[llvm-commits] [llvm] r58967 - /llvm/branches/release_24/docs/ReleaseNotes.html
Tanya Lattner
tonic at nondot.org
Sun Nov 9 21:50:58 PST 2008
Author: tbrethou
Date: Sun Nov 9 23:50:57 2008
New Revision: 58967
URL: http://llvm.org/viewvc/llvm-project?rev=58967&view=rev
Log:
Merge from mainline.
Modified:
llvm/branches/release_24/docs/ReleaseNotes.html
Modified: llvm/branches/release_24/docs/ReleaseNotes.html
URL: http://llvm.org/viewvc/llvm-project/llvm/branches/release_24/docs/ReleaseNotes.html?rev=58967&r1=58966&r2=58967&view=diff
==============================================================================
--- llvm/branches/release_24/docs/ReleaseNotes.html (original)
+++ llvm/branches/release_24/docs/ReleaseNotes.html Sun Nov 9 23:50:57 2008
@@ -1,32 +1,29 @@
-
<!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">
- <title>LLVM 2.3 Release Notes</title>
+ <title>LLVM 2.4 Release Notes</title>
</head>
<body>
-<div class="doc_title">LLVM 2.3 Release Notes</div>
-
+<div class="doc_title">LLVM 2.4 Release Notes</div>
+
<ol>
<li><a href="#intro">Introduction</a></li>
- <li><a href="#changes">Major Changes and Sub-project Status</a></li>
- <li><a href="#whatsnew">What's New?</a></li>
+ <li><a href="#subproj">Sub-project Status Update</a></li>
+ <li><a href="#whatsnew">What's New in LLVM?</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>
+ <li><a href="#knownproblems">Known Problems</a></li>
<li><a href="#additionalinfo">Additional Information</a></li>
</ol>
<div class="doc_author">
- <p>Written by the <a href="http://llvm.org">LLVM Team</a><p>
+ <p>Written by the <a href="http://llvm.org">LLVM Team</a></p>
</div>
-<!-- Done through Week-of-Mon-20080324.txt -->
-
<!-- *********************************************************************** -->
<div class="doc_section">
<a name="intro">Introduction</a>
@@ -35,174 +32,175 @@
<div class="doc_text">
-<p>This document contains the release notes for the LLVM compiler
-infrastructure, release 2.3. Here we describe the status of LLVM, including
-major improvements from the previous release and any known problems. All LLVM
-releases may be downloaded from the <a href="http://llvm.org/releases/">LLVM
-releases web site</a>.</p>
+<p>This document contains the release notes for the LLVM Compiler
+Infrastructure, release 2.4. Here we describe the status of LLVM, including
+major improvements from the previous release and significant known problems.
+All LLVM releases may be downloaded from the <a
+href="http://llvm.org/releases/">LLVM releases web site</a>.</p>
<p>For more information about LLVM, including information about the latest
release, please check out the <a href="http://llvm.org/">main LLVM
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>
+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 a Subversion checkout or the
+<p>Note that if you are reading this file from a Subversion checkout or the
main LLVM web page, this document applies to the <i>next</i> release, not the
-current one. To see the release notes for a specific releases, please see the
+current one. To see the release notes for a specific release, please see the
<a href="http://llvm.org/releases/">releases page</a>.</p>
</div>
+<!-- Unfinished features in 2.4:
+ Machine LICM
+ Machine Sinking
+ LegalizeDAGTypes
+ llc -enable-value-prop, propagation of value info (sign/zero ext info) from
+ one MBB to another
+ -->
+
+ <!-- for announcement email:
+ mention dev mtg
+ Xcode 3.1 and 3.1.1.
+ -->
+
<!-- *********************************************************************** -->
<div class="doc_section">
- <a name="changes">Major Changes and Sub-project Status</a>
+ <a name="subproj">Sub-project Status Update</a>
</div>
<!-- *********************************************************************** -->
<div class="doc_text">
-
-<p>This is the fourteenth public release of the LLVM Compiler Infrastructure.
-It includes a large number of features and refinements from LLVM 2.2.</p>
+<p>
+The LLVM 2.4 distribution currently consists of code from the core LLVM
+repository (which roughly includes the LLVM optimizers, code generators and
+supporting tools) and the llvm-gcc repository. In addition to this code, the
+LLVM Project includes other sub-projects that are in development. The two which
+are the most actively developed are the <a href="#clang">Clang Project</a> and
+the <a href="#vmkit">VMKit Project</a>.
+</p>
</div>
-<!-- Unfinished features in 2.3:
- Machine LICM
- Machine Sinking
- LegalizeDAGTypes
- -->
<!--=========================================================================-->
<div class="doc_subsection">
-<a name="changes">Major Changes in LLVM 2.3</a>
+<a name="clang">Clang: C/C++/Objective-C Frontend Toolkit</a>
</div>
<div class="doc_text">
-<p>LLVM 2.3 no longer supports llvm-gcc 4.0, it has been replaced with
- llvm-gcc 4.2.</p>
+<p>The <a href="http://clang.llvm.org/">Clang project</a> is an effort to build
+a set of new 'LLVM native' front-end technologies for the LLVM optimizer
+and code generator. Clang is continuing to make major strides forward in all
+areas. Its C and Objective-C parsing support is very solid, and the code
+generation support is far enough along to build many C applications. While not
+yet production quality, it is progressing very nicely. In addition, C++
+front-end work has started to make significant progress.</p>
-<p>LLVM 2.3 no longer includes the <tt>llvm-upgrade</tt> tool. It was useful
- for upgrading LLVM 1.9 files to LLVM 2.x syntax, but you can always use a
- previous LLVM release to do this. One nice impact of this is that the LLVM
- regression test suite no longer depends on llvm-upgrade, which makes it run
- faster.</p>
+<p>Clang, in conjunction with the <tt>ccc</tt> driver, is now usable as a
+replacement for gcc for building some small- to medium-sized C applications.
