[llvm-branch-commits] [llvm-branch] r134689 - /llvm/branches/type-system-rewrite/docs/ProgrammersManual.html
Chris Lattner
sabre at nondot.org
Thu Jul 7 23:21:37 PDT 2011
Author: lattner
Date: Fri Jul 8 01:21:37 2011
New Revision: 134689
URL: http://llvm.org/viewvc/llvm-project?rev=134689&view=rev
Log:
rip out all mention of PATypeHolder and other dead abominations.
Modified:
llvm/branches/type-system-rewrite/docs/ProgrammersManual.html
Modified: llvm/branches/type-system-rewrite/docs/ProgrammersManual.html
URL: http://llvm.org/viewvc/llvm-project/llvm/branches/type-system-rewrite/docs/ProgrammersManual.html?rev=134689&r1=134688&r2=134689&view=diff
==============================================================================
--- llvm/branches/type-system-rewrite/docs/ProgrammersManual.html (original)
+++ llvm/branches/type-system-rewrite/docs/ProgrammersManual.html Fri Jul 8 01:21:37 2011
@@ -160,13 +160,6 @@
<li><a href="#advanced">Advanced Topics</a>
<ul>
- <li><a href="#TypeResolve">LLVM Type Resolution</a>
- <ul>
- <li><a href="#BuildRecType">Basic Recursive Type Construction</a></li>
- <li><a href="#refineAbstractTypeTo">The <tt>refineAbstractTypeTo</tt> method</a></li>
- <li><a href="#PATypeHolder">The PATypeHolder Class</a></li>
- <li><a href="#AbstractTypeUser">The AbstractTypeUser Class</a></li>
- </ul></li>
<li><a href="#SymbolTable">The <tt>ValueSymbolTable</tt> class</a></li>
<li><a href="#UserLayout">The <tt>User</tt> and owned <tt>Use</tt> classes' memory layout</a></li>
@@ -2645,169 +2638,7 @@
LLVM system, and only need to be accessed in unusual circumstances.
</p>
-<!-- ======================================================================= -->
-<h3>
- <a name="TypeResolve">LLVM Type Resolution</a>
-</h3>
-
-<div>
-
-<p>
-The LLVM type system has a very simple goal: allow clients to compare types for
-structural equality with a simple pointer comparison (aka a shallow compare).
-This goal makes clients much simpler and faster, and is used throughout the LLVM
-system.
-</p>
-
-<p>
-Unfortunately achieving this goal is not a simple matter. In particular,
-recursive types and late resolution of opaque types makes the situation very
-difficult to handle. Fortunately, for the most part, our implementation makes
-most clients able to be completely unaware of the nasty internal details. The
-primary case where clients are exposed to the inner workings of it are when
-building a recursive type. In addition to this case, the LLVM bitcode reader,
-assembly parser, and linker also have to be aware of the inner workings of this
-system.
-</p>
-
-<p>
-For our purposes below, we need three concepts. First, an "Opaque Type" is
-exactly as defined in the <a href="LangRef.html#t_opaque">language
-reference</a>. Second an "Abstract Type" is any type which includes an
-opaque type as part of its type graph (for example "<tt>{ opaque, i32 }</tt>").
-Third, a concrete type is a type that is not an abstract type (e.g. "<tt>{ i32,
-float }</tt>").
-</p>
-
-<!-- ______________________________________________________________________ -->
-<h4>
- <a name="BuildRecType">Basic Recursive Type Construction</a>
-</h4>
-
-<div>
-
-<p>
-Because the most common question is "how do I build a recursive type with LLVM",
-we answer it now and explain it as we go. Here we include enough to cause this
-to be emitted to an output .ll file:
-</p>
-
-<div class="doc_code">
-<pre>
-%mylist = type { %mylist*, i32 }
-</pre>
-</div>
-
-<p>
-To build this, use the following LLVM APIs:
-</p>
-
-<div class="doc_code">
-<pre>
-// <i>Create the initial outer struct</i>
-<a href="#PATypeHolder">PATypeHolder</a> StructTy = OpaqueType::get();
-std::vector<const Type*> Elts;
-Elts.push_back(PointerType::getUnqual(StructTy));
-Elts.push_back(Type::Int32Ty);
-StructType *NewSTy = StructType::get(Elts);
-
-// <i>At this point, NewSTy = "{ opaque*, i32 }". Tell VMCore that</i>
-// <i>the struct and the opaque type are actually the same.</i>
-cast<OpaqueType>(StructTy.get())-><a href="#refineAbstractTypeTo">refineAbstractTypeTo</a>(NewSTy);
-
-// <i>NewSTy is potentially invalidated, but StructTy (a <a href="#PATypeHolder">PATypeHolder</a>) is</i>
-// <i>kept up-to-date</i>
-NewSTy = cast<StructType>(StructTy.get());
-
-// <i>Add a name for the type to the module symbol table (optional)</i>
-MyModule->addTypeName("mylist", NewSTy);
-</pre>
-</div>
-
-<p>
-This code shows the basic approach used to build recursive types: build a
-non-recursive type using 'opaque', then use type unification to close the cycle.
