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1683 lines
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HTML
1683 lines
86 KiB
HTML
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
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<html>
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<head>
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<title>LLVM Programmer's Manual</title>
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</head>
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<body style="background-color: white;">
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<table width="100%" bgcolor="#330077" border="0" cellpadding="4"
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cellspacing="0">
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<tbody>
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<tr>
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<td> <font size="+3" color="#eeeeff"
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face="Georgia,Palatino,Times,Roman"><b>LLVM Programmer's Manual</b></font></td>
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</tr>
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</tbody>
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</table>
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<ol>
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<li><a href="#introduction">Introduction</a> </li>
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<li><a href="#general">General Information</a>
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<ul>
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<li><a href="#stl">The C++ Standard Template Library</a><!--
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<li>The <tt>-time-passes</tt> option
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<li>How to use the LLVM Makefile system
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<li>How to write a regression test
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--> </li>
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</ul>
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</li>
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<li><a href="#apis">Important and useful LLVM APIs</a>
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<ul>
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<li><a href="#isa">The <tt>isa<></tt>, <tt>cast<></tt>
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and <tt>dyn_cast<></tt> templates</a> </li>
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<li><a href="#DEBUG">The <tt>DEBUG()</tt> macro & <tt>-debug</tt>
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option</a>
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<ul>
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<li><a href="#DEBUG_TYPE">Fine grained debug info with <tt>DEBUG_TYPE</tt>
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and the <tt>-debug-only</tt> option</a> </li>
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</ul>
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</li>
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<li><a href="#Statistic">The <tt>Statistic</tt> template & <tt>-stats</tt>
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option</a><!--
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<li>The <tt>InstVisitor</tt> template
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<li>The general graph API
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--> </li>
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</ul>
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</li>
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<li><a href="#common">Helpful Hints for Common Operations</a>
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<ul>
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<li><a href="#inspection">Basic Inspection and Traversal Routines</a>
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<ul>
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<li><a href="#iterate_function">Iterating over the <tt>BasicBlock</tt>s
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in a <tt>Function</tt></a> </li>
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<li><a href="#iterate_basicblock">Iterating over the <tt>Instruction</tt>s
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in a <tt>BasicBlock</tt></a> </li>
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<li><a href="#iterate_institer">Iterating over the <tt>Instruction</tt>s
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in a <tt>Function</tt></a> </li>
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<li><a href="#iterate_convert">Turning an iterator into a
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class pointer</a> </li>
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<li><a href="#iterate_complex">Finding call sites: a more
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complex example</a> </li>
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<li><a href="#calls_and_invokes">Treating calls and invokes
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the same way</a> </li>
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<li><a href="#iterate_chains">Iterating over def-use &
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use-def chains</a> </li>
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</ul>
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</li>
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<li><a href="#simplechanges">Making simple changes</a>
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<ul>
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<li><a href="#schanges_creating">Creating and inserting new
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<tt>Instruction</tt>s</a> </li>
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<li><a href="#schanges_deleting">Deleting <tt>Instruction</tt>s</a> </li>
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<li><a href="#schanges_replacing">Replacing an <tt>Instruction</tt>
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with another <tt>Value</tt></a> </li>
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</ul>
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<!--
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<li>Working with the Control Flow Graph
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<ul>
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<li>Accessing predecessors and successors of a <tt>BasicBlock</tt>
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<li>
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<li>
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</ul>
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--> </li>
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</ul>
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</li>
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<li><a href="#coreclasses">The Core LLVM Class Hierarchy Reference</a>
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<ul>
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<li><a href="#Value">The <tt>Value</tt> class</a>
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<ul>
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<li><a href="#User">The <tt>User</tt> class</a>
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<ul>
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<li><a href="#Instruction">The <tt>Instruction</tt> class</a>
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<ul>
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<li> <a href="#GetElementPtrInst">The <span
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style="font-family: monospace;">GetElementPtrInst</span> class</a><br>
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</li>
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</ul>
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</li>
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<li><a href="#GlobalValue">The <tt>GlobalValue</tt> class</a>
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<ul>
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<li><a href="#BasicBlock">The <tt>BasicBlock</tt>
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class</a> </li>
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<li><a href="#Function">The <tt>Function</tt> class</a> </li>
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<li><a href="#GlobalVariable">The <tt>GlobalVariable</tt>
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class</a> </li>
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</ul>
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</li>
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<li><a href="#Module">The <tt>Module</tt> class</a> </li>
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<li><a href="#Constant">The <tt>Constant</tt> class</a>
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<ul>
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<li> <br>
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</li>
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<li> <br>
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</li>
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</ul>
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</li>
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</ul>
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</li>
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<li><a href="#Type">The <tt>Type</tt> class</a> </li>
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<li><a href="#Argument">The <tt>Argument</tt> class</a> </li>
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</ul>
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</li>
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<li>The <tt>SymbolTable</tt> class </li>
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<li>The <tt>ilist</tt> and <tt>iplist</tt> classes
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<ul>
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<li>Creating, inserting, moving and deleting from LLVM lists </li>
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</ul>
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</li>
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<li>Important iterator invalidation semantics to be aware of </li>
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</ul>
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<p><b>Written by <a href="mailto:sabre@nondot.org">Chris Lattner</a>,<a
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href="mailto:dhurjati@cs.uiuc.edu">Dinakar Dhurjati</a>, and <a
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href="mailto:jstanley@cs.uiuc.edu">Joel Stanley</a></b></p>
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<p> </p>
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</li>
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</ol>
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<!-- *********************************************************************** -->
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<table width="100%" bgcolor="#330077" border="0" cellpadding="4"
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cellspacing="0">
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<tbody>
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<tr>
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<td align="center"><font color="#eeeeff" size="+2"
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face="Georgia,Palatino"><b> <a name="introduction">Introduction </a></b></font></td>
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</tr>
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</tbody>
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</table>
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<ul>
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<!-- *********************************************************************** -->
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This document is meant to highlight some of the important classes and
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interfaces available in the LLVM source-base. This manual is not
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intended to explain what LLVM is, how it works, and what LLVM code looks
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like. It assumes that you know the basics of LLVM and are interested
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in writing transformations or otherwise analyzing or manipulating the
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code.
