalVariable</tt> class. Like functions, <tt>GlobalVariable</tt>s are also
+ subclasses of <a href="#GlobalValue"><tt>GlobalValue</tt></a>, and as such are
+ always referenced by their address (global values must live in memory, so their
+ "name" refers to their address). See <a
+ href="#GlobalValue"><tt>GlobalValue</tt></a> for more on this. Global variables
+ may have an initial value (which must be a <a
+ href="#Constant"><tt>Constant</tt></a>), and if they have an initializer, they
+ may be marked as "constant" themselves (indicating that their contents never
+ change at runtime).</p>
+
+ </div>
+
+ <!-- _______________________________________________________________________ -->
+ <div class="doc_subsubsection">
+ <a name="m_GlobalVariable">Important Public Members of the
+ <tt>GlobalVariable</tt> class</a>
+ </div>
+
+ <div class="doc_text">
+
+ <ul>
+ <li><tt>GlobalVariable(const </tt><tt><a href="#Type">Type</a> *Ty, bool
+ isConstant, LinkageTypes& Linkage, <a href="#Constant">Constant</a>
+ *Initializer = 0, const std::string &Name = "", Module* Parent = 0)</tt>
+
+ <p>Create a new global variable of the specified type. If
+ <tt>isConstant</tt> is true then the global variable will be marked as
+ unchanging for the program. The Linkage parameter specifies the type of
+ linkage (internal, external, weak, linkonce, appending) for the variable. If
+ the linkage is InternalLinkage, WeakLinkage, or LinkOnceLinkage, then
+ the resultant global variable will have internal linkage. AppendingLinkage
+ concatenates together all instances (in different translation units) of the
+ variable into a single variable but is only applicable to arrays. See
+ the <a href="LangRef.html#modulestructure">LLVM Language Reference</a> for
+ further details on linkage types. Optionally an initializer, a name, and the
+ module to put the variable into may be specified for the global variable as
+ well.</p></li>
+
+ <li><tt>bool isConstant() const</tt>
+
+ <p>Returns true if this is a global variable that is known not to
+ be modified at runtime.</p></li>
+
+ <li><tt>bool hasInitializer()</tt>
+
+ <p>Returns true if this <tt>GlobalVariable</tt> has an intializer.</p></li>
+
+ <li><tt><a href="#Constant">Constant</a> *getInitializer()</tt>
+
+ <p>Returns the intial value for a <tt>GlobalVariable</tt>. It is not legal
+ to call this method if there is no initializer.</p></li>
+ </ul>
+
+ </div>
+
+ <!-- ======================================================================= -->
+ <div class="doc_subsection">
+ <a name="Module">The <tt>Module</tt> class</a>
+ </div>
+
+ <div class="doc_text">
+
+ <p><tt>#include "<a
+ href="/doxygen/Module_8h-source.html">llvm/Module.h</a>"</tt><br> doxygen info:
+ <a href="/doxygen/classllvm_1_1Module.html">Module Class</a></p>
+
+ <p>The <tt>Module</tt> class represents the top level structure present in LLVM
+ programs. An LLVM module is effectively either a translation unit of the
+ original program or a combination of several translation units merged by the
+ linker. The <tt>Module</tt> class keeps track of a list of <a
+ href="#Function"><tt>Function</tt></a>s, a list of <a
+ href="#GlobalVariable"><tt>GlobalVariable</tt></a>s, and a <a
+ href="#SymbolTable"><tt>SymbolTable</tt></a>. Additionally, it contains a few
+ helpful member functions that try to make common operations easy.</p>
+
+ </div>
+
+ <!-- _______________________________________________________________________ -->
+ <div class="doc_subsubsection">
+ <a name="m_Module">Important Public Members of the <tt>Module</tt> class</a>
+ </div>
+
+ <div class="doc_text">
+
+ <ul>
+ <li><tt>Module::Module(std::string name = "")</tt></li>
+ </ul>
+
+ <p>Constructing a <a href="#Module">Module</a> is easy. You can optionally
+ provide a name for it (probably based on the name of the translation unit).</p>
+
+ <ul>
+ <li><tt>Module::iterator</tt> - Typedef for function list iterator<br>
+ <tt>Module::const_iterator</tt> - Typedef for const_iterator.<br>
+
+ <tt>begin()</tt>, <tt>end()</tt>, <tt>front()</tt>, <tt>back()</tt>,
+ <tt>size()</tt>, <tt>empty()</tt>, <tt>rbegin()</tt>, <tt>rend()</tt>
+
+ <p>These are forwarding methods that make it easy to access the contents of
+ a <tt>Module</tt> object's <a href="#Function"><tt>Function</tt></a>
+ list.</p></li>
+
+ <li><tt>Module::FunctionListType &getFunctionList()</tt>
+
+ <p> Returns the list of <a href="#Function"><tt>Function</tt></a>s. This is
+ necessary to use when you need to update the list or perform a complex
+ action that doesn't have a forwarding method.</p>
+
+ <p><!-- Global Variable --></p></li>
+ </ul>
+
+ <hr>
+
+ <ul>
+ <li><tt>Module::giterator</tt> - Typedef for global variable list iterator<br>
+
+ <tt>Module::const_giterator</tt> - Typedef for const_iterator.<br>
+
+ <tt>gbegin()</tt>, <tt>gend()</tt>, <tt>gfront()</tt>, <tt>gback()</tt>,
+ <tt>gsize()</tt>, <tt>gempty()</tt>, <tt>grbegin()</tt>, <tt>grend()</tt>
+
+ <p> These are forwarding methods that make it easy to access the contents of
+ a <tt>Module</tt> object's <a
+ href="#GlobalVariable"><tt>GlobalVariable</tt></a> list.</p></li>
+
+ <li><tt>Module::GlobalListType &getGlobalList()</tt>
+
+ <p>Returns the list of <a
+ href="#GlobalVariable"><tt>GlobalVariable</tt></a>s. This is necessary to
+ use when you need to update the list or perform a complex action that
+ doesn't have a forwarding method.</p>
+
+ <p><!-- Symbol table stuff --> </p></li>
+ </ul>
+
+ <hr>
+
+ <ul>
+ <li><tt><a href="#SymbolTable">SymbolTable</a> *getSymbolTable()</tt>
+
+ <p>Return a reference to the <a href="#SymbolTable"><tt>SymbolTable</tt></a>
+ for this <tt>Module</tt>.</p>
+
+ <p><!-- Convenience methods --></p></li>
+ </ul>
+
+ <hr>
+
+ <ul>
+ <li><tt><a href="#Function">Function</a> *getFunction(const std::string
+ &Name, const <a href="#FunctionType">FunctionType</a> *Ty)</tt>
+
+ <p>Look up the specified function in the <tt>Module</tt> <a
+ href="#SymbolTable"><tt>SymbolTable</tt></a>. If it does not exist, return
+ <tt>null</tt>.</p></li>
+
+ <li><tt><a href="#Function">Function</a> *getOrInsertFunction(const
+ std::string &Name, const <a href="#FunctionType">FunctionType</a> *T)</tt>
+
+ <p>Look up the specified function in the <tt>Module</tt> <a
+ href="#SymbolTable"><tt>SymbolTable</tt></a>. If it does not exist, add an
+ external declaration for the function and return it.</p></li>
+
+ <li><tt>std::string getTypeName(const <a href="#Type">Type</a> *Ty)</tt>
+
+ <p>If there is at least one entry in the <a
+ href="#SymbolTable"><tt>SymbolTable</tt></a> for the specified <a
+ href="#Type"><tt>Type</tt></a>, return it. Otherwise return the empty
+ string.</p></li>
+
+ <li><tt>bool addTypeName(const std::string &Name, const <a
+ href="#Type">Type</a> *Ty)</tt>
+
+ <p>Insert an entry in the <a href="#SymbolTable"><tt>SymbolTable</tt></a>
+ mapping <tt>Name</tt> to <tt>Ty</tt>. If there is already an entry for this
+ name, true is returned and the <a
+ href="#SymbolTable"><tt>SymbolTable</tt></a> is not modified.</p></li>
+ </ul>
+
+ </div>
+
+ <!-- ======================================================================= -->
+ <div class="doc_subsection">
+ <a name="Constant">The <tt>Constant</tt> class and subclasses</a>
+ </div>
+
+ <div class="doc_text">
+
+ <p>Constant represents a base class for different types of constants. It
+ is subclassed by ConstantBool, ConstantInt, ConstantSInt, ConstantUInt,
+ ConstantArray etc for representing the various types of Constants.</p>
+
+ </div>
+
+ <!-- _______________________________________________________________________ -->
+ <div class="doc_subsubsection">
+ <a name="m_Value">Important Public Methods</a>
+ </div>
+
+ <div class="doc_text">
+
+ <ul>
+ <hr> Important Subclasses of Constant
+ <p> </p>
+ <ul>
+ <li>ConstantSInt : This subclass of Constant represents a signed
+ integer constant.
+ <ul>
+ <li><tt>int64_t getValue() const</tt>: Returns the underlying value of
+ this constant. </li>
+ </ul>
+ </li>
+ <li>ConstantUInt : This class represents an unsigned integer.
+ <ul>
+ <li><tt>uint64_t getValue() const</tt>: Returns the underlying value
+ of this constant. </li>
+ </ul>
+ </li>
+ <li>ConstantFP : This class represents a floating point constant.
+ <ul>
+ <li><tt>double getValue() const</tt>: Returns the underlying value of
+ this constant. </li>
+ </ul>
+ </li>
+ <li>ConstantBool : This represents a boolean constant.
+ <ul>
+ <li><tt>bool getValue() const</tt>: Returns the underlying value of
+ this constant. </li>
+ </ul>
+ </li>
+ <li>ConstantArray : This represents a constant array.
+ <ul>
+ <li><tt>const std::vector<Use> &getValues() const</tt>:
+ Returns a Vecotr of component constants that makeup this array. </li>
+ </ul>
+ </li>
+ <li>ConstantStruct : This represents a constant struct.
+ <ul>
+ <li><tt>const std::vector<Use> &getValues() const</tt>:
+ Returns a Vecotr of component constants that makeup this array. </li>
+ </ul>
+ </li>
+ <li>GlobalValue : This represents either a global variable or a
+ function. In either case, the value is a constant fixed address
+ (after linking).
+ </li>
+ </ul>
+ </li>
+ </ul>
+ </div>
+
+ <!-- ======================================================================= -->
+ <div class="doc_subsection">
+ <a name="Type">The <tt>Type</tt> class and Derived Types</a>
+ </div>
+
+ <div class="doc_text">
+
+ <p>Type as noted earlier is also a subclass of a Value class. Any primitive
+ type (like int, short etc) in LLVM is an instance of Type Class. All other
+ types are instances of subclasses of type like FunctionType, ArrayType
+ etc. DerivedType is the interface for all such dervied types including
+ FunctionType, ArrayType, PointerType, StructType. Types can have names. They can
+ be recursive (StructType). There exists exactly one instance of any type
+ structure at a time. This allows using pointer equality of Type *s for comparing
+ types.</p>
+
+ </div>
+
+ <!-- _______________________________________________________________________ -->
+ <div class="doc_subsubsection">
+ <a name="m_Value">Important Public Methods</a>
+ </div>
+
+ <div class="doc_text">
+
+ <ul>
+
+ <li><tt>bool isSigned() const</tt>: Returns whether an integral numeric type
+ is signed. This is true for SByteTy, ShortTy, IntTy, LongTy. Note that this is
+ not true for Float and Double. </li>
+
+ <li><tt>bool isUnsigned() const</tt>: Returns whether a numeric type is
+ unsigned. This is not quite the complement of isSigned... nonnumeric types
+ return false as they do with isSigned. This returns true for UByteTy,
+ UShortTy, UIntTy, and ULongTy. </li>
+
+ <li><tt>bool isInteger() const</tt>: Equivalent to isSigned() || isUnsigned().</li>
+
+ <li><tt>bool isIntegral() const</tt>: Returns true if this is an integral
+ type, which is either Bool type or one of the Integer types.</li>
+
+ <li><tt>bool isFloatingPoint()</tt>: Return true if this is one of the two
+ floating point types.</li>
+
+ <li><tt>isLosslesslyConvertableTo (const Type *Ty) const</tt>: Return true if
+ this type can be converted to 'Ty' without any reinterpretation of bits. For
+ example, uint to int or one pointer type to another.</li>
+
+ <br>
+ <p>Derived Types</p>
+
+ <ul>
+ <li>SequentialType : This is subclassed by ArrayType and PointerType
+ <ul>
+ <li><tt>const Type * getElementType() const</tt>: Returns the type of
+ each of the elements in the sequential type. </li>
+ </ul>
+ </li>
+ <li>ArrayType : This is a subclass of SequentialType and defines
+ interface for array types.
+ <ul>
+ <li><tt>unsigned getNumElements() const</tt>: Returns the number of
+ elements in the array. </li>
+ </ul>
+ </li>
+ <li>PointerType : Subclass of SequentialType for pointer types. </li>
+ <li>StructType : subclass of DerivedTypes for struct types </li>
+ <li>FunctionType : subclass of DerivedTypes for function types.
+ <ul>
+ <li><tt>bool isVarArg() const</tt>: Returns true if its a vararg
+ function</li>
+ <li><tt> const Type * getReturnType() const</tt>: Returns the
+ return type of the function.</li>
+ <li><tt>const Type * getParamType (unsigned i)</tt>: Returns
+ the type of the ith parameter.</li>
+ <li><tt> const unsigned getNumParams() const</tt>: Returns the
+ number of formal parameters.</li>
+ </ul>
+ </li>
+ </ul>
+ </li>
+ </ul>
+
+ </div>
+
+ <!-- ======================================================================= -->
+ <div class="doc_subsection">
+ <a name="Argument">The <tt>Argument</tt> class</a>
+ </div>
+
+ <div class="doc_text">
+
+ <p>This subclass of Value defines the interface for incoming formal
+ arguments to a function. A Function maitanis a list of its formal
+ arguments. An argument has a pointer to the parent Function.</p>
+
+ </div>
+
+ <!-- ======================================================================= -->
+ <div class="doc_subsection">
+ <a name="SymbolTable">The <tt>SymbolTable</tt> class</a>
+ </div>
+ <div class="doc_text">
+ <p>This class provides a symbol table that the
+ <a href="#Function"><tt>Function</tt></a> and <a href="#Module">
+ <tt>Module</tt></a> classes use for naming definitions. The symbol table can
+ provide a name for any <a href="#Value"><tt>Value</tt></a> or
+ <a href="#Type"><tt>Type</tt></a>. <tt>SymbolTable</tt> is an abstract data
+ type. It hides the data it contains and provides access to it through a
+ controlled interface.</p>
+
+ <p>To use the <tt>SymbolTable</tt> well, you need to understand the
+ structure of the information it holds. The class contains two
+ <tt>std::map</tt> objects. The first, <tt>pmap</tt>, is a map of
+ <tt>Type*</tt> to maps of name (<tt>std::string</tt>) to <tt>Value*</tt>.
+ The second, <tt>tmap</tt>, is a map of names to <tt>Type*</tt>. Thus, Values
+ are stored in two-dimensions and accessed by <tt>Type</tt> and name. Types,
+ however, are stored in a single dimension and accessed only by name.</p>
+
+ <p>The interface of this class provides three basic types of operations:
+ <ol>
+ <li><em>Accessors</em>. Accessors provide read-only access to information
+ such as finding a value for a name with the
+ <a href="#SymbolTable_lookup">lookup</a> method.</li>
+ <li><em>Mutators</em>. Mutators allow the user to add information to the
+ <tt>SymbolTable</tt> with methods like
+ <a href="#SymbolTable_insert"><tt>insert</tt></a>.</li>
+ <li><em>Iterators</em>. Iterators allow the user to traverse the content
+ of the symbol table in well defined ways, such as the method
+ <a href="#SymbolTable_type_begin"><tt>type_begin</tt></a>.</li>
+ </ol>
+
+ <h3>Accessors</h3>
+ <dl>
+ <dt><tt>Value* lookup(const Type* Ty, const std::string& name) const</tt>:
+ </dt>
+ <dd>The <tt>lookup</tt> method searches the type plane given by the
+ <tt>Ty</tt> parameter for a <tt>Value</tt> with the provided <tt>name</tt>.
+ If a suitable <tt>Value</tt> is not found, null is returned.</dd>
+
+ <dt><tt>Type* lookupType( const std::string& name) const</tt>:</dt>
+ <dd>The <tt>lookupType</tt> method searches through the types for a
+ <tt>Type</tt> with the provided <tt>name</tt>. If a suitable <tt>Type</tt>
+ is not found, null is returned.</dd>
+
+ <dt><tt>bool hasTypes() const</tt>:</dt>
+ <dd>This function returns true if an entry has been made into the type
+ map.</dd>
+
+ <dt><tt>bool isEmpty() const</tt>:</dt>
+ <dd>This function returns true if both the value and types maps are
+ empty</dd>
+
+ <dt><tt>std::string get_name(const Value*) const</tt>:</dt>
+ <dd>This function returns the name of the Value provided or the empty
+ string if the Value is not in the symbol table.</dd>
+
+ <dt><tt>std::string get_name(const Type*) const</tt>:</dt>
+ <dd>This function returns the name of the Type provided or the empty
+ string if the Type is not in the symbol table.</dd>
+ </dl>
+
+ <h3>Mutators</h3>
+ <dl>
+ <dt><tt>void insert(Value *Val)</tt>:</dt>
+ <dd>This method adds the provided value to the symbol table. The Value must
+ have both a name and a type which are extracted and used to place the value
+ in the correct type plane under the value's name.</dd>
+
+ <dt><tt>void insert(const std::string& Name, Value *Val)</tt>:</dt>
+ <dd> Inserts a constant or type into the symbol table with the specified
+ name. There can be a many to one mapping between names and constants
+ or types.</dd>
+
+ <dt><tt>void insert(const std::string& Name, Type *Typ)</tt>:</dt>
+ <dd> Inserts a type into the symbol table with the specified name. There
+ can be a many-to-one mapping between names and types. This method
+ allows a type with an existing entry in the symbol table to get
+ a new name.</dd>
+
+ <dt><tt>void remove(Value* Val)</tt>:</dt>
+ <dd> This method removes a named value from the symbol table. The
+ type and name of the Value are extracted from \p N and used to
+ lookup the Value in the correct type plane. If the Value is
+ not in the symbol table, this method silently ignores the
+ request.</dd>
+
+ <dt><tt>void remove(Type* Typ)</tt>:</dt>
+ <dd> This method removes a named type from the symbol table. The
+ name of the type is extracted from \P T and used to look up
+ the Type in the type map. If the Type is not in the symbol
+ table, this method silently ignores the request.</dd>
+
+ <dt><tt>Value* remove(const std::string& Name, Value *Val)</tt>:</dt>
+ <dd> Remove a constant or type with the specified name from the
+ symbol table.</dd>
+
+ <dt><tt>Type* remove(const std::string& Name, Type* T)</tt>:</dt>
+ <dd> Remove a type with the specified name from the symbol table.
+ Returns the removed Type.</dd>
+
+ <dt><tt>Value *value_remove(const value_iterator& It)</tt>:</dt>
+ <dd> Removes a specific value from the symbol table.
+ Returns the removed value.</dd>
+
+ <dt><tt>bool strip()</tt>:</dt>
+ <dd> This method will strip the symbol table of its names leaving
+ the type and values. </dd>
+
+ <dt><tt>void clear()</tt>:</dt>
+ <dd>Empty the symbol table completely.</dd>
+ </dl>
+
+ <h3>Iteration</h3>
+ <p>The following functions describe three types of iterators you can obtain
+ the beginning or end of the sequence for both const and non-const. It is
+ important to keep track of the different kinds of iterators. There are
+ three idioms worth pointing out:</p>
+ <table class="doc_table">
+ <tr><th>Units</th><th>Iterator</th><th>Idiom</th></tr>
+ <tr>
+ <td>Planes Of name/Value maps</td><td>PI</td>
+ <td><tt><pre>
+ for (SymbolTable::plane_const_iterator PI = ST.plane_begin(),
+ PE = ST.plane_end(); PI != PE; ++PI ) {
+ PI->first // This is the Type* of the plane
+ PI->second // This is the SymbolTable::ValueMap of name/Value pairs
+ </pre></tt></td>
+ </tr>
+ <tr>
+ <td>All name/Type Pairs</td><td>TI</td>
+ <td><tt><pre>
+ for (SymbolTable::type_const_iterator TI = ST.type_begin(),
+ TE = ST.type_end(); TI != TE; ++TI )
+ TI->first // This is the name of the type
+ TI->second // This is the Type* value associated with the name
+ </pre></tt></td>
+ </tr>
+ <tr>
+ <td>name/Value pairs in a plane</td><td>VI</td>
+ <td><tt><pre>
+ for (SymbolTable::value_const_iterator VI = ST.value_begin(SomeType),
+ VE = ST.value_end(SomeType); VI != VE; ++VI )
+ VI->first // This is the name of the Value
+ VI->second // This is the Value* value associated with the name
+ </pre></tt></td>
+ </tr>
+ </table>
+ <p>Using the recommended iterator names and idioms will help you avoid
+ making mistakes. Of particular note, make sure that whenever you use
+ value_begin(SomeType) that you always compare the resulting iterator
+ with value_end(SomeType) not value_end(SomeOtherType) or else you
+ will loop infinitely.</p>
+
+ <dl>
+
+ <dt><tt>plane_iterator plane_begin()</tt>:</dt>
+ <dd>Get an iterator that starts at the beginning of the type planes.
+ The iterator will iterate over the Type/ValueMap pairs in the
+ type planes. </dd>
+
+ <dt><tt>plane_const_iterator plane_begin() const</tt>:</dt>
+ <dd>Get a const_iterator that starts at the beginning of the type
+ planes. The iterator will iterate over the Type/ValueMap pairs
+ in the type planes. </dd>
+
+ <dt><tt>plane_iterator plane_end()</tt>:</dt>
+ <dd>Get an iterator at the end of the type planes. This serves as
+ the marker for end of iteration over the type planes.</dd>
+
+ <dt><tt>plane_const_iterator plane_end() const</tt>:</dt>
+ <dd>Get a const_iterator at the end of the type planes. This serves as
+ the marker for end of iteration over the type planes.</dd>
+
+ <dt><tt>value_iterator value_begin(const Type *Typ)</tt>:</dt>
+ <dd>Get an iterator that starts at the beginning of a type plane.
+ The iterator will iterate over the name/value pairs in the type plane.
+ Note: The type plane must already exist before using this.</dd>
+
+ <dt><tt>value_const_iterator value_begin(const Type *Typ) const</tt>:</dt>
+ <dd>Get a const_iterator that starts at the beginning of a type plane.
+ The iterator will iterate over the name/value pairs in the type plane.
+ Note: The type plane must already exist before using this.</dd>
+
+ <dt><tt>value_iterator value_end(const Type *Typ)</tt>:</dt>
+ <dd>Get an iterator to the end of a type plane. This serves as the marker
+ for end of iteration of the type plane.
+ Note: The type plane must already exist before using this.</dd>
+
+ <dt><tt>value_const_iterator value_end(const Type *Typ) const</tt>:</dt>
+ <dd>Get a const_iterator to the end of a type plane. This serves as the
+ marker for end of iteration of the type plane.
+ Note: the type plane must already exist before using this.</dd>
+
+ <dt><tt>type_iterator type_begin()</tt>:</dt>
+ <dd>Get an iterator to the start of the name/Type map.</dd>
+
+ <dt><tt>type_const_iterator type_begin() cons</tt>:</dt>
+ <dd> Get a const_iterator to the start of the name/Type map.</dd>
+
+ <dt><tt>type_iterator type_end()</tt>:</dt>
+ <dd>Get an iterator to the end of the name/Type map. This serves as the
+ marker for end of iteration of the types.</dd>
+
+ <dt><tt>type_const_iterator type_end() const</tt>:</dt>
+ <dd>Get a const-iterator to the end of the name/Type map. This serves
+ as the marker for end of iteration of the types.</dd>
+
+ <dt><tt>plane_const_iterator find(const Type* Typ ) const</tt>:</dt>
+ <dd>This method returns a plane_const_iterator for iteration over
+ the type planes starting at a specific plane, given by \p Ty.</dd>
+
+ <dt><tt>plane_iterator find( const Type* Typ </tt>:</dt>
+ <dd>This method returns a plane_iterator for iteration over the
+ type planes starting at a specific plane, given by \p Ty.</dd>
+
+ <dt><tt>const ValueMap* findPlane( const Type* Typ ) cons</tt>:</dt>
+ <dd>This method returns a ValueMap* for a specific type plane. This
+ interface is deprecated and may go away in the future.</dd>
+ </dl>
+ </div>
+
+ <!-- *********************************************************************** -->
+ <hr>
+ <address>
+ <a href="http://jigsaw.w3.org/css-validator/check/referer"><img
+ src="http://jigsaw.w3.org/css-validator/images/vcss" alt="Valid CSS!"></a>
+ <a href="http://validator.w3.org/check/referer"><img
+ src="http://www.w3.org/Icons/valid-html401" alt="Valid HTML 4.01!" /></a>
+
+ <a href="mailto:dhurjati at cs.uiuc.edu">Dinakar Dhurjati</a> and
+ <a href="mailto:sabre at nondot.org">Chris Lattner</a><br>
+ <a href="http://llvm.cs.uiuc.edu">The LLVM Compiler Infrastructure</a><br>
+ Last modified: $Date: 2004/08/13 22:03:04 $
+ </address>
+
+ </body>
+ </html>
+ <!-- vim: sw=2 noai
+ -->
Index: llvm-www/releases/1.3/docs/Projects.html
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+ <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"
+ "http://www.w3.org/TR/html4/strict.dtd">
+ <html>
+ <head>
+ <title>Creating an LLVM Project</title>
+ <link rel="stylesheet" href="llvm.css" type="text/css">
+ </head>
+ <body>
+
+ <div class="doc_title">Creating an LLVM Project</div>
+
+ <ol>
+ <li><a href="#overview">Overview</a></li>
+ <li><a href="#create">Create a project from the Sample Project</a></li>
+ <li><a href="#source">Source tree layout</a></li>
+ <li><a href="#makefiles">Writing LLVM-style Makefiles</a>
+ <ol>
+ <li><a href="#reqVars">Required Variables</a></li>
+ <li><a href="#varsBuildDir">Variables for Building Subdirectories</a></li>
+ <li><a href="#varsBuildLib">Variables for Building Libraries</a></li>
+ <li><a href="#varsBuildProg">Variables for Building Programs</a></li>
+ <li><a href="#miscVars">Miscellaneous Variables</a></li>
+ </ol></li>
+ <li><a href="#objcode">Placement of object code</a></li>
+ <li><a href="#help">Further help</a></li>
+ </ol>
+
+ <div class="doc_author">
+ <p>Written by John Criswell</p>
+ </div>
+
+ <!-- *********************************************************************** -->
+ <div class="doc_section"><a name="overview">Overview</a></div>
+ <!-- *********************************************************************** -->
+
+ <div class="doc_text">
+
+ <p>The LLVM build system is designed to facilitate the building of third party
+ projects that use LLVM header files, libraries, and tools. In order to use
+ these facilities, a Makefile from a project must do the following things:</p>
+
+ <ol>
+ <li>Set environment variables.There are several environment variables that a
+ Makefile needs to set to use the LLVM build system:
+
+ <ul>
+ <li><tt>LLVM_SRC_ROOT</tt> - The root of the LLVM source tree.</li>
+ <li><tt>LLVM_OBJ_ROOT</tt> - The root of the LLVM object tree.</li>
+ <li><tt>BUILD_SRC_ROOT</tt> - The root of the project's source tree.</li>
+ <li><tt>BUILD_OBJ_ROOT</tt> - The root of the project's object tree.</li>
+ <li><tt>BUILD_SRC_DIR</tt> - The directory containing the current source to be
+ compiled.</li>
+ <li><tt>BUILD_OBJ_DIR</tt> - The directory where the current source will place
+ the new object files. This should always be the current directory.</li>
+ <li><tt>LEVEL</tt> - The relative path from the current directory to the root
+ of the object tree.</li>
+ </ul></li>
+ <li>Include <tt>Makefile.config</tt> from <tt>$(LLVM_OBJ_ROOT)</tt>.</li>
+ <li>Include <tt>Makefile.rules</tt> from <tt>$(LLVM_SRC_ROOT)</tt>.</li>
+ </ol>
+
+ <p>There are two ways that you can set all of these variables:</p>
+
+ <ol>
+ <li>You can write your own Makefiles which hard-code these values.</li>
+
+ <li> You can use the pre-made LLVM sample project. This sample project includes
+ Makefiles, a configure script that can be used to configure the location of
+ LLVM, and the ability to support multiple object directories from a single
+ source directory.</li>
+ </ol>
+
+ <p>This document assumes that you will base your project off of the LLVM sample
+ project found in <tt>llvm/projects/sample</tt>. If you want to devise your own
+ build system, studying the sample project and LLVM Makefiles will probably
+ provide enough information on how to write your own Makefiles.</p>
+
+ </div>
+
+ <!-- *********************************************************************** -->
+ <div class="doc_section">
+ <a name="create">Create a Project from the Sample Project</a>
+ </div>
+ <!-- *********************************************************************** -->
+
+ <div class="doc_text">
+
+ <p>Follow these simple steps to start your project:</p>
+
+ <ol>
+ <li>Copy the <tt>llvm/projects/sample</tt> directory to any place of your
+ choosing. You can place it anywhere you like. Rename the directory to match
+ the name of your project.</li>
+
+ <li>Add your source code and Makefiles to your source tree.</li>
+
+ <li>If you want your Makefiles to be configured by the <tt>configure</tt>
+ script, or if you want to support multiple object directories, add your
+ Makefiles to the <tt>configure</tt> script by adding them into the
+ <tt>autoconf/configure.ac</tt> file. The macro <tt>AC_CONFIG_MAKEFILE</tt> will
+ copy a file, unmodified, from the source directory to the object directory.</li>
+
+ <li>After updating <tt>autoconf/configure.ac</tt>, regenerate the
+ configure script with these commands:
+
+ <div class="doc_code">
+ <p><tt>% cd autoconf<br>
+ % autoconf -o ../configure</tt></p>
+ </div>
+
+ <p>You must be using Autoconf version 2.57 or higher.</p></li>
+
+ <li>Run <tt>configure</tt> in the directory in which you want to place
+ object code. Use the following options to tell your project where it
+ can find LLVM:
+
+ <dl>
+ <dt><tt>--with-llvmsrc=<directory></tt>
+ <dd>
+ Tell your project where the LLVM source tree is located.
+ <p>
+ <dt><tt>--with-llvmobj=<directory></tt>
+ <dd>
+ Tell your project where the LLVM object tree is located.
+ </dl>
+ </ol>
+
+ <p>That's it! Now all you have to do is type <tt>gmake</tt> in the root of
+ your object directory, and your project should build.</p>
+
+ </div>
+
+ <!-- *********************************************************************** -->
+ <div class="doc_section">
+ <a name="source">Source Tree Layout</a>
+ </div>
+ <!-- *********************************************************************** -->
+
+ <div class="doc_text">
+
+ <p>In order to use the LLVM build system, you will want to organize your
+ source code so that it can benefit from the build system's features.
+ Mainly, you want your source tree layout to look similar to the LLVM
+ source tree layout. The best way to do this is to just copy the
+ project tree from <tt>llvm/projects/sample</tt> and modify it to meet
+ your needs, but you can certainly add to it if you want.</p>
+
+ <p>Underneath your top level directory, you should have the following
+ directories:</p>
+
+ <dl>
+ <dt><b>lib</b>
+ <dd>
+ This subdirectory should contain all of your library source
+ code. For each library that you build, you will have one
+ directory in <b>lib</b> that will contain that library's source
+ code.
+
+ <p>
+ Libraries can be object files, archives, or dynamic libraries.
+ The <b>lib</b> directory is just a convenient place for libraries
+ as it places them all in a directory from which they can be linked
+ later.
+
+ <dt><b>include</b>
+ <dd>
+ This subdirectory should contain any header files that are
+ global to your project. By global, we mean that they are used
+ by more than one library or executable of your project.
+ <p>
+ By placing your header files in <b>include</b>, they will be
+ found automatically by the LLVM build system. For example, if
+ you have a file <b>include/jazz/note.h</b>, then your source
+ files can include it simply with <b>#include "jazz/note.h"</b>.
+
+ <dt><b>tools</b>
+ <dd>
+ This subdirectory should contain all of your source
+ code for executables. For each program that you build, you
+ will have one directory in <b>tools</b> that will contain that
+ program's source code.
+ <p>
+
+ <dt><b>test</b>
+ <dd>
+ This subdirectory should contain tests that verify that your code
+ works correctly. Automated tests are especially useful.
+ <p>
+ Currently, the LLVM build system provides little support for tests,
+ although some exists. Expanded support for tests will hopefully
+ occur in the future. In the meantime, the LLVM system does provide the
+ following:
+ <ul>
+ <li>
+ LLVM provides several QMTest test classes that can be used to
+ create tests. They can be found in
+ <tt>llvm/test/QMTest/llvm.py</tt>. These test classes perform a
+ variety of functions, including code optimization tests, assembly
+ tests, and code analysis tests. The Makefile in
+ <tt>llvm/test</tt> provides the QMTest context needed by LLVM test
+ classes.
+ <p>
+
+ <li>
+ The LLVM source tree provides benchmarks and programs which are
+ known to compile with the LLVM GCC front ends. You can use these
+ programs to test your code, gather statistics information, and
+ compare it to the current LLVM performance statistics. These
+ programs are found in the <tt>llvm/test/Programs</tt> directory.
+ <p>
+ Currently, there is no way to hook your tests directly into the
+ <tt>llvm/test/Programs</tt> testing harness. You will simply
+ need to find a way to use the source provided within that directory
+ on your own.
+ </ul>
+ </dl>
+
+ <p>Typically, you will want to build your <b>lib</b> directory first followed by
+ your <b>tools</b> directory.</p>
+
+ </div>
+
+ <!-- *********************************************************************** -->
+ <div class="doc_section">
+ <a name="makefiles">Writing LLVM Style Makefiles</a>
+ </div>
+ <!-- *********************************************************************** -->
+
+ <div class="doc_text">
+
+ <p>The LLVM build system provides a convenient way to build libraries and
+ executables. Most of your project Makefiles will only need to define a few
+ variables. Below is a list of the variables one can set and what they can
+ do:</p>
+
+ </div>
+
+ <!-- ======================================================================= -->
+ <div class="doc_subsection">
+ <a name="reqVars">Required Variables</a>
+ </div>
+
+ <div class="doc_text">
+
+ <dl>
+ <dt>LEVEL
+ <dd>
+ This variable is the relative path from this Makefile to the
+ top directory of your project's source code. For example, if
+ your source code is in <tt>/tmp/src</tt>, then the Makefile in
+ <tt>/tmp/src/jump/high</tt> would set <tt>LEVEL</tt> to <tt>"../.."</tt>.
+ </dl>
+
+ </div>
+
+ <!-- ======================================================================= -->
+ <div class="doc_subsection">
+ <a name="varsBuildDir">Variables for Building Subdirectories</a>
+ </div>
+
+ <div class="doc_text">
+
+ <dl>
+ <dt>DIRS
+ <dd>
+ This is a space separated list of subdirectories that should be
+ built. They will be built, one at a time, in the order
+ specified.
+ <p>
+
+ <dt>PARALLEL_DIRS
+ <dd>
+ This is a list of directories that can be built in parallel.
+ These will be built after the directories in DIRS have been
+ built.
+ <p>
+
+ <dt>OPTIONAL_DIRS
+ <dd>
+ This is a list of directories that can be built if they exist,
+ but will not cause an error if they do not exist. They are
+ built serially in the order in which they are listed.
+ </dl>
+
+ </div>
+
+ <!-- ======================================================================= -->
+ <div class="doc_subsection">
+ <a name="varsBuildLib">Variables for Building Libraries</a>
+ </div>
+
+ <div class="doc_text">
+
+ <dl>
+ <dt>LIBRARYNAME
+ <dd>
+ This variable contains the base name of the library that will
+ be built. For example, to build a library named
+ <tt>libsample.a</tt>, LIBRARYNAME should be set to
+ <tt>sample</tt>.
+ <p>
+
+ <dt>BUILD_ARCHIVE
+ <dd>
+ By default, a library is a <tt>.o</tt> file that is linked
+ directly into a program. To build an archive (also known as
+ a static library), set the BUILD_ARCHIVE variable.
+ <p>
+
+ <dt>SHARED_LIBRARY
+ <dd>
+ If SHARED_LIBRARY is defined in your Makefile, a shared
+ (or dynamic) library will be built.
+ </dl>
+
+ </div>
+
+ <!-- ======================================================================= -->
+ <div class="doc_subsection">
+ <a name="varsBuildProg">Variables for Building Programs</a>
+ </div>
+
+ <div class="doc_text">
+
+ <dl>
+ <dt>TOOLNAME
+ <dd>
+ This variable contains the name of the program that will
+ be built. For example, to build an executable named
+ <tt>sample</tt>, TOOLNAME should be set to <tt>sample</tt>.
+ <p>
+
+ <dt>USEDLIBS
+ <dd>
+ This variable holds a space separated list of libraries that
+ should be linked into the program. These libraries must either
+ be LLVM libraries or libraries that come from your <b>lib</b>
+ directory. The libraries must be specified by their base name.
+ For example, to link libsample.a, you would set USEDLIBS to
+ <tt>sample</tt>.
+ <p>
+ Note that this works only for statically linked libraries.
+ <p>
+
+ <dt>LIBS
+ <dd>
+ To link dynamic libraries, add <tt>-l<library base name></tt> to
+ the LIBS variable. The LLVM build system will look in the same places
+ for dynamic libraries as it does for static libraries.
