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<meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
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<link rel="stylesheet" href="llvm.css" type="text/css" media="screen" />
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<title>Alias Analysis Infrastructure in LLVM</title>
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</head>
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<body>
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<div class="doc_title">
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Alias Analysis Infrastructure in LLVM
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</div>
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<ol>
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<li><a href="#introduction">Introduction</a></li>
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<li><a href="#overview">AliasAnalysis Overview</a></li>
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<ul>
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<li><a href="#pointers">Representation of Pointers</a></li>
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<li><a href="#MustMayNo">Must, May, and No Alias Responses</a></li>
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<li><a href="#ModRefInfo">The <tt>getModRefInfo</tt> methods</a></li>
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</ul>
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<li><a href="#writingnew">Writing a new AliasAnalysis Implementation</a></li>
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<ul>
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<li><a href="#passsubclasses">Different Pass styles</a></li>
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<li><a href="#requiredcalls">Required initialization calls</a></li>
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<li><a href="#interfaces">Interfaces which may be specified</a></li>
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<li><a href="#chaining">The AliasAnalysis chaining behavior</a></li>
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<li><a href="#implefficiency">Efficiency Issues</a></li>
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</ul>
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<li><a href="#using">Using AliasAnalysis results</a></li>
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<ul>
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<li><a href="#loadvn">Using the <tt>-load-vn</tt> Pass</a></li>
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<li><a href="#ast">Using the <tt>AliasSetTracker</tt> class</a></li>
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<li><a href="#direct">Using the AliasAnalysis interface directly</a></li>
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</ul>
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<li><a href="#tools">Helpful alias analysis related tools</a></li>
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<ul>
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<li><a href="#no-aa">The <tt>-no-aa</tt> pass</a></li>
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<li><a href="#print-alias-sets">The <tt>-print-alias-sets</tt> pass</a></li>
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<li><a href="#count-aa">The <tt>-count-aa</tt> pass</a></li>
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<li><a href="#aa-eval">The <tt>-aa-eval</tt> pass</a></li>
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</ul>
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</ul>
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2003-10-23 02:29:42 +00:00
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<p><b>Written by <a href="mailto:sabre@nondot.org">Chris Lattner</a></b></p>
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</ol>
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<!-- *********************************************************************** -->
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<div class="doc_section">
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<a name="introduction">Introduction</a>
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</div>
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<!-- *********************************************************************** -->
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<div class="doc_text">
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<p>
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Alias Analysis (or Pointer Analysis) is a technique which attempts to determine
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whether or not two pointers ever can point to the same object in memory.
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Traditionally, Alias Analyses respond to a query with either a <a
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href="#MustNoMay">Must, May, or No</a> alias response, indicating that two
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pointers do point to the same object, might point to the same object, or are
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known not to point to the same object.
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</p>
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<p>
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The <a href="/doxygen/classAliasAnalysis.html">AliasAnalysis</a> class is the
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centerpiece of the LLVM Alias Analysis related infrastructure. This class is
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the common interface between clients of alias analysis information and the
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implementations providing it. In addition to simple alias analysis information,
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this class exposes Mod/Ref information from those implementations which can
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provide it, allowing for powerful analyses and transformations to work well
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together.
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</p>
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<p>
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This document contains information necessary to successfully implement this
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interface, use it, and to test both sides. It also explains some of the finer
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points about what exactly results mean. If you feel that something is unclear
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or should be added, please <a href="mailto:sabre@nondot.org">let me
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know</a>.
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</p>
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</div>
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<!-- *********************************************************************** -->
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<div class="doc_section">
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<a name="overview">AliasAnalysis Overview</a>
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</div>
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<!-- *********************************************************************** -->
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<div class="doc_text">
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<p>
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The <a href="/doxygen/classAliasAnalysis.html">AliasAnalysis</a> class defines
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the interface that Alias Analysis implementations should support. This class
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exports two important enums: <tt>AliasResult</tt> and <tt>ModRefResult</tt>
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which represent the result of an alias query or a mod/ref query,
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respectively.