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<p> This document should get you oriented so that you can find your
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way in the continuously growing source code that makes up the LLVM
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infrastructure. Note that this manual is not intended to serve as a
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replacement for reading the source code, so if you think there should be
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a method in one of these classes to do something, but it's not listed,
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check the source. Links to the <a href="/doxygen/">doxygen</a> sources
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are provided to make this as easy as possible.</p>
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<p> The first section of this document describes general information
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that is useful to know when working in the LLVM infrastructure, and the
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second describes the Core LLVM classes. In the future this manual will
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be extended with information describing how to use extension libraries,
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such as dominator information, CFG traversal routines, and useful
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utilities like the <tt><a href="/doxygen/InstVisitor_8h-source.html">InstVisitor</a></tt>
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template.</p>
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<p><!-- *********************************************************************** --> </p>
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</ul>
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<table width="100%" bgcolor="#330077" border="0" cellpadding="4"
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cellspacing="0">
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<tbody>
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<tr>
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<td align="center"><font color="#eeeeff" size="+2"
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face="Georgia,Palatino"><b> <a name="general">General Information </a></b></font></td>
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</tr>
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</tbody>
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</table>
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<ul>
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<!-- *********************************************************************** -->
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This section contains general information that is useful if you are
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working in the LLVM source-base, but that isn't specific to any
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particular API.
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<p><!-- ======================================================================= --> </p>
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</ul>
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<table width="100%" bgcolor="#441188" border="0" cellpadding="4"
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cellspacing="0">
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<tbody>
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<tr>
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<td> </td>
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<td width="100%"> <font color="#eeeeff"
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face="Georgia,Palatino"><b> <a name="stl">The C++ Standard Template
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Library</a> </b></font></td>
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</tr>
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</tbody>
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</table>
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<ul>
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LLVM makes heavy use of the C++ Standard Template Library (STL),
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perhaps much more than you are used to, or have seen before. Because of
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this, you might want to do a little background reading in the
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techniques used and capabilities of the library. There are many good
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pages that discuss the STL, and several books on the subject that you
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can get, so it will not be discussed in this document.
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<p> Here are some useful links:</p>
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<p> </p>
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<ol>
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<li><a href="http://www.dinkumware.com/refxcpp.html">Dinkumware C++
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Library reference</a> - an excellent reference for the STL and other
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parts of the standard C++ library. </li>
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<li><a href="http://www.tempest-sw.com/cpp/">C++ In a Nutshell</a> -
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This is an O'Reilly book in the making. It has a decent <a
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href="http://www.tempest-sw.com/cpp/ch13-libref.html">Standard Library
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Reference</a> that rivals Dinkumware's, and is actually free until the
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book is published. </li>
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<li><a href="http://www.parashift.com/c++-faq-lite/">C++ Frequently
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Asked Questions</a> </li>
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<li><a href="http://www.sgi.com/tech/stl/">SGI's STL Programmer's
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Guide</a> - Contains a useful <a
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href="http://www.sgi.com/tech/stl/stl_introduction.html">Introduction
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to the STL</a>. </li>
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<li><a href="http://www.research.att.com/%7Ebs/C++.html">Bjarne
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Stroustrup's C++ Page</a> </li>
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</ol>
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<p> You are also encouraged to take a look at the <a
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href="CodingStandards.html">LLVM Coding Standards</a> guide which
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focuses on how to write maintainable code more than where to put your
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curly braces.</p>
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<p><!-- ======================================================================= --> </p>
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</ul>
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<table width="100%" bgcolor="#441188" border="0" cellpadding="4"
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cellspacing="0">
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<tbody>
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<tr>
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<td> </td>
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<td width="100%"> <font color="#eeeeff"
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face="Georgia,Palatino"><b> <a name="stl">Other useful references</a> </b></font></td>
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</tr>
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</tbody>
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</table>
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<ul>
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LLVM is currently using CVS as its source versioning system. You may
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find this reference handy:
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<p> </p>
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<ol>
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<li><a href="http://www.psc.edu/%7Esemke/cvs_branches.html">CVS
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Branch and Tag Primer</a></li>
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</ol>
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<p><!-- *********************************************************************** --> </p>
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</ul>
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<table width="100%" bgcolor="#330077" border="0" cellpadding="4"
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cellspacing="0">
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<tbody>
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<tr>
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<td align="center"><font color="#eeeeff" size="+2"
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face="Georgia,Palatino"><b> <a name="apis">Important and useful LLVM
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APIs </a></b></font></td>
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</tr>
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</tbody>
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</table>
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<ul>
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<!-- *********************************************************************** -->
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Here we highlight some LLVM APIs that are generally useful and good to
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know about when writing transformations.
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<p><!-- ======================================================================= --> </p>
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</ul>
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<table width="100%" bgcolor="#441188" border="0" cellpadding="4"
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cellspacing="0">
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<tbody>
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<tr>
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<td> </td>
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<td width="100%"> <font color="#eeeeff"
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face="Georgia,Palatino"><b> <a name="isa">The isa<>,
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cast<> and dyn_cast<> templates</a> </b></font></td>
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</tr>
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</tbody>
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</table>
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<ul>
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The LLVM source-base makes extensive use of a custom form of RTTI.