+Additionally, Clang now has code generation support for Objective-C on Mac OS X
+platform. Major highlights include:</p>
-<p>The <tt>llvm2cpp</tt> tool has been folded into llc, use
- <tt>llc -march=cpp</tt> instead of <tt>llvm2cpp</tt>.</p>
+<ul>
+ <li> Clang/ccc pass almost all of the LLVM test suite on Mac OS X and Linux
+on the 32-bit x86 architecture. This includes significant C
+applications such as <a href="http://www.sqlite.org">sqlite3</a>,
+<a href="http://www.lua.org">lua</a>, and
+<a href="http://www.clamav.net">Clam AntiVirus</a>. </li>
-<p>LLVM API Changes:</p>
+ <li> Clang can build the majority of Objective-C examples shipped with the
+Mac OS X Developer Tools. </li>
+</ul>
-<ul>
-<li>Several core LLVM IR classes have migrated to use the
- '<tt>FOOCLASS::Create(...)</tt>' pattern instead of '<tt>new
- FOOCLASS(...)</tt>' (e.g. where FOOCLASS=<tt>BasicBlock</tt>). We hope to
- standardize on <tt>FOOCLASS::Create</tt> for all IR classes in the future,
- but not all of them have been moved over yet.</li>
-<li>LLVM 2.3 renames the LLVMBuilder and LLVMFoldingBuilder classes to
- <a href="http://llvm.org/doxygen/classllvm_1_1IRBuilder.html">IRBuilder</a>.
- </li>
-<li>MRegisterInfo was renamed to
- <a href="http://llvm.org/doxygen/classllvm_1_1TargetRegisterInfo.html">
- TargetRegisterInfo</a>.</li>
-<li>The MappedFile class is gone, please use
- <a href="http://llvm.org/doxygen/classllvm_1_1MemoryBuffer.html">
- MemoryBuffer</a> instead.</li>
-<li>The '<tt>-enable-eh</tt>' flag to llc has been removed. Now code should
- encode whether it is safe to omit unwind information for a function by
- tagging the Function object with the '<tt>nounwind</tt>' attribute.</li>
-<li>The ConstantFP::get method that uses APFloat now takes one argument
- instead of two. The type argument has been removed, and the type is
- now inferred from the size of the given APFloat value.</li>
+<p>Clang code generation still needs considerable testing and development,
+however. Some areas under active development include:</p>
+<ul>
+ <li> Improved support for C and Objective-C features, for example
+ variable-length arrays, va_arg, exception handling (Obj-C), and garbage
+ collection (Obj-C). </li>
+ <li> ABI compatibility, especially for platforms other than 32-bit
+ x86. </li>
</ul>
+
</div>
<!--=========================================================================-->
<div class="doc_subsection">
-<a name="otherprojects">Other LLVM Sub-Projects</a>
+<a name="clangsa">Clang Static Analyzer</a>
</div>
<div class="doc_text">
-<p>
-The core LLVM 2.3 distribution currently consists of code from the core LLVM
-repository (which roughly contains the LLVM optimizer, code generators and
-supporting tools) and the llvm-gcc repository. In addition to this code, the
-LLVM Project includes other sub-projects that are in development. The two which
-are the most actively developed are the new <a href="#vmkit">vmkit Project</a>
-and the <a href="#clang">Clang Project</a>.
-</p>
-</div>
-
-<!--=========================================================================-->
-<div class="doc_subsubsection">
-<a name="vmkit">vmkit</a>
-</div>
-<div class="doc_text">
-<p>
-The "vmkit" project is a new addition to the LLVM family. It is an
-implementation of a JVM and a CLI Virtual Machines (Microsoft .NET is an
-implementation of the CLI) using the Just-In-Time compiler of LLVM.</p>
+<p>The Clang project also includes an early stage static source code analysis
+tool for <a href="http://clang.llvm.org/StaticAnalysis.html">automatically
+finding bugs</a> in C and Objective-C programs. The tool performs a growing set
+of checks to find bugs that occur on a specific path within a program. Examples
+of bugs the tool finds include logic errors such as null dereferences,
+violations of various API rules, dead code, and potential memory leaks in
+Objective-C programs. Since its inception, public feedback on the tool has been
+extremely positive, and conservative estimates put the number of real bugs it
+has found in industrial-quality software on the order of thousands.</p>
-<p>The JVM, called JnJVM, executes real-world applications such as Apache
-projects (e.g. Felix and Tomcat) and the SpecJVM98 benchmark. It uses the GNU
-Classpath project for the base classes. The CLI implementation, called N3, is
-its in early stages but can execute simple applications and the "pnetmark"
-benchmark. It uses the pnetlib project as its core library.</p>
-
-<p>The 'vmkit' VMs compare in performance with industrial and top open-source
-VMs on scientific applications. Besides the JIT, the VMs use many features of
-the LLVM framework, including the standard set of optimizations, atomic
-operations, custom function provider and memory manager for JITed methods, and
-specific virtual machine optimizations. vmkit is not an official part of LLVM
-2.3 release. It is publicly available under the LLVM license and can be
-downloaded from:
-</p>
+<p>The tool also provides a simple web GUI to inspect potential bugs found by
+the tool. While still early in development, the GUI illustrates some of the key
+features of Clang: accurate source location information, which is used by the
+GUI to highlight specific code expressions that relate to a bug (including those
+that span multiple lines); and built-in knowledge of macros, which is used to
+perform inline expansion of macros within the GUI itself.</p>
-<div class="doc_code">
-<pre>svn co http://llvm.org/svn/llvm-project/vmkit/trunk vmkit</pre>
-</div>
+<p>The set of checks performed by the static analyzer is gradually expanding,
+and future plans for the tool include full source-level inter-procedural
+analysis and deeper checks such as buffer overrun detection. There are many
+opportunities to extend and enhance the static analyzer, and anyone interested
+in working on this project is encouraged to get involved!</p>
</div>
<!--=========================================================================-->
-<div class="doc_subsubsection">
-<a name="clang">Clang</a>
+<div class="doc_subsection">
