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10 <div class="doc_title">
11 LLVM Programmer's Manual
15 <li><a href="#introduction">Introduction</a></li>
16 <li><a href="#general">General Information</a>
18 <li><a href="#stl">The C++ Standard Template Library</a></li>
20 <li>The <tt>-time-passes</tt> option</li>
21 <li>How to use the LLVM Makefile system</li>
22 <li>How to write a regression test</li>
27 <li><a href="#apis">Important and useful LLVM APIs</a>
29 <li><a href="#isa">The <tt>isa<></tt>, <tt>cast<></tt>
30 and <tt>dyn_cast<></tt> templates</a> </li>
31 <li><a href="#DEBUG">The <tt>DEBUG()</tt> macro and <tt>-debug</tt>
34 <li><a href="#DEBUG_TYPE">Fine grained debug info with <tt>DEBUG_TYPE</tt>
35 and the <tt>-debug-only</tt> option</a> </li>
38 <li><a href="#Statistic">The <tt>Statistic</tt> class & <tt>-stats</tt>
41 <li>The <tt>InstVisitor</tt> template
42 <li>The general graph API
44 <li><a href="#ViewGraph">Viewing graphs while debugging code</a></li>
47 <li><a href="#common">Helpful Hints for Common Operations</a>
49 <li><a href="#inspection">Basic Inspection and Traversal Routines</a>
51 <li><a href="#iterate_function">Iterating over the <tt>BasicBlock</tt>s
52 in a <tt>Function</tt></a> </li>
53 <li><a href="#iterate_basicblock">Iterating over the <tt>Instruction</tt>s
54 in a <tt>BasicBlock</tt></a> </li>
55 <li><a href="#iterate_institer">Iterating over the <tt>Instruction</tt>s
56 in a <tt>Function</tt></a> </li>
57 <li><a href="#iterate_convert">Turning an iterator into a
58 class pointer</a> </li>
59 <li><a href="#iterate_complex">Finding call sites: a more
60 complex example</a> </li>
61 <li><a href="#calls_and_invokes">Treating calls and invokes
62 the same way</a> </li>
63 <li><a href="#iterate_chains">Iterating over def-use &
64 use-def chains</a> </li>
67 <li><a href="#simplechanges">Making simple changes</a>
69 <li><a href="#schanges_creating">Creating and inserting new
70 <tt>Instruction</tt>s</a> </li>
71 <li><a href="#schanges_deleting">Deleting <tt>Instruction</tt>s</a> </li>
72 <li><a href="#schanges_replacing">Replacing an <tt>Instruction</tt>
73 with another <tt>Value</tt></a> </li>
77 <li>Working with the Control Flow Graph
79 <li>Accessing predecessors and successors of a <tt>BasicBlock</tt>
87 <li><a href="#advanced">Advanced Topics</a>
89 <li><a href="#TypeResolve">LLVM Type Resolution</a>
91 <li><a href="#BuildRecType">Basic Recursive Type Construction</a></li>
92 <li><a href="#refineAbstractTypeTo">The <tt>refineAbstractTypeTo</tt> method</a></li>
93 <li><a href="#PATypeHolder">The PATypeHolder Class</a></li>
94 <li><a href="#AbstractTypeUser">The AbstractTypeUser Class</a></li>
97 <li><a href="#SymbolTable">The <tt>SymbolTable</tt> class </a></li>
100 <li><a href="#coreclasses">The Core LLVM Class Hierarchy Reference</a>
102 <li><a href="#Type">The <tt>Type</tt> class</a> </li>
103 <li><a href="#Value">The <tt>Value</tt> class</a>
105 <li><a href="#User">The <tt>User</tt> class</a>
107 <li><a href="#Instruction">The <tt>Instruction</tt> class</a>
109 <li><a href="#GetElementPtrInst">The <tt>GetElementPtrInst</tt> class</a></li>
112 <li><a href="#Module">The <tt>Module</tt> class</a></li>
113 <li><a href="#Constant">The <tt>Constant</tt> class</a>
115 <li><a href="#GlobalValue">The <tt>GlobalValue</tt> class</a>
117 <li><a href="#BasicBlock">The <tt>BasicBlock</tt>class</a></li>
118 <li><a href="#Function">The <tt>Function</tt> class</a></li>
119 <li><a href="#GlobalVariable">The <tt>GlobalVariable</tt> class</a></li>
126 <li><a href="#Argument">The <tt>Argument</tt> class</a></li>
133 <div class="doc_author">
134 <p>Written by <a href="mailto:sabre@nondot.org">Chris Lattner</a>,
135 <a href="mailto:dhurjati@cs.uiuc.edu">Dinakar Dhurjati</a>,
136 <a href="mailto:jstanley@cs.uiuc.edu">Joel Stanley</a>, and
137 <a href="mailto:rspencer@x10sys.com">Reid Spencer</a></p>
140 <!-- *********************************************************************** -->
141 <div class="doc_section">
142 <a name="introduction">Introduction </a>
144 <!-- *********************************************************************** -->
146 <div class="doc_text">
148 <p>This document is meant to highlight some of the important classes and
149 interfaces available in the LLVM source-base. This manual is not
150 intended to explain what LLVM is, how it works, and what LLVM code looks
151 like. It assumes that you know the basics of LLVM and are interested
152 in writing transformations or otherwise analyzing or manipulating the
155 <p>This document should get you oriented so that you can find your
156 way in the continuously growing source code that makes up the LLVM
157 infrastructure. Note that this manual is not intended to serve as a
158 replacement for reading the source code, so if you think there should be
159 a method in one of these classes to do something, but it's not listed,
160 check the source. Links to the <a href="/doxygen/">doxygen</a> sources
161 are provided to make this as easy as possible.</p>
163 <p>The first section of this document describes general information that is
164 useful to know when working in the LLVM infrastructure, and the second describes
165 the Core LLVM classes. In the future this manual will be extended with
166 information describing how to use extension libraries, such as dominator
167 information, CFG traversal routines, and useful utilities like the <tt><a
168 href="/doxygen/InstVisitor_8h-source.html">InstVisitor</a></tt> template.</p>
172 <!-- *********************************************************************** -->
173 <div class="doc_section">
174 <a name="general">General Information</a>
176 <!-- *********************************************************************** -->
178 <div class="doc_text">
180 <p>This section contains general information that is useful if you are working
181 in the LLVM source-base, but that isn't specific to any particular API.</p>
185 <!-- ======================================================================= -->
186 <div class="doc_subsection">
187 <a name="stl">The C++ Standard Template Library</a>
190 <div class="doc_text">
192 <p>LLVM makes heavy use of the C++ Standard Template Library (STL),
193 perhaps much more than you are used to, or have seen before. Because of
194 this, you might want to do a little background reading in the
195 techniques used and capabilities of the library. There are many good
196 pages that discuss the STL, and several books on the subject that you
197 can get, so it will not be discussed in this document.</p>
199 <p>Here are some useful links:</p>
203 <li><a href="http://www.dinkumware.com/refxcpp.html">Dinkumware C++ Library
204 reference</a> - an excellent reference for the STL and other parts of the
205 standard C++ library.</li>
207 <li><a href="http://www.tempest-sw.com/cpp/">C++ In a Nutshell</a> - This is an
208 O'Reilly book in the making. It has a decent
210 Reference that rivals Dinkumware's, and is unfortunately no longer free since the book has been
213 <li><a href="http://www.parashift.com/c++-faq-lite/">C++ Frequently Asked
216 <li><a href="http://www.sgi.com/tech/stl/">SGI's STL Programmer's Guide</a> -
218 href="http://www.sgi.com/tech/stl/stl_introduction.html">Introduction to the
221 <li><a href="http://www.research.att.com/%7Ebs/C++.html">Bjarne Stroustrup's C++
224 <li><a href="http://64.78.49.204/">
225 Bruce Eckel's Thinking in C++, 2nd ed. Volume 2 Revision 4.0 (even better, get
230 <p>You are also encouraged to take a look at the <a
231 href="CodingStandards.html">LLVM Coding Standards</a> guide which focuses on how
232 to write maintainable code more than where to put your curly braces.</p>
236 <!-- ======================================================================= -->
237 <div class="doc_subsection">
238 <a name="stl">Other useful references</a>
241 <div class="doc_text">
244 <li><a href="http://www.psc.edu/%7Esemke/cvs_branches.html">CVS
245 Branch and Tag Primer</a></li>
246 <li><a href="http://www.fortran-2000.com/ArnaudRecipes/sharedlib.html">Using
247 static and shared libraries across platforms</a></li>
252 <!-- *********************************************************************** -->
253 <div class="doc_section">
254 <a name="apis">Important and useful LLVM APIs</a>
256 <!-- *********************************************************************** -->
258 <div class="doc_text">
260 <p>Here we highlight some LLVM APIs that are generally useful and good to
261 know about when writing transformations.</p>
265 <!-- ======================================================================= -->
266 <div class="doc_subsection">
267 <a name="isa">The <tt>isa<></tt>, <tt>cast<></tt> and
268 <tt>dyn_cast<></tt> templates</a>
271 <div class="doc_text">
273 <p>The LLVM source-base makes extensive use of a custom form of RTTI.