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</p>
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<p>
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The AliasAnalysis interface exposes information about memory, represented in
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several different ways. In particular, memory objects are represented as a
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starting address and size, and function calls are represented as the actual
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<tt>call</tt> or <tt>invoke</tt> instructions that performs the call. The
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AliasAnalysis interface also exposes some helper methods which allow you to get
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mod/ref information for arbitrary instructions.
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</p>
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</div>
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<!-- ======================================================================= -->
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<div class="doc_subsection">
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<a name="pointers">Representation of Pointers</a>
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</div>
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<div class="doc_text">
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<p>
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Most importantly, the AliasAnalysis class provides several methods which are
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used to query whether or not pointers alias, whether function calls can modify
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or read memory, etc.
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</p>
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<p>
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Representing memory objects as a starting address and a size is critically
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important for precise Alias Analyses. For example, consider this (silly) C
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code:
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</p>
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<p>
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<pre>
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int i;
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char C[2];
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char A[10];
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/* ... */
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for (i = 0; i != 10; ++i) {
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C[0] = A[i]; /* One byte store */
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C[1] = A[9-i]; /* One byte store */
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}
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</pre>
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</p>
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<p>
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In this case, the <tt>basicaa</tt> pass will disambiguate the stores to
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<tt>C[0]</tt> and <tt>C[1]</tt> because they are accesses to two distinct
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locations one byte apart, and the accesses are each one byte. In this case, the
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LICM pass can use store motion to remove the stores from the loop. In
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constrast, the following code:
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</p>
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<p>
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<pre>
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int i;
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char C[2];
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char A[10];
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/* ... */
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for (i = 0; i != 10; ++i) {
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((short*)C)[0] = A[i]; /* Two byte store! */
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C[1] = A[9-i]; /* One byte store */
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}
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</pre>
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</p>
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<p>
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In this case, the two stores to C do alias each other, because the access to the
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<tt>&C[0]</tt> element is a two byte access. If size information wasn't
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available in the query, even the first case would have to conservatively assume
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that the accesses alias.
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</p>
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</div>
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<!-- ======================================================================= -->
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<div class="doc_subsection">
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<a name="MustMayNo">Must, May, and No Alias Responses</a>
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</div>
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<div class="doc_text">
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<p>
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An Alias Analysis implementation can return one of three responses: MustAlias,
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MayAlias, and NoAlias. The No and May alias results are obvious: if the two
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pointers may never equal each other, return NoAlias, if they might, return
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MayAlias.
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</p>
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<p>
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The Must Alias response is trickier though. In LLVM, the Must Alias response
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may only be returned if the two memory objects are guaranteed to always start at
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exactly the same location. If two memory objects overlap, but do not start at
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the same location, MayAlias must be returned.
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</p>
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</div>
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<!-- ======================================================================= -->
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<div class="doc_subsection">
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<a name="ModRefInfo">The <tt>getModRefInfo</tt> methods</a>
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</div>
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<div class="doc_text">
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<p>
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The <tt>getModRefInfo</tt> methods return information about whether the
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execution of an instruction can read or modify a memory location. Mod/Ref
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information is always conservative: if an action <b>may</b> read a location, Ref
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is returned.
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</p>
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</div>
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<!-- *********************************************************************** -->
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<div class="doc_section">
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<a name="writingnew">Writing a new AliasAnalysis Implementation</a>
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</div>
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<!-- *********************************************************************** -->
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<div class="doc_text">
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<p>
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Writing a new alias analysis implementation for LLVM is quite straight-forward.
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There are already several implementations that you can use for examples, and the
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following information should help fill in any details. For a minimal example,
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take a look at the <a href="/doxygen/structNoAA.html"><tt>no-aa</tt></a>
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implementation.