+<a name="vmkit">VMKit: JVM/CLI Virtual Machine Implementation</a>
</div>
<div class="doc_text">
+<p>
+The <a href="http://vmkit.llvm.org/">VMKit project</a> is an implementation of
+a JVM and a CLI Virtual Machines (Microsoft .NET is an
+implementation of the CLI) using the Just-In-Time compiler of LLVM.</p>
-<p>The <a href="http://clang.llvm.org/">Clang project</a> is an effort to build
-a set of new 'LLVM native' front-end technologies for the LLVM optimizer
-and code generator. Clang is continuing to make major strides forward in all
-areas. Its C and Objective-C parsing support is very solid, and the code
-generation support is far enough along to build many C applications. While not
-yet production quality, it is progressing very nicely. In addition, C++
-front-end work has started to make significant progress.</p>
+<p>Following LLVM 2.4, VMKit has its first release 0.24 that you can find on its
+<a href="http://vmkit.llvm.org/releases/">webpage</a>. The release includes
+bug fixes, cleanup and new features. The major changes are:</p>
+
+<ul>
-<p>At this point, Clang is most useful if you are interested in source-to-source
-transformations (such as refactoring) and other source-level tools for C and
-Objective-C. Clang now also includes tools for turning C code into pretty HTML,
-and includes a new <a href="http://clang.llvm.org/StaticAnalysis.html">static
-analysis tool</a> in development. This tool focuses on automatically finding
-bugs in C and Objective-C code.</p>
+<li> Support for generics in the .Net virtual machine.</li>
+<li> Initial support for the Mono class libraries. </li>
+<li> Support for MacOSX/x86, following LLVM's support for exceptions in
+JIT on MacOSX/x86. </li>
+<li> A new vmkit driver: a program to run java or .net applications. The driver
+supports llvm command line arguments including the new "-fast" option. </li>
+<li> A new memory allocation scheme in the JVM that makes unloading a
+class loader very fast. </li>
+<li> VMKit now follows the LLVM Makefile machinery. </li>
+</ul>
</div>
<!-- *********************************************************************** -->
<div class="doc_section">
- <a name="whatsnew">What's New?</a>
+ <a name="whatsnew">What's New in LLVM?</a>
</div>
<!-- *********************************************************************** -->
<div class="doc_text">
-<p>LLVM 2.3 includes a huge number of bug fixes, performance tweaks and minor
-improvements. Some of the major improvements and new features are listed in
-this section.
+<p>This release includes a huge number of bug fixes, performance tweaks, and
+minor improvements. Some of the major improvements and new features are listed
+in this section.
</p>
</div>
@@ -213,52 +211,29 @@
<div class="doc_text">
-<p>LLVM 2.3 includes several major new capabilities:</p>
+<p>LLVM 2.4 includes several major new capabilities:</p>
<ul>
-<li><p>The biggest change in LLVM 2.3 is Multiple Return Value (MRV) support.
- MRVs allow LLVM IR to directly represent functions that return multiple
- values without having to pass them "by reference" in the LLVM IR. This
- allows a front-end to generate more efficient code, as MRVs are generally
- returned in registers if a target supports them. See the <a
- href="LangRef.html#i_getresult">LLVM IR Reference</a> for more details.</p>
-
- <p>MRVs are fully supported in the LLVM IR, but are not yet fully supported in
- on all targets. However, it is generally safe to return up to 2 values from
- a function: most targets should be able to handle at least that. MRV
- support is a critical requirement for X86-64 ABI support, as X86-64 requires
- the ability to return multiple registers from functions, and we use MRVs to
- accomplish this in a direct way.</p></li>
-
-<li><p>LLVM 2.3 includes a complete reimplementation of the "<tt>llvmc</tt>"
- tool. It is designed to overcome several problems with the original
- <tt>llvmc</tt> and to provide a superset of the features of the
- '<tt>gcc</tt>' driver.</p>
-
- <p>The main features of <tt>llvmc2</tt> are:
- <ul>
- <li>Extended handling of command line options and smart rules for
- dispatching them to different tools.</li>
- <li>Flexible (and extensible) rules for defining different tools.</li>
- <li>The different intermediate steps performed by tools are represented
- as edges in the abstract graph.</li>
- <li>The 'language' for driver behavior definition is tablegen and thus
- it's relatively easy to add new features.</li>
- <li>The definition of driver is transformed into set of C++ classes, thus
- no runtime interpretation is needed.</li>
- </ul>
-</li>
-
-<li><p>LLVM 2.3 includes a completely rewritten interface for <a
- href="LinkTimeOptimization.html">Link Time Optimization</a>. This interface
- is written in C, which allows for easier integration with C code bases, and
- incorporates improvements we learned about from the first incarnation of the
- interface.</p></li>
-
-<li><p>The <a href="tutorial/LangImpl1.html">Kaleidoscope tutorial</a> now
- includes a "port" of the tutorial that <a
- href="tutorial/OCamlLangImpl1.html">uses the Ocaml bindings</a> to implement
- the Kaleidoscope language.</p></li>
+<li><p>The most visible end-user change in LLVM 2.4 is that it includes many
+optimizations and changes to make -O0 compile times much faster. You should see
+improvements in speed on the order of 30% (or more) than in LLVM 2.3. There are
+many pieces to this change described in more detail below. The speedups and new
+components can also be used for JIT compilers that want fast
+compilation.</p></li>
+
+<li><p>The biggest change to the LLVM IR is that Multiple Return Values (which
+were introduced in LLVM 2.3) have been generalized to full support for "First
+Class Aggregate" values in LLVM 2.4. This means that LLVM IR supports using
+structs and arrays as values in a function. This capability is mostly useful
+for front-end authors, who prefer to treat things like complex numbers, simple
+tuples, dope vectors, etc., as Value*'s instead of as a tuple of Value*'s or as
+memory values. Bitcode files from LLVM 2.3 will automatically migrate to the