+ <p>
+ For example, to link <tt>libsample.so</tt>, you would have the
+ following line in your <tt>Makefile</tt>:
+ <p>
+ <tt>
+ LIBS += -lsample
+ </tt>
+ </dl>
+
+ </div>
+
+ <!-- ======================================================================= -->
+ <div class="doc_subsection">
+ <a name="miscVars">Miscellaneous Variables</a>
+ </div>
+
+ <div class="doc_text">
+
+ <dl>
+ <dt>ExtraSource
+ <dd>
+ This variable contains a space separated list of extra source
+ files that need to be built. It is useful for including the
+ output of Lex and Yacc programs.
+ <p>
+
+ <dt>CFLAGS
+ <dt>CPPFLAGS
+ <dd>
+ This variable can be used to add options to the C and C++
+ compiler, respectively. It is typically used to add options
+ that tell the compiler the location of additional directories
+ to search for header files.
+ <p>
+ It is highly suggested that you append to CFLAGS and CPPFLAGS as
+ opposed to overwriting them. The master Makefiles may already
+ have useful options in them that you may not want to overwrite.
+ <p>
+ </dl>
+
+ </div>
+
+ <!-- *********************************************************************** -->
+ <div class="doc_section">
+ <a name="objcode">Placement of Object Code</a>
+ </div>
+ <!-- *********************************************************************** -->
+
+ <div class="doc_text">
+
+ <p>The final location of built libraries and executables will depend upon
+ whether you do a Debug, Release, or Profile build.</p>
+
+ <dl>
+ <dt>Libraries
+ <dd>
+ All libraries (static and dynamic) will be stored in
+ <tt>BUILD_OBJ_ROOT/lib/<type></tt>, where type is <tt>Debug</tt>,
+ <tt>Release</tt>, or <tt>Profile</tt> for a debug, optimized, or
+ profiled build, respectively.<p>
+
+ <dt>Executables
+ <dd>All executables will be stored in
+ <tt>BUILD_OBJ_ROOT/tools/<type></tt>, where type is <tt>Debug</tt>,
+ <tt>Release</tt>, or <tt>Profile</tt> for a debug, optimized, or profiled
+ build, respectively.
+ </dl>
+
+ </div>
+
+ <!-- *********************************************************************** -->
+ <div class="doc_section">
+ <a name="help">Further Help</a>
+ </div>
+ <!-- *********************************************************************** -->
+
+ <div class="doc_text">
+
+ <p>If you have any questions or need any help creating an LLVM project,
+ the LLVM team would be more than happy to help. You can always post your
+ questions to the <a
+ href="http://mail.cs.uiuc.edu/mailman/listinfo/llvmdev">LLVM Developers
+ Mailing List</a>.</p>
+
+ </div>
+
+ <!-- *********************************************************************** -->
+ <hr>
+ <address>
+ <a href="http://jigsaw.w3.org/css-validator/check/referer"><img
+ src="http://jigsaw.w3.org/css-validator/images/vcss" alt="Valid CSS!"></a>
+ <a href="http://validator.w3.org/check/referer"><img
+ src="http://www.w3.org/Icons/valid-html401" alt="Valid HTML 4.01!" /></a>
+
+ <a href="mailto:criswell at uiuc.edu">John Criswell</a><br>
+ <a href="http://llvm.cs.uiuc.edu">The LLVM Compiler Infrastructure</a>
+ <br>
+ Last modified: $Date: 2004/08/13 22:03:04 $
+ </address>
+
+ </body>
+ </html>
Index: llvm-www/releases/1.3/docs/ReleaseNotes.html
diff -c /dev/null llvm-www/releases/1.3/docs/ReleaseNotes.html:1.1
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***************
*** 0 ****
--- 1,773 ----
+ <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"
+ "http://www.w3.org/TR/html4/strict.dtd">
+ <html>
+ <head>
+ <link rel="stylesheet" href="llvm.css" type="text/css">
+ <title>LLVM 1.3 Release Notes</title>
+ </head>
+ <body>
+
+ <div class="doc_title">LLVM 1.3 Release Notes</div>
+
+ <ol>
+ <li><a href="#intro">Introduction</a></li>
+ <li><a href="#whatsnew">What's New?</a></li>
+ <li><a href="GettingStarted.html">Installation Instructions</a></li>
+ <li><a href="#portability">Portability and Supported Platforms</a></li>
+ <li><a href="#knownproblems">Known Problems</a>
+ <ul>
+ <li><a href="#experimental">Experimental features included in this
+ release</a>
+ <li><a href="#core">Known problems with the LLVM Core</a>
+ <li><a href="#c-fe">Known problems with the C Front-end</a>
+ <li><a href="#c++-fe">Known problems with the C++ Front-end</a>
+ <li><a href="#x86-be">Known problems with the X86 Back-end</a>
+ <li><a href="#sparcv9-be">Known problems with the SparcV9 Back-end</a>
+ <li><a href="#c-be">Known problems with the C back-end</a>
+ </ul></li>
+ <li><a href="#additionalinfo">Additional Information</a></li>
+ </ol>
+
+ <div class="doc_author">
+ <p>Written by the <a href="http://llvm.cs.uiuc.edu">LLVM team</a><p>
+ </div>
+
+ <!-- *********************************************************************** -->
+ <div class="doc_section">
+ <a name="intro">Introduction</a>
+ </div>
+ <!-- *********************************************************************** -->
+
+ <div class="doc_text">
+
+ <p>This document contains the release notes for the LLVM compiler
+ infrastructure, release 1.3. Here we describe the status of LLVM, including any
+ known problems and bug fixes from the previous release. The most up-to-date
+ version of this document can be found on the <a
+ href="http://llvm.cs.uiuc.edu/releases/1.3/">LLVM 1.3 web site</a>. If you are
+ not reading this on the LLVM web pages, you should probably go there because
+ this document may be updated after the release.</p>
+
+ <p>For more information about LLVM, including information about potentially more
+ current releases, please check out the <a href="http://llvm.cs.uiuc.edu">main
+ web site</a>. If you have questions or comments, the <a
+ href="http://mail.cs.uiuc.edu/mailman/listinfo/llvmdev">LLVM developer's mailing
+ list</a> is a good place to send them.</p>
+
+ <p>Note that if you are reading this file from CVS, this document applies
+ to the <i>next</i> release, not the current one. To see the release notes for
+ the current or previous releases, see the <a
+ href="http://llvm.cs.uiuc.edu/releases/">releases page</a>.</p>
+
+ </div>
+
+ <!-- *********************************************************************** -->
+ <div class="doc_section">
+ <a name="whatsnew">What's New?</a>
+ </div>
+ <!-- *********************************************************************** -->
+
+ <div class="doc_text">
+
+ <p>This is the fourth public release of the LLVM compiler infrastructure. This
+ release primarily improves the <a href="#codequality">performance of the
+ code</a> produced by all aspects of the LLVM compiler, adds many <a
+ href="#newfeatures">new features</a>, <a href="#bugfix">fixes a few
+ bugs</a>, speeds up the compiler, and introduces a new (experimental)
+ PowerPC code generator.</p>
+
+ <p> At this time, LLVM is known to correctly compile and run all C & C++
+ SPEC CPU95 & 2000 benchmarks, the Olden benchmarks, and the Ptrdist
+ benchmarks, and <b>many</b> other programs. LLVM now also works
+ with a broad variety of C++ programs.</p>
+
+ </div>
+
+ <!--=========================================================================-->
+ <div class="doc_subsubsection">
+ <a name="newfeatures">This release implements the following new features:</a>
+ </div>
+
+ <div class="doc_text">
+
+ <ol>
+ <li>The LLVM <a href="LangRef.html#i_select"><tt>select</tt></a> instruction is
+ now fully implemented and supported by all transformations, native code
+ generators, and the interpreter.</li>
+ <li>Bugpoint can now narrow down code-generation bugs to a loop nest, where
+ before it could only narrow them down to a function being miscompiled.</li>
+ <li><a href="http://llvm.cs.uiuc.edu/PR40">Bugpoint can now debug arbitrary
+ modes of llc</a> and lli, by passing them command line flags (e.g.
+ <tt>-regalloc=linearscan</tt>).</li>
+ <li>The Control Flow Graph in the native code generators is no longer
+ constrained to be the same as the CFG for the LLVM input code.</li>
+ <li>The LLVM induction variable analysis routines have been rewritten.</li>
+ <li>LLVM now has new loop unrolling and loop unswitching passes.</li>
+ <li>The induction variable substitution pass performs linear function test
+ replacement and exit value replacement optimizations.</li>
+ <li>LLVM now has first-class support for <a
+ href="GarbageCollection.html">Accurate Garbage Collection</a>, enabling the use
+ of aggressive copying and generational collectors.</li>
+ <li>LLVM now includes a simple implementation of <a
+ href="AliasAnalysis.html#anders-aa">Andersen's interprocedural alias
+ analysis</a> algorithm.</li>
+ <li>Bugpoint can <a href="http://llvm.cs.uiuc.edu/PR327">extract individual
+ basic blocks</a> to track down reduce miscompilation testcases.</li>
+ <li>LLVM and the C front-end now work under Win32 using the
+ <a href="http://www.cygwin.com">Cygwin</a> runtime libraries.
+ This includes the JIT compiler.</li>
+ <li>The LLVM code generator is now being <a
+ href="CodeGenerator.html">documented</a>.</li>
+ <li>LLVM includes a new tool, <a
+ href="CommandGuide/html/llvm-bcanalyzer.html">llvm-bcanalyzer</a>, This tool
+ can compute various statistics and dump information about LLVM bytecode
+ encoding.</li>
+ <li>The <a href="BytecodeFormat.html">LLVM bytecode file format</a> is now
+ documented.</li>
+ <li>LLVM now provides an <a
+ href="LangRef.html#i_isunordered">llvm.isunordered</a> intrinsic for efficient
+ implementation of unordered floating point comparisons.</li>
+ <li>The llvmgcc front-end now supports the GCC builtins for ISO C99 floating
+ point comparison macros (e.g., <tt>__builtin_islessequal</tt>).</li>
+ <li>We now generate <a href="CommandGuide/">HTML documentation and man pages</a>
+ for the tools from a single source (perl-style POD files).</li>
+ <li>The LLVM code generator can now dynamically load targets from shared
+ objects.</li>
+ <li>LLVM now includes a "skeleton" target, which makes it easier to get
+ started porting LLVM to new architectures.</li>
+ <li>The linear scan register allocator is now enabled by default in the
+ target-independent code generator.</li>
+ <li>LLVM now includes a dead store elimination pass.</li>
+ <li>Bugpoint can now debug miscompilations that lead to the program going
+ into an infinite loop.</li>
+ <li>LLVM now provides interfaces to support ML-style pattern matching on the
+ LLVM IR.</li>
+ <li>LLVM now includes a <a
+ href="AliasAnalysis.html#globalsmodref">context-sensitive mod/ref analysis</a>
+ for global variables, which is now enabled by default in gccld.</li>
+ <li>LLVM can now autogenerate assembly printers for code generators from the
+ tablegen description of the target (before they were hand coded).</li>
+ <li>All LLVM tools will now respond to the
+ <a href="http://llvm.cs.uiuc.edu/PR413"><tt>--version</tt> option</a> which
+ will tell you the version of LLVM on which the tool is based.</li>
+ <li>An experimental PowerPC backend has been added, capable of compiling several
+ SPEC benchmarks.</li>
+ </ol>
+
+ </div>
+
+
+ <!--=========================================================================-->
+ <div class="doc_subsubsection">
+ In this release, the following missing features were implemented:
+ </div>
+
+ <div class="doc_text">
+
+ <ol>
+ <li><a href="http://llvm.cs.uiuc.edu/PR82">LLVM cannot handle structures with
+ more than 256 elements</a></li>
+ <li><a href="http://llvm.cs.uiuc.edu/PR38">[bugpoint] External functions used in
+ non-instruction entities, such as global constant initializer</a></li>
+ <li><a href="http://llvm.cs.uiuc.edu/PR178">Stacker does not handle targets
+ with 64-bit pointers.</a></li>
+ <li><a href="http://llvm.cs.uiuc.edu/PR290">Bugpoint doesn't support
+ uses of external fns by immediate constant exprs</a></li>
+ <li><a href="http://llvm.cs.uiuc.edu/PR407">Can't add function passes that
+ depend on immutable passes to the FunctionPassManager</a>.</li>
+ <li><a href="http://llvm.cs.uiuc.edu/PR308">Archive file reader doesn't
+ understand abbreviated names in headers</a></li>
+ </ol>
+
+ </div>
+
+ <!--=========================================================================-->
+ <div class="doc_subsubsection">
+ <a name="qualityofimp">In this release, the following Quality of Implementation
+ issues were fixed:</a>
+ </div>
+
+ <div class="doc_text">
+
+ <ol>
+ <li><a href="http://llvm.cs.uiuc.edu/PR305">LLVM tools will happily spew
+ bytecode onto your terminal</a></li>
+ <li><a href="http://llvm.cs.uiuc.edu/PR329">[llvmgcc] type names are not emitted
+ for structure typedefs</a></li>
+ <li>All documentation is now conformant to the HTML 4.01 (Strict) level.</li>
+ <li>The spurious "WARNING: Found global types that are not compatible" warning
+ produced when linking C++ programs has been fixed.</li>
+ <li><a href="http://llvm.cs.uiuc.edu/PR391">lli Doesn't Handle Exceptions From
+ Bytecode Reader</a></li>
+ <li><a href="http://llvm.cs.uiuc.edu/PR392">Global Vars Have (Somewhat) Limited
+ Type Range</a></li>
+ <li><a href="http://llvm.cs.uiuc.edu/PR341">operator<< on a Value* now
+ prints the address of the object instead of its contents.</a></li>
+ <li><a href="http://llvm.cs.uiuc.edu/PR402">Bytecode Enhancements
+ Needed</a></li>
+ <li><a href="http://llvm.cs.uiuc.edu/PR404">[loopsimplify] Loop simplify is
+ really slow on 252.eon</a></li>
+ <li><a href="http://llvm.cs.uiuc.edu/PR122">[code-cleanup] SymbolTable class
+ cleanup, Type should not derive from Value, eliminate ConstantPointerRef
+ class</a>.</li>
+ <li>The memory footprint of the LLVM IR has been reduced substantially.</li>
+ <li>The LLVM linker and many core classes have been sped up substantially.</li>
+ </ol>
+
+ </div>
+
+ <!--=========================================================================-->
+ <div class="doc_subsubsection">
+ In this release, the following build problems were fixed:
+ </div>
+
+ <div class="doc_text">
+ <ol>
+ <li><a href="http://llvm.cs.uiuc.edu/PR301">Minor configure bugs with
+ -disable/enable-povray and -disable-spec</a></li>
+ <li><a href="http://llvm.cs.uiuc.edu/PR289">shell scripts output by gccld don't
+ work if you change PATH</a></li>
+ <li><a href="http://llvm.cs.uiuc.edu/PR364">[llvmgcc] llvmgcc does not compile
+ with gcc 3.4</a></li>
+ <li><a href="http://llvm.cs.uiuc.edu/PR373">[llvmgcc] obstack.h relies on
+ obsolete casts-as-lvalues GCC extension</a></li>
+ </ol>
+ </div>
+
+ <!--=========================================================================-->
+ <div class="doc_subsubsection">
+ <a name="codequality">This release includes the following Code Quality
+ improvements:</a>
+ </div>
+
+ <div class="doc_text">
+ <ol>
+ <li>Fixed: <a href="http://llvm.cs.uiuc.edu/PR309">[vmcore] Code quality problem
+ due to long operand of getelementptr</a></li>
+
+ <li>The X86 backend now generates substantially better code for 64-bit integer
+ and floating point operations.</li>
+
+ <li>The -inline pass no longer inlines mutually recursive functions until it
+ hits the inlining threshold.</li>
+
+ <li>The -inline pass no longer misses obvious inlining opportunities just
+ because the callee eventually calls into an external function.</li>
+
+ <li>The -simplifycfg pass can now "if convert" simple statements into the
+ <tt>select</tt> instruction.</li>
+
+ <li>The -loopsimplify pass can now break <a
+ href="http://llvm.cs.uiuc.edu/PR35">natural loops with multiple backedges</a>
+ into multiple nested loops. This enables a variety of subsequent
+ optimizations.</li>
+
+ <li>The -adce pass can now eliminate calls to functions that do not not write to
+ memory.</li>
+
+ <li>The link-time optimizer now runs the -prune-eh pass (to remove unused
+ exception handlers).</li>
+
+ <li>The link-time optimizer now runs dead store elimination and uses a simple
+ interprocedural alias analysis.</li>
+
+ <li>The -simplifycfg pass can now eliminate simple correlated branches (such as
+ "<tt>if (A < B && A < B)</tt>", and can turn short-circuiting
+ operators into the strict versions when useful (such as "<tt>if (A < B || A
+ > C)</tt>" into "<tt>if (A < B | A > C)</tt>"</li>
+
+ <li>LLVM now has infrastructure for (simple and sparse conditional) constant
+ propagation of function calls. It currently supports a few math library
+ functions like sqrt/sin/cos/etc.</li>
+
+ <li>The C backend now emits <a href="http://llvm.cs.uiuc.edu/PR334">syntactic
+ loops</a> in the code to help C compilers whose optimizers do not recognize
+ loops formed from gotos (like GCC).</li>
+
+ <li>The SparcV9 backend no longers <a
+ href="http://llvm.cs.uiuc.edu/PR368">spills the null constant to the constant
+ pool</a>.</li>
+ </ol>
+ </div>
+
+ <!--=========================================================================-->
+ <div class="doc_subsubsection">
+ <a name="bugfix">In this release, the following bugs in the previous release
+ were fixed:</a>
+ </div>
+
+ <div class="doc_text">
+
+ <p>Bugs fixed in the LLVM Core:</p>
+
+ <ol>
+ <li><a href="http://llvm.cs.uiuc.edu/PR306">[loopsimplify] Loop simplify
+ incorrectly updates dominator information</a></li>
+ <li><a href="http://llvm.cs.uiuc.edu/PR310">[tailduplicate] DemoteRegToStack
+ breaks SSA form</a></li>
+ <li><a href="http://llvm.cs.uiuc.edu/PR313">[X86] JIT miscompiles unsigned short
+ to floating point cast</a></li>
+ <li><a href="http://llvm.cs.uiuc.edu/PR330">[vmcore] Linker causes erroneous
+ asssertion</a></li>
+ <li><a href="http://llvm.cs.uiuc.edu/PR332">[adce] Crash handling unreachable
+ code that unwinds</a></li>
+ <li><a href="http://llvm.cs.uiuc.edu/PR333">[sparcv9] LLC can't emit 2 functions
+ of the same name, both having constant pools</a></li>
+ <li><a href="http://llvm.cs.uiuc.edu/PR337">[livevar] Live variables missed
+ physical register use of aliased definition</a></li>
+ <li><a href="http://llvm.cs.uiuc.edu/PR369">[X86] stackifier crash on floating
+ point setcc X, X</a></li>
+ </ol>
+
+ <p>Bugs in the C/C++ front-end:</p>
+
+ <ol>
+ <li><a href="http://llvm.cs.uiuc.edu/PR298">[llvmgcc] Variable length array
+ indexing miscompiled</a></li>
+ <li><a href="http://llvm.cs.uiuc.edu/PR326">[llvmgcc] Crash on use of undeclared
+ enum type</a></li>
+ <li><a href="http://llvm.cs.uiuc.edu/PR355">[llvmgcc] Errors handling function
+ prototypes that take opaque structs by-value</a></li>
+ <li><a href="http://llvm.cs.uiuc.edu/PR374">[llvmgcc] Crash compiling variable
+ length array of structures</a></li>
+ <li><a href="http://llvm.cs.uiuc.edu/PR377">[llvmgcc] miscompilation of staticly
+ initialized unsigned bitfields</a></li>
+ <li><a href="http://llvm.cs.uiuc.edu/PR396">[llvm-gcc] Crash casting function to void</a></li>
+ </ol>
+ </div>
+
+ <!-- *********************************************************************** -->
+ <div class="doc_section">
+ <a name="portability">Portability and Supported Platforms</a>
+ </div>
+ <!-- *********************************************************************** -->
+
+ <div class="doc_text">
+
+ <p>LLVM is known to work in the following platforms:</p>
+
+ <ul>
+ <li>Intel and AMD machines running Red Hat Linux and FreeBSD (and probably
+ other unix-like systems).</li>
+ <li>Sun UltraSPARC workstations running Solaris 8.</li>
+ <li>Intel and AMD machines running on Win32 with the Cygwin libraries.</li>
+ <li>PowerPC-based Mac OS X boxes, running 10.2 and above. Note that no JIT
+ support is available yet, and LLC support is beta. The C backend can be used
+ to produce stable code for this platform.</li>
+ </ul>
+
+ <p>The core LLVM infrastructure uses
+ <a href="http://www.gnu.org/software/autoconf/">GNU autoconf</a> to adapt itself
+ to the machine and operating system on which it is built. However, minor
+ porting may be required to get LLVM to work on new platforms. We welcome your
+ portability patches and reports of successful builds or error messages.</p>
+
+ <p>Note that the LLVM build system does not currently support directories with
+ spaces on them when running on Win32/cygwin. We strongly recommend running
+ LLVM and the C frontend out of a top-level directory without spaces (e.g.,
+ <tt>/cygdrive/c/llvm</tt>). Also, make sure to install <b>all</b> of the
+ cygwin packages. By default, many important tools are not installed that
+ are needed by the LLVM build process or test suite (e.g., /bin/time).</p>
+
+ </div>
+
+ <!-- *********************************************************************** -->
+ <div class="doc_section">
+ <a name="knownproblems">Known Problems</a>
+ </div>
+ <!-- *********************************************************************** -->
+
+ <div class="doc_text">
+
+ <p>This section contains all known problems with the LLVM system, listed by
+ component. As new problems are discovered, they will be added to these
+ sections. If you run into a problem, please check the <a
+ href="http://llvm.cs.uiuc.edu/bugs/">LLVM bug database</a> and submit a bug if
+ there isn't already one.</p>
+
+ </div>
+
+ <!-- ======================================================================= -->
+ <div class="doc_subsection">
+ <a name="experimental">Experimental features included with this release</a>
+ </div>
+
+ <div class="doc_text">
+
+ <p>The following components of this LLVM release are either untested, known to
+ be broken or unreliable, or are in early development. These components should
+ not be relied on, and bugs should not be filed against them, but they may be
+ useful to some people. In particular, if you would like to work on one of these
+ components, please contact us on the llvmdev list.</p>
+
+ <ul>
+ <li>The PowerPC backend is incomplete and is known to miscompile several SPEC
+ benchmarks. The file <tt>llvm/lib/Target/PowerPC/README.txt</tt> has
+ details.</li>
+ <li>The following passes are incomplete or buggy: <tt>-pgmdep, -memdep,
+ -ipmodref, -cee</tt></li>
+ <li>The <tt>-pre</tt> pass is incomplete (there are cases it doesn't handle that
+ it should) and not thoroughly tested.</li>
+ <li>The <tt>llvm-ar</tt> tool is incomplete and probably buggy.</li>
+ <li>The <tt>llvm-db</tt> tool is in a very early stage of development.</li>
+ </ul>
+
+ </div>
+
+ <!-- ======================================================================= -->
+ <div class="doc_subsection">
+ <a name="core">Known problems with the LLVM Core</a>
+ </div>
+
+ <div class="doc_text">
+
+ <ul>
+
+ <li>In the JIT, <tt>dlsym</tt> on a symbol compiled by the JIT will not
+ work.</li>
+
+ <li>The JIT does not use mutexes to protect its internal data structures. As
+ such, execution of a threaded program could cause these data structures to be
+ corrupted.</li>
+
+ <li>Linking in static archive files (.a files) is slow (there is no symbol
+ table in the archive).</li>
+
+ <li>The gccld program <a href="http://llvm.cs.uiuc.edu/PR139">does not link
+ objects/archives in the order specified on the command line.</a></li>
+
+ <li><a href="http://llvm.cs.uiuc.edu/PR240">The lower-invoke pass does not mark
+ values live across a setjmp as volatile</a>. This missing feature only affects
+ targets whose setjmp/longjmp libraries do not save and restore the entire
+ register file.</li>
+ </ul>
+ </div>
+
+ <!-- ======================================================================= -->
+ <div class="doc_subsection">
+ <a name="c-fe">Known problems with the C front-end</a>
+ </div>
+
+ <!-- _______________________________________________________________________ -->
+ <div class="doc_subsubsection">Bugs</div>
+
+ <div class="doc_text">
+ <ul>
+ <li>C99 Variable sized arrays do not release stack memory when they go out of
+ scope. Thus, the following program may run out of stack space:
+ <pre>
+ for (i = 0; i != 1000000; ++i) {
+ int X[n];
+ foo(X);
+ }
+ </pre></li>
+
+ <li>Initialization of global union variables can only be done <a
+ href="http://llvm.cs.uiuc.edu/bugs/show_bug.cgi?id=162">with the largest union
+ member</a>.</li>
+
+ <li><a href="http://llvm.cs.uiuc.edu/PR244">[llvm-gcc] Error when an implicitly
+ external function is re-declared as static</a></li>
+
+ </ul>
+ </div>
+
+ <!-- _______________________________________________________________________ -->
+ <div class="doc_subsubsection">
+ Notes
+ </div>
+
+ <div class="doc_text">
+
+ <ul>
+
+ <li>Inline assembly is not yet supported.</li>
+
+ <li>"long double" is transformed by the front-end into "double". There is no
+ support for floating point data types of any size other than 32 and 64
+ bits.</li>
+
+ <li>The following Unix system functionality has not been tested and may not
+ work:
+ <ol>
+ <li><tt>sigsetjmp</tt>, <tt>siglongjmp</tt> - These are not turned into the
+ appropriate <tt>invoke</tt>/<tt>unwind</tt> instructions. Note that
+ <tt>setjmp</tt> and <tt>longjmp</tt> <em>are</em> compiled correctly.
+ <li><tt>getcontext</tt>, <tt>setcontext</tt>, <tt>makecontext</tt>
+ - These functions have not been tested.
+ </ol></li>
+
+ <li>Although many GCC extensions are supported, some are not. In particular,
+ the following extensions are known to <b>not be</b> supported:
+ <ol>
+ <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Local-Labels.html#Local%20Labels">Local Labels</a>: Labels local to a block.</li>
+ <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Nested-Functions.html#Nested%20Functions">Nested Functions</a>: As in Algol and Pascal, lexical scoping of functions.</li>
+ <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Constructing-Calls.html#Constructing%20Calls">Constructing Calls</a>: Dispatching a call to another function.</li>
+ <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Extended-Asm.html#Extended%20Asm">Extended Asm</a>: Assembler instructions with C expressions as operands.</li>
+ <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Constraints.html#Constraints">Constraints</a>: Constraints for asm operands.</li>
+ <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Asm-Labels.html#Asm%20Labels">Asm Labels</a>: Specifying the assembler name to use for a C symbol.</li>
+ <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Explicit-Reg-Vars.html#Explicit%20Reg%20Vars">Explicit Reg Vars</a>: Defining variables residing in specified registers.</li>
+ <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Vector-Extensions.html#Vector%20Extensions">Vector Extensions</a>: Using vector instructions through built-in functions.</li>
+ <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Target-Builtins.html#Target%20Builtins">Target Builtins</a>: Built-in functions specific to particular targets.</li>
+ <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Thread-Local.html#Thread-Local">Thread-Local</a>: Per-thread variables.</li>
+ <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Pragmas.html#Pragmas">Pragmas</a>: Pragmas accepted by GCC.</li>
+ </ol>
+
+ <p>The following GCC extensions are <b>partially</b> supported. An ignored
+ attribute means that the LLVM compiler ignores the presence of the attribute,
+ but the code should still work. An unsupported attribute is one which is
+ ignored by the LLVM compiler and will cause a different interpretation of
+ the program.</p>
+
+ <ol>
+ <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Variable-Length.html#Variable%20Length">Variable Length</a>:
+ Arrays whose length is computed at run time.<br>
+ Supported, but allocated stack space is not freed until the function returns (noted above).</li>
+
+ <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Function-Attributes.html#Function%20Attributes">Function Attributes</a>:
+
+ Declaring that functions have no side effects or that they can never
+ return.<br>
+
+ <b>Supported:</b> <tt>format</tt>, <tt>format_arg</tt>, <tt>non_null</tt>,
+ <tt>constructor</tt>, <tt>destructor</tt>, <tt>unused</tt>,
+ <tt>deprecated</tt>, <tt>warn_unused_result</tt>, <tt>weak</tt><br>
+
+ <b>Ignored:</b> <tt>noreturn</tt>, <tt>noinline</tt>,
+ <tt>always_inline</tt>, <tt>pure</tt>, <tt>const</tt>, <tt>nothrow</tt>,
+ <tt>malloc</tt>, <tt>no_instrument_function</tt>, <tt>cdecl</tt><br>
+
+ <b>Unsupported:</b> <tt>used</tt>, <tt>section</tt>, <tt>alias</tt>,
+ <tt>visibility</tt>, <tt>regparm</tt>, <tt>stdcall</tt>,
+ <tt>fastcall</tt>, all other target specific attributes</li>
+
+ <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Variable-Attributes.html#Variable%20Attributes">Variable Attributes</a>:
+ Specifying attributes of variables.<br>
+ <b>Supported:</b> <tt>cleanup</tt>, <tt>common</tt>, <tt>nocommon</tt>,
+ <tt>deprecated</tt>, <tt>transparent_union</tt>,
+ <tt>unused</tt>, <tt>weak</tt><br>
+
+ <b>Unsupported:</b> <tt>aligned</tt>, <tt>mode</tt>, <tt>packed</tt>,
+ <tt>section</tt>, <tt>shared</tt>, <tt>tls_model</tt>,
+ <tt>vector_size</tt>, <tt>dllimport</tt>,
+ <tt>dllexport</tt>, all target specific attributes.</li>
+
+ <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Type-Attributes.html#Type%20Attributes">Type Attributes</a>: Specifying attributes of types.<br>
+ <b>Supported:</b> <tt>transparent_union</tt>, <tt>unused</tt>,
+ <tt>deprecated</tt>, <tt>may_alias</tt><br>
+
+ <b>Unsupported:</b> <tt>aligned</tt>, <tt>packed</tt>,
+ all target specific attributes.</li>
+
+ <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Other-Builtins.html#Other%20Builtins">Other Builtins</a>:
+ Other built-in functions.<br>
+ We support all builtins which have a C language equivalent (e.g.,
+ <tt>__builtin_cos</tt>), <tt>__builtin_alloca</tt>,
+ <tt>__builtin_types_compatible_p</tt>, <tt>__builtin_choose_expr</tt>,
+ <tt>__builtin_constant_p</tt>, and <tt>__builtin_expect</tt>
+ (currently ignored). We also support builtins for ISO C99 floating
+ point comparison macros (e.g., <tt>__builtin_islessequal</tt>).</li>
+ </ol>
+
+ <p>The following extensions <b>are</b> known to be supported:</p>
+
+ <ol>
+ <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Labels-as-Values.html#Labels%20as%20Values">Labels as Values</a>: Getting pointers to labels and computed gotos.</li>
+ <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Statement-Exprs.html#Statement%20Exprs">Statement Exprs</a>: Putting statements and declarations inside expressions.</li>
+ <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Typeof.html#Typeof">Typeof</a>: <code>typeof</code>: referring to the type of an expression.</li>
+ <li><a href="http://gcc.gnu.org/onlinedocs/gcc-3.4.0/gcc/Lvalues.html#Lvalues">Lvalues</a>: Using <code>?:</code>, "<code>,</code>" and casts in lvalues.</li>
+ <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Conditionals.html#Conditionals">Conditionals</a>: Omitting the middle operand of a <code>?:</code> expression.</li>
+ <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Long-Long.html#Long%20Long">Long Long</a>: Double-word integers.</li>
+ <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Complex.html#Complex">Complex</a>: Data types for complex numbers.</li>
+ <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Hex-Floats.html#Hex%20Floats">Hex Floats</a>:Hexadecimal floating-point constants.</li>
+ <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html#Zero%20Length">Zero Length</a>: Zero-length arrays.</li>
+ <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Empty-Structures.html#Empty%20Structures">Empty Structures</a>: Structures with no members.</li>
+ <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Variadic-Macros.html#Variadic%20Macros">Variadic Macros</a>: Macros with a variable number of arguments.</li>
+ <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Escaped-Newlines.html#Escaped%20Newlines">Escaped Newlines</a>: Slightly looser rules for escaped newlines.</li>
+ <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Subscripting.html#Subscripting">Subscripting</a>: Any array can be subscripted, even if not an lvalue.</li>
+ <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Pointer-Arith.html#Pointer%20Arith">Pointer Arith</a>: Arithmetic on <code>void</code>-pointers and function pointers.</li>
+ <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Initializers.html#Initializers">Initializers</a>: Non-constant initializers.</li>
+ <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Compound-Literals.html#Compound%20Literals">Compound Literals</a>: Compound literals give structures, unions,
+ or arrays as values.</li>
+ <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Designated-Inits.html#Designated%20Inits">Designated Inits</a>: Labeling elements of initializers.</li>
+ <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Cast-to-Union.html#Cast%20to%20Union">Cast to Union</a>: Casting to union type from any member of the union.</li>
+ <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Case-Ranges.html#Case%20Ranges">Case Ranges</a>: `case 1 ... 9' and such.</li>
+ <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Mixed-Declarations.html#Mixed%20Declarations">Mixed Declarations</a>: Mixing declarations and code.</li>
+ <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Function-Prototypes.html#Function%20Prototypes">Function Prototypes</a>: Prototype declarations and old-style definitions.</li>
+ <li><a href="http://gcc.gnu.org/onlinedocs/gcc/C---Comments.html#C++%20Comments">C++ Comments</a>: C++ comments are recognized.</li>
+ <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Dollar-Signs.html#Dollar%20Signs">Dollar Signs</a>: Dollar sign is allowed in identifiers.</li>
+ <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Character-Escapes.html#Character%20Escapes">Character Escapes</a>: <code>\e</code> stands for the character <ESC>.</li>
+ <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Alignment.html#Alignment">Alignment</a>: Inquiring about the alignment of a type or variable.</li>
+ <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Inline.html#Inline">Inline</a>: Defining inline functions (as fast as macros).</li>
+ <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Alternate-Keywords.html#Alternate%20Keywords">Alternate Keywords</a>:<code>__const__</code>, <code>__asm__</code>, etc., for header files.</li>
+ <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Incomplete-Enums.html#Incomplete%20Enums">Incomplete Enums</a>: <code>enum foo;</code>, with details to follow.</li>
+ <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Function-Names.html#Function%20Names">Function Names</a>: Printable strings which are the name of the current function.</li>
+ <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Return-Address.html#Return%20Address">Return Address</a>: Getting the return or frame address of a function.</li>
+ <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Unnamed-Fields.html#Unnamed%20Fields">Unnamed Fields</a>: Unnamed struct/union fields within structs/unions.</li>
+ <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Attribute-Syntax.html#Attribute%20Syntax">Attribute Syntax</a>: Formal syntax for attributes.</li>
+ </ol></li>
+
+ </ul>
+
+ <p>If you run into GCC extensions which have not been included in any of these
+ lists, please let us know (also including whether or not they work).</p>
+
+ </div>
+
+ <!-- ======================================================================= -->
+ <div class="doc_subsection">
+ <a name="c++-fe">Known problems with the C++ front-end</a>
+ </div>
+
+ <div class="doc_text">
+
+ <p>For this release, the C++ front-end is considered to be fully functional but
+ has not been tested as thoroughly as the C front-end. It has been tested and
+ works for a number of non-trivial programs, but there may be lurking bugs.
+ Please report any bugs or problems.</p>
+
+ </div>
+
+ <!-- _______________________________________________________________________ -->
+ <div class="doc_subsubsection">Bugs</div>
+
+ <div class="doc_text">
+
+ <ul>
+ <li>The C++ front-end inherits all problems afflicting the <a href="#c-fe">C
+ front-end</a>.</li>
+
+ <li><b>IA-64 specific</b>: The C++ front-end does not use <a
+ href="http://llvm.cs.uiuc.edu/PR406">IA64 ABI compliant layout of v-tables</a>.
+ In particular, it just stores function pointers instead of function
+ descriptors in the vtable. This bug prevents mixing C++ code compiled with
+ LLVM with C++ objects compiled by other C++ compilers.</li>
+
+ </ul>
+
+ </div>
+
+ <!-- _______________________________________________________________________ -->
+ <div class="doc_subsubsection">
+ Notes
+ </div>
+
+ <div class="doc_text">
+
+ <ul>
+
+ <li>The C++ front-end is based on a pre-release of the GCC 3.4 C++ parser. This
+ parser is significantly more standards compliant (and picky) than prior GCC
+ versions. For more information, see the C++ section of the <a
+ href="http://gcc.gnu.org/gcc-3.4/changes.html">GCC 3.4 release notes</a>.</li>
+
+ <li>Destructors for local objects are not always run when a <tt>longjmp</tt> is
+ performed. In particular, destructors for objects in the <tt>longjmp</tt>ing
+ function and in the <tt>setjmp</tt> receiver function may not be run.
+ Objects in intervening stack frames will be destroyed, however (which is
+ better than most compilers).</li>
+
+ <li>The LLVM C++ front-end follows the <a
+ href="http://www.codesourcery.com/cxx-abi">Itanium C++ ABI</a>.
+ This document, which is not Itanium specific, specifies a standard for name
+ mangling, class layout, v-table layout, RTTI formats, and other C++
+ representation issues. Because we use this API, code generated by the LLVM
+ compilers should be binary compatible with machine code generated by other
+ Itanium ABI C++ compilers (such as G++, the Intel and HP compilers, etc).