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</p>
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</div>
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<!-- ======================================================================= -->
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<div class="doc_subsection">
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<a name="passsubclasses">Different Pass styles</a>
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</div>
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<div class="doc_text">
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<p>
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The first step to determining what type of <a href="WritingAnLLVMPass.html">LLVM
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pass</a> you need to use for your Alias Analysis. As is the case with most
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other analyses and transformations, the answer should be fairly obvious from
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what type of problem you are trying to solve:
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</p>
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<p>
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<ol>
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<li>If you require interprocedural analysis, it should be a
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<tt>Pass</tt>.</li>
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<li>If you are a global analysis, subclass <tt>FunctionPass</tt>.</li>
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<li>If you are a local pass, subclass <tt>BasicBlockPass</tt>.</li>
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<li>If you don't need to look at the program at all, subclass
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<tt>ImmutablePass</tt>.</li>
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</ol>
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</p>
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<p>
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In addition to the pass that you subclass, you should also inherit from the
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<tt>AliasAnalysis</tt> interface, of course, and use the
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<tt>RegisterAnalysisGroup</tt> template to register as an implementation of
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<tt>AliasAnalysis</tt>.
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</p>
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</div>
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<!-- ======================================================================= -->
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<div class="doc_subsection">
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<a name="requiredcalls">Required initialization calls</a>
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</div>
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<div class="doc_text">
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<p>
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Your subclass of AliasAnalysis is required to invoke two methods on the
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AliasAnalysis base class: <tt>getAnalysisUsage</tt> and
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<tt>InitializeAliasAnalysis</tt>. In particular, your implementation of
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<tt>getAnalysisUsage</tt> should explicitly call into the
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<tt>AliasAnalysis::getAnalysisUsage</tt> method in addition to doing any
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declaring any pass dependencies your pass has. Thus you should have something
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like this:
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</p>
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<p>
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<pre>
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void getAnalysisUsage(AnalysisUsage &AU) const {
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AliasAnalysis::getAnalysisUsage(AU);
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<i>// declare your dependencies here.</i>
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|
|
|
|
}
|
|
|
|
|
</pre>
|
2003-10-22 23:27:16 +00:00
|
|
|
</p>
|
|
|
|
|
<p>
|
2003-03-04 19:37:49 +00:00
|
|
|
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>, <tt>runOnBasicBlock</tt> for
|
|
|
|
|
a <tt>BasicBlockPass</tt>, or <tt>InitializeAliasAnalysis</tt> for an
|
2003-10-22 23:27:16 +00:00
|
|
|
<tt>ImmutablePass</tt>). For example (as part of a <tt>Pass</tt>):
|
|
|
|
|
</p>
|
|
|
|
|
<p>
|
2003-03-04 19:37:49 +00:00
|
|
|
<pre>
|
|
|
|
|
bool run(Module &M) {
|
|
|
|
|
InitializeAliasAnalysis(this);
|
|
|
|
|
<i>// Perform analysis here...</i>
|
|
|
|
|
return false;
|
|
|
|
|
}
|
|
|
|
|
</pre>
|
2003-10-22 23:27:16 +00:00
|
|
|
</p>
|
|
|
|
|
</div>
|
2003-03-04 19:37:49 +00:00
|
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|
|
|
|
<!-- ======================================================================= -->
|
2003-10-22 23:27:16 +00:00
|
|
|
<div class="doc_subsection">
|
|
|
|
|
<a name="interfaces">Interfaces which may be specified</a>
|
|
|
|
|
</div>
|
2003-03-04 19:37:49 +00:00
|
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|
|
2003-10-22 23:27:16 +00:00
|
|
|
<div class="doc_text">
|
|
|
|
|
<p>
|
2003-03-04 19:37:49 +00:00
|
|
|
All of the <a href="/doxygen/classAliasAnalysis.html">AliasAnalysis</a> virtual
|
|
|
|
|
methods default to providing 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.
|
2003-10-22 23:27:16 +00:00
|
|
|
</p>
|
|
|
|
|
</div>
|
2003-03-04 19:37:49 +00:00
|
|
|
|
|
|
|
|
<!-- ======================================================================= -->
|
2003-10-22 23:27:16 +00:00
|
|
|
<div class="doc_subsection">
|
|
|
|
|
<a name="chaining">The AliasAnalysis chaining behavior</a>
|
|
|
|
|
</div>
|
2003-03-04 19:37:49 +00:00
|
|
|
|
2003-10-22 23:27:16 +00:00
|
|
|
<div class="doc_text">
|
|
|
|
|
<p>
|
2003-03-04 19:37:49 +00:00
|
|
|
With only two special exceptions (the <tt>basicaa</tt> and <a
|
|
|
|
|
href="#no-aa"><tt>no-aa</tt></a> passes) every alias analysis pass should chain
|
|
|
|
|
to another alias analysis implementation (for example, you could specify
|
|
|
|
|
"<tt>-basic-aa -ds-aa -andersens-aa -licm</tt>" to get the maximum benefit from
|
|
|
|
|
the three alias analyses). To do this, simply "Require" AliasAnalysis in your
|
|
|
|
|
<tt>getAnalysisUsage</tt> method, and if you need to return a conservative
|
2003-10-22 23:27:16 +00:00
|
|
|
MayAlias or Mod/Ref result, simply chain to a lower analysis.