274 These templates have many similarities to the C++ <tt>dynamic_cast<></tt>
275 operator, but they don't have some drawbacks (primarily stemming from
276 the fact that <tt>dynamic_cast<></tt> only works on classes that
277 have a v-table). Because they are used so often, you must know what they
278 do and how they work. All of these templates are defined in the <a
279 href="/doxygen/Casting_8h-source.html"><tt>llvm/Support/Casting.h</tt></a>
280 file (note that you very rarely have to include this file directly).</p>
283 <dt><tt>isa<></tt>: </dt>
285 <dd><p>The <tt>isa<></tt> operator works exactly like the Java
286 "<tt>instanceof</tt>" operator. It returns true or false depending on whether
287 a reference or pointer points to an instance of the specified class. This can
288 be very useful for constraint checking of various sorts (example below).</p>
291 <dt><tt>cast<></tt>: </dt>
293 <dd><p>The <tt>cast<></tt> operator is a "checked cast" operation. It
294 converts a pointer or reference from a base class to a derived cast, causing
295 an assertion failure if it is not really an instance of the right type. This
296 should be used in cases where you have some information that makes you believe
297 that something is of the right type. An example of the <tt>isa<></tt>
298 and <tt>cast<></tt> template is:</p>
300 <div class="doc_code">
302 static bool isLoopInvariant(const <a href="#Value">Value</a> *V, const Loop *L) {
303 if (isa<<a href="#Constant">Constant</a>>(V) || isa<<a href="#Argument">Argument</a>>(V) || isa<<a href="#GlobalValue">GlobalValue</a>>(V))
306 // <i>Otherwise, it must be an instruction...</i>
307 return !L->contains(cast<<a href="#Instruction">Instruction</a>>(V)->getParent());
312 <p>Note that you should <b>not</b> use an <tt>isa<></tt> test followed
313 by a <tt>cast<></tt>, for that use the <tt>dyn_cast<></tt>
318 <dt><tt>dyn_cast<></tt>:</dt>
320 <dd><p>The <tt>dyn_cast<></tt> operator is a "checking cast" operation.
321 It checks to see if the operand is of the specified type, and if so, returns a
322 pointer to it (this operator does not work with references). If the operand is
323 not of the correct type, a null pointer is returned. Thus, this works very
324 much like the <tt>dynamic_cast<></tt> operator in C++, and should be
325 used in the same circumstances. Typically, the <tt>dyn_cast<></tt>
326 operator is used in an <tt>if</tt> statement or some other flow control
327 statement like this:</p>
329 <div class="doc_code">
331 if (<a href="#AllocationInst">AllocationInst</a> *AI = dyn_cast<<a href="#AllocationInst">AllocationInst</a>>(Val)) {
337 <p>This form of the <tt>if</tt> statement effectively combines together a call
338 to <tt>isa<></tt> and a call to <tt>cast<></tt> into one
339 statement, which is very convenient.</p>
341 <p>Note that the <tt>dyn_cast<></tt> operator, like C++'s
342 <tt>dynamic_cast<></tt> or Java's <tt>instanceof</tt> operator, can be
343 abused. In particular, you should not use big chained <tt>if/then/else</tt>
344 blocks to check for lots of different variants of classes. If you find
345 yourself wanting to do this, it is much cleaner and more efficient to use the
346 <tt>InstVisitor</tt> class to dispatch over the instruction type directly.</p>
350 <dt><tt>cast_or_null<></tt>: </dt>
352 <dd><p>The <tt>cast_or_null<></tt> operator works just like the
353 <tt>cast<></tt> operator, except that it allows for a null pointer as an
354 argument (which it then propagates). This can sometimes be useful, allowing
355 you to combine several null checks into one.</p></dd>
357 <dt><tt>dyn_cast_or_null<></tt>: </dt>
359 <dd><p>The <tt>dyn_cast_or_null<></tt> operator works just like the
360 <tt>dyn_cast<></tt> operator, except that it allows for a null pointer
361 as an argument (which it then propagates). This can sometimes be useful,
362 allowing you to combine several null checks into one.</p></dd>
366 <p>These five templates can be used with any classes, whether they have a
367 v-table or not. To add support for these templates, you simply need to add
368 <tt>classof</tt> static methods to the class you are interested casting
369 to. Describing this is currently outside the scope of this document, but there
370 are lots of examples in the LLVM source base.</p>
374 <!-- ======================================================================= -->
375 <div class="doc_subsection">
376 <a name="DEBUG">The <tt>DEBUG()</tt> macro and <tt>-debug</tt> option</a>
379 <div class="doc_text">
381 <p>Often when working on your pass you will put a bunch of debugging printouts
382 and other code into your pass. After you get it working, you want to remove
383 it, but you may need it again in the future (to work out new bugs that you run
386 <p> Naturally, because of this, you don't want to delete the debug printouts,
387 but you don't want them to always be noisy. A standard compromise is to comment
388 them out, allowing you to enable them if you need them in the future.</p>
390 <p>The "<tt><a href="/doxygen/Debug_8h-source.html">llvm/Support/Debug.h</a></tt>"
391 file provides a macro named <tt>DEBUG()</tt> that is a much nicer solution to
392 this problem. Basically, you can put arbitrary code into the argument of the
393 <tt>DEBUG</tt> macro, and it is only executed if '<tt>opt</tt>' (or any other
394 tool) is run with the '<tt>-debug</tt>' command line argument:</p>
396 <div class="doc_code">
398 DOUT << "I am here!\n";
402 <p>Then you can run your pass like this:</p>
404 <div class="doc_code">
406 $ opt < a.bc > /dev/null -mypass
407 <i><no output></i>
408 $ opt < a.bc > /dev/null -mypass -debug
413 <p>Using the <tt>DEBUG()</tt> macro instead of a home-brewed solution allows you
414 to not have to create "yet another" command line option for the debug output for
415 your pass. Note that <tt>DEBUG()</tt> macros are disabled for optimized builds,
416 so they do not cause a performance impact at all (for the same reason, they
417 should also not contain side-effects!).</p>
419 <p>One additional nice thing about the <tt>DEBUG()</tt> macro is that you can
420 enable or disable it directly in gdb. Just use "<tt>set DebugFlag=0</tt>" or
421 "<tt>set DebugFlag=1</tt>" from the gdb if the program is running. If the
422 program hasn't been started yet, you can always just run it with
427 <!-- _______________________________________________________________________ -->
428 <div class="doc_subsubsection">
429 <a name="DEBUG_TYPE">Fine grained debug info with <tt>DEBUG_TYPE</tt> and
430 the <tt>-debug-only</tt> option</a>
433 <div class="doc_text">
435 <p>Sometimes you may find yourself in a situation where enabling <tt>-debug</tt>
436 just turns on <b>too much</b> information (such as when working on the code
437 generator). If you want to enable debug information with more fine-grained
438 control, you define the <tt>DEBUG_TYPE</tt> macro and the <tt>-debug</tt> only
439 option as follows:</p>
441 <div class="doc_code">
443 DOUT << "No debug type\n";
445 #define DEBUG_TYPE "foo"
446 DOUT << "'foo' debug type\n";
448 #define DEBUG_TYPE "bar"
449 DOUT << "'bar' debug type\n";
451 #define DEBUG_TYPE ""
452 DOUT << "No debug type (2)\n";
456 <p>Then you can run your pass like this:</p>
458 <div class="doc_code">
460 $ opt < a.bc > /dev/null -mypass
461 <i><no output></i>
462 $ opt < a.bc > /dev/null -mypass -debug
467 $ opt < a.bc > /dev/null -mypass -debug-only=foo
469 $ opt < a.bc > /dev/null -mypass -debug-only=bar
474 <p>Of course, in practice, you should only set <tt>DEBUG_TYPE</tt> at the top of
475 a file, to specify the debug type for the entire module (if you do this before
476 you <tt>#include "llvm/Support/Debug.h"</tt>, you don't have to insert the ugly
477 <tt>#undef</tt>'s). Also, you should use names more meaningful than "foo" and
478 "bar", because there is no system in place to ensure that names do not
479 conflict. If two different modules use the same string, they will all be turned
480 on when the name is specified. This allows, for example, all debug information
481 for instruction scheduling to be enabled with <tt>-debug-type=InstrSched</tt>,
482 even if the source lives in multiple files.</p>
486 <!-- ======================================================================= -->
487 <div class="doc_subsection">
488 <a name="Statistic">The <tt>Statistic</tt> class & <tt>-stats</tt>
492 <div class="doc_text">
495 href="/doxygen/Statistic_8h-source.html">llvm/ADT/Statistic.h</a></tt>" file
496 provides a class named <tt>Statistic</tt> that is used as a unified way to
497 keep track of what the LLVM compiler is doing and how effective various
498 optimizations are. It is useful to see what optimizations are contributing to
499 making a particular program run faster.</p>
501 <p>Often you may run your pass on some big program, and you're interested to see
502 how many times it makes a certain transformation. Although you can do this with
503 hand inspection, or some ad-hoc method, this is a real pain and not very useful
504 for big programs. Using the <tt>Statistic</tt> class makes it very easy to
505 keep track of this information, and the calculated information is presented in a
506 uniform manner with the rest of the passes being executed.</p>
508 <p>There are many examples of <tt>Statistic</tt> uses, but the basics of using
509 it are as follows:</p>
512 <li><p>Define your statistic like this:</p>
514 <div class="doc_code">
516 #define <a href="#DEBUG_TYPE">DEBUG_TYPE</a> "mypassname" <i>// This goes before any #includes.</i>
517 STATISTIC(NumXForms, "The # of times I did stuff");
521 <p>The <tt>STATISTIC</tt> macro defines a static variable, whose name is
522 specified by the first argument. The pass name is taken from the DEBUG_TYPE
523 macro, and the description is taken from the second argument. The variable
524 defined ("NumXForms" in this case) acts like an unsigned integer.</p></li>
526 <li><p>Whenever you make a transformation, bump the counter:</p>
528 <div class="doc_code">
530 ++NumXForms; // <i>I did stuff!</i>
537 <p>That's all you have to do. To get '<tt>opt</tt>' to print out the
538 statistics gathered, use the '<tt>-stats</tt>' option:</p>
540 <div class="doc_code">
542 $ opt -stats -mypassname < program.bc > /dev/null
543 <i>... statistics output ...</i>
547 <p> When running <tt>gccas</tt> on a C file from the SPEC benchmark
548 suite, it gives a report that looks like this:</p>
550 <div class="doc_code">
552 7646 bytecodewriter - Number of normal instructions
553 725 bytecodewriter - Number of oversized instructions
554 129996 bytecodewriter - Number of bytecode bytes written
555 2817 raise - Number of insts DCEd or constprop'd
556 3213 raise - Number of cast-of-self removed
557 5046 raise - Number of expression trees converted
558 75 raise - Number of other getelementptr's formed