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These templates have many similarities to the C++ <tt>dynamic_cast<></tt>
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operator, but they don't have some drawbacks (primarily stemming from
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the fact that <tt>dynamic_cast<></tt> only works on classes that
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have a v-table). Because they are used so often, you must know what they
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do and how they work. All of these templates are defined in the <a
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href="/doxygen/Casting_8h-source.html"><tt>Support/Casting.h</tt></a>
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file (note that you very rarely have to include this file directly).
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<p> </p>
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<dl>
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<dt><tt>isa<></tt>: </dt>
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<dd>The <tt>isa<></tt> operator works exactly like the Java "<tt>instanceof</tt>"
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operator. It returns true or false depending on whether a reference or
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pointer points to an instance of the specified class. This can be very
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useful for constraint checking of various sorts (example below).
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<p> </p>
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</dd>
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<dt><tt>cast<></tt>: </dt>
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<dd>The <tt>cast<></tt> operator is a "checked cast"
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operation. It converts a pointer or reference from a base class to a
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derived cast, causing an assertion failure if it is not really an
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instance of the right type. This should be used in cases where you have
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some information that makes you believe that something is of the right
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type. An example of the <tt>isa<></tt> and <tt>cast<></tt>
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template is:
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<p> </p>
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<pre>static bool isLoopInvariant(const <a href="#Value">Value</a> *V, const Loop *L) {<br> if (isa<<a
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href="#Constant">Constant</a>>(V) || isa<<a href="#Argument">Argument</a>>(V) || isa<<a
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href="#GlobalValue">GlobalValue</a>>(V))<br> return true;<br><br> <i>// Otherwise, it must be an instruction...</i><br> return !L->contains(cast<<a
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href="#Instruction">Instruction</a>>(V)->getParent());<br></pre>
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<p> Note that you should <b>not</b> use an <tt>isa<></tt>
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test followed by a <tt>cast<></tt>, for that use the <tt>dyn_cast<></tt>
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operator.</p>
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<p> </p>
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</dd>
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<dt><tt>dyn_cast<></tt>: </dt>
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<dd>The <tt>dyn_cast<></tt> operator is a "checking cast"
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operation. It checks to see if the operand is of the specified type, and
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if so, returns a pointer to it (this operator does not work with
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references). If the operand is not of the correct type, a null pointer
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is returned. Thus, this works very much like the <tt>dynamic_cast</tt>
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operator in C++, and should be used in the same circumstances.
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Typically, the <tt>dyn_cast<></tt> operator is used in an <tt>if</tt>
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statement or some other flow control statement like this:
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<p> </p>
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<pre> if (<a href="#AllocationInst">AllocationInst</a> *AI = dyn_cast<<a
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href="#AllocationInst">AllocationInst</a>>(Val)) {<br> ...<br> }<br></pre>
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<p> This form of the <tt>if</tt> statement effectively combines
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together a call to <tt>isa<></tt> and a call to <tt>cast<></tt>
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into one statement, which is very convenient.</p>
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<p> Another common example is:</p>
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<p> </p>
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<pre> <i>// Loop over all of the phi nodes in a basic block</i><br> BasicBlock::iterator BBI = BB->begin();<br> for (; <a
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href="#PhiNode">PHINode</a> *PN = dyn_cast<<a href="#PHINode">PHINode</a>>(BBI); ++BBI)<br> cerr << *PN;<br></pre>
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<p> Note that the <tt>dyn_cast<></tt> operator, like C++'s <tt>dynamic_cast</tt>
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or Java's <tt>instanceof</tt> operator, can be abused. In particular
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you should not use big chained <tt>if/then/else</tt> blocks to check for
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lots of different variants of classes. If you find yourself wanting to
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do this, it is much cleaner and more efficient to use the InstVisitor
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class to dispatch over the instruction type directly.</p>
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<p> </p>
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</dd>
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<dt><tt>cast_or_null<></tt>: </dt>
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<dd>The <tt>cast_or_null<></tt> operator works just like the <tt>cast<></tt>
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operator, except that it allows for a null pointer as an argument (which
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it then propagates). This can sometimes be useful, allowing you to
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combine several null checks into one.
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<p> </p>
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</dd>
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<dt><tt>dyn_cast_or_null<></tt>: </dt>
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<dd>The <tt>dyn_cast_or_null<></tt> operator works just like
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the <tt>dyn_cast<></tt> operator, except that it allows for a null
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pointer as an argument (which it then propagates). This can sometimes
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be useful, allowing you to combine several null checks into one.
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<p> </p>
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</dd>
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</dl>
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These five templates can be used with any classes, whether they have a
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v-table or not. To add support for these templates, you simply need to
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add <tt>classof</tt> static methods to the class you are interested
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casting to. Describing this is currently outside the scope of this
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document, but there are lots of examples in the LLVM source base.
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<p><!-- ======================================================================= --> </p>
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</ul>
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<table width="100%" bgcolor="#441188" border="0" cellpadding="4"
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cellspacing="0">
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<tbody>
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<tr>
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<td> </td>
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<td width="100%"> <font color="#eeeeff"
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face="Georgia,Palatino"><b> <a name="DEBUG">The <tt>DEBUG()</tt> macro
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& <tt>-debug</tt> option</a> </b></font></td>
|
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</tr>
|
|
</tbody>
|
|
</table>
|
|
<ul>
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Often when working on your pass you will put a bunch of debugging
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printouts and other code into your pass. After you get it working, you
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want to remove it... but you may need it again in the future (to work
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out new bugs that you run across).
