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            <div class="doc_title">

            
              LLVM Programmer's Manual

            
            </div>


            <ol>

            
              <li><a href="#introduction">Introduction</a></li>

            
              <li><a href="#general">General Information</a>

            
                <ul>

            
                  <li><a href="#stl">The C++ Standard Template Library</a></li>

            
            <!--

            
                  <li>The <tt>-time-passes</tt> option</li>

            
                  <li>How to use the LLVM Makefile system</li>

            
                  <li>How to write a regression test</li>


            -->

            
                </ul>

            
              </li>

            
              <li><a href="#apis">Important and useful LLVM APIs</a>

            
                <ul>

            
                  <li><a href="#isa">The <tt>isa&lt;&gt;</tt>, <tt>cast&lt;&gt;</tt>

            
            and <tt>dyn_cast&lt;&gt;</tt> templates</a> </li>

            
                  <li><a href="#DEBUG">The <tt>DEBUG()</tt> macro and <tt>-debug</tt>

            
            option</a>

            
                    <ul>

            
                      <li><a href="#DEBUG_TYPE">Fine grained debug info with <tt>DEBUG_TYPE</tt>

            
            and the <tt>-debug-only</tt> option</a> </li>

            
                    </ul>

            
                  </li>

            
                  <li><a href="#Statistic">The <tt>Statistic</tt> class &amp; <tt>-stats</tt>

            
            option</a></li>

            
            <!--

            
                  <li>The <tt>InstVisitor</tt> template

            
                  <li>The general graph API

            
            -->

            
                  <li><a href="#ViewGraph">Viewing graphs while debugging code</a></li>

            
                </ul>

            
              </li>

            
              <li><a href="#datastructure">Picking the Right Data Structure for a Task</a>

            
                <ul>

            
                <li><a href="#ds_sequential">Sequential Containers (std::vector, std::list, etc)</a>

            
                <ul>

            
                  <li><a href="#dss_fixedarrays">Fixed Size Arrays</a></li>

            
                  <li><a href="#dss_heaparrays">Heap Allocated Arrays</a></li>

            
                  <li><a href="#dss_smallvector">"llvm/ADT/SmallVector.h"</a></li>

            
                  <li><a href="#dss_vector">&lt;vector&gt;</a></li>

            
                  <li><a href="#dss_deque">&lt;deque&gt;</a></li>

            
                  <li><a href="#dss_list">&lt;list&gt;</a></li>

            
                  <li><a href="#dss_ilist">llvm/ADT/ilist</a></li>

            
                  <li><a href="#dss_other">Other Sequential Container Options</a></li>

            
                </ul></li>

            
                <li><a href="#ds_set">Set-Like Containers (std::set, SmallSet, SetVector, etc)</a>

            
                <ul>

            
                  <li><a href="#dss_sortedvectorset">A sorted 'vector'</a></li>

            
                  <li><a href="#dss_smallset">"llvm/ADT/SmallSet.h"</a></li>

            
                  <li><a href="#dss_smallptrset">"llvm/ADT/SmallPtrSet.h"</a></li>

            
                  <li><a href="#dss_FoldingSet">"llvm/ADT/FoldingSet.h"</a></li>

            
                  <li><a href="#dss_set">&lt;set&gt;</a></li>

            
                  <li><a href="#dss_setvector">"llvm/ADT/SetVector.h"</a></li>

            
                  <li><a href="#dss_uniquevector">"llvm/ADT/UniqueVector.h"</a></li>

            
                  <li><a href="#dss_otherset">Other Set-Like ContainerOptions</a></li>

            
                </ul></li>

            
                <li><a href="#ds_map">Map-Like Containers (std::map, DenseMap, etc)</a>

            
                <ul>

            
                  <li><a href="#dss_sortedvectormap">A sorted 'vector'</a></li>

            
                  <li><a href="#dss_stringmap">"llvm/ADT/StringMap.h"</a></li>

            
                  <li><a href="#dss_indexedmap">"llvm/ADT/IndexedMap.h"</a></li>

            
                  <li><a href="#dss_densemap">"llvm/ADT/DenseMap.h"</a></li>

            
                  <li><a href="#dss_map">&lt;map&gt;</a></li>

            
                  <li><a href="#dss_othermap">Other Map-Like Container Options</a></li>

            
                </ul></li>

            
              </ul>

            
              </li>

            
              <li><a href="#common">Helpful Hints for Common Operations</a>

            
                <ul>

            
                  <li><a href="#inspection">Basic Inspection and Traversal Routines</a>

            
                    <ul>

            
                      <li><a href="#iterate_function">Iterating over the <tt>BasicBlock</tt>s

            
            in a <tt>Function</tt></a> </li>

            
                      <li><a href="#iterate_basicblock">Iterating over the <tt>Instruction</tt>s

            
            in a <tt>BasicBlock</tt></a> </li>

            
                      <li><a href="#iterate_institer">Iterating over the <tt>Instruction</tt>s

            
            in a <tt>Function</tt></a> </li>

            
                      <li><a href="#iterate_convert">Turning an iterator into a

            
            class pointer</a> </li>

            
                      <li><a href="#iterate_complex">Finding call sites: a more

            
            complex example</a> </li>

            
                      <li><a href="#calls_and_invokes">Treating calls and invokes

            
            the same way</a> </li>

            
                      <li><a href="#iterate_chains">Iterating over def-use &amp;

            
            use-def chains</a> </li>

            
                    </ul>

            
                  </li>

            
                  <li><a href="#simplechanges">Making simple changes</a>

            
                    <ul>

            
                      <li><a href="#schanges_creating">Creating and inserting new

            
            		 <tt>Instruction</tt>s</a> </li>

            
                      <li><a href="#schanges_deleting">Deleting 		 <tt>Instruction</tt>s</a> </li>

            
                      <li><a href="#schanges_replacing">Replacing an 		 <tt>Instruction</tt>

            
            with another <tt>Value</tt></a> </li>

            
                      <li><a href="#schanges_deletingGV">Deleting <tt>GlobalVariable</tt>s</a> </li>

            
                    </ul>

            
                  </li>

            
            <!--

            
                <li>Working with the Control Flow Graph

            
                <ul>

            
                  <li>Accessing predecessors and successors of a <tt>BasicBlock</tt>

            
                  <li>

            
                  <li>

            
                </ul>

            
            -->

            
                </ul>

            
              </li>


              <li><a href="#advanced">Advanced Topics</a>

            
              <ul>

            
              <li><a href="#TypeResolve">LLVM Type Resolution</a>

            
              <ul>

            
                <li><a href="#BuildRecType">Basic Recursive Type Construction</a></li>

            
                <li><a href="#refineAbstractTypeTo">The <tt>refineAbstractTypeTo</tt> method</a></li>

            
                <li><a href="#PATypeHolder">The PATypeHolder Class</a></li>

            
                <li><a href="#AbstractTypeUser">The AbstractTypeUser Class</a></li>

            
              </ul></li>


              <li><a href="#SymbolTable">The <tt>ValueSymbolTable</tt> and <tt>TypeSymbolTable</tt> classes </a></li>

            
              </ul></li>


              <li><a href="#coreclasses">The Core LLVM Class Hierarchy Reference</a>

            
                <ul>

            
                  <li><a href="#Type">The <tt>Type</tt> class</a> </li>

            
                  <li><a href="#Module">The <tt>Module</tt> class</a></li>

            
                  <li><a href="#Value">The <tt>Value</tt> class</a>

            
                  <ul>

            
                    <li><a href="#User">The <tt>User</tt> class</a>

            
                    <ul>

            
                      <li><a href="#Instruction">The <tt>Instruction</tt> class</a></li>

            
                      <li><a href="#Constant">The <tt>Constant</tt> class</a>

            
                      <ul>

            
                        <li><a href="#GlobalValue">The <tt>GlobalValue</tt> class</a>

            
                        <ul>

            
                          <li><a href="#Function">The <tt>Function</tt> class</a></li>

            
                          <li><a href="#GlobalVariable">The <tt>GlobalVariable</tt> class</a></li>

            
                        </ul>

            
                        </li>

            
                      </ul>

            
                      </li>

            
                    </ul>

            
                    </li>

            
                    <li><a href="#BasicBlock">The <tt>BasicBlock</tt> class</a></li>

            
                    <li><a href="#Argument">The <tt>Argument</tt> class</a></li>

            
                  </ul>

            
                  </li>

            
                </ul>

            
              </li>

            
            </ol>


            <div class="doc_author">

            
              <p>Written by <a href="mailto:sabre@nondot.org">Chris Lattner</a>,

            
                            <a href="mailto:dhurjati@cs.uiuc.edu">Dinakar Dhurjati</a>,

            
                            <a href="mailto:jstanley@cs.uiuc.edu">Joel Stanley</a>, and

            
                            <a href="mailto:rspencer@x10sys.com">Reid Spencer</a></p>

            
            </div>


            <!-- *********************************************************************** -->

            
            <div class="doc_section">

            
              <a name="introduction">Introduction </a>

            
            </div>

            
            <!-- *********************************************************************** -->


            <div class="doc_text">


            <p>This document is meant to highlight some of the important classes and

            
            interfaces available in the LLVM source-base.  This manual is not

            
            intended to explain what LLVM is, how it works, and what LLVM code looks

            
            like.  It assumes that you know the basics of LLVM and are interested

            
            in writing transformations or otherwise analyzing or manipulating the

            
            code.</p>


            <p>This document should get you oriented so that you can find your

            
            way in the continuously growing source code that makes up the LLVM

            
            infrastructure. Note that this manual is not intended to serve as a

            
            replacement for reading the source code, so if you think there should be

            
            a method in one of these classes to do something, but it's not listed,

            
            check the source.  Links to the <a href="/doxygen/">doxygen</a> sources

            
            are provided to make this as easy as possible.</p>


            <p>The first section of this document describes general information that is

            
            useful to know when working in the LLVM infrastructure, and the second describes

            
            the Core LLVM classes.  In the future this manual will be extended with

            
            information describing how to use extension libraries, such as dominator

            
            information, CFG traversal routines, and useful utilities like the <tt><a

            
            href="/doxygen/InstVisitor_8h-source.html">InstVisitor</a></tt> template.</p>


            </div>


            <!-- *********************************************************************** -->

            
            <div class="doc_section">

            
              <a name="general">General Information</a>

            
            </div>

            
            <!-- *********************************************************************** -->


            <div class="doc_text">


            <p>This section contains general information that is useful if you are working

            
            in the LLVM source-base, but that isn't specific to any particular API.</p>


            </div>


            <!-- ======================================================================= -->

            
            <div class="doc_subsection">

            
              <a name="stl">The C++ Standard Template Library</a>

            
            </div>


            <div class="doc_text">


            <p>LLVM makes heavy use of the C++ Standard Template Library (STL),

            
            perhaps much more than you are used to, or have seen before.  Because of

            
            this, you might want to do a little background reading in the

            
            techniques used and capabilities of the library.  There are many good

            
            pages that discuss the STL, and several books on the subject that you

            
            can get, so it will not be discussed in this document.</p>


            <p>Here are some useful links:</p>


            <ol>


            <li><a href="http://www.dinkumware.com/refxcpp.html">Dinkumware C++ Library

            
            reference</a> - an excellent reference for the STL and other parts of the

            
            standard C++ library.</li>


            <li><a href="http://www.tempest-sw.com/cpp/">C++ In a Nutshell</a> - This is an

            
            O'Reilly book in the making.  It has a decent

            
            Standard Library

            
            Reference that rivals Dinkumware's, and is unfortunately no longer free since the book has been

            
            published.</li>


            <li><a href="http://www.parashift.com/c++-faq-lite/">C++ Frequently Asked

            
            Questions</a></li>


            <li><a href="http://www.sgi.com/tech/stl/">SGI's STL Programmer's Guide</a> -

            
            Contains a useful <a

            
            href="http://www.sgi.com/tech/stl/stl_introduction.html">Introduction to the

            
            STL</a>.</li>


            <li><a href="http://www.research.att.com/%7Ebs/C++.html">Bjarne Stroustrup's C++

            
            Page</a></li>


            <li><a href="http://64.78.49.204/">

            
            Bruce Eckel's Thinking in C++, 2nd ed. Volume 2 Revision 4.0 (even better, get

            
            the book).</a></li>


            </ol>


            <p>You are also encouraged to take a look at the <a

            
            href="CodingStandards.html">LLVM Coding Standards</a> guide which focuses on how

            
            to write maintainable code more than where to put your curly braces.</p>


            </div>


            <!-- ======================================================================= -->

            
            <div class="doc_subsection">

            
              <a name="stl">Other useful references</a>

            
            </div>


            <div class="doc_text">


            <ol>

            
            <li><a href="http://www.psc.edu/%7Esemke/cvs_branches.html">CVS

            
            Branch and Tag Primer</a></li>

            
            <li><a href="http://www.fortran-2000.com/ArnaudRecipes/sharedlib.html">Using

            
            static and shared libraries across platforms</a></li>

            
            </ol>


            </div>


            <!-- *********************************************************************** -->

            
            <div class="doc_section">

            
              <a name="apis">Important and useful LLVM APIs</a>

            
            </div>

            
            <!-- *********************************************************************** -->


            <div class="doc_text">


            <p>Here we highlight some LLVM APIs that are generally useful and good to

            
            know about when writing transformations.</p>


            </div>


            <!-- ======================================================================= -->

            
            <div class="doc_subsection">

            
              <a name="isa">The <tt>isa&lt;&gt;</tt>, <tt>cast&lt;&gt;</tt> and

            
              <tt>dyn_cast&lt;&gt;</tt> templates</a>

            
            </div>


            <div class="doc_text">


            <p>The LLVM source-base makes extensive use of a custom form of RTTI.

            
            These templates have many similarities to the C++ <tt>dynamic_cast&lt;&gt;</tt>

            
            operator, but they don't have some drawbacks (primarily stemming from

            
            the fact that <tt>dynamic_cast&lt;&gt;</tt> only works on classes that

            
            have a v-table). Because they are used so often, you must know what they

            
            do and how they work. All of these templates are defined in the <a

            
             href="/doxygen/Casting_8h-source.html"><tt>llvm/Support/Casting.h</tt></a>

            
            file (note that you very rarely have to include this file directly).</p>


            <dl>

            
              <dt><tt>isa&lt;&gt;</tt>: </dt>


              <dd><p>The <tt>isa&lt;&gt;</tt> operator works exactly like the Java

            
              "<tt>instanceof</tt>" operator.  It returns true or false depending on whether

            
              a reference or pointer points to an instance of the specified class.  This can

            
              be very useful for constraint checking of various sorts (example below).</p>

            
              </dd>


              <dt><tt>cast&lt;&gt;</tt>: </dt>


              <dd><p>The <tt>cast&lt;&gt;</tt> operator is a "checked cast" operation. It

            
              converts a pointer or reference from a base class to a derived cast, causing

            
              an assertion failure if it is not really an instance of the right type.  This

            
              should be used in cases where you have some information that makes you believe

            
              that something is of the right type.  An example of the <tt>isa&lt;&gt;</tt>

            
              and <tt>cast&lt;&gt;</tt> template is:</p>


            <div class="doc_code">

            
            <pre>

            
            static bool isLoopInvariant(const <a href="#Value">Value</a> *V, const Loop *L) {

            
              if (isa&lt;<a href="#Constant">Constant</a>&gt;(V) || isa&lt;<a href="#Argument">Argument</a>&gt;(V) || isa&lt;<a href="#GlobalValue">GlobalValue</a>&gt;(V))

            
                return true;


              // <i>Otherwise, it must be an instruction...</i>

            
              return !L-&gt;contains(cast&lt;<a href="#Instruction">Instruction</a>&gt;(V)-&gt;getParent());

            
            }

            
            </pre>

            
            </div>


              <p>Note that you should <b>not</b> use an <tt>isa&lt;&gt;</tt> test followed

            
              by a <tt>cast&lt;&gt;</tt>, for that use the <tt>dyn_cast&lt;&gt;</tt>

            
              operator.</p>


              </dd>


              <dt><tt>dyn_cast&lt;&gt;</tt>:</dt>


              <dd><p>The <tt>dyn_cast&lt;&gt;</tt> operator is a "checking cast" operation.