559 138 raise - Number of load/store peepholes
560 42 deadtypeelim - Number of unused typenames removed from symtab
561 392 funcresolve - Number of varargs functions resolved
562 27 globaldce - Number of global variables removed
563 2 adce - Number of basic blocks removed
564 134 cee - Number of branches revectored
565 49 cee - Number of setcc instruction eliminated
566 532 gcse - Number of loads removed
567 2919 gcse - Number of instructions removed
568 86 indvars - Number of canonical indvars added
569 87 indvars - Number of aux indvars removed
570 25 instcombine - Number of dead inst eliminate
571 434 instcombine - Number of insts combined
572 248 licm - Number of load insts hoisted
573 1298 licm - Number of insts hoisted to a loop pre-header
574 3 licm - Number of insts hoisted to multiple loop preds (bad, no loop pre-header)
575 75 mem2reg - Number of alloca's promoted
576 1444 cfgsimplify - Number of blocks simplified
580 <p>Obviously, with so many optimizations, having a unified framework for this
581 stuff is very nice. Making your pass fit well into the framework makes it more
582 maintainable and useful.</p>
586 <!-- ======================================================================= -->
587 <div class="doc_subsection">
588 <a name="ViewGraph">Viewing graphs while debugging code</a>
591 <div class="doc_text">
593 <p>Several of the important data structures in LLVM are graphs: for example
594 CFGs made out of LLVM <a href="#BasicBlock">BasicBlock</a>s, CFGs made out of
595 LLVM <a href="CodeGenerator.html#machinebasicblock">MachineBasicBlock</a>s, and
596 <a href="CodeGenerator.html#selectiondag_intro">Instruction Selection
597 DAGs</a>. In many cases, while debugging various parts of the compiler, it is
598 nice to instantly visualize these graphs.</p>
600 <p>LLVM provides several callbacks that are available in a debug build to do
601 exactly that. If you call the <tt>Function::viewCFG()</tt> method, for example,
602 the current LLVM tool will pop up a window containing the CFG for the function
603 where each basic block is a node in the graph, and each node contains the
604 instructions in the block. Similarly, there also exists
605 <tt>Function::viewCFGOnly()</tt> (does not include the instructions), the
606 <tt>MachineFunction::viewCFG()</tt> and <tt>MachineFunction::viewCFGOnly()</tt>,
607 and the <tt>SelectionDAG::viewGraph()</tt> methods. Within GDB, for example,
608 you can usually use something like <tt>call DAG.viewGraph()</tt> to pop
609 up a window. Alternatively, you can sprinkle calls to these functions in your
610 code in places you want to debug.</p>
612 <p>Getting this to work requires a small amount of configuration. On Unix
613 systems with X11, install the <a href="http://www.graphviz.org">graphviz</a>
614 toolkit, and make sure 'dot' and 'gv' are in your path. If you are running on
615 Mac OS/X, download and install the Mac OS/X <a
616 href="http://www.pixelglow.com/graphviz/">Graphviz program</a>, and add
617 <tt>/Applications/Graphviz.app/Contents/MacOS/</tt> (or whereever you install
618 it) to your path. Once in your system and path are set up, rerun the LLVM
619 configure script and rebuild LLVM to enable this functionality.</p>
621 <p><tt>SelectionDAG</tt> has been extended to make it easier to locate
622 <i>interesting</i> nodes in large complex graphs. From gdb, if you
623 <tt>call DAG.setGraphColor(<i>node</i>, "<i>color</i>")</tt>, then the
624 next <tt>call DAG.viewGraph()</tt> would hilight the node in the
625 specified color (choices of colors can be found at <a
626 href="http://www.graphviz.org/doc/info/colors.html">Colors<a>.) More
627 complex node attributes can be provided with <tt>call
628 DAG.setGraphAttrs(<i>node</i>, "<i>attributes</i>")</tt> (choices can be
629 found at <a href="http://www.graphviz.org/doc/info/attrs.html">Graph
630 Attributes</a>.) If you want to restart and clear all the current graph
631 attributes, then you can <tt>call DAG.clearGraphAttrs()</tt>. </p>
636 <!-- *********************************************************************** -->
637 <div class="doc_section">
638 <a name="common">Helpful Hints for Common Operations</a>
640 <!-- *********************************************************************** -->
642 <div class="doc_text">
644 <p>This section describes how to perform some very simple transformations of
645 LLVM code. This is meant to give examples of common idioms used, showing the
646 practical side of LLVM transformations. <p> Because this is a "how-to" section,
647 you should also read about the main classes that you will be working with. The
648 <a href="#coreclasses">Core LLVM Class Hierarchy Reference</a> contains details
649 and descriptions of the main classes that you should know about.</p>
653 <!-- NOTE: this section should be heavy on example code -->
654 <!-- ======================================================================= -->
655 <div class="doc_subsection">
656 <a name="inspection">Basic Inspection and Traversal Routines</a>
659 <div class="doc_text">
661 <p>The LLVM compiler infrastructure have many different data structures that may
662 be traversed. Following the example of the C++ standard template library, the
663 techniques used to traverse these various data structures are all basically the
664 same. For a enumerable sequence of values, the <tt>XXXbegin()</tt> function (or
665 method) returns an iterator to the start of the sequence, the <tt>XXXend()</tt>
666 function returns an iterator pointing to one past the last valid element of the
667 sequence, and there is some <tt>XXXiterator</tt> data type that is common
668 between the two operations.</p>
670 <p>Because the pattern for iteration is common across many different aspects of
671 the program representation, the standard template library algorithms may be used
672 on them, and it is easier to remember how to iterate. First we show a few common
673 examples of the data structures that need to be traversed. Other data
674 structures are traversed in very similar ways.</p>
678 <!-- _______________________________________________________________________ -->
679 <div class="doc_subsubsection">
680 <a name="iterate_function">Iterating over the </a><a
681 href="#BasicBlock"><tt>BasicBlock</tt></a>s in a <a
682 href="#Function"><tt>Function</tt></a>
685 <div class="doc_text">
687 <p>It's quite common to have a <tt>Function</tt> instance that you'd like to
688 transform in some way; in particular, you'd like to manipulate its
689 <tt>BasicBlock</tt>s. To facilitate this, you'll need to iterate over all of
690 the <tt>BasicBlock</tt>s that constitute the <tt>Function</tt>. The following is
691 an example that prints the name of a <tt>BasicBlock</tt> and the number of
692 <tt>Instruction</tt>s it contains:</p>
694 <div class="doc_code">
696 // <i>func is a pointer to a Function instance</i>
697 for (Function::iterator i = func->begin(), e = func->end(); i != e; ++i)
698 // <i>Print out the name of the basic block if it has one, and then the</i>
699 // <i>number of instructions that it contains</i>
700 llvm::cerr << "Basic block (name=" << i->getName() << ") has "
701 << i->size() << " instructions.\n";
705 <p>Note that i can be used as if it were a pointer for the purposes of
706 invoking member functions of the <tt>Instruction</tt> class. This is
707 because the indirection operator is overloaded for the iterator
708 classes. In the above code, the expression <tt>i->size()</tt> is
709 exactly equivalent to <tt>(*i).size()</tt> just like you'd expect.</p>
713 <!-- _______________________________________________________________________ -->
714 <div class="doc_subsubsection">
715 <a name="iterate_basicblock">Iterating over the </a><a
716 href="#Instruction"><tt>Instruction</tt></a>s in a <a
717 href="#BasicBlock"><tt>BasicBlock</tt></a>
720 <div class="doc_text">
722 <p>Just like when dealing with <tt>BasicBlock</tt>s in <tt>Function</tt>s, it's
723 easy to iterate over the individual instructions that make up
724 <tt>BasicBlock</tt>s. Here's a code snippet that prints out each instruction in
725 a <tt>BasicBlock</tt>:</p>
727 <div class="doc_code">
729 // <i>blk is a pointer to a BasicBlock instance</i>
730 for (BasicBlock::iterator i = blk->begin(), e = blk->end(); i != e; ++i)
731 // <i>The next statement works since operator<<(ostream&,...)</i>
732 // <i>is overloaded for Instruction&</i>
733 llvm::cerr << *i << "\n";
737 <p>However, this isn't really the best way to print out the contents of a
738 <tt>BasicBlock</tt>! Since the ostream operators are overloaded for virtually
739 anything you'll care about, you could have just invoked the print routine on the
740 basic block itself: <tt>llvm::cerr << *blk << "\n";</tt>.</p>
744 <!-- _______________________________________________________________________ -->
745 <div class="doc_subsubsection">
746 <a name="iterate_institer">Iterating over the </a><a
747 href="#Instruction"><tt>Instruction</tt></a>s in a <a
748 href="#Function"><tt>Function</tt></a>
751 <div class="doc_text">
753 <p>If you're finding that you commonly iterate over a <tt>Function</tt>'s
754 <tt>BasicBlock</tt>s and then that <tt>BasicBlock</tt>'s <tt>Instruction</tt>s,
755 <tt>InstIterator</tt> should be used instead. You'll need to include <a
756 href="/doxygen/InstIterator_8h-source.html"><tt>llvm/Support/InstIterator.h</tt></a>,
757 and then instantiate <tt>InstIterator</tt>s explicitly in your code. Here's a
758 small example that shows how to dump all instructions in a function to the standard error stream:<p>
760 <div class="doc_code">
762 #include "<a href="/doxygen/InstIterator_8h-source.html">llvm/Support/InstIterator.h</a>"
764 // <i>F is a ptr to a Function instance</i>
765 for (inst_iterator i = inst_begin(F), e = inst_end(F); i != e; ++i)
766 llvm::cerr << *i << "\n";
770 <p>Easy, isn't it? You can also use <tt>InstIterator</tt>s to fill a
771 worklist with its initial contents. For example, if you wanted to
772 initialize a worklist to contain all instructions in a <tt>Function</tt>
773 F, all you would need to do is something like:</p>
775 <div class="doc_code">
777 std::set<Instruction*> worklist;
778 worklist.insert(inst_begin(F), inst_end(F));
782 <p>The STL set <tt>worklist</tt> would now contain all instructions in the
783 <tt>Function</tt> pointed to by F.</p>
787 <!-- _______________________________________________________________________ -->
788 <div class="doc_subsubsection">
789 <a name="iterate_convert">Turning an iterator into a class pointer (and
793 <div class="doc_text">
795 <p>Sometimes, it'll be useful to grab a reference (or pointer) to a class
796 instance when all you've got at hand is an iterator. Well, extracting
797 a reference or a pointer from an iterator is very straight-forward.