+ <i>However</i>, the exception handling mechanism used by LLVM is very
+ different from the model used in the Itanium ABI, so <b>exceptions will not
+ interact correctly</b>. </li>
+
+ </ul>
+
+ </div>
+
+ <!-- ======================================================================= -->
+ <div class="doc_subsection">
+ <a name="x86-be">Known problems with the X86 back-end</a>
+ </div>
+
+ <div class="doc_text">
+
+ <ul>
+ <li>none yet</li>
+ </ul>
+
+ </div>
+
+ <!-- ======================================================================= -->
+ <div class="doc_subsection">
+ <a name="sparcv9-be">Known problems with the SparcV9 back-end</a>
+ </div>
+
+ <div class="doc_text">
+
+ <ul>
+ <li><a href="http://llvm.cs.uiuc.edu/PR60">[sparcv9] SparcV9 backend miscompiles
+ several programs in the LLVM test suite</a></li>
+ </ul>
+
+ </div>
+
+ <!-- ======================================================================= -->
+ <div class="doc_subsection">
+ <a name="c-be">Known problems with the C back-end</a>
+ </div>
+
+ <div class="doc_text">
+
+ <ul>
+
+ <li>The C back-end produces code that violates the ANSI C Type-Based Alias
+ Analysis rules. As such, special options may be necessary to compile the code
+ (for example, GCC requires the <tt>-fno-strict-aliasing</tt> option). This
+ problem probably cannot be fixed.</li>
+
+ <li><a href="http://llvm.cs.uiuc.edu/PR33">Initializers for global variables</a>
+ cannot include special floating point numbers like Not-A-Number or
+ Infinity.</li>
+
+ <li><a href="http://llvm.cs.uiuc.edu/PR56">Zero arg vararg functions are not
+ supported</a>. This should not affect LLVM produced by the C or C++
+ frontends.</li>
+
+ </ul>
+
+ </div>
+
+ <!-- *********************************************************************** -->
+ <div class="doc_section">
+ <a name="additionalinfo">Additional Information</a>
+ </div>
+ <!-- *********************************************************************** -->
+
+ <div class="doc_text">
+
+ <p>A wide variety of additional information is available on the LLVM web page,
+ including mailing lists and publications describing algorithms and components
+ implemented in LLVM. The web page also contains versions of the API
+ documentation which is up-to-date with the CVS version of the source code. You
+ can access versions of these documents specific to this release by going into
+ the "<tt>llvm/doc/</tt>" directory in the LLVM tree.</p>
+
+ <p>If you have any questions or comments about LLVM, please feel free to contact
+ us via the <a href="http://mail.cs.uiuc.edu/mailman/listinfo/llvmdev">mailing
+ lists</a>.</p>
+
+ </div>
+
+ <!-- *********************************************************************** -->
+
+ <hr>
+ <address>
+ <a href="http://jigsaw.w3.org/css-validator/check/referer"><img
+ src="http://jigsaw.w3.org/css-validator/images/vcss" alt="Valid CSS!"></a>
+ <a href="http://validator.w3.org/check/referer"><img
+ src="http://www.w3.org/Icons/valid-html401" alt="Valid HTML 4.01!" /></a>
+
+ <a href="http://llvm.cs.uiuc.edu">The LLVM Compiler Infrastructure</a><br>
+ Last modified: $Date: 2004/08/13 22:03:04 $
+ </address>
+
+ </body>
+ </html>
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+ <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"
+ "http://www.w3.org/TR/html4/strict.dtd">
+ <html>
+ <head>
+ <title>Source Level Debugging with LLVM</title>
+ <link rel="stylesheet" href="llvm.css" type="text/css">
+ </head>
+ <body>
+
+ <div class="doc_title">Source Level Debugging with LLVM</div>
+
+ <table border="0" width="100%">
+ <tr>
+ <td valign="top">
+ <ul>
+
+ <li><a href="#introduction">Introduction</a>
+ <ol>
+ <li><a href="#phil">Philosophy behind LLVM debugging information</a></li>
+ <li><a href="#debugopt">Debugging optimized code</a></li>
+ <li><a href="#future">Future work</a></li>
+ </ol></li>
+ <li><a href="#llvm-db">Using the <tt>llvm-db</tt> tool</a>
+ <ol>
+ <li><a href="#limitations">Limitations of <tt>llvm-db</tt></a></li>
+ <li><a href="#sample">A sample <tt>llvm-db</tt> session</a></li>
+ <li><a href="#startup">Starting the debugger</a></li>
+ <li><a href="#commands">Commands recognized by the debugger</a></li>
+ </ol></li>
+
+ <li><a href="#architecture">Architecture of the LLVM debugger</a>
+ <ol>
+ <li><a href="#arch_debugger">The Debugger and InferiorProcess classes</a></li>
+ <li><a href="#arch_info">The RuntimeInfo, ProgramInfo, and SourceLanguage classes</a></li>
+ <li><a href="#arch_llvm-db">The <tt>llvm-db</tt> tool</a></li>
+ <li><a href="#arch_todo">Short-term TODO list</a></li>
+ </ol></li>
+
+ <li><a href="#format">Debugging information format</a>
+ <ol>
+ <li><a href="#format_common_anchors">Anchors for global objects</a></li>
+ <li><a href="#format_common_stoppoint">Representing stopping points in the source program</a></li>
+ <li><a href="#format_common_lifetime">Object lifetimes and scoping</a></li>
+ <li><a href="#format_common_descriptors">Object descriptor formats</a>
+ <ul>
+ <li><a href="#format_common_source_files">Representation of source files</a></li>
+ <li><a href="#format_common_program_objects">Representation of program objects</a></li>
+ <li><a href="#format_common_object_contexts">Program object contexts</a></li>
+ </ul></li>
+ <li><a href="#format_common_intrinsics">Debugger intrinsic functions</a></li>
+ <li><a href="#format_common_tags">Values for debugger tags</a></li>
+ </ol></li>
+ <li><a href="#ccxx_frontend">C/C++ front-end specific debug information</a>
+ <ol>
+ <li><a href="#ccxx_pse">Program Scope Entries</a>
+ <ul>
+ <li><a href="#ccxx_compilation_units">Compilation unit entries</a></li>
+ <li><a href="#ccxx_modules">Module, namespace, and importing entries</a></li>
+ </ul></li>
+ <li><a href="#ccxx_dataobjects">Data objects (program variables)</a></li>
+ </ol></li>
+ </ul>
+ </td>
+ <td align="right" valign="top">
+ <img src="img/venusflytrap.jpg" alt="A leafy and green bug eater" width="247"
+ height="369">
+ </td>
+ </tr>
+ </table>
+
+ <div class="doc_author">
+ <p>Written by <a href="mailto:sabre at nondot.org">Chris Lattner</a></p>
+ </div>
+
+
+ <!-- *********************************************************************** -->
+ <div class="doc_section"><a name="introduction">Introduction</a></div> <!--
+ *********************************************************************** -->
+
+ <div class="doc_text">
+
+ <p>This document is the central repository for all information pertaining to
+ debug information in LLVM. It describes the <a href="#llvm-db">user
+ interface</a> for the <tt>llvm-db</tt> tool, which provides a
+ powerful <a href="#llvm-db">source-level debugger</a>
+ to users of LLVM-based compilers. It then describes the <a
+ href="#architecture">various components</a> that make up the debugger and the
+ libraries which future clients may use. Finally, it describes the <a
+ href="#format">actual format that the LLVM debug information</a> takes,
+ which is useful for those interested in creating front-ends or dealing directly
+ with the information.</p>
+
+ </div>
+
+ <!-- ======================================================================= -->
+ <div class="doc_subsection">
+ <a name="phil">Philosophy behind LLVM debugging information</a>
+ </div>
+
+ <div class="doc_text">
+
+ <p>The idea of the LLVM debugging information is to capture how the important
+ pieces of the source-language's Abstract Syntax Tree map onto LLVM code.
+ Several design aspects have shaped the solution that appears here. The
+ important ones are:</p>
+
+ <ul>
+ <li>Debugging information should have very little impact on the rest of the
+ compiler. No transformations, analyses, or code generators should need to be
+ modified because of debugging information.</li>
+
+ <li>LLVM optimizations should interact in <a href="#debugopt">well-defined and
+ easily described ways</a> with the debugging information.</li>
+
+ <li>Because LLVM is designed to support arbitrary programming languages,
+ LLVM-to-LLVM tools should not need to know anything about the semantics of the
+ source-level-language.</li>
+
+ <li>Source-level languages are often <b>widely</b> different from one another.
+ LLVM should not put any restrictions of the flavor of the source-language, and
+ the debugging information should work with any language.</li>
+
+ <li>With code generator support, it should be possible to use an LLVM compiler
+ to compile a program to native machine code and standard debugging formats.
+ This allows compatibility with traditional machine-code level debuggers, like
+ GDB or DBX.</li>
+
+ </ul>
+
+ <p>The approach used by the LLVM implementation is to use a small set of <a
+ href="#format_common_intrinsics">intrinsic functions</a> to define a mapping
+ between LLVM program objects and the source-level objects. The description of
+ the source-level program is maintained in LLVM global variables in an <a
+ href="#ccxx_frontend">implementation-defined format</a> (the C/C++ front-end
+ currently uses working draft 7 of the <a
+ href="http://www.eagercon.com/dwarf/dwarf3std.htm">Dwarf 3 standard</a>).</p>
+
+ <p>When a program is debugged, the debugger interacts with the user and turns
+ the stored debug information into source-language specific information. As
+ such, the debugger must be aware of the source-language, and is thus tied to a
+ specific language of family of languages. The <a href="#llvm-db">LLVM
+ debugger</a> is designed to be modular in its support for source-languages.</p>
+
+ </div>
+
+
+ <!-- ======================================================================= -->
+ <div class="doc_subsection">
+ <a name="debugopt">Debugging optimized code</a>
+ </div>
+
+ <div class="doc_text">
+
+ <p>An extremely high priority of LLVM debugging information is to make it
+ interact well with optimizations and analysis. In particular, the LLVM debug
+ information provides the following guarantees:</p>
+
+ <ul>
+
+ <li>LLVM debug information <b>always provides information to accurately read the
+ source-level state of the program</b>, regardless of which LLVM optimizations
+ have been run, and without any modification to the optimizations themselves.
+ However, some optimizations may impact the ability to modify the current state
+ of the program with a debugger, such as setting program variables, or calling
+ function that have been deleted.</li>
+
+ <li>LLVM optimizations gracefully interact with debugging information. If they
+ are not aware of debug information, they are automatically disabled as necessary
+ in the cases that would invalidate the debug info. This retains the LLVM
+ features making it easy to write new transformations.</li>
+
+ <li>As desired, LLVM optimizations can be upgraded to be aware of the LLVM
+ debugging information, allowing them to update the debugging information as they
+ perform aggressive optimizations. This means that, with effort, the LLVM
+ optimizers could optimize debug code just as well as non-debug code.</li>
+
+ <li>LLVM debug information does not prevent many important optimizations from
+ happening (for example inlining, basic block reordering/merging/cleanup, tail
+ duplication, etc), further reducing the amount of the compiler that eventually
+ is "aware" of debugging information.</li>
+
+ <li>LLVM debug information is automatically optimized along with the rest of the
+ program, using existing facilities. For example, duplicate information is
+ automatically merged by the linker, and unused information is automatically
+ removed.</li>
+
+ </ul>
+
+ <p>Basically, the debug information allows you to compile a program with
+ "<tt>-O0 -g</tt>" and get full debug information, allowing you to arbitrarily
+ modify the program as it executes from the debugger. Compiling a program with
+ "<tt>-O3 -g</tt>" gives you full debug information that is always available and
+ accurate for reading (e.g., you get accurate stack traces despite tail call
+ elimination and inlining), but you might lose the ability to modify the program
+ and call functions where were optimized out of the program, or inlined away
+ completely.</p>
+
+ </div>
+
+ <!-- ======================================================================= -->
+ <div class="doc_subsection">
+ <a name="future">Future work</a>
+ </div>
+
+ <div class="doc_text">
+ <p>There are several important extensions that could be eventually added to the
+ LLVM debugger. The most important extension would be to upgrade the LLVM code
+ generators to support debugging information. This would also allow, for
+ example, the X86 code generator to emit native objects that contain debugging
+ information consumable by traditional source-level debuggers like GDB or
+ DBX.</p>
+
+ <p>Additionally, LLVM optimizations can be upgraded to incrementally update the
+ debugging information, <a href="#commands">new commands</a> can be added to the
+ debugger, and thread support could be added to the debugger.</p>
+
+ <p>The "SourceLanguage" modules provided by <tt>llvm-db</tt> could be
+ substantially improved to provide good support for C++ language features like
+ namespaces and scoping rules.</p>
+
+ <p>After working with the debugger for a while, perhaps the nicest improvement
+ would be to add some sort of line editor, such as GNU readline (but one that is
+ compatible with the LLVM license).</p>
+
+ <p>For someone so inclined, it should be straight-forward to write different
+ front-ends for the LLVM debugger, as the LLVM debugging engine is cleanly
+ separated from the <tt>llvm-db</tt> front-end. A new LLVM GUI debugger or IDE
+ would be nice. :)</p>
+
+ </div>
+
+ <!-- *********************************************************************** -->
+ <div class="doc_section">
+ <a name="llvm-db">Using the <tt>llvm-db</tt> tool</a>
+ </div>
+ <!-- *********************************************************************** -->
+
+ <div class="doc_text">
+
+ <p>The <tt>llvm-db</tt> tool provides a GDB-like interface for source-level
+ debugging of programs. This tool provides many standard commands for inspecting
+ and modifying the program as it executes, loading new programs, single stepping,
+ placing breakpoints, etc. This section describes how to use the debugger.</p>
+
+ <p><tt>llvm-db</tt> has been designed to be as similar to GDB in its user
+ interface as possible. This should make it extremely easy to learn
+ <tt>llvm-db</tt> if you already know <tt>GDB</tt>. In general, <tt>llvm-db</tt>
+ provides the subset of GDB commands that are applicable to LLVM debugging users.
+ If there is a command missing that make a reasonable amount of sense within the
+ <a href="#limitations">limitations of <tt>llvm-db</tt></a>, please report it as
+ a bug or, better yet, submit a patch to add it. :)</p>
+
+ </div>
+
+ <!-- ======================================================================= -->
+ <div class="doc_subsection">
+ <a name="limitations">Limitations of <tt>llvm-db</tt></a>
+ </div>
+
+ <div class="doc_text">
+
+ <p><tt>llvm-db</tt> is designed to be modular and easy to extend. This
+ extensibility was key to getting the debugger up-and-running quickly, because we
+ can start with simple-but-unsophisicated implementations of various components.
+ Because of this, it is currently missing many features, though they should be
+ easy to add over time (patches welcomed!). The biggest inherent limitations of
+ <tt>llvm-db</tt> are currently due to extremely simple <a
+ href="#arch_debugger">debugger backend</a> (implemented in
+ "lib/Debugger/UnixLocalInferiorProcess.cpp") which is designed to work without
+ any cooperation from the code generators. Because it is so simple, it suffers
+ from the following inherent limitations:</p>
+
+ <ul>
+
+ <li>Running a program in <tt>llvm-db</tt> is a bit slower than running it with
+ <tt>lli</tt> (i.e., in the JIT).</li>
+
+ <li>Inspection of the target hardware is not supported. This means that you
+ cannot, for example, print the contents of X86 registers.</li>
+
+ <li>Inspection of LLVM code is not supported. This means that you cannot print
+ the contents of arbitrary LLVM values, or use commands such as <tt>stepi</tt>.
+ This also means that you cannot debug code without debug information.</li>
+
+ <li>Portions of the debugger run in the same address space as the program being
+ debugged. This means that memory corruption by the program could trample on
+ portions of the debugger.</li>
+
+ <li>Attaching to existing processes and core files is not currently
+ supported.</li>
+
+ </ul>
+
+ <p>That said, the debugger is still quite useful, and all of these limitations
+ can be eliminated by integrating support for the debugger into the code
+ generators, and writing a new <a href="#arch_debugger">InferiorProcess</a>
+ subclass to use it. See the <a href="#future">future work</a> section for ideas
+ of how to extend the LLVM debugger despite these limitations.</p>
+
+ </div>
+
+
+ <!-- ======================================================================= -->
+ <div class="doc_subsection">
+ <a name="sample">A sample <tt>llvm-db</tt> session</a>
+ </div>
+
+ <div class="doc_text">
+
+ <p>TODO: this is obviously lame, when more is implemented, this can be much
+ better.</p>
+
+ <pre>
+ $ <b>llvm-db funccall</b>
+ llvm-db: The LLVM source-level debugger
+ Loading program... successfully loaded 'funccall.bc'!
+ (llvm-db) <b>create</b>
+ Starting program: funccall.bc
+ main at funccall.c:9:2
+ 9 -> q = 0;
+ (llvm-db) <b>list main</b>
+ 4 void foo() {
+ 5 int t = q;
+ 6 q = t + 1;
+ 7 }
+ 8 int main() {
+ 9 -> q = 0;
+ 10 foo();
+ 11 q = q - 1;
+ 12
+ 13 return q;
+ (llvm-db) <b>list</b>
+ 14 }
+ (llvm-db) <b>step</b>
+ 10 -> foo();
+ (llvm-db) <b>s</b>
+ foo at funccall.c:5:2
+ 5 -> int t = q;
+ (llvm-db) <b>bt</b>
+ #0 -> 0x85ffba0 in foo at funccall.c:5:2
+ #1 0x85ffd98 in main at funccall.c:10:2
+ (llvm-db) <b>finish</b>
+ main at funccall.c:11:2
+ 11 -> q = q - 1;
+ (llvm-db) <b>s</b>
+ 13 -> return q;
+ (llvm-db) <b>s</b>
+ The program stopped with exit code 0
+ (llvm-db) <b>quit</b>
+ $
+ </pre>
+
+ </div>
+
+
+
+ <!-- ======================================================================= -->
+ <div class="doc_subsection">
+ <a name="startup">Starting the debugger</a>
+ </div>
+
+ <div class="doc_text">
+
+ <p>There are three ways to start up the <tt>llvm-db</tt> debugger:</p>
+
+ <p>When run with no options, just <tt>llvm-db</tt>, the debugger starts up
+ without a program loaded at all. You must use the <a
+ href="#c_file"><tt>file</tt> command</a> to load a program, and the <a
+ href="#c_set_args"><tt>set args</tt></a> or <a href="#c_run"><tt>run</tt></a>
+ commands to specify the arguments for the program.</p>
+
+ <p>If you start the debugger with one argument, as <tt>llvm-db
+ <program></tt>, the debugger will start up and load in the specified
+ program. You can then optionally specify arguments to the program with the <a
+ href="#c_set_args"><tt>set args</tt></a> or <a href="#c_run"><tt>run</tt></a>
+ commands.</p>
+
+ <p>The third way to start the program is with the <tt>--args</tt> option. This
+ option allows you to specify the program to load and the arguments to start out
+ with. <!-- No options to <tt>llvm-db</tt> may be specified after the
+ <tt>-args</tt> option. --> Example use: <tt>llvm-db --args ls /home</tt></p>
+
+ </div>
+
+ <!-- ======================================================================= -->
+ <div class="doc_subsection">
+ <a name="commands">Commands recognized by the debugger</a>
+ </div>
+
+ <div class="doc_text">
+
+ <p>FIXME: this needs work obviously. See the <a
+ href="http://sources.redhat.com/gdb/documentation/">GDB documentation</a> for
+ information about what these do, or try '<tt>help [command]</tt>' within
+ <tt>llvm-db</tt> to get information.</p>
+
+ <p>
+ <h2>General usage:</h2>
+ <ul>
+ <li>help [command]</li>
+ <li>quit</li>
+ <li><a name="c_file">file</a> [program]</li>
+ </ul>
+
+ <h2>Program inspection and interaction:</h2>
+ <ul>
+ <li>create (start the program, stopping it ASAP in <tt>main</tt>)</li>
+ <li>kill</li>
+ <li>run [args]</li>
+ <li>step [num]</li>
+ <li>next [num]</li>
+ <li>cont</li>
+ <li>finish</li>
+
+ <li>list [start[, end]]</li>
+ <li>info source</li>
+ <li>info sources</li>
+ <li>info functions</li>
+ </ul>
+
+ <h2>Call stack inspection:</h2>
+ <ul>
+ <li>backtrace</li>
+ <li>up [n]</li>
+ <li>down [n]</li>
+ <li>frame [n]</li>
+ </ul>
+
+
+ <h2>Debugger inspection and interaction:</h2>
+ <ul>
+ <li>info target</li>
+ <li>show prompt</li>
+ <li>set prompt</li>
+ <li>show listsize</li>
+ <li>set listsize</li>
+ <li>show language</li>
+ <li>set language</li>
+ <li>show args</li>
+ <li>set args [args]</li>
+ </ul>
+
+ <h2>TODO:</h2>
+ <ul>
+ <li>info frame</li>
+ <li>break</li>
+ <li>print</li>
+ <li>ptype</li>
+
+ <li>info types</li>
+ <li>info variables</li>
+ <li>info program</li>
+
+ <li>info args</li>
+ <li>info locals</li>
+ <li>info catch</li>
+ <li>... many others</li>
+ </ul>
+
+ </div>
+
+ <!-- *********************************************************************** -->
+ <div class="doc_section">
+ <a name="architecture">Architecture of the LLVM debugger</a>
+ </div>
+ <!-- *********************************************************************** -->
+
+ <div class="doc_text">
+ <p>The LLVM debugger is built out of three distinct layers of software. These
+ layers provide clients with different interface options depending on what pieces
+ of they want to implement themselves, and it also promotes code modularity and
+ good design. The three layers are the <a href="#arch_debugger">Debugger
+ interface</a>, the <a href="#arch_info">"info" interfaces</a>, and the <a
+ href="#arch_llvm-db"><tt>llvm-db</tt> tool</a> itself.</p>
+ </div>
+
+ <!-- ======================================================================= -->
+ <div class="doc_subsection">
+ <a name="arch_debugger">The Debugger and InferiorProcess classes</a>
+ </div>
+
+ <div class="doc_text">
+ <p>The Debugger class (defined in the <tt>include/llvm/Debugger/</tt> directory)
+ is a low-level class which is used to maintain information about the loaded
+ program, as well as start and stop the program running as necessary. This class
+ does not provide any high-level analysis or control over the program, only
+ exposing simple interfaces like <tt>load/unloadProgram</tt>,
+ <tt>create/killProgram</tt>, <tt>step/next/finish/contProgram</tt>, and
+ low-level methods for installing breakpoints.</p>
+
+ <p>
+ The Debugger class is itself a wrapper around the lowest-level InferiorProcess
+ class. This class is used to represent an instance of the program running under
+ debugger control. The InferiorProcess class can be implemented in different
+ ways for different targets and execution scenarios (e.g., remote debugging).
+ The InferiorProcess class exposes a small and simple collection of interfaces
+ which are useful for inspecting the current state of the program (such as
+ collecting stack trace information, reading the memory image of the process,
+ etc). The interfaces in this class are designed to be as low-level and simple
+ as possible, to make it easy to create new instances of the class.
+ </p>
+
+ <p>
+ The Debugger class exposes the currently active instance of InferiorProcess
+ through the <tt>Debugger::getRunningProcess</tt> method, which returns a
+ <tt>const</tt> reference to the class. This means that clients of the Debugger
+ class can only <b>inspect</b> the running instance of the program directly. To
+ change the executing process in some way, they must use the interces exposed by
+ the Debugger class.
+ </p>
+ </div>
+
+ <!-- ======================================================================= -->
+ <div class="doc_subsection">
+ <a name="arch_info">The RuntimeInfo, ProgramInfo, and SourceLanguage classes</a>
+ </div>
+
+ <div class="doc_text">
+ <p>
+ The next-highest level of debugger abstraction is provided through the
+ ProgramInfo, RuntimeInfo, SourceLanguage and related classes (also defined in
+ the <tt>include/llvm/Debugger/</tt> directory). These classes efficiently
+ decode the debugging information and low-level interfaces exposed by
+ InferiorProcess into a higher-level representation, suitable for analysis by the
+ debugger.
+ </p>
+
+ <p>
+ The ProgramInfo class exposes a variety of different kinds of information about
+ the program objects in the source-level-language. The SourceFileInfo class
+ represents a source-file in the program (e.g. a .cpp or .h file). The
+ SourceFileInfo class captures information such as which SourceLanguage was used
+ to compile the file, where the debugger can get access to the actual file text
+ (which is lazily loaded on demand), etc. The SourceFunctionInfo class
+ represents a... <b>FIXME: finish</b>. The ProgramInfo class provides interfaces
+ to lazily find and decode the information needed to create the Source*Info
+ classes requested by the debugger.
+ </p>
+
+ <p>
+ The RuntimeInfo class exposes information about the currently executed program,
+ by decoding information from the InferiorProcess and ProgramInfo classes. It
+ provides a StackFrame class which provides an easy-to-use interface for
+ inspecting the current and suspended stack frames in the program.
+ </p>
+
+ <p>
+ The SourceLanguage class is an abstract interface used by the debugger to
+ perform all source-language-specific tasks. For example, this interface is used
+ by the ProgramInfo class to decode language-specific types and functions and by
+ the debugger front-end (such as <a href="#arch_llvm-db"><tt>llvm-db</tt></a> to
+ evaluate source-langauge expressions typed into the debugger. This class uses
+ the RuntimeInfo & ProgramInfo classes to get information about the current
+ execution context and the loaded program, respectively.
+ </p>
+
+ </div>
+
+ <!-- ======================================================================= -->
+ <div class="doc_subsection">
+ <a name="arch_llvm-db">The <tt>llvm-db</tt> tool</a>
+ </div>
+
+ <div class="doc_text">
+ <p>
+ The <tt>llvm-db</tt> is designed to be a debugger providing an interface as <a
+ href="#llvm-db">similar to GDB</a> as reasonable, but no more so than that.
+ Because the <a href="#arch_debugger">Debugger</a> and <a
+ href="#arch_info">info</a> classes implement all of the heavy lifting and
+ analysis, <tt>llvm-db</tt> (which lives in <tt>llvm/tools/llvm-db</tt>) consists
+ mainly of of code to interact with the user and parse commands. The CLIDebugger
+ constructor registers all of the builtin commands for the debugger, and each
+ command is implemented as a CLIDebugger::[name]Command method.
+ </p>
+ </div>
+
+
+ <!-- ======================================================================= -->
+ <div class="doc_subsection">
+ <a name="arch_todo">Short-term TODO list</a>
+ </div>
+
+ <div class="doc_text">
+
+ <p>
+ FIXME: this section will eventually go away. These are notes to myself of
+ things that should be implemented, but haven't yet.
+ </p>
+
+ <p>
+ <b>Breakpoints:</b> Support is already implemented in the 'InferiorProcess'
+ class, though it hasn't been tested yet. To finish breakpoint support, we need
+ to implement breakCommand (which should reuse the linespec parser from the list
+ command), and handle the fact that 'break foo' or 'break file.c:53' may insert
+ multiple breakpoints. Also, if you say 'break file.c:53' and there is no
+ stoppoint on line 53, the breakpoint should go on the next available line. My
+ idea was to have the Debugger class provide a "Breakpoint" class which
+ encapsulated this messiness, giving the debugger front-end a simple interface.
+ The debugger front-end would have to map the really complex semantics of
+ temporary breakpoints and 'conditional' breakpoints onto this intermediate
+ level. Also, breakpoints should survive as much as possible across program
+ reloads.
+ </p>
+
+ <p>
+ <b>UnixLocalInferiorProcess.cpp speedup</b>: There is no reason for the debugged
+ process to code gen the globals corresponding to debug information. The
+ IntrinsicLowering object could instead change descriptors into constant expr
+ casts of the constant address of the LLVM objects for the descriptors. This
+ would also allow us to eliminate the mapping back and forth between physical
+ addresses that must be done.</p>
+
+ <p>
+ <b>Process deaths</b>: The InferiorProcessDead exception should be extended to
+ know "how" a process died, i.e., it was killed by a signal. This is easy to
+ collect in the UnixLocalInferiorProcess, we just need to represent it.</p>
+
+ </div>
+
+ <!-- *********************************************************************** -->
+ <div class="doc_section">
+ <a name="format">Debugging information format</a>
+ </div>
+ <!-- *********************************************************************** -->
+
+ <div class="doc_text">
+
+ <p>LLVM debugging information has been carefully designed to make it possible
+ for the optimizer to optimize the program and debugging information without
+ necessarily having to know anything about debugging information. In particular,
+ the global constant merging pass automatically eliminates duplicated debugging
+ information (often caused by header files), the global dead code elimination
+ pass automatically deletes debugging information for a function if it decides to
+ delete the function, and the linker eliminates debug information when it merges
+ <tt>linkonce</tt> functions.</p>
+
+ <p>To do this, most of the debugging information (descriptors for types,
+ variables, functions, source files, etc) is inserted by the language front-end
+ in the form of LLVM global variables. These LLVM global variables are no
+ different from any other global variables, except that they have a web of LLVM
+ intrinsic functions that point to them. If the last references to a particular
+ piece of debugging information are deleted (for example, by the
+ <tt>-globaldce</tt> pass), the extraneous debug information will automatically
+ become dead and be removed by the optimizer.</p>
+
+ <p>The debugger is designed to be agnostic about the contents of most of the
+ debugging information. It uses a <a href="#arch_info">source-language-specific
+ module</a> to decode the information that represents variables, types,
+ functions, namespaces, etc: this allows for arbitrary source-language semantics
+ and type-systems to be used, as long as there is a module written for the
+ debugger to interpret the information.</p>
+
+ <p>To provide basic functionality, the LLVM debugger does have to make some
+ assumptions about the source-level language being debugged, though it keeps
+ these to a minimum. The only common features that the LLVM debugger assumes
+ exist are <a href="#format_common_source_files">source files</a>, and <a
+ href="#format_program_objects">program objects</a>. These abstract objects are
+ used by the debugger to form stack traces, show information about local
+ variables, etc.</p>
+
+ <p>This section of the documentation first describes the representation aspects
+ common to any source-language. The <a href="#ccxx_frontend">next section</a>
+ describes the data layout conventions used by the C and C++ front-ends.</p>
+
+ </div>
+
+ <!-- ======================================================================= -->
+ <div class="doc_subsection">
+ <a name="format_common_anchors">Anchors for global objects</a>
+ </div>
+
+ <div class="doc_text">
+ <p>One important aspect of the LLVM debug representation is that it allows the
+ LLVM debugger to efficiently index all of the global objects without having the
+ scan the program. To do this, all of the global objects use "anchor" globals of
+ type "<tt>{}</tt>", with designated names. These anchor objects obviously do
+ not contain any content or meaning by themselves, but all of the global objects
+ of a particular type (e.g., source file descriptors) contain a pointer to the
+ anchor. This pointer allows the debugger to use def-use chains to find all
+ global objects of that type.</p>
+
+ <p>So far, the following names are recognized as anchors by the LLVM
+ debugger:</p>
+
+ <pre>
+ %<a href="#format_common_source_files">llvm.dbg.translation_units</a> = linkonce global {} {}
+ %<a href="#format_program_objects">llvm.dbg.globals</a> = linkonce global {} {}
+ </pre>
+
+ <p>Using anchors in this way (where the source file descriptor points to the
+ anchors, as opposed to having a list of source file descriptors) allows for the
+ standard dead global elimination and merging passes to automatically remove
+ unused debugging information. If the globals were kept track of through lists,
+ there would always be an object pointing to the descriptors, thus would never be
+ deleted.</p>
+
+ </div>
+
+ <!-- ======================================================================= -->
+ <div class="doc_subsection">
+ <a name="format_common_stoppoint">
+ Representing stopping points in the source program
+ </a>
+ </div>
+
+ <div class="doc_text">
+
+ <p>LLVM debugger "stop points" are a key part of the debugging representation
+ that allows the LLVM to maintain simple semantics for <a
+ href="#debugopt">debugging optimized code</a>. The basic idea is that the
+ front-end inserts calls to the <tt>%llvm.dbg.stoppoint</tt> intrinsic function
+ at every point in the program where the debugger should be able to inspect the
+ program (these correspond to places the debugger stops when you "<tt>step</tt>"
+ through it). The front-end can choose to place these as fine-grained as it
+ would like (for example, before every subexpression evaluated), but it is
+ recommended to only put them after every source statement that includes
+ executable code.</p>
+
+ <p>Using calls to this intrinsic function to demark legal points for the
+ debugger to inspect the program automatically disables any optimizations that
+ could potentially confuse debugging information. To non-debug-information-aware
+ transformations, these calls simply look like calls to an external function,
+ which they must assume to do anything (including reading or writing to any part
+ of reachable memory). On the other hand, it does not impact many optimizations,
+ such as code motion of non-trapping instructions, nor does it impact
+ optimization of subexpressions, code duplication transformations, or basic-block
+ reordering transformations.</p>
+
+ <p>An important aspect of the calls to the <tt>%llvm.dbg.stoppoint</tt>
+ intrinsic is that the function-local debugging information is woven together
+ with use-def chains. This makes it easy for the debugger to, for example,
+ locate the 'next' stop point. For a concrete example of stop points, see the
+ example in <a href="#format_common_lifetime">the next section</a>.</p>
+
+ </div>
+
+
+ <!-- ======================================================================= -->
+ <div class="doc_subsection">
+ <a name="format_common_lifetime">Object lifetimes and scoping</a>
+ </div>
+
+ <div class="doc_text">
+ <p>In many languages, the local variables in functions can have their lifetime
+ or scope limited to a subset of a function. In the C family of languages, for
+ example, variables are only live (readable and writable) within the source block
+ that they are defined in. In functional languages, values are only readable
+ after they have been defined. Though this is a very obvious concept, it is also
+ non-trivial to model in LLVM, because it has no notion of scoping in this sense,
+ and does not want to be tied to a language's scoping rules.</p>
+
+ <p>In order to handle this, the LLVM debug format uses the notion of "regions"
+ of a function, delineated by calls to intrinsic functions. These intrinsic
+ functions define new regions of the program and indicate when the region
+ lifetime expires. Consider the following C fragment, for example:</p>
+
+ <pre>
+ 1. void foo() {
+ 2. int X = ...;
+ 3. int Y = ...;
+ 4. {
+ 5. int Z = ...;
+ 6. ...
+ 7. }
+ 8. ...
+ 9. }
+ </pre>
+
+ <p>Compiled to LLVM, this function would be represented like this (FIXME: CHECK
+ AND UPDATE THIS):</p>
+
+ <pre>
+ void %foo() {
+ %X = alloca int
+ %Y = alloca int
+ %Z = alloca int
+ <a name="#icl_ex_D1">%D1</a> = call {}* %llvm.dbg.func.start(<a href="#format_program_objects">%lldb.global</a>* %d.foo)
+ %D2 = call {}* <a href="#format_common_stoppoint">%llvm.dbg.stoppoint</a>({}* %D1, uint 2, uint 2, <a href="#format_common_source_files">%lldb.compile_unit</a>* %file)
+
+ %D3 = call {}* %llvm.dbg.DEFINEVARIABLE({}* %D2, ...)
+ <i>;; Evaluate expression on line 2, assigning to X.</i>
+ %D4 = call {}* <a href="#format_common_stoppoint">%llvm.dbg.stoppoint</a>({}* %D3, uint 3, uint 2, <a href="#format_common_source_files">%lldb.compile_unit</a>* %file)
+
+ %D5 = call {}* %llvm.dbg.DEFINEVARIABLE({}* %D4, ...)
+ <i>;; Evaluate expression on line 3, assigning to Y.</i>
+ %D6 = call {}* <a href="#format_common_stoppoint">%llvm.dbg.stoppoint</a>({}* %D5, uint 5, uint 4, <a href="#format_common_source_files">%lldb.compile_unit</a>* %file)
+
+ <a name="#icl_ex_D1">%D7</a> = call {}* %llvm.region.start({}* %D6)
+ %D8 = call {}* %llvm.dbg.DEFINEVARIABLE({}* %D7, ...)