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<p> Naturally, because of this, you don't want to delete the debug
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printouts, but you don't want them to always be noisy. A standard
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compromise is to comment them out, allowing you to enable them if you
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need them in the future.</p>
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<p> The "<tt><a href="/doxygen/Debug_8h-source.html">Support/Debug.h</a></tt>"
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file provides a macro named <tt>DEBUG()</tt> that is a much nicer
|
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solution to this problem. Basically, you can put arbitrary code into
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the argument of the <tt>DEBUG</tt> macro, and it is only executed if '<tt>opt</tt>'
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(or any other tool) is run with the '<tt>-debug</tt>' command line
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argument: </p>
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<pre> ... <br> DEBUG(std::cerr << "I am here!\n");<br> ...<br></pre>
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<p> Then you can run your pass like this:</p>
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<p> </p>
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<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>
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<p> Using the <tt>DEBUG()</tt> macro instead of a home-brewed solution
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allows you to now have to create "yet another" command line option for
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the debug output for your pass. Note that <tt>DEBUG()</tt> macros are
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disabled for optimized builds, so they do not cause a performance impact
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at all (for the same reason, they should also not contain
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side-effects!).</p>
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<p> One additional nice thing about the <tt>DEBUG()</tt> macro is that
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you can enable or disable it directly in gdb. Just use "<tt>set
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DebugFlag=0</tt>" or "<tt>set DebugFlag=1</tt>" from the gdb if the
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program is running. If the program hasn't been started yet, you can
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|
always just run it with <tt>-debug</tt>.</p>
|
|
<p><!-- _______________________________________________________________________ --> </p>
|
|
</ul>
|
|
<h4><a name="DEBUG_TYPE">
|
|
<hr size="1">Fine grained debug info with <tt>DEBUG_TYPE()</tt> and the <tt>-debug-only</tt>
|
|
option</a> </h4>
|
|
<ul>
|
|
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> </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>
|
|
<p> </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>
|
|
<p><!-- ======================================================================= --> </p>
|
|
</ul>
|
|
<table width="100%" bgcolor="#441188" border="0" cellpadding="4"
|
|
cellspacing="0">
|
|
<tbody>
|
|
<tr>
|
|
<td> </td>
|
|
<td width="100%"> <font color="#eeeeff"
|
|
face="Georgia,Palatino"><b> <a name="Statistic">The <tt>Statistic</tt>
|
|
template & <tt>-stats</tt> option</a> </b></font></td>
|
|
</tr>
|
|
</tbody>
|
|
</table>
|
|
<ul>
|
|
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> 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>
|
|
<p> </p>
|
|
<ol>
|
|
<li>Define your statistic like this:
|
|
<p> </p>
|
|
<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>
|
|
<p> </p>
|
|
</li>
|
|
<li>Whenever you make a transformation, bump the counter:
|
|
<p> </p>
|
|
<pre> ++NumXForms; // I did stuff<br></pre>
|
|
<p> </p>
|
|
</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>
|
|
<p> </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>
|
|
<p> </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>
|
|
<p><!-- *********************************************************************** --> </p>
|
|
</ul>
|
|
<table width="100%" bgcolor="#330077" border="0" cellpadding="4"
|
|
cellspacing="0">
|
|
<tbody>
|
|
<tr>
|
|
<td align="center"><font color="#eeeeff" size="+2"
|
|
face="Georgia,Palatino"><b> <a name="common">Helpful Hints for Common
|
|
Operations </a></b></font></td>
|
|
</tr>
|
|
</tbody>
|
|
</table>
|
|
<ul>
|
|
<!--
|
|
*********************************************************************** -->
|
|
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>
|
|
<p><!-- NOTE: this section should be heavy on example code --><!-- ======================================================================= --> </p>
|
|
</ul>
|
|
<table width="100%" bgcolor="#441188" border="0" cellpadding="4"
|
|
cellspacing="0">
|
|
<tbody>
|
|
<tr>
|
|
<td> </td>
|
|
<td width="100%"> <font color="#eeeeff"
|
|
face="Georgia,Palatino"><b> <a name="inspection">Basic Inspection and
|
|
Traversal Routines</a> </b></font></td>
|
|
</tr>
|
|
</tbody>
|
|
</table>
|
|
<ul>
|
|
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> 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>
|
|
<p><!-- _______________________________________________________________________ --> </p>
|
|
</ul>
|
|
<h4>
|
|
<hr size="1"><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> </h4>
|
|
<ul>
|
|
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:
|
|
<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>
|
|
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.<!-- _______________________________________________________________________ -->
|
|
</ul>
|
|
<h4>
|
|
<hr size="1"><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> </h4>
|
|
<ul>
|
|
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>:
|
|
<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>
|
|
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> 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>
|
|
<p><!-- _______________________________________________________________________ --> </p>
|
|
</ul>
|
|
<h4>
|
|
<hr size="1"><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></h4>
|
|
<ul>
|
|
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 stderr (<b>Note:</b> Dereferencing an <tt>InstIterator</tt>
|
|
yields an <tt>Instruction*</tt>, <i>not</i> an <tt>Instruction&</tt>!):
|
|
<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>
|
|
The STL set <tt>worklist</tt> would now contain all instructions in the <tt>Function</tt>
|
|
pointed to by F.<!-- _______________________________________________________________________ -->
|
|
</ul>
|
|
<h4>
|
|
<hr size="1"><a name="iterate_convert">Turning an iterator into a class
|
|
pointer (and vice-versa) </a></h4>
|
|
<ul>
|
|
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 straightforward.