            
              It checks to see if the operand is of the specified type, and if so, returns a

            
              pointer to it (this operator does not work with references). If the operand is

            
              not of the correct type, a null pointer is returned.  Thus, this works very

            
              much like the <tt>dynamic_cast&lt;&gt;</tt> operator in C++, and should be

            
              used in the same circumstances.  Typically, the <tt>dyn_cast&lt;&gt;</tt>

            
              operator is used in an <tt>if</tt> statement or some other flow control

            
              statement like this:</p>


            <div class="doc_code">

            
            <pre>

            
            if (<a href="#AllocationInst">AllocationInst</a> *AI = dyn_cast&lt;<a href="#AllocationInst">AllocationInst</a>&gt;(Val)) {

            
              // <i>...</i>

            
            }

            
            </pre>

            
            </div>


              <p>This form of the <tt>if</tt> statement effectively combines together a call

            
              to <tt>isa&lt;&gt;</tt> and a call to <tt>cast&lt;&gt;</tt> into one

            
              statement, which is very convenient.</p>


              <p>Note that the <tt>dyn_cast&lt;&gt;</tt> operator, like C++'s

            
              <tt>dynamic_cast&lt;&gt;</tt> or Java's <tt>instanceof</tt> operator, can be

            
              abused.  In particular, you should not use big chained <tt>if/then/else</tt>

            
              blocks to check for lots of different variants of classes.  If you find

            
              yourself wanting to do this, it is much cleaner and more efficient to use the

            
              <tt>InstVisitor</tt> class to dispatch over the instruction type directly.</p>


              </dd>


              <dt><tt>cast_or_null&lt;&gt;</tt>: </dt>


              <dd><p>The <tt>cast_or_null&lt;&gt;</tt> operator works just like the

            
              <tt>cast&lt;&gt;</tt> operator, except that it allows for a null pointer as an

            
              argument (which it then propagates).  This can sometimes be useful, allowing

            
              you to combine several null checks into one.</p></dd>


              <dt><tt>dyn_cast_or_null&lt;&gt;</tt>: </dt>


              <dd><p>The <tt>dyn_cast_or_null&lt;&gt;</tt> operator works just like the

            
              <tt>dyn_cast&lt;&gt;</tt> operator, except that it allows for a null pointer

            
              as an argument (which it then propagates).  This can sometimes be useful,

            
              allowing you to combine several null checks into one.</p></dd>


            </dl>


            <p>These five templates can be used with any classes, whether they have a

            
            v-table or not.  To add support for these templates, you simply need to add

            
            <tt>classof</tt> static methods to the class you are interested casting

            
            to. Describing this is currently outside the scope of this document, but there

            
            are lots of examples in the LLVM source base.</p>


            </div>


            <!-- ======================================================================= -->

            
            <div class="doc_subsection">

            
              <a name="DEBUG">The <tt>DEBUG()</tt> macro and <tt>-debug</tt> option</a>

            
            </div>


            <div class="doc_text">


            <p>Often when working on your pass you will put a bunch of debugging printouts

            
            and other code into your pass.  After you get it working, you want to remove

            
            it, but you may need it again in the future (to work out new bugs that you run

            
            across).</p>


            <p> Naturally, because of this, you don't want to delete the debug printouts,

            
            but you don't want them to always be noisy.  A standard compromise is to comment

            
            them out, allowing you to enable them if you need them in the future.</p>


            <p>The "<tt><a href="/doxygen/Debug_8h-source.html">llvm/Support/Debug.h</a></tt>"

            
            file provides a macro named <tt>DEBUG()</tt> that is a much nicer solution to

            
            this problem.  Basically, you can put arbitrary code into the argument of the

            
            <tt>DEBUG</tt> macro, and it is only executed if '<tt>opt</tt>' (or any other

            
            tool) is run with the '<tt>-debug</tt>' command line argument:</p>


            <div class="doc_code">

            
            <pre>

            
            DOUT &lt;&lt; "I am here!\n";

            
            </pre>

            
            </div>


            <p>Then you can run your pass like this:</p>


            <div class="doc_code">

            
            <pre>

            
            $ opt &lt; a.bc &gt; /dev/null -mypass

            
            <i>&lt;no output&gt;</i>

            
            $ opt &lt; a.bc &gt; /dev/null -mypass -debug

            
            I am here!

            
            </pre>

            
            </div>


            <p>Using the <tt>DEBUG()</tt> macro instead of a home-brewed solution allows you

            
            to not have to create "yet another" command line option for the debug output for

            
            your pass.  Note that <tt>DEBUG()</tt> macros are disabled for optimized builds,

            
            so they do not cause a performance impact at all (for the same reason, they

            
            should also not contain side-effects!).</p>


            <p>One additional nice thing about the <tt>DEBUG()</tt> macro is that you can

            
            enable or disable it directly in gdb.  Just use "<tt>set DebugFlag=0</tt>" or

            
            "<tt>set DebugFlag=1</tt>" from the gdb if the program is running.  If the

            
            program hasn't been started yet, you can always just run it with

            
            <tt>-debug</tt>.</p>


            </div>


            <!-- _______________________________________________________________________ -->

            
            <div class="doc_subsubsection">

            
              <a name="DEBUG_TYPE">Fine grained debug info with <tt>DEBUG_TYPE</tt> and

            
              the <tt>-debug-only</tt> option</a>

            
            </div>


            <div class="doc_text">


            <p>Sometimes you may find yourself in a situation where enabling <tt>-debug</tt>

            
            just turns on <b>too much</b> information (such as when working on the code

            
            generator).  If you want to enable debug information with more fine-grained

            
            control, you define the <tt>DEBUG_TYPE</tt> macro and the <tt>-debug</tt> only

            
            option as follows:</p>


            <div class="doc_code">

            
            <pre>

            
            DOUT &lt;&lt; "No debug type\n";

            
            #undef  DEBUG_TYPE

            
            #define DEBUG_TYPE "foo"

            
            DOUT &lt;&lt; "'foo' debug type\n";

            
            #undef  DEBUG_TYPE

            
            #define DEBUG_TYPE "bar"

            
            DOUT &lt;&lt; "'bar' debug type\n";

            
            #undef  DEBUG_TYPE

            
            #define DEBUG_TYPE ""

            
            DOUT &lt;&lt; "No debug type (2)\n";

            
            </pre>

            
            </div>


            <p>Then you can run your pass like this:</p>


            <div class="doc_code">

            
            <pre>

            
            $ opt &lt; a.bc &gt; /dev/null -mypass

            
            <i>&lt;no output&gt;</i>

            
            $ opt &lt; a.bc &gt; /dev/null -mypass -debug

            
            No debug type

            
            'foo' debug type

            
            'bar' debug type

            
            No debug type (2)

            
            $ opt &lt; a.bc &gt; /dev/null -mypass -debug-only=foo

            
            'foo' debug type

            
            $ opt &lt; a.bc &gt; /dev/null -mypass -debug-only=bar

            
            'bar' debug type

            
            </pre>

            
            </div>


            <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 "llvm/Support/Debug.h"</tt>, you don't have to insert the ugly

            
            <tt>#undef</tt>'s).  Also, you should use names more meaningful than "foo" and

            
            "bar", because there is no system in place to ensure that names do not

            
            conflict. If two different modules use the same string, they will all be turned

            
            on when the name is specified. This allows, for example, all debug information

            
            for instruction scheduling to be enabled with <tt>-debug-type=InstrSched</tt>,

            
            even if the source lives in multiple files.</p>


            </div>


            <!-- ======================================================================= -->

            
            <div class="doc_subsection">

            
              <a name="Statistic">The <tt>Statistic</tt> class &amp; <tt>-stats</tt>

            
              option</a>

            
            </div>


            <div class="doc_text">


            <p>The "<tt><a

            
            href="/doxygen/Statistic_8h-source.html">llvm/ADT/Statistic.h</a></tt>" file

            
            provides a class named <tt>Statistic</tt> that is used as a unified way to

            
            keep track of what the LLVM compiler is doing and how effective various

            
            optimizations are.  It is useful to see what optimizations are contributing to

            
            making a particular program run faster.</p>


            <p>Often you may run your pass on some big program, and you're interested to see

            
            how many times it makes a certain transformation.  Although you can do this with

            
            hand inspection, or some ad-hoc method, this is a real pain and not very useful

            
            for big programs.  Using the <tt>Statistic</tt> class makes it very easy to

            
            keep track of this information, and the calculated information is presented in a

            
            uniform manner with the rest of the passes being executed.</p>


            <p>There are many examples of <tt>Statistic</tt> uses, but the basics of using

            
            it are as follows:</p>


            <ol>

            
                <li><p>Define your statistic like this:</p>


            <div class="doc_code">

            
            <pre>

            
            #define <a href="#DEBUG_TYPE">DEBUG_TYPE</a> "mypassname"   <i>// This goes before any #includes.</i>

            
            STATISTIC(NumXForms, "The # of times I did stuff");

            
            </pre>

            
            </div>


              <p>The <tt>STATISTIC</tt> macro defines a static variable, whose name is

            
                specified by the first argument.  The pass name is taken from the DEBUG_TYPE

            
                macro, and the description is taken from the second argument.  The variable

            
                defined ("NumXForms" in this case) acts like an unsigned integer.</p></li>


                <li><p>Whenever you make a transformation, bump the counter:</p>


            <div class="doc_code">

            
            <pre>

            
            ++NumXForms;   // <i>I did stuff!</i>

            
            </pre>

            
            </div>


                </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>


            <div class="doc_code">

            
            <pre>

            
            $ opt -stats -mypassname &lt; program.bc &gt; /dev/null

            
            <i>... statistics output ...</i>

            
            </pre>

            
            </div>


              <p> When running <tt>opt</tt> on a C file from the SPEC benchmark

            
            suite, it gives a report that looks like this:</p>


            <div class="doc_code">

            
            <pre>

            
               7646 bitcodewriter   - Number of normal instructions

            
                725 bitcodewriter   - Number of oversized instructions

            
             129996 bitcodewriter   - Number of bitcode bytes written

            
               2817 raise           - Number of insts DCEd or constprop'd

            
               3213 raise           - Number of cast-of-self removed

            
               5046 raise           - Number of expression trees converted

            
                 75 raise           - Number of other getelementptr's formed

            
                138 raise           - Number of load/store peepholes

            
                 42 deadtypeelim    - Number of unused typenames removed from symtab

            
                392 funcresolve     - Number of varargs functions resolved

            
                 27 globaldce       - Number of global variables removed

            
                  2 adce            - Number of basic blocks removed

            
                134 cee             - Number of branches revectored

            
                 49 cee             - Number of setcc instruction eliminated

            
                532 gcse            - Number of loads removed

            
               2919 gcse            - Number of instructions removed

            
                 86 indvars         - Number of canonical indvars added

            
                 87 indvars         - Number of aux indvars removed

            
                 25 instcombine     - Number of dead inst eliminate

            
                434 instcombine     - Number of insts combined

            
                248 licm            - Number of load insts hoisted

            
               1298 licm            - Number of insts hoisted to a loop pre-header

            
                  3 licm            - Number of insts hoisted to multiple loop preds (bad, no loop pre-header)

            
                 75 mem2reg         - Number of alloca's promoted

            
               1444 cfgsimplify     - Number of blocks simplified

            
            </pre>

            
            </div>


            <p>Obviously, with so many optimizations, having a unified framework for this

            
            stuff is very nice.  Making your pass fit well into the framework makes it more

            
            maintainable and useful.</p>


            </div>


            <!-- ======================================================================= -->

            
            <div class="doc_subsection">

            
              <a name="ViewGraph">Viewing graphs while debugging code</a>

            
            </div>


            <div class="doc_text">


            <p>Several of the important data structures in LLVM are graphs: for example

            
            CFGs made out of LLVM <a href="#BasicBlock">BasicBlock</a>s, CFGs made out of

            
            LLVM <a href="CodeGenerator.html#machinebasicblock">MachineBasicBlock</a>s, and

            
            <a href="CodeGenerator.html#selectiondag_intro">Instruction Selection

            
            DAGs</a>.  In many cases, while debugging various parts of the compiler, it is

            
            nice to instantly visualize these graphs.</p>


            <p>LLVM provides several callbacks that are available in a debug build to do

            
            exactly that.  If you call the <tt>Function::viewCFG()</tt> method, for example,

            
            the current LLVM tool will pop up a window containing the CFG for the function

            
            where each basic block is a node in the graph, and each node contains the

            
            instructions in the block.  Similarly, there also exists

            
            <tt>Function::viewCFGOnly()</tt> (does not include the instructions), the

            
            <tt>MachineFunction::viewCFG()</tt> and <tt>MachineFunction::viewCFGOnly()</tt>,

            
            and the <tt>SelectionDAG::viewGraph()</tt> methods.  Within GDB, for example,

            
            you can usually use something like <tt>call DAG.viewGraph()</tt> to pop

            
            up a window.  Alternatively, you can sprinkle calls to these functions in your

            
            code in places you want to debug.</p>


            <p>Getting this to work requires a small amount of configuration.  On Unix

            
            systems with X11, install the <a href="http://www.graphviz.org">graphviz</a>

            
            toolkit, and make sure 'dot' and 'gv' are in your path.  If you are running on

            
            Mac OS/X, download and install the Mac OS/X <a

            
            href="http://www.pixelglow.com/graphviz/">Graphviz program</a>, and add

            
            <tt>/Applications/Graphviz.app/Contents/MacOS/</tt> (or wherever you install

            
            it) to your path.  Once in your system and path are set up, rerun the LLVM

            
            configure script and rebuild LLVM to enable this functionality.</p>


            <p><tt>SelectionDAG</tt> has been extended to make it easier to locate

            
            <i>interesting</i> nodes in large complex graphs.  From gdb, if you

            
            <tt>call DAG.setGraphColor(<i>node</i>, "<i>color</i>")</tt>, then the

            
            next <tt>call DAG.viewGraph()</tt> would highlight the node in the

            
            specified color (choices of colors can be found at <a

            
            href="http://www.graphviz.org/doc/info/colors.html">colors</a>.) More

            
            complex node attributes can be provided with <tt>call

            
            DAG.setGraphAttrs(<i>node</i>, "<i>attributes</i>")</tt> (choices can be

            
            found at <a href="http://www.graphviz.org/doc/info/attrs.html">Graph

            
            Attributes</a>.)  If you want to restart and clear all the current graph

            
            attributes, then you can <tt>call DAG.clearGraphAttrs()</tt>. </p>


            </div>


            <!-- *********************************************************************** -->

            
            <div class="doc_section">

            
              <a name="datastructure">Picking the Right Data Structure for a Task</a>

            
            </div>

            
            <!-- *********************************************************************** -->


            <div class="doc_text">


            <p>LLVM has a plethora of data structures in the <tt>llvm/ADT/</tt> directory,

            
             and we commonly use STL data structures.  This section describes the trade-offs

            
             you should consider when you pick one.</p>


            <p>

            
            The first step is a choose your own adventure: do you want a sequential

            
            container, a set-like container, or a map-like container?  The most important

            
            thing when choosing a container is the algorithmic properties of how you plan to

            
            access the container.  Based on that, you should use:</p>


            <ul>

            
            <li>a <a href="#ds_map">map-like</a> container if you need efficient look-up

            
                of an value based on another value.  Map-like containers also support

            
                efficient queries for containment (whether a key is in the map).  Map-like

            
                containers generally do not support efficient reverse mapping (values to

            
                keys).  If you need that, use two maps.  Some map-like containers also

            
                support efficient iteration through the keys in sorted order.  Map-like

            
                containers are the most expensive sort, only use them if you need one of

            
                these capabilities.</li>


            <li>a <a href="#ds_set">set-like</a> container if you need to put a bunch of

            
                stuff into a container that automatically eliminates duplicates.  Some

            
                set-like containers support efficient iteration through the elements in

            
                sorted order.  Set-like containers are more expensive than sequential

            
                containers.

            
            </li>


            <li>a <a href="#ds_sequential">sequential</a> container provides

            
                the most efficient way to add elements and keeps track of the order they are

            
                added to the collection.  They permit duplicates and support efficient

            
                iteration, but do not support efficient look-up based on a key.

            
            </li>


            </ul>


            <p>

            
            Once the proper category of container is determined, you can fine tune the

            
            memory use, constant factors, and cache behaviors of access by intelligently

            
            picking a member of the category.  Note that constant factors and cache behavior

            
            can be a big deal.  If you have a vector that usually only contains a few

            
            elements (but could contain many), for example, it's much better to use

            
            <a href="#dss_smallvector">SmallVector</a> than <a href="#dss_vector">vector</a>

            
            .  Doing so avoids (relatively) expensive malloc/free calls, which dwarf the

            
            cost of adding the elements to the container. </p>


            </div>


            <!-- ======================================================================= -->

            
            <div class="doc_subsection">

            
              <a name="ds_sequential">Sequential Containers (std::vector, std::list, etc)</a>

            
            </div>


            <div class="doc_text">

            
            There are a variety of sequential containers available for you, based on your

            
            needs.  Pick the first in this section that will do what you want.