798 Assuming that <tt>i</tt> is a <tt>BasicBlock::iterator</tt> and <tt>j</tt>
799 is a <tt>BasicBlock::const_iterator</tt>:</p>
801 <div class="doc_code">
803 Instruction& inst = *i; // <i>Grab reference to instruction reference</i>
804 Instruction* pinst = &*i; // <i>Grab pointer to instruction reference</i>
805 const Instruction& inst = *j;
809 <p>However, the iterators you'll be working with in the LLVM framework are
810 special: they will automatically convert to a ptr-to-instance type whenever they
811 need to. Instead of dereferencing the iterator and then taking the address of
812 the result, you can simply assign the iterator to the proper pointer type and
813 you get the dereference and address-of operation as a result of the assignment
814 (behind the scenes, this is a result of overloading casting mechanisms). Thus
815 the last line of the last example,</p>
817 <div class="doc_code">
819 Instruction* pinst = &*i;
823 <p>is semantically equivalent to</p>
825 <div class="doc_code">
827 Instruction* pinst = i;
831 <p>It's also possible to turn a class pointer into the corresponding iterator,
832 and this is a constant time operation (very efficient). The following code
833 snippet illustrates use of the conversion constructors provided by LLVM
834 iterators. By using these, you can explicitly grab the iterator of something
835 without actually obtaining it via iteration over some structure:</p>
837 <div class="doc_code">
839 void printNextInstruction(Instruction* inst) {
840 BasicBlock::iterator it(inst);
841 ++it; // <i>After this line, it refers to the instruction after *inst</i>
842 if (it != inst->getParent()->end()) llvm::cerr << *it << "\n";
849 <!--_______________________________________________________________________-->
850 <div class="doc_subsubsection">
851 <a name="iterate_complex">Finding call sites: a slightly more complex
855 <div class="doc_text">
857 <p>Say that you're writing a FunctionPass and would like to count all the
858 locations in the entire module (that is, across every <tt>Function</tt>) where a
859 certain function (i.e., some <tt>Function</tt>*) is already in scope. As you'll
860 learn later, you may want to use an <tt>InstVisitor</tt> to accomplish this in a
861 much more straight-forward manner, but this example will allow us to explore how
862 you'd do it if you didn't have <tt>InstVisitor</tt> around. In pseudocode, this
863 is what we want to do:</p>
865 <div class="doc_code">
867 initialize callCounter to zero
868 for each Function f in the Module
869 for each BasicBlock b in f
870 for each Instruction i in b
871 if (i is a CallInst and calls the given function)
872 increment callCounter
876 <p>And the actual code is (remember, because we're writing a
877 <tt>FunctionPass</tt>, our <tt>FunctionPass</tt>-derived class simply has to
878 override the <tt>runOnFunction</tt> method):</p>
880 <div class="doc_code">
882 Function* targetFunc = ...;
884 class OurFunctionPass : public FunctionPass {
886 OurFunctionPass(): callCounter(0) { }
888 virtual runOnFunction(Function& F) {
889 for (Function::iterator b = F.begin(), be = F.end(); b != be; ++b) {
890 for (BasicBlock::iterator i = b->begin(); ie = b->end(); i != ie; ++i) {
891 if (<a href="#CallInst">CallInst</a>* callInst = <a href="#isa">dyn_cast</a><<a
892 href="#CallInst">CallInst</a>>(&*i)) {
893 // <i>We know we've encountered a call instruction, so we</i>
894 // <i>need to determine if it's a call to the</i>
895 // <i>function pointed to by m_func or not</i>
897 if (callInst->getCalledFunction() == targetFunc)
905 unsigned callCounter;
912 <!--_______________________________________________________________________-->
913 <div class="doc_subsubsection">
914 <a name="calls_and_invokes">Treating calls and invokes the same way</a>
917 <div class="doc_text">
919 <p>You may have noticed that the previous example was a bit oversimplified in
920 that it did not deal with call sites generated by 'invoke' instructions. In
921 this, and in other situations, you may find that you want to treat
922 <tt>CallInst</tt>s and <tt>InvokeInst</tt>s the same way, even though their
923 most-specific common base class is <tt>Instruction</tt>, which includes lots of
924 less closely-related things. For these cases, LLVM provides a handy wrapper
926 href="http://llvm.org/doxygen/classllvm_1_1CallSite.html"><tt>CallSite</tt></a>.
927 It is essentially a wrapper around an <tt>Instruction</tt> pointer, with some
928 methods that provide functionality common to <tt>CallInst</tt>s and
929 <tt>InvokeInst</tt>s.</p>
931 <p>This class has "value semantics": it should be passed by value, not by
932 reference and it should not be dynamically allocated or deallocated using
933 <tt>operator new</tt> or <tt>operator delete</tt>. It is efficiently copyable,
934 assignable and constructable, with costs equivalents to that of a bare pointer.
935 If you look at its definition, it has only a single pointer member.</p>
939 <!--_______________________________________________________________________-->
940 <div class="doc_subsubsection">
941 <a name="iterate_chains">Iterating over def-use & use-def chains</a>
944 <div class="doc_text">
946 <p>Frequently, we might have an instance of the <a
947 href="/doxygen/classllvm_1_1Value.html">Value Class</a> and we want to
948 determine which <tt>User</tt>s use the <tt>Value</tt>. The list of all
949 <tt>User</tt>s of a particular <tt>Value</tt> is called a <i>def-use</i> chain.
950 For example, let's say we have a <tt>Function*</tt> named <tt>F</tt> to a
951 particular function <tt>foo</tt>. Finding all of the instructions that
952 <i>use</i> <tt>foo</tt> is as simple as iterating over the <i>def-use</i> chain
955 <div class="doc_code">
959 for (Value::use_iterator i = F->use_begin(), e = F->use_end(); i != e; ++i)
960 if (Instruction *Inst = dyn_cast<Instruction>(*i)) {
961 llvm::cerr << "F is used in instruction:\n";
962 llvm::cerr << *Inst << "\n";
967 <p>Alternately, it's common to have an instance of the <a
968 href="/doxygen/classllvm_1_1User.html">User Class</a> and need to know what
969 <tt>Value</tt>s are used by it. The list of all <tt>Value</tt>s used by a
970 <tt>User</tt> is known as a <i>use-def</i> chain. Instances of class
971 <tt>Instruction</tt> are common <tt>User</tt>s, so we might want to iterate over
972 all of the values that a particular instruction uses (that is, the operands of
973 the particular <tt>Instruction</tt>):</p>
975 <div class="doc_code">
977 Instruction* pi = ...;
979 for (User::op_iterator i = pi->op_begin(), e = pi->op_end(); i != e; ++i) {
987 def-use chains ("finding all users of"): Value::use_begin/use_end
988 use-def chains ("finding all values used"): User::op_begin/op_end [op=operand]
993 <!-- ======================================================================= -->
994 <div class="doc_subsection">
995 <a name="simplechanges">Making simple changes</a>
998 <div class="doc_text">
1000 <p>There are some primitive transformation operations present in the LLVM
1001 infrastructure that are worth knowing about. When performing
1002 transformations, it's fairly common to manipulate the contents of basic
1003 blocks. This section describes some of the common methods for doing so
1004 and gives example code.</p>
1008 <!--_______________________________________________________________________-->
1009 <div class="doc_subsubsection">
1010 <a name="schanges_creating">Creating and inserting new
1011 <tt>Instruction</tt>s</a>
1014 <div class="doc_text">
1016 <p><i>Instantiating Instructions</i></p>
1018 <p>Creation of <tt>Instruction</tt>s is straight-forward: simply call the
1019 constructor for the kind of instruction to instantiate and provide the necessary
1020 parameters. For example, an <tt>AllocaInst</tt> only <i>requires</i> a
1021 (const-ptr-to) <tt>Type</tt>. Thus:</p>
1023 <div class="doc_code">
1025 AllocaInst* ai = new AllocaInst(Type::IntTy);
1029 <p>will create an <tt>AllocaInst</tt> instance that represents the allocation of
1030 one integer in the current stack frame, at runtime. Each <tt>Instruction</tt>
1031 subclass is likely to have varying default parameters which change the semantics
1032 of the instruction, so refer to the <a
1033 href="/doxygen/classllvm_1_1Instruction.html">doxygen documentation for the subclass of
1034 Instruction</a> that you're interested in instantiating.</p>
1036 <p><i>Naming values</i></p>
1038 <p>It is very useful to name the values of instructions when you're able to, as
1039 this facilitates the debugging of your transformations. If you end up looking
1040 at generated LLVM machine code, you definitely want to have logical names
1041 associated with the results of instructions! By supplying a value for the
1042 <tt>Name</tt> (default) parameter of the <tt>Instruction</tt> constructor, you
1043 associate a logical name with the result of the instruction's execution at
1044 runtime. For example, say that I'm writing a transformation that dynamically
1045 allocates space for an integer on the stack, and that integer is going to be
1046 used as some kind of index by some other code. To accomplish this, I place an
1047 <tt>AllocaInst</tt> at the first point in the first <tt>BasicBlock</tt> of some
1048 <tt>Function</tt>, and I'm intending to use it within the same
1049 <tt>Function</tt>. I might do:</p>
1051 <div class="doc_code">
1053 AllocaInst* pa = new AllocaInst(Type::IntTy, 0, "indexLoc");
1057 <p>where <tt>indexLoc</tt> is now the logical name of the instruction's