+general representation.</p></li>
+
+<li><p>LLVM 2.4 also includes an initial port for the PIC16 microprocessor. This
+target only has support for 8 bit registers, and a number of other crazy
+constraints. While the port is still in early development stages, it shows some
+interesting things you can do with LLVM.</p></li>
</ul>
@@ -272,20 +247,34 @@
<div class="doc_text">
-<p>LLVM 2.3 fully supports the llvm-gcc 4.2 front-end, and includes support
-for the C, C++, Objective-C, Ada, and Fortran front-ends.</p>
-
-<p>
-<ul>
-<li>llvm-gcc 4.2 includes numerous fixes to better support the Objective-C
-front-end. Objective-C now works very well on Mac OS/X.</li>
-
-<li>Fortran <tt>EQUIVALENCE</tt>s are now supported by the gfortran
-front-end.</li>
-
-<li>llvm-gcc 4.2 includes many other fixes which improve conformance with the
-relevant parts of the GCC testsuite.</li>
-
+<p>LLVM fully supports the llvm-gcc 4.2 front-end, which marries the GCC
+front-ends and driver with the LLVM optimizer and code generator. It currently
+includes support for the C, C++, Objective-C, Ada, and Fortran front-ends.</p>
+
+<ul>
+<li>LLVM 2.4 supports the full set of atomic <tt>__sync_*</tt> builtins. LLVM
+2.3 only supported those used by OpenMP, but 2.4 supports them all. Note that
+while llvm-gcc supports all of these builtins, not all targets do. X86 support
+them all in both 32-bit and 64-bit mode and PowerPC supports them all except for
+the 64-bit operations when in 32-bit mode.</li>
+
+<li>llvm-gcc now supports an <tt>-flimited-precision</tt> option, which tells
+the compiler that it is okay to use low-precision approximations of certain libm
+functions (like <tt>exp</tt>, <tt>log</tt>, etc). This allows you to get high
+performance if you only need (say) 12-bits of precision.</li>
+
+<li>llvm-gcc now supports a C language extension known as "<a
+href="http://lists.cs.uiuc.edu/pipermail/cfe-dev/2008-August/002670.html">Blocks</a>".
+This feature is similar to nested functions and closures, but does not
+require stack trampolines (with most ABIs), and supports returning closures
+from functions that define them. Note that actually <em>using</em> Blocks
+requires a small runtime that is not included with llvm-gcc.</li>
+
+<li>llvm-gcc now supports a new <tt>-flto</tt> option. On systems that support
+transparent Link Time Optimization (currently Darwin systems with Xcode 3.1 and
+later) this allows the use of LTO with other optimization levels like -Os.
+Previously, LTO could only be used with -O4, which implied optimizations in
+-O3 that can increase code size.</li>
</ul>
</div>
@@ -297,23 +286,49 @@
</div>
<div class="doc_text">
-<p>New features include:
-</p>
+<p>New features include:</p>
<ul>
-<li>LLVM IR now directly represents "common" linkage, instead of representing it
-as a form of weak linkage.</li>
+<li>A major change to the <tt>Use</tt> class landed, which shrank it by 25%. Since
+this is a pervasive part of the LLVM, it ended up reducing the memory use of
+LLVM IR in general by 15% for most programs.</li>
+
+<li>Values with no names are now pretty printed by <tt>llvm-dis</tt> more
+nicely. They now print as "<tt>%3 = add i32 %A, 4</tt>" instead of
+"<tt>add i32 %A, 4 ; <i32>:3</tt>", which makes it much easier to read.
+</li>
-<li>LLVM IR now has support for atomic operations, and this functionality can be
-accessed through the llvm-gcc "<tt>__sync_synchronize</tt>",
-"<tt>__sync_val_compare_and_swap</tt>", and related builtins. Support for
-atomics are available in the Alpha, X86, X86-64, and PowerPC backends.</li>
-
-<li>The C and Ocaml bindings have extended to cover pass managers, several
-transformation passes, iteration over the LLVM IR, target data, and parameter
-attribute lists.</li>
+<li>LLVM 2.4 includes some changes for better vector support. First, the shift
+operations (<tt>shl</tt>, <tt>ashr</tt>, and <tt>lshr</tt>) now all support
+vectors and do an element-by-element shift (shifts of the whole vector can be
+accomplished by bitcasting the vector to <tt><1 x i128></tt>, for example). Second,
+there is initial support in development for vector comparisons with the
+<tt><a href="LangRef.html#i_fcmp">fcmp</a>/<a href="LangRef.html#i_icmp">icmp</a></tt>
+instructions. These instructions compare two vectors and return a vector of
+<tt>i1</tt>'s for each result. Note that there is very little codegen support
+available for any of these IR features though.</li>
+
+<li>A new <tt>DebugInfoBuilder</tt> class is available, which makes it much
+easier for front-ends to create debug info descriptors, similar to the way that
+<tt>IRBuilder</tt> makes it easier to create LLVM IR.</li>
+
+<li>The <tt>IRBuilder</tt> class is now parameterized by a class responsible
+for constant folding. The default <tt>ConstantFolder</tt> class does target independent
+constant folding. The <tt>NoFolder</tt> class does no constant folding at all, which is
+useful when learning how LLVM works. The <tt>TargetFolder</tt> class folds the most,
+doing target dependent constant folding.</li>
+
+<li>LLVM now supports "function attributes", which allow us to separate return
+value attributes from function attributes. LLVM now supports attributes on a
+function itself, a return value, and its parameters. New supported function
+attributes include <tt>noinline/alwaysinline</tt> and the <tt>opt-size</tt> flag,
+which says the function should be optimized for code size.</li>
+
+<li>LLVM IR now directly represents "common" linkage, instead of
+ representing it as a form of weak linkage.</li>
+
</ul>
-
+
</div>
<!--=========================================================================-->
@@ -323,66 +338,45 @@
<div class="doc_text">
-<p>In addition to a huge array of bug fixes and minor performance tweaks, the
-LLVM 2.3 optimizers support a few major enhancements:</p>
+<p>In addition to a huge array of bug fixes and minor performance tweaks, this
+release includes a few major enhancements and additions to the optimizers:</p>
<ul>
-<li><p>Loop index set splitting on by default.