            
            </div>


            <!-- _______________________________________________________________________ -->

            
            <div class="doc_subsubsection">

            
              <a name="dss_fixedarrays">Fixed Size Arrays</a>

            
            </div>


            <div class="doc_text">

            
            <p>Fixed size arrays are very simple and very fast.  They are good if you know

            
            exactly how many elements you have, or you have a (low) upper bound on how many

            
            you have.</p>

            
            </div>


            <!-- _______________________________________________________________________ -->

            
            <div class="doc_subsubsection">

            
              <a name="dss_heaparrays">Heap Allocated Arrays</a>

            
            </div>


            <div class="doc_text">

            
            <p>Heap allocated arrays (new[] + delete[]) are also simple.  They are good if

            
            the number of elements is variable, if you know how many elements you will need

            
            before the array is allocated, and if the array is usually large (if not,

            
            consider a <a href="#dss_smallvector">SmallVector</a>).  The cost of a heap

            
            allocated array is the cost of the new/delete (aka malloc/free).  Also note that

            
            if you are allocating an array of a type with a constructor, the constructor and

            
            destructors will be run for every element in the array (re-sizable vectors only

            
            construct those elements actually used).</p>

            
            </div>


            <!-- _______________________________________________________________________ -->

            
            <div class="doc_subsubsection">

            
              <a name="dss_smallvector">"llvm/ADT/SmallVector.h"</a>

            
            </div>


            <div class="doc_text">

            
            <p><tt>SmallVector&lt;Type, N&gt;</tt> is a simple class that looks and smells

            
            just like <tt>vector&lt;Type&gt;</tt>:

            
            it supports efficient iteration, lays out elements in memory order (so you can

            
            do pointer arithmetic between elements), supports efficient push_back/pop_back

            
            operations, supports efficient random access to its elements, etc.</p>


            <p>The advantage of SmallVector is that it allocates space for

            
            some number of elements (N) <b>in the object itself</b>.  Because of this, if

            
            the SmallVector is dynamically smaller than N, no malloc is performed.  This can

            
            be a big win in cases where the malloc/free call is far more expensive than the

            
            code that fiddles around with the elements.</p>


            <p>This is good for vectors that are "usually small" (e.g. the number of

            
            predecessors/successors of a block is usually less than 8).  On the other hand,

            
            this makes the size of the SmallVector itself large, so you don't want to

            
            allocate lots of them (doing so will waste a lot of space).  As such,

            
            SmallVectors are most useful when on the stack.</p>


            <p>SmallVector also provides a nice portable and efficient replacement for

            
            <tt>alloca</tt>.</p>


            </div>


            <!-- _______________________________________________________________________ -->

            
            <div class="doc_subsubsection">

            
              <a name="dss_vector">&lt;vector&gt;</a>

            
            </div>


            <div class="doc_text">

            
            <p>

            
            std::vector is well loved and respected.  It is useful when SmallVector isn't:

            
            when the size of the vector is often large (thus the small optimization will

            
            rarely be a benefit) or if you will be allocating many instances of the vector

            
            itself (which would waste space for elements that aren't in the container).

            
            vector is also useful when interfacing with code that expects vectors :).

            
            </p>


            <p>One worthwhile note about std::vector: avoid code like this:</p>


            <div class="doc_code">

            
            <pre>

            
            for ( ... ) {

            
               std::vector&lt;foo&gt; V;

            
               use V;

            
            }

            
            </pre>

            
            </div>


            <p>Instead, write this as:</p>


            <div class="doc_code">

            
            <pre>

            
            std::vector&lt;foo&gt; V;

            
            for ( ... ) {

            
               use V;

            
               V.clear();

            
            }

            
            </pre>

            
            </div>


            <p>Doing so will save (at least) one heap allocation and free per iteration of

            
            the loop.</p>


            </div>


            <!-- _______________________________________________________________________ -->

            
            <div class="doc_subsubsection">

            
              <a name="dss_deque">&lt;deque&gt;</a>

            
            </div>


            <div class="doc_text">

            
            <p>std::deque is, in some senses, a generalized version of std::vector.  Like

            
            std::vector, it provides constant time random access and other similar

            
            properties, but it also provides efficient access to the front of the list.  It

            
            does not guarantee continuity of elements within memory.</p>


            <p>In exchange for this extra flexibility, std::deque has significantly higher

            
            constant factor costs than std::vector.  If possible, use std::vector or

            
            something cheaper.</p>

            
            </div>


            <!-- _______________________________________________________________________ -->

            
            <div class="doc_subsubsection">

            
              <a name="dss_list">&lt;list&gt;</a>

            
            </div>


            <div class="doc_text">

            
            <p>std::list is an extremely inefficient class that is rarely useful.

            
            It performs a heap allocation for every element inserted into it, thus having an

            
            extremely high constant factor, particularly for small data types.  std::list

            
            also only supports bidirectional iteration, not random access iteration.</p>


            <p>In exchange for this high cost, std::list supports efficient access to both

            
            ends of the list (like std::deque, but unlike std::vector or SmallVector).  In

            
            addition, the iterator invalidation characteristics of std::list are stronger

            
            than that of a vector class: inserting or removing an element into the list does

            
            not invalidate iterator or pointers to other elements in the list.</p>

            
            </div>


            <!-- _______________________________________________________________________ -->

            
            <div class="doc_subsubsection">

            
              <a name="dss_ilist">llvm/ADT/ilist</a>

            
            </div>


            <div class="doc_text">

            
            <p><tt>ilist&lt;T&gt;</tt> implements an 'intrusive' doubly-linked list.  It is

            
            intrusive, because it requires the element to store and provide access to the

            
            prev/next pointers for the list.</p>


            <p>ilist has the same drawbacks as std::list, and additionally requires an

            
            ilist_traits implementation for the element type, but it provides some novel

            
            characteristics.  In particular, it can efficiently store polymorphic objects,

            
            the traits class is informed when an element is inserted or removed from the

            
            list, and ilists are guaranteed to support a constant-time splice operation.

            
            </p>


            <p>These properties are exactly what we want for things like Instructions and

            
            basic blocks, which is why these are implemented with ilists.</p>

            
            </div>


            <!-- _______________________________________________________________________ -->

            
            <div class="doc_subsubsection">

            
              <a name="dss_other">Other Sequential Container options</a>

            
            </div>


            <div class="doc_text">

            
            <p>Other STL containers are available, such as std::string.</p>


            <p>There are also various STL adapter classes such as std::queue,

            
            std::priority_queue, std::stack, etc.  These provide simplified access to an

            
            underlying container but don't affect the cost of the container itself.</p>


            </div>


            <!-- ======================================================================= -->

            
            <div class="doc_subsection">

            
              <a name="ds_set">Set-Like Containers (std::set, SmallSet, SetVector, etc)</a>

            
            </div>


            <div class="doc_text">


            <p>Set-like containers are useful when you need to canonicalize multiple values

            
            into a single representation.  There are several different choices for how to do

            
            this, providing various trade-offs.</p>


            </div>


            <!-- _______________________________________________________________________ -->

            
            <div class="doc_subsubsection">

            
              <a name="dss_sortedvectorset">A sorted 'vector'</a>

            
            </div>


            <div class="doc_text">


            <p>If you intend to insert a lot of elements, then do a lot of queries, a

            
            great approach is to use a vector (or other sequential container) with

            
            std::sort+std::unique to remove duplicates.  This approach works really well if

            
            your usage pattern has these two distinct phases (insert then query), and can be

            
            coupled with a good choice of <a href="#ds_sequential">sequential container</a>.

            
            </p>


            <p>

            
            This combination provides the several nice properties: the result data is

            
            contiguous in memory (good for cache locality), has few allocations, is easy to

            
            address (iterators in the final vector are just indices or pointers), and can be

            
            efficiently queried with a standard binary or radix search.</p>


            </div>


            <!-- _______________________________________________________________________ -->

            
            <div class="doc_subsubsection">

            
              <a name="dss_smallset">"llvm/ADT/SmallSet.h"</a>

            
            </div>


            <div class="doc_text">


            <p>If you have a set-like data structure that is usually small and whose elements

            
            are reasonably small, a <tt>SmallSet&lt;Type, N&gt;</tt> is a good choice.  This set

            
            has space for N elements in place (thus, if the set is dynamically smaller than

            
            N, no malloc traffic is required) and accesses them with a simple linear search.

            
            When the set grows beyond 'N' elements, it allocates a more expensive representation that

            
            guarantees efficient access (for most types, it falls back to std::set, but for

            
            pointers it uses something far better, <a

            
            href="#dss_smallptrset">SmallPtrSet</a>).</p>


            <p>The magic of this class is that it handles small sets extremely efficiently,

            
            but gracefully handles extremely large sets without loss of efficiency.  The

            
            drawback is that the interface is quite small: it supports insertion, queries

            
            and erasing, but does not support iteration.</p>


            </div>


            <!-- _______________________________________________________________________ -->

            
            <div class="doc_subsubsection">

            
              <a name="dss_smallptrset">"llvm/ADT/SmallPtrSet.h"</a>

            
            </div>


            <div class="doc_text">


            <p>SmallPtrSet has all the advantages of SmallSet (and a SmallSet of pointers is

            
            transparently implemented with a SmallPtrSet), but also supports iterators.  If

            
            more than 'N' insertions are performed, a single quadratically

            
            probed hash table is allocated and grows as needed, providing extremely

            
            efficient access (constant time insertion/deleting/queries with low constant

            
            factors) and is very stingy with malloc traffic.</p>


            <p>Note that, unlike std::set, the iterators of SmallPtrSet are invalidated

            
            whenever an insertion occurs.  Also, the values visited by the iterators are not

            
            visited in sorted order.</p>


            </div>


            <!-- _______________________________________________________________________ -->

            
            <div class="doc_subsubsection">

            
              <a name="dss_FoldingSet">"llvm/ADT/FoldingSet.h"</a>

            
            </div>


            <div class="doc_text">


            <p>

            
            FoldingSet is an aggregate class that is really good at uniquing

            
            expensive-to-create or polymorphic objects.  It is a combination of a chained

            
            hash table with intrusive links (uniqued objects are required to inherit from

            
            FoldingSetNode) that uses <a href="#dss_smallvector">SmallVector</a> as part of

            
            its ID process.</p>


            <p>Consider a case where you want to implement a "getOrCreateFoo" method for

            
            a complex object (for example, a node in the code generator).  The client has a

            
            description of *what* it wants to generate (it knows the opcode and all the

            
            operands), but we don't want to 'new' a node, then try inserting it into a set

            
            only to find out it already exists, at which point we would have to delete it

            
            and return the node that already exists.

            
            </p>


            <p>To support this style of client, FoldingSet perform a query with a

            
            FoldingSetNodeID (which wraps SmallVector) that can be used to describe the

            
            element that we want to query for.  The query either returns the element

            
            matching the ID or it returns an opaque ID that indicates where insertion should

            
            take place.  Construction of the ID usually does not require heap traffic.</p>


            <p>Because FoldingSet uses intrusive links, it can support polymorphic objects

            
            in the set (for example, you can have SDNode instances mixed with LoadSDNodes).

            
            Because the elements are individually allocated, pointers to the elements are

            
            stable: inserting or removing elements does not invalidate any pointers to other

            
            elements.

            
            </p>


            </div>


            <!-- _______________________________________________________________________ -->

            
            <div class="doc_subsubsection">

            
              <a name="dss_set">&lt;set&gt;</a>

            
            </div>


            <div class="doc_text">


            <p><tt>std::set</tt> is a reasonable all-around set class, which is decent at

            
            many things but great at nothing.  std::set allocates memory for each element

            
            inserted (thus it is very malloc intensive) and typically stores three pointers

            
            per element in the set (thus adding a large amount of per-element space

            
            overhead).  It offers guaranteed log(n) performance, which is not particularly

            
            fast from a complexity standpoint (particularly if the elements of the set are

            
            expensive to compare, like strings), and has extremely high constant factors for

            
            lookup, insertion and removal.</p>


            <p>The advantages of std::set are that its iterators are stable (deleting or

            
            inserting an element from the set does not affect iterators or pointers to other

            
            elements) and that iteration over the set is guaranteed to be in sorted order.

            
            If the elements in the set are large, then the relative overhead of the pointers

            
            and malloc traffic is not a big deal, but if the elements of the set are small,

            
            std::set is almost never a good choice.</p>


            </div>


            <!-- _______________________________________________________________________ -->

            
            <div class="doc_subsubsection">

            
              <a name="dss_setvector">"llvm/ADT/SetVector.h"</a>

            
            </div>


            <div class="doc_text">

            
            <p>LLVM's SetVector&lt;Type&gt; is an adapter class that combines your choice of

            
            a set-like container along with a <a href="#ds_sequential">Sequential

            
            Container</a>.  The important property

            
            that this provides is efficient insertion with uniquing (duplicate elements are

            
            ignored) with iteration support.  It implements this by inserting elements into

            
            both a set-like container and the sequential container, using the set-like

            
            container for uniquing and the sequential container for iteration.

            
            </p>


            <p>The difference between SetVector and other sets is that the order of

            
            iteration is guaranteed to match the order of insertion into the SetVector.

            
            This property is really important for things like sets of pointers.  Because

            
            pointer values are non-deterministic (e.g. vary across runs of the program on

            
            different machines), iterating over the pointers in the set will

            
            not be in a well-defined order.</p>


            <p>

            
            The drawback of SetVector is that it requires twice as much space as a normal

            
            set and has the sum of constant factors from the set-like container and the

            
            sequential container that it uses.  Use it *only* if you need to iterate over

            
            the elements in a deterministic order.  SetVector is also expensive to delete

            
            elements out of (linear time), unless you use it's "pop_back" method, which is

            
            faster.

            
            </p>


            <p>SetVector is an adapter class that defaults to using std::vector and std::set

            
            for the underlying containers, so it is quite expensive.  However,

            
            <tt>"llvm/ADT/SetVector.h"</tt> also provides a SmallSetVector class, which

            
            defaults to using a SmallVector and SmallSet of a specified size.  If you use

            
            this, and if your sets are dynamically smaller than N, you will save a lot of

            
            heap traffic.</p>


            </div>


            <!-- _______________________________________________________________________ -->

            
            <div class="doc_subsubsection">

            
              <a name="dss_uniquevector">"llvm/ADT/UniqueVector.h"</a>

            
            </div>


            <div class="doc_text">


            <p>

            
            UniqueVector is similar to <a href="#dss_setvector">SetVector</a>, but it

            
            retains a unique ID for each element inserted into the set.  It internally

            
            contains a map and a vector, and it assigns a unique ID for each value inserted

            
            into the set.</p>


            <p>UniqueVector is very expensive: its cost is the sum of the cost of

            
            maintaining both the map and vector, it has high complexity, high constant

            
            factors, and produces a lot of malloc traffic.  It should be avoided.</p>


            </div>


            <!-- _______________________________________________________________________ -->

            
            <div class="doc_subsubsection">

            
              <a name="dss_otherset">Other Set-Like Container Options</a>

            
            </div>


            <div class="doc_text">


            <p>

            
            The STL provides several other options, such as std::multiset and the various

            
            "hash_set" like containers (whether from C++ TR1 or from the SGI library).</p>


            <p>std::multiset is useful if you're not interested in elimination of

            
            duplicates, but has all the drawbacks of std::set.  A sorted vector (where you

            
            don't delete duplicate entries) or some other approach is almost always

            
            better.</p>


            <p>The various hash_set implementations (exposed portably by

            
            "llvm/ADT/hash_set") is a simple chained hashtable.  This algorithm is as malloc

            
            intensive as std::set (performing an allocation for each element inserted,

            
            thus having really high constant factors) but (usually) provides O(1)

            
            insertion/deletion of elements.  This can be useful if your elements are large

            
            (thus making the constant-factor cost relatively low) or if comparisons are

            
            expensive.  Element iteration does not visit elements in a useful order.</p>


            </div>


            <!-- ======================================================================= -->

            
            <div class="doc_subsection">

            
              <a name="ds_map">Map-Like Containers (std::map, DenseMap, etc)</a>

            
            </div>


            <div class="doc_text">

            
            Map-like containers are useful when you want to associate data to a key.  As

            
            usual, there are a lot of different ways to do this. :)

            
            </div>


            <!-- _______________________________________________________________________ -->

            
            <div class="doc_subsubsection">

            
              <a name="dss_sortedvectormap">A sorted 'vector'</a>

            
            </div>


            <div class="doc_text">


            <p>

            
            If your usage pattern follows a strict insert-then-query approach, you can

            
            trivially use the same approach as <a href="#dss_sortedvectorset">sorted vectors

            
            for set-like containers</a>.  The only difference is that your query function

            
            (which uses std::lower_bound to get efficient log(n) lookup) should only compare

            
            the key, not both the key and value.  This yields the same advantages as sorted

            
            vectors for sets.