+ <i>;; Evaluate expression on line 5, assigning to Z.</i>
+ %D9 = call {}* <a href="#format_common_stoppoint">%llvm.dbg.stoppoint</a>({}* %D8, uint 6, uint 4, <a href="#format_common_source_files">%lldb.compile_unit</a>* %file)
+
+ <i>;; Code for line 6.</i>
+ %D10 = call {}* %llvm.region.end({}* %D9)
+ %D11 = call {}* <a href="#format_common_stoppoint">%llvm.dbg.stoppoint</a>({}* %D10, uint 8, uint 2, <a href="#format_common_source_files">%lldb.compile_unit</a>* %file)
+
+ <i>;; Code for line 8.</i>
+ <a name="#icl_ex_D1">%D12</a> = call {}* %llvm.region.end({}* %D11)
+ ret void
+ }
+ </pre>
+
+ <p>This example illustrates a few important details about the LLVM debugging
+ information. In particular, it shows how the various intrinsics used are woven
+ together with def-use and use-def chains, similar to how <a
+ href="#format_common_anchors">anchors</a> are used with globals. This allows
+ the debugger to analyze the relationship between statements, variable
+ definitions, and the code used to implement the function.</p>
+
+ <p>In this example, two explicit regions are defined, one with the <a
+ href="#icl_ex_D1">definition of the <tt>%D1</tt> variable</a> and one with the
+ <a href="#icl_ex_D7">definition of <tt>%D7</tt></a>. In the case of
+ <tt>%D1</tt>, the debug information indicates that the function whose <a
+ href="#format_program_objects">descriptor</a> is specified as an argument to the
+ intrinsic. This defines a new stack frame whose lifetime ends when the region
+ is ended by <a href="#icl_ex_D12">the <tt>%D12</tt> call</a>.</p>
+
+ <p>Using regions to represent the boundaries of source-level functions allow
+ LLVM interprocedural optimizations to arbitrarily modify LLVM functions without
+ having to worry about breaking mapping information between the LLVM code and the
+ and source-level program. In particular, the inliner requires no modification
+ to support inlining with debugging information: there is no explicit correlation
+ drawn between LLVM functions and their source-level counterparts (note however,
+ that if the inliner inlines all instances of a non-strong-linkage function into
+ its caller that it will not be possible for the user to manually invoke the
+ inlined function from the debugger).</p>
+
+ <p>Once the function has been defined, the <a
+ href="#format_common_stoppoint">stopping point</a> corresponding to line #2 of
+ the function is encountered. At this point in the function, <b>no</b> local
+ variables are live. As lines 2 and 3 of the example are executed, their
+ variable definitions are automatically introduced into the program, without the
+ need to specify a new region. These variables do not require new regions to be
+ introduced because they go out of scope at the same point in the program: line
+ 9.</p>
+
+ <p>In contrast, the <tt>Z</tt> variable goes out of scope at a different time,
+ on line 7. For this reason, it is defined within <a href="#icl_ex_D7">the
+ <tt>%D7</tt> region</a>, which kills the availability of <tt>Z</tt> before the
+ code for line 8 is executed. In this way, regions can support arbitrary
+ source-language scoping rules, as long as they can only be nested (ie, one scope
+ cannot partially overlap with a part of another scope).</p>
+
+ <p>It is worth noting that this scoping mechanism is used to control scoping of
+ all declarations, not just variable declarations. For example, the scope of a
+ C++ using declaration is controlled with this, and the <tt>llvm-db</tt> C++
+ support routines could use this to change how name lookup is performed (though
+ this is not implemented yet).</p>
+
+ </div>
+
+ <!-- ======================================================================= -->
+ <div class="doc_subsection">
+ <a name="format_common_descriptors">Object descriptor formats</a>
+ </div>
+
+ <div class="doc_text">
+ <p>The LLVM debugger expects the descriptors for program objects to start in a
+ canonical format, but the descriptors can include additional information
+ appended at the end that is source-language specific. All LLVM debugging
+ information is versioned, allowing backwards compatibility in the case that the
+ core structures need to change in some way. Also, all debugging information
+ objects start with a <a href="#format_common_tags">tag</a> to indicate what type
+ of object it is. The source-language is allows to define its own objects, by
+ using unreserved tag numbers.</p>
+
+ <p>The lowest-level descriptor are those describing <a
+ href="#format_common_source_files">the files containing the program source
+ code</a>, as most other descriptors (sometimes indirectly) refer to them.
+ </p>
+ </div>
+
+
+ <!-- ------------------------------------------------------------------------ ->
+ <div class="doc_subsubsection">
+ <a name="format_common_source_files">Representation of source files</a>
+ </div>
+
+ <div class="doc_text">
+ <p>
+ Source file descriptors are patterned after the Dwarf "compile_unit" object.
+ The descriptor currently is defined to have at least the following LLVM
+ type entries:</p>
+
+ <pre>
+ %lldb.compile_unit = type {
+ uint, <i>;; Tag: <a href="#tag_compile_unit">LLVM_COMPILE_UNIT</a></i>
+ ushort, <i>;; LLVM debug version number</i>
+ ushort, <i>;; Dwarf language identifier</i>
+ sbyte*, <i>;; Filename</i>
+ sbyte*, <i>;; Working directory when compiled</i>
+ sbyte* <i>;; Producer of the debug information</i>
+ }
+ </pre>
+
+ <p>
+ These descriptors contain the version number for the debug info, a source
+ language ID for the file (we use the Dwarf 3.0 ID numbers, such as
+ <tt>DW_LANG_C89</tt>, <tt>DW_LANG_C_plus_plus</tt>, <tt>DW_LANG_Cobol74</tt>,
+ etc), three strings describing the filename, working directory of the compiler,
+ and an identifier string for the compiler that produced it. Note that actual
+ compile_unit declarations must also include an <a
+ href="#format_common_anchors">anchor</a> to <tt>llvm.dbg.translation_units</tt>,
+ but it is not specified where the anchor is to be located. Here is an example
+ descriptor:
+ </p>
+
+ <p><pre>
+ %arraytest_source_file = internal constant %lldb.compile_unit {
+ <a href="#tag_compile_unit">uint 17</a>, ; Tag value
+ ushort 0, ; Version #0
+ ushort 1, ; DW_LANG_C89
+ sbyte* getelementptr ([12 x sbyte]* %.str_1, long 0, long 0), ; filename
+ sbyte* getelementptr ([12 x sbyte]* %.str_2, long 0, long 0), ; working dir
+ sbyte* getelementptr ([12 x sbyte]* %.str_3, long 0, long 0), ; producer
+ {}* %llvm.dbg.translation_units ; Anchor
+ }
+ %.str_1 = internal constant [12 x sbyte] c"arraytest.c\00"
+ %.str_2 = internal constant [12 x sbyte] c"/home/sabre\00"
+ %.str_3 = internal constant [12 x sbyte] c"llvmgcc 3.4\00"
+ </pre></p>
+
+ <p>
+ Note that the LLVM constant merging pass should eliminate duplicate copies of
+ the strings that get emitted to each translation unit, such as the producer.
+ </p>
+
+ </div>
+
+
+ <!-- ----------------------------------------------------------------------- -->
+ <div class="doc_subsubsection">
+ <a name="format_program_objects">Representation of program objects</a>
+ </div>
+
+ <div class="doc_text">
+ <p>
+ The LLVM debugger needs to know about some source-language program objects, in
+ order to build stack traces, print information about local variables, and other
+ related activities. The LLVM debugger differentiates between three different
+ types of program objects: subprograms (functions, messages, methods, etc),
+ variables (locals and globals), and others. Because source-languages have
+ widely varying forms of these objects, the LLVM debugger expects only a few
+ fields in the descriptor for each object:
+ </p>
+
+ <pre>
+ %lldb.object = type {
+ uint, <i>;; <a href="#format_common_tag">A tag</a></i>
+ <i>any</i>*, <i>;; The <a href="#format_common_object_contexts">context</a> for the object</i>
+ sbyte* <i>;; The object 'name'</i>
+ }
+ </pre>
+
+ <p>The first field contains a tag for the descriptor. The second field contains
+ either a pointer to the descriptor for the containing <a
+ href="#format_common_source_files">source file</a>, or it contains a pointer to
+ another program object whose context pointer eventually reaches a source file.
+ Through this <a href="#format_common_object_contexts">context</a> pointer, the
+ LLVM debugger can establish the debug version number of the object.</p>
+
+ <p>The third field contains a string that the debugger can use to identify the
+ object if it does not contain explicit support for the source-language in use
+ (ie, the 'unknown' source language handler uses this string). This should be
+ some sort of unmangled string that corresponds to the object, but it is a
+ quality of implementation issue what exactly it contains (it is legal, though
+ not useful, for all of these strings to be null).</p>
+
+ <p>Note again that descriptors can be extended to include
+ source-language-specific information in addition to the fields required by the
+ LLVM debugger. See the <a href="#ccxx_descriptors">section on the C/C++
+ front-end</a> for more information. Also remember that global objects
+ (functions, selectors, global variables, etc) must contain an <a
+ href="#format_common_anchors">anchor</a> to the <tt>llvm.dbg.globals</tt>
+ variable.</p>
+ </div>
+
+
+ <!-- ======================================================================= -->
+ <div class="doc_subsection">
+ <a name="format_common_object_contexts">Program object contexts</a>
+ </div>
+
+ <div class="doc_text">
+ <pre>
+ Allow source-language specific contexts, use to identify namespaces etc
+ Must end up in a source file descriptor.
+ Debugger core ignores all unknown context objects.
+ </pre>
+ </div>
+
+ <!-- ======================================================================= -->
+ <div class="doc_subsection">
+ <a name="format_common_intrinsics">Debugger intrinsic functions</a>
+ </div>
+
+ <div class="doc_text">
+ <pre>
+ Define each intrinsics, as an extension of the language reference manual.
+
+ llvm.dbg.stoppoint
+ llvm.dbg.region.start
+ llvm.dbg.region.end
+ llvm.dbg.function.start
+ llvm.dbg.declare
+ </pre>
+ </div>
+
+ <!-- ======================================================================= -->
+ <div class="doc_subsection">
+ <a name="format_common_tags">Values for debugger tags</a>
+ </div>
+
+ <div class="doc_text">
+
+ <p>Happen to be the same value as the similarly named Dwarf-3 tags, this may
+ change in the future.</p>
+
+ <pre>
+ <a name="tag_compile_unit">LLVM_COMPILE_UNIT</a> : 17
+ <a name="tag_subprogram">LLVM_SUBPROGRAM</a> : 46
+ <a name="tag_variable">LLVM_VARIABLE</a> : 52
+ <!-- <a name="tag_formal_parameter">LLVM_FORMAL_PARAMETER : 5-->
+ </pre>
+ </div>
+
+
+
+ <!-- *********************************************************************** -->
+ <div class="doc_section">
+ <a name="ccxx_frontend">C/C++ front-end specific debug information</a>
+ </div>
+
+ <div class="doc_text">
+
+ <p>The C and C++ front-ends represent information about the program in a format
+ that is effectively identical to <a
+ href="http://www.eagercon.com/dwarf/dwarf3std.htm">Dwarf 3.0</a> in terms of
+ information content. This allows code generators to trivially support native
+ debuggers by generating standard dwarf information, and contains enough
+ information for non-dwarf targets to translate it as needed.</p>
+
+ <p>The basic debug information required by the debugger is (intentionally)
+ designed to be as minimal as possible. This basic information is so minimal
+ that it is unlikely that <b>any</b> source-language could be adequately
+ described by it. Because of this, the debugger format was designed for
+ extension to support source-language-specific information. The extended
+ descriptors are read and interpreted by the <a
+ href="#arch_info">language-specific</a> modules in the debugger if there is
+ support available, otherwise it is ignored.</p>
+
+ <p>This section describes the extensions used to represent C and C++ programs.
+ Other languages could pattern themselves after this (which itself is tuned to
+ representing programs in the same way that Dwarf 3 does), or they could choose
+ to provide completely different extensions if they don't fit into the Dwarf
+ model. As support for debugging information gets added to the various LLVM
+ source-language front-ends, the information used should be documented here.</p>
+
+ </div>
+
+ <!-- ======================================================================= -->
+ <div class="doc_subsection">
+ <a name="ccxx_pse">Program Scope Entries</a>
+ </div>
+
+ <div class="doc_text">
+ <p>TODO</p>
+ </div>
+
+ <!-- -------------------------------------------------------------------------->
+ <div class="doc_subsubsection">
+ <a name="ccxx_compilation_units">Compilation unit entries</a>
+ </div>
+
+ <div class="doc_text">
+ <p>
+ Translation units do not add any information over the standard <a
+ href="#format_common_source_files">source file representation</a> already
+ expected by the debugger. As such, it uses descriptors of the type specified,
+ with a trailing <a href="#format_common_anchors">anchor</a>.
+ </p>
+ </div>
+
+ <!-- -------------------------------------------------------------------------->
+ <div class="doc_subsubsection">
+ <a name="ccxx_modules">Module, namespace, and importing entries</a>
+ </div>
+
+ <div class="doc_text">
+ <p>TODO</p>
+ </div>
+
+ <!-- ======================================================================= -->
+ <div class="doc_subsection">
+ <a name="ccxx_dataobjects">Data objects (program variables)</a>
+ </div>
+
+ <div class="doc_text">
+ <p>TODO</p>
+ </div>
+
+
+ <!-- *********************************************************************** -->
+
+ <hr>
+ <address>
+ <a href="http://jigsaw.w3.org/css-validator/check/referer"><img
+ src="http://jigsaw.w3.org/css-validator/images/vcss" alt="Valid CSS!"></a>
+ <a href="http://validator.w3.org/check/referer"><img
+ src="http://www.w3.org/Icons/valid-html401" alt="Valid HTML 4.01!"></a>
+
+ <a href="mailto:sabre at nondot.org">Chris Lattner</a><br>
+ <a href="http://llvm.cs.uiuc.edu">LLVM Compiler Infrastructure</a><br>
+ Last modified: $Date: 2004/08/13 22:03:04 $
+ </address>
+
+ </body>
+ </html>
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+ <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"
+ "http://www.w3.org/TR/html4/strict.dtd">
+ <html>
+ <head>
+ <title>Stacker: An Example Of Using LLVM</title>
+ <link rel="stylesheet" href="llvm.css" type="text/css">
+ <style>
+ table, tr, td { border: 2px solid gray }
+ table { border-collapse: collapse; margin-bottom: 2em }
+ </style>
+ </head>
+ <body>
+
+ <div class="doc_title">Stacker: An Example Of Using LLVM</div>
+
+ <ol>
+ <li><a href="#abstract">Abstract</a></li>
+ <li><a href="#introduction">Introduction</a></li>
+ <li><a href="#lessons">Lessons I Learned About LLVM</a>
+ <ol>
+ <li><a href="#value">Everything's a Value!</a></li>
+ <li><a href="#terminate">Terminate Those Blocks!</a></li>
+ <li><a href="#blocks">Concrete Blocks</a></li>
+ <li><a href="#push_back">push_back Is Your Friend</a></li>
+ <li><a href="#gep">The Wily GetElementPtrInst</a></li>
+ <li><a href="#linkage">Getting Linkage Types Right</a></li>
+ <li><a href="#constants">Constants Are Easier Than That!</a></li>
+ </ol></li>
+ <li><a href="#lexicon">The Stacker Lexicon</a>
+ <ol>
+ <li><a href="#stack">The Stack</a></li>
+ <li><a href="#punctuation">Punctuation</a></li>
+ <li><a href="#comments">Comments</a></li>
+ <li><a href="#literals">Literals</a></li>
+ <li><a href="#words">Words</a></li>
+ <li><a href="#style">Standard Style</a></li>
+ <li><a href="#builtins">Built-Ins</a></li>
+ </ol></li>
+ <li><a href="#example">Prime: A Complete Example</a></li>
+ <li><a href="#internal">Internal Code Details</a>
+ <ol>
+ <li><a href="#directory">The Directory Structure </a></li>
+ <li><a href="#lexer">The Lexer</a></li>
+ <li><a href="#parser">The Parser</a></li>
+ <li><a href="#compiler">The Compiler</a></li>
+ <li><a href="#runtime">The Runtime</a></li>
+ <li><a href="#driver">Compiler Driver</a></li>
+ <li><a href="#tests">Test Programs</a></li>
+ <li><a href="#exercise">Exercise</a></li>
+ <li><a href="#todo">Things Remaining To Be Done</a></li>
+ </ol></li>
+ </ol>
+
+ <div class="doc_author">
+ <p>Written by <a href="mailto:rspencer at x10sys.com">Reid Spencer</a></p>
+ </div>
+
+ <!-- ======================================================================= -->
+ <div class="doc_section"><a name="abstract">Abstract</a></div>
+ <div class="doc_text">
+ <p>This document is another way to learn about LLVM. Unlike the
+ <a href="LangRef.html">LLVM Reference Manual</a> or
+ <a href="ProgrammersManual.html">LLVM Programmer's Manual</a>, here we learn
+ about LLVM through the experience of creating a simple programming language
+ named Stacker. Stacker was invented specifically as a demonstration of
+ LLVM. The emphasis in this document is not on describing the
+ intricacies of LLVM itself but on how to use it to build your own
+ compiler system.</p>
+ </div>
+ <!-- ======================================================================= -->
+ <div class="doc_section"> <a name="introduction">Introduction</a> </div>
+ <div class="doc_text">
+ <p>Amongst other things, LLVM is a platform for compiler writers.
+ Because of its exceptionally clean and small IR (intermediate
+ representation), compiler writing with LLVM is much easier than with
+ other system. As proof, I wrote the entire compiler (language definition,
+ lexer, parser, code generator, etc.) in about <em>four days</em>!
+ That's important to know because it shows how quickly you can get a new
+ language running when using LLVM. Furthermore, this was the <em >first</em>
+ language the author ever created using LLVM. The learning curve is
+ included in that four days.</p>
+ <p>The language described here, Stacker, is Forth-like. Programs
+ are simple collections of word definitions, and the only thing definitions
+ can do is manipulate a stack or generate I/O. Stacker is not a "real"
+ programming language; it's very simple. Although it is computationally
+ complete, you wouldn't use it for your next big project. However,
+ the fact that it is complete, it's simple, and it <em>doesn't</em> have
+ a C-like syntax make it useful for demonstration purposes. It shows
+ that LLVM could be applied to a wide variety of languages.</p>
+ <p>The basic notions behind stacker is very simple. There's a stack of
+ integers (or character pointers) that the program manipulates. Pretty
+ much the only thing the program can do is manipulate the stack and do
+ some limited I/O operations. The language provides you with several
+ built-in words that manipulate the stack in interesting ways. To get
+ your feet wet, here's how you write the traditional "Hello, World"
+ program in Stacker:</p>
+ <p><code>: hello_world "Hello, World!" >s DROP CR ;<br>
+ : MAIN hello_world ;<br></code></p>
+ <p>This has two "definitions" (Stacker manipulates words, not
+ functions and words have definitions): <code>MAIN</code> and <code>
+ hello_world</code>. The <code>MAIN</code> definition is standard; it
+ tells Stacker where to start. Here, <code>MAIN</code> is defined to
+ simply invoke the word <code>hello_world</code>. The
+ <code>hello_world</code> definition tells stacker to push the
+ <code>"Hello, World!"</code> string on to the stack, print it out
+ (<code>>s</code>), pop it off the stack (<code>DROP</code>), and
+ finally print a carriage return (<code>CR</code>). Although
+ <code>hello_world</code> uses the stack, its net effect is null. Well
+ written Stacker definitions have that characteristic. </p>
+ <p>Exercise for the reader: how could you make this a one line program?</p>
+ </div>
+ <!-- ======================================================================= -->
+ <div class="doc_section"><a name="lessons"></a>Lessons I Learned About LLVM</div>
+ <div class="doc_text">
+ <p>Stacker was written for two purposes: </p>
+ <ol>
+ <li>to get the author over the learning curve, and</li>
+ <li>to provide a simple example of how to write a compiler using LLVM.</li>
+ </ol>
+ <p>During the development of Stacker, many lessons about LLVM were
+ learned. Those lessons are described in the following subsections.<p>
+ </div>
+ <!-- ======================================================================= -->
+ <div class="doc_subsection"><a name="value"></a>Everything's a Value!</div>
+ <div class="doc_text">
+ <p>Although I knew that LLVM uses a Single Static Assignment (SSA) format,
+ it wasn't obvious to me how prevalent this idea was in LLVM until I really
+ started using it. Reading the <a href="ProgrammersManual.html">
+ Programmer's Manual</a> and <a href="LangRef.html">Language Reference</a>,
+ I noted that most of the important LLVM IR (Intermediate Representation) C++
+ classes were derived from the Value class. The full power of that simple
+ design only became fully understood once I started constructing executable
+ expressions for Stacker.</p>
+
+ <p>This really makes your programming go faster. Think about compiling code
+ for the following C/C++ expression: <code>(a|b)*((x+1)/(y+1))</code>. Assuming
+ the values are on the stack in the order a, b, x, y, this could be
+ expressed in stacker as: <code>1 + SWAP 1 + / ROT2 OR *</code>.
+ You could write a function using LLVM that computes this expression like
+ this: </p>
+
+ <div class="doc_code"><pre>
+ Value*
+ expression(BasicBlock* bb, Value* a, Value* b, Value* x, Value* y )
+ {
+ ConstantSInt* one = ConstantSInt::get(Type::IntTy, 1);
+ BinaryOperator* or1 = BinaryOperator::createOr(a, b, "", bb);
+ BinaryOperator* add1 = BinaryOperator::createAdd(x, one, "", bb);
+ BinaryOperator* add2 = BinaryOperator::createAdd(y, one, "", bb);
+ BinaryOperator* div1 = BinaryOperator::createDiv(add1, add2, "", bb);
+ BinaryOperator* mult1 = BinaryOperator::createMul(or1, div1, "", bb);
+ return mult1;
+ }
+ </pre></div>
+
+ <p>"Okay, big deal," you say? It is a big deal. Here's why. Note that I didn't
+ have to tell this function which kinds of Values are being passed in. They could be
+ <code>Instruction</code>s, <code>Constant</code>s, <code>GlobalVariable</code>s, or
+ any of the other subclasses of <code>Value</code> that LLVM supports.
+ Furthermore, if you specify Values that are incorrect for this sequence of
+ operations, LLVM will either notice right away (at compilation time) or the LLVM
+ Verifier will pick up the inconsistency when the compiler runs. In either case
+ LLVM prevents you from making a type error that gets passed through to the
+ generated program. This <em>really</em> helps you write a compiler that
+ always generates correct code!<p>
+ <p>The second point is that we don't have to worry about branching, registers,
+ stack variables, saving partial results, etc. The instructions we create
+ <em>are</em> the values we use. Note that all that was created in the above
+ code is a Constant value and five operators. Each of the instructions <em>is</em>
+ the resulting value of that instruction. This saves a lot of time.</p>
+ <p>The lesson is this: <em>SSA form is very powerful: there is no difference
+ between a value and the instruction that created it.</em> This is fully
+ enforced by the LLVM IR. Use it to your best advantage.</p>
+ </div>
+ <!-- ======================================================================= -->
+ <div class="doc_subsection"><a name="terminate"></a>Terminate Those Blocks!</div>
+ <div class="doc_text">
+ <p>I had to learn about terminating blocks the hard way: using the debugger
+ to figure out what the LLVM verifier was trying to tell me and begging for
+ help on the LLVMdev mailing list. I hope you avoid this experience.</p>
+ <p>Emblazon this rule in your mind:</p>
+ <ul>
+ <li><em>All</em> <code>BasicBlock</code>s in your compiler <b>must</b> be
+ terminated with a terminating instruction (branch, return, etc.).
+ </li>
+ </ul>
+ <p>Terminating instructions are a semantic requirement of the LLVM IR. There
+ is no facility for implicitly chaining together blocks placed into a function
+ in the order they occur. Indeed, in the general case, blocks will not be
+ added to the function in the order of execution because of the recursive
+ way compilers are written.</p>
+ <p>Furthermore, if you don't terminate your blocks, your compiler code will
+ compile just fine. You won't find out about the problem until you're running
+ the compiler and the module you just created fails on the LLVM Verifier.</p>
+ </div>
+ <!-- ======================================================================= -->
+ <div class="doc_subsection"><a name="blocks"></a>Concrete Blocks</div>
+ <div class="doc_text">
+ <p>After a little initial fumbling around, I quickly caught on to how blocks
+ should be constructed. In general, here's what I learned:
+ <ol>
+ <li><em>Create your blocks early.</em> While writing your compiler, you
+ will encounter several situations where you know apriori that you will
+ need several blocks. For example, if-then-else, switch, while, and for
+ statements in C/C++ all need multiple blocks for expression in LVVM.
+ The rule is, create them early.</li>
+ <li><em>Terminate your blocks early.</em> This just reduces the chances
+ that you forget to terminate your blocks which is required (go
+ <a href="#terminate">here</a> for more).
+ <li><em>Use getTerminator() for instruction insertion.</em> I noticed early on
+ that many of the constructors for the Instruction classes take an optional
+ <code>insert_before</code> argument. At first, I thought this was a mistake
+ because clearly the normal mode of inserting instructions would be one at
+ a time <em>after</em> some other instruction, not <em>before</em>. However,
+ if you hold on to your terminating instruction (or use the handy dandy
+ <code>getTerminator()</code> method on a <code>BasicBlock</code>), it can
+ always be used as the <code>insert_before</code> argument to your instruction
+ constructors. This causes the instruction to automatically be inserted in
+ the RightPlace™ place, just before the terminating instruction. The
+ nice thing about this design is that you can pass blocks around and insert
+ new instructions into them without ever knowing what instructions came
+ before. This makes for some very clean compiler design.</li>
+ </ol>
+ <p>The foregoing is such an important principal, its worth making an idiom:</p>
+ <pre>
+ BasicBlock* bb = new BasicBlock();
+ bb->getInstList().push_back( new Branch( ... ) );
+ new Instruction(..., bb->getTerminator() );
+ </pre>
+ <p>To make this clear, consider the typical if-then-else statement
+ (see StackerCompiler::handle_if() method). We can set this up
+ in a single function using LLVM in the following way: </p>
+ <pre>
+ using namespace llvm;
+ BasicBlock*
+ MyCompiler::handle_if( BasicBlock* bb, SetCondInst* condition )
+ {
+ // Create the blocks to contain code in the structure of if/then/else
+ BasicBlock* then_bb = new BasicBlock();
+ BasicBlock* else_bb = new BasicBlock();
+ BasicBlock* exit_bb = new BasicBlock();
+
+ // Insert the branch instruction for the "if"
+ bb->getInstList().push_back( new BranchInst( then_bb, else_bb, condition ) );
+
+ // Set up the terminating instructions
+ then->getInstList().push_back( new BranchInst( exit_bb ) );
+ else->getInstList().push_back( new BranchInst( exit_bb ) );
+
+ // Fill in the then part .. details excised for brevity
+ this->fill_in( then_bb );
+
+ // Fill in the else part .. details excised for brevity
+ this->fill_in( else_bb );
+
+ // Return a block to the caller that can be filled in with the code
+ // that follows the if/then/else construct.
+ return exit_bb;
+ }
+ </pre>
+ <p>Presumably in the foregoing, the calls to the "fill_in" method would add
+ the instructions for the "then" and "else" parts. They would use the third part
+ of the idiom almost exclusively (inserting new instructions before the
+ terminator). Furthermore, they could even recurse back to <code>handle_if</code>
+ should they encounter another if/then/else statement, and it will just work.</p>
+ <p>Note how cleanly this all works out. In particular, the push_back methods on
+ the <code>BasicBlock</code>'s instruction list. These are lists of type
+ <code>Instruction</code> (which is also of type <code>Value</code>). To create
+ the "if" branch we merely instantiate a <code>BranchInst</code> that takes as
+ arguments the blocks to branch to and the condition to branch on. The
+ <code>BasicBlock</code> objects act like branch labels! This new
+ <code>BranchInst</code> terminates the <code>BasicBlock</code> provided
+ as an argument. To give the caller a way to keep inserting after calling
+ <code>handle_if</code>, we create an <code>exit_bb</code> block which is
+ returned
+ to the caller. Note that the <code>exit_bb</code> block is used as the
+ terminator for both the <code>then_bb</code> and the <code>else_bb</code>
+ blocks. This guarantees that no matter what else <code>handle_if</code>
+ or <code>fill_in</code> does, they end up at the <code>exit_bb</code> block.
+ </p>
+ </div>
+ <!-- ======================================================================= -->
+ <div class="doc_subsection"><a name="push_back"></a>push_back Is Your Friend</div>
+ <div class="doc_text">
+ <p>
+ One of the first things I noticed is the frequent use of the "push_back"
+ method on the various lists. This is so common that it is worth mentioning.
+ The "push_back" inserts a value into an STL list, vector, array, etc. at the
+ end. The method might have also been named "insert_tail" or "append".
+ Although I've used STL quite frequently, my use of push_back wasn't very
+ high in other programs. In LLVM, you'll use it all the time.
+ </p>
+ </div>
+ <!-- ======================================================================= -->
+ <div class="doc_subsection"><a name="gep"></a>The Wily GetElementPtrInst</div>
+ <div class="doc_text">
+ <p>
+ It took a little getting used to and several rounds of postings to the LLVM
+ mailing list to wrap my head around this instruction correctly. Even though I had
+ read the Language Reference and Programmer's Manual a couple times each, I still
+ missed a few <em>very</em> key points:
+ </p>
+ <ul>
+ <li>GetElementPtrInst gives you back a Value for the last thing indexed.</li>
+ <li>All global variables in LLVM are <em>pointers</em>.</li>
+ <li>Pointers must also be dereferenced with the GetElementPtrInst
+ instruction.</li>
+ </ul>
+ <p>This means that when you look up an element in the global variable (assuming
+ it's a struct or array), you <em>must</em> deference the pointer first! For many
+ things, this leads to the idiom:
+ </p>
+ <pre>
+ std::vector<Value*> index_vector;
+ index_vector.push_back( ConstantSInt::get( Type::LongTy, 0 );
+ // ... push other indices ...
+ GetElementPtrInst* gep = new GetElementPtrInst( ptr, index_vector );
+ </pre>
+ <p>For example, suppose we have a global variable whose type is [24 x int]. The
+ variable itself represents a <em>pointer</em> to that array. To subscript the
+ array, we need two indices, not just one. The first index (0) dereferences the
+ pointer. The second index subscripts the array. If you're a "C" programmer, this
+ will run against your grain because you'll naturally think of the global array
+ variable and the address of its first element as the same. That tripped me up
+ for a while until I realized that they really do differ .. by <em>type</em>.
+ Remember that LLVM is strongly typed. Everything has a type.
+ The "type" of the global variable is [24 x int]*. That is, it's
+ a pointer to an array of 24 ints. When you dereference that global variable with
+ a single (0) index, you now have a "[24 x int]" type. Although
+ the pointer value of the dereferenced global and the address of the zero'th element
+ in the array will be the same, they differ in their type. The zero'th element has
+ type "int" while the pointer value has type "[24 x int]".</p>
+ <p>Get this one aspect of LLVM right in your head, and you'll save yourself
+ a lot of compiler writing headaches down the road.</p>
+ </div>
+ <!-- ======================================================================= -->
+ <div class="doc_subsection"><a name="linkage"></a>Getting Linkage Types Right</div>
+ <div class="doc_text">
+ <p>Linkage types in LLVM can be a little confusing, especially if your compiler
+ writing mind has affixed firm concepts to particular words like "weak",
+ "external", "global", "linkonce", etc. LLVM does <em>not</em> use the precise
+ definitions of, say, ELF or GCC, even though they share common terms. To be fair,
+ the concepts are related and similar but not precisely the same. This can lead
+ you to think you know what a linkage type represents but in fact it is slightly
+ different. I recommend you read the
+ <a href="LangRef.html#linkage"> Language Reference on this topic</a> very
+ carefully. Then, read it again.<p>
+ <p>Here are some handy tips that I discovered along the way:</p>
+ <ul>
+ <li><em>Uninitialized means external.</em> That is, the symbol is declared in the current
+ module and can be used by that module, but it is not defined by that module.</li>
+ <li><em>Setting an initializer changes a global' linkage type.</em> Setting an
+ initializer changes a global's linkage type from whatever it was to a normal,
+ defined global (not external). You'll need to call the setLinkage() method to
+ reset it if you specify the initializer after the GlobalValue has been constructed.
+ This is important for LinkOnce and Weak linkage types.</li>
+ <li><em>Appending linkage can keep track of things.</em> Appending linkage can
+ be used to keep track of compilation information at runtime. It could be used,
+ for example, to build a full table of all the C++ virtual tables or hold the
+ C++ RTTI data, or whatever. Appending linkage can only be applied to arrays.
+ All arrays with the same name in each module are concatenated together at link
+ time.</li>
+ </ul>
+ </div>
+ <!-- ======================================================================= -->
+ <div class="doc_subsection"><a name="constants"></a>Constants Are Easier Than That!</div>
+ <div class="doc_text">
+ <p>
+ Constants in LLVM took a little getting used to until I discovered a few utility
+ functions in the LLVM IR that make things easier. Here's what I learned: </p>
+ <ul>
+ <li>Constants are Values like anything else and can be operands of instructions</li>
+ <li>Integer constants, frequently needed, can be created using the static "get"
+ methods of the ConstantInt, ConstantSInt, and ConstantUInt classes. The nice thing
+ about these is that you can "get" any kind of integer quickly.</li>
+ <li>There's a special method on Constant class which allows you to get the null
+ constant for <em>any</em> type. This is really handy for initializing large
+ arrays or structures, etc.</li>
+ </ul>
+ </div>
+ <!-- ======================================================================= -->
+ <div class="doc_section"> <a name="lexicon">The Stacker Lexicon</a></div>
+ <div class="doc_text"><p>This section describes the Stacker language</p></div>
+ <div class="doc_subsection"><a name="stack"></a>The Stack</div>
+ <div class="doc_text">
+ <p>Stacker definitions define what they do to the global stack. Before
+ proceeding, a few words about the stack are in order. The stack is simply
+ a global array of 32-bit integers or pointers. A global index keeps track
+ of the location of the top of the stack. All of this is hidden from the
+ programmer, but it needs to be noted because it is the foundation of the
+ conceptual programming model for Stacker. When you write a definition,
+ you are, essentially, saying how you want that definition to manipulate
+ the global stack.</p>
+ <p>Manipulating the stack can be quite hazardous. There is no distinction
+ given and no checking for the various types of values that can be placed
+ on the stack. Automatic coercion between types is performed. In many
+ cases, this is useful. For example, a boolean value placed on the stack
+ can be interpreted as an integer with good results. However, using a
+ word that interprets that boolean value as a pointer to a string to
+ print out will almost always yield a crash. Stacker simply leaves it
+ to the programmer to get it right without any interference or hindering
+ on interpretation of the stack values. You've been warned. :) </p>
+ </div>
+ <!-- ======================================================================= -->
+ <div class="doc_subsection"> <a name="punctuation"></a>Punctuation</div>
+ <div class="doc_text">
+ <p>Punctuation in Stacker is very simple. The colon and semi-colon
+ characters are used to introduce and terminate a definition
+ (respectively). Except for <em>FORWARD</em> declarations, definitions
+ are all you can specify in Stacker. Definitions are read left to right.
+ Immediately after the colon comes the name of the word being defined.
+ The remaining words in the definition specify what the word does. The definition
+ is terminated by a semi-colon.</p>
+ <p>So, your typical definition will have the form:</p>
+ <pre><code>: name ... ;</code></pre>
+ <p>The <code>name</code> is up to you but it must start with a letter and contain
+ only letters, numbers, and underscore. Names are case sensitive and must not be
+ the same as the name of a built-in word. The <code>...</code> is replaced by
+ the stack manipulating words that you wish to define <code>name</code> as. <p>
+ </div>
+ <!-- ======================================================================= -->
+ <div class="doc_subsection"><a name="comments"></a>Comments</div>
+ <div class="doc_text">
+ <p>Stacker supports two types of comments. A hash mark (#) starts a comment
+ that extends to the end of the line. It is identical to the kind of comments
+ commonly used in shell scripts. A pair of parentheses also surround a comment.
+ In both cases, the content of the comment is ignored by the Stacker compiler. The
+ following does nothing in Stacker.
+ </p>
+ <pre><code>
+ # This is a comment to end of line
+ ( This is an enclosed comment )
+ </code></pre>
+ <p>See the <a href="#example">example</a> program to see comments in use in
+ a real program.</p>
+ </div>
+ <!-- ======================================================================= -->
+ <div class="doc_subsection"><a name="literals"></a>Literals</div>
+ <div class="doc_text">
+ <p>There are three kinds of literal values in Stacker: Integers, Strings,
+ and Booleans. In each case, the stack operation is to simply push the
+ value on to the stack. So, for example:<br/>
+ <code> 42 " is the answer." TRUE </code><br/>
+ will push three values on to the stack: the integer 42, the
+ string " is the answer.", and the boolean TRUE.</p>
+ </div>
+ <!-- ======================================================================= -->
+ <div class="doc_subsection"><a name="words"></a>Words</div>
+ <div class="doc_text">
+ <p>Each definition in Stacker is composed of a set of words. Words are
+ read and executed in order from left to right. There is very little
+ checking in Stacker to make sure you're doing the right thing with
+ the stack. It is assumed that the programmer knows how the stack
+ transformation he applies will affect the program.</p>
+ <p>Words in a definition come in two flavors: built-in and programmer
+ defined. Simply mentioning the name of a previously defined or declared
+ programmer-defined word causes that word's stack actions to be invoked. It
+ is somewhat like a function call in other languages. The built-in
+ words have various effects, described <a href="#builtins">below</a>.</p>
+ <p>Sometimes you need to call a word before it is defined. For this, you can
+ use the <code>FORWARD</code> declaration. It looks like this:</p>
+ <p><code>FORWARD name ;</code></p>
+ <p>This simply states to Stacker that "name" is the name of a definition
+ that is defined elsewhere. Generally it means the definition can be found
+ "forward" in the file. But, it doesn't have to be in the current compilation
+ unit. Anything declared with <code>FORWARD</code> is an external symbol for
+ linking.</p>
+ </div>
+ <!-- ======================================================================= -->
+ <div class="doc_subsection"><a name="style"></a>Standard Style</div>
+ <div class="doc_text">
+ <p>TODO</p>
+ </div>
+ <!-- ======================================================================= -->
+ <div class="doc_subsection"><a name="builtins"></a>Built In Words</div>
+ <div class="doc_text">
+ <p>The built-in words of the Stacker language are put in several groups
+ depending on what they do. The groups are as follows:</p>
+ <ol>
+ <li><em>Logical</em>: These words provide the logical operations for
+ comparing stack operands.<br/>The words are: < > <= >=
+ = <> true false.</li>
+ <li><em>Bitwise</em>: These words perform bitwise computations on
+ their operands. <br/> The words are: << >> XOR AND NOT</li>
+ <li><em>Arithmetic</em>: These words perform arithmetic computations on
+ their operands. <br/> The words are: ABS NEG + - * / MOD */ ++ -- MIN MAX</li>
+ <li><em>Stack</em>These words manipulate the stack directly by moving
+ its elements around.<br/> The words are: DROP DROP2 NIP NIP2 DUP DUP2
+ SWAP SWAP2 OVER OVER2 ROT ROT2 RROT RROT2 TUCK TUCK2 PICK SELECT ROLL</li>
+ <li><em>Memory</em>These words allocate, free, and manipulate memory
+ areas outside the stack.<br/>The words are: MALLOC FREE GET PUT</li>
+ <li><em>Control</em>: These words alter the normal left to right flow
+ of execution.<br/>The words are: IF ELSE ENDIF WHILE END RETURN EXIT RECURSE</li>
+ <li><em>I/O</em>: These words perform output on the standard output
+ and input on the standard input. No other I/O is possible in Stacker.