|
|
|
|
|
</p>
|
|
|
|
|
</div>
|
2003-03-04 19:37:49 +00:00
|
|
|
|
|
|
|
|
<!-- ======================================================================= -->
|
2003-10-22 23:27:16 +00:00
|
|
|
<div class="doc_subsection">
|
|
|
|
|
<a name="implefficiency">Efficiency Issues</a>
|
|
|
|
|
</div>
|
2003-03-04 19:37:49 +00:00
|
|
|
|
2003-10-22 23:27:16 +00:00
|
|
|
<div class="doc_text">
|
|
|
|
|
<p>
|
2003-03-04 19:37:49 +00:00
|
|
|
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
|
2003-10-22 23:27:16 +00:00
|
|
|
as possible (within reason).
|
|
|
|
|
</p>
|
|
|
|
|
</div>
|
2003-03-04 19:37:49 +00:00
|
|
|
|
|
|
|
|
<!-- *********************************************************************** -->
|
2003-10-22 23:27:16 +00:00
|
|
|
<div class="doc_section">
|
|
|
|
|
<a name="using">Using AliasAnalysis results</a>
|
|
|
|
|
</div>
|
2003-03-04 19:37:49 +00:00
|
|
|
<!-- *********************************************************************** -->
|
|
|
|
|
|
2003-10-22 23:27:16 +00:00
|
|
|
<div class="doc_text">
|
|
|
|
|
<p>
|
2003-03-04 19:37:49 +00:00
|
|
|
There are several different ways to use alias analysis results. In order of
|
2003-10-22 23:27:16 +00:00
|
|
|
preference, these are...
|
|
|
|
|
</p>
|
|
|
|
|
</div>
|
2003-03-04 19:37:49 +00:00
|
|
|
|
|
|
|
|
<!-- ======================================================================= -->
|
2003-10-22 23:27:16 +00:00
|
|
|
<div class="doc_subsection">
|
|
|
|
|
<a name="loadvn">Using the <tt>-load-vn</tt> Pass</a>
|
|
|
|
|
</div>
|
2003-03-04 19:37:49 +00:00
|
|
|
|
2003-10-22 23:27:16 +00:00
|
|
|
<div class="doc_text">
|
|
|
|
|
<p>
|
2003-03-04 19:37:49 +00:00
|
|
|
The <tt>load-vn</tt> pass uses alias analysis to provide value numbering
|
|
|
|
|
information for <tt>load</tt> instructions. If your analysis or transformation
|
|
|
|
|
can be modelled in a form that uses value numbering information, you don't have
|
|
|
|
|
to do anything special to handle load instructions: just use the
|
2003-10-22 23:27:16 +00:00
|
|
|
<tt>load-vn</tt> pass, which uses alias analysis.
|
|
|
|
|
</p>
|
|
|
|
|
</div>
|
2003-03-04 19:37:49 +00:00
|
|
|
|
|
|
|
|
<!-- ======================================================================= -->
|
2003-10-22 23:27:16 +00:00
|
|
|
<div class="doc_subsection">
|
|
|
|
|
<a name="ast">Using the <tt>AliasSetTracker</tt> class</a>
|
|
|
|
|
</div>
|
2003-03-04 19:37:49 +00:00
|
|
|
|
2003-10-22 23:27:16 +00:00
|
|
|
<div class="doc_text">
|
|
|
|
|
<p>
|
2003-03-04 19:37:49 +00:00
|
|
|
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/classAliasSetTracker.html">AliasSetTracker</a></tt> class is used
|
|
|
|
|
to efficiently build these Alias Sets from the pairwise alias analysis
|
2003-10-22 23:27:16 +00:00
|
|
|
information provided by the AliasAnalysis interface.