            
            </p>

            
            </div>


            <!-- _______________________________________________________________________ -->

            
            <div class="doc_subsubsection">

            
              <a name="dss_stringmap">"llvm/ADT/StringMap.h"</a>

            
            </div>


            <div class="doc_text">


            <p>

            
            Strings are commonly used as keys in maps, and they are difficult to support

            
            efficiently: they are variable length, inefficient to hash and compare when

            
            long, expensive to copy, etc.  StringMap is a specialized container designed to

            
            cope with these issues.  It supports mapping an arbitrary range of bytes to an

            
            arbitrary other object.</p>


            <p>The StringMap implementation uses a quadratically-probed hash table, where

            
            the buckets store a pointer to the heap allocated entries (and some other

            
            stuff).  The entries in the map must be heap allocated because the strings are

            
            variable length.  The string data (key) and the element object (value) are

            
            stored in the same allocation with the string data immediately after the element

            
            object.  This container guarantees the "<tt>(char*)(&amp;Value+1)</tt>" points

            
            to the key string for a value.</p>


            <p>The StringMap is very fast for several reasons: quadratic probing is very

            
            cache efficient for lookups, the hash value of strings in buckets is not

            
            recomputed when lookup up an element, StringMap rarely has to touch the

            
            memory for unrelated objects when looking up a value (even when hash collisions

            
            happen), hash table growth does not recompute the hash values for strings

            
            already in the table, and each pair in the map is store in a single allocation

            
            (the string data is stored in the same allocation as the Value of a pair).</p>


            <p>StringMap also provides query methods that take byte ranges, so it only ever

            
            copies a string if a value is inserted into the table.</p>

            
            </div>


            <!-- _______________________________________________________________________ -->

            
            <div class="doc_subsubsection">

            
              <a name="dss_indexedmap">"llvm/ADT/IndexedMap.h"</a>

            
            </div>


            <div class="doc_text">

            
            <p>

            
            IndexedMap is a specialized container for mapping small dense integers (or

            
            values that can be mapped to small dense integers) to some other type.  It is

            
            internally implemented as a vector with a mapping function that maps the keys to

            
            the dense integer range.

            
            </p>


            <p>

            
            This is useful for cases like virtual registers in the LLVM code generator: they

            
            have a dense mapping that is offset by a compile-time constant (the first

            
            virtual register ID).</p>


            </div>


            <!-- _______________________________________________________________________ -->

            
            <div class="doc_subsubsection">

            
              <a name="dss_densemap">"llvm/ADT/DenseMap.h"</a>

            
            </div>


            <div class="doc_text">


            <p>

            
            DenseMap is a simple quadratically probed hash table.  It excels at supporting

            
            small keys and values: it uses a single allocation to hold all of the pairs that

            
            are currently inserted in the map.  DenseMap is a great way to map pointers to

            
            pointers, or map other small types to each other.

            
            </p>


            <p>

            
            There are several aspects of DenseMap that you should be aware of, however.  The

            
            iterators in a densemap are invalidated whenever an insertion occurs, unlike

            
            map.  Also, because DenseMap allocates space for a large number of key/value

            
            pairs (it starts with 64 by default), it will waste a lot of space if your keys

            
            or values are large.  Finally, you must implement a partial specialization of

            
            DenseMapKeyInfo for the key that you want, if it isn't already supported.  This

            
            is required to tell DenseMap about two special marker values (which can never be

            
            inserted into the map) that it needs internally.</p>


            </div>


            <!-- _______________________________________________________________________ -->

            
            <div class="doc_subsubsection">

            
              <a name="dss_map">&lt;map&gt;</a>

            
            </div>


            <div class="doc_text">


            <p>

            
            std::map has similar characteristics to <a href="#dss_set">std::set</a>: it uses

            
            a single allocation per pair inserted into the map, it offers log(n) lookup with

            
            an extremely large constant factor, imposes a space penalty of 3 pointers per

            
            pair in the map, etc.</p>


            <p>std::map is most useful when your keys or values are very large, if you need

            
            to iterate over the collection in sorted order, or if you need stable iterators

            
            into the map (i.e. they don't get invalidated if an insertion or deletion of

            
            another element takes place).</p>


            </div>


            <!-- _______________________________________________________________________ -->

            
            <div class="doc_subsubsection">

            
              <a name="dss_othermap">Other Map-Like Container Options</a>

            
            </div>


            <div class="doc_text">


            <p>

            
            The STL provides several other options, such as std::multimap and the various

            
            "hash_map" like containers (whether from C++ TR1 or from the SGI library).</p>


            <p>std::multimap is useful if you want to map a key to multiple values, but has

            
            all the drawbacks of std::map.  A sorted vector or some other approach is almost

            
            always better.</p>


            <p>The various hash_map implementations (exposed portably by

            
            "llvm/ADT/hash_map") are simple chained hash tables.  This algorithm is as

            
            malloc intensive as std::map (performing an allocation for each element

            
            inserted, thus having really high constant factors) but (usually) provides O(1)

            
            insertion/deletion of elements.  This can be useful if your elements are large

            
            (thus making the constant-factor cost relatively low) or if comparisons are

            
            expensive.  Element iteration does not visit elements in a useful order.</p>


            </div>


            <!-- *********************************************************************** -->

            
            <div class="doc_section">

            
              <a name="common">Helpful Hints for Common Operations</a>

            
            </div>

            
            <!-- *********************************************************************** -->


            <div class="doc_text">


            <p>This section describes how to perform some very simple transformations of

            
            LLVM code.  This is meant to give examples of common idioms used, showing the

            
            practical side of LLVM transformations.  <p> Because this is a "how-to" section,

            
            you should also read about the main classes that you will be working with.  The

            
            <a href="#coreclasses">Core LLVM Class Hierarchy Reference</a> contains details

            
            and descriptions of the main classes that you should know about.</p>


            </div>


            <!-- NOTE: this section should be heavy on example code -->

            
            <!-- ======================================================================= -->

            
            <div class="doc_subsection">

            
              <a name="inspection">Basic Inspection and Traversal Routines</a>

            
            </div>


            <div class="doc_text">


            <p>The LLVM compiler infrastructure have many different data structures that may

            
            be traversed.  Following the example of the C++ standard template library, the

            
            techniques used to traverse these various data structures are all basically the

            
            same.  For a enumerable sequence of values, the <tt>XXXbegin()</tt> function (or

            
            method) returns an iterator to the start of the sequence, the <tt>XXXend()</tt>

            
            function returns an iterator pointing to one past the last valid element of the

            
            sequence, and there is some <tt>XXXiterator</tt> data type that is common

            
            between the two operations.</p>


            <p>Because the pattern for iteration is common across many different aspects of

            
            the program representation, the standard template library algorithms may be used

            
            on them, and it is easier to remember how to iterate. First we show a few common

            
            examples of the data structures that need to be traversed.  Other data

            
            structures are traversed in very similar ways.</p>


            </div>


            <!-- _______________________________________________________________________ -->

            
            <div class="doc_subsubsection">

            
              <a name="iterate_function">Iterating over the </a><a

            
              href="#BasicBlock"><tt>BasicBlock</tt></a>s in a <a

            
              href="#Function"><tt>Function</tt></a>

            
            </div>


            <div class="doc_text">


            <p>It's quite common to have a <tt>Function</tt> instance that you'd like to

            
            transform in some way; in particular, you'd like to manipulate its

            
            <tt>BasicBlock</tt>s.  To facilitate this, you'll need to iterate over all of

            
            the <tt>BasicBlock</tt>s that constitute the <tt>Function</tt>. The following is

            
            an example that prints the name of a <tt>BasicBlock</tt> and the number of

            
            <tt>Instruction</tt>s it contains:</p>


            <div class="doc_code">

            
            <pre>

            
            // <i>func is a pointer to a Function instance</i>

            
            for (Function::iterator i = func-&gt;begin(), e = func-&gt;end(); i != e; ++i)

            
              // <i>Print out the name of the basic block if it has one, and then the</i>

            
              // <i>number of instructions that it contains</i>

            
              llvm::cerr &lt;&lt; "Basic block (name=" &lt;&lt; i-&gt;getName() &lt;&lt; ") has "

            
                         &lt;&lt; i-&gt;size() &lt;&lt; " instructions.\n";

            
            </pre>

            
            </div>


            <p>Note that i can be used as if it were a pointer for the purposes of

            
            invoking member functions of the <tt>Instruction</tt> class.  This is

            
            because the indirection operator is overloaded for the iterator

            
            classes.  In the above code, the expression <tt>i-&gt;size()</tt> is

            
            exactly equivalent to <tt>(*i).size()</tt> just like you'd expect.</p>


            </div>


            <!-- _______________________________________________________________________ -->

            
            <div class="doc_subsubsection">

            
              <a name="iterate_basicblock">Iterating over the </a><a

            
              href="#Instruction"><tt>Instruction</tt></a>s in a <a

            
              href="#BasicBlock"><tt>BasicBlock</tt></a>

            
            </div>


            <div class="doc_text">


            <p>Just like when dealing with <tt>BasicBlock</tt>s in <tt>Function</tt>s, it's

            
            easy to iterate over the individual instructions that make up

            
            <tt>BasicBlock</tt>s. Here's a code snippet that prints out each instruction in

            
            a <tt>BasicBlock</tt>:</p>


            <div class="doc_code">

            
            <pre>

            
            // <i>blk is a pointer to a BasicBlock instance</i>

            
            for (BasicBlock::iterator i = blk-&gt;begin(), e = blk-&gt;end(); i != e; ++i)

            
               // <i>The next statement works since operator&lt;&lt;(ostream&amp;,...)</i>

            
               // <i>is overloaded for Instruction&amp;</i>

            
               llvm::cerr &lt;&lt; *i &lt;&lt; "\n";

            
            </pre>

            
            </div>


            <p>However, this isn't really the best way to print out the contents of a

            
            <tt>BasicBlock</tt>!  Since the ostream operators are overloaded for virtually

            
            anything you'll care about, you could have just invoked the print routine on the

            
            basic block itself: <tt>llvm::cerr &lt;&lt; *blk &lt;&lt; "\n";</tt>.</p>


            </div>


            <!-- _______________________________________________________________________ -->

            
            <div class="doc_subsubsection">

            
              <a name="iterate_institer">Iterating over the </a><a

            
              href="#Instruction"><tt>Instruction</tt></a>s in a <a

            
              href="#Function"><tt>Function</tt></a>

            
            </div>


            <div class="doc_text">


            <p>If you're finding that you commonly iterate over a <tt>Function</tt>'s

            
            <tt>BasicBlock</tt>s and then that <tt>BasicBlock</tt>'s <tt>Instruction</tt>s,

            
            <tt>InstIterator</tt> should be used instead. You'll need to include <a

            
            href="/doxygen/InstIterator_8h-source.html"><tt>llvm/Support/InstIterator.h</tt></a>,

            
            and then instantiate <tt>InstIterator</tt>s explicitly in your code.  Here's a

            
            small example that shows how to dump all instructions in a function to the standard error stream:<p>


            <div class="doc_code">

            
            <pre>

            
            #include "<a href="/doxygen/InstIterator_8h-source.html">llvm/Support/InstIterator.h</a>"


            // <i>F is a pointer to a Function instance</i>

            
            for (inst_iterator i = inst_begin(F), e = inst_end(F); i != e; ++i)

            
              llvm::cerr &lt;&lt; *i &lt;&lt; "\n";

            
            </pre>

            
            </div>


            <p>Easy, isn't it?  You can also use <tt>InstIterator</tt>s to fill a

            
            work list with its initial contents.  For example, if you wanted to

            
            initialize a work list to contain all instructions in a <tt>Function</tt>

            
            F, all you would need to do is something like:</p>


            <div class="doc_code">

            
            <pre>

            
            std::set&lt;Instruction*&gt; worklist;

            
            worklist.insert(inst_begin(F), inst_end(F));

            
            </pre>

            
            </div>


            <p>The STL set <tt>worklist</tt> would now contain all instructions in the

            
            <tt>Function</tt> pointed to by F.</p>


            </div>


            <!-- _______________________________________________________________________ -->

            
            <div class="doc_subsubsection">

            
              <a name="iterate_convert">Turning an iterator into a class pointer (and

            
              vice-versa)</a>

            
            </div>


            <div class="doc_text">


            <p>Sometimes, it'll be useful to grab a reference (or pointer) to a class

            
            instance when all you've got at hand is an iterator.  Well, extracting

            
            a reference or a pointer from an iterator is very straight-forward.

            
            Assuming that <tt>i</tt> is a <tt>BasicBlock::iterator</tt> and <tt>j</tt>

            
            is a <tt>BasicBlock::const_iterator</tt>:</p>


            <div class="doc_code">

            
            <pre>

            
            Instruction&amp; inst = *i;   // <i>Grab reference to instruction reference</i>

            
            Instruction* pinst = &amp;*i; // <i>Grab pointer to instruction reference</i>

            
            const Instruction&amp; inst = *j;

            
            </pre>

            
            </div>


            <p>However, the iterators you'll be working with in the LLVM framework are

            
            special: they will automatically convert to a ptr-to-instance type whenever they

            
            need to.  Instead of dereferencing the iterator and then taking the address of

            
            the result, you can simply assign the iterator to the proper pointer type and

            
            you get the dereference and address-of operation as a result of the assignment

            
            (behind the scenes, this is a result of overloading casting mechanisms).  Thus

            
            the last line of the last example,</p>


            <div class="doc_code">

            
            <pre>

            
            Instruction* pinst = &amp;*i;

            
            </pre>

            
            </div>


            <p>is semantically equivalent to</p>


            <div class="doc_code">

            
            <pre>

            
            Instruction* pinst = i;

            
            </pre>

            
            </div>


            <p>It's also possible to turn a class pointer into the corresponding iterator,

            
            and this is a constant time operation (very efficient).  The following code

            
            snippet illustrates use of the conversion constructors provided by LLVM

            
            iterators.  By using these, you can explicitly grab the iterator of something

            
            without actually obtaining it via iteration over some structure:</p>


            <div class="doc_code">

            
            <pre>

            
            void printNextInstruction(Instruction* inst) {

            
              BasicBlock::iterator it(inst);

            
              ++it; // <i>After this line, it refers to the instruction after *inst</i>

            
              if (it != inst-&gt;getParent()-&gt;end()) llvm::cerr &lt;&lt; *it &lt;&lt; "\n";

            
            }

            
            </pre>

            
            </div>


            </div>


            <!--_______________________________________________________________________-->

            
            <div class="doc_subsubsection">

            
              <a name="iterate_complex">Finding call sites: a slightly more complex

            
              example</a>

            
            </div>


            <div class="doc_text">


            <p>Say that you're writing a FunctionPass and would like to count all the

            
            locations in the entire module (that is, across every <tt>Function</tt>) where a

            
            certain function (i.e., some <tt>Function</tt>*) is already in scope.  As you'll

            
            learn later, you may want to use an <tt>InstVisitor</tt> to accomplish this in a

            
            much more straight-forward manner, but this example will allow us to explore how

            
            you'd do it if you didn't have <tt>InstVisitor</tt> around. In pseudo-code, this

            
            is what we want to do:</p>


            <div class="doc_code">

            
            <pre>

            
            initialize callCounter to zero

            
            for each Function f in the Module

            
              for each BasicBlock b in f

            
                for each Instruction i in b

            
                  if (i is a CallInst and calls the given function)

            
                    increment callCounter

            
            </pre>

            
            </div>


            <p>And the actual code is (remember, because we're writing a

            
            <tt>FunctionPass</tt>, our <tt>FunctionPass</tt>-derived class simply has to

            
            override the <tt>runOnFunction</tt> method):</p>


            <div class="doc_code">

            
            <pre>

            
            Function* targetFunc = ...;


            class OurFunctionPass : public FunctionPass {

            
              public:

            
                OurFunctionPass(): callCounter(0) { }


                virtual runOnFunction(Function&amp; F) {

            
                  for (Function::iterator b = F.begin(), be = F.end(); b != be; ++b) {

            
                    for (BasicBlock::iterator i = b-&gt;begin(); ie = b-&gt;end(); i != ie; ++i) {

            
                      if (<a href="#CallInst">CallInst</a>* callInst = <a href="#isa">dyn_cast</a>&lt;<a

            
             href="#CallInst">CallInst</a>&gt;(&amp;*i)) {

            
                        // <i>We know we've encountered a call instruction, so we</i>

            
                        // <i>need to determine if it's a call to the</i>

            
                        // <i>function pointed to by m_func or not</i>


                        if (callInst-&gt;getCalledFunction() == targetFunc)

            
                          ++callCounter;

            
                      }

            
                    }

            
                  }

            
                }


              private:

            
                unsigned  callCounter;

            
            };

            
            </pre>

            
            </div>


            </div>


            <!--_______________________________________________________________________-->

            
            <div class="doc_subsubsection">

            
              <a name="calls_and_invokes">Treating calls and invokes the same way</a>

            
            </div>


            <div class="doc_text">


            <p>You may have noticed that the previous example was a bit oversimplified in

            
            that it did not deal with call sites generated by 'invoke' instructions. In

            
            this, and in other situations, you may find that you want to treat

            
            <tt>CallInst</tt>s and <tt>InvokeInst</tt>s the same way, even though their

            
            most-specific common base class is <tt>Instruction</tt>, which includes lots of

            
            less closely-related things. For these cases, LLVM provides a handy wrapper

            
            class called <a

            
            href="http://llvm.org/doxygen/classllvm_1_1CallSite.html"><tt>CallSite</tt></a>.