+ <br/>The words are: SPACE TAB CR >s >d >c <s <d <c.</li>
+ </ol>
+ <p>While you may be familiar with many of these operations from other
+ programming languages, a careful review of their semantics is important
+ for correct programming in Stacker. Of most importance is the effect
+ that each of these built-in words has on the global stack. The effect is
+ not always intuitive. To better describe the effects, we'll borrow from Forth the idiom of
+ describing the effect on the stack with:</p>
+ <p><code> BEFORE -- AFTER </code></p>
+ <p>That is, to the left of the -- is a representation of the stack before
+ the operation. To the right of the -- is a representation of the stack
+ after the operation. In the table below that describes the operation of
+ each of the built in words, we will denote the elements of the stack
+ using the following construction:</p>
+ <ol>
+ <li><em>b</em> - a boolean truth value</li>
+ <li><em>w</em> - a normal integer valued word.</li>
+ <li><em>s</em> - a pointer to a string value</li>
+ <li><em>p</em> - a pointer to a malloc'd memory block</li>
+ </ol>
+ </div>
+ <div class="doc_text" >
+ <table class="doc_table">
+ <tr class="doc_table"><td colspan="4">Definition Of Operation Of Built In Words</td></tr>
+ <tr class="doc_table"><td colspan="4"><b>LOGICAL OPERATIONS</b></td></tr>
+ <tr class="doc_table">
+ <td>Word</td>
+ <td>Name</td>
+ <td>Operation</td>
+ <td>Description</td>
+ </tr>
+ <tr class="doc_table">
+ <td><</td>
+ <td>LT</td>
+ <td>w1 w2 -- b</td>
+ <td>Two values (w1 and w2) are popped off the stack and
+ compared. If w1 is less than w2, TRUE is pushed back on
+ the stack, otherwise FALSE is pushed back on the stack.</td>
+ </tr>
+ <tr><td>></td>
+ <td>GT</td>
+ <td>w1 w2 -- b</td>
+ <td>Two values (w1 and w2) are popped off the stack and
+ compared. If w1 is greater than w2, TRUE is pushed back on
+ the stack, otherwise FALSE is pushed back on the stack.</td>
+ </tr>
+ <tr><td>>=</td>
+ <td>GE</td>
+ <td>w1 w2 -- b</td>
+ <td>Two values (w1 and w2) are popped off the stack and
+ compared. If w1 is greater than or equal to w2, TRUE is
+ pushed back on the stack, otherwise FALSE is pushed back
+ on the stack.</td>
+ </tr>
+ <tr><td><=</td>
+ <td>LE</td>
+ <td>w1 w2 -- b</td>
+ <td>Two values (w1 and w2) are popped off the stack and
+ compared. If w1 is less than or equal to w2, TRUE is
+ pushed back on the stack, otherwise FALSE is pushed back
+ on the stack.</td>
+ </tr>
+ <tr><td>=</td>
+ <td>EQ</td>
+ <td>w1 w2 -- b</td>
+ <td>Two values (w1 and w2) are popped off the stack and
+ compared. If w1 is equal to w2, TRUE is
+ pushed back on the stack, otherwise FALSE is pushed back
+ </td>
+ </tr>
+ <tr><td><></td>
+ <td>NE</td>
+ <td>w1 w2 -- b</td>
+ <td>Two values (w1 and w2) are popped off the stack and
+ compared. If w1 is equal to w2, TRUE is
+ pushed back on the stack, otherwise FALSE is pushed back
+ </td>
+ </tr>
+ <tr><td>FALSE</td>
+ <td>FALSE</td>
+ <td> -- b</td>
+ <td>The boolean value FALSE (0) is pushed on to the stack.</td>
+ </tr>
+ <tr><td>TRUE</td>
+ <td>TRUE</td>
+ <td> -- b</td>
+ <td>The boolean value TRUE (-1) is pushed on to the stack.</td>
+ </tr>
+ <tr><td colspan="4"><b>BITWISE OPERATORS</b></td></tr>
+ <tr>
+ <td>Word</td>
+ <td>Name</td>
+ <td>Operation</td>
+ <td>Description</td>
+ </tr>
+ <tr><td><<</td>
+ <td>SHL</td>
+ <td>w1 w2 -- w1<<w2</td>
+ <td>Two values (w1 and w2) are popped off the stack. The w2
+ operand is shifted left by the number of bits given by the
+ w1 operand. The result is pushed back to the stack.</td>
+ </tr>
+ <tr><td>>></td>
+ <td>SHR</td>
+ <td>w1 w2 -- w1>>w2</td>
+ <td>Two values (w1 and w2) are popped off the stack. The w2
+ operand is shifted right by the number of bits given by the
+ w1 operand. The result is pushed back to the stack.</td>
+ </tr>
+ <tr><td>OR</td>
+ <td>OR</td>
+ <td>w1 w2 -- w2|w1</td>
+ <td>Two values (w1 and w2) are popped off the stack. The values
+ are bitwise OR'd together and pushed back on the stack. This is
+ not a logical OR. The sequence 1 2 OR yields 3 not 1.</td>
+ </tr>
+ <tr><td>AND</td>
+ <td>AND</td>
+ <td>w1 w2 -- w2&w1</td>
+ <td>Two values (w1 and w2) are popped off the stack. The values
+ are bitwise AND'd together and pushed back on the stack. This is
+ not a logical AND. The sequence 1 2 AND yields 0 not 1.</td>
+ </tr>
+ <tr><td>XOR</td>
+ <td>XOR</td>
+ <td>w1 w2 -- w2^w1</td>
+ <td>Two values (w1 and w2) are popped off the stack. The values
+ are bitwise exclusive OR'd together and pushed back on the stack.
+ For example, The sequence 1 3 XOR yields 2.</td>
+ </tr>
+ <tr><td colspan="4"><b>ARITHMETIC OPERATORS</b></td></tr>
+ <tr>
+ <td>Word</td>
+ <td>Name</td>
+ <td>Operation</td>
+ <td>Description</td>
+ </tr>
+ <tr><td>ABS</td>
+ <td>ABS</td>
+ <td>w -- |w|</td>
+ <td>One value s popped off the stack; its absolute value is computed
+ and then pushed on to the stack. If w1 is -1 then w2 is 1. If w1 is
+ 1 then w2 is also 1.</td>
+ </tr>
+ <tr><td>NEG</td>
+ <td>NEG</td>
+ <td>w -- -w</td>
+ <td>One value is popped off the stack which is negated and then
+ pushed back on to the stack. If w1 is -1 then w2 is 1. If w1 is
+ 1 then w2 is -1.</td>
+ </tr>
+ <tr><td> + </td>
+ <td>ADD</td>
+ <td>w1 w2 -- w2+w1</td>
+ <td>Two values are popped off the stack. Their sum is pushed back
+ on to the stack</td>
+ </tr>
+ <tr><td> - </td>
+ <td>SUB</td>
+ <td>w1 w2 -- w2-w1</td>
+ <td>Two values are popped off the stack. Their difference is pushed back
+ on to the stack</td>
+ </tr>
+ <tr><td> * </td>
+ <td>MUL</td>
+ <td>w1 w2 -- w2*w1</td>
+ <td>Two values are popped off the stack. Their product is pushed back
+ on to the stack</td>
+ </tr>
+ <tr><td> / </td>
+ <td>DIV</td>
+ <td>w1 w2 -- w2/w1</td>
+ <td>Two values are popped off the stack. Their quotient is pushed back
+ on to the stack</td>
+ </tr>
+ <tr><td>MOD</td>
+ <td>MOD</td>
+ <td>w1 w2 -- w2%w1</td>
+ <td>Two values are popped off the stack. Their remainder after division
+ of w1 by w2 is pushed back on to the stack</td>
+ </tr>
+ <tr><td> */ </td>
+ <td>STAR_SLAH</td>
+ <td>w1 w2 w3 -- (w3*w2)/w1</td>
+ <td>Three values are popped off the stack. The product of w1 and w2 is
+ divided by w3. The result is pushed back on to the stack.</td>
+ </tr>
+ <tr><td> ++ </td>
+ <td>INCR</td>
+ <td>w -- w+1</td>
+ <td>One value is popped off the stack. It is incremented by one and then
+ pushed back on to the stack.</td>
+ </tr>
+ <tr><td> -- </td>
+ <td>DECR</td>
+ <td>w -- w-1</td>
+ <td>One value is popped off the stack. It is decremented by one and then
+ pushed back on to the stack.</td>
+ </tr>
+ <tr><td>MIN</td>
+ <td>MIN</td>
+ <td>w1 w2 -- (w2<w1?w2:w1)</td>
+ <td>Two values are popped off the stack. The larger one is pushed back
+ on to the stack.</td>
+ </tr>
+ <tr><td>MAX</td>
+ <td>MAX</td>
+ <td>w1 w2 -- (w2>w1?w2:w1)</td>
+ <td>Two values are popped off the stack. The larger value is pushed back
+ on to the stack.</td>
+ </tr>
+ <tr><td colspan="4"><b>STACK MANIPULATION OPERATORS</b></td></tr>
+ <tr>
+ <td>Word</td>
+ <td>Name</td>
+ <td>Operation</td>
+ <td>Description</td>
+ </tr>
+ <tr><td>DROP</td>
+ <td>DROP</td>
+ <td>w -- </td>
+ <td>One value is popped off the stack.</td>
+ </tr>
+ <tr><td>DROP2</td>
+ <td>DROP2</td>
+ <td>w1 w2 -- </td>
+ <td>Two values are popped off the stack.</td>
+ </tr>
+ <tr><td>NIP</td>
+ <td>NIP</td>
+ <td>w1 w2 -- w2</td>
+ <td>The second value on the stack is removed from the stack. That is,
+ a value is popped off the stack and retained. Then a second value is
+ popped and the retained value is pushed.</td>
+ </tr>
+ <tr><td>NIP2</td>
+ <td>NIP2</td>
+ <td>w1 w2 w3 w4 -- w3 w4</td>
+ <td>The third and fourth values on the stack are removed from it. That is,
+ two values are popped and retained. Then two more values are popped and
+ the two retained values are pushed back on.</td>
+ </tr>
+ <tr><td>DUP</td>
+ <td>DUP</td>
+ <td>w1 -- w1 w1</td>
+ <td>One value is popped off the stack. That value is then pushed on to
+ the stack twice to duplicate the top stack vaue.</td>
+ </tr>
+ <tr><td>DUP2</td>
+ <td>DUP2</td>
+ <td>w1 w2 -- w1 w2 w1 w2</td>
+ <td>The top two values on the stack are duplicated. That is, two vaues
+ are popped off the stack. They are alternately pushed back on the
+ stack twice each.</td>
+ </tr>
+ <tr><td>SWAP</td>
+ <td>SWAP</td>
+ <td>w1 w2 -- w2 w1</td>
+ <td>The top two stack items are reversed in their order. That is, two
+ values are popped off the stack and pushed back on to the stack in
+ the opposite order they were popped.</td>
+ </tr>
+ <tr><td>SWAP2</td>
+ <td>SWAP2</td>
+ <td>w1 w2 w3 w4 -- w3 w4 w2 w1</td>
+ <td>The top four stack items are swapped in pairs. That is, two values
+ are popped and retained. Then, two more values are popped and retained.
+ The values are pushed back on to the stack in the reverse order but
+ in pairs.</td>
+ </tr>
+ <tr><td>OVER</td>
+ <td>OVER</td>
+ <td>w1 w2-- w1 w2 w1</td>
+ <td>Two values are popped from the stack. They are pushed back
+ on to the stack in the order w1 w2 w1. This seems to cause the
+ top stack element to be duplicated "over" the next value.</td>
+ </tr>
+ <tr><td>OVER2</td>
+ <td>OVER2</td>
+ <td>w1 w2 w3 w4 -- w1 w2 w3 w4 w1 w2</td>
+ <td>The third and fourth values on the stack are replicated on to the
+ top of the stack</td>
+ </tr>
+ <tr><td>ROT</td>
+ <td>ROT</td>
+ <td>w1 w2 w3 -- w2 w3 w1</td>
+ <td>The top three values are rotated. That is, three value are popped
+ off the stack. They are pushed back on to the stack in the order
+ w1 w3 w2.</td>
+ </tr>
+ <tr><td>ROT2</td>
+ <td>ROT2</td>
+ <td>w1 w2 w3 w4 w5 w6 -- w3 w4 w5 w6 w1 w2</td>
+ <td>Like ROT but the rotation is done using three pairs instead of
+ three singles.</td>
+ </tr>
+ <tr><td>RROT</td>
+ <td>RROT</td>
+ <td>w1 w2 w3 -- w2 w3 w1</td>
+ <td>Reverse rotation. Like ROT, but it rotates the other way around.
+ Essentially, the third element on the stack is moved to the top
+ of the stack.</td>
+ </tr>
+ <tr><td>RROT2</td>
+ <td>RROT2</td>
+ <td>w1 w2 w3 w4 w5 w6 -- w3 w4 w5 w6 w1 w2</td>
+ <td>Double reverse rotation. Like RROT but the rotation is done using
+ three pairs instead of three singles. The fifth and sixth stack
+ elements are moved to the first and second positions</td>
+ </tr>
+ <tr><td>TUCK</td>
+ <td>TUCK</td>
+ <td>w1 w2 -- w2 w1 w2</td>
+ <td>Similar to OVER except that the second operand is being
+ replicated. Essentially, the first operand is being "tucked"
+ in between two instances of the second operand. Logically, two
+ values are popped off the stack. They are placed back on the
+ stack in the order w2 w1 w2.</td>
+ </tr>
+ <tr><td>TUCK2</td>
+ <td>TUCK2</td>
+ <td>w1 w2 w3 w4 -- w3 w4 w1 w2 w3 w4</td>
+ <td>Like TUCK but a pair of elements is tucked over two pairs.
+ That is, the top two elements of the stack are duplicated and
+ inserted into the stack at the fifth and positions.</td>
+ </tr>
+ <tr><td>PICK</td>
+ <td>PICK</td>
+ <td>x0 ... Xn n -- x0 ... Xn x0</td>
+ <td>The top of the stack is used as an index into the remainder of
+ the stack. The element at the nth position replaces the index
+ (top of stack). This is useful for cycling through a set of
+ values. Note that indexing is zero based. So, if n=0 then you
+ get the second item on the stack. If n=1 you get the third, etc.
+ Note also that the index is replaced by the n'th value. </td>
+ </tr>
+ <tr><td>SELECT</td>
+ <td>SELECT</td>
+ <td>m n X0..Xm Xm+1 .. Xn -- Xm</td>
+ <td>This is like PICK but the list is removed and you need to specify
+ both the index and the size of the list. Careful with this one,
+ the wrong value for n can blow away a huge amount of the stack.</td>
+ </tr>
+ <tr><td>ROLL</td>
+ <td>ROLL</td>
+ <td>x0 x1 .. xn n -- x1 .. xn x0</td>
+ <td><b>Not Implemented</b>. This one has been left as an exercise to
+ the student. See <a href="#exercise">Exercise</a>. ROLL requires
+ a value, "n", to be on the top of the stack. This value specifies how
+ far into the stack to "roll". The n'th value is <em>moved</em> (not
+ copied) from its location and replaces the "n" value on the top of the
+ stack. In this way, all the values between "n" and x0 roll up the stack.
+ The operation of ROLL is a generalized ROT. The "n" value specifies
+ how much to rotate. That is, ROLL with n=1 is the same as ROT and
+ ROLL with n=2 is the same as ROT2.</td>
+ </tr>
+ <tr><td colspan="4"><b>MEMORY OPERATORS</b></td></tr>
+ <tr>
+ <td>Word</td>
+ <td>Name</td>
+ <td>Operation</td>
+ <td>Description</td>
+ </tr>
+ <tr><td>MALLOC</td>
+ <td>MALLOC</td>
+ <td>w1 -- p</td>
+ <td>One value is popped off the stack. The value is used as the size
+ of a memory block to allocate. The size is in bytes, not words.
+ The memory allocation is completed and the address of the memory
+ block is pushed on to the stack.</td>
+ </tr>
+ <tr><td>FREE</td>
+ <td>FREE</td>
+ <td>p -- </td>
+ <td>One pointer value is popped off the stack. The value should be
+ the address of a memory block created by the MALLOC operation. The
+ associated memory block is freed. Nothing is pushed back on the
+ stack. Many bugs can be created by attempting to FREE something
+ that isn't a pointer to a MALLOC allocated memory block. Make
+ sure you know what's on the stack. One way to do this is with
+ the following idiom:<br/>
+ <code>64 MALLOC DUP DUP (use ptr) DUP (use ptr) ... FREE</code>
+ <br/>This ensures that an extra copy of the pointer is placed on
+ the stack (for the FREE at the end) and that every use of the
+ pointer is preceded by a DUP to retain the copy for FREE.</td>
+ </tr>
+ <tr><td>GET</td>
+ <td>GET</td>
+ <td>w1 p -- w2 p</td>
+ <td>An integer index and a pointer to a memory block are popped of
+ the block. The index is used to index one byte from the memory
+ block. That byte value is retained, the pointer is pushed again
+ and the retained value is pushed. Note that the pointer value
+ s essentially retained in its position so this doesn't count
+ as a "use ptr" in the FREE idiom.</td>
+ </tr>
+ <tr><td>PUT</td>
+ <td>PUT</td>
+ <td>w1 w2 p -- p </td>
+ <td>An integer value is popped of the stack. This is the value to
+ be put into a memory block. Another integer value is popped of
+ the stack. This is the indexed byte in the memory block. A
+ pointer to the memory block is popped off the stack. The
+ first value (w1) is then converted to a byte and written
+ to the element of the memory block(p) at the index given
+ by the second value (w2). The pointer to the memory block is
+ pushed back on the stack so this doesn't count as a "use ptr"
+ in the FREE idiom.</td>
+ </tr>
+ <tr><td colspan="4"><b>CONTROL FLOW OPERATORS</b></td></tr>
+ <tr>
+ <td>Word</td>
+ <td>Name</td>
+ <td>Operation</td>
+ <td>Description</td>
+ </tr>
+ <tr><td>RETURN</td>
+ <td>RETURN</td>
+ <td> -- </td>
+ <td>The currently executing definition returns immediately to its caller.
+ Note that there is an implicit <code>RETURN</code> at the end of each
+ definition, logically located at the semi-colon. The sequence
+ <code>RETURN ;</code> is valid but redundant.</td>
+ </tr>
+ <tr><td>EXIT</td>
+ <td>EXIT</td>
+ <td>w1 -- </td>
+ <td>A return value for the program is popped off the stack. The program is
+ then immediately terminated. This is normally an abnormal exit from the
+ program. For a normal exit (when <code>MAIN</code> finishes), the exit
+ code will always be zero in accordance with UNIX conventions.</td>
+ </tr>
+ <tr><td>RECURSE</td>
+ <td>RECURSE</td>
+ <td> -- </td>
+ <td>The currently executed definition is called again. This operation is
+ needed since the definition of a word doesn't exist until the semi colon
+ is reacher. Attempting something like:<br/>
+ <code> : recurser recurser ; </code><br/> will yield and error saying that
+ "recurser" is not defined yet. To accomplish the same thing, change this
+ to:<br/>
+ <code> : recurser RECURSE ; </code></td>
+ </tr>
+ <tr><td>IF (words...) ENDIF</td>
+ <td>IF (words...) ENDIF</td>
+ <td>b -- </td>
+ <td>A boolean value is popped of the stack. If it is non-zero then the "words..."
+ are executed. Otherwise, execution continues immediately following the ENDIF.</td>
+ </tr>
+ <tr><td>IF (words...) ELSE (words...) ENDIF</td>
+ <td>IF (words...) ELSE (words...) ENDIF</td>
+ <td>b -- </td>
+ <td>A boolean value is popped of the stack. If it is non-zero then the "words..."
+ between IF and ELSE are executed. Otherwise the words between ELSE and ENDIF are
+ executed. In either case, after the (words....) have executed, execution continues
+ immediately following the ENDIF. </td>
+ </tr>
+ <tr><td>WHILE (words...) END</td>
+ <td>WHILE (words...) END</td>
+ <td>b -- b </td>
+ <td>The boolean value on the top of the stack is examined. If it is non-zero then the
+ "words..." between WHILE and END are executed. Execution then begins again at the WHILE where another
+ boolean is popped off the stack. To prevent this operation from eating up the entire
+ stack, you should push on to the stack (just before the END) a boolean value that indicates
+ whether to terminate. Note that since booleans and integers can be coerced you can
+ use the following "for loop" idiom:<br/>
+ <code>(push count) WHILE (words...) -- END</code><br/>
+ For example:<br/>
+ <code>10 WHILE DUP >d -- END</code><br/>
+ This will print the numbers from 10 down to 1. 10 is pushed on the stack. Since that is
+ non-zero, the while loop is entered. The top of the stack (10) is duplicated and then
+ printed out with >d. The top of the stack is decremented, yielding 9 and control is
+ transfered back to the WHILE keyword. The process starts all over again and repeats until
+ the top of stack is decremented to 0 at which the WHILE test fails and control is
+ transfered to the word after the END.</td>
+ </tr>
+ <tr><td colspan="4"><b>INPUT & OUTPUT OPERATORS</b></td></tr>
+ <tr>
+ <td>Word</td>
+ <td>Name</td>
+ <td>Operation</td>
+ <td>Description</td>
+ </tr>
+ <tr><td>SPACE</td>
+ <td>SPACE</td>
+ <td> -- </td>
+ <td>A space character is put out. There is no stack effect.</td>
+ </tr>
+ <tr><td>TAB</td>
+ <td>TAB</td>
+ <td> -- </td>
+ <td>A tab character is put out. There is no stack effect.</td>
+ </tr>
+ <tr><td>CR</td>
+ <td>CR</td>
+ <td> -- </td>
+ <td>A carriage return character is put out. There is no stack effect.</td>
+ </tr>
+ <tr><td>>s</td>
+ <td>OUT_STR</td>
+ <td> -- </td>
+ <td>A string pointer is popped from the stack. It is put out.</td>
+ </tr>
+ <tr><td>>d</td>
+ <td>OUT_STR</td>
+ <td> -- </td>
+ <td>A value is popped from the stack. It is put out as a decimal
+ integer.</td>
+ </tr>
+ <tr><td>>c</td>
+ <td>OUT_CHR</td>
+ <td> -- </td>
+ <td>A value is popped from the stack. It is put out as an ASCII
+ character.</td>
+ </tr>
+ <tr><td><s</td>
+ <td>IN_STR</td>
+ <td> -- s </td>
+ <td>A string is read from the input via the scanf(3) format string " %as".
+ The resulting string is pushed on to the stack.</td>
+ </tr>
+ <tr><td><d</td>
+ <td>IN_STR</td>
+ <td> -- w </td>
+ <td>An integer is read from the input via the scanf(3) format string " %d".
+ The resulting value is pushed on to the stack</td>
+ </tr>
+ <tr><td><c</td>
+ <td>IN_CHR</td>
+ <td> -- w </td>
+ <td>A single character is read from the input via the scanf(3) format string
+ " %c". The value is converted to an integer and pushed on to the stack.</td>
+ </tr>
+ <tr><td>DUMP</td>
+ <td>DUMP</td>
+ <td> -- </td>
+ <td>The stack contents are dumped to standard output. This is useful for
+ debugging your definitions. Put DUMP at the beginning and end of a definition
+ to see instantly the net effect of the definition.</td>
+ </tr>
+ </table>
+
+ </div>
+ <!-- ======================================================================= -->
+ <div class="doc_section"> <a name="example">Prime: A Complete Example</a></div>
+ <div class="doc_text">
+ <p>The following fully documented program highlights many features of both
+ the Stacker language and what is possible with LLVM. The program has two modes
+ of operation. If you provide numeric arguments to the program, it checks to see
+ if those arguments are prime numbers and prints out the results. Without any
+ arguments, the program prints out any prime numbers it finds between 1 and one
+ million (there's a lot of them!). The source code comments below tell the
+ remainder of the story.
+ </p>
+ </div>
+ <div class="doc_text">
+ <pre><code>
+ ################################################################################
+ #
+ # Brute force prime number generator
+ #
+ # This program is written in classic Stacker style, that being the style of a
+ # stack. Start at the bottom and read your way up !
+ #
+ # Reid Spencer - Nov 2003
+ ################################################################################
+ # Utility definitions
+ ################################################################################
+ : print >d CR ;
+ : it_is_a_prime TRUE ;
+ : it_is_not_a_prime FALSE ;
+ : continue_loop TRUE ;
+ : exit_loop FALSE;
+
+ ################################################################################
+ # This definition tries an actual division of a candidate prime number. It
+ # determines whether the division loop on this candidate should continue or
+ # not.
+ # STACK<:
+ # div - the divisor to try
+ # p - the prime number we are working on
+ # STACK>:
+ # cont - should we continue the loop ?
+ # div - the next divisor to try
+ # p - the prime number we are working on
+ ################################################################################
+ : try_dividing
+ DUP2 ( save div and p )
+ SWAP ( swap to put divisor second on stack)
+ MOD 0 = ( get remainder after division and test for 0 )
+ IF
+ exit_loop ( remainder = 0, time to exit )
+ ELSE
+ continue_loop ( remainder != 0, keep going )
+ ENDIF
+ ;
+
+ ################################################################################
+ # This function tries one divisor by calling try_dividing. But, before doing
+ # that it checks to see if the value is 1. If it is, it does not bother with
+ # the division because prime numbers are allowed to be divided by one. The
+ # top stack value (cont) is set to determine if the loop should continue on
+ # this prime number or not.
+ # STACK<:
+ # cont - should we continue the loop (ignored)?
+ # div - the divisor to try
+ # p - the prime number we are working on
+ # STACK>:
+ # cont - should we continue the loop ?
+ # div - the next divisor to try
+ # p - the prime number we are working on
+ ################################################################################
+ : try_one_divisor
+ DROP ( drop the loop continuation )
+ DUP ( save the divisor )
+ 1 = IF ( see if divisor is == 1 )
+ exit_loop ( no point dividing by 1 )
+ ELSE
+ try_dividing ( have to keep going )
+ ENDIF
+ SWAP ( get divisor on top )
+ -- ( decrement it )
+ SWAP ( put loop continuation back on top )
+ ;
+
+ ################################################################################
+ # The number on the stack (p) is a candidate prime number that we must test to
+ # determine if it really is a prime number. To do this, we divide it by every
+ # number from one p-1 to 1. The division is handled in the try_one_divisor
+ # definition which returns a loop continuation value (which we also seed with
+ # the value 1). After the loop, we check the divisor. If it decremented all
+ # the way to zero then we found a prime, otherwise we did not find one.
+ # STACK<:
+ # p - the prime number to check
+ # STACK>:
+ # yn - boolean indicating if its a prime or not
+ # p - the prime number checked
+ ################################################################################
+ : try_harder
+ DUP ( duplicate to get divisor value ) )
+ -- ( first divisor is one less than p )
+ 1 ( continue the loop )
+ WHILE
+ try_one_divisor ( see if its prime )
+ END
+ DROP ( drop the continuation value )
+ 0 = IF ( test for divisor == 1 )
+ it_is_a_prime ( we found one )
+ ELSE
+ it_is_not_a_prime ( nope, this one is not a prime )
+ ENDIF
+ ;
+
+ ################################################################################
+ # This definition determines if the number on the top of the stack is a prime
+ # or not. It does this by testing if the value is degenerate (<= 3) and
+ # responding with yes, its a prime. Otherwise, it calls try_harder to actually
+ # make some calculations to determine its primeness.
+ # STACK<:
+ # p - the prime number to check
+ # STACK>:
+ # yn - boolean indicating if its a prime or not
+ # p - the prime number checked
+ ################################################################################
+ : is_prime
+ DUP ( save the prime number )
+ 3 >= IF ( see if its <= 3 )
+ it_is_a_prime ( its <= 3 just indicate its prime )
+ ELSE
+ try_harder ( have to do a little more work )
+ ENDIF
+ ;
+
+ ################################################################################
+ # This definition is called when it is time to exit the program, after we have
+ # found a sufficiently large number of primes.
+ # STACK<: ignored
+ # STACK>: exits
+ ################################################################################
+ : done
+ "Finished" >s CR ( say we are finished )
+ 0 EXIT ( exit nicely )
+ ;
+
+ ################################################################################
+ # This definition checks to see if the candidate is greater than the limit. If
+ # it is, it terminates the program by calling done. Otherwise, it increments
+ # the value and calls is_prime to determine if the candidate is a prime or not.
+ # If it is a prime, it prints it. Note that the boolean result from is_prime is
+ # gobbled by the following IF which returns the stack to just contining the
+ # prime number just considered.
+ # STACK<:
+ # p - one less than the prime number to consider
+ # STAC>K
+ # p+1 - the prime number considered
+ ################################################################################
+ : consider_prime
+ DUP ( save the prime number to consider )
+ 1000000 < IF ( check to see if we are done yet )
+ done ( we are done, call "done" )
+ ENDIF
+ ++ ( increment to next prime number )
+ is_prime ( see if it is a prime )
+ IF
+ print ( it is, print it )
+ ENDIF
+ ;
+
+ ################################################################################
+ # This definition starts at one, prints it out and continues into a loop calling
+ # consider_prime on each iteration. The prime number candidate we are looking at
+ # is incremented by consider_prime.
+ # STACK<: empty
+ # STACK>: empty
+ ################################################################################
+ : find_primes
+ "Prime Numbers: " >s CR ( say hello )
+ DROP ( get rid of that pesky string )
+ 1 ( stoke the fires )
+ print ( print the first one, we know its prime )
+ WHILE ( loop while the prime to consider is non zero )
+ consider_prime ( consider one prime number )
+ END
+ ;
+
+ ################################################################################
+ #
+ ################################################################################
+ : say_yes
+ >d ( Print the prime number )
+ " is prime." ( push string to output )
+ >s ( output it )
+ CR ( print carriage return )
+ DROP ( pop string )
+ ;
+
+ : say_no
+ >d ( Print the prime number )
+ " is NOT prime." ( push string to put out )
+ >s ( put out the string )
+ CR ( print carriage return )
+ DROP ( pop string )
+ ;
+
+ ################################################################################
+ # This definition processes a single command line argument and determines if it
+ # is a prime number or not.
+ # STACK<:
+ # n - number of arguments
+ # arg1 - the prime numbers to examine
+ # STACK>:
+ # n-1 - one less than number of arguments
+ # arg2 - we processed one argument
+ ################################################################################
+ : do_one_argument
+ -- ( decrement loop counter )
+ SWAP ( get the argument value )
+ is_prime IF ( determine if its prime )
+ say_yes ( uhuh )
+ ELSE
+ say_no ( nope )
+ ENDIF
+ DROP ( done with that argument )
+ ;
+
+ ################################################################################
+ # The MAIN program just prints a banner and processes its arguments.
+ # STACK<:
+ # n - number of arguments
+ # ... - the arguments
+ ################################################################################
+ : process_arguments
+ WHILE ( while there are more arguments )
+ do_one_argument ( process one argument )
+ END
+ ;
+
+ ################################################################################
+ # The MAIN program just prints a banner and processes its arguments.
+ # STACK<: arguments
+ ################################################################################
+ : MAIN
+ NIP ( get rid of the program name )
+ -- ( reduce number of arguments )
+ DUP ( save the arg counter )
+ 1 <= IF ( See if we got an argument )
+ process_arguments ( tell user if they are prime )
+ ELSE
+ find_primes ( see how many we can find )
+ ENDIF
+ 0 ( push return code )
+ ;
+ </code>
+ </pre>
+ </div>
+ <!-- ======================================================================= -->
+ <div class="doc_section"> <a name="internal">Internals</a></div>
+ <div class="doc_text">
+ <p><b>This section is under construction.</b>
+ <p>In the mean time, you can always read the code! It has comments!</p>
+ </div>
+ <!-- ======================================================================= -->
+ <div class="doc_subsection"> <a name="directory">Directory Structure</a></div>
+ <div class="doc_text">
+ <p>The source code, test programs, and sample programs can all be found
+ under the LLVM "projects" directory. You will need to obtain the LLVM sources
+ to find it (either via anonymous CVS or a tarball. See the
+ <a href="GettingStarted.html">Getting Started</a> document).</p>
+ <p>Under the "projects" directory there is a directory named "Stacker". That
+ directory contains everything, as follows:</p>
+ <ul>
+ <li><em>lib</em> - contains most of the source code
+ <ul>
+ <li><em>lib/compiler</em> - contains the compiler library
+ <li><em>lib/runtime</em> - contains the runtime library
+ </ul></li>
+ <li><em>test</em> - contains the test programs</li>
+ <li><em>tools</em> - contains the Stacker compiler main program, stkrc
+ <ul>
+ <li><em>lib/stkrc</em> - contains the Stacker compiler main program
+ </ul</li>
+ <li><em>sample</em> - contains the sample programs</li>
+ </ul>
+ </div>
+ <!-- ======================================================================= -->
+ <div class="doc_subsection"><a name="lexer"></a>The Lexer</div>
+ <div class="doc_text">
+ <p>See projects/Stacker/lib/compiler/Lexer.l</p>
+ </div>
+ <!-- ======================================================================= -->
+ <div class="doc_subsection"><a name="parser"></a>The Parser</div>
+ <div class="doc_text">
+ <p>See projects/Stacker/lib/compiler/StackerParser.y</p>
+ </div>
+ <!-- ======================================================================= -->
+ <div class="doc_subsection"><a name="compiler"></a>The Compiler</div>
+ <div class="doc_text">
+ <p>See projects/Stacker/lib/compiler/StackerCompiler.cpp</p>
+ </div>
+ <!-- ======================================================================= -->
+ <div class="doc_subsection"><a name="runtime"></a>The Runtime</div>
+ <div class="doc_text">
+ <p>See projects/Stacker/lib/runtime/stacker_rt.c</p>
+ </div>
+ <!-- ======================================================================= -->
+ <div class="doc_subsection"><a name="driver"></a>Compiler Driver</div>
+ <div class="doc_text">
+ <p>See projects/Stacker/tools/stkrc/stkrc.cpp</p>
+ </div>
+ <!-- ======================================================================= -->
+ <div class="doc_subsection"><a name="tests"></a>Test Programs</div>
+ <div class="doc_text">
+ <p>See projects/Stacker/test/*.st</p>
+ </div>
+ <!-- ======================================================================= -->
+ <div class="doc_subsection"> <a name="exercise">Exercise</a></div>
+ <div class="doc_text">
+ <p>As you may have noted from a careful inspection of the Built-In word
+ definitions, the ROLL word is not implemented. This word was left out of
+ Stacker on purpose so that it can be an exercise for the student. The exercise
+ is to implement the ROLL functionality (in your own workspace) and build a test
+ program for it. If you can implement ROLL, you understand Stacker and probably
+ a fair amount about LLVM since this is one of the more complicated Stacker
+ operations. The work will almost be completely limited to the
+ <a href="#compiler">compiler</a>.
+ <p>The ROLL word is already recognized by both the lexer and parser but ignored
+ by the compiler. That means you don't have to futz around with figuring out how
+ to get the keyword recognized. It already is. The part of the compiler that
+ you need to implement is the <code>ROLL</code> case in the
+ <code>StackerCompiler::handle_word(int)</code> method.</p> See the
+ implementations of PICK and SELECT in the same method to get some hints about
+ how to complete this exercise.<p>
+ <p>Good luck!</p>
+ </div>
+ <!-- ======================================================================= -->
+ <div class="doc_subsection"><a name="todo">Things Remaining To Be Done</a></div>
+ <div class="doc_text">
+ <p>The initial implementation of Stacker has several deficiencies. If you're
+ interested, here are some things that could be implemented better:</p>
+ <ol>
+ <li>Write an LLVM pass to compute the correct stack depth needed by the
+ program. Currently the stack is set to a fixed number which means programs
+ with large numbers of definitions might fail.</li>
+ <li>Write an LLVM pass to optimize the use of the global stack. The code
+ emitted currently is somewhat wasteful. It gets cleaned up a lot by existing
+ passes but more could be done.</li>
+ <li>Add -O -O1 -O2 and -O3 optimization switches to the compiler driver to
+ allow LLVM optimization without using "opt."</li>
+ <li>Make the compiler driver use the LLVM linking facilities (with IPO)
+ before depending on GCC to do the final link.</li>
+ <li>Clean up parsing. It doesn't handle errors very well.</li>
+ <li>Rearrange the StackerCompiler.cpp code to make better use of inserting
+ instructions before a block's terminating instruction. I didn't figure this
+ technique out until I was nearly done with LLVM. As it is, its a bad example
+ of how to insert instructions!</li>
+ <li>Provide for I/O to arbitrary files instead of just stdin/stdout.</li>
+ <li>Write additional built-in words; with inspiration from FORTH</li>
+ <li>Write additional sample Stacker programs.</li>
+ <li>Add your own compiler writing experiences and tips in the
+ <a href="#lessons">Lessons I Learned About LLVM</a> section.</li>
+ </ol>
+ </div>
+
+ <!-- *********************************************************************** -->
+
+ <hr>
+ <address>
+ <a href="http://jigsaw.w3.org/css-validator/check/referer"><img
+ src="http://jigsaw.w3.org/css-validator/images/vcss" alt="Valid CSS!"></a>
+ <a href="http://validator.w3.org/check/referer"><img
+ src="http://www.w3.org/Icons/valid-html401" alt="Valid HTML 4.01!"></a>
+
+ <a href="mailto:rspencer at x10sys.com">Reid Spencer</a><br>
+ <a href="http://llvm.cs.uiuc.edu">LLVM Compiler Infrastructure</a><br>
+ Last modified: $Date: 2004/08/13 22:03:04 $
+ </address>
+
+ </body>
+ </html>
Index: llvm-www/releases/1.3/docs/SystemLibrary.html
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*** 0 ****
--- 1,203 ----
+ <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"
+ "http://www.w3.org/TR/html4/strict.dtd">
+ <html>
+ <head>
+ <title>System Library</title>
+ <link rel="stylesheet" href="llvm.css" type="text/css">
+ </head>
+ <body>
+
+ <div class="doc_title">System Library</div>
+
+ <div class="doc_warning">
+ <p>Warning: This document is a work in progress.</p>
+ </div>
+
+ <ul>
+ <li><a href="#abstract">Abstract</a></li>
+ <li><a href="#requirements">System Library Requirements</a>
+ <ol>
+ <li><a href="#headers">Hide System Header Files</a></li>
+ <li><a href="#nofunc">No Exposed Functions</a></li>
+ <li><a href="#nodata">No Exposed Data</a></li>
+ <li><a href="#xcptns">No Exceptions</a></li>
+ <li><a href="#errors">Standard Error Codes</a></li>
+ <li><a href="#overhead">Minimize Overhead</a></li>
+ </ol></li>
+ <li><a href="#design">System Library Design</a>
+ <ol>
+ <li><a href="#opaque">Use Opaque Classes</a></li>
+ <li><a href="#common">Common Implementations</a></li>
+ <li><a href="#multi_imps">Multiple Implementations</a></li>
+ <li><a href="#lowlevel">Use Low Level Interfaces</a></li>
+ <li><a href="#memalloc">No Memory Allocation</a></li>
+ <li><a href="#virtuals">No Virtual Methods</a></li>
+ </ol></li>
+ <li><a href="#detail">System Library Details</a>
+ <ol>
+ <li><a href="#bug">Tracking Bugzilla Bug: 351</a></li>
+ <li><a href="#refimpl">Reference Implementatation</a></li>
+ </ol></li>
+ </ul>
+
+ <div class="doc_author">
+ <p>Written by <a href="rspencer at x10sys.com">Reid Spencer</a></p>
+ </div>
+
+
+ <!-- *********************************************************************** -->
+ <div class="doc_section"><a name="abstract">Abstract</a></div>
+ <div class="doc_text">
+ <p>This document describes the requirements, design, and implementation
+ details of LLVM's System Library. The library is composed of the header files
+ in <tt>llvm/include/llvm/System</tt> and the source files in
+ <tt>llvm/lib/System</tt>. The goal of this library is to completely shield
+ LLVM from the variations in operating system interfaces. By centralizing
+ LLVM's use of operating system interfaces, we make it possible for the LLVM
+ tool chain and runtime libraries to be more easily ported to new platforms.