1058 execution value, which is a pointer to an integer on the runtime stack.</p>
1060 <p><i>Inserting instructions</i></p>
1062 <p>There are essentially two ways to insert an <tt>Instruction</tt>
1063 into an existing sequence of instructions that form a <tt>BasicBlock</tt>:</p>
1066 <li>Insertion into an explicit instruction list
1068 <p>Given a <tt>BasicBlock* pb</tt>, an <tt>Instruction* pi</tt> within that
1069 <tt>BasicBlock</tt>, and a newly-created instruction we wish to insert
1070 before <tt>*pi</tt>, we do the following: </p>
1072 <div class="doc_code">
1074 BasicBlock *pb = ...;
1075 Instruction *pi = ...;
1076 Instruction *newInst = new Instruction(...);
1078 pb->getInstList().insert(pi, newInst); // <i>Inserts newInst before pi in pb</i>
1082 <p>Appending to the end of a <tt>BasicBlock</tt> is so common that
1083 the <tt>Instruction</tt> class and <tt>Instruction</tt>-derived
1084 classes provide constructors which take a pointer to a
1085 <tt>BasicBlock</tt> to be appended to. For example code that
1088 <div class="doc_code">
1090 BasicBlock *pb = ...;
1091 Instruction *newInst = new Instruction(...);
1093 pb->getInstList().push_back(newInst); // <i>Appends newInst to pb</i>
1099 <div class="doc_code">
1101 BasicBlock *pb = ...;
1102 Instruction *newInst = new Instruction(..., pb);
1106 <p>which is much cleaner, especially if you are creating
1107 long instruction streams.</p></li>
1109 <li>Insertion into an implicit instruction list
1111 <p><tt>Instruction</tt> instances that are already in <tt>BasicBlock</tt>s
1112 are implicitly associated with an existing instruction list: the instruction
1113 list of the enclosing basic block. Thus, we could have accomplished the same
1114 thing as the above code without being given a <tt>BasicBlock</tt> by doing:
1117 <div class="doc_code">
1119 Instruction *pi = ...;
1120 Instruction *newInst = new Instruction(...);
1122 pi->getParent()->getInstList().insert(pi, newInst);
1126 <p>In fact, this sequence of steps occurs so frequently that the
1127 <tt>Instruction</tt> class and <tt>Instruction</tt>-derived classes provide
1128 constructors which take (as a default parameter) a pointer to an
1129 <tt>Instruction</tt> which the newly-created <tt>Instruction</tt> should
1130 precede. That is, <tt>Instruction</tt> constructors are capable of
1131 inserting the newly-created instance into the <tt>BasicBlock</tt> of a
1132 provided instruction, immediately before that instruction. Using an
1133 <tt>Instruction</tt> constructor with a <tt>insertBefore</tt> (default)
1134 parameter, the above code becomes:</p>
1136 <div class="doc_code">
1138 Instruction* pi = ...;
1139 Instruction* newInst = new Instruction(..., pi);
1143 <p>which is much cleaner, especially if you're creating a lot of
1144 instructions and adding them to <tt>BasicBlock</tt>s.</p></li>
1149 <!--_______________________________________________________________________-->
1150 <div class="doc_subsubsection">
1151 <a name="schanges_deleting">Deleting <tt>Instruction</tt>s</a>
1154 <div class="doc_text">
1156 <p>Deleting an instruction from an existing sequence of instructions that form a
1157 <a href="#BasicBlock"><tt>BasicBlock</tt></a> is very straight-forward. First,
1158 you must have a pointer to the instruction that you wish to delete. Second, you
1159 need to obtain the pointer to that instruction's basic block. You use the
1160 pointer to the basic block to get its list of instructions and then use the
1161 erase function to remove your instruction. For example:</p>
1163 <div class="doc_code">
1165 <a href="#Instruction">Instruction</a> *I = .. ;
1166 <a href="#BasicBlock">BasicBlock</a> *BB = I->getParent();
1168 BB->getInstList().erase(I);
1174 <!--_______________________________________________________________________-->
1175 <div class="doc_subsubsection">
1176 <a name="schanges_replacing">Replacing an <tt>Instruction</tt> with another
1180 <div class="doc_text">
1182 <p><i>Replacing individual instructions</i></p>
1184 <p>Including "<a href="/doxygen/BasicBlockUtils_8h-source.html">llvm/Transforms/Utils/BasicBlockUtils.h</a>"
1185 permits use of two very useful replace functions: <tt>ReplaceInstWithValue</tt>
1186 and <tt>ReplaceInstWithInst</tt>.</p>
1188 <h4><a name="schanges_deleting">Deleting <tt>Instruction</tt>s</a></h4>
1191 <li><tt>ReplaceInstWithValue</tt>
1193 <p>This function replaces all uses (within a basic block) of a given
1194 instruction with a value, and then removes the original instruction. The
1195 following example illustrates the replacement of the result of a particular
1196 <tt>AllocaInst</tt> that allocates memory for a single integer with a null
1197 pointer to an integer.</p>
1199 <div class="doc_code">
1201 AllocaInst* instToReplace = ...;
1202 BasicBlock::iterator ii(instToReplace);
1204 ReplaceInstWithValue(instToReplace->getParent()->getInstList(), ii,
1205 Constant::getNullValue(PointerType::get(Type::IntTy)));
1208 <li><tt>ReplaceInstWithInst</tt>
1210 <p>This function replaces a particular instruction with another
1211 instruction. The following example illustrates the replacement of one
1212 <tt>AllocaInst</tt> with another.</p>
1214 <div class="doc_code">
1216 AllocaInst* instToReplace = ...;
1217 BasicBlock::iterator ii(instToReplace);
1219 ReplaceInstWithInst(instToReplace->getParent()->getInstList(), ii,
1220 new AllocaInst(Type::IntTy, 0, "ptrToReplacedInt"));
1224 <p><i>Replacing multiple uses of <tt>User</tt>s and <tt>Value</tt>s</i></p>
1226 <p>You can use <tt>Value::replaceAllUsesWith</tt> and
1227 <tt>User::replaceUsesOfWith</tt> to change more than one use at a time. See the
1228 doxygen documentation for the <a href="/doxygen/classllvm_1_1Value.html">Value Class</a>
1229 and <a href="/doxygen/classllvm_1_1User.html">User Class</a>, respectively, for more
1232 <!-- Value::replaceAllUsesWith User::replaceUsesOfWith Point out:
1233 include/llvm/Transforms/Utils/ especially BasicBlockUtils.h with:
1234 ReplaceInstWithValue, ReplaceInstWithInst -->
1238 <!-- *********************************************************************** -->
1239 <div class="doc_section">
1240 <a name="advanced">Advanced Topics</a>
1242 <!-- *********************************************************************** -->
1244 <div class="doc_text">
1246 This section describes some of the advanced or obscure API's that most clients
1247 do not need to be aware of. These API's tend manage the inner workings of the
1248 LLVM system, and only need to be accessed in unusual circumstances.
1252 <!-- ======================================================================= -->
1253 <div class="doc_subsection">
1254 <a name="TypeResolve">LLVM Type Resolution</a>
1257 <div class="doc_text">
1260 The LLVM type system has a very simple goal: allow clients to compare types for
1261 structural equality with a simple pointer comparison (aka a shallow compare).
1262 This goal makes clients much simpler and faster, and is used throughout the LLVM
1267 Unfortunately achieving this goal is not a simple matter. In particular,
1268 recursive types and late resolution of opaque types makes the situation very
1269 difficult to handle. Fortunately, for the most part, our implementation makes
1270 most clients able to be completely unaware of the nasty internal details. The
1271 primary case where clients are exposed to the inner workings of it are when
1272 building a recursive type. In addition to this case, the LLVM bytecode reader,
1273 assembly parser, and linker also have to be aware of the inner workings of this
1278 For our purposes below, we need three concepts. First, an "Opaque Type" is
1279 exactly as defined in the <a href="LangRef.html#t_opaque">language
1280 reference</a>. Second an "Abstract Type" is any type which includes an
1281 opaque type as part of its type graph (for example "<tt>{ opaque, i32 }</tt>").
1282 Third, a concrete type is a type that is not an abstract type (e.g. "<tt>{ i32,
1288 <!-- ______________________________________________________________________ -->
1289 <div class="doc_subsubsection">
1290 <a name="BuildRecType">Basic Recursive Type Construction</a>
1293 <div class="doc_text">
1296 Because the most common question is "how do I build a recursive type with LLVM",
1297 we answer it now and explain it as we go. Here we include enough to cause this
1298 to be emitted to an output .ll file:
1301 <div class="doc_code">
1303 %mylist = type { %mylist*, i32 }
1308 To build this, use the following LLVM APIs:
1311 <div class="doc_code">
1313 // <i>Create the initial outer struct</i>
1314 <a href="#PATypeHolder">PATypeHolder</a> StructTy = OpaqueType::get();
1315 std::vector<const Type*> Elts;
1316 Elts.push_back(PointerType::get(StructTy));
1317 Elts.push_back(Type::IntTy);
1318 StructType *NewSTy = StructType::get(Elts);
1320 // <i>At this point, NewSTy = "{ opaque*, i32 }". Tell VMCore that</i>
1321 // <i>the struct and the opaque type are actually the same.</i>
1322 cast<OpaqueType>(StructTy.get())-><a href="#refineAbstractTypeTo">refineAbstractTypeTo</a>(NewSTy);
1324 // <i>NewSTy is potentially invalidated, but StructTy (a <a href="#PATypeHolder">PATypeHolder</a>) is</i>
1325 // <i>kept up-to-date</i>
1326 NewSTy = cast<StructType>(StructTy.get());
1328 // <i>Add a name for the type to the module symbol table (optional)</i>
1329 MyModule->addTypeName("mylist", NewSTy);
1334 This code shows the basic approach used to build recursive types: build a
1335 non-recursive type using 'opaque', then use type unification to close the cycle.