            
            It is essentially a wrapper around an <tt>Instruction</tt> pointer, with some

            
            methods that provide functionality common to <tt>CallInst</tt>s and

            
            <tt>InvokeInst</tt>s.</p>


            <p>This class has "value semantics": it should be passed by value, not by

            
            reference and it should not be dynamically allocated or deallocated using

            
            <tt>operator new</tt> or <tt>operator delete</tt>. It is efficiently copyable,

            
            assignable and constructable, with costs equivalents to that of a bare pointer.

            
            If you look at its definition, it has only a single pointer member.</p>


            </div>


            <!--_______________________________________________________________________-->

            
            <div class="doc_subsubsection">

            
              <a name="iterate_chains">Iterating over def-use &amp; use-def chains</a>

            
            </div>


            <div class="doc_text">


            <p>Frequently, we might have an instance of the <a

            
            href="/doxygen/classllvm_1_1Value.html">Value Class</a> and we want to

            
            determine which <tt>User</tt>s use the <tt>Value</tt>.  The list of all

            
            <tt>User</tt>s of a particular <tt>Value</tt> is called a <i>def-use</i> chain.

            
            For example, let's say we have a <tt>Function*</tt> named <tt>F</tt> to a

            
            particular function <tt>foo</tt>. Finding all of the instructions that

            
            <i>use</i> <tt>foo</tt> is as simple as iterating over the <i>def-use</i> chain

            
            of <tt>F</tt>:</p>


            <div class="doc_code">

            
            <pre>

            
            Function* F = ...;


            for (Value::use_iterator i = F-&gt;use_begin(), e = F-&gt;use_end(); i != e; ++i)

            
              if (Instruction *Inst = dyn_cast&lt;Instruction&gt;(*i)) {

            
                llvm::cerr &lt;&lt; "F is used in instruction:\n";

            
                llvm::cerr &lt;&lt; *Inst &lt;&lt; "\n";

            
              }

            
            </pre>

            
            </div>


            <p>Alternately, it's common to have an instance of the <a

            
            href="/doxygen/classllvm_1_1User.html">User Class</a> and need to know what

            
            <tt>Value</tt>s are used by it.  The list of all <tt>Value</tt>s used by a

            
            <tt>User</tt> is known as a <i>use-def</i> chain.  Instances of class

            
            <tt>Instruction</tt> are common <tt>User</tt>s, so we might want to iterate over

            
            all of the values that a particular instruction uses (that is, the operands of

            
            the particular <tt>Instruction</tt>):</p>


            <div class="doc_code">

            
            <pre>

            
            Instruction* pi = ...;


            for (User::op_iterator i = pi-&gt;op_begin(), e = pi-&gt;op_end(); i != e; ++i) {

            
              Value* v = *i;

            
              // <i>...</i>

            
            }

            
            </pre>

            
            </div>


            <!--

            
              def-use chains ("finding all users of"): Value::use_begin/use_end

            
              use-def chains ("finding all values used"): User::op_begin/op_end [op=operand]

            
            -->


            </div>


            <!-- ======================================================================= -->

            
            <div class="doc_subsection">

            
              <a name="simplechanges">Making simple changes</a>

            
            </div>


            <div class="doc_text">


            <p>There are some primitive transformation operations present in the LLVM

            
            infrastructure that are worth knowing about.  When performing

            
            transformations, it's fairly common to manipulate the contents of basic

            
            blocks. This section describes some of the common methods for doing so

            
            and gives example code.</p>


            </div>


            <!--_______________________________________________________________________-->

            
            <div class="doc_subsubsection">

            
              <a name="schanges_creating">Creating and inserting new

            
              <tt>Instruction</tt>s</a>

            
            </div>


            <div class="doc_text">


            <p><i>Instantiating Instructions</i></p>


            <p>Creation of <tt>Instruction</tt>s is straight-forward: simply call the

            
            constructor for the kind of instruction to instantiate and provide the necessary

            
            parameters. For example, an <tt>AllocaInst</tt> only <i>requires</i> a

            
            (const-ptr-to) <tt>Type</tt>. Thus:</p>


            <div class="doc_code">

            
            <pre>

            
            AllocaInst* ai = new AllocaInst(Type::IntTy);

            
            </pre>

            
            </div>


            <p>will create an <tt>AllocaInst</tt> instance that represents the allocation of

            
            one integer in the current stack frame, at run time. Each <tt>Instruction</tt>

            
            subclass is likely to have varying default parameters which change the semantics

            
            of the instruction, so refer to the <a

            
            href="/doxygen/classllvm_1_1Instruction.html">doxygen documentation for the subclass of

            
            Instruction</a> that you're interested in instantiating.</p>


            <p><i>Naming values</i></p>


            <p>It is very useful to name the values of instructions when you're able to, as

            
            this facilitates the debugging of your transformations.  If you end up looking

            
            at generated LLVM machine code, you definitely want to have logical names

            
            associated with the results of instructions!  By supplying a value for the

            
            <tt>Name</tt> (default) parameter of the <tt>Instruction</tt> constructor, you

            
            associate a logical name with the result of the instruction's execution at

            
            run time.  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>


            <div class="doc_code">

            
            <pre>

            
            AllocaInst* pa = new AllocaInst(Type::IntTy, 0, "indexLoc");

            
            </pre>

            
            </div>


            <p>where <tt>indexLoc</tt> is now the logical name of the instruction's

            
            execution value, which is a pointer to an integer on the run time stack.</p>


            <p><i>Inserting instructions</i></p>


            <p>There are essentially two ways to insert an <tt>Instruction</tt>

            
            into an existing sequence of instructions that form a <tt>BasicBlock</tt>:</p>


            <ul>

            
              <li>Insertion into an explicit instruction list


                <p>Given a <tt>BasicBlock* pb</tt>, an <tt>Instruction* pi</tt> within that

            
                <tt>BasicBlock</tt>, and a newly-created instruction we wish to insert

            
                before <tt>*pi</tt>, we do the following: </p>


            <div class="doc_code">

            
            <pre>

            
            BasicBlock *pb = ...;

            
            Instruction *pi = ...;

            
            Instruction *newInst = new Instruction(...);


            pb-&gt;getInstList().insert(pi, newInst); // <i>Inserts newInst before pi in pb</i>

            
            </pre>

            
            </div>


                <p>Appending to the end of a <tt>BasicBlock</tt> is so common that

            
                the <tt>Instruction</tt> class and <tt>Instruction</tt>-derived

            
                classes provide constructors which take a pointer to a

            
                <tt>BasicBlock</tt> to be appended to. For example code that

            
                looked like: </p>


            <div class="doc_code">

            
            <pre>

            
            BasicBlock *pb = ...;

            
            Instruction *newInst = new Instruction(...);


            pb-&gt;getInstList().push_back(newInst); // <i>Appends newInst to pb</i>

            
            </pre>

            
            </div>


                <p>becomes: </p>


            <div class="doc_code">

            
            <pre>

            
            BasicBlock *pb = ...;

            
            Instruction *newInst = new Instruction(..., pb);

            
            </pre>

            
            </div>


                <p>which is much cleaner, especially if you are creating

            
                long instruction streams.</p></li>


              <li>Insertion into an implicit instruction list


                <p><tt>Instruction</tt> instances that are already in <tt>BasicBlock</tt>s

            
                are implicitly associated with an existing instruction list: the instruction

            
                list of the enclosing basic block. Thus, we could have accomplished the same

            
                thing as the above code without being given a <tt>BasicBlock</tt> by doing:

            
                </p>


            <div class="doc_code">

            
            <pre>

            
            Instruction *pi = ...;

            
            Instruction *newInst = new Instruction(...);


            pi-&gt;getParent()-&gt;getInstList().insert(pi, newInst);

            
            </pre>

            
            </div>


                <p>In fact, this sequence of steps occurs so frequently that the

            
                <tt>Instruction</tt> class and <tt>Instruction</tt>-derived classes provide

            
                constructors which take (as a default parameter) a pointer to an

            
                <tt>Instruction</tt> which the newly-created <tt>Instruction</tt> should

            
                precede.  That is, <tt>Instruction</tt> constructors are capable of

            
                inserting the newly-created instance into the <tt>BasicBlock</tt> of a

            
                provided instruction, immediately before that instruction.  Using an

            
                <tt>Instruction</tt> constructor with a <tt>insertBefore</tt> (default)

            
                parameter, the above code becomes:</p>


            <div class="doc_code">

            
            <pre>

            
            Instruction* pi = ...;

            
            Instruction* newInst = new Instruction(..., pi);

            
            </pre>

            
            </div>


                <p>which is much cleaner, especially if you're creating a lot of

            
                instructions and adding them to <tt>BasicBlock</tt>s.</p></li>

            
            </ul>


            </div>


            <!--_______________________________________________________________________-->

            
            <div class="doc_subsubsection">

            
              <a name="schanges_deleting">Deleting <tt>Instruction</tt>s</a>

            
            </div>


            <div class="doc_text">


            <p>Deleting an instruction from an existing sequence of instructions that form a

            
            <a href="#BasicBlock"><tt>BasicBlock</tt></a> is very straight-forward. First,

            
            you must have a pointer to the instruction that you wish to delete.  Second, you

            
            need to obtain the pointer to that instruction's basic block. You use the

            
            pointer to the basic block to get its list of instructions and then use the

            
            erase function to remove your instruction. For example:</p>


            <div class="doc_code">

            
            <pre>

            
            <a href="#Instruction">Instruction</a> *I = .. ;

            
            <a href="#BasicBlock">BasicBlock</a> *BB = I-&gt;getParent();


            BB-&gt;getInstList().erase(I);

            
            </pre>

            
            </div>


            </div>


            <!--_______________________________________________________________________-->

            
            <div class="doc_subsubsection">

            
              <a name="schanges_replacing">Replacing an <tt>Instruction</tt> with another

            
              <tt>Value</tt></a>

            
            </div>


            <div class="doc_text">


            <p><i>Replacing individual instructions</i></p>


            <p>Including "<a href="/doxygen/BasicBlockUtils_8h-source.html">llvm/Transforms/Utils/BasicBlockUtils.h</a>"

            
            permits use of two very useful replace functions: <tt>ReplaceInstWithValue</tt>

            
            and <tt>ReplaceInstWithInst</tt>.</p>


            <h4><a name="schanges_deleting">Deleting <tt>Instruction</tt>s</a></h4>


            <ul>

            
              <li><tt>ReplaceInstWithValue</tt>


                <p>This function replaces all uses (within a basic block) of a given

            
                instruction with a value, and then removes the original instruction. The

            
                following example illustrates the replacement of the result of a particular

            
                <tt>AllocaInst</tt> that allocates memory for a single integer with a null

            
                pointer to an integer.</p>


            <div class="doc_code">

            
            <pre>

            
            AllocaInst* instToReplace = ...;

            
            BasicBlock::iterator ii(instToReplace);


            ReplaceInstWithValue(instToReplace-&gt;getParent()-&gt;getInstList(), ii,

            
                                 Constant::getNullValue(PointerType::get(Type::IntTy)));

            
            </pre></div></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>


            <div class="doc_code">

            
            <pre>

            
            AllocaInst* instToReplace = ...;

            
            BasicBlock::iterator ii(instToReplace);


            ReplaceInstWithInst(instToReplace-&gt;getParent()-&gt;getInstList(), ii,

            
                                new AllocaInst(Type::IntTy, 0, "ptrToReplacedInt"));

            
            </pre></div></li>

            
            </ul>


            <p><i>Replacing multiple uses of <tt>User</tt>s and <tt>Value</tt>s</i></p>


            <p>You can use <tt>Value::replaceAllUsesWith</tt> and

            
            <tt>User::replaceUsesOfWith</tt> to change more than one use at a time.  See the

            
            doxygen documentation for the <a href="/doxygen/classllvm_1_1Value.html">Value Class</a>

            
            and <a href="/doxygen/classllvm_1_1User.html">User Class</a>, respectively, for more

            
            information.</p>


            <!-- Value::replaceAllUsesWith User::replaceUsesOfWith Point out:

            
            include/llvm/Transforms/Utils/ especially BasicBlockUtils.h with:

            
            ReplaceInstWithValue, ReplaceInstWithInst -->


            </div>


            <!--_______________________________________________________________________-->

            
            <div class="doc_subsubsection">

            
              <a name="schanges_deletingGV">Deleting <tt>GlobalVariable</tt>s</a>

            
            </div>


            <div class="doc_text">


            <p>Deleting a global variable from a module is just as easy as deleting an

            
            Instruction. First, you must have a pointer to the global variable that you wish

            
             to delete.  You use this pointer to erase it from its parent, the module.

            
             For example:</p>


            <div class="doc_code">

            
            <pre>

            
            <a href="#GlobalVariable">GlobalVariable</a> *GV = .. ;


            GV-&gt;eraseFromParent();

            
            </pre>

            
            </div>


            </div>


            <!-- *********************************************************************** -->

            
            <div class="doc_section">

            
              <a name="advanced">Advanced Topics</a>

            
            </div>

            
            <!-- *********************************************************************** -->


            <div class="doc_text">

            
            <p>

            
            This section describes some of the advanced or obscure API's that most clients

            
            do not need to be aware of.  These API's tend manage the inner workings of the

            
            LLVM system, and only need to be accessed in unusual circumstances.

            
            </p>

            
            </div>


            <!-- ======================================================================= -->

            
            <div class="doc_subsection">

            
              <a name="TypeResolve">LLVM Type Resolution</a>

            
            </div>


            <div class="doc_text">


            <p>

            
            The LLVM type system has a very simple goal: allow clients to compare types for

            
            structural equality with a simple pointer comparison (aka a shallow compare).

            
            This goal makes clients much simpler and faster, and is used throughout the LLVM

            
            system.

            
            </p>


            <p>

            
            Unfortunately achieving this goal is not a simple matter.  In particular,

            
            recursive types and late resolution of opaque types makes the situation very

            
            difficult to handle.  Fortunately, for the most part, our implementation makes

            
            most clients able to be completely unaware of the nasty internal details.  The

            
            primary case where clients are exposed to the inner workings of it are when

            
            building a recursive type.  In addition to this case, the LLVM bitcode reader,

            
            assembly parser, and linker also have to be aware of the inner workings of this

            
            system.

            
            </p>


            <p>

            
            For our purposes below, we need three concepts.  First, an "Opaque Type" is

            
            exactly as defined in the <a href="LangRef.html#t_opaque">language

            
            reference</a>.  Second an "Abstract Type" is any type which includes an

            
            opaque type as part of its type graph (for example "<tt>{ opaque, i32 }</tt>").

            
            Third, a concrete type is a type that is not an abstract type (e.g. "<tt>{ i32,

            
            float }</tt>").

            
            </p>


            </div>


            <!-- ______________________________________________________________________ -->

            
            <div class="doc_subsubsection">

            
              <a name="BuildRecType">Basic Recursive Type Construction</a>

            
            </div>


            <div class="doc_text">


            <p>

            
            Because the most common question is "how do I build a recursive type with LLVM",

            
            we answer it now and explain it as we go.  Here we include enough to cause this

            
            to be emitted to an output .ll file:

            
            </p>


            <div class="doc_code">

            
            <pre>

            
            %mylist = type { %mylist*, i32 }

            
            </pre>

            
            </div>


            <p>

            
            To build this, use the following LLVM APIs:

            
            </p>


            <div class="doc_code">

            
            <pre>

            
            // <i>Create the initial outer struct</i>

            
            <a href="#PATypeHolder">PATypeHolder</a> StructTy = OpaqueType::get();

            
            std::vector&lt;const Type*&gt; Elts;

            
            Elts.push_back(PointerType::get(StructTy));

            
            Elts.push_back(Type::IntTy);

            
            StructType *NewSTy = StructType::get(Elts);


            // <i>At this point, NewSTy = "{ opaque*, i32 }". Tell VMCore that</i>

            
            // <i>the struct and the opaque type are actually the same.</i>

            
            cast&lt;OpaqueType&gt;(StructTy.get())-&gt;<a href="#refineAbstractTypeTo">refineAbstractTypeTo</a>(NewSTy);


            // <i>NewSTy is potentially invalidated, but StructTy (a <a href="#PATypeHolder">PATypeHolder</a>) is</i>

            
            // <i>kept up-to-date</i>

            
            NewSTy = cast&lt;StructType&gt;(StructTy.get());


            // <i>Add a name for the type to the module symbol table (optional)</i>

            
            MyModule-&gt;addTypeName("mylist", NewSTy);

            
            </pre>

            
            </div>


            <p>

            
            This code shows the basic approach used to build recursive types: build a

            
            non-recursive type using 'opaque', then use type unification to close the cycle.