+ The library also unclutters the rest of LLVM from #ifdef use and special
+ cases for specific operating systems.</p>
+ <p>The System Library was donated to LLVM by Reid Spencer who formulated the
+ original design as part of the eXtensible Programming System (XPS) which is
+ based, in part, on LLVM.</p>
+ </div>
+
+ <!-- *********************************************************************** -->
+ <div class="doc_section">
+ <a name="requirements">System Library Requirements</a>
+ </div>
+ <div class="doc_text">
+ <p>The System library's requirements are aimed at shielding LLVM from the
+ variations in operating system interfaces. The following sections define the
+ requirements needed to fulfill this objective.</p>
+ </div>
+
+ <!-- ======================================================================= -->
+ <div class="doc_subsection"><a name="headers">Hide System Header Files</a></div>
+ <div class="doc_text">
+ <p>To be written.</p>
+ </div>
+
+ <!-- ======================================================================= -->
+ <div class="doc_subsection"><a name="nofunc">No Exposed Functions</a></div>
+ <div class="doc_text">
+ <p>To be written.</p>
+ </div>
+
+ <!-- ======================================================================= -->
+ <div class="doc_subsection"><a name="nodata">No Exposed Data</a></div>
+ <div class="doc_text">
+ <p>To be written.</p>
+ </div>
+
+ <!-- ======================================================================= -->
+ <div class="doc_subsection"><a name="xcptns">No Exceptions</a></div>
+ <div class="doc_text">
+ <p>To be written.</p>
+ </div>
+
+ <!-- ======================================================================= -->
+ <div class="doc_subsection"><a name="errors">Standard Error Codes</a></div>
+ <div class="doc_text">
+ <p>To be written.</p>
+ </div>
+
+ <!-- ======================================================================= -->
+ <div class="doc_subsection"><a name="overhead">Minimize Overhead</a></div>
+ <div class="doc_text">
+ <p>To be written.</p>
+ </div>
+
+ <!-- *********************************************************************** -->
+ <div class="doc_section"><a name="design">System Library Design</a></div>
+ <div class="doc_text">
+ <p>In order to fulfill the requirements of the system library, strict design
+ objectives must be maintained in the library as it evolves. The goal here
+ is to provide interfaces to operating system concepts (files, memory maps,
+ sockets, signals, locking, etc) efficiently and in such a way that the
+ remainder of LLVM is completely operating system agnostic.</p>
+ </div>
+
+ <!-- ======================================================================= -->
+ <div class="doc_subsection"><a name="opaque">Use Opaque Classes</a></div>
+ <div class="doc_text">
+ <p>no public data</p>
+ <p>onlyprimitive typed private/protected data</p>
+ <p>data size is "right" for platform, not max of all platforms</p>
+ <p>each class corresponds to O/S concept</p>
+ </div>
+
+ <!-- ======================================================================= -->
+ <div class="doc_subsection"><a name="common">Common Implementations</a></div>
+ <div class="doc_text">
+ <p>To be written.</p>
+ </div>
+
+ <!-- ======================================================================= -->
+ <div class="doc_subsection">
+ <a name="multi_imps">Multiple Implementations</a>
+ </div>
+ <div class="doc_text">
+ <p>To be written.</p>
+ </div>
+
+ <!-- ======================================================================= -->
+ <div class="doc_subsection">
+ <a name="low_level">Use Low Level Interfaces</a>
+ </div>
+ <div class="doc_text">
+ <p>To be written.</p>
+ </div>
+
+ <!-- ======================================================================= -->
+ <div class="doc_subsection"><a name="memalloc">No Memory Allocation</a></div>
+ <div class="doc_text">
+ <p>To be written.</p>
+ </div>
+
+ <!-- ======================================================================= -->
+ <div class="doc_subsection"><a name="virtuals">No Virtual Methods</a></div>
+ <div class="doc_text">
+ <p>To be written.</p>
+ </div>
+
+ <!-- *********************************************************************** -->
+ <div class="doc_section"><a name="detail">System Library Details</a></div>
+ <div class="doc_text">
+ <p>To be written.</p>
+ </div>
+
+ <!-- ======================================================================= -->
+ <div class="doc_subsection"><a name="bug">Bug 351</a></div>
+ <div class="doc_text">
+ <p>See <a href="http://llvm.cs.uiuc.edu/PR351">bug 351</a>
+ for further details on the progress of this work</p>
+ </div>
+
+ <!-- ======================================================================= -->
+ <div class="doc_subsection">
+ <a name="refimpl">Reference Implementation</a>
+ </div>
+ <div class="doc_text">
+ <p>The <tt>linux</tt> implementation of the system library will always be the
+ reference implementation. This means that (a) the concepts defined by the
+ linux must be identically replicated in the other implementations and (b) the
+ linux implementation must always be complete (provide implementations for all
+ concepts).</p>
+ </div>
+
+ <!-- *********************************************************************** -->
+
+ <hr>
+ <address>
+ <a href="http://jigsaw.w3.org/css-validator/check/referer"><img
+ src="http://jigsaw.w3.org/css-validator/images/vcss" alt="Valid CSS!"></a>
+ <a href="http://validator.w3.org/check/referer"><img
+ src="http://www.w3.org/Icons/valid-html401" alt="Valid HTML 4.01!"></a>
+
+ <a href="mailto:rspencer at x10sys.com">Reid Spencer</a><br>
+ <a href="http://llvm.cs.uiuc.edu">LLVM Compiler Infrastructure</a><br>
+ Last modified: $Date: 2004/08/13 22:03:04 $
+ </address>
+ </body>
+ </html>
Index: llvm-www/releases/1.3/docs/TableGenFundamentals.html
diff -c /dev/null llvm-www/releases/1.3/docs/TableGenFundamentals.html:1.1
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*** 0 ****
--- 1,565 ----
+ <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"
+ "http://www.w3.org/TR/html4/strict.dtd">
+ <html>
+ <head>
+ <title>TableGen Fundamentals</title>
+ <link rel="stylesheet" href="llvm.css" type="text/css">
+ </head>
+ <body>
+
+ <div class="doc_title">TableGen Fundamentals</div>
+
+ <div class="doc_text">
+ <ul>
+ <li><a href="#introduction">Introduction</a>
+ <ol>
+ <li><a href="#concepts">Basic concepts</a></li>
+ <li><a href="#example">An example record</a></li>
+ <li><a href="#running">Running TableGen</a></li>
+ </ol></li>
+ <li><a href="#syntax">TableGen syntax</a>
+ <ol>
+ <li><a href="#primitives">TableGen primitives</a>
+ <ol>
+ <li><a href="#comments">TableGen comments</a></li>
+ <li><a href="#types">The TableGen type system</a></li>
+ <li><a href="#values">TableGen values and expressions</a></li>
+ </ol></li>
+ <li><a href="#classesdefs">Classes and definitions</a>
+ <ol>
+ <li><a href="#valuedef">Value definitions</a></li>
+ <li><a href="#recordlet">'let' expressions</a></li>
+ <li><a href="#templateargs">Class template arguments</a></li>
+ </ol></li>
+ <li><a href="#filescope">File scope entities</a>
+ <ol>
+ <li><a href="#include">File inclusion</a></li>
+ <li><a href="#globallet">'let' expressions</a></li>
+ </ol></li>
+ </ol></li>
+ <li><a href="#backends">TableGen backends</a>
+ <ol>
+ <li><a href="#">todo</a></li>
+ </ol></li>
+ </ul>
+ </div>
+
+ <div class="doc_author">
+ <p>Written by <a href="mailto:sabre at nondot.org">Chris Lattner</a></p>
+ </div>
+
+ <!-- *********************************************************************** -->
+ <div class="doc_section"><a name="introduction">Introduction</a></div>
+ <!-- *********************************************************************** -->
+
+ <div class="doc_text">
+
+ <p>TableGen's purpose is to help a human develop and maintain records of
+ domain-specific information. Because there may be a large number of these
+ records, it is specifically designed to allow writing flexible descriptions and
+ for common features of these records to be factored out. This reduces the
+ amount of duplication in the description, reduces the chance of error, and
+ makes it easier to structure domain specific information.</p>
+
+ <p>The core part of TableGen <a href="#syntax">parses a file</a>, instantiates
+ the declarations, and hands the result off to a domain-specific "<a
+ href="#backends">TableGen backend</a>" for processing. The current major user
+ of TableGen is the <a href="CodeGenerator.html">LLVM code generator</a>.</p>
+
+ <p>Note that if you work on TableGen much, and use emacs or vim, that you can
+ find an emacs "TableGen mode" and a vim language file in
+ <tt>llvm/utils/emacs</tt> and <tt>llvm/utils/vim</tt> directory of your LLVM
+ distribution, respectively.</p>
+
+ </div>
+
+ <!-- ======================================================================= -->
+ <div class="doc_subsection"><a name="running">Basic concepts</a></div>
+
+ <div class="doc_text">
+
+ <p>TableGen files consist of two key parts: 'classes' and 'definitions', both
+ of which are considered 'records'.</p>
+
+ <p><b>TableGen records</b> have a unique name, a list of values, and a list of
+ superclasses. The list of values is main data that TableGen builds for each
+ record, it is this that holds the domain specific information for the
+ application. The interpretation of this data is left to a specific <a
+ href="#backends">TableGen backend</a>, but the structure and format rules are
+ taken care of and fixed by TableGen.</p>
+
+ <p><b>TableGen definitions</b> are the concrete form of 'records'. These
+ generally do not have any undefined values, and are marked with the
+ '<tt>def</tt>' keyword.</p>
+
+ <p><b>TableGen classes</b> are abstract records that are used to build and
+ describe other records. These 'classes' allow the end-user to build
+ abstractions for either the domain they are targetting (such as "Register",
+ "RegisterClass", and "Instruction" in the LLVM code generator) or for the
+ implementor to help factor out common properties of records (such as "FPInst",
+ which is used to represent floating point instructions in the X86 backend).
+ TableGen keeps track of all of the classes that are used to build up a
+ definition, so the backend can find all definitions of a particular class, such
+ as "Instruction".</p>
+
+ </div>
+
+ <!-- ======================================================================= -->
+ <div class="doc_subsection"><a name="example">An example record</a></div>
+
+ <div class="doc_text">
+
+ <p>With no other arguments, TableGen parses the specified file and prints out
+ all of the classes, then all of the definitions. This is a good way to see what
+ the various definitions expand to fully. Running this on the <tt>X86.td</tt>
+ file prints this (at the time of this writing):</p>
+
+ <pre>
+ ...
+ <b>def</b> ADDrr8 { <i>// Instruction X86Inst I2A8 Pattern</i>
+ <b>string</b> Name = "add";
+ <b>string</b> Namespace = "X86";
+ <b>list</b><Register> Uses = [];
+ <b>list</b><Register> Defs = [];
+ <b>bit</b> isReturn = 0;
+ <b>bit</b> isBranch = 0;
+ <b>bit</b> isCall = 0;
+ <b>bit</b> isTwoAddress = 1;
+ <b>bit</b> isTerminator = 0;
+ <b>dag</b> Pattern = (set R8, (plus R8, R8));
+ <b>bits</b><8> Opcode = { 0, 0, 0, 0, 0, 0, 0, 0 };
+ Format Form = MRMDestReg;
+ <b>bits</b><5> FormBits = { 0, 0, 0, 1, 1 };
+ ArgType Type = Arg8;
+ <b>bits</b><3> TypeBits = { 0, 0, 1 };
+ <b>bit</b> hasOpSizePrefix = 0;
+ <b>bit</b> printImplicitUses = 0;
+ <b>bits</b><4> Prefix = { 0, 0, 0, 0 };
+ FPFormat FPForm = ?;
+ <b>bits</b><3> FPFormBits = { 0, 0, 0 };
+ }
+ ...
+ </pre>
+
+ <p>This definition corresponds to an 8-bit register-register add instruction in
+ the X86. The string after the '<tt>def</tt>' string indicates the name of the
+ record ("<tt>ADDrr8</tt>" in this case), and the comment at the end of the line
+ indicates the superclasses of the definition. The body of the record contains
+ all of the data that TableGen assembled for the record, indicating that the
+ instruction is part of the "X86" namespace, should be printed as "<tt>add</tt>"
+ in the assembly file, it is a two-address instruction, has a particular
+ encoding, etc. The contents and semantics of the information in the record is
+ specific to the needs of the X86 backend, and is only shown as an example.</p>
+
+ <p>As you can see, a lot of information is needed for every instruction
+ supported by the code generator, and specifying it all manually would be
+ unmaintainble, prone to bugs, and tiring to do in the first place. Because we
+ are using TableGen, all of the information was derived from the following
+ definition:</p>
+
+ <pre>
+ <b>def</b> ADDrr8 : I2A8<"add", 0x00, MRMDestReg>,
+ Pattern<(set R8, (plus R8, R8))>;
+ </pre>
+
+ <p>This definition makes use of the custom I2A8 (two address instruction with
+ 8-bit operand) class, which is defined in the X86-specific TableGen file to
+ factor out the common features that instructions of its class share. A key
+ feature of TableGen is that it allows the end-user to define the abstractions
+ they prefer to use when describing their information.</p>
+
+ </div>
+
+ <!-- ======================================================================= -->
+ <div class="doc_subsection"><a name="running">Running TableGen</a></div>
+
+ <div class="doc_text">
+
+ <p>TableGen runs just like any other LLVM tool. The first (optional) argument
+ specifies the file to read. If a filename is not specified, <tt>tblgen</tt>
+ reads from standard input.</p>
+
+ <p>To be useful, one of the <a href="#backends">TableGen backends</a> must be
+ used. These backends are selectable on the command line (type '<tt>tblgen
+ --help</tt>' for a list). For example, to get a list of all of the definitions
+ that subclass a particular type (which can be useful for building up an enum
+ list of these records), use the <tt>--print-enums</tt> option:</p>
+
+ <pre>
+ $ tblgen X86.td -print-enums -class=Register
+ AH, AL, AX, BH, BL, BP, BX, CH, CL, CX, DH, DI, DL, DX,
+ EAX, EBP, EBX, ECX, EDI, EDX, ESI, ESP, FP0, FP1, FP2, FP3, FP4, FP5, FP6,
+ SI, SP, ST0, ST1, ST2, ST3, ST4, ST5, ST6, ST7,
+
+ $ tblgen X86.td -print-enums -class=Instruction
+ ADCrr32, ADDri16, ADDri16b, ADDri32, ADDri32b, ADDri8, ADDrr16, ADDrr32,
+ ADDrr8, ADJCALLSTACKDOWN, ADJCALLSTACKUP, ANDri16, ANDri16b, ANDri32, ANDri32b,
+ ANDri8, ANDrr16, ANDrr32, ANDrr8, BSWAPr32, CALLm32, CALLpcrel32, ...
+ </pre>
+
+ <p>The default backend prints out all of the records, as described <a
+ href="#example">above</a>.</p>
+
+ <p>If you plan to use TableGen for some purpose, you will most likely have to
+ <a href="#backends">write a backend</a> that extracts the information specific
+ to what you need and formats it in the appropriate way.</p>
+
+ </div>
+
+
+ <!-- *********************************************************************** -->
+ <div class="doc_section"><a name="syntax">TableGen syntax</a></div>
+ <!-- *********************************************************************** -->
+
+ <div class="doc_text">
+ <p>TableGen doesn't care about the meaning of data (that is up to the backend
+ to define), but it does care about syntax, and it enforces a simple type system.
+ This section describes the syntax and the constructs allowed in a TableGen file.
+ </p>
+ </div>
+
+ <!-- ======================================================================= -->
+ <div class="doc_subsection"><a name="primitives">TableGen primitives</a></div>
+
+ <!-- -------------------------------------------------------------------------->
+ <div class="doc_subsubsection"><a name="comments">TableGen comments</a></div>
+
+ <div class="doc_text">
+ <p>TableGen supports BCPL style "<tt>//</tt>" comments, which run to the end of
+ the line, and it also supports <b>nestable</b> "<tt>/* */</tt>" comments.</p>
+ </div>
+
+ <!-- -------------------------------------------------------------------------->
+ <div class="doc_subsubsection">
+ <a name="types">The TableGen type system</a>
+ </div>
+
+ <div class="doc_text">
+ <p>TableGen files are strongly typed, in a simple (but complete) type-system.
+ These types are used to perform automatic conversions, check for errors, and to
+ help interface designers constrain the input that they allow. Every <a
+ href="#valuedef">value definition</a> is required to have an associated type.
+ </p>
+
+ <p>TableGen supports a mixture of very low-level types (such as <tt>bit</tt>)
+ and very high-level types (such as <tt>dag</tt>). This flexibility is what
+ allows it to describe a wide range of information conveniently and compactly.
+ The TableGen types are:</p>
+
+ <ul>
+ <li>"<tt><b>bit</b></tt>" - A 'bit' is a boolean value that can hold either 0 or
+ 1.</li>
+
+ <li>"<tt><b>int</b></tt>" - The 'int' type represents a simple 32-bit integer
+ value, such as 5.</li>
+
+ <li>"<tt><b>string</b></tt>" - The 'string' type represents an ordered sequence
+ of characters of arbitrary length.</li>
+
+ <li>"<tt><b>bits</b><n></tt>" - A 'bits' type is an arbitrary, but fixed,
+ size integer that is broken up into individual bits. This type is useful
+ because it can handle some bits being defined while others are undefined.</li>
+
+ <li>"<tt><b>list</b><ty></tt>" - This type represents a list whose
+ elements are some other type. The contained type is arbitrary: it can even be
+ another list type.</li>
+
+ <li>Class type - Specifying a class name in a type context means that the
+ defined value must be a subclass of the specified class. This is useful in
+ conjunction with the "list" type, for example, to constrain the elements of the
+ list to a common base class (e.g., a <tt><b>list</b><Register></tt> can
+ only contain definitions derived from the "<tt>Register</tt>" class).</li>
+
+ <li>"<tt><b>code</b></tt>" - This represents a big hunk of text. NOTE: I don't
+ remember why this is distinct from string!</li>
+
+ <li>"<tt><b>dag</b></tt>" - This type represents a nestable directed graph of
+ elements.</li>
+ </ul>
+
+ <p>To date, these types have been sufficient for describing things that
+ TableGen has been used for, but it is straight-forward to extend this list if
+ needed.</p>
+
+ </div>
+
+ <!-- -------------------------------------------------------------------------->
+ <div class="doc_subsubsection">
+ <a name="values">TableGen values and expressions</a>
+ </div>
+
+ <div class="doc_text">
+
+ <p>TableGen allows for a pretty reasonable number of different expression forms
+ when building up values. These forms allow the TableGen file to be written in a
+ natural syntax and flavor for the application. The current expression forms
+ supported include:</p>
+
+ <ul>
+ <li><tt>?</tt> - uninitialized field</li>
+ <li><tt>0b1001011</tt> - binary integer value</li>
+ <li><tt>07654321</tt> - octal integer value (indicated by a leading 0)</li>
+ <li><tt>7</tt> - decimal integer value</li>
+ <li><tt>0x7F</tt> - hexadecimal integer value</li>
+ <li><tt>"foo"</tt> - string value</li>
+ <li><tt>[{ ... }]</tt> - code fragment</li>
+ <li><tt>[ X, Y, Z ]</tt> - list value.</li>
+ <li><tt>{ a, b, c }</tt> - initializer for a "bits<3>" value</li>
+ <li><tt>value</tt> - value reference</li>
+ <li><tt>value{17}</tt> - access to one bit of a value</li>
+ <li><tt>value{15-17}</tt> - access to multiple bits of a value</li>
+ <li><tt>DEF</tt> - reference to a record definition</li>
+ <li><tt>X.Y</tt> - reference to the subfield of a value</li>
+ <li><tt>list[4-7,17,2-3]</tt> - A slice of the 'list' list, including elements
+ 4,5,6,7,17,2, and 3 from it. Elements may be included multiple times.</li>
+ <li><tt>(DEF a, b)</tt> - a dag value. The first element is required to be a
+ record definition, the remaining elements in the list may be arbitrary other
+ values, including nested `<tt>dag</tt>' values.</li>
+ </ul>
+
+ <p>Note that all of the values have rules specifying how they convert to values
+ for different types. These rules allow you to assign a value like "7" to a
+ "bits<4>" value, for example.</p>
+
+ </div>
+
+ <!-- ======================================================================= -->
+ <div class="doc_subsection">
+ <a name="classesdefs">Classes and definitions</a>
+ </div>
+
+ <div class="doc_text">
+
+ <p>As mentioned in the <a href="#concepts">intro</a>, classes and definitions
+ (collectively known as 'records') in TableGen are the main high-level unit of
+ information that TableGen collects. Records are defined with a <tt>def</tt> or
+ <tt>class</tt> keyword, the record name, and an optional list of "<a
+ href="#templateargs">template arguments</a>". If the record has superclasses,
+ they are specified as a comma seperated list that starts with a colon character
+ (":"). If <a href="#valuedef">value definitions</a> or <a href="#recordlet">let
+ expressions</a> are needed for the class, they are enclosed in curly braces
+ ("{}"); otherwise, the record ends with a semicolon. Here is a simple TableGen
+ file:</p>
+
+ <pre>
+ <b>class</b> C { <b>bit</b> V = 1; }
+ <b>def</b> X : C;
+ <b>def</b> Y : C {
+ <b>string</b> Greeting = "hello";
+ }
+ </pre>
+
+ <p>This example defines two definitions, <tt>X</tt> and <tt>Y</tt>, both of
+ which derive from the <tt>C</tt> class. Because of this, they both get the
+ <tt>V</tt> bit value. The <tt>Y</tt> definition also gets the Greeting member
+ as well.</p>
+
+ <p>In general, classes are useful for collecting together the commonality
+ between a group of records and isolating it in a single place. Also, classes
+ permit the specification of default values for their subclasses, allowing the
+ subclasses to override them as they wish.</p>
+
+ </div>
+
+ <!---------------------------------------------------------------------------->
+ <div class="doc_subsubsection">
+ <a name="valuedef">Value definitions</a>
+ </div>
+
+ <div class="doc_text">
+ <p>Value definitions define named entries in records. A value must be defined
+ before it can be referred to as the operand for another value definition or
+ before the value is reset with a <a href="#recordlet">let expression</a>. A
+ value is defined by specifying a <a href="#types">TableGen type</a> and a name.
+ If an initial value is available, it may be specified after the type with an
+ equal sign. Value definitions require terminating semicolons.</p>
+ </div>
+
+ <!-- -------------------------------------------------------------------------->
+ <div class="doc_subsubsection">
+ <a name="recordlet">'let' expressions</a>
+ </div>
+
+ <div class="doc_text">
+ <p>A record-level let expression is used to change the value of a value
+ definition in a record. This is primarily useful when a superclass defines a
+ value that a derived class or definition wants to override. Let expressions
+ consist of the '<tt>let</tt>' keyword followed by a value name, an equal sign
+ ("="), and a new value. For example, a new class could be added to the example
+ above, redefining the <tt>V</tt> field for all of its subclasses:</p>
+
+ <pre>
+ <b>class</b> D : C { let V = 0; }
+ <b>def</b> Z : D;
+ </pre>
+
+ <p>In this case, the <tt>Z</tt> definition will have a zero value for its "V"
+ value, despite the fact that it derives (indirectly) from the <tt>C</tt> class,
+ because the <tt>D</tt> class overrode its value.</p>
+
+ </div>
+
+ <!-- -------------------------------------------------------------------------->
+ <div class="doc_subsubsection">
+ <a name="templateargs">Class template arguments</a>
+ </div>
+
+ <div class="doc_text">
+ <p>TableGen permits the definition of parameterized classes as well as normal
+ concrete classes. Parameterized TableGen classes specify a list of variable
+ bindings (which may optionally have defaults) that are bound when used. Here is
+ a simple example:</p>
+
+ <pre>
+ <b>class</b> FPFormat<<b>bits</b><3> val> {
+ <b>bits</b><3> Value = val;
+ }
+ <b>def</b> NotFP : FPFormat<0>;
+ <b>def</b> ZeroArgFP : FPFormat<1>;
+ <b>def</b> OneArgFP : FPFormat<2>;
+ <b>def</b> OneArgFPRW : FPFormat<3>;
+ <b>def</b> TwoArgFP : FPFormat<4>;
+ <b>def</b> SpecialFP : FPFormat<5>;
+ </pre>
+
+ <p>In this case, template arguments are used as a space efficient way to specify
+ a list of "enumeration values", each with a "Value" field set to the specified
+ integer.</p>
+
+ <p>The more esoteric forms of <a href="#values">TableGen expressions</a> are
+ useful in conjunction with template arguments. As an example:</p>
+
+ <pre>
+ <b>class</b> ModRefVal<<b>bits</b><2> val> {
+ <b>bits</b><2> Value = val;
+ }
+
+ <b>def</b> None : ModRefVal<0>;
+ <b>def</b> Mod : ModRefVal<1>;
+ <b>def</b> Ref : ModRefVal<2>;
+ <b>def</b> ModRef : ModRefVal<3>;
+
+ <b>class</b> Value<ModRefVal MR> {
+ <i>// decode some information into a more convenient format, while providing
+ // a nice interface to the user of the "Value" class.</i>
+ <b>bit</b> isMod = MR.Value{0};
+ <b>bit</b> isRef = MR.Value{1};
+
+ <i>// other stuff...</i>
+ }
+
+ <i>// Example uses</i>
+ <b>def</b> bork : Value<Mod>;
+ <b>def</b> zork : Value<Ref>;
+ <b>def</b> hork : Value<ModRef>;
+ </pre>
+
+ <p>This is obviously a contrived example, but it shows how template arguments
+ can be used to decouple the interface provided to the user of the class from the
+ actual internal data representation expected by the class. In this case,
+ running <tt>tblgen</tt> on the example prints the following definitions:</p>
+
+ <pre>
+ <b>def</b> bork { <i>// Value</i>
+ bit isMod = 1;
+ bit isRef = 0;
+ }
+ <b>def</b> hork { <i>// Value</i>
+ bit isMod = 1;
+ bit isRef = 1;
+ }
+ <b>def</b> zork { <i>// Value</i>
+ bit isMod = 0;
+ bit isRef = 1;
+ }
+ </pre>
+
+ <p> This shows that TableGen was able to dig into the argument and extract a
+ piece of information that was requested by the designer of the "Value" class.
+ For more realistic examples, please see existing users of TableGen, such as the
+ X86 backend.</p>
+
+ </div>
+
+ <!-- ======================================================================= -->
+ <div class="doc_subsection">
+ <a name="filescope">File scope entities</a>
+ </div>
+
+ <!-- -------------------------------------------------------------------------->
+ <div class="doc_subsubsection">
+ <a name="include">File inclusion</a>
+ </div>
+
+ <div class="doc_text">
+ <p>TableGen supports the '<tt>include</tt>' token, which textually substitutes
+ the specified file in place of the include directive. The filename should be
+ specified as a double quoted string immediately after the '<tt>include</tt>'
+ keyword. Example:</p>
+
+ <pre>
+ <b>include</b> "foo.td"
+ </pre>
+
+ </div>
+
+ <!-- -------------------------------------------------------------------------->
+ <div class="doc_subsubsection">
+ <a name="globallet">'let' expressions</a>
+ </div>
+
+ <div class="doc_text">
+ <p> "let" expressions at file scope are similar to <a href="#recordlet">"let"
+ expressions within a record</a>, except they can specify a value binding for
+ multiple records at a time, and may be useful in certain other cases.
+ File-scope let expressions are really just another way that TableGen allows the
+ end-user to factor out commonality from the records.</p>
+
+ <p>File-scope "let" expressions take a comma-seperated list of bindings to
+ apply, and one of more records to bind the values in. Here are some
+ examples:</p>
+
+ <pre>
+ <b>let</b> isTerminator = 1, isReturn = 1 <b>in</b>
+ <b>def</b> RET : X86Inst<"ret", 0xC3, RawFrm, NoArg>;
+
+ <b>let</b> isCall = 1 <b>in</b>
+ <i>// All calls clobber the non-callee saved registers...</i>
+ <b>let</b> Defs = [EAX, ECX, EDX, FP0, FP1, FP2, FP3, FP4, FP5, FP6] in {
+ <b>def</b> CALLpcrel32 : X86Inst<"call", 0xE8, RawFrm, NoArg>;
+ <b>def</b> CALLr32 : X86Inst<"call", 0xFF, MRMS2r, Arg32>;
+ <b>def</b> CALLm32 : X86Inst<"call", 0xFF, MRMS2m, Arg32>;
+ }
+ </pre>
+
+ <p>File-scope "let" expressions are often useful when a couple of definitions
+ need to be added to several records, and the records do not otherwise need to be
+ opened, as in the case with the CALL* instructions above.</p>
+ </div>
+
+ <!-- *********************************************************************** -->
+ <div class="doc_section"><a name="backends">TableGen backends</a></div>
+ <!-- *********************************************************************** -->
+
+ <div class="doc_text">
+ <p>How they work, how to write one. This section should not contain details
+ about any particular backend, except maybe -print-enums as an example. This
+ should highlight the APIs in <tt>TableGen/Record.h</tt>.</p>
+ </div>
+
+ <!-- *********************************************************************** -->
+
+ <hr>
+ <address>
+ <a href="http://jigsaw.w3.org/css-validator/check/referer"><img
+ src="http://jigsaw.w3.org/css-validator/images/vcss" alt="Valid CSS!"></a>
+ <a href="http://validator.w3.org/check/referer"><img
+ src="http://www.w3.org/Icons/valid-html401" alt="Valid HTML 4.01!" /></a>
+
+ <a href="mailto:sabre at nondot.org">Chris Lattner</a><br>
+ <a href="http://llvm.cs.uiuc.edu">LLVM Compiler Infrastructure</a><br>
+ Last modified: $Date: 2004/08/13 22:03:04 $
+ </address>
+
+ </body>
+ </html>
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+ <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"
+ "http://www.w3.org/TR/html4/strict.dtd">
+ <html>
+ <head>
+ <title>LLVM Test Suite Guide</title>
+ <link rel="stylesheet" href="llvm.css" type="text/css">
+ </head>
+ <body>
+
+ <div class="doc_title">
+ LLVM Test Suite Guide
+ </div>
+
+ <ol>
+ <li><a href="#overview">Overview</a></li>
+ <li><a href="#Requirements">Requirements</a></li>
+ <li><a href="#quick">Quick Start</a></li>
+ <li><a href="#org">LLVM Test Suite Organization</a>
+ <ul>
+ <li><a href="#codefragments">Code Fragments</a></li>
+ <li><a href="#wholeprograms">Whole Programs</a></li>
+ </ul></li>
+ <li><a href="#tree">LLVM Test Suite Tree</a></li>
+ <li><a href="#qmstructure">QMTest Structure</a></li>
+ <li><a href="#progstructure">Programs Structure</a></li>
+ <li><a href="#run">Running the LLVM Tests</a></li>
+ <li><a href="#nightly">Running the nightly tester</a></li>
+ </ol>
+
+ <div class="doc_author">
+ <p>Written by John T. Criswell</p>
+ </div>
+
+ <!--===============================================================-->
+ <div class="doc_section"><a name="overview">Overview</a></div>
+ <!--===============================================================-->
+
+ <div class="doc_text">
+
+ <p>This document is the reference manual for the LLVM test suite. It documents
+ the structure of the LLVM test suite, the tools needed to use it, and how to add
+ and run tests.</p>
+
+ </div>
+
+ <!--===============================================================-->
+ <div class="doc_section"><a name="Requirements">Requirements</a></div>
+ <!--===============================================================-->
+
+ <div class="doc_text">
+
+ <p>In order to use the LLVM test suite, you will need all of the software
+ required to build LLVM, plus the following:</p>
+
+ <dl>
+ <dt><a href="http://www.qmtest.com">QMTest</A></dt>
+ <dd>The LLVM test suite uses QMTest to organize and run tests. <b>Note:
+ you will need <a href="http://llvm.cs.uiuc.edu/qm-2.0.3.tar.gz">QMTest
+ 2.0.3 (source tar.gz file)</a> to be successful. The tests do not run with
+ any other version.</b></dd>
+
+ <dt><a href="http://www.python.org">Python</A></dt>
+ <dd>You will need a Python interpreter that works with QMTest. Python will
+ need zlib and SAX support enabled.</dd>
+ </dl>
+
+ </div>
+
+ <!--===============================================================-->
+ <div class="doc_section"><a name="quick">Quick Start</a></div>
+ <!--===============================================================-->
+
+ <div class="doc_text">
+
+ <p> The tests are located in the LLVM source tree under the directory
+ <tt>llvm/test</tt>. To run all of the tests in LLVM, use the Master Makefile in
+ that directory:</p>
+
+ <pre>
+ % gmake -C llvm/test
+ </pre>
+
+ <p>To run only the code fragment tests (i.e. those that do basic testing of
+ LLVM), run the tests organized by QMTest:</p>
+
+ <pre>
+ % gmake -C llvm/test qmtest
+ </pre>
+
+ <p>To run only the tests that compile and execute whole programs, run the
+ Programs tests:</p>
+
+ <pre>
+ % gmake -C llvm/test/Programs
+ </pre>
+
+ </div>
+
+ <!--===============================================================-->
+ <div class="doc_section"><a name="org">LLVM Test Suite Organization</a></div>
+ <!--===============================================================-->
+
+ <div class="doc_text">
+
+ <p>The LLVM test suite contains two major categories of tests: code
+ fragments and whole programs.</p>
+
+ </div>
+
+ <div class="doc_subsection"><a name="codefragments">Code Fragments</a>
+ </div>
+
+ <div class="doc_text">
+
+ <p>Code fragments are small pieces of code that test a specific feature of LLVM
+ or trigger a specific bug in LLVM. They are usually written in LLVM assembly
+ language, but can be written in other languages if the test targets a particular
+ language front end.</p>
+
+ <p>Code fragments are not complete programs, and they are never executed to
+ determine correct behavior.</p>
+
+ <p>The tests in the Features and Regression directories contain code
+ fragments.</p>
+
+ </div>
+
+ <div class="doc_subsection"><a name="wholeprograms">Whole Programs</a></div>
+
+ <div class="doc_text">
+
+ <p>Whole Programs are pieces of code which can be compiled and linked into a
+ stand-alone program that can be executed. These programs are generally written
+ in high level languages such as C or C++, but sometimes they are written
+ straight in LLVM assembly.</p>
+
+ <p>These programs are compiled and then executed using several different
+ methods (native compiler, LLVM C backend, LLVM JIT, LLVM native code generation,
+ etc). The output of these programs is compared to ensure that LLVM is compiling
+ the program correctly.</p>
+
+ <p>In addition to compiling and executing programs, whole program tests serve as
+ a way of benchmarking LLVM performance, both in terms of the efficiency of the
+ programs generated as well as the speed with which LLVM compiles, optimizes, and
+ generates code.</p>
+
+ <p>The Programs directory contains all tests which compile and benchmark whole
+ programs.</p>
+
+ </div>
+
+ <!--===============================================================-->
+ <div class="doc_section"><a name="tree">LLVM Test Suite Tree</a></div>
+ <!--===============================================================-->
+
+ <div class="doc_text">
+
+ <p>Each type of test in the LLVM test suite has its own directory. The major
+ subtrees of the test suite directory tree are as follows:</p>
+
+ <ul>
+ <li>Features
+ <p>This directory contains sample codes that test various features of the
+ LLVM language. These pieces of sample code are run through various
+ assembler, disassembler, and optimizer passes.</p>
+
+ <li>Regression
+ <p>This directory contains regression tests for LLVM. When a bug is found
+ in LLVM, a regression test containing just enough code to reproduce the
+ problem should be written and placed somewhere underneath this directory.