-This transformation hoists conditions from loop bodies and reduces a loop's
-iteration space to improve performance. For example,</p>
-
-<div class="doc_code">
-<pre>
-for (i = LB; i < UB; ++i)
- if (i <= NV)
- LOOP_BODY
-</pre>
-</div>
-
-<p>is transformed into:</p>
-
-<p><div class="doc_code">
-<pre>
-NUB = min(NV+1, UB)
-for (i = LB; i < NUB; ++i)
- LOOP_BODY
-</pre>
-</div>
-</p>
-</li>
-
-<li>LLVM now includes a new <tt>memcpy</tt> optimization pass which removes
-dead <tt>memcpy</tt> calls, unneeded copies of aggregates, and performs
-return slot optimization. The LLVM optimizer now notices long sequences of
-consecutive stores and merges them into <tt>memcpy</tt>'s where profitable.</li>
-
-<li>Alignment detection for vector memory references and for <tt>memcpy</tt> and
-<tt>memset</tt> is now more aggressive.</li>
-
-<li>The Aggressive Dead Code Elimination (ADCE) optimization has been rewritten
-to make it both faster and safer in the presence of code containing infinite
-loops. Some of its prior functionality has been factored out into the loop
-deletion pass, which <em>is</em> safe for infinite loops. The new ADCE pass is
-no longer based on control dependence, making it run faster.</li>
-
-<li>The 'SimplifyLibCalls' pass, which optimizes calls to libc and libm
- functions for C-based languages, has been rewritten to be a FunctionPass
- instead a ModulePass. This allows it to be run more often and to be
- included at -O1 in llvm-gcc. It was also extended to include more
- optimizations and several corner case bugs were fixed.</li>
-
-<li>LLVM now includes a simple 'Jump Threading' pass, which attempts to simplify
- conditional branches using information about predecessor blocks, simplifying
- the control flow graph. This pass is pretty basic at this point, but
- catches some important cases and provides a foundation to build on.</li>
-
-<li>Several corner case bugs which could lead to deleting volatile memory
- accesses have been fixed.</li>
+<li>The Global Value Numbering (GVN) pass now does local Partial Redundancy
+Elimination (PRE) to eliminate some partially redundant expressions in cases
+where doing so won't grow code size.</li>
+
+<li>LLVM 2.4 includes a new loop deletion pass (which removes output-free
+provably-finite loops) and a rewritten Aggressive Dead Code Elimination (ADCE)
+pass that no longer uses control dependence information. These changes speed up
+the optimizer and also prevent it from deleting output-free infinite
+loops.</li>
+
+<li>The new AddReadAttrs pass works out which functions are read-only or
+read-none (these correspond to 'pure' and 'const' in GCC) and marks them
+with the appropriate attribute.</li>
+
+<li>LLVM 2.4 now includes a new SparsePropagation framework, which makes it
+trivial to build lattice-based dataflow solvers that operate over LLVM IR. Using
+this interface means that you just define objects to represent your lattice
+values and the transfer functions that operate on them. It handles the
+mechanics of worklist processing, liveness tracking, handling PHI nodes,
+etc.</li>
+
+<li>The Loop Strength Reduction and induction variable optimization passes have
+several improvements to avoid inserting MAX expressions, to optimize simple
+floating point induction variables and to analyze trip counts of more
+loops.</li>
+
+<li>Various helper functions (ComputeMaskedBits, ComputeNumSignBits, etc) were
+pulled out of the Instruction Combining pass and put into a new
+<tt>ValueTracking.h</tt> header, where they can be reused by other passes.</li>
+
+<li>The tail duplication pass has been removed from the standard optimizer
+sequence used by llvm-gcc. This pass still exists, but the benefits it once
+provided are now achieved by other passes.</li>
-<li>Several optimizations have been sped up, leading to faster code generation
- with the same code quality.</li>
-
</ul>
</div>
@@ -394,50 +388,47 @@
<div class="doc_text">
-<p>We put a significant amount of work into the code generator infrastructure,
+<p>We have put a significant amount of work into the code generator infrastructure,
which allows us to implement more aggressive algorithms and make it run
faster:</p>
<ul>
-<li>The code generator now has support for carrying information about memory
- references throughout the entire code generation process, via the
- <a href="http://llvm.org/doxygen/classllvm_1_1MachineMemOperand.html">
- MachineMemOperand</a> class. In the future this will be used to improve
- both pre-pass and post-pass scheduling, and to improve compiler-debugging
- output.</li>
-
-<li>The target-independent code generator infrastructure now uses LLVM's
- <a href="http://llvm.org/doxygen/classllvm_1_1APInt.html">APInt</a>
- class to handle integer values, which allows it to support integer types
- larger than 64 bits (for example i128). Note that support for such types is
- also dependent on target-specific support. Use of APInt is also a step
- toward support for non-power-of-2 integer sizes.</li>
-
-<li>LLVM 2.3 includes several compile time speedups for code with large basic
- blocks, particularly in the instruction selection phase, register
- allocation, scheduling, and tail merging/jump threading.</li>
-
-<li>LLVM 2.3 includes several improvements which make llc's
- <tt>--view-sunit-dags</tt> visualization of scheduling dependency graphs
- easier to understand.</li>
-
-<li>The code generator allows targets to write patterns that generate subreg
- references directly in .td files now.</li>
-
-<li><tt>memcpy</tt> lowering in the backend is more aggressive, particularly for
- <tt>memcpy</tt> calls introduced by the code generator when handling
- pass-by-value structure argument copies.</li>
-
-<li>Inline assembly with multiple register results now returns those results
- directly in the appropriate registers, rather than going through memory.