|
|
|
|
|
</p>
|
|
|
|
|
<p>
|
2003-03-04 19:37:49 +00:00
|
|
|
First you initialize the AliasSetTracker by use 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 AliasSetTracker
|
2003-10-22 23:27:16 +00:00
|
|
|
<tt>begin()</tt>/<tt>end()</tt> methods.
|
|
|
|
|
</p>
|
|
|
|
|
<p>
|
2003-03-04 19:37:49 +00:00
|
|
|
The <tt>AliasSet</tt>s formed by the <tt>AliasSetTracker</tt> are guaranteed to
|
|
|
|
|
be disjoint, calculate mod/ref information 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
|
2003-10-22 23:27:16 +00:00
|
|
|
instructions, and can provide a list of pointers in each set.
|
|
|
|
|
</p>
|
|
|
|
|
<p>
|
2003-03-04 19:37:49 +00:00
|
|
|
As an example user of this, the <a href="/doxygen/structLICM.html">Loop
|
|
|
|
|
Invariant Code Motion</a> pass uses AliasSetTrackers to build alias information
|
|
|
|
|
about each loop nest. If an AliasSet 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 <b>and</b> are must alias sets, then the stores may be sunk to
|
|
|
|
|
outside of the loop. Both of these transformations obviously only apply if the
|
2003-10-22 23:27:16 +00:00
|
|
|
pointer argument is loop-invariant.
|
|
|
|
|
</p>
|
|
|
|
|
</div>
|
2003-03-04 19:37:49 +00:00
|
|
|
|
|
|
|
|
<!-- ======================================================================= -->
|
2003-10-22 23:27:16 +00:00
|
|
|
<div class="doc_subsection">
|
|
|
|
|
<a name="direct">Using the AliasAnalysis interface directly</a>
|
|
|
|
|
</div>
|
2003-03-04 19:37:49 +00:00
|
|
|
|
2003-10-22 23:27:16 +00:00
|
|
|
<div class="doc_text">
|
|
|
|
|
<p>
|
2003-03-04 19:37:49 +00:00
|
|
|
As a last resort, your pass could use the AliasAnalysis interface directly to
|
|
|
|
|
service your pass. If you find the need to do this, please <a
|
|
|
|
|
href="mailto:sabre@nondot.org">let me know</a> so I can see if something new
|
2003-10-22 23:27:16 +00:00
|
|
|
needs to be added to LLVM.
|
|
|
|
|
</p>
|
|
|
|
|
</div>
|
2003-03-04 19:37:49 +00:00
|
|
|
|
|
|
|
|
<!-- *********************************************************************** -->
|
2003-10-22 23:27:16 +00:00
|
|
|
<div class="doc_section">
|
|
|
|
|
<a name="tools">Helpful alias-analysis-related tools</a>
|
|
|
|
|
</div>
|
2003-03-04 19:37:49 +00:00
|
|
|
<!-- *********************************************************************** -->
|
|
|
|
|
|
2003-10-22 23:27:16 +00:00
|
|
|
<div class="doc_text">
|
|
|
|
|
<p>
|
2003-03-04 19:37:49 +00:00
|
|
|
If you're going to be working with the AliasAnalysis infrastructure, there are
|
2003-10-22 23:27:16 +00:00
|
|
|
several nice tools that may be useful for you and are worth knowing about...
|
|
|
|
|
</p>
|
|
|
|
|
</div>
|
2003-03-04 19:37:49 +00:00
|
|
|
|
|
|
|
|
<!-- ======================================================================= -->
|
2003-10-22 23:27:16 +00:00
|
|
|
<div class="doc_subsection">
|
|
|
|
|
<a name="no-aa">The <tt>-no-aa</tt> pass</a>
|
|
|
|
|
</div>
|
2003-03-04 19:37:49 +00:00
|
|
|
|
2003-10-22 23:27:16 +00:00
|
|
|
<div class="doc_text">
|
|
|
|
|
<p>
|
2003-03-04 19:37:49 +00:00
|
|
|
The <tt>-no-aa</tt> analysis 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.