            
            The type unification step is performed by the <tt><a

            
            href="#refineAbstractTypeTo">refineAbstractTypeTo</a></tt> method, which is

            
            described next.  After that, we describe the <a

            
            href="#PATypeHolder">PATypeHolder class</a>.

            
            </p>


            </div>


            <!-- ______________________________________________________________________ -->

            
            <div class="doc_subsubsection">

            
              <a name="refineAbstractTypeTo">The <tt>refineAbstractTypeTo</tt> method</a>

            
            </div>


            <div class="doc_text">

            
            <p>

            
            The <tt>refineAbstractTypeTo</tt> method starts the type unification process.

            
            While this method is actually a member of the DerivedType class, it is most

            
            often used on OpaqueType instances.  Type unification is actually a recursive

            
            process.  After unification, types can become structurally isomorphic to

            
            existing types, and all duplicates are deleted (to preserve pointer equality).

            
            </p>


            <p>

            
            In the example above, the OpaqueType object is definitely deleted.

            
            Additionally, if there is an "{ \2*, i32}" type already created in the system,

            
            the pointer and struct type created are <b>also</b> deleted.  Obviously whenever

            
            a type is deleted, any "Type*" pointers in the program are invalidated.  As

            
            such, it is safest to avoid having <i>any</i> "Type*" pointers to abstract types

            
            live across a call to <tt>refineAbstractTypeTo</tt> (note that non-abstract

            
            types can never move or be deleted).  To deal with this, the <a

            
            href="#PATypeHolder">PATypeHolder</a> class is used to maintain a stable

            
            reference to a possibly refined type, and the <a

            
            href="#AbstractTypeUser">AbstractTypeUser</a> class is used to update more

            
            complex datastructures.

            
            </p>


            </div>


            <!-- ______________________________________________________________________ -->

            
            <div class="doc_subsubsection">

            
              <a name="PATypeHolder">The PATypeHolder Class</a>

            
            </div>


            <div class="doc_text">

            
            <p>

            
            PATypeHolder is a form of a "smart pointer" for Type objects.  When VMCore

            
            happily goes about nuking types that become isomorphic to existing types, it

            
            automatically updates all PATypeHolder objects to point to the new type.  In the

            
            example above, this allows the code to maintain a pointer to the resultant

            
            resolved recursive type, even though the Type*'s are potentially invalidated.

            
            </p>


            <p>

            
            PATypeHolder is an extremely light-weight object that uses a lazy union-find

            
            implementation to update pointers.  For example the pointer from a Value to its

            
            Type is maintained by PATypeHolder objects.

            
            </p>


            </div>


            <!-- ______________________________________________________________________ -->

            
            <div class="doc_subsubsection">

            
              <a name="AbstractTypeUser">The AbstractTypeUser Class</a>

            
            </div>


            <div class="doc_text">


            <p>

            
            Some data structures need more to perform more complex updates when types get

            
            resolved.  To support this, a class can derive from the AbstractTypeUser class.

            
            This class

            
            allows it to get callbacks when certain types are resolved.  To register to get

            
            callbacks for a particular type, the DerivedType::{add/remove}AbstractTypeUser

            
            methods can be called on a type.  Note that these methods only work for <i>

            
              abstract</i> types.  Concrete types (those that do not include any opaque

            
            objects) can never be refined.

            
            </p>

            
            </div>


            <!-- ======================================================================= -->

            
            <div class="doc_subsection">

            
              <a name="SymbolTable">The <tt>ValueSymbolTable</tt> and

            
               <tt>TypeSymbolTable</tt> classes</a>

            
            </div>


            <div class="doc_text">

            
            <p>The <tt><a href="http://llvm.org/doxygen/classllvm_1_1ValueSymbolTable.html">

            
            ValueSymbolTable</a></tt> class provides a symbol table that the <a

            
            href="#Function"><tt>Function</tt></a> and <a href="#Module">

            
            <tt>Module</tt></a> classes use for naming value definitions. The symbol table

            
            can provide a name for any <a href="#Value"><tt>Value</tt></a>.

            
            The <tt><a href="http://llvm.org/doxygen/classllvm_1_1TypeSymbolTable.html">

            
            TypeSymbolTable</a></tt> class is used by the <tt>Module</tt> class to store

            
            names for types.</p>


            <p>Note that the <tt>SymbolTable</tt> class should not be directly accessed

            
            by most clients.  It should only be used when iteration over the symbol table

            
            names themselves are required, which is very special purpose.  Note that not

            
            all LLVM

            
            <a href="#Value">Value</a>s have names, and those without names (i.e. they have

            
            an empty name) do not exist in the symbol table.

            
            </p>


            <p>These symbol tables support iteration over the values/types in the symbol

            
            table with <tt>begin/end/iterator</tt> and supports querying to see if a

            
            specific name is in the symbol table (with <tt>lookup</tt>).  The

            
            <tt>ValueSymbolTable</tt> class exposes no public mutator methods, instead,

            
            simply call <tt>setName</tt> on a value, which will autoinsert it into the

            
            appropriate symbol table.  For types, use the Module::addTypeName method to

            
            insert entries into the symbol table.</p>


            </div>


            <!-- *********************************************************************** -->

            
            <div class="doc_section">

            
              <a name="coreclasses">The Core LLVM Class Hierarchy Reference </a>

            
            </div>

            
            <!-- *********************************************************************** -->


            <div class="doc_text">

            
            <p><tt>#include "<a href="/doxygen/Type_8h-source.html">llvm/Type.h</a>"</tt>

            
            <br>doxygen info: <a href="/doxygen/classllvm_1_1Type.html">Type Class</a></p>


            <p>The Core LLVM classes are the primary means of representing the program

            
            being inspected or transformed.  The core LLVM classes are defined in

            
            header files in the <tt>include/llvm/</tt> directory, and implemented in

            
            the <tt>lib/VMCore</tt> directory.</p>


            </div>


            <!-- ======================================================================= -->

            
            <div class="doc_subsection">

            
              <a name="Type">The <tt>Type</tt> class and Derived Types</a>

            
            </div>


            <div class="doc_text">


              <p><tt>Type</tt> is a superclass of all type classes. Every <tt>Value</tt> has

            
              a <tt>Type</tt>. <tt>Type</tt> cannot be instantiated directly but only

            
              through its subclasses. Certain primitive types (<tt>VoidType</tt>,

            
              <tt>LabelType</tt>, <tt>FloatType</tt> and <tt>DoubleType</tt>) have hidden

            
              subclasses. They are hidden because they offer no useful functionality beyond

            
              what the <tt>Type</tt> class offers except to distinguish themselves from

            
              other subclasses of <tt>Type</tt>.</p>

            
              <p>All other types are subclasses of <tt>DerivedType</tt>.  Types can be

            
              named, but this is not a requirement. There exists exactly

            
              one instance of a given shape at any one time.  This allows type equality to

            
              be performed with address equality of the Type Instance. That is, given two

            
              <tt>Type*</tt> values, the types are identical if the pointers are identical.

            
              </p>

            
            </div>


            <!-- _______________________________________________________________________ -->

            
            <div class="doc_subsubsection">

            
              <a name="m_Value">Important Public Methods</a>

            
            </div>


            <div class="doc_text">


            <ul>

            
              <li><tt>bool isInteger() const</tt>: Returns true for any integer type.</li>


              <li><tt>bool isFloatingPoint()</tt>: Return true if this is one of the two

            
              floating point types.</li>


              <li><tt>bool isAbstract()</tt>: Return true if the type is abstract (contains

            
              an OpaqueType anywhere in its definition).</li>


              <li><tt>bool isSized()</tt>: Return true if the type has known size. Things

            
              that don't have a size are abstract types, labels and void.</li>


            </ul>

            
            </div>


            <!-- _______________________________________________________________________ -->

            
            <div class="doc_subsubsection">

            
              <a name="m_Value">Important Derived Types</a>

            
            </div>

            
            <div class="doc_text">

            
            <dl>

            
              <dt><tt>IntegerType</tt></dt>

            
              <dd>Subclass of DerivedType that represents integer types of any bit width.

            
              Any bit width between <tt>IntegerType::MIN_INT_BITS</tt> (1) and

            
              <tt>IntegerType::MAX_INT_BITS</tt> (~8 million) can be represented.

            
              <ul>

            
                <li><tt>static const IntegerType* get(unsigned NumBits)</tt>: get an integer

            
                type of a specific bit width.</li>

            
                <li><tt>unsigned getBitWidth() const</tt>: Get the bit width of an integer

            
                type.</li>

            
              </ul>

            
              </dd>

            
              <dt><tt>SequentialType</tt></dt>

            
              <dd>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>

            
              </dd>

            
              <dt><tt>ArrayType</tt></dt>

            
              <dd>This is a subclass of SequentialType and defines the interface for array

            
              types.

            
                <ul>

            
                  <li><tt>unsigned getNumElements() const</tt>: Returns the number of

            
                  elements in the array. </li>

            
                </ul>

            
              </dd>

            
              <dt><tt>PointerType</tt></dt>

            
              <dd>Subclass of SequentialType for pointer types.</dd>

            
              <dt><tt>VectorType</tt></dt>

            
              <dd>Subclass of SequentialType for vector types. A

            
              vector type is similar to an ArrayType but is distinguished because it is

            
              a first class type wherease ArrayType is not. Vector types are used for

            
              vector operations and are usually small vectors of of an integer or floating

            
              point type.</dd>

            
              <dt><tt>StructType</tt></dt>

            
              <dd>Subclass of DerivedTypes for struct types.</dd>

            
              <dt><tt><a name="FunctionType">FunctionType</a></tt></dt>

            
              <dd>Subclass of DerivedTypes for function types.

            
                <ul>

            
                  <li><tt>bool isVarArg() const</tt>: Returns true if its a vararg

            
                  function</li>

            
                  <li><tt> const Type * getReturnType() const</tt>: Returns the

            
                  return type of the function.</li>

            
                  <li><tt>const Type * getParamType (unsigned i)</tt>: Returns

            
                  the type of the ith parameter.</li>

            
                  <li><tt> const unsigned getNumParams() const</tt>: Returns the

            
                  number of formal parameters.</li>

            
                </ul>

            
              </dd>

            
              <dt><tt>OpaqueType</tt></dt>

            
              <dd>Sublcass of DerivedType for abstract types. This class

            
              defines no content and is used as a placeholder for some other type. Note

            
              that OpaqueType is used (temporarily) during type resolution for forward

            
              references of types. Once the referenced type is resolved, the OpaqueType

            
              is replaced with the actual type. OpaqueType can also be used for data

            
              abstraction. At link time opaque types can be resolved to actual types

            
              of the same name.</dd>

            
            </dl>

            
            </div>


            <!-- ======================================================================= -->

            
            <div class="doc_subsection">

            
              <a name="Module">The <tt>Module</tt> class</a>

            
            </div>


            <div class="doc_text">


            <p><tt>#include "<a

            
            href="/doxygen/Module_8h-source.html">llvm/Module.h</a>"</tt><br> doxygen info:

            
            <a href="/doxygen/classllvm_1_1Module.html">Module Class</a></p>


            <p>The <tt>Module</tt> class represents the top level structure present in LLVM

            
            programs.  An LLVM module is effectively either a translation unit of the

            
            original program or a combination of several translation units merged by the

            
            linker.  The <tt>Module</tt> class keeps track of a list of <a

            
            href="#Function"><tt>Function</tt></a>s, a list of <a

            
            href="#GlobalVariable"><tt>GlobalVariable</tt></a>s, and a <a

            
            href="#SymbolTable"><tt>SymbolTable</tt></a>.  Additionally, it contains a few

            
            helpful member functions that try to make common operations easy.</p>


            </div>


            <!-- _______________________________________________________________________ -->

            
            <div class="doc_subsubsection">

            
              <a name="m_Module">Important Public Members of the <tt>Module</tt> class</a>

            
            </div>


            <div class="doc_text">


            <ul>

            
              <li><tt>Module::Module(std::string name = "")</tt></li>

            
            </ul>


            <p>Constructing a <a href="#Module">Module</a> is easy. You can optionally

            
            provide a name for it (probably based on the name of the translation unit).</p>


            <ul>

            
              <li><tt>Module::iterator</tt> - Typedef for function list iterator<br>

            
                <tt>Module::const_iterator</tt> - Typedef for const_iterator.<br>


                <tt>begin()</tt>, <tt>end()</tt>

            
                <tt>size()</tt>, <tt>empty()</tt>


                <p>These are forwarding methods that make it easy to access the contents of

            
                a <tt>Module</tt> object's <a href="#Function"><tt>Function</tt></a>

            
                list.</p></li>


              <li><tt>Module::FunctionListType &amp;getFunctionList()</tt>


                <p> Returns the list of <a href="#Function"><tt>Function</tt></a>s.  This is

            
                necessary to use when you need to update the list or perform a complex

            
                action that doesn't have a forwarding method.</p>


                <p><!--  Global Variable --></p></li>

            
            </ul>


            <hr>


            <ul>

            
              <li><tt>Module::global_iterator</tt> - Typedef for global variable list iterator<br>