|
|
Assuming that <tt>i</tt> is a <tt>BasicBlock::iterator</tt> and <tt>j</tt>
|
|
is a <tt>BasicBlock::const_iterator</tt>:
|
|
<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>
|
|
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,
|
|
<pre>Instruction* pinst = &*i;</pre>
|
|
is semantically equivalent to
|
|
<pre>Instruction* pinst = i;</pre>
|
|
It's also possible to turn a class pointer into the corresponding
|
|
iterator. Usually, this conversion is quite inexpensive. 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:
|
|
<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>
|
|
Of course, this example is strictly pedagogical, because it'd be much
|
|
better to explicitly grab the next instruction directly from inst.<!--_______________________________________________________________________-->
|
|
</ul>
|
|
<h4>
|
|
<hr size="1"><a name="iterate_complex">Finding call sites: a slightly
|
|
more complex example </a></h4>
|
|
<ul>
|
|
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 straightforward 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:
|
|
<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>
|
|
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...):
|
|
<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>
|
|
<!--_______________________________________________________________________-->
|
|
</ul>
|
|
<h4>
|
|
<hr size="1"><a name="calls_and_invokes">Treating calls and invokes the
|
|
same way</a></h4>
|
|
<ul>
|
|
<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/classCallSite.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 is supposed to have "value semantics". So it should be
|
|
passed by value, not by reference; 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. (You will notice, if
|
|
you look at its definition, that it has only a single data member.)</p>
|
|
<!--_______________________________________________________________________-->
|
|
</ul>
|
|
<h4>
|
|
<hr size="1"><a name="iterate_chains">Iterating over def-use &
|
|
use-def chains</a></h4>
|
|
<ul>
|
|
Frequently, we might have an instance of the <a
|
|
href="/doxygen/classValue.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>:
|
|
<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>
|
|
Alternately, it's common to have an instance of the <a
|
|
href="/doxygen/classUser.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>):
|
|
<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]
|
|
--><!-- ======================================================================= -->
|
|
</ul>
|
|
<table width="100%" bgcolor="#441188" border="0" cellpadding="4"
|
|
cellspacing="0">
|
|
<tbody>
|
|
<tr>
|
|
<td> </td>
|
|
<td width="100%"> <font color="#eeeeff"
|
|
face="Georgia,Palatino"><b> <a name="simplechanges">Making simple
|
|
changes</a> </b></font></td>
|
|
</tr>
|
|
</tbody>
|
|
</table>
|
|
<ul>
|
|
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.<!--_______________________________________________________________________-->
|
|
</ul>
|
|
<h4>
|
|
<hr size="1"><a name="schanges_creating">Creating and inserting new <tt>Instruction</tt>s</a></h4>
|
|
<ul>
|
|
<i>Instantiating Instructions</i>
|
|
<p>Creation of <tt>Instruction</tt>s is straightforward: 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>
|
|
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/classInstruction.html">doxygen documentation for the
|
|
subclass of Instruction</a> that you're interested in instantiating.
|
|
<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>
|
|
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><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>
|
|
</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>
|
|
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:
|
|
<pre>Instruction* pi = ...;<br>Instruction* newInst = new Instruction(..., pi);<br></pre>
|
|
which is much cleaner, especially if you're creating a lot of
|
|
instructions and adding them to <tt>BasicBlock</tt>s. </li>
|
|
</ul>
|
|
<!--_______________________________________________________________________-->
|
|
</ul>
|
|
<h4>
|
|
<hr size="1"><a name="schanges_deleting">Deleting <tt>Instruction</tt>s</a></h4>
|
|
<ul>
|
|
Deleting an instruction from an existing sequence of instructions that
|
|
form a <a href="#BasicBlock"><tt>BasicBlock</tt></a> is very
|
|
straightforward. 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.
|
|
<p> For example:</p>
|
|
<p> </p>
|
|
<pre> <a href="#Instruction">Instruction</a> *I = .. ;<br> <a
|
|
href="#BasicBlock">BasicBlock</a> *BB = I->getParent();<br> BB->getInstList().erase(I);<br></pre>
|
|
<p><!--_______________________________________________________________________--> </p>
|
|
</ul>
|
|
<h4>
|
|
<hr size="1"><a name="schanges_replacing">Replacing an <tt>Instruction</tt>
|
|
with another <tt>Value</tt></a></h4>
|
|
<ul>
|
|
<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>
|
|
</ul>
|
|
<h4><a name="schanges_deleting">Deleting <tt>Instruction</tt>s</a></h4>
|
|
<ul>
|
|
<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>
|
|
<p> </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>
|
|
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/classValue.html">Value Class</a> and <a
|
|
href="/doxygen/classUser.html">User Class</a>, respectively, for more
|
|
information.<!-- Value::replaceAllUsesWith User::replaceUsesOfWith Point out:
|
|
include/llvm/Transforms/Utils/ especially BasicBlockUtils.h with:
|
|
ReplaceInstWithValue, ReplaceInstWithInst
|
|
--><!-- *********************************************************************** -->
|
|
</ul>
|
|
<table width="100%" bgcolor="#330077" border="0" cellpadding="4"
|
|
cellspacing="0">
|
|
<tbody>
|
|
<tr>
|
|
<td align="center"><font color="#eeeeff" size="+2"