+ In most cases, this will be a small piece of LLVM assembly language code,
+ often distilled from an actual application or benchmark.</p>
+
+ <li>Programs
+ <p>The Programs directory contains programs that can be compiled with LLVM
+ and executed. These programs are compiled using the native compiler and
+ various LLVM backends. The output from the program compiled with the native
+ compiler is assumed correct; the results from the other programs are
+ compared to the native program output and pass if they match. </p>
+
+ <p> In addition for testing correctness, the Programs directory also
+ performs timing tests of various LLVM optimizations. It also records
+ compilation times for the compilers and the JIT. This information can be
+ used to compare the effectiveness of LLVM's optimizations and code
+ generation.</p>
+
+ <p>The Programs directory is subdivided into several smaller subdirectories:
+ </p>
+
+ <ul>
+ <li>Programs/SingleSource
+ <p>The SingleSource directory contains test programs that are only a
+ single source file in size. These are usually small benchmark programs
+ or small programs that calculate a particular value. Several such
+ programs are grouped together in each directory.</p></li>
+
+ <li>Programs/MultiSource
+ <p>The MultiSource directory contains subdirectories which contain
+ entire programs with multiple source files. Large benchmarks and whole
+ applications go here.</p></li>
+
+ <li>Programs/External
+ <p>The External directory contains Makefiles for building code that is
+ external to (i.e. not distributed with) LLVM. The most prominent member
+ of this directory is the SPEC 2000 benchmark suite. The presence and
+ location of these external programs is configured by the LLVM
+ <tt>configure</tt> script.</p></li>
+
+ </ul></li>
+
+ <li>QMTest
+ <p>This directory contains the QMTest information files. Inside this
+ directory are QMTest administration files and the Python code that
+ implements the LLVM test and database classes.</p>
+
+ </ul>
+
+ </div>
+
+ <!--===============================================================-->
+ <div class="doc_section"><a name="qmstructure">QMTest Structure</a></div>
+ <!--===============================================================-->
+
+ <div class="doc_text">
+
+ <p>The LLVM test suite is partially driven by QMTest and partially
+ driven by GNU Make. Specifically, the Features and Regression tests
+ are all driven by QMTest. The Programs directory is currently
+ driven by a set of Makefiles.</p>
+
+ <p>The QMTest system needs to have several pieces of information
+ available; these pieces of configuration information are known
+ collectively as the "context" in QMTest parlance. Since the context
+ for LLVM is relatively large, the master Makefile in llvm/test
+ sets it for you.</p>
+
+ <p>The LLVM database class makes the subdirectories of llvm/test a
+ QMTest test database. For each directory that contains tests driven by
+ QMTest, it knows what type of test the source file is and how to run it.</p>
+
+ <p>Hence, the QMTest namespace is essentially what you see in the
+ Feature and Regression directories, but there is some magic that
+ the database class performs (as described below).</p>
+
+ <p>The QMTest namespace is currently composed of the following tests and test
+ suites:</p>
+
+ <ul>
+ <li>Feature
+ <p>
+ These are the feature tests found in the Feature directory.
+ They are broken up into the following categories:
+ </p>
+ <ul>
+ <li>ad
+ <p>Assembler/Disassembler tests. These tests verify that a piece of LLVM
+ assembly language can be assembled into bytecode and then disassembled
+ into the original assembly language code. It does this several times to
+ ensure that assembled output can be disassembled and disassembler output
+ can be assembled. It also verifies that the give assembly language file
+ can be assembled correctly.</p></li>
+
+ <li>opt
+ <p>Optimizer tests. These tests verify that two of the optimizer passes
+ completely optimize a program (i.e. after a single pass, they cannot
+ optimize a program any further).</p></li>
+
+ <li>mc
+ <p> Machine code tests. These tests verify that the LLVM assembly
+ language file can be translated into native assembly code.</p></li>
+
+ <li>cc
+ <p>C code tests. These tests verify that the specified LLVM assembly
+ code can be converted into C source code using the C backend.</p></li>
+ </ul>
+
+ <p>The LLVM database class looks at every file in the Feature directory and
+ creates a fake test hierarchy containing
+ <tt>Feature.<testtype>.<testname></tt>. So, if you add an LLVM
+ assembly language file to the Feature directory, it actually creates 5 new
+ tests: assembler/disassembler, assembler, optimizer, machine code, and C code.
+ </p>
+
+ <li>Regression
+ <p>These are the regression tests. There is one suite for each
+ subdirectory of the Regression directory. If you add a new subdirectory
+ there, you will need to modify, at least, the <tt>RegressionMap</tt>
+ variable in <tt>QMTest/llvmdb.py</tt> so that QMTest knows how to run the
+ tests in the new subdirectory.</p>
+
+ </ul>
+
+ </div>
+
+ <!--===============================================================-->
+ <div class="doc_section"><a name="progstructure">Programs Structure</a></div>
+ <!--===============================================================-->
+
+ <div class="doc_text">
+
+ <p>As mentioned previously, the Programs tree in llvm/test provides three types
+ of tests: MultiSource, SingleSource, and External. Each tree is then subdivided
+ into several categories, including applications, benchmarks, regression tests,
+ code that is strange grammatically, etc. These organizations should be
+ relatively self explanatory.</p>
+
+ <p>In addition to the regular Programs tests, the Programs tree also provides a
+ mechanism for compiling the programs in different ways. If the variable TEST is
+ defined on the gmake command line, the test system will include a Makefile named
+ <tt>TEST.<value of TEST variable>.Makefile</tt>. This Makefile can modify
+ build rules to yield different results.</p>
+
+ <p>For example, the LLVM nightly tester uses <tt>TEST.nightly.Makefile</tt> to
+ create the nightly test reports. To run the nightly tests, run <tt>gmake
+ TEST=nightly</tt>.</p>
+
+ <p>There are several TEST Makefiles available in the tree. Some of them are
+ designed for internal LLVM research and will not work outside of the LLVM
+ research group. They may still be valuable, however, as a guide to writing your
+ own TEST Makefile for any optimization or analysis passes that you develop with
+ LLVM.</p>
+
+ </div>
+
+ <!--===============================================================-->
+ <div class="doc_section"><a name="run">Running the LLVM Tests</a></div>
+ <!--===============================================================-->
+
+ <div class="doc_text">
+
+ <p>First, all tests are executed within the LLVM object directory tree. They
+ <i>are not</i> executed inside of the LLVM source tree. This is because the
+ test suite creates temporary files during execution. </p>
+
+ <p>The master Makefile in llvm/test is capable of running both the QMTest driven
+ tests and the Programs tests. By default, it will run all of the tests.</p>
+
+ <p>To run only the QMTest driven tests, run <tt>gmake qmtest</tt> at the
+ command line in llvm/tests. To run a specific qmtest, suffix the test name with
+ ".t" when running gmake.</p>
+
+ <p>For example, to run the Regression.LLC tests, type <tt>gmake
+ Regression.LLC.t</tt> in llvm/tests.</p>
+
+ <p>Note that the Makefiles in llvm/test/Features and llvm/test/Regression are
+ gone. You must now use QMTest from the llvm/test directory to run them.</p>
+
+ <p>To run the Programs test, cd into the llvm/test/Programs directory and type
+ <tt>gmake</tt>. Alternatively, you can type <tt>gmake TEST=<type>
+ test</tt> to run one of the specialized tests in
+ llvm/test/Programs/TEST.<type>.Makefile. For example, you could run the
+ nightly tester tests using the following commands:</p>
+
+ <pre>
+ % cd llvm/test/Programs
+ % gmake TEST=nightly test
+ </pre>
+
+ <p>Regardless of which test you're running, the results are printed on standard
+ output and standard error. You can redirect these results to a file if you
+ choose.</p>
+
+ <p>Some tests are known to fail. Some are bugs that we have not fixed yet;
+ others are features that we haven't added yet (or may never add). In QMTest,
+ the result for such tests will be XFAIL (eXpected FAILure). In this way, you
+ can tell the difference between an expected and unexpected failure.</p>
+
+ <p>The Programs tests have no such feature as of this time. If the test passes,
+ only warnings and other miscellaneous output will be generated. If a test
+ fails, a large <program> FAILED message will be displayed. This will help
+ you separate benign warnings from actual test failures.</p>
+
+ </div>
+
+ <!--===============================================================-->
+ <div class="doc_section"><a name="nightly">Running the nightly tester</a></div>
+ <!--===============================================================-->
+
+ <div class="doc_text">
+
+ <p>
+ The <a href="http://llvm.cs.uiuc.edu/testresults/">LLVM Nightly Testers</a>
+ automatically check out an LLVM tree, build it, run the "nightly"
+ program test (described above) and all of the regression tests, then
+ delete the checked out tree. This tester is designed to ensure that
+ programs don't break as well as keep track of LLVM's progress over time.</p>
+
+ <p>
+ If you'd like to set up an instance of the nightly tester to run on your
+ machine, take a look at the comments at the top of the utils/NightlyTester.pl
+ file. We usually run it from a crontab entry that looks ilke this:
+ </p>
+
+ <pre>
+ 5 3 * * * LLVM_LIB_SEARCH_PATH=.../llvm-gcc/bytecode-libs $HOME/llvm/utils/NightlyTest.pl -parallel -enable-linscan ...CVSREPOSTRING... $HOME/buildtest-X86 $HOME/cvs/testresults-X86
+ </pre>
+
+ <p>
+ Take a look at the NightlyTest.pl file to see what all of the flags and
+ strings do. If you start running the nightly tests, please let us know and
+ we'll link your page to the global tester page. Thanks!
+ </p>
+
+ </div>
+
+ <!-- *********************************************************************** -->
+
+ <hr>
+ <address>
+ <a href="http://jigsaw.w3.org/css-validator/check/referer"><img
+ src="http://jigsaw.w3.org/css-validator/images/vcss" alt="Valid CSS!"></a>
+ <a href="http://validator.w3.org/check/referer"><img
+ src="http://www.w3.org/Icons/valid-html401" alt="Valid HTML 4.01!" /></a>
+
+ John T. Criswell<br>
+ <a href="http://llvm.cs.uiuc.edu">The LLVM Compiler Infrastructure</a><br>
+ Last modified: $Date: 2004/08/13 22:03:04 $
+ </address>
+ </body>
+ </html>
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+ <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"
+ "http://www.w3.org/TR/html4/strict.dtd">
+ <html>
+ <head>
+ <title>Writing an LLVM Pass</title>
+ <link rel="stylesheet" href="llvm.css" type="text/css">
+ </head>
+ <body>
+
+ <div class="doc_title">
+ Writing an LLVM Pass
+ </div>
+
+ <ol>
+ <li><a href="#introduction">Introduction - What is a pass?</a></li>
+ <li><a href="#quickstart">Quick Start - Writing hello world</a>
+ <ul>
+ <li><a href="#makefile">Setting up the build environment</a></li>
+ <li><a href="#basiccode">Basic code required</a></li>
+ <li><a href="#running">Running a pass with <tt>opt</tt>
+ or <tt>analyze</tt></a></li>
+ </ul></li>
+ <li><a href="#passtype">Pass classes and requirements</a>
+ <ul>
+ <li><a href="#ImmutablePass">The <tt>ImmutablePass</tt> class</a></li>
+ <li><a href="#Pass">The <tt>Pass</tt> class</a>
+ <ul>
+ <li><a href="#run">The <tt>run</tt> method</a></li>
+ </ul></li>
+ <li><a href="#FunctionPass">The <tt>FunctionPass</tt> class</a>
+ <ul>
+ <li><a href="#doInitialization_mod">The <tt>doInitialization(Module
+ &)</tt> method</a></li>
+ <li><a href="#runOnFunction">The <tt>runOnFunction</tt> method</a></li>
+ <li><a href="#doFinalization_mod">The <tt>doFinalization(Module
+ &)</tt> method</a></li>
+ </ul></li>
+ <li><a href="#BasicBlockPass">The <tt>BasicBlockPass</tt> class</a>
+ <ul>
+ <li><a href="#doInitialization_fn">The <tt>doInitialization(Function
+ &)</tt> method</a></li>
+ <li><a href="#runOnBasicBlock">The <tt>runOnBasicBlock</tt>
+ method</a></li>
+ <li><a href="#doFinalization_fn">The <tt>doFinalization(Function
+ &)</tt> method</a></li>
+ </ul></li>
+ <li><a href="#MachineFunctionPass">The <tt>MachineFunctionPass</tt>
+ class</a>
+ <ul>
+ <li><a href="#runOnMachineFunction">The
+ <tt>runOnMachineFunction(MachineFunction &)</tt> method</a></li>
+ </ul></li>
+ </ul>
+ <li><a href="#registration">Pass Registration</a>
+ <ul>
+ <li><a href="#print">The <tt>print</tt> method</a></li>
+ </ul></li>
+ <li><a href="#interaction">Specifying interactions between passes</a>
+ <ul>
+ <li><a href="#getAnalysisUsage">The <tt>getAnalysisUsage</tt>
+ method</a></li>
+ <li><a href="#AU::addRequired">The <tt>AnalysisUsage::addRequired<></tt> and <tt>AnalysisUsage::addRequiredTransitive<></tt> methods</a></li>
+ <li><a href="#AU::addPreserved">The <tt>AnalysisUsage::addPreserved<></tt> method</a></li>
+ <li><a href="#AU::examples">Example implementations of <tt>getAnalysisUsage</tt></a></li>
+ <li><a href="#getAnalysis">The <tt>getAnalysis<></tt> and <tt>getAnalysisToUpdate<></tt> methods</a></li>
+ </ul></li>
+ <li><a href="#analysisgroup">Implementing Analysis Groups</a>
+ <ul>
+ <li><a href="#agconcepts">Analysis Group Concepts</a></li>
+ <li><a href="#registerag">Using <tt>RegisterAnalysisGroup</tt></a></li>
+ </ul></li>
+ <li><a href="#passmanager">What PassManager does</a>
+ <ul>
+ <li><a href="#releaseMemory">The <tt>releaseMemory</tt> method</a></li>
+ </ul></li>
+ <li><a href="#debughints">Using GDB with dynamically loaded passes</a>
+ <ul>
+ <li><a href="#breakpoint">Setting a breakpoint in your pass</a></li>
+ <li><a href="#debugmisc">Miscellaneous Problems</a></li>
+ </ul></li>
+ <li><a href="#future">Future extensions planned</a>
+ <ul>
+ <li><a href="#SMP">Multithreaded LLVM</a></li>
+ <li><a href="#ModuleSource">A new <tt>ModuleSource</tt> interface</a></li>
+ <li><a href="#PassFunctionPass"><tt>Pass</tt>es requiring
+ <tt>FunctionPass</tt>es</a></li>
+ </ul></li>
+ </ol>
+
+ <div class="doc_author">
+ <p>Written by <a href="mailto:sabre at nondot.org">Chris Lattner</a></p>
+ </div>
+
+ <!-- *********************************************************************** -->
+ <div class="doc_section">
+ <a name="introduction">Introduction - What is a pass?</a>
+ </div>
+ <!-- *********************************************************************** -->
+
+ <div class="doc_text">
+
+ <p>The LLVM Pass Framework is an important part of the LLVM system, because LLVM
+ passes are where the interesting parts of the compiler exist. Passes perform
+ the transformations and optimizations that make up the compiler, they build
+ the analysis results that are used by these transformations, and they are, above
+ all, a structuring technique for compiler code.</p>
+
+ <p>All LLVM passes are subclasses of the <tt><a
+ href="http://llvm.cs.uiuc.edu/doxygen/classllvm_1_1Pass.html">Pass</a></tt>
+ class, which implement functionality by overriding virtual methods inherited
+ from <tt>Pass</tt>. Depending on how your pass works, you may be able to
+ inherit from the <tt><a
+ href="http://llvm.cs.uiuc.edu/doxygen/structllvm_1_1FunctionPass.html">FunctionPass</a></tt>
+ or <tt><a
+ href="http://llvm.cs.uiuc.edu/doxygen/structllvm_1_1BasicBlockPass.html">BasicBlockPass</a></tt>,
+ which gives the system more information about what your pass does, and how it
+ can be combined with other passes. One of the main features of the LLVM Pass
+ Framework is that it schedules passes to run in an efficient way based on the
+ constraints that your pass has.</p>
+
+ <p>We start by showing you how to construct a pass, everything from setting up
+ the code, to compiling, loading, and executing it. After the basics are down,
+ more advanced features are discussed.</p>
+
+ </div>
+
+ <!-- *********************************************************************** -->
+ <div class="doc_section">
+ <a name="quickstart">Quick Start - Writing hello world</a>
+ </div>
+ <!-- *********************************************************************** -->
+
+ <div class="doc_text">
+
+ <p>Here we describe how to write the "hello world" of passes. The "Hello" pass
+ is designed to simply print out the name of non-external functions that exist in
+ the program being compiled. It does not modify the program at all, just
+ inspects it. The source code and files for this pass are available in the LLVM
+ source tree in the <tt>lib/Transforms/Hello</tt> directory.</p>
+
+ </div>
+
+ <!-- ======================================================================= -->
+ <div class="doc_subsection">
+ <a name="makefile">Setting up the build environment</a>
+ </div>
+
+ <div class="doc_text">
+
+ <p>First thing you need to do is create a new directory somewhere in the LLVM
+ source base. For this example, we'll assume that you made
+ "<tt>lib/Transforms/Hello</tt>". The first thing you must do is set up a build
+ script (Makefile) that will compile the source code for the new pass. To do
+ this, copy this into "<tt>Makefile</tt>":</p>
+
+ <hr>
+
+ <pre>
+ # Makefile for hello pass
+
+ # Path to top level of LLVM heirarchy
+ LEVEL = ../../..
+
+ # Name of the library to build
+ LIBRARYNAME = hello
+
+ # Build a dynamically loadable shared object
+ SHARED_LIBRARY = 1
+
+ # Include the makefile implementation stuff
+ include $(LEVEL)/Makefile.common
+ </pre>
+
+ <p>This makefile specifies that all of the <tt>.cpp</tt> files in the current
+ directory are to be compiled and linked together into a
+ <tt>lib/Debug/libhello.so</tt> shared object that can be dynamically loaded by
+ the <tt>opt</tt> or <tt>analyze</tt> tools. If your operating system uses a
+ suffix other than .so (such as windows of Mac OS/X), the appropriate extension
+ will be used.</p>
+
+ <p>Now that we have the build scripts set up, we just need to write the code for
+ the pass itself.</p>
+
+ </div>
+
+ <!-- ======================================================================= -->
+ <div class="doc_subsection">
+ <a name="basiccode">Basic code required</a>
+ </div>
+
+ <div class="doc_text">
+
+ <p>Now that we have a way to compile our new pass, we just have to write it.
+ Start out with:</p>
+
+ <pre>
+ <b>#include</b> "<a href="http://llvm.cs.uiuc.edu/doxygen/Pass_8h-source.html">llvm/Pass.h</a>"
+ <b>#include</b> "<a href="http://llvm.cs.uiuc.edu/doxygen/Function_8h-source.html">llvm/Function.h</a>"
+ </pre>
+
+ <p>Which are needed because we are writing a <tt><a
+ href="http://llvm.cs.uiuc.edu/doxygen/classllvm_1_1Pass.html">Pass</a></tt>, and
+ we are operating on <tt><a
+ href="http://llvm.cs.uiuc.edu/doxygen/classllvm_1_1Function.html">Function</a></tt>'s.</p>
+
+ <p>Next we have:</p>
+ <pre>
+ <b>using namespace llvm;</b>
+ </pre>
+ <p>... which is required because the functions from the include files
+ live in the llvm namespace.
+ </p>
+
+ <p>Next we have:</p>
+
+ <pre>
+ <b>namespace</b> {
+ </pre>
+
+ <p>... which starts out an anonymous namespace. Anonymous namespaces are to C++
+ what the "<tt>static</tt>" keyword is to C (at global scope). It makes the
+ things declared inside of the anonymous namespace only visible to the current
+ file. If you're not familiar with them, consult a decent C++ book for more
+ information.</p>
+
+ <p>Next, we declare our pass itself:</p>
+
+ <pre>
+ <b>struct</b> Hello : <b>public</b> <a href="#FunctionPass">FunctionPass</a> {
+ </pre><p>
+
+ <p>This declares a "<tt>Hello</tt>" class that is a subclass of <tt><a
+ href="http://llvm.cs.uiuc.edu/doxygen/structllvm_1_1FunctionPass.html">FunctionPass</a></tt>.
+ The different builtin pass subclasses are described in detail <a
+ href="#passtype">later</a>, but for now, know that <a
+ href="#FunctionPass"><tt>FunctionPass</tt></a>'s operate a function at a
+ time.</p>
+
+ <pre>
+ <b>virtual bool</b> <a href="#runOnFunction">runOnFunction</a>(Function &F) {
+ std::cerr << "<i>Hello: </i>" << F.getName() << "\n";
+ <b>return false</b>;
+ }
+ }; <i>// end of struct Hello</i>
+ </pre>
+
+ <p>We declare a "<a href="#runOnFunction"><tt>runOnFunction</tt></a>" method,
+ which overloads an abstract virtual method inherited from <a
+ href="#FunctionPass"><tt>FunctionPass</tt></a>. This is where we are supposed
+ to do our thing, so we just print out our message with the name of each
+ function.</p>
+
+ <pre>
+ RegisterOpt<Hello> X("<i>hello</i>", "<i>Hello World Pass</i>");
+ } <i>// end of anonymous namespace</i>
+ </pre>
+
+ <p>Lastly, we register our class <tt>Hello</tt>, giving it a command line
+ argument "<tt>hello</tt>", and a name "<tt>Hello World Pass</tt>". There are
+ several different ways of <a href="#registration">registering your pass</a>,
+ depending on what it is to be used for. For "optimizations" we use the
+ <tt>RegisterOpt</tt> template.</p>
+
+ <p>As a whole, the <tt>.cpp</tt> file looks like:</p>
+
+ <pre>
+ <b>#include</b> "<a href="http://llvm.cs.uiuc.edu/doxygen/Pass_8h-source.html">llvm/Pass.h</a>"
+ <b>#include</b> "<a href="http://llvm.cs.uiuc.edu/doxygen/Function_8h-source.html">llvm/Function.h</a>"
+
+ <b>using namespace llvm;</b>
+
+ <b>namespace</b> {
+ <b>struct Hello</b> : <b>public</b> <a href="#FunctionPass">FunctionPass</a> {
+ <b>virtual bool</b> <a href="#runOnFunction">runOnFunction</a>(Function &F) {
+ std::cerr << "<i>Hello: </i>" << F.getName() << "\n";
+ <b>return false</b>;
+ }
+ };
+
+ RegisterOpt<Hello> X("<i>hello</i>", "<i>Hello World Pass</i>");
+ }
+ </pre>
+
+ <p>Now that it's all together, compile the file with a simple "<tt>gmake</tt>"
+ command in the local directory and you should get a new
+ "<tt>lib/Debug/libhello.so</tt> file. Note that everything in this file is
+ contained in an anonymous namespace: this reflects the fact that passes are self
+ contained units that do not need external interfaces (although they can have
+ them) to be useful.</p>
+
+ </div>
+
+ <!-- ======================================================================= -->
+ <div class="doc_subsection">
+ <a name="running">Running a pass with <tt>opt</tt> or <tt>analyze</tt></a>
+ </div>
+
+ <div class="doc_text">
+
+ <p>Now that you have a brand new shiny shared object file, we can use the
+ <tt>opt</tt> command to run an LLVM program through your pass. Because you
+ registered your pass with the <tt>RegisterOpt</tt> template, you will be able to
+ use the <tt>opt</tt> tool to access it, once loaded.</p>
+
+ <p>To test it, follow the example at the end of the <a
+ href="GettingStarted.html">Getting Started Guide</a> to compile "Hello World" to
+ LLVM. We can now run the bytecode file (<tt>hello.bc</tt>) for the program
+ through our transformation like this (or course, any bytecode file will
+ work):</p>
+
+ <pre>
+ $ opt -load ../../../lib/Debug/libhello.so -hello < hello.bc > /dev/null
+ Hello: __main
+ Hello: puts
+ Hello: main
+ </pre>
+
+ <p>The '<tt>-load</tt>' option specifies that '<tt>opt</tt>' should load your
+ pass as a shared object, which makes '<tt>-hello</tt>' a valid command line
+ argument (which is one reason you need to <a href="#registration">register your
+ pass</a>). Because the hello pass does not modify the program in any
+ interesting way, we just throw away the result of <tt>opt</tt> (sending it to
+ <tt>/dev/null</tt>).</p>
+
+ <p>To see what happened to the other string you registered, try running
+ <tt>opt</tt> with the <tt>--help</tt> option:</p>
+
+ <pre>
+ $ opt -load ../../../lib/Debug/libhello.so --help
+ OVERVIEW: llvm .bc -> .bc modular optimizer
+
+ USAGE: opt [options] <input bytecode>
+
+ OPTIONS:
+ Optimizations available:
+ ...
+ -funcresolve - Resolve Functions
+ -gcse - Global Common Subexpression Elimination
+ -globaldce - Dead Global Elimination
+ <b>-hello - Hello World Pass</b>
+ -indvars - Canonicalize Induction Variables
+ -inline - Function Integration/Inlining
+ -instcombine - Combine redundant instructions
+ ...
+ </pre>
+
+ <p>The pass name get added as the information string for your pass, giving some
+ documentation to users of <tt>opt</tt>. Now that you have a working pass, you
+ would go ahead and make it do the cool transformations you want. Once you get
+ it all working and tested, it may become useful to find out how fast your pass
+ is. The <a href="#passManager"><tt>PassManager</tt></a> provides a nice command
+ line option (<tt>--time-passes</tt>) that allows you to get information about
+ the execution time of your pass along with the other passes you queue up. For
+ example:</p>
+
+ <pre>
+ $ opt -load ../../../lib/Debug/libhello.so -hello -time-passes < hello.bc > /dev/null
+ Hello: __main
+ Hello: puts
+ Hello: main
+ ===============================================================================
+ ... Pass execution timing report ...
+ ===============================================================================
+ Total Execution Time: 0.02 seconds (0.0479059 wall clock)
+
+ ---User Time--- --System Time-- --User+System-- ---Wall Time--- --- Pass Name ---
+ 0.0100 (100.0%) 0.0000 ( 0.0%) 0.0100 ( 50.0%) 0.0402 ( 84.0%) Bytecode Writer
+ 0.0000 ( 0.0%) 0.0100 (100.0%) 0.0100 ( 50.0%) 0.0031 ( 6.4%) Dominator Set Construction
+ 0.0000 ( 0.0%) 0.0000 ( 0.0%) 0.0000 ( 0.0%) 0.0013 ( 2.7%) Module Verifier
+ <b> 0.0000 ( 0.0%) 0.0000 ( 0.0%) 0.0000 ( 0.0%) 0.0033 ( 6.9%) Hello World Pass</b>
+ 0.0100 (100.0%) 0.0100 (100.0%) 0.0200 (100.0%) 0.0479 (100.0%) TOTAL
+ </pre>
+
+ <p>As you can see, our implementation above is pretty fast :). The additional
+ passes listed are automatically inserted by the '<tt>opt</tt>' tool to verify
+ that the LLVM emitted by your pass is still valid and well formed LLVM, which
+ hasn't been broken somehow.</p>
+
+ <p>Now that you have seen the basics of the mechanics behind passes, we can talk
+ about some more details of how they work and how to use them.</p>
+
+ </div>
+
+ <!-- *********************************************************************** -->
+ <div class="doc_section">
+ <a name="passtype">Pass classes and requirements</a>
+ </div>
+ <!-- *********************************************************************** -->
+
+ <div class="doc_text">
+
+ <p>One of the first things that you should do when designing a new pass is to
+ decide what class you should subclass for your pass. The <a
+ href="#basiccode">Hello World</a> example uses the <tt><a
+ href="#FunctionPass">FunctionPass</a></tt> class for its implementation, but we
+ did not discuss why or when this should occur. Here we talk about the classes
+ available, from the most general to the most specific.</p>
+
+ <p>When choosing a superclass for your Pass, you should choose the <b>most
+ specific</b> class possible, while still being able to meet the requirements
+ listed. This gives the LLVM Pass Infrastructure information necessary to
+ optimize how passes are run, so that the resultant compiler isn't unneccesarily
+ slow.</p>
+
+ </div>
+
+ <!-- ======================================================================= -->
+ <div class="doc_subsection">
+ <a name="ImmutablePass">The <tt>ImmutablePass</tt> class</a>
+ </div>
+
+ <div class="doc_text">
+
+ <p>The most plain and boring type of pass is the "<tt><a
+ href="http://llvm.cs.uiuc.edu/doxygen/structllvm_1_1ImmutablePass.html">ImmutablePass</a></tt>"
+ class. This pass type is used for passes that do not have to be run, do not
+ change state, and never need to be updated. This is not a normal type of
+ transformation or analysis, but can provide information about the current
+ compiler configuration.</p>
+
+ <p>Although this pass class is very infrequently used, it is important for
+ providing information about the current target machine being compiled for, and
+ other static information that can affect the various transformations.</p>
+
+ <p><tt>ImmutablePass</tt>es never invalidate other transformations, are never
+ invalidated, and are never "run".</p>
+
+ </div>
+
+ <!-- ======================================================================= -->
+ <div class="doc_subsection">
+ <a name="Pass">The <tt>Pass</tt> class</a>
+ </div>
+
+ <div class="doc_text">
+
+ <p>The "<tt><a
+ href="http://llvm.cs.uiuc.edu/doxygen/classllvm_1_1Pass.html">Pass</a></tt>"
+ class is the most general of all superclasses that you can use. Deriving from
+ <tt>Pass</tt> indicates that your pass uses the entire program as a unit,
+ refering to function bodies in no predictable order, or adding and removing
+ functions. Because nothing is known about the behavior of direct <tt>Pass</tt>
+ subclasses, no optimization can be done for their execution.</p>
+
+ <p>To write a correct <tt>Pass</tt> subclass, derive from <tt>Pass</tt> and
+ overload the <tt>run</tt> method with the following signature:</p>
+
+ </div>
+
+ <!-- _______________________________________________________________________ -->
+ <div class="doc_subsubsection">
+ <a name="run">The <tt>run</tt> method</a>
+ </div>
+
+ <div class="doc_text">
+
+ <pre>
+ <b>virtual bool</b> run(Module &M) = 0;
+ </pre>
+
+ <p>The <tt>run</tt> method performs the interesting work of the pass, and should
+ return true if the module was modified by the transformation, false
+ otherwise.</p>
+
+ </div>
+
+ <!-- ======================================================================= -->
+ <div class="doc_subsection">
+ <a name="FunctionPass">The <tt>FunctionPass</tt> class</a>
+ </div>
+
+ <div class="doc_text">
+
+ <p>In contrast to direct <tt>Pass</tt> subclasses, direct <tt><a
+ href="http://llvm.cs.uiuc.edu/doxygen/classllvm_1_1Pass.html">FunctionPass</a></tt>
+ subclasses do have a predictable, local behavior that can be expected by the
+ system. All <tt>FunctionPass</tt> execute on each function in the program
+ independent of all of the other functions in the program.
+ <tt>FunctionPass</tt>'s do not require that they are executed in a particular
+ order, and <tt>FunctionPass</tt>'s do not modify external functions.</p>
+
+ <p>To be explicit, <tt>FunctionPass</tt> subclasses are not allowed to:</p>
+
+ <ol>
+ <li>Modify a Function other than the one currently being processed.</li>
+ <li>Add or remove Function's from the current Module.</li>
+ <li>Add or remove global variables from the current Module.</li>
+ <li>Maintain state across invocations of
+ <a href="#runOnFunction"><tt>runOnFunction</tt></a> (including global data)</li>
+ </ol>
+
+ <p>Implementing a <tt>FunctionPass</tt> is usually straightforward (See the <a
+ href="#basiccode">Hello World</a> pass for example). <tt>FunctionPass</tt>'s
+ may overload three virtual methods to do their work. All of these methods
+ should return true if they modified the program, or false if they didn't.</p>
+
+ </div>
+
+ <!-- _______________________________________________________________________ -->
+ <div class="doc_subsubsection">
+ <a name="doInitialization_mod">The <tt>doInitialization(Module &)</tt>
+ method</a>
+ </div>
+
+ <div class="doc_text">
+
+ <pre>
+ <b>virtual bool</b> doInitialization(Module &M);
+ </pre>
+
+ <p>The <tt>doIninitialize</tt> method is allowed to do most of the things that
+ <tt>FunctionPass</tt>'s are not allowed to do. They can add and remove
+ functions, get pointers to functions, etc. The <tt>doInitialization</tt> method
+ is designed to do simple initialization type of stuff that does not depend on
+ the functions being processed. The <tt>doInitialization</tt> method call is not
+ scheduled to overlap with any other pass executions (thus it should be very
+ fast).</p>
+
+ <p>A good example of how this method should be used is the <a
+ href="http://llvm.cs.uiuc.edu/doxygen/LowerAllocations_8cpp-source.html">LowerAllocations</a>
+ pass. This pass converts <tt>malloc</tt> and <tt>free</tt> instructions into
+ platform dependent <tt>malloc()</tt> and <tt>free()</tt> function calls. It
+ uses the <tt>doInitialization</tt> method to get a reference to the malloc and
+ free functions that it needs, adding prototypes to the module if necessary.</p>
+
+ </div>
+
+ <!-- _______________________________________________________________________ -->
+ <div class="doc_subsubsection">
+ <a name="runOnFunction">The <tt>runOnFunction</tt> method</a>
+ </div>
+
+ <div class="doc_text">
+
+ <pre>
+ <b>virtual bool</b> runOnFunction(Function &F) = 0;
+ </pre><p>
+
+ <p>The <tt>runOnFunction</tt> method must be implemented by your subclass to do
+ the transformation or analysis work of your pass. As usual, a true value should
+ be returned if the function is modified.</p>
+
+ </div>
+
+ <!-- _______________________________________________________________________ -->
+ <div class="doc_subsubsection">
+ <a name="doFinalization_mod">The <tt>doFinalization(Module
+ &)</tt> method</a>
+ </div>
+
+ <div class="doc_text">
+
+ <pre>
+ <b>virtual bool</b> doFinalization(Module &M);
+ </pre>
+
+ <p>The <tt>doFinalization</tt> method is an infrequently used method that is
+ called when the pass framework has finished calling <a
+ href="#runOnFunction"><tt>runOnFunction</tt></a> for every function in the
+ program being compiled.</p>
+
+ </div>
+
+ <!-- ======================================================================= -->
+ <div class="doc_subsection">
+ <a name="BasicBlockPass">The <tt>BasicBlockPass</tt> class</a>
+ </div>
+
+ <div class="doc_text">
+
+ <p><tt>BasicBlockPass</tt>'s are just like <a
+ href="#FunctionPass"><tt>FunctionPass</tt></a>'s, except that they must limit
+ their scope of inspection and modification to a single basic block at a time.
+ As such, they are <b>not</b> allowed to do any of the following:</p>
+
+ <ol>
+ <li>Modify or inspect any basic blocks outside of the current one</li>
+ <li>Maintain state across invocations of
+ <a href="#runOnBasicBlock"><tt>runOnBasicBlock</tt></a></li>
+ <li>Modify the constrol flow graph (by altering terminator instructions)</li>
+ <li>Any of the things verboten for
+ <a href="#FunctionPass"><tt>FunctionPass</tt></a>es.</li>
+ </ol>
+
+ <p><tt>BasicBlockPass</tt>es are useful for traditional local and "peephole"
+ optimizations. They may override the same <a
+ href="#doInitialization_mod"><tt>doInitialization(Module &)</tt></a> and <a
+ href="#doFinalization_mod"><tt>doFinalization(Module &)</tt></a> methods that <a
+ href="#FunctionPass"><tt>FunctionPass</tt></a>'s have, but also have the following virtual methods that may also be implemented:</p>
+
+ </div>
+
+ <!-- _______________________________________________________________________ -->
+ <div class="doc_subsubsection">
+ <a name="doInitialization_fn">The <tt>doInitialization(Function
+ &)</tt> method</a>
+ </div>
+
+ <div class="doc_text">
+
+ <pre>
+ <b>virtual bool</b> doInitialization(Function &F);
+ </pre>
+
+ <p>The <tt>doIninitialize</tt> method is allowed to do most of the things that
+ <tt>BasicBlockPass</tt>'s are not allowed to do, but that
+ <tt>FunctionPass</tt>'s can. The <tt>doInitialization</tt> method is designed
+ to do simple initialization type of stuff that does not depend on the
+ BasicBlocks being processed. The <tt>doInitialization</tt> method call is not
+ scheduled to overlap with any other pass executions (thus it should be very
+ fast).</p>
+
+ </div>
+
+ <!-- _______________________________________________________________________ -->
+ <div class="doc_subsubsection">
+ <a name="runOnBasicBlock">The <tt>runOnBasicBlock</tt> method</a>
+ </div>
+
+ <div class="doc_text">
+
+ <pre>
+ <b>virtual bool</b> runOnBasicBlock(BasicBlock &BB) = 0;
+ </pre>
+
+ <p>Override this function to do the work of the <tt>BasicBlockPass</tt>. This
+ function is not allowed to inspect or modify basic blocks other than the
+ parameter, and are not allowed to modify the CFG. A true value must be returned
+ if the basic block is modified.</p>
+
+ </div>
+
+ <!-- _______________________________________________________________________ -->
+ <div class="doc_subsubsection">
+ <a name="doFinalization_fn">The <tt>doFinalization(Function &)</tt>
+ method</a>
+ </div>
+
+ <div class="doc_text">
+
+ <pre>
+ <b>virtual bool</b> doFinalization(Function &F);
+ </pre>
+
+ <p>The <tt>doFinalization</tt> method is an infrequently used method that is
+ called when the pass framework has finished calling <a
+ href="#runOnBasicBlock"><tt>runOnBasicBlock</tt></a> for every BasicBlock in the
+ program being compiled. This can be used to perform per-function
+ finalization.</p>
+
+ </div>
+
+ <!-- ======================================================================= -->
+ <div class="doc_subsection">
+ <a name="MachineFunctionPass">The <tt>MachineFunctionPass</tt> class</a>
+ </div>
+
+ <div class="doc_text">
+
+ <p>A <tt>MachineFunctionPass</tt> is a part of the LLVM code generator that
+ executes on the machine-dependent representation of each LLVM function in the
+ program. A <tt>MachineFunctionPass</tt> is also a <tt>FunctionPass</tt>, so all
+ the restrictions that apply to a <tt>FunctionPass</tt> also apply to it.