- Inline assembly that uses constraints like "ir" with immediates now use the
- 'i' form when possible instead of always loading the value in a register.
- This saves an instruction and reduces register use.</li>
+<li>The target-independent code generator supports (and the X86 backend
+ currently implements) a new interface for "fast" instruction selection. This
+ interface is optimized to produce code as quickly as possible, sacrificing
+ code quality to do it. This is used by default at -O0 or when using
+ "llc -fast" on X86. It is straight-forward to add support for
+ other targets if faster -O0 compilation is desired.</li>
+
+<li>In addition to the new 'fast' instruction selection path, many existing
+ pieces of the code generator have been optimized in significant ways.
+ SelectionDAG's are now pool allocated and use better algorithms in many
+ places, the ".s" file printers now use <tt>raw_ostream</tt> to emit text much faster,
+ etc. The end result of these improvements is that the compiler also takes
+ substantially less time to generate code that is just as good (and often
+ better) than before.</li>
+
+<li>Each target has been split to separate the ".s" file printing logic from the
+ rest of the target. This enables JIT compilers that don't link in the
+ (somewhat large) code and data tables used for printing a ".s" file.</li>
+
+<li>The code generator now includes a "stack slot coloring" pass, which packs
+ together individual spilled values into common stack slots. This reduces
+ the size of stack frames with many spills, which tends to increase L1 cache
+ effectiveness.</li>
+
+<li>Various pieces of the register allocator (e.g. the coalescer and two-address
+ operation elimination pass) now know how to rematerialize trivial operations
+ to avoid copies and include several other optimizations.</li>
+
+<li>The <a href="CodeGenerator.html#selectiondag_process">graphs</a> produced by
+ the <tt>llc -view-*-dags</tt> options are now significantly prettier and
+ easier to read.</li>
+
+<li>LLVM 2.4 includes a new register allocator based on Partitioned Boolean
+ Quadratic Programming (PBQP). This register allocator is still in
+ development, but is very simple and clean.</li>
-<li>Added support for PIC/GOT style <a
- href="CodeGenerator.html#tailcallopt">tail calls</a> on X86/32 and initial
- support for tail calls on PowerPC 32 (it may also work on PowerPC 64 but is
- not thoroughly tested).</li>
</ul>
</div>
@@ -445,7 +436,7 @@
<!--=========================================================================-->
<div class="doc_subsection">
-<a name="x86specific">X86/X86-64 Specific Improvements</a>
+<a name="targetspecific">Target Specific Improvements</a>
</div>
<div class="doc_text">
@@ -453,90 +444,131 @@
</p>
<ul>
-<li>llvm-gcc's X86-64 ABI conformance is far improved, particularly in the
- area of passing and returning structures by value. llvm-gcc compiled code
- now interoperates very well on X86-64 systems with other compilers.</li>
-
-<li>Support for Win64 was added. This includes code generation itself, JIT
- support, and necessary changes to llvm-gcc.</li>
-
-<li>The LLVM X86 backend now supports the support SSE 4.1 instruction set, and
- the llvm-gcc 4.2 front-end supports the SSE 4.1 compiler builtins. Various
- generic vector operations (insert/extract/shuffle) are much more efficient
- when SSE 4.1 is enabled. The JIT automatically takes advantage of these
- instructions, but llvm-gcc must be explicitly told to use them, e.g. with
- <tt>-march=penryn</tt>.</li>
-
-<li>The X86 backend now does a number of optimizations that aim to avoid
- converting numbers back and forth from SSE registers to the X87 floating
- point stack. This is important because most X86 ABIs require return values
- to be on the X87 Floating Point stack, but most CPUs prefer computation in
- the SSE units.</li>
+<li>Exception handling is supported by default on Linux/x86-64.</li>
+<li>Position Independent Code (PIC) is now supported on Linux/x86-64.</li>
+<li><tt>@llvm.frameaddress</tt> now supports getting the frame address of stack frames
+ > 0 on x86/x86-64.</li>
+<li>MIPS has improved a lot since last release, the most important changes
+ are: Little endian support, floating point support, allegrex core and
+ intrinsics support. O32 ABI is improved but isn't complete. The EABI
+ was implemented and is fully supported. We also have support for small
+ sections and gp_rel relocation for its access, a threshold in bytes can be
+ specified through command line.</li>
+<li>The PowerPC backend now supports trampolines.</li>
+</ul>
-<li>The X86 backend supports stack realignment, which is particularly useful for
- vector code on OS's without 16-byte aligned stacks, such as Linux and
- Windows.</li>
+</div>
-<li>The X86 backend now supports the "sseregparm" options in GCC, which allow
- functions to be tagged as passing floating point values in SSE
- registers.</li>
-<li>Trampolines (taking the address of a nested function) now work on
- Linux/X86-64.</li>
+<!--=========================================================================-->
+<div class="doc_subsection">
+<a name="otherimprovements">Other Improvements</a>
+</div>
-<li><tt>__builtin_prefetch</tt> is now compiled into the appropriate prefetch
- instructions instead of being ignored.</li>
+<div class="doc_text">
+<p>New features include:
+</p>
-<li>128-bit integers are now supported on X86-64 targets. This can be used
- through <tt>__attribute__((TImode))</tt> in llvm-gcc.</li>
+<ul>
+<li><tt>llvmc2</tt> (the generic compiler driver) gained plugin
+ support. It is now easier to experiment with <tt>llvmc2</tt> and
+ build your own tools based on it.</li>
-<li>The register allocator can now rematerialize PIC-base computations, which is
- an important optimization for register use.</li>
+<li>LLVM 2.4 includes a number of new generic algorithms and data structures,
+ including a scoped hash table, 'immutable' data structures, a simple
+ free-list manager, and a <tt>raw_ostream</tt> class.