|
|
face="Georgia,Palatino"><b> <a name="coreclasses">The Core LLVM Class
|
|
Hierarchy Reference </a></b></font></td>
|
|
</tr>
|
|
</tbody>
|
|
</table>
|
|
<ul>
|
|
<!-- *********************************************************************** -->
|
|
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><!-- ======================================================================= --> </p>
|
|
</ul>
|
|
<table width="100%" bgcolor="#441188" border="0" cellpadding="4"
|
|
cellspacing="0">
|
|
<tbody>
|
|
<tr>
|
|
<td> </td>
|
|
<td width="100%"> <font color="#eeeeff"
|
|
face="Georgia,Palatino"><b> <a name="Value">The <tt>Value</tt> class</a> </b></font></td>
|
|
</tr>
|
|
</tbody>
|
|
</table>
|
|
<ul>
|
|
<tt>#include "<a href="/doxygen/Value_8h-source.html">llvm/Value.h</a>"</tt><br>
|
|
doxygen info: <a href="/doxygen/classValue.html">Value Class</a>
|
|
<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>
|
|
<p> </p>
|
|
<pre> %<b>foo</b> = add int 1, 2<br></pre>
|
|
<a name="#nameWarning">The name of this instruction is "foo". <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.</a>
|
|
<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 class that represents this value. Although
|
|
this may take some getting used to, it simplifies the representation
|
|
and makes it easier to manipulate.</p>
|
|
<p><!-- _______________________________________________________________________ --> </p>
|
|
</ul>
|
|
<h4>
|
|
<hr size="1"><a name="m_Value">Important Public Members of the <tt>Value</tt>
|
|
class</a></h4>
|
|
<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>
|
|
<p> </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>
|
|
<p> </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>
|
|
<p> </p>
|
|
<pre> Inst->replaceAllUsesWith(ConstVal);<br></pre>
|
|
<p><!-- ======================================================================= --> </p>
|
|
</li>
|
|
</ul>
|
|
<table width="100%" bgcolor="#441188" border="0" cellpadding="4"
|
|
cellspacing="0">
|
|
<tbody>
|
|
<tr>
|
|
<td> </td>
|
|
<td width="100%"> <font color="#eeeeff"
|
|
face="Georgia,Palatino"><b> <a name="User">The <tt>User</tt> class</a> </b></font></td>
|
|
</tr>
|
|
</tbody>
|
|
</table>
|
|
<ul>
|
|
<tt>#include "<a href="/doxygen/User_8h-source.html">llvm/User.h</a>"</tt><br>
|
|
doxygen info: <a href="/doxygen/classUser.html">User Class</a><br>
|
|
Superclass: <a href="#Value"><tt>Value</tt></a>
|
|
<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>
|
|
<p><!-- _______________________________________________________________________ --> </p>
|
|
</ul>
|
|
<h4>
|
|
<hr size="1"><a name="m_User">Important Public Members of the <tt>User</tt>
|
|
class</a></h4>
|
|
<ul>
|
|
The <tt>User</tt> class exposes the operand list in two ways: through
|
|
an index access interface and through an iterator based interface.
|
|
<p> </p>
|
|
<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>
|
|
<p> </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>
|
|
<p><!-- ======================================================================= --> </p>
|
|
</li>
|
|
</ul>
|
|
<table width="100%" bgcolor="#441188" border="0" cellpadding="4"
|
|
cellspacing="0">
|
|
<tbody>
|
|
<tr>
|
|
<td> </td>
|
|
<td width="100%"> <font color="#eeeeff"
|
|
face="Georgia,Palatino"><b> <a name="Instruction">The <tt>Instruction</tt>
|
|
class</a> </b></font></td>
|
|
</tr>
|
|
</tbody>
|
|
</table>
|
|
<ul>
|
|
<tt>#include "</tt><tt><a href="/doxygen/Instruction_8h-source.html">llvm/Instruction.h</a>"</tt><br>
|
|
doxygen info: <a href="/doxygen/classInstruction.html">Instruction
|
|
Class</a><br>
|
|
Superclasses: <a href="#User"><tt>User</tt></a>, <a href="#Value"><tt>Value</tt></a>
|
|
<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/classInstruction.html">doxygen
|
|
output</a>.</p>
|
|
<p><!-- _______________________________________________________________________ --> </p>
|
|
</ul>
|
|
<h4>
|
|
<hr size="1"><a name="m_Instruction">Important Public Members of the <tt>Instruction</tt>
|
|
class</a></h4>
|
|
<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>
|
|
<p> </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>
|
|
<p> </p>
|
|
</li>
|
|
<li><tt>unsigned getOpcode()</tt>
|
|
<p> Returns the opcode for the <tt>Instruction</tt>.</p>
|
|
<p> </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>
|
|
<table width="100%" bgcolor="#441188" border="0" cellpadding="4"
|
|
cellspacing="0">
|
|
<tbody>
|
|
<tr>
|
|
<td> </td>
|
|
<td width="100%"> <font color="#eeeeff"
|
|
face="Georgia,Palatino"><b> <a name="BasicBlock">The <tt>BasicBlock</tt>
|
|
class</a> </b></font></td>
|
|
</tr>
|
|
</tbody>
|
|
</table>
|
|
<ul>
|
|
<tt>#include "<a href="/doxygen/BasicBlock_8h-source.html">llvm/BasicBlock.h</a>"</tt><br>
|
|
doxygen info: <a href="/doxygen/classBasicBlock.html">BasicBlock Class</a><br>
|
|
Superclass: <a href="#Value"><tt>Value</tt></a>
|
|
<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>
|
|
<p><!-- _______________________________________________________________________ --> </p>
|
|
</ul>
|
|
<h4>
|
|
<hr size="1"><a name="m_BasicBlock">Important Public Members of the <tt>BasicBlock</tt>
|
|
class</a></h4>
|
|
<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>
|
|
<p> </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>
|
|
<p> </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>
|
|
<p> </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>
|
|
<p> </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>
|
|
<p><!-- ======================================================================= --> </p>
|
|
</li>
|
|
</ul>
|
|
<table width="100%" bgcolor="#441188" border="0" cellpadding="4"
|
|
cellspacing="0">
|
|
<tbody>
|
|
<tr>
|
|
<td> </td>
|
|
<td width="100%"> <font color="#eeeeff"