-The type unification step is performed by the <tt><a
-href="#refineAbstractTypeTo">refineAbstractTypeTo</a></tt> method, which is
-described next. After that, we describe the <a
-href="#PATypeHolder">PATypeHolder class</a>.
-</p>
-
-</div>
-
-<!-- ______________________________________________________________________ -->
-<h4>
- <a name="refineAbstractTypeTo">The <tt>refineAbstractTypeTo</tt> method</a>
-</h4>
-
-<div>
-<p>
-The <tt>refineAbstractTypeTo</tt> method starts the type unification process.
-While this method is actually a member of the DerivedType class, it is most
-often used on OpaqueType instances. Type unification is actually a recursive
-process. After unification, types can become structurally isomorphic to
-existing types, and all duplicates are deleted (to preserve pointer equality).
-</p>
-
-<p>
-In the example above, the OpaqueType object is definitely deleted.
-Additionally, if there is an "{ \2*, i32}" type already created in the system,
-the pointer and struct type created are <b>also</b> deleted. Obviously whenever
-a type is deleted, any "Type*" pointers in the program are invalidated. As
-such, it is safest to avoid having <i>any</i> "Type*" pointers to abstract types
-live across a call to <tt>refineAbstractTypeTo</tt> (note that non-abstract
-types can never move or be deleted). To deal with this, the <a
-href="#PATypeHolder">PATypeHolder</a> class is used to maintain a stable
-reference to a possibly refined type, and the <a
-href="#AbstractTypeUser">AbstractTypeUser</a> class is used to update more
-complex datastructures.
-</p>
-
-</div>
-
-<!-- ______________________________________________________________________ -->
-<h4>
- <a name="PATypeHolder">The PATypeHolder Class</a>
-</h4>
-
-<div>
-<p>
-PATypeHolder is a form of a "smart pointer" for Type objects. When VMCore
-happily goes about nuking types that become isomorphic to existing types, it
-automatically updates all PATypeHolder objects to point to the new type. In the
-example above, this allows the code to maintain a pointer to the resultant
-resolved recursive type, even though the Type*'s are potentially invalidated.
-</p>
-
-<p>
-PATypeHolder is an extremely light-weight object that uses a lazy union-find
-implementation to update pointers. For example the pointer from a Value to its
-Type is maintained by PATypeHolder objects.
-</p>
-
-</div>
-
-<!-- ______________________________________________________________________ -->
-<h4>
- <a name="AbstractTypeUser">The AbstractTypeUser Class</a>
-</h4>
-
-<div>
-
-<p>
-Some data structures need more to perform more complex updates when types get
-resolved. To support this, a class can derive from the AbstractTypeUser class.
-This class
-allows it to get callbacks when certain types are resolved. To register to get
-callbacks for a particular type, the DerivedType::{add/remove}AbstractTypeUser
-methods can be called on a type. Note that these methods only work for <i>
- abstract</i> types. Concrete types (those that do not include any opaque
-objects) can never be refined.
-</p>
-</div>
-
-</div>
-
+
<!-- ======================================================================= -->
<h3>
<a name="SymbolTable">The <tt>ValueSymbolTable</tt> class</a>
@@ -3124,9 +2955,6 @@
<li><tt>bool isFloatingPointTy()</tt>: Return true if this is one of the five
floating point types.</li>
- <li><tt>bool isAbstract()</tt>: Return true if the type is abstract (contains
- an OpaqueType anywhere in its definition).</li>
-
<li><tt>bool isSized()</tt>: Return true if the type has known size. Things
that don't have a size are abstract types, labels and void.</li>
@@ -3188,14 +3016,6 @@
number of formal parameters.</li>
</ul>
</dd>
- <dt><tt>OpaqueType</tt></dt>
- <dd>Sublcass of DerivedType for abstract types. This class
- defines no content and is used as a placeholder for some other type. Note
- that OpaqueType is used (temporarily) during type resolution for forward
- references of types. Once the referenced type is resolved, the OpaqueType
- is replaced with the actual type. OpaqueType can also be used for data
- abstraction. At link time opaque types can be resolved to actual types
- of the same name.</dd>
</dl>
</div>
More information about the llvm-branch-commits
mailing list