+ The <tt>raw_ostream</tt> class and
+ <tt>format</tt> allow for efficient file output, and various pieces of LLVM
+ have switched over to use it. The eventual goal is to eliminate
+ use of <tt>std::ostream</tt> in favor of it.</li>
-<li>The "t" and "f" inline assembly constraints for the X87 floating point stack
- now work. However, the "u" constraint is still not fully supported.</li>
+<li>LLVM 2.4 includes an optional build system based on CMake. It
+ still is in its early stages but can be useful for Visual C++
+ users who can not use the Visual Studio IDE.</li>
</ul>
-
+
</div>
<!--=========================================================================-->
<div class="doc_subsection">
-<a name="targetspecific">Other Target Specific Improvements</a>
+<a name="changes">Major Changes and Removed Features</a>
</div>
<div class="doc_text">
-<p>New target-specific features include:
-</p>
+
+<p>If you're already an LLVM user or developer with out-of-tree changes based
+on LLVM 2.3, this section lists some "gotchas" that you may run into upgrading
+from the previous release.</p>
<ul>
-<li>The LLVM C backend now supports vector code.</li>
-<li>The Cell SPU backend includes a number of improvements. It generates better
- code and its stability/completeness is improving.</li>
-</ul>
-
-</div>
+<li>The LLVM IR generated by llvm-gcc no longer names all instructions. This
+ makes it run faster, but may be more confusing to some people. If you
+ prefer to have names, the '<tt>opt -instnamer</tt>' pass will add names to
+ all instructions.</li>
+<li>The LoadVN and GCSE passes have been removed from the tree. They are
+ obsolete and have been replaced with the GVN and MemoryDependence passes.
+ </li>
+</ul>
-<!--=========================================================================-->
-<div class="doc_subsection">
-<a name="otherimprovements">Other Improvements</a>
-</div>
-<div class="doc_text">
-<p>New features include:
-</p>
+<p>In addition, many APIs have changed in this release. Some of the major LLVM
+API changes are:</p>
<ul>
-<li>LLVM now builds with GCC 4.3.</li>
-<li>Bugpoint now supports running custom scripts (with the <tt>-run-custom</tt>
- option) to determine how to execute the command and whether it is making
- forward process.</li>
+
+<li>Now, function attributes and return value attributes are managed
+separately. Interface exported by <tt>ParameterAttributes.h</tt> header is now
+exported by <tt>Attributes.h</tt> header. The new attributes interface changes are:
+<ul>
+<li><tt>getParamAttrs</tt> method is now replaced by
+<tt>getParamAttributes</tt>, <tt>getRetAttributes</tt> and
+<tt>getFnAttributes</tt> methods.</li>
+<li> Return value attributes are stored at index 0. Function attributes are
+stored at index ~0U. Parameter attributes are stored at index that matches
+parameter number.</li>
+<li> <tt>ParamAttr</tt> namespace is now renamed as <tt>Attribute</tt>.</li>
+<li> The name of the class that manages reference count of opaque
+attributes is changed from <tt>PAListPtr</tt> to <tt>AttrListPtr</tt>.</li>
+<li> <tt>ParamAttrsWithIndex</tt> is now renamed as <tt>AttributeWithIndex</tt>.
+</li>
</ul>
-
+</li>
+
+<li>The <tt>DbgStopPointInst</tt> methods <tt>getDirectory</tt> and
+<tt>getFileName</tt> now return <tt>Value*</tt> instead of strings. These can be
+converted to strings using <tt>llvm::GetConstantStringInfo</tt> defined via
+"<tt>llvm/Analysis/ValueTracking.h</tt>".</li>
+
+<li>The APIs to create various instructions have changed from lower case
+ "create" methods to upper case "Create" methods (e.g.
+ <tt>BinaryOperator::create</tt>). LLVM 2.4 includes both cases, but the
+ lower case ones are removed in mainline (2.5 and later), please migrate.</li>
+
+<li>Various header files like "<tt>llvm/ADT/iterator</tt>" were given a ".h" suffix.