|
|
|
|
|
If you don't specify an alias analysis, the default will be to use the
|
2003-10-22 23:27:16 +00:00
|
|
|
<tt>basicaa</tt> pass which does quite a bit of disambiguation on its own.
|
|
|
|
|
</p>
|
|
|
|
|
</div>
|
2003-03-04 19:37:49 +00:00
|
|
|
|
|
|
|
|
|
|
|
|
|
<!-- ======================================================================= -->
|
2003-10-22 23:27:16 +00:00
|
|
|
<div class="doc_subsection">
|
|
|
|
|
<a name="print-alias-sets">The <tt>-print-alias-sets</tt> pass</a>
|
|
|
|
|
</div>
|
2003-03-04 19:37:49 +00:00
|
|
|
|
2003-10-22 23:27:16 +00:00
|
|
|
<div class="doc_text">
|
|
|
|
|
<p>
|
2003-03-04 19:37:49 +00:00
|
|
|
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
|
2003-10-22 23:27:16 +00:00
|
|
|
the <tt>AliasSetTracker</tt>.
|
|
|
|
|
</p>
|
|
|
|
|
</div>
|
2003-03-04 19:37:49 +00:00
|
|
|
|
|
|
|
|
<!-- ======================================================================= -->
|
2003-10-22 23:27:16 +00:00
|
|
|
<div class="doc_subsection">
|
|
|
|
|
<a name="count-aa">The <tt>-count-aa</tt> pass</a>
|
|
|
|
|
</div>
|
2003-03-04 19:37:49 +00:00
|
|
|
|
2003-10-22 23:27:16 +00:00
|
|
|
<div class="doc_text">
|
|
|
|
|
<p>
|
2003-03-04 19:37:49 +00:00
|
|
|
The <tt>-count-aa</tt> pass is useful to see how many queries a particular pass
|
|
|
|
|
is making and what kinds of responses are returned by the alias analysis. An
|
2003-10-22 23:27:16 +00:00
|
|
|
example usage is:
|
|
|
|
|
</p>
|
|
|
|
|
<p>
|
2003-03-04 19:37:49 +00:00
|
|
|
<pre>
|
|
|
|
|
$ opt -basicaa -count-aa -ds-aa -count-aa -licm
|
|
|
|
|
</pre>
|
2003-10-22 23:27:16 +00:00
|
|
|
</p>
|
|
|
|
|
<p>
|
2003-03-04 19:37:49 +00:00
|
|
|
Which 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
|
2003-10-22 23:27:16 +00:00
|
|
|
when evaluating an alias analysis for precision.
|
|
|
|
|
</p>
|
|
|
|
|
</div>
|
2003-03-04 19:37:49 +00:00
|
|
|
|
|
|
|
|
<!-- ======================================================================= -->
|
2003-10-22 23:27:16 +00:00
|
|
|
<div class="doc_subsection">
|
|
|
|
|
<a name="aa-eval">The <tt>-aa-eval</tt> pass</a>
|
|
|
|
|
</div>
|
2003-03-04 19:37:49 +00:00
|
|
|
|
2003-10-22 23:27:16 +00:00
|
|
|
<div class="doc_text">
|
|
|
|
|
<p>
|
2003-03-04 19:37:49 +00:00
|
|
|
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
|
2003-10-22 23:27:16 +00:00
|
|
|
printed.
|
|
|
|
|
</p>
|
|
|
|
|
</div>
|
2003-03-04 19:37:49 +00:00
|
|
|
|
|
|
|
|
<!-- *********************************************************************** -->
|
|
|
|
|
|
2003-10-23 01:49:47 +00:00
|
|
|
<hr><font size="-1">
|
2003-03-04 19:37:49 +00:00
|
|
|
<address><a href="mailto:sabre@nondot.org">Chris Lattner</a></address>
|
2003-10-23 01:49:47 +00:00
|
|
|
Last modified: $Date$
|
2003-10-22 23:27:16 +00:00
|
|
|
</font>
|
|
|
|
|
|
|
|
|
|
</body>
|
|
|
|
|
</html>
|