|
|
face="Georgia,Palatino"><b> <a name="GlobalValue">The <tt>GlobalValue</tt>
|
|
class</a> </b></font></td>
|
|
</tr>
|
|
</tbody>
|
|
</table>
|
|
<ul>
|
|
<tt>#include "<a href="/doxygen/GlobalValue_8h-source.html">llvm/GlobalValue.h</a>"</tt><br>
|
|
doxygen info: <a href="/doxygen/classGlobalValue.html">GlobalValue
|
|
Class</a><br>
|
|
Superclasses: <a href="#User"><tt>User</tt></a>, <a href="#Value"><tt>Value</tt></a>
|
|
<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 <span
|
|
style="font-family: monospace;">LinkageTypes</span> enumerator.</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 <span style="font-weight: bold;">address</span><span
|
|
style="font-weight: bold;">.</span> 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 <span style="font-family: monospace;">GetElementPtrInst</span>
|
|
instruction because this pointer must be dereferenced first. For
|
|
example, if you have a <span style="font-family: monospace;">GlobalVariable</span>
|
|
(a subclass of <span style="font-family: monospace;">GlobalValue)</span>
|
|
that is an array of 24 ints, type <span style="font-family: monospace;">[24
|
|
x int]</span>, then the <span style="font-family: monospace;">GlobalVariable</span>
|
|
is a pointer to that array. Although the address of the first element of
|
|
this array and the value of the <span style="font-family: monospace;">GlobalVariable</span>
|
|
are the same, they have different types. The <span
|
|
style="font-family: monospace;">GlobalVariable</span>'s type is <span
|
|
style="font-family: monospace;">[24 x int]</span>. The first element's
|
|
type is <span style="font-family: monospace;">int.</span> Because of
|
|
this, accessing a global value requires you to dereference the pointer
|
|
with <span style="font-family: monospace;">GetElementPtrInst</span>
|
|
first, then its elements can be accessed. This is explained in
|
|
the <a href="LangRef.html#globalvars">LLVM Language Reference Manual</a>.</p>
|
|
<p><!-- _______________________________________________________________________ --> </p>
|
|
</ul>
|
|
<h4>
|
|
<hr size="1"><a name="m_GlobalValue">Important Public Members of the <tt>GlobalValue</tt>
|
|
class</a></h4>
|
|
<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>
|
|
<p><!-- ======================================================================= --> </p>
|
|
</li>
|
|
</ul>
|
|
<table width="100%" bgcolor="#441188" border="0" cellpadding="4"
|
|
cellspacing="0">
|
|
<tbody>
|
|
<tr>
|
|
<td> </td>
|
|
<td width="100%"> <font color="#eeeeff"
|
|
face="Georgia,Palatino"><b> <a name="Function">The <tt>Function</tt>
|
|
class</a> </b></font></td>
|
|
</tr>
|
|
</tbody>
|
|
</table>
|
|
<ul>
|
|
<tt>#include "<a href="/doxygen/Function_8h-source.html">llvm/Function.h</a>"</tt><br>
|
|
doxygen info: <a href="/doxygen/classFunction.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> 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><!-- _______________________________________________________________________ --> </p>
|
|
</ul>
|
|
<h4>
|
|
<hr size="1"><a name="m_Function">Important Public Members of the <tt>Function</tt>
|
|
class</a></h4>
|
|
<ul>
|
|
<li><tt>Function(const </tt><tt><a href="#FunctionType">FunctionType</a>
|
|
*Ty, bool isInternal, 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 whether or not it should start out with internal
|
|
or external linkage. The <a href="#FunctionType"
|
|
style="font-family: monospace;">FunctionType</a> argument specifies the
|
|
formal arguments and return value for the function. The same <a
|
|
href="#FunctionTypel" style="font-family: monospace;">FunctionType</a>
|
|
value can be used to create multiple functions. The <span
|
|
style="font-family: monospace;">Parent</span> 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>
|
|
<p> </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>
|
|
<p> </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>
|
|
<p> </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>
|
|
<p> </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>
|
|
<p> </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>
|
|
<p> </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>
|
|
<p> </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>
|
|
<p> </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>
|
|
<p><!-- ======================================================================= --> </p>
|
|
</li>
|
|
</ul>
|
|
<table width="100%" bgcolor="#441188" border="0" cellpadding="4"
|
|
cellspacing="0">
|
|
<tbody>
|
|
<tr>
|
|
<td> </td>
|
|
<td width="100%"> <font color="#eeeeff"
|
|
face="Georgia,Palatino"><b> <a name="GlobalVariable">The <tt>GlobalVariable</tt>
|
|
class</a> </b></font></td>
|
|
</tr>
|
|
</tbody>
|
|
</table>
|
|
<ul>
|
|
<tt>#include "<a href="/doxygen/GlobalVariable_8h-source.html">llvm/GlobalVariable.h</a>"</tt><br>
|
|
doxygen info: <a href="/doxygen/classGlobalVariable.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> 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"><span
|
|
style="font-family: monospace;">GlobalValue</span></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>
|
|
<p><!-- _______________________________________________________________________ --> </p>
|
|
</ul>
|
|
<h4>
|
|
<hr size="1"><a name="m_GlobalVariable">Important Public Members of the <tt>GlobalVariable</tt>
|
|
class</a></h4>
|
|
<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>
|
|
<p> </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>
|
|
<p> </p>
|
|
</li>
|
|
<li><tt>bool hasInitializer()</tt>
|
|
<p> Returns true if this <tt>GlobalVariable</tt> has an intializer.</p>
|
|
<p> </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>
|
|