+ <tt>MachineFunctionPass</tt>es also have additional restrictions. In particular,
+ <tt>MachineFunctionPass</tt>es are not allowed to do any of the following:</p>
+
+ <ol>
+ <li>Modify any LLVM Instructions, BasicBlocks or Functions.</li>
+ <li>Modify a MachineFunction other than the one currently being processed.</li>
+ <li>Add or remove MachineFunctions from the current Module.</li>
+ <li>Add or remove global variables from the current Module.</li>
+ <li>Maintain state across invocations of <a
+ href="#runOnMachineFunction"><tt>runOnMachineFunction</tt></a> (including global
+ data)</li>
+ </ol>
+
+ </div>
+
+ <!-- _______________________________________________________________________ -->
+ <div class="doc_subsubsection">
+ <a name="runOnMachineFunction">The <tt>runOnMachineFunction(MachineFunction
+ &MF)</tt> method</a>
+ </div>
+
+ <div class="doc_text">
+
+ <pre>
+ <b>virtual bool</b> runOnMachineFunction(MachineFunction &MF) = 0;
+ </pre>
+
+ <p><tt>runOnMachineFunction</tt> can be considered the main entry point of a
+ <tt>MachineFunctionPass</tt>; that is, you should override this method to do the
+ work of your <tt>MachineFunctionPass</tt>.</p>
+
+ <p>The <tt>runOnMachineFunction</tt> method is called on every
+ <tt>MachineFunction</tt> in a <tt>Module</tt>, so that the
+ <tt>MachineFunctionPass</tt> may perform optimizations on the machine-dependent
+ representation of the function. If you want to get at the LLVM <tt>Function</tt>
+ for the <tt>MachineFunction</tt> you're working on, use
+ <tt>MachineFunction</tt>'s <tt>getFunction()</tt> accessor method -- but
+ remember, you may not modify the LLVM <tt>Function</tt> or its contents from a
+ <tt>MachineFunctionPass</tt>.</p>
+
+ </div>
+
+ <!-- *********************************************************************** -->
+ <div class="doc_section">
+ <a name="registration">Pass registration</a>
+ </div>
+ <!-- *********************************************************************** -->
+
+ <div class="doc_text">
+
+ <p>In the <a href="#basiccode">Hello World</a> example pass we illustrated how
+ pass registration works, and discussed some of the reasons that it is used and
+ what it does. Here we discuss how and why passes are registered.</p>
+
+ <p>Passes can be registered in several different ways. Depending on the general
+ classification of the pass, you should use one of the following templates to
+ register the pass:</p>
+
+ <ul>
+ <li><b><tt>RegisterOpt</tt></b> - This template should be used when you are
+ registering a pass that logically should be available for use in the
+ '<tt>opt</tt>' utility.</li>
+
+ <li><b><tt>RegisterAnalysis</tt></b> - This template should be used when you are
+ registering a pass that logically should be available for use in the
+ '<tt>analyze</tt>' utility.</li>
+
+ <li><b><tt>RegisterPass</tt></b> - This is the generic form of the
+ <tt>Register*</tt> templates that should be used if you want your pass listed by
+ multiple or no utilities. This template takes an extra third argument that
+ specifies which tools it should be listed in. See the <a
+ href="http://llvm.cs.uiuc.edu/doxygen/PassSupport_8h-source.html">PassSupport.h</a>
+ file for more information.</li>
+
+ </ul>
+
+ <p>Regardless of how you register your pass, you must specify at least two
+ parameters. The first parameter is the name of the pass that is to be used on
+ the command line to specify that the pass should be added to a program (for
+ example <tt>opt</tt> or <tt>analyze</tt>). The second argument is the name of
+ the pass, which is to be used for the <tt>--help</tt> output of programs, as
+ well as for debug output generated by the <tt>--debug-pass</tt> option.</p>
+
+ <p>If a pass is registered to be used by the <tt>analyze</tt> utility, you
+ should implement the virtual <tt>print</tt> method:</p>
+
+ </div>
+
+ <!-- _______________________________________________________________________ -->
+ <div class="doc_subsubsection">
+ <a name="print">The <tt>print</tt> method</a>
+ </div>
+
+ <div class="doc_text">
+
+ <pre>
+ <b>virtual void</b> print(std::ostream &O, <b>const</b> Module *M) <b>const</b>;
+ </pre>
+
+ <p>The <tt>print</tt> method must be implemented by "analyses" in order to print
+ a human readable version of the analysis results. This is useful for debugging
+ an analysis itself, as well as for other people to figure out how an analysis
+ works. The <tt>analyze</tt> tool uses this method to generate its output.</p>
+
+ <p>The <tt>ostream</tt> parameter specifies the stream to write the results on,
+ and the <tt>Module</tt> parameter gives a pointer to the top level module of the
+ program that has been analyzed. Note however that this pointer may be null in
+ certain circumstances (such as calling the <tt>Pass::dump()</tt> from a
+ debugger), so it should only be used to enhance debug output, it should not be
+ depended on.</p>
+
+ </div>
+
+ <!-- *********************************************************************** -->
+ <div class="doc_section">
+ <a name="interaction">Specifying interactions between passes</a>
+ </div>
+ <!-- *********************************************************************** -->
+
+ <div class="doc_text">
+
+ <p>One of the main responsibilities of the <tt>PassManager</tt> is the make sure
+ that passes interact with each other correctly. Because <tt>PassManager</tt>
+ tries to <a href="#passmanager">optimize the execution of passes</a> it must
+ know how the passes interact with each other and what dependencies exist between
+ the various passes. To track this, each pass can declare the set of passes that
+ are required to be executed before the current pass, and the passes which are
+ invalidated by the current pass.</p>
+
+ <p>Typically this functionality is used to require that analysis results are
+ computed before your pass is run. Running arbitrary transformation passes can
+ invalidate the computed analysis results, which is what the invalidation set
+ specifies. If a pass does not implement the <tt><a
+ href="#getAnalysisUsage">getAnalysisUsage</a></tt> method, it defaults to not
+ having any prerequisite passes, and invalidating <b>all</b> other passes.</p>
+
+ </div>
+
+ <!-- _______________________________________________________________________ -->
+ <div class="doc_subsubsection">
+ <a name="getAnalysisUsage">The <tt>getAnalysisUsage</tt> method</a>
+ </div>
+
+ <div class="doc_text">
+
+ <pre>
+ <b>virtual void</b> getAnalysisUsage(AnalysisUsage &Info) <b>const</b>;
+ </pre>
+
+ <p>By implementing the <tt>getAnalysisUsage</tt> method, the required and
+ invalidated sets may be specified for your transformation. The implementation
+ should fill in the <tt><a
+ href="http://llvm.cs.uiuc.edu/doxygen/classllvm_1_1AnalysisUsage.html">AnalysisUsage</a></tt>
+ object with information about which passes are required and not invalidated. To
+ do this, a pass may call any of the following methods on the AnalysisUsage
+ object:</p>
+ </div>
+
+ <!-- _______________________________________________________________________ -->
+ <div class="doc_subsubsection">
+ <a name="AU::addRequired">The <tt>AnalysisUsage::addRequired<></tt> and <tt>AnalysisUsage::addRequiredTransitive<></tt> methods</a>
+ </div>
+
+ <div class="doc_text">
+ <p>
+ If you pass requires a previous pass to be executed (an analysis for example),
+ it can use one of these methods to arrange for it to be run before your pass.
+ LLVM has many different types of analyses and passes that can be required,
+ spaning the range from <tt>DominatorSet</tt> to <tt>BreakCriticalEdges</tt>.
+ requiring <tt>BreakCriticalEdges</tt>, for example, guarantees that there will
+ be no critical edges in the CFG when your pass has been run.
+ </p>
+
+ <p>
+ Some analyses chain to other analyses to do their job. For example, an <a
+ href="AliasAnalysis.html">AliasAnalysis</a> implementation is required to <a
+ href="AliasAnalysis.html#chaining">chain</a> to other alias analysis passes. In
+ cases where analyses chain, the <tt>addRequiredTransitive</tt> method should be
+ used instead of the <tt>addRequired</tt> method. This informs the PassManager
+ that the transitively required pass should be alive as long as the requiring
+ pass is.
+ </p>
+ </div>
+
+ <!-- _______________________________________________________________________ -->
+ <div class="doc_subsubsection">
+ <a name="AU::addPreserved">The <tt>AnalysisUsage::addPreserved<></tt> method</a>
+ </div>
+
+ <div class="doc_text">
+ <p>
+ One of the jobs of the PassManager is to optimize how and when analyses are run.
+ In particular, it attempts to avoid recomputing data unless it needs to. For
+ this reason, passes are allowed to declare that they preserve (i.e., they don't
+ invalidate) an existing analysis if it's available. For example, a simple
+ constant folding pass would not modify the CFG, so it can't possible effect the
+ results of dominator analysis. By default, all passes are assumed to invalidate
+ all others.
+ </p>
+
+ <p>
+ The <tt>AnalysisUsage</tt> class provides several methods which are useful in
+ certain circumstances that are related to <tt>addPreserved</tt>. In particular,
+ the <tt>setPreservesAll</tt> method can be called to indicate that the pass does
+ not modify the LLVM program at all (which is true for analyses), and the
+ <tt>setPreservesCFG</tt> method can be used by transformations that change
+ instructions in the program but do not modify the CFG or terminator instructions
+ (note that this property is implicitly set for <a
+ href="#BasicBlockPass">BasicBlockPass</a>'s).
+ </p>
+
+ <p>
+ <tt>addPreserved</tt> is particularly useful for transformations like
+ <tt>BreakCriticalEdges</tt>. This pass knows how to update a small set of loop
+ and dominator related analyses if they exist, so it can preserve them, despite
+ the fact that it hacks on the CFG.
+ </p>
+ </div>
+
+ <!-- _______________________________________________________________________ -->
+ <div class="doc_subsubsection">
+ <a name="AU::examples">Example implementations of <tt>getAnalysisUsage</tt></a>
+ </div>
+
+ <div class="doc_text">
+
+ <pre>
+ <i>// This is an example implementation from an analysis, which does not modify
+ // the program at all, yet has a prerequisite.</i>
+ <b>void</b> <a href="http://llvm.cs.uiuc.edu/doxygen/structllvm_1_1PostDominanceFrontier.html">PostDominanceFrontier</a>::getAnalysisUsage(AnalysisUsage &AU) <b>const</b> {
+ AU.setPreservesAll();
+ AU.addRequired<<a href="http://llvm.cs.uiuc.edu/doxygen/structllvm_1_1PostDominatorTree.html">PostDominatorTree</a>>();
+ }
+ </pre>
+
+ <p>and:</p>
+
+ <pre>
+ <i>// This example modifies the program, but does not modify the CFG</i>
+ <b>void</b> <a href="http://llvm.cs.uiuc.edu/doxygen/structLICM.html">LICM</a>::getAnalysisUsage(AnalysisUsage &AU) <b>const</b> {
+ AU.setPreservesCFG();
+ AU.addRequired<<a href="http://llvm.cs.uiuc.edu/doxygen/classllvm_1_1LoopInfo.html">LoopInfo</a>>();
+ }
+ </pre>
+
+ </div>
+
+ <!-- _______________________________________________________________________ -->
+ <div class="doc_subsubsection">
+ <a name="getAnalysis">The <tt>getAnalysis<></tt> and <tt>getAnalysisToUpdate<></tt> methods</a>
+ </div>
+
+ <div class="doc_text">
+
+ <p>The <tt>Pass::getAnalysis<></tt> method is automatically inherited by
+ your class, providing you with access to the passes that you declared that you
+ required with the <a href="#getAnalysisUsage"><tt>getAnalysisUsage</tt></a>
+ method. It takes a single template argument that specifies which pass class you
+ want, and returns a reference to that pass. For example:</p>
+
+ <pre>
+ bool LICM::runOnFunction(Function &F) {
+ LoopInfo &LI = getAnalysis<LoopInfo>();
+ ...
+ }
+ </pre>
+
+ <p>This method call returns a reference to the pass desired. You may get a
+ runtime assertion failure if you attempt to get an analysis that you did not
+ declare as required in your <a
+ href="#getAnalysisUsage"><tt>getAnalysisUsage</tt></a> implementation. This
+ method can be called by your <tt>run*</tt> method implementation, or by any
+ other local method invoked by your <tt>run*</tt> method.</p>
+
+ <p>
+ If your pass is capable of updating analyses if they exist (e.g.,
+ <tt>BreakCriticalEdges</tt>, as described above), you can use the
+ <tt>getAnalysisToUpdate</tt> method, which returns a pointer to the analysis if
+ it is active. For example:</p>
+
+ <pre>
+ ...
+ if (DominatorSet *DS = getAnalysisToUpdate<DominatorSet>()) {
+ <i>// A DominatorSet is active. This code will update it.</i>
+ }
+ ...
+ </pre>
+
+ </div>
+
+ <!-- *********************************************************************** -->
+ <div class="doc_section">
+ <a name="analysisgroup">Implementing Analysis Groups</a>
+ </div>
+ <!-- *********************************************************************** -->
+
+ <div class="doc_text">
+
+ <p>Now that we understand the basics of how passes are defined, how the are
+ used, and how they are required from other passes, it's time to get a little bit
+ fancier. All of the pass relationships that we have seen so far are very
+ simple: one pass depends on one other specific pass to be run before it can run.
+ For many applications, this is great, for others, more flexibility is
+ required.</p>
+
+ <p>In particular, some analyses are defined such that there is a single simple
+ interface to the analysis results, but multiple ways of calculating them.
+ Consider alias analysis for example. The most trivial alias analysis returns
+ "may alias" for any alias query. The most sophisticated analysis a
+ flow-sensitive, context-sensitive interprocedural analysis that can take a
+ significant amount of time to execute (and obviously, there is a lot of room
+ between these two extremes for other implementations). To cleanly support
+ situations like this, the LLVM Pass Infrastructure supports the notion of
+ Analysis Groups.</p>
+
+ </div>
+
+ <!-- _______________________________________________________________________ -->
+ <div class="doc_subsubsection">
+ <a name="agconcepts">Analysis Group Concepts</a>
+ </div>
+
+ <div class="doc_text">
+
+ <p>An Analysis Group is a single simple interface that may be implemented by
+ multiple different passes. Analysis Groups can be given human readable names
+ just like passes, but unlike passes, they need not derive from the <tt>Pass</tt>
+ class. An analysis group may have one or more implementations, one of which is
+ the "default" implementation.</p>
+
+ <p>Analysis groups are used by client passes just like other passes are: the
+ <tt>AnalysisUsage::addRequired()</tt> and <tt>Pass::getAnalysis()</tt> methods.
+ In order to resolve this requirement, the <a href="#passmanager">PassManager</a>
+ scans the available passes to see if any implementations of the analysis group
+ are available. If none is available, the default implementation is created for
+ the pass to use. All standard rules for <A href="#interaction">interaction
+ between passes</a> still apply.</p>
+
+ <p>Although <a href="#registration">Pass Registration</a> is optional for normal
+ passes, all analysis group implementations must be registered, and must use the
+ <A href="#registerag"><tt>RegisterAnalysisGroup</tt></a> template to join the
+ implementation pool. Also, a default implementation of the interface
+ <b>must</b> be registered with <A
+ href="#registerag"><tt>RegisterAnalysisGroup</tt></a>.</p>
+
+ <p>As a concrete example of an Analysis Group in action, consider the <a
+ href="http://llvm.cs.uiuc.edu/doxygen/classllvm_1_1AliasAnalysis.html">AliasAnalysis</a>
+ analysis group. The default implementation of the alias analysis interface (the
+ <tt><a
+ href="http://llvm.cs.uiuc.edu/doxygen/structBasicAliasAnalysis.html">basicaa</a></tt>
+ pass) just does a few simple checks that don't require significant analysis to
+ compute (such as: two different globals can never alias each other, etc).
+ Passes that use the <tt><a
+ href="http://llvm.cs.uiuc.edu/doxygen/classllvm_1_1AliasAnalysis.html">AliasAnalysis</a></tt>
+ interface (for example the <tt><a
+ href="http://llvm.cs.uiuc.edu/doxygen/structGCSE.html">gcse</a></tt> pass), do
+ not care which implementation of alias analysis is actually provided, they just
+ use the designated interface.</p>
+
+ <p>From the user's perspective, commands work just like normal. Issuing the
+ command '<tt>opt -gcse ...</tt>' will cause the <tt>basicaa</tt> class to be
+ instantiated and added to the pass sequence. Issuing the command '<tt>opt
+ -somefancyaa -gcse ...</tt>' will cause the <tt>gcse</tt> pass to use the
+ <tt>somefancyaa</tt> alias analysis (which doesn't actually exist, it's just a
+ hypothetical example) instead.</p>
+
+ </div>
+
+ <!-- _______________________________________________________________________ -->
+ <div class="doc_subsubsection">
+ <a name="registerag">Using <tt>RegisterAnalysisGroup</tt></a>
+ </div>
+
+ <div class="doc_text">
+
+ <p>The <tt>RegisterAnalysisGroup</tt> template is used to register the analysis
+ group itself as well as add pass implementations to the analysis group. First,
+ an analysis should be registered, with a human readable name provided for it.
+ Unlike registration of passes, there is no command line argument to be specified
+ for the Analysis Group Interface itself, because it is "abstract":</p>
+
+ <pre>
+ <b>static</b> RegisterAnalysisGroup<<a href="http://llvm.cs.uiuc.edu/doxygen/classllvm_1_1AliasAnalysis.html">AliasAnalysis</a>> A("<i>Alias Analysis</i>");
+ </pre>
+
+ <p>Once the analysis is registered, passes can declare that they are valid
+ implementations of the interface by using the following code:</p>
+
+ <pre>
+ <b>namespace</b> {
+ //<i> Analysis Group implementations <b>must</b> be registered normally...</i>
+ RegisterOpt<FancyAA>
+ B("<i>somefancyaa</i>", "<i>A more complex alias analysis implementation</i>");
+
+ //<i> Declare that we implement the AliasAnalysis interface</i>
+ RegisterAnalysisGroup<<a href="http://llvm.cs.uiuc.edu/doxygen/classllvm_1_1AliasAnalysis.html">AliasAnalysis</a>, FancyAA> C;
+ }
+ </pre>
+
+ <p>This just shows a class <tt>FancyAA</tt> that is registered normally, then
+ uses the <tt>RegisterAnalysisGroup</tt> template to "join" the <tt><a
+ href="http://llvm.cs.uiuc.edu/doxygen/classllvm_1_1AliasAnalysis.html">AliasAnalysis</a></tt>
+ analysis group. Every implementation of an analysis group should join using
+ this template. A single pass may join multiple different analysis groups with
+ no problem.</p>
+
+ <pre>
+ <b>namespace</b> {
+ //<i> Analysis Group implementations <b>must</b> be registered normally...</i>
+ RegisterOpt<<a href="http://llvm.cs.uiuc.edu/doxygen/structBasicAliasAnalysis.html">BasicAliasAnalysis</a>>
+ D("<i>basicaa</i>", "<i>Basic Alias Analysis (default AA impl)</i>");
+
+ //<i> Declare that we implement the AliasAnalysis interface</i>
+ RegisterAnalysisGroup<<a href="http://llvm.cs.uiuc.edu/doxygen/classllvm_1_1AliasAnalysis.html">AliasAnalysis</a>, <a href="http://llvm.cs.uiuc.edu/doxygen/structBasicAliasAnalysis.html">BasicAliasAnalysis</a>, <b>true</b>> E;
+ }
+ </pre>
+
+ <p>Here we show how the default implementation is specified (using the extra
+ argument to the <tt>RegisterAnalysisGroup</tt> template). There must be exactly
+ one default implementation available at all times for an Analysis Group to be
+ used. Here we declare that the <tt><a
+ href="http://llvm.cs.uiuc.edu/doxygen/structBasicAliasAnalysis.html">BasicAliasAnalysis</a></tt>
+ pass is the default implementation for the interface.</p>
+
+ </div>
+
+ <!-- *********************************************************************** -->
+ <div class="doc_section">
+ <a name="passmanager">What PassManager does</a>
+ </div>
+ <!-- *********************************************************************** -->
+
+ <div class="doc_text">
+
+ <p>The <a
+ href="http://llvm.cs.uiuc.edu/doxygen/PassManager_8h-source.html"><tt>PassManager</tt></a>
+ <a
+ href="http://llvm.cs.uiuc.edu/doxygen/classllvm_1_1PassManager.html">class</a>
+ takes a list of passes, ensures their <a href="#interaction">prerequisites</a>
+ are set up correctly, and then schedules passes to run efficiently. All of the
+ LLVM tools that run passes use the <tt>PassManager</tt> for execution of these
+ passes.</p>
+
+ <p>The <tt>PassManager</tt> does two main things to try to reduce the execution
+ time of a series of passes:</p>
+
+ <ol>
+ <li><b>Share analysis results</b> - The PassManager attempts to avoid
+ recomputing analysis results as much as possible. This means keeping track of
+ which analyses are available already, which analyses get invalidated, and which
+ analyses are needed to be run for a pass. An important part of work is that the
+ <tt>PassManager</tt> tracks the exact lifetime of all analysis results, allowing
+ it to <a href="#releaseMemory">free memory</a> allocated to holding analysis
+ results as soon as they are no longer needed.</li>
+
+ <li><b>Pipeline the execution of passes on the program</b> - The
+ <tt>PassManager</tt> attempts to get better cache and memory usage behavior out
+ of a series of passes by pipelining the passes together. This means that, given
+ a series of consequtive <a href="#FunctionPass"><tt>FunctionPass</tt></a>'s, it
+ will execute all of the <a href="#FunctionPass"><tt>FunctionPass</tt></a>'s on
+ the first function, then all of the <a
+ href="#FunctionPass"><tt>FunctionPass</tt></a>es on the second function,
+ etc... until the entire program has been run through the passes.
+
+ <p>This improves the cache behavior of the compiler, because it is only touching
+ the LLVM program representation for a single function at a time, instead of
+ traversing the entire program. It reduces the memory consumption of compiler,
+ because, for example, only one <a
+ href="http://llvm.cs.uiuc.edu/doxygen/structllvm_1_1DominatorSet.html"><tt>DominatorSet</tt></a>
+ needs to be calculated at a time. This also makes it possible some <a
+ href="#SMP">interesting enhancements</a> in the future.</p></li>
+
+ </ol>
+
+ <p>The effectiveness of the <tt>PassManager</tt> is influenced directly by how
+ much information it has about the behaviors of the passes it is scheduling. For
+ example, the "preserved" set is intentionally conservative in the face of an
+ unimplemented <a href="#getAnalysisUsage"><tt>getAnalysisUsage</tt></a> method.
+ Not implementing when it should be implemented will have the effect of not
+ allowing any analysis results to live across the execution of your pass.</p>
+
+ <p>The <tt>PassManager</tt> class exposes a <tt>--debug-pass</tt> command line
+ options that is useful for debugging pass execution, seeing how things work, and
+ diagnosing when you should be preserving more analyses than you currently are
+ (To get information about all of the variants of the <tt>--debug-pass</tt>
+ option, just type '<tt>opt --help-hidden</tt>').</p>
+
+ <p>By using the <tt>--debug-pass=Structure</tt> option, for example, we can see
+ how our <a href="#basiccode">Hello World</a> pass interacts with other passes.
+ Lets try it out with the <tt>gcse</tt> and <tt>licm</tt> passes:</p>
+
+ <pre>
+ $ opt -load ../../../lib/Debug/libhello.so -gcse -licm --debug-pass=Structure < hello.bc > /dev/null
+ Module Pass Manager
+ Function Pass Manager
+ Dominator Set Construction
+ Immediate Dominators Construction
+ Global Common Subexpression Elimination
+ -- Immediate Dominators Construction
+ -- Global Common Subexpression Elimination
+ Natural Loop Construction
+ Loop Invariant Code Motion
+ -- Natural Loop Construction
+ -- Loop Invariant Code Motion
+ Module Verifier
+ -- Dominator Set Construction
+ -- Module Verifier
+ Bytecode Writer
+ --Bytecode Writer
+ </pre>
+
+ <p>This output shows us when passes are constructed and when the analysis
+ results are known to be dead (prefixed with '<tt>--</tt>'). Here we see that
+ GCSE uses dominator and immediate dominator information to do its job. The LICM
+ pass uses natural loop information, which uses dominator sets, but not immediate
+ dominators. Because immediate dominators are no longer useful after the GCSE
+ pass, it is immediately destroyed. The dominator sets are then reused to
+ compute natural loop information, which is then used by the LICM pass.</p>
+
+ <p>After the LICM pass, the module verifier runs (which is automatically added
+ by the '<tt>opt</tt>' tool), which uses the dominator set to check that the
+ resultant LLVM code is well formed. After it finishes, the dominator set
+ information is destroyed, after being computed once, and shared by three
+ passes.</p>
+
+ <p>Lets see how this changes when we run the <a href="#basiccode">Hello
+ World</a> pass in between the two passes:</p>
+
+ <pre>
+ $ opt -load ../../../lib/Debug/libhello.so -gcse -hello -licm --debug-pass=Structure < hello.bc > /dev/null
+ Module Pass Manager
+ Function Pass Manager
+ Dominator Set Construction
+ Immediate Dominators Construction
+ Global Common Subexpression Elimination
+ <b>-- Dominator Set Construction</b>
+ -- Immediate Dominators Construction
+ -- Global Common Subexpression Elimination
+ <b> Hello World Pass
+ -- Hello World Pass
+ Dominator Set Construction</b>
+ Natural Loop Construction
+ Loop Invariant Code Motion
+ -- Natural Loop Construction
+ -- Loop Invariant Code Motion
+ Module Verifier
+ -- Dominator Set Construction
+ -- Module Verifier
+ Bytecode Writer
+ --Bytecode Writer
+ Hello: __main
+ Hello: puts
+ Hello: main
+ </pre>
+
+ <p>Here we see that the <a href="#basiccode">Hello World</a> pass has killed the
+ Dominator Set pass, even though it doesn't modify the code at all! To fix this,
+ we need to add the following <a
+ href="#getAnalysisUsage"><tt>getAnalysisUsage</tt></a> method to our pass:</p>
+
+ <pre>
+ <i>// We don't modify the program, so we preserve all analyses</i>
+ <b>virtual void</b> getAnalysisUsage(AnalysisUsage &AU) <b>const</b> {
+ AU.setPreservesAll();
+ }
+ </pre>
+
+ <p>Now when we run our pass, we get this output:</p>
+
+ <pre>
+ $ opt -load ../../../lib/Debug/libhello.so -gcse -hello -licm --debug-pass=Structure < hello.bc > /dev/null
+ Pass Arguments: -gcse -hello -licm
+ Module Pass Manager
+ Function Pass Manager
+ Dominator Set Construction
+ Immediate Dominators Construction
+ Global Common Subexpression Elimination
+ -- Immediate Dominators Construction
+ -- Global Common Subexpression Elimination
+ Hello World Pass
+ -- Hello World Pass
+ Natural Loop Construction
+ Loop Invariant Code Motion
+ -- Loop Invariant Code Motion
+ -- Natural Loop Construction
+ Module Verifier
+ -- Dominator Set Construction
+ -- Module Verifier
+ Bytecode Writer
+ --Bytecode Writer
+ Hello: __main
+ Hello: puts
+ Hello: main
+ </pre>
+
+ <p>Which shows that we don't accidentally invalidate dominator information
+ anymore, and therefore do not have to compute it twice.</p>
+
+ </div>
+
+ <!-- _______________________________________________________________________ -->
+ <div class="doc_subsubsection">
+ <a name="releaseMemory">The <tt>releaseMemory</tt> method</a>
+ </div>
+
+ <div class="doc_text">
+
+ <pre>
+ <b>virtual void</b> releaseMemory();
+ </pre>
+
+ <p>The <tt>PassManager</tt> automatically determines when to compute analysis
+ results, and how long to keep them around for. Because the lifetime of the pass
+ object itself is effectively the entire duration of the compilation process, we
+ need some way to free analysis results when they are no longer useful. The
+ <tt>releaseMemory</tt> virtual method is the way to do this.</p>
+
+ <p>If you are writing an analysis or any other pass that retains a significant
+ amount of state (for use by another pass which "requires" your pass and uses the
+ <a href="#getAnalysis">getAnalysis</a> method) you should implement
+ <tt>releaseMEmory</tt> to, well, release the memory allocated to maintain this
+ internal state. This method is called after the <tt>run*</tt> method for the
+ class, before the next call of <tt>run*</tt> in your pass.</p>
+
+ </div>
+
+ <!-- *********************************************************************** -->
+ <div class="doc_section">
+ <a name="debughints">Using GDB with dynamically loaded passes</a>
+ </div>
+ <!-- *********************************************************************** -->
+
+ <div class="doc_text">
+
+ <p>Unfortunately, using GDB with dynamically loaded passes is not as easy as it
+ should be. First of all, you can't set a breakpoint in a shared object that has
+ not been loaded yet, and second of all there are problems with inlined functions
+ in shared objects. Here are some suggestions to debugging your pass with
+ GDB.</p>
+
+ <p>For sake of discussion, I'm going to assume that you are debugging a
+ transformation invoked by <tt>opt</tt>, although nothing described here depends
+ on that.</p>
+
+ </div>
+
+ <!-- _______________________________________________________________________ -->
+ <div class="doc_subsubsection">
+ <a name="breakpoint">Setting a breakpoint in your pass</a>
+ </div>
+
+ <div class="doc_text">
+
+ <p>First thing you do is start <tt>gdb</tt> on the <tt>opt</tt> process:</p>
+
+ <pre>
+ $ <b>gdb opt</b>
+ GNU gdb 5.0
+ Copyright 2000 Free Software Foundation, Inc.
+ GDB is free software, covered by the GNU General Public License, and you are
+ welcome to change it and/or distribute copies of it under certain conditions.
+ Type "show copying" to see the conditions.
+ There is absolutely no warranty for GDB. Type "show warranty" for details.
+ This GDB was configured as "sparc-sun-solaris2.6"...
+ (gdb)
+ </pre>
+
+ <p>Note that <tt>opt</tt> has a lot of debugging information in it, so it takes
+ time to load. Be patient. Since we cannot set a breakpoint in our pass yet
+ (the shared object isn't loaded until runtime), we must execute the process, and
+ have it stop before it invokes our pass, but after it has loaded the shared
+ object. The most foolproof way of doing this is to set a breakpoint in
+ <tt>PassManager::run</tt> and then run the process with the arguments you
+ want:</p>
+
+ <pre>
+ (gdb) <b>break PassManager::run</b>
+ Breakpoint 1 at 0x2413bc: file Pass.cpp, line 70.
+ (gdb) <b>run test.bc -load $(LLVMTOP)/llvm/lib/Debug/[libname].so -[passoption]</b>
+ Starting program: opt test.bc -load $(LLVMTOP)/llvm/lib/Debug/[libname].so -[passoption]
+ Breakpoint 1, PassManager::run (this=0xffbef174, M=@0x70b298) at Pass.cpp:70
+ 70 bool PassManager::run(Module &M) { return PM->run(M); }
+ (gdb)
+ </pre>
+
+ <p>Once the <tt>opt</tt> stops in the <tt>PassManager::run</tt> method you are
+ now free to set breakpoints in your pass so that you can trace through execution
+ or do other standard debugging stuff.</p>
+
+ </div>
+
+ <!-- _______________________________________________________________________ -->
+ <div class="doc_subsubsection">
+ <a name="debugmisc">Miscellaneous Problems</a>
+ </div>
+
+ <div class="doc_text">
+
+ <p>Once you have the basics down, there are a couple of problems that GDB has,
+ some with solutions, some without.</p>
+
+ <ul>
+ <li>Inline functions have bogus stack information. In general, GDB does a
+ pretty good job getting stack traces and stepping through inline functions.
+ When a pass is dynamically loaded however, it somehow completely loses this
+ capability. The only solution I know of is to de-inline a function (move it
+ from the body of a class to a .cpp file).</li>
+
+ <li>Restarting the program breaks breakpoints. After following the information
+ above, you have succeeded in getting some breakpoints planted in your pass. Nex
+ thing you know, you restart the program (i.e., you type '<tt>run</tt>' again),
+ and you start getting errors about breakpoints being unsettable. The only way I
+ have found to "fix" this problem is to <tt>delete</tt> the breakpoints that are
+ already set in your pass, run the program, and re-set the breakpoints once
+ execution stops in <tt>PassManager::run</tt>.</li>
+
+ </ul>
+
+ <p>Hopefully these tips will help with common case debugging situations. If
+ you'd like to contribute some tips of your own, just contact <a
+ href="mailto:sabre at nondot.org">Chris</a>.</p>
+
+ </div>
+
+ <!-- *********************************************************************** -->
+ <div class="doc_section">
+ <a name="future">Future extensions planned</a>
+ </div>
+ <!-- *********************************************************************** -->
+
+ <div class="doc_text">
+
+ <p>Although the LLVM Pass Infrastructure is very capable as it stands, and does
+ some nifty stuff, there are things we'd like to add in the future. Here is
+ where we are going:</p>
+
+ </div>
+
+ <!-- _______________________________________________________________________ -->
+ <div class="doc_subsubsection">
+ <a name="SMP">Multithreaded LLVM</a>
+ </div>
+
+ <div class="doc_text">
+
+ <p>Multiple CPU machines are becoming more common and compilation can never be
+ fast enough: obviously we should allow for a multithreaded compiler. Because of
+ the semantics defined for passes above (specifically they cannot maintain state
+ across invocations of their <tt>run*</tt> methods), a nice clean way to
+ implement a multithreaded compiler would be for the <tt>PassManager</tt> class
+ to create multiple instances of each pass object, and allow the separate
+ instances to be hacking on different parts of the program at the same time.</p>
+
+ <p>This implementation would prevent each of the passes from having to implement
+ multithreaded constructs, requiring only the LLVM core to have locking in a few
+ places (for global resources). Although this is a simple extension, we simply
+ haven't had time (or multiprocessor machines, thus a reason) to implement this.
+ Despite that, we have kept the LLVM passes SMP ready, and you should too.</p>
+
+ </div>
+
+ <!-- _______________________________________________________________________ -->
+ <div class="doc_subsubsection">
+ <a name="ModuleSource">A new <tt>ModuleSource</tt> interface</a>
+ </div>
+
+ <div class="doc_text">
+
+ <p>Currently, the <tt>PassManager</tt>'s <tt>run</tt> method takes a <tt><a
+ href="http://llvm.cs.uiuc.edu/doxygen/classllvm_1_1Module.html">Module</a></tt>
+ as input, and runs all of the passes on this module. The problem with this
+ approach is that none of the <tt>PassManager</tt> features can be used for
+ timing and debugging the actual <b>loading</b> of the module from disk or
+ standard input.</p>
+
+ <p>To solve this problem, eventually the <tt>PassManager</tt> class will accept
+ a <tt>ModuleSource</tt> object instead of a Module itself. When complete, this
+ will also allow for streaming of functions out of the bytecode representation,
+ allowing us to avoid holding the entire program in memory at once if we only are
+ dealing with <a href="#FunctionPass">FunctionPass</a>es.</p>
+
+ <p>As part of a different issue, eventually the bytecode loader will be extended
+ to allow on-demand loading of functions from the bytecode representation, in
+ order to better support the runtime reoptimizer. The bytecode format is already
+ capable of this, the loader just needs to be reworked a bit.</p>
+
+ </div>
+
+ <!-- _______________________________________________________________________ -->
+ <div class="doc_subsubsection">
+ <a name="PassFunctionPass"><tt>Pass</tt>es requiring <tt>FunctionPass</tt>es</a>
+ </div>
+
+ <div class="doc_text">
+
+ <p>Currently it is illegal for a <a href="#Pass"><tt>Pass</tt></a> to require a
+ <a href="#FunctionPass"><tt>FunctionPass</tt></a>. This is because there is
+ only one instance of the <a href="#FunctionPass"><tt>FunctionPass</tt></a>
+ object ever created, thus nowhere to store information for all of the functions
+ in the program at the same time. Although this has come up a couple of times
+ before, this has always been worked around by factoring one big complicated pass
+ into a global and an interprocedural part, both of which are distinct. In the
+ future, it would be nice to have this though.</p>
+
+ <p>Note that it is no problem for a <a
+ href="#FunctionPass"><tt>FunctionPass</tt></a> to require the results of a <a
+ href="#Pass"><tt>Pass</tt></a>, only the other way around.</p>
+
+ </div>
+
+ <!-- *********************************************************************** -->
+ <hr>
+ <address>
+ <a href="http://jigsaw.w3.org/css-validator/check/referer"><img
+ src="http://jigsaw.w3.org/css-validator/images/vcss" alt="Valid CSS!"></a>
+ <a href="http://validator.w3.org/check/referer"><img
+ src="http://www.w3.org/Icons/valid-html401" alt="Valid HTML 4.01!" /></a>
+
+ <a href="mailto:sabre at nondot.org">Chris Lattner</a><br>
+ <a href="http://llvm.cs.uiuc.edu">The LLVM Compiler Infrastructure</a><br>
+ Last modified: $Date: 2004/08/13 22:03:04 $
+ </address>
+
+ </body>
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