1336 The type unification step is performed by the <tt><a
1337 ref="#refineAbstractTypeTo">refineAbstractTypeTo</a></tt> method, which is
1338 described next. After that, we describe the <a
1339 href="#PATypeHolder">PATypeHolder class</a>.
1344 <!-- ______________________________________________________________________ -->
1345 <div class="doc_subsubsection">
1346 <a name="refineAbstractTypeTo">The <tt>refineAbstractTypeTo</tt> method</a>
1349 <div class="doc_text">
1351 The <tt>refineAbstractTypeTo</tt> method starts the type unification process.
1352 While this method is actually a member of the DerivedType class, it is most
1353 often used on OpaqueType instances. Type unification is actually a recursive
1354 process. After unification, types can become structurally isomorphic to
1355 existing types, and all duplicates are deleted (to preserve pointer equality).
1359 In the example above, the OpaqueType object is definitely deleted.
1360 Additionally, if there is an "{ \2*, i32}" type already created in the system,
1361 the pointer and struct type created are <b>also</b> deleted. Obviously whenever
1362 a type is deleted, any "Type*" pointers in the program are invalidated. As
1363 such, it is safest to avoid having <i>any</i> "Type*" pointers to abstract types
1364 live across a call to <tt>refineAbstractTypeTo</tt> (note that non-abstract
1365 types can never move or be deleted). To deal with this, the <a
1366 href="#PATypeHolder">PATypeHolder</a> class is used to maintain a stable
1367 reference to a possibly refined type, and the <a
1368 href="#AbstractTypeUser">AbstractTypeUser</a> class is used to update more
1369 complex datastructures.
1374 <!-- ______________________________________________________________________ -->
1375 <div class="doc_subsubsection">
1376 <a name="PATypeHolder">The PATypeHolder Class</a>
1379 <div class="doc_text">
1381 PATypeHolder is a form of a "smart pointer" for Type objects. When VMCore
1382 happily goes about nuking types that become isomorphic to existing types, it
1383 automatically updates all PATypeHolder objects to point to the new type. In the
1384 example above, this allows the code to maintain a pointer to the resultant
1385 resolved recursive type, even though the Type*'s are potentially invalidated.
1389 PATypeHolder is an extremely light-weight object that uses a lazy union-find
1390 implementation to update pointers. For example the pointer from a Value to its
1391 Type is maintained by PATypeHolder objects.
1396 <!-- ______________________________________________________________________ -->
1397 <div class="doc_subsubsection">
1398 <a name="AbstractTypeUser">The AbstractTypeUser Class</a>
1401 <div class="doc_text">
1404 Some data structures need more to perform more complex updates when types get
1405 resolved. The <a href="#SymbolTable">SymbolTable</a> class, for example, needs
1406 move and potentially merge type planes in its representation when a pointer
1410 To support this, a class can derive from the AbstractTypeUser class. This class
1411 allows it to get callbacks when certain types are resolved. To register to get
1412 callbacks for a particular type, the DerivedType::{add/remove}AbstractTypeUser
1413 methods can be called on a type. Note that these methods only work for <i>
1414 abstract</i> types. Concrete types (those that do not include any opaque
1415 objects) can never be refined.
1420 <!-- ======================================================================= -->
1421 <div class="doc_subsection">
1422 <a name="SymbolTable">The <tt>SymbolTable</tt> class</a>
1425 <div class="doc_text">
1426 <p>This class provides a symbol table that the <a
1427 href="#Function"><tt>Function</tt></a> and <a href="#Module">
1428 <tt>Module</tt></a> classes use for naming definitions. The symbol table can
1429 provide a name for any <a href="#Value"><tt>Value</tt></a>.
1430 <tt>SymbolTable</tt> is an abstract data type. It hides the data it contains
1431 and provides access to it through a controlled interface.</p>
1433 <p>Note that the <tt>SymbolTable</tt> class should not be directly accessed
1434 by most clients. It should only be used when iteration over the symbol table
1435 names themselves are required, which is very special purpose. Note that not
1437 <a href="#Value">Value</a>s have names, and those without names (i.e. they have
1438 an empty name) do not exist in the symbol table.
1441 <p>To use the <tt>SymbolTable</tt> well, you need to understand the
1442 structure of the information it holds. The class contains two
1443 <tt>std::map</tt> objects. The first, <tt>pmap</tt>, is a map of
1444 <tt>Type*</tt> to maps of name (<tt>std::string</tt>) to <tt>Value*</tt>.
1445 Thus, Values are stored in two-dimensions and accessed by <tt>Type</tt> and
1448 <p>The interface of this class provides three basic types of operations:
1450 <li><em>Accessors</em>. Accessors provide read-only access to information
1451 such as finding a value for a name with the
1452 <a href="#SymbolTable_lookup">lookup</a> method.</li>
1453 <li><em>Mutators</em>. Mutators allow the user to add information to the
1454 <tt>SymbolTable</tt> with methods like
1455 <a href="#SymbolTable_insert"><tt>insert</tt></a>.</li>
1456 <li><em>Iterators</em>. Iterators allow the user to traverse the content
1457 of the symbol table in well defined ways, such as the method
1458 <a href="#SymbolTable_plane_begin"><tt>plane_begin</tt></a>.</li>
1463 <dt><tt>Value* lookup(const Type* Ty, const std::string& name) const</tt>:
1465 <dd>The <tt>lookup</tt> method searches the type plane given by the
1466 <tt>Ty</tt> parameter for a <tt>Value</tt> with the provided <tt>name</tt>.
1467 If a suitable <tt>Value</tt> is not found, null is returned.</dd>
1469 <dt><tt>bool isEmpty() const</tt>:</dt>
1470 <dd>This function returns true if both the value and types maps are
1476 <dt><tt>void insert(Value *Val)</tt>:</dt>
1477 <dd>This method adds the provided value to the symbol table. The Value must
1478 have both a name and a type which are extracted and used to place the value
1479 in the correct type plane under the value's name.</dd>
1481 <dt><tt>void insert(const std::string& Name, Value *Val)</tt>:</dt>
1482 <dd> Inserts a constant or type into the symbol table with the specified
1483 name. There can be a many to one mapping between names and constants
1486 <dt><tt>void remove(Value* Val)</tt>:</dt>
1487 <dd> This method removes a named value from the symbol table. The
1488 type and name of the Value are extracted from \p N and used to
1489 lookup the Value in the correct type plane. If the Value is
1490 not in the symbol table, this method silently ignores the
1493 <dt><tt>Value* remove(const std::string& Name, Value *Val)</tt>:</dt>
1494 <dd> Remove a constant or type with the specified name from the
1497 <dt><tt>Value *remove(const value_iterator& It)</tt>:</dt>
1498 <dd> Removes a specific value from the symbol table.
1499 Returns the removed value.</dd>
1501 <dt><tt>bool strip()</tt>:</dt>
1502 <dd> This method will strip the symbol table of its names leaving
1503 the type and values. </dd>
1505 <dt><tt>void clear()</tt>:</dt>
1506 <dd>Empty the symbol table completely.</dd>
1510 <p>The following functions describe three types of iterators you can obtain
1511 the beginning or end of the sequence for both const and non-const. It is
1512 important to keep track of the different kinds of iterators. There are
1513 three idioms worth pointing out:</p>
1516 <tr><th>Units</th><th>Iterator</th><th>Idiom</th></tr>
1518 <td align="left">Planes Of name/Value maps</td><td>PI</td>
1519 <td align="left"><pre><tt>
1520 for (SymbolTable::plane_const_iterator PI = ST.plane_begin(),
1521 PE = ST.plane_end(); PI != PE; ++PI ) {
1522 PI->first // <i>This is the Type* of the plane</i>
1523 PI->second // <i>This is the SymbolTable::ValueMap of name/Value pairs</i>
1528 <td align="left">name/Value pairs in a plane</td><td>VI</td>
1529 <td align="left"><pre><tt>
1530 for (SymbolTable::value_const_iterator VI = ST.value_begin(SomeType),
1531 VE = ST.value_end(SomeType); VI != VE; ++VI ) {
1532 VI->first // <i>This is the name of the Value</i>
1533 VI->second // <i>This is the Value* value associated with the name</i>
1539 <p>Using the recommended iterator names and idioms will help you avoid
1540 making mistakes. Of particular note, make sure that whenever you use
1541 value_begin(SomeType) that you always compare the resulting iterator
1542 with value_end(SomeType) not value_end(SomeOtherType) or else you
1543 will loop infinitely.</p>
1547 <dt><tt>plane_iterator plane_begin()</tt>:</dt>
1548 <dd>Get an iterator that starts at the beginning of the type planes.
1549 The iterator will iterate over the Type/ValueMap pairs in the
1552 <dt><tt>plane_const_iterator plane_begin() const</tt>:</dt>
1553 <dd>Get a const_iterator that starts at the beginning of the type
1554 planes. The iterator will iterate over the Type/ValueMap pairs
1555 in the type planes. </dd>
1557 <dt><tt>plane_iterator plane_end()</tt>:</dt>
1558 <dd>Get an iterator at the end of the type planes. This serves as
1559 the marker for end of iteration over the type planes.</dd>
1561 <dt><tt>plane_const_iterator plane_end() const</tt>:</dt>
1562 <dd>Get a const_iterator at the end of the type planes. This serves as
1563 the marker for end of iteration over the type planes.</dd>
1565 <dt><tt>value_iterator value_begin(const Type *Typ)</tt>:</dt>
1566 <dd>Get an iterator that starts at the beginning of a type plane.