+ Change your code to #include "<tt>llvm/ADT/iterator.h</tt>" instead.</li>
+
+<li>The <tt>getresult</tt> instruction has been removed and replaced with the
+ <tt>extractvalue</tt> instruction. This is part of support for first class
+ aggregates.</li>
+
+<li>In the code generator, many <tt>MachineOperand</tt> predicates were renamed to be
+ shorter (e.g. <tt>isFrameIndex()</tt> -> <tt>isFI()</tt>),
+ <tt>SDOperand</tt> was renamed to <tt>SDValue</tt> (and the "<tt>Val</tt>"
+ member was changed to be the <tt>getNode()</tt> accessor), and the
+ <tt>MVT::ValueType</tt> enum has been replaced with an "<tt>MVT</tt>"
+ struct. The <tt>getSignExtended</tt> and <tt>getValue</tt> methods in the
+ ConstantSDNode class were renamed to <tt>getSExtValue</tt> and
+ <tt>getZExtValue</tt> respectively, to be more consistent with
+ the <tt>ConstantInt</tt> class.</li>
+</ul>
+
</div>
+
+
<!-- *********************************************************************** -->
<div class="doc_section">
<a name="portability">Portability and Supported Platforms</a>
@@ -548,10 +580,10 @@
<p>LLVM is known to work on the following platforms:</p>
<ul>
-<li>Intel and AMD machines (IA32) running Red Hat Linux, Fedora Core and FreeBSD
- (and probably other unix-like systems).</li>
-<li>PowerPC and X86-based Mac OS X systems, running 10.3 and above in 32-bit and
- 64-bit modes.</li>
+<li>Intel and AMD machines (IA32, X86-64, AMD64, EMT-64) running Red Hat
+Linux, Fedora Core and FreeBSD (and probably other unix-like systems).</li>
+<li>PowerPC and X86-based Mac OS X systems, running 10.3 and above in 32-bit
+and 64-bit modes.</li>
<li>Intel and AMD machines running on Win32 using MinGW libraries (native).</li>
<li>Intel and AMD machines running on Win32 with the Cygwin libraries (limited
support is available for native builds with Visual C++).</li>
@@ -575,9 +607,8 @@
<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
+<p>This section contains significant known problems with the LLVM system,
+listed by component. If you run into a problem, please check the <a
href="http://llvm.org/bugs/">LLVM bug database</a> and submit a bug if
there isn't already one.</p>
@@ -598,7 +629,7 @@
href="http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev">LLVMdev list</a>.</p>
<ul>
-<li>The MSIL, IA64, Alpha, SPU, and MIPS backends are experimental.</li>
+<li>The MSIL, IA64, Alpha, SPU, MIPS, and PIC16 backends are experimental.</li>
<li>The llc "<tt>-filetype=asm</tt>" (the default) is the only supported
value for this option.</li>
</ul>
@@ -625,8 +656,6 @@
to <a href="http://llvm.org/PR2255">several</a>
<a href="http://llvm.org/PR2257">bugs</a> due to lack of support for the
'u' inline assembly constraint and X87 floating point inline assembly.</li>
- <li>The X86-64 backend does not yet support position-independent code (PIC)
- generation on Linux targets.</li>
<li>The X86-64 backend does not yet support the LLVM IR instruction
<tt>va_arg</tt>. Currently, the llvm-gcc front-end supports variadic
argument constructs on X86-64 by lowering them manually.</li>
@@ -684,6 +713,20 @@
<!-- ======================================================================= -->
<div class="doc_subsection">
+ <a name="mips-be">Known problems with the MIPS back-end</a>
+</div>
+
+<div class="doc_text">
+
+<ul>
+<li>The O32 ABI is not fully supported.</li>
+<li>64-bit MIPS targets are not supported yet.</li>
+</ul>
+
+</div>
+
+<!-- ======================================================================= -->
+<div class="doc_subsection">
<a name="alpha-be">Known problems with the Alpha back-end</a>
</div>
@@ -707,7 +750,7 @@
<ul>
<li>The Itanium backend is highly experimental, and has a number of known
issues. We are looking for a maintainer for the Itanium backend. If you
- are interested, please contact the llvmdev mailing list.</li>
+ are interested, please contact the LLVMdev mailing list.</li>
</ul>
</div>
@@ -740,7 +783,7 @@
<p>llvm-gcc does not currently support <a href="http://llvm.org/PR869">Link-Time
Optimization</a> on most platforms "out-of-the-box". Please inquire on the
-llvmdev mailing list if you are interested.</p>
+LLVMdev mailing list if you are interested.</p>
<p>The only major language feature of GCC not supported by llvm-gcc is
the <tt>__builtin_apply</tt> family of builtins. However, some extensions
@@ -765,13 +808,26 @@
itself, Qt, Mozilla, etc.</p>
<ul>
-<li>Exception handling works well on the X86 and PowerPC targets, including
-X86-64 darwin. This works when linking to a libstdc++ compiled by GCC. It is
-supported on X86-64 linux, but that is disabled by default in this release.</li>
+<li>Exception handling works well on the X86 and PowerPC targets. Currently
+ only Linux and Darwin targets are supported (both 32 and 64 bit).</li>
</ul>
</div>
+<!-- ======================================================================= -->
+<div class="doc_subsection">
+ <a name="fortran-fe">Known problems with the llvm-gcc Fortran front-end</a>
+</div>
+
+<div class="doc_text">
+<ul>
+<li>Fortran support generally works, but there are still several unresolved bugs
+ in Bugzilla. Please see the tools/gfortran component for details.</li>
+
+<li>The Fortran front-end currently does not build on Darwin (without tweaks)
+ due to unresolved dependencies on the C front-end.</li>
+</ul>
+</div>
<!-- ======================================================================= -->
<div class="doc_subsection">
@@ -788,11 +844,10 @@
which does support trampolines.</li>
<li>The Ada front-end <a href="http://llvm.org/PR2007">fails to bootstrap</a>.
Workaround: configure with --disable-bootstrap.</li>
-<li>The c380004 and <a href="http://llvm.org/PR2010">c393010</a> ACATS tests
-fail (c380004 also fails with gcc-4.2 mainline). When built at -O3, the
-<a href="http://llvm.org/PR2421">cxg2021</a> ACATS test also fails.</li>
-<li>Some gcc specific Ada tests continue to crash the compiler. The testsuite
-reports most tests as having failed even though they pass.</li>
+<li>The c380004, <a href="http://llvm.org/PR2010">c393010</a>
+and <a href="http://llvm.org/PR2421">cxg2021</a> ACATS tests fail
+(c380004 also fails with gcc-4.2 mainline).</li>
+<li>Some gcc specific Ada tests continue to crash the compiler.</li>
<li>The -E binder option (exception backtraces)
<a href="http://llvm.org/PR1982">does not work</a> and will result in programs
crashing if an exception is raised. Workaround: do not use -E.</li>
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