                <tt>Module::const_global_iterator</tt> - Typedef for const_iterator.<br>


                <tt>global_begin()</tt>, <tt>global_end()</tt>

            
                <tt>global_size()</tt>, <tt>global_empty()</tt>


                <p> These are forwarding methods that make it easy to access the contents of

            
                a <tt>Module</tt> object's <a

            
                href="#GlobalVariable"><tt>GlobalVariable</tt></a> list.</p></li>


              <li><tt>Module::GlobalListType &amp;getGlobalList()</tt>


                <p>Returns the list of <a

            
                href="#GlobalVariable"><tt>GlobalVariable</tt></a>s.  This is necessary to

            
                use when you need to update the list or perform a complex action that

            
                doesn't have a forwarding method.</p>


                <p><!--  Symbol table stuff --> </p></li>

            
            </ul>


            <hr>


            <ul>

            
              <li><tt><a href="#SymbolTable">SymbolTable</a> *getSymbolTable()</tt>


                <p>Return a reference to the <a href="#SymbolTable"><tt>SymbolTable</tt></a>

            
                for this <tt>Module</tt>.</p>


                <p><!--  Convenience methods --></p></li>

            
            </ul>


            <hr>


            <ul>

            
              <li><tt><a href="#Function">Function</a> *getFunction(const std::string

            
              &amp;Name, const <a href="#FunctionType">FunctionType</a> *Ty)</tt>


                <p>Look up the specified function in the <tt>Module</tt> <a

            
                href="#SymbolTable"><tt>SymbolTable</tt></a>. If it does not exist, return

            
                <tt>null</tt>.</p></li>


              <li><tt><a href="#Function">Function</a> *getOrInsertFunction(const

            
              std::string &amp;Name, const <a href="#FunctionType">FunctionType</a> *T)</tt>


                <p>Look up the specified function in the <tt>Module</tt> <a

            
                href="#SymbolTable"><tt>SymbolTable</tt></a>. If it does not exist, add an

            
                external declaration for the function and return it.</p></li>


              <li><tt>std::string getTypeName(const <a href="#Type">Type</a> *Ty)</tt>


                <p>If there is at least one entry in the <a

            
                href="#SymbolTable"><tt>SymbolTable</tt></a> for the specified <a

            
                href="#Type"><tt>Type</tt></a>, return it.  Otherwise return the empty

            
                string.</p></li>


              <li><tt>bool addTypeName(const std::string &amp;Name, const <a

            
              href="#Type">Type</a> *Ty)</tt>


                <p>Insert an entry in the <a href="#SymbolTable"><tt>SymbolTable</tt></a>

            
                mapping <tt>Name</tt> to <tt>Ty</tt>. If there is already an entry for this

            
                name, true is returned and the <a

            
                href="#SymbolTable"><tt>SymbolTable</tt></a> is not modified.</p></li>

            
            </ul>


            </div>


            <!-- ======================================================================= -->

            
            <div class="doc_subsection">

            
              <a name="Value">The <tt>Value</tt> class</a>

            
            </div>


            <div class="doc_text">


            <p><tt>#include "<a href="/doxygen/Value_8h-source.html">llvm/Value.h</a>"</tt>

            
            <br>

            
            doxygen info: <a href="/doxygen/classllvm_1_1Value.html">Value Class</a></p>


            <p>The <tt>Value</tt> class is the most important class in the LLVM Source

            
            base.  It represents a typed value that may be used (among other things) as an

            
            operand to an instruction.  There are many different types of <tt>Value</tt>s,

            
            such as <a href="#Constant"><tt>Constant</tt></a>s,<a

            
            href="#Argument"><tt>Argument</tt></a>s. Even <a

            
            href="#Instruction"><tt>Instruction</tt></a>s and <a

            
            href="#Function"><tt>Function</tt></a>s are <tt>Value</tt>s.</p>


            <p>A particular <tt>Value</tt> may be used many times in the LLVM representation

            
            for a program.  For example, an incoming argument to a function (represented

            
            with an instance of the <a href="#Argument">Argument</a> class) is "used" by

            
            every instruction in the function that references the argument.  To keep track

            
            of this relationship, the <tt>Value</tt> class keeps a list of all of the <a

            
            href="#User"><tt>User</tt></a>s that is using it (the <a

            
            href="#User"><tt>User</tt></a> class is a base class for all nodes in the LLVM

            
            graph that can refer to <tt>Value</tt>s).  This use list is how LLVM represents

            
            def-use information in the program, and is accessible through the <tt>use_</tt>*

            
            methods, shown below.</p>


            <p>Because LLVM is a typed representation, every LLVM <tt>Value</tt> is typed,

            
            and this <a href="#Type">Type</a> is available through the <tt>getType()</tt>

            
            method. In addition, all LLVM values can be named.  The "name" of the

            
            <tt>Value</tt> is a symbolic string printed in the LLVM code:</p>


            <div class="doc_code">

            
            <pre>

            
            %<b>foo</b> = add i32 1, 2

            
            </pre>

            
            </div>


            <p><a name="nameWarning">The name of this instruction is "foo".</a> <b>NOTE</b>

            
            that the name of any value may be missing (an empty string), so names should

            
            <b>ONLY</b> be used for debugging (making the source code easier to read,

            
            debugging printouts), they should not be used to keep track of values or map

            
            between them.  For this purpose, use a <tt>std::map</tt> of pointers to the

            
            <tt>Value</tt> itself instead.</p>


            <p>One important aspect of LLVM is that there is no distinction between an SSA

            
            variable and the operation that produces it.  Because of this, any reference to

            
            the value produced by an instruction (or the value available as an incoming

            
            argument, for example) is represented as a direct pointer to the instance of

            
            the class that

            
            represents this value.  Although this may take some getting used to, it

            
            simplifies the representation and makes it easier to manipulate.</p>


            </div>


            <!-- _______________________________________________________________________ -->

            
            <div class="doc_subsubsection">

            
              <a name="m_Value">Important Public Members of the <tt>Value</tt> class</a>

            
            </div>


            <div class="doc_text">


            <ul>

            
              <li><tt>Value::use_iterator</tt> - Typedef for iterator over the

            
            use-list<br>

            
                <tt>Value::use_const_iterator</tt> - Typedef for const_iterator over

            
            the use-list<br>

            
                <tt>unsigned use_size()</tt> - Returns the number of users of the

            
            value.<br>

            
                <tt>bool use_empty()</tt> - Returns true if there are no users.<br>

            
                <tt>use_iterator use_begin()</tt> - Get an iterator to the start of

            
            the use-list.<br>

            
                <tt>use_iterator use_end()</tt> - Get an iterator to the end of the

            
            use-list.<br>

            
                <tt><a href="#User">User</a> *use_back()</tt> - Returns the last

            
            element in the list.

            
                <p> These methods are the interface to access the def-use

            
            information in LLVM.  As with all other iterators in LLVM, the naming

            
            conventions follow the conventions defined by the <a href="#stl">STL</a>.</p>

            
              </li>

            
              <li><tt><a href="#Type">Type</a> *getType() const</tt>

            
                <p>This method returns the Type of the Value.</p>

            
              </li>

            
              <li><tt>bool hasName() const</tt><br>

            
                <tt>std::string getName() const</tt><br>

            
                <tt>void setName(const std::string &amp;Name)</tt>

            
                <p> This family of methods is used to access and assign a name to a <tt>Value</tt>,

            
            be aware of the <a href="#nameWarning">precaution above</a>.</p>

            
              </li>

            
              <li><tt>void replaceAllUsesWith(Value *V)</tt>


                <p>This method traverses the use list of a <tt>Value</tt> changing all <a

            
                href="#User"><tt>User</tt>s</a> of the current value to refer to

            
                "<tt>V</tt>" instead.  For example, if you detect that an instruction always

            
                produces a constant value (for example through constant folding), you can

            
                replace all uses of the instruction with the constant like this:</p>


            <div class="doc_code">

            
            <pre>

            
            Inst-&gt;replaceAllUsesWith(ConstVal);

            
            </pre>

            
            </div>


            </ul>


            </div>


            <!-- ======================================================================= -->

            
            <div class="doc_subsection">

            
              <a name="User">The <tt>User</tt> class</a>

            
            </div>


            <div class="doc_text">


            <p>

            
            <tt>#include "<a href="/doxygen/User_8h-source.html">llvm/User.h</a>"</tt><br>

            
            doxygen info: <a href="/doxygen/classllvm_1_1User.html">User Class</a><br>

            
            Superclass: <a href="#Value"><tt>Value</tt></a></p>


            <p>The <tt>User</tt> class is the common base class of all LLVM nodes that may

            
            refer to <a href="#Value"><tt>Value</tt></a>s.  It exposes a list of "Operands"

            
            that are all of the <a href="#Value"><tt>Value</tt></a>s that the User is

            
            referring to.  The <tt>User</tt> class itself is a subclass of

            
            <tt>Value</tt>.</p>


            <p>The operands of a <tt>User</tt> point directly to the LLVM <a

            
            href="#Value"><tt>Value</tt></a> that it refers to.  Because LLVM uses Static

            
            Single Assignment (SSA) form, there can only be one definition referred to,

            
            allowing this direct connection.  This connection provides the use-def

            
            information in LLVM.</p>


            </div>


            <!-- _______________________________________________________________________ -->

            
            <div class="doc_subsubsection">

            
              <a name="m_User">Important Public Members of the <tt>User</tt> class</a>

            
            </div>


            <div class="doc_text">


            <p>The <tt>User</tt> class exposes the operand list in two ways: through

            
            an index access interface and through an iterator based interface.</p>


            <ul>

            
              <li><tt>Value *getOperand(unsigned i)</tt><br>

            
                <tt>unsigned getNumOperands()</tt>

            
                <p> These two methods expose the operands of the <tt>User</tt> in a

            
            convenient form for direct access.</p></li>


              <li><tt>User::op_iterator</tt> - Typedef for iterator over the operand

            
            list<br>

            
                <tt>op_iterator op_begin()</tt> - Get an iterator to the start of

            
            the operand list.<br>

            
                <tt>op_iterator op_end()</tt> - Get an iterator to the end of the

            
            operand list.

            
                <p> Together, these methods make up the iterator based interface to

            
            the operands of a <tt>User</tt>.</p></li>

            
            </ul>


            </div>


            <!-- ======================================================================= -->

            
            <div class="doc_subsection">

            
              <a name="Instruction">The <tt>Instruction</tt> class</a>

            
            </div>


            <div class="doc_text">


            <p><tt>#include "</tt><tt><a

            
            href="/doxygen/Instruction_8h-source.html">llvm/Instruction.h</a>"</tt><br>

            
            doxygen info: <a href="/doxygen/classllvm_1_1Instruction.html">Instruction Class</a><br>

            
            Superclasses: <a href="#User"><tt>User</tt></a>, <a

            
            href="#Value"><tt>Value</tt></a></p>


            <p>The <tt>Instruction</tt> class is the common base class for all LLVM

            
            instructions.  It provides only a few methods, but is a very commonly used

            
            class.  The primary data tracked by the <tt>Instruction</tt> class itself is the

            
            opcode (instruction type) and the parent <a

            
            href="#BasicBlock"><tt>BasicBlock</tt></a> the <tt>Instruction</tt> is embedded

            
            into.  To represent a specific type of instruction, one of many subclasses of

            
            <tt>Instruction</tt> are used.</p>


            <p> Because the <tt>Instruction</tt> class subclasses the <a

            
            href="#User"><tt>User</tt></a> class, its operands can be accessed in the same

            
            way as for other <a href="#User"><tt>User</tt></a>s (with the

            
            <tt>getOperand()</tt>/<tt>getNumOperands()</tt> and

            
            <tt>op_begin()</tt>/<tt>op_end()</tt> methods).</p> <p> An important file for

            
            the <tt>Instruction</tt> class is the <tt>llvm/Instruction.def</tt> file. This

            
            file contains some meta-data about the various different types of instructions

            
            in LLVM.  It describes the enum values that are used as opcodes (for example

            
            <tt>Instruction::Add</tt> and <tt>Instruction::ICmp</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="#CmpInst">CmpInst</a></tt>).  Unfortunately, the use of macros in

            
            this file confuses doxygen, so these enum values don't show up correctly in the

            
            <a href="/doxygen/classllvm_1_1Instruction.html">doxygen output</a>.</p>


            </div>


            <!-- _______________________________________________________________________ -->

            
            <div class="doc_subsubsection">

            
              <a name="s_Instruction">Important Subclasses of the <tt>Instruction</tt>

            
              class</a>

            
            </div>

            
            <div class="doc_text">

            
              <ul>

            
                <li><tt><a name="BinaryOperator">BinaryOperator</a></tt>

            
                <p>This subclasses represents all two operand instructions whose operands

            
                must be the same type, except for the comparison instructions.</p></li>

            
                <li><tt><a name="CastInst">CastInst</a></tt>

            
                <p>This subclass is the parent of the 12 casting instructions. It provides

            
                common operations on cast instructions.</p>

            
                <li><tt><a name="CmpInst">CmpInst</a></tt>

            
                <p>This subclass respresents the two comparison instructions,

            
                <a href="LangRef.html#i_icmp">ICmpInst</a> (integer opreands), and

            
                <a href="LangRef.html#i_fcmp">FCmpInst</a> (floating point operands).</p>

            
                <li><tt><a name="TerminatorInst">TerminatorInst</a></tt>

            
                <p>This subclass is the parent of all terminator instructions (those which

            
                can terminate a block).</p>

            
              </ul>

            
              </div>


            <!-- _______________________________________________________________________ -->

            
            <div class="doc_subsubsection">

            
              <a name="m_Instruction">Important Public Members of the <tt>Instruction</tt>

            
              class</a>

            
            </div>


            <div class="doc_text">


            <ul>

            
              <li><tt><a href="#BasicBlock">BasicBlock</a> *getParent()</tt>

            
                <p>Returns the <a href="#BasicBlock"><tt>BasicBlock</tt></a> that

            
            this  <tt>Instruction</tt> is embedded into.</p></li>

            
              <li><tt>bool mayWriteToMemory()</tt>

            
                <p>Returns true if the instruction writes to memory, i.e. it is a

            
                  <tt>call</tt>,<tt>free</tt>,<tt>invoke</tt>, or <tt>store</tt>.</p></li>

            
              <li><tt>unsigned getOpcode()</tt>

            
                <p>Returns the opcode for the <tt>Instruction</tt>.</p></li>

            
              <li><tt><a href="#Instruction">Instruction</a> *clone() const</tt>

            
                <p>Returns another instance of the specified instruction, identical

            
            in all ways to the original except that the instruction has no parent

            
            (ie it's not embedded into a <a href="#BasicBlock"><tt>BasicBlock</tt></a>),

            
            and it has no name</p></li>

            
            </ul>


            </div>


            <!-- ======================================================================= -->

            
            <div class="doc_subsection">

            
              <a name="Constant">The <tt>Constant</tt> class and subclasses</a>

            
            </div>


            <div class="doc_text">


            <p>Constant represents a base class for different types of constants. It

            
            is subclassed by ConstantInt, ConstantArray, etc. for representing

            
            the various types of Constants.  <a href="#GlobalValue">GlobalValue</a> is also

            
            a subclass, which represents the address of a global variable or function.

            
            </p>


            </div>


            <!-- _______________________________________________________________________ -->

            
            <div class="doc_subsubsection">Important Subclasses of Constant </div>

            
            <div class="doc_text">

            
            <ul>

            
              <li>ConstantInt : This subclass of Constant represents an integer constant of

            
              any width.

            
                <ul>

            
                  <li><tt>const APInt&amp; getValue() const</tt>: Returns the underlying

            
                  value of this constant, an APInt value.</li>

            
                  <li><tt>int64_t getSExtValue() const</tt>: Converts the underlying APInt

            
                  value to an int64_t via sign extension. If the value (not the bit width)

            
                  of the APInt is too large to fit in an int64_t, an assertion will result.

            
                  For this reason, use of this method is discouraged.</li>

            
                  <li><tt>uint64_t getZExtValue() const</tt>: Converts the underlying APInt

            
                  value to a uint64_t via zero extension. IF the value (not the bit width)

            
                  of the APInt is too large to fit in a uint64_t, an assertion will result.

            
                  For this reason, use of this method is discouraged.</li>

            
                  <li><tt>static ConstantInt* get(const APInt&amp; Val)</tt>: Returns the

            
                  ConstantInt object that represents the value provided by <tt>Val</tt>.

            
                  The type is implied as the IntegerType that corresponds to the bit width

            
                  of <tt>Val</tt>.</li>

            
                  <li><tt>static ConstantInt* get(const Type *Ty, uint64_t Val)</tt>:

            
                  Returns the ConstantInt object that represents the value provided by

            
                  <tt>Val</tt> for integer type <tt>Ty</tt>.</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>ConstantArray : This represents a constant array.

            
                <ul>

            
                  <li><tt>const std::vector&lt;Use&gt; &amp;getValues() const</tt>: Returns

            
                  a vector of component constants that makeup this array. </li>

            
                </ul>

            
              </li>

            
              <li>ConstantStruct : This represents a constant struct.

            
                <ul>

            
                  <li><tt>const std::vector&lt;Use&gt; &amp;getValues() const</tt>: Returns

            
                  a vector of component constants that makeup this array. </li>

            
                </ul>

            
              </li>

            
              <li>GlobalValue : This represents either a global variable or a function. In

            
              either case, the value is a constant fixed address (after linking).

            
              </li>

            
            </ul>

            
            </div>


            <!-- ======================================================================= -->

            
            <div class="doc_subsection">

            
              <a name="GlobalValue">The <tt>GlobalValue</tt> class</a>

            
            </div>


            <div class="doc_text">


            <p><tt>#include "<a

            
            href="/doxygen/GlobalValue_8h-source.html">llvm/GlobalValue.h</a>"</tt><br>

            
            doxygen info: <a href="/doxygen/classllvm_1_1GlobalValue.html">GlobalValue

            
            Class</a><br>

            
            Superclasses: <a href="#Constant"><tt>Constant</tt></a>,

            
            <a href="#User"><tt>User</tt></a>, <a href="#Value"><tt>Value</tt></a></p>


            <p>Global values (<a href="#GlobalVariable"><tt>GlobalVariable</tt></a>s or <a

            
            href="#Function"><tt>Function</tt></a>s) are the only LLVM values that are

            
            visible in the bodies of all <a href="#Function"><tt>Function</tt></a>s.