1567 The iterator will iterate over the name/value pairs in the type plane.
1568 Note: The type plane must already exist before using this.</dd>
1570 <dt><tt>value_const_iterator value_begin(const Type *Typ) const</tt>:</dt>
1571 <dd>Get a const_iterator that starts at the beginning of a type plane.
1572 The iterator will iterate over the name/value pairs in the type plane.
1573 Note: The type plane must already exist before using this.</dd>
1575 <dt><tt>value_iterator value_end(const Type *Typ)</tt>:</dt>
1576 <dd>Get an iterator to the end of a type plane. This serves as the marker
1577 for end of iteration of the type plane.
1578 Note: The type plane must already exist before using this.</dd>
1580 <dt><tt>value_const_iterator value_end(const Type *Typ) const</tt>:</dt>
1581 <dd>Get a const_iterator to the end of a type plane. This serves as the
1582 marker for end of iteration of the type plane.
1583 Note: the type plane must already exist before using this.</dd>
1585 <dt><tt>plane_const_iterator find(const Type* Typ ) const</tt>:</dt>
1586 <dd>This method returns a plane_const_iterator for iteration over
1587 the type planes starting at a specific plane, given by \p Ty.</dd>
1589 <dt><tt>plane_iterator find( const Type* Typ </tt>:</dt>
1590 <dd>This method returns a plane_iterator for iteration over the
1591 type planes starting at a specific plane, given by \p Ty.</dd>
1598 <!-- *********************************************************************** -->
1599 <div class="doc_section">
1600 <a name="coreclasses">The Core LLVM Class Hierarchy Reference </a>
1602 <!-- *********************************************************************** -->
1604 <div class="doc_text">
1605 <p><tt>#include "<a href="/doxygen/Type_8h-source.html">llvm/Type.h</a>"</tt>
1606 <br>doxygen info: <a href="/doxygen/classllvm_1_1Type.html">Type Class</a></p>
1608 <p>The Core LLVM classes are the primary means of representing the program
1609 being inspected or transformed. The core LLVM classes are defined in
1610 header files in the <tt>include/llvm/</tt> directory, and implemented in
1611 the <tt>lib/VMCore</tt> directory.</p>
1615 <!-- ======================================================================= -->
1616 <div class="doc_subsection">
1617 <a name="Type">The <tt>Type</tt> class and Derived Types</a>
1620 <div class="doc_text">
1622 <p><tt>Type</tt> is a superclass of all type classes. Every <tt>Value</tt> has
1623 a <tt>Type</tt>. <tt>Type</tt> cannot be instantiated directly but only
1624 through its subclasses. Certain primitive types (<tt>VoidType</tt>,
1625 <tt>LabelType</tt>, <tt>FloatType</tt> and <tt>DoubleType</tt>) have hidden
1626 subclasses. They are hidden because they offer no useful functionality beyond
1627 what the <tt>Type</tt> class offers except to distinguish themselves from
1628 other subclasses of <tt>Type</tt>.</p>
1629 <p>All other types are subclasses of <tt>DerivedType</tt>. Types can be
1630 named, but this is not a requirement. There exists exactly
1631 one instance of a given shape at any one time. This allows type equality to
1632 be performed with address equality of the Type Instance. That is, given two
1633 <tt>Type*</tt> values, the types are identical if the pointers are identical.
1637 <!-- _______________________________________________________________________ -->
1638 <div class="doc_subsubsection">
1639 <a name="m_Value">Important Public Methods</a>
1642 <div class="doc_text">
1645 <li><tt>bool isInteger() const</tt>: Returns true for any integer type.</li>
1647 <li><tt>bool isFloatingPoint()</tt>: Return true if this is one of the two
1648 floating point types.</li>
1650 <li><tt>bool isAbstract()</tt>: Return true if the type is abstract (contains
1651 an OpaqueType anywhere in its definition).</li>
1653 <li><tt>bool isSized()</tt>: Return true if the type has known size. Things
1654 that don't have a size are abstract types, labels and void.</li>
1659 <!-- _______________________________________________________________________ -->
1660 <div class="doc_subsubsection">
1661 <a name="m_Value">Important Derived Types</a>
1663 <div class="doc_text">
1665 <dt><tt>IntegerType</tt></dt>
1666 <dd>Subclass of DerivedType that represents integer types of any bit width.
1667 Any bit width between <tt>IntegerType::MIN_INT_BITS</tt> (1) and
1668 <tt>IntegerType::MAX_INT_BITS</tt> (~8 million) can be represented.
1670 <li><tt>static const IntegerType* get(unsigned NumBits)</tt>: get an integer
1671 type of a specific bit width.</li>
1672 <li><tt>unsigned getBitWidth() const</tt>: Get the bit width of an integer
1676 <dt><tt>SequentialType</tt></dt>
1677 <dd>This is subclassed by ArrayType and PointerType
1679 <li><tt>const Type * getElementType() const</tt>: Returns the type of each
1680 of the elements in the sequential type. </li>
1683 <dt><tt>ArrayType</tt></dt>
1684 <dd>This is a subclass of SequentialType and defines the interface for array
1687 <li><tt>unsigned getNumElements() const</tt>: Returns the number of
1688 elements in the array. </li>
1691 <dt><tt>PointerType</tt></dt>
1692 <dd>Subclass of SequentialType for pointer types.</li>
1693 <dt><tt>PackedType</tt></dt>
1694 <dd>Subclass of SequentialType for packed (vector) types. A
1695 packed type is similar to an ArrayType but is distinguished because it is
1696 a first class type wherease ArrayType is not. Packed types are used for
1697 vector operations and are usually small vectors of of an integer or floating
1699 <dt><tt>StructType</tt></dt>
1700 <dd>Subclass of DerivedTypes for struct types.</dd>
1701 <dt><tt>FunctionType</tt></dt>
1702 <dd>Subclass of DerivedTypes for function types.
1704 <li><tt>bool isVarArg() const</tt>: Returns true if its a vararg
1706 <li><tt> const Type * getReturnType() const</tt>: Returns the
1707 return type of the function.</li>
1708 <li><tt>const Type * getParamType (unsigned i)</tt>: Returns
1709 the type of the ith parameter.</li>
1710 <li><tt> const unsigned getNumParams() const</tt>: Returns the
1711 number of formal parameters.</li>
1714 <dt><tt>OpaqueType</tt></dt>
1715 <dd>Sublcass of DerivedType for abstract types. This class
1716 defines no content and is used as a placeholder for some other type. Note
1717 that OpaqueType is used (temporarily) during type resolution for forward
1718 references of types. Once the referenced type is resolved, the OpaqueType
1719 is replaced with the actual type. OpaqueType can also be used for data
1720 abstraction. At link time opaque types can be resolved to actual types
1721 of the same name.</dd>
1725 <!-- ======================================================================= -->
1726 <div class="doc_subsection">
1727 <a name="Value">The <tt>Value</tt> class</a>
1732 <p><tt>#include "<a href="/doxygen/Value_8h-source.html">llvm/Value.h</a>"</tt>
1734 doxygen info: <a href="/doxygen/classllvm_1_1Value.html">Value Class</a></p>
1736 <p>The <tt>Value</tt> class is the most important class in the LLVM Source
1737 base. It represents a typed value that may be used (among other things) as an
1738 operand to an instruction. There are many different types of <tt>Value</tt>s,
1739 such as <a href="#Constant"><tt>Constant</tt></a>s,<a
1740 href="#Argument"><tt>Argument</tt></a>s. Even <a
1741 href="#Instruction"><tt>Instruction</tt></a>s and <a
1742 href="#Function"><tt>Function</tt></a>s are <tt>Value</tt>s.</p>
1744 <p>A particular <tt>Value</tt> may be used many times in the LLVM representation
1745 for a program. For example, an incoming argument to a function (represented
1746 with an instance of the <a href="#Argument">Argument</a> class) is "used" by
1747 every instruction in the function that references the argument. To keep track
1748 of this relationship, the <tt>Value</tt> class keeps a list of all of the <a
1749 href="#User"><tt>User</tt></a>s that is using it (the <a
1750 href="#User"><tt>User</tt></a> class is a base class for all nodes in the LLVM
1751 graph that can refer to <tt>Value</tt>s). This use list is how LLVM represents
1752 def-use information in the program, and is accessible through the <tt>use_</tt>*
1753 methods, shown below.</p>
1755 <p>Because LLVM is a typed representation, every LLVM <tt>Value</tt> is typed,
1756 and this <a href="#Type">Type</a> is available through the <tt>getType()</tt>
1757 method. In addition, all LLVM values can be named. The "name" of the
1758 <tt>Value</tt> is a symbolic string printed in the LLVM code:</p>
1760 <div class="doc_code">
1762 %<b>foo</b> = add i32 1, 2
1766 <p><a name="#nameWarning">The name of this instruction is "foo".</a> <b>NOTE</b>
1767 that the name of any value may be missing (an empty string), so names should
1768 <b>ONLY</b> be used for debugging (making the source code easier to read,
1769 debugging printouts), they should not be used to keep track of values or map
1770 between them. For this purpose, use a <tt>std::map</tt> of pointers to the
1771 <tt>Value</tt> itself instead.</p>
1773 <p>One important aspect of LLVM is that there is no distinction between an SSA
1774 variable and the operation that produces it. Because of this, any reference to
1775 the value produced by an instruction (or the value available as an incoming
1776 argument, for example) is represented as a direct pointer to the instance of
1778 represents this value. Although this may take some getting used to, it
1779 simplifies the representation and makes it easier to manipulate.</p>
1783 <!-- _______________________________________________________________________ -->
1784 <div class="doc_subsubsection">
1785 <a name="m_Value">Important Public Members of the <tt>Value</tt> class</a>
1788 <div class="doc_text">
1791 <li><tt>Value::use_iterator</tt> - Typedef for iterator over the
1793 <tt>Value::use_const_iterator</tt> - Typedef for const_iterator over
1795 <tt>unsigned use_size()</tt> - Returns the number of users of the
1797 <tt>bool use_empty()</tt> - Returns true if there are no users.<br>
1798 <tt>use_iterator use_begin()</tt> - Get an iterator to the start of
1800 <tt>use_iterator use_end()</tt> - Get an iterator to the end of the
1802 <tt><a href="#User">User</a> *use_back()</tt> - Returns the last
1803 element in the list.