<p><!-- ======================================================================= --> </p>
|
|
</li>
|
|
</ul>
|
|
<table width="100%" bgcolor="#441188" border="0" cellpadding="4"
|
|
cellspacing="0">
|
|
<tbody>
|
|
<tr>
|
|
<td> </td>
|
|
<td width="100%"> <font color="#eeeeff"
|
|
face="Georgia,Palatino"><b> <a name="Module">The <tt>Module</tt> class</a> </b></font></td>
|
|
</tr>
|
|
</tbody>
|
|
</table>
|
|
<ul>
|
|
<tt>#include "<a href="/doxygen/Module_8h-source.html">llvm/Module.h</a>"</tt><br>
|
|
doxygen info: <a href="/doxygen/classModule.html">Module Class</a>
|
|
<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>
|
|
<p><!-- _______________________________________________________________________ --> </p>
|
|
</ul>
|
|
<h4>
|
|
<hr size="1"><a name="m_Module">Important Public Members of the <tt>Module</tt>
|
|
class<span style="font-family: monospace;"></span></a></h4>
|
|
<ul>
|
|
<li><span style="font-family: monospace;">Module::Module( std::string
|
|
name = "" ) </span></li>
|
|
</ul>
|
|
<p style="margin-left: 40px;">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>
|
|
<p> </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>
|
|
<hr size="1"> </li>
|
|
<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>
|
|
<p> </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>
|
|
<hr size="1"> </li>
|
|
<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>
|
|
<hr size="1"> </li>
|
|
<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>
|
|
<p> </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>
|
|
<p> </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>
|
|
<p> </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>
|
|
<p><!-- ======================================================================= --> </p>
|
|
</li>
|
|
</ul>
|
|
<table width="100%" bgcolor="#441188" border="0" cellpadding="4"
|
|
cellspacing="0">
|
|
<tbody>
|
|
<tr>
|
|
<td> </td>
|
|
<td width="100%"> <font color="#eeeeff"
|
|
face="Georgia,Palatino"><b> <a name="Constant">The <tt>Constant</tt>
|
|
class and subclasses</a> </b></font></td>
|
|
</tr>
|
|
</tbody>
|
|
</table>
|
|
<ul>
|
|
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><!-- _______________________________________________________________________ --> </p>
|
|
</ul>
|
|
<h4>
|
|
<hr size="1"><a name="m_Value">Important Public Methods</a></h4>
|
|
<ul>
|
|
<li><tt>bool isConstantExpr()</tt>: Returns true if it is a
|
|
ConstantExpr
|
|
<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>ConstantPointerRef : This represents a constant pointer value
|
|
that is initialized to point to a global value, which lies at a
|
|
constant fixed address.
|
|
<ul>
|
|
<li><tt>GlobalValue *getValue()</tt>: Returns the global
|
|
value to which this pointer is pointing to. </li>
|
|
</ul>
|
|
</li>
|
|
</ul>
|
|
<!-- ======================================================================= --> </li>
|
|
</ul>
|
|
<table width="100%" bgcolor="#441188" border="0" cellpadding="4"
|
|
cellspacing="0">
|
|
<tbody>
|
|
<tr>
|
|
<td> </td>
|
|
<td width="100%"> <font color="#eeeeff"
|
|
face="Georgia,Palatino"><b> <a name="Type">The <tt>Type</tt> class and
|
|
Derived Types</a> </b></font></td>
|
|
</tr>
|
|
</tbody>
|
|
</table>
|
|
<ul>
|
|
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.<!-- _______________________________________________________________________ -->
|
|
</ul>
|
|
<h4>
|
|
<hr size="1"><a name="m_Value">Important Public Methods</a></h4>
|
|
<ul>
|
|
<li><tt>PrimitiveID getPrimitiveID() const</tt>: Returns the base
|
|
type of the type. </li>
|
|
<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>: Equilivent to isSigned() ||
|
|
isUnsigned(), but with only a single virtual function invocation. </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>bool isRecursive() const</tt>: Returns rue if the type graph
|
|
contains a cycle. </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. </li>
|
|
<li><tt>bool isPrimitiveType() const</tt>: Returns true if it is a
|
|
primitive type. </li>
|
|
<li><tt>bool isDerivedType() const</tt>: Returns true if it is a
|
|
derived type. </li>
|
|
<li><tt>const Type * getContainedType (unsigned i) const</tt>: This
|
|
method is used to implement the type iterator. For derived types, this
|
|
returns the types 'contained' in the derived type, returning 0 when 'i'
|
|
becomes invalid. This allows the user to iterate over the types in a
|
|
struct, for example, really easily. </li>
|
|
<li><tt>unsigned getNumContainedTypes() const</tt>: Return the number
|
|
of types in the derived type.
|
|
<p> </p>
|
|
<hr> Derived Types
|
|
<p> </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 ParamTypes &getParamTypes() const</tt>:
|
|
Returns a vector of parameter types. </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>
|
|
<table width="100%" bgcolor="#441188" border="0" cellpadding="4"
|
|
cellspacing="0">
|
|
<tbody>
|
|
<tr>
|
|
<td> </td>
|
|
<td width="100%"> <font color="#eeeeff"
|
|
face="Georgia,Palatino"><b> <a name="Argument">The <tt>Argument</tt>
|
|
class</a> </b></font></td>
|
|
</tr>
|
|
</tbody>
|
|
</table>
|
|
<ul>
|
|
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.<!-- *********************************************************************** -->
|
|
</ul>
|
|
<!-- *********************************************************************** -->
|
|
<hr><font size-1="">
|
|
<address>By: <a href="mailto:dhurjati@cs.uiuc.edu">Dinakar Dhurjati</a>
|
|
and <a href="mailto:sabre@nondot.org">Chris Lattner</a></address>
|
|
</font><font size-1=""><a href="http://llvm.cs.uiuc.edu">The LLVM
|
|
Compiler Infrastructure</a> <br>
|
|
<!-- Created: Tue Aug 6 15:00:33 CDT 2002 --><!-- hhmts start --> Last
|
|
modified: Fri Nov 7 13:24:22 CST 2003<!-- hhmts end --> </font>
|
|
</body>
|
|
</html>
|