            
            Because they are visible at global scope, they are also subject to linking with

            
            other globals defined in different translation units.  To control the linking

            
            process, <tt>GlobalValue</tt>s know their linkage rules. Specifically,

            
            <tt>GlobalValue</tt>s know whether they have internal or external linkage, as

            
            defined by the <tt>LinkageTypes</tt> enumeration.</p>


            <p>If a <tt>GlobalValue</tt> has internal linkage (equivalent to being

            
            <tt>static</tt> in C), it is not visible to code outside the current translation

            
            unit, and does not participate in linking.  If it has external linkage, it is

            
            visible to external code, and does participate in linking.  In addition to

            
            linkage information, <tt>GlobalValue</tt>s keep track of which <a

            
            href="#Module"><tt>Module</tt></a> they are currently part of.</p>


            <p>Because <tt>GlobalValue</tt>s are memory objects, they are always referred to

            
            by their <b>address</b>. As such, the <a href="#Type"><tt>Type</tt></a> of a

            
            global is always a pointer to its contents. It is important to remember this

            
            when using the <tt>GetElementPtrInst</tt> instruction because this pointer must

            
            be dereferenced first. For example, if you have a <tt>GlobalVariable</tt> (a

            
            subclass of <tt>GlobalValue)</tt> that is an array of 24 ints, type <tt>[24 x

            
            i32]</tt>, then the <tt>GlobalVariable</tt> is a pointer to that array. Although

            
            the address of the first element of this array and the value of the

            
            <tt>GlobalVariable</tt> are the same, they have different types. The

            
            <tt>GlobalVariable</tt>'s type is <tt>[24 x i32]</tt>. The first element's type

            
            is <tt>i32.</tt> Because of this, accessing a global value requires you to

            
            dereference the pointer with <tt>GetElementPtrInst</tt> first, then its elements

            
            can be accessed. This is explained in the <a href="LangRef.html#globalvars">LLVM

            
            Language Reference Manual</a>.</p>


            </div>


            <!-- _______________________________________________________________________ -->

            
            <div class="doc_subsubsection">

            
              <a name="m_GlobalValue">Important Public Members of the <tt>GlobalValue</tt>

            
              class</a>

            
            </div>


            <div class="doc_text">


            <ul>

            
              <li><tt>bool hasInternalLinkage() const</tt><br>

            
                <tt>bool hasExternalLinkage() const</tt><br>

            
                <tt>void setInternalLinkage(bool HasInternalLinkage)</tt>

            
                <p> These methods manipulate the linkage characteristics of the <tt>GlobalValue</tt>.</p>

            
                <p> </p>

            
              </li>

            
              <li><tt><a href="#Module">Module</a> *getParent()</tt>

            
                <p> This returns the <a href="#Module"><tt>Module</tt></a> that the

            
            GlobalValue is currently embedded into.</p></li>

            
            </ul>


            </div>


            <!-- ======================================================================= -->

            
            <div class="doc_subsection">

            
              <a name="Function">The <tt>Function</tt> class</a>

            
            </div>


            <div class="doc_text">


            <p><tt>#include "<a

            
            href="/doxygen/Function_8h-source.html">llvm/Function.h</a>"</tt><br> doxygen

            
            info: <a href="/doxygen/classllvm_1_1Function.html">Function Class</a><br>

            
            Superclasses: <a href="#GlobalValue"><tt>GlobalValue</tt></a>,

            
            <a href="#Constant"><tt>Constant</tt></a>,

            
            <a href="#User"><tt>User</tt></a>,

            
            <a href="#Value"><tt>Value</tt></a></p>


            <p>The <tt>Function</tt> class represents a single procedure in LLVM.  It is

            
            actually one of the more complex classes in the LLVM heirarchy because it must

            
            keep track of a large amount of data.  The <tt>Function</tt> class keeps track

            
            of a list of <a href="#BasicBlock"><tt>BasicBlock</tt></a>s, a list of formal

            
            <a href="#Argument"><tt>Argument</tt></a>s, and a

            
            <a href="#SymbolTable"><tt>SymbolTable</tt></a>.</p>


            <p>The list of <a href="#BasicBlock"><tt>BasicBlock</tt></a>s is the most

            
            commonly used part of <tt>Function</tt> objects.  The list imposes an implicit

            
            ordering of the blocks in the function, which indicate how the code will be

            
            layed out by the backend.  Additionally, the first <a

            
            href="#BasicBlock"><tt>BasicBlock</tt></a> is the implicit entry node for the

            
            <tt>Function</tt>.  It is not legal in LLVM to explicitly branch to this initial

            
            block.  There are no implicit exit nodes, and in fact there may be multiple exit

            
            nodes from a single <tt>Function</tt>.  If the <a

            
            href="#BasicBlock"><tt>BasicBlock</tt></a> list is empty, this indicates that

            
            the <tt>Function</tt> is actually a function declaration: the actual body of the

            
            function hasn't been linked in yet.</p>


            <p>In addition to a list of <a href="#BasicBlock"><tt>BasicBlock</tt></a>s, the

            
            <tt>Function</tt> class also keeps track of the list of formal <a

            
            href="#Argument"><tt>Argument</tt></a>s that the function receives.  This

            
            container manages the lifetime of the <a href="#Argument"><tt>Argument</tt></a>

            
            nodes, just like the <a href="#BasicBlock"><tt>BasicBlock</tt></a> list does for

            
            the <a href="#BasicBlock"><tt>BasicBlock</tt></a>s.</p>


            <p>The <a href="#SymbolTable"><tt>SymbolTable</tt></a> is a very rarely used

            
            LLVM feature that is only used when you have to look up a value by name.  Aside

            
            from that, the <a href="#SymbolTable"><tt>SymbolTable</tt></a> is used

            
            internally to make sure that there are not conflicts between the names of <a

            
            href="#Instruction"><tt>Instruction</tt></a>s, <a

            
            href="#BasicBlock"><tt>BasicBlock</tt></a>s, or <a

            
            href="#Argument"><tt>Argument</tt></a>s in the function body.</p>


            <p>Note that <tt>Function</tt> is a <a href="#GlobalValue">GlobalValue</a>

            
            and therefore also a <a href="#Constant">Constant</a>. The value of the function

            
            is its address (after linking) which is guaranteed to be constant.</p>

            
            </div>


            <!-- _______________________________________________________________________ -->

            
            <div class="doc_subsubsection">

            
              <a name="m_Function">Important Public Members of the <tt>Function</tt>

            
              class</a>

            
            </div>


            <div class="doc_text">


            <ul>

            
              <li><tt>Function(const </tt><tt><a href="#FunctionType">FunctionType</a>

            
              *Ty, LinkageTypes Linkage, const std::string &amp;N = "", Module* Parent = 0)</tt>


                <p>Constructor used when you need to create new <tt>Function</tt>s to add

            
                the the program.  The constructor must specify the type of the function to

            
                create and what type of linkage the function should have. The <a

            
                href="#FunctionType"><tt>FunctionType</tt></a> argument

            
                specifies the formal arguments and return value for the function. The same

            
                <a href="#FunctionType"><tt>FunctionType</tt></a> value can be used to

            
                create multiple functions. The <tt>Parent</tt> argument specifies the Module

            
                in which the function is defined. If this argument is provided, the function

            
                will automatically be inserted into that module's list of

            
                functions.</p></li>


              <li><tt>bool isExternal()</tt>


                <p>Return whether or not the <tt>Function</tt> has a body defined.  If the

            
                function is "external", it does not have a body, and thus must be resolved

            
                by linking with a function defined in a different translation unit.</p></li>


              <li><tt>Function::iterator</tt> - Typedef for basic block list iterator<br>

            
                <tt>Function::const_iterator</tt> - Typedef for const_iterator.<br>


                <tt>begin()</tt>, <tt>end()</tt>

            
                <tt>size()</tt>, <tt>empty()</tt>


                <p>These are forwarding methods that make it easy to access the contents of

            
                a <tt>Function</tt> object's <a href="#BasicBlock"><tt>BasicBlock</tt></a>

            
                list.</p></li>


              <li><tt>Function::BasicBlockListType &amp;getBasicBlockList()</tt>


                <p>Returns the list of <a href="#BasicBlock"><tt>BasicBlock</tt></a>s.  This

            
                is necessary to use when you need to update the list or perform a complex

            
                action that doesn't have a forwarding method.</p></li>


              <li><tt>Function::arg_iterator</tt> - Typedef for the argument list

            
            iterator<br>

            
                <tt>Function::const_arg_iterator</tt> - Typedef for const_iterator.<br>


                <tt>arg_begin()</tt>, <tt>arg_end()</tt>

            
                <tt>arg_size()</tt>, <tt>arg_empty()</tt>


                <p>These are forwarding methods that make it easy to access the contents of

            
                a <tt>Function</tt> object's <a href="#Argument"><tt>Argument</tt></a>

            
                list.</p></li>


              <li><tt>Function::ArgumentListType &amp;getArgumentList()</tt>


                <p>Returns the list of <a href="#Argument"><tt>Argument</tt></a>s.  This is

            
                necessary to use when you need to update the list or perform a complex

            
                action that doesn't have a forwarding method.</p></li>


              <li><tt><a href="#BasicBlock">BasicBlock</a> &amp;getEntryBlock()</tt>


                <p>Returns the entry <a href="#BasicBlock"><tt>BasicBlock</tt></a> for the

            
                function.  Because the entry block for the function is always the first

            
                block, this returns the first block of the <tt>Function</tt>.</p></li>


              <li><tt><a href="#Type">Type</a> *getReturnType()</tt><br>

            
                <tt><a href="#FunctionType">FunctionType</a> *getFunctionType()</tt>


                <p>This traverses the <a href="#Type"><tt>Type</tt></a> of the

            
                <tt>Function</tt> and returns the return type of the function, or the <a

            
                href="#FunctionType"><tt>FunctionType</tt></a> of the actual

            
                function.</p></li>


              <li><tt><a href="#SymbolTable">SymbolTable</a> *getSymbolTable()</tt>


                <p> Return a pointer to the <a href="#SymbolTable"><tt>SymbolTable</tt></a>

            
                for this <tt>Function</tt>.</p></li>

            
            </ul>


            </div>


            <!-- ======================================================================= -->

            
            <div class="doc_subsection">

            
              <a name="GlobalVariable">The <tt>GlobalVariable</tt> class</a>

            
            </div>


            <div class="doc_text">


            <p><tt>#include "<a

            
            href="/doxygen/GlobalVariable_8h-source.html">llvm/GlobalVariable.h</a>"</tt>

            
            <br>

            
            doxygen info: <a href="/doxygen/classllvm_1_1GlobalVariable.html">GlobalVariable

            
             Class</a><br>

            
            Superclasses: <a href="#GlobalValue"><tt>GlobalValue</tt></a>,

            
            <a href="#Constant"><tt>Constant</tt></a>,

            
            <a href="#User"><tt>User</tt></a>,

            
            <a href="#Value"><tt>Value</tt></a></p>


            <p>Global variables are represented with the (suprise suprise)

            
            <tt>GlobalVariable</tt> class. Like functions, <tt>GlobalVariable</tt>s are also

            
            subclasses of <a href="#GlobalValue"><tt>GlobalValue</tt></a>, and as such are

            
            always referenced by their address (global values must live in memory, so their

            
            "name" refers to their constant address). See

            
            <a href="#GlobalValue"><tt>GlobalValue</tt></a> for more on this.  Global

            
            variables may have an initial value (which must be a

            
            <a href="#Constant"><tt>Constant</tt></a>), and if they have an initializer,

            
            they may be marked as "constant" themselves (indicating that their contents

            
            never change at runtime).</p>

            
            </div>


            <!-- _______________________________________________________________________ -->

            
            <div class="doc_subsubsection">

            
              <a name="m_GlobalVariable">Important Public Members of the

            
              <tt>GlobalVariable</tt> class</a>

            
            </div>


            <div class="doc_text">


            <ul>

            
              <li><tt>GlobalVariable(const </tt><tt><a href="#Type">Type</a> *Ty, bool

            
              isConstant, LinkageTypes&amp; Linkage, <a href="#Constant">Constant</a>

            
              *Initializer = 0, const std::string &amp;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,&nbsp; 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.  &nbsp;See

            
                the <a href="LangRef.html#modulestructure">LLVM Language Reference</a> for

            
                further details on linkage types. Optionally an initializer, a name, and the

            
                module to put the variable into may be specified for the global variable as

            
                well.</p></li>


              <li><tt>bool isConstant() const</tt>


                <p>Returns true if this is a global variable that is known not to

            
                be modified at runtime.</p></li>


              <li><tt>bool hasInitializer()</tt>


                <p>Returns true if this <tt>GlobalVariable</tt> has an intializer.</p></li>


              <li><tt><a href="#Constant">Constant</a> *getInitializer()</tt>


                <p>Returns the intial value for a <tt>GlobalVariable</tt>.  It is not legal

            
                to call this method if there is no initializer.</p></li>

            
            </ul>


            </div>


            <!-- ======================================================================= -->

            
            <div class="doc_subsection">

            
              <a name="BasicBlock">The <tt>BasicBlock</tt> class</a>

            
            </div>


            <div class="doc_text">


            <p><tt>#include "<a

            
            href="/doxygen/BasicBlock_8h-source.html">llvm/BasicBlock.h</a>"</tt><br>

            
            doxygen info: <a href="/doxygen/structllvm_1_1BasicBlock.html">BasicBlock

            
            Class</a><br>

            
            Superclass: <a href="#Value"><tt>Value</tt></a></p>


            <p>This class represents a single entry multiple exit section of the code,

            
            commonly known as a basic block by the compiler community.  The

            
            <tt>BasicBlock</tt> class maintains a list of <a

            
            href="#Instruction"><tt>Instruction</tt></a>s, which form the body of the block.

            
            Matching the language definition, the last element of this list of instructions

            
            is always a terminator instruction (a subclass of the <a

            
            href="#TerminatorInst"><tt>TerminatorInst</tt></a> class).</p>


            <p>In addition to tracking the list of instructions that make up the block, the

            
            <tt>BasicBlock</tt> class also keeps track of the <a

            
            href="#Function"><tt>Function</tt></a> that it is embedded into.</p>


            <p>Note that <tt>BasicBlock</tt>s themselves are <a

            
            href="#Value"><tt>Value</tt></a>s, because they are referenced by instructions

            
            like branches and can go in the switch tables. <tt>BasicBlock</tt>s have type

            
            <tt>label</tt>.</p>


            </div>


            <!-- _______________________________________________________________________ -->

            
            <div class="doc_subsubsection">

            
              <a name="m_BasicBlock">Important Public Members of the <tt>BasicBlock</tt>

            
              class</a>

            
            </div>


            <div class="doc_text">

            
            <ul>


            <li><tt>BasicBlock(const std::string &amp;Name = "", </tt><tt><a

            
             href="#Function">Function</a> *Parent = 0)</tt>


            <p>The <tt>BasicBlock</tt> constructor is used to create new basic blocks for

            
            insertion into a function.  The constructor optionally takes a name for the new

            
            block, and a <a href="#Function"><tt>Function</tt></a> to insert it into.  If

            
            the <tt>Parent</tt> parameter is specified, the new <tt>BasicBlock</tt> is

            
            automatically inserted at the end of the specified <a

            
            href="#Function"><tt>Function</tt></a>, if not specified, the BasicBlock must be

            
            manually inserted into the <a href="#Function"><tt>Function</tt></a>.</p></li>


            <li><tt>BasicBlock::iterator</tt> - Typedef for instruction list iterator<br>

            
            <tt>BasicBlock::const_iterator</tt> - Typedef for const_iterator.<br>

            
            <tt>begin()</tt>, <tt>end()</tt>, <tt>front()</tt>, <tt>back()</tt>,

            
            <tt>size()</tt>, <tt>empty()</tt>

            
            STL-style functions for accessing the instruction list.


            <p>These methods and typedefs are forwarding functions that have the same

            
            semantics as the standard library methods of the same names.  These methods

            
            expose the underlying instruction list of a basic block in a way that is easy to

            
            manipulate.  To get the full complement of container operations (including

            
            operations to update the list), you must use the <tt>getInstList()</tt>

            
            method.</p></li>


            <li><tt>BasicBlock::InstListType &amp;getInstList()</tt>


            <p>This method is used to get access to the underlying container that actually

            
            holds the Instructions.  This method must be used when there isn't a forwarding

            
            function in the <tt>BasicBlock</tt> class for the operation that you would like

            
            to perform.  Because there are no forwarding functions for "updating"

            
            operations, you need to use this if you want to update the contents of a

            
            <tt>BasicBlock</tt>.</p></li>


            <li><tt><a href="#Function">Function</a> *getParent()</tt>


            <p> Returns a pointer to <a href="#Function"><tt>Function</tt></a> the block is

            
            embedded into, or a null pointer if it is homeless.</p></li>


            <li><tt><a href="#TerminatorInst">TerminatorInst</a> *getTerminator()</tt>


            <p> Returns a pointer to the terminator instruction that appears at the end of

            
            the <tt>BasicBlock</tt>.  If there is no terminator instruction, or if the last

            
            instruction in the block is not a terminator, then a null pointer is

            
            returned.</p></li>


            </ul>


            </div>


            <!-- ======================================================================= -->

            
            <div class="doc_subsection">

            
              <a name="Argument">The <tt>Argument</tt> class</a>

            
            </div>


            <div class="doc_text">


            <p>This subclass of Value defines the interface for incoming formal

            
            arguments to a function. A Function maintains a list of its formal

            
            arguments. An argument has a pointer to the parent Function.</p>


            </div>


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