1804 <p> These methods are the interface to access the def-use
1805 information in LLVM. As with all other iterators in LLVM, the naming
1806 conventions follow the conventions defined by the <a href="#stl">STL</a>.</p>
1808 <li><tt><a href="#Type">Type</a> *getType() const</tt>
1809 <p>This method returns the Type of the Value.</p>
1811 <li><tt>bool hasName() const</tt><br>
1812 <tt>std::string getName() const</tt><br>
1813 <tt>void setName(const std::string &Name)</tt>
1814 <p> This family of methods is used to access and assign a name to a <tt>Value</tt>,
1815 be aware of the <a href="#nameWarning">precaution above</a>.</p>
1817 <li><tt>void replaceAllUsesWith(Value *V)</tt>
1819 <p>This method traverses the use list of a <tt>Value</tt> changing all <a
1820 href="#User"><tt>User</tt>s</a> of the current value to refer to
1821 "<tt>V</tt>" instead. For example, if you detect that an instruction always
1822 produces a constant value (for example through constant folding), you can
1823 replace all uses of the instruction with the constant like this:</p>
1825 <div class="doc_code">
1827 Inst->replaceAllUsesWith(ConstVal);
1835 <!-- ======================================================================= -->
1836 <div class="doc_subsection">
1837 <a name="User">The <tt>User</tt> class</a>
1840 <div class="doc_text">
1843 <tt>#include "<a href="/doxygen/User_8h-source.html">llvm/User.h</a>"</tt><br>
1844 doxygen info: <a href="/doxygen/classllvm_1_1User.html">User Class</a><br>
1845 Superclass: <a href="#Value"><tt>Value</tt></a></p>
1847 <p>The <tt>User</tt> class is the common base class of all LLVM nodes that may
1848 refer to <a href="#Value"><tt>Value</tt></a>s. It exposes a list of "Operands"
1849 that are all of the <a href="#Value"><tt>Value</tt></a>s that the User is
1850 referring to. The <tt>User</tt> class itself is a subclass of
1853 <p>The operands of a <tt>User</tt> point directly to the LLVM <a
1854 href="#Value"><tt>Value</tt></a> that it refers to. Because LLVM uses Static
1855 Single Assignment (SSA) form, there can only be one definition referred to,
1856 allowing this direct connection. This connection provides the use-def
1857 information in LLVM.</p>
1861 <!-- _______________________________________________________________________ -->
1862 <div class="doc_subsubsection">
1863 <a name="m_User">Important Public Members of the <tt>User</tt> class</a>
1866 <div class="doc_text">
1868 <p>The <tt>User</tt> class exposes the operand list in two ways: through
1869 an index access interface and through an iterator based interface.</p>
1872 <li><tt>Value *getOperand(unsigned i)</tt><br>
1873 <tt>unsigned getNumOperands()</tt>
1874 <p> These two methods expose the operands of the <tt>User</tt> in a
1875 convenient form for direct access.</p></li>
1877 <li><tt>User::op_iterator</tt> - Typedef for iterator over the operand
1879 <tt>op_iterator op_begin()</tt> - Get an iterator to the start of
1880 the operand list.<br>
1881 <tt>op_iterator op_end()</tt> - Get an iterator to the end of the
1883 <p> Together, these methods make up the iterator based interface to
1884 the operands of a <tt>User</tt>.</p></li>
1889 <!-- ======================================================================= -->
1890 <div class="doc_subsection">
1891 <a name="Instruction">The <tt>Instruction</tt> class</a>
1894 <div class="doc_text">
1896 <p><tt>#include "</tt><tt><a
1897 href="/doxygen/Instruction_8h-source.html">llvm/Instruction.h</a>"</tt><br>
1898 doxygen info: <a href="/doxygen/classllvm_1_1Instruction.html">Instruction Class</a><br>
1899 Superclasses: <a href="#User"><tt>User</tt></a>, <a
1900 href="#Value"><tt>Value</tt></a></p>
1902 <p>The <tt>Instruction</tt> class is the common base class for all LLVM
1903 instructions. It provides only a few methods, but is a very commonly used
1904 class. The primary data tracked by the <tt>Instruction</tt> class itself is the
1905 opcode (instruction type) and the parent <a
1906 href="#BasicBlock"><tt>BasicBlock</tt></a> the <tt>Instruction</tt> is embedded
1907 into. To represent a specific type of instruction, one of many subclasses of
1908 <tt>Instruction</tt> are used.</p>
1910 <p> Because the <tt>Instruction</tt> class subclasses the <a
1911 href="#User"><tt>User</tt></a> class, its operands can be accessed in the same
1912 way as for other <a href="#User"><tt>User</tt></a>s (with the
1913 <tt>getOperand()</tt>/<tt>getNumOperands()</tt> and
1914 <tt>op_begin()</tt>/<tt>op_end()</tt> methods).</p> <p> An important file for
1915 the <tt>Instruction</tt> class is the <tt>llvm/Instruction.def</tt> file. This
1916 file contains some meta-data about the various different types of instructions
1917 in LLVM. It describes the enum values that are used as opcodes (for example
1918 <tt>Instruction::Add</tt> and <tt>Instruction::ICmp</tt>), as well as the
1919 concrete sub-classes of <tt>Instruction</tt> that implement the instruction (for
1920 example <tt><a href="#BinaryOperator">BinaryOperator</a></tt> and <tt><a
1921 href="#CmpInst">CmpInst</a></tt>). Unfortunately, the use of macros in
1922 this file confuses doxygen, so these enum values don't show up correctly in the
1923 <a href="/doxygen/classllvm_1_1Instruction.html">doxygen output</a>.</p>
1927 <!-- _______________________________________________________________________ -->
1928 <div class="doc_subsubsection">
1929 <a name="s_Instruction">Important Subclasses of the <tt>Instruction</tt>
1932 <div class="doc_text">
1934 <li><tt><a name="BinaryOperator">BinaryOperator</a></tt>
1935 <p>This subclasses represents all two operand instructions whose operands
1936 must be the same type, except for the comparison instructions.</p></li>
1937 <li><tt><a name="CastInst">CastInst</a></tt>
1938 <p>This subclass is the parent of the 12 casting instructions. It provides
1939 common operations on cast instructions.</p>
1940 <li><tt><a name="CmpInst">CmpInst</a></tt>
1941 <p>This subclass respresents the two comparison instructions,
1942 <a href="LangRef.html#i_icmp">ICmpInst</a> (integer opreands), and
1943 <a href="LangRef.html#i_fcmp">FCmpInst</a> (floating point operands).</p>
1944 <li><tt><a name="TerminatorInst">TerminatorInst</a></tt>
1945 <p>This subclass is the parent of all terminator instructions (those which
1946 can terminate a block).</p>
1950 <!-- _______________________________________________________________________ -->
1951 <div class="doc_subsubsection">
1952 <a name="m_Instruction">Important Public Members of the <tt>Instruction</tt>
1956 <div class="doc_text">
1959 <li><tt><a href="#BasicBlock">BasicBlock</a> *getParent()</tt>
1960 <p>Returns the <a href="#BasicBlock"><tt>BasicBlock</tt></a> that
1961 this <tt>Instruction</tt> is embedded into.</p></li>
1962 <li><tt>bool mayWriteToMemory()</tt>
1963 <p>Returns true if the instruction writes to memory, i.e. it is a
1964 <tt>call</tt>,<tt>free</tt>,<tt>invoke</tt>, or <tt>store</tt>.</p></li>
1965 <li><tt>unsigned getOpcode()</tt>
1966 <p>Returns the opcode for the <tt>Instruction</tt>.</p></li>
1967 <li><tt><a href="#Instruction">Instruction</a> *clone() const</tt>
1968 <p>Returns another instance of the specified instruction, identical
1969 in all ways to the original except that the instruction has no parent
1970 (ie it's not embedded into a <a href="#BasicBlock"><tt>BasicBlock</tt></a>),
1971 and it has no name</p></li>
1976 <!-- ======================================================================= -->
1977 <div class="doc_subsection">
1978 <a name="BasicBlock">The <tt>BasicBlock</tt> class</a>
1981 <div class="doc_text">
1984 href="/doxygen/BasicBlock_8h-source.html">llvm/BasicBlock.h</a>"</tt><br>
1985 doxygen info: <a href="/doxygen/structllvm_1_1BasicBlock.html">BasicBlock
1987 Superclass: <a href="#Value"><tt>Value</tt></a></p>
1989 <p>This class represents a single entry multiple exit section of the code,
1990 commonly known as a basic block by the compiler community. The
1991 <tt>BasicBlock</tt> class maintains a list of <a
1992 href="#Instruction"><tt>Instruction</tt></a>s, which form the body of the block.
1993 Matching the language definition, the last element of this list of instructions
1994 is always a terminator instruction (a subclass of the <a
1995 href="#TerminatorInst"><tt>TerminatorInst</tt></a> class).</p>
1997 <p>In addition to tracking the list of instructions that make up the block, the
1998 <tt>BasicBlock</tt> class also keeps track of the <a
1999 href="#Function"><tt>Function</tt></a> that it is embedded into.</p>
2001 <p>Note that <tt>BasicBlock</tt>s themselves are <a
2002 href="#Value"><tt>Value</tt></a>s, because they are referenced by instructions
2003 like branches and can go in the switch tables. <tt>BasicBlock</tt>s have type
2008 <!-- _______________________________________________________________________ -->
2009 <div class="doc_subsubsection">
2010 <a name="m_BasicBlock">Important Public Members of the <tt>BasicBlock</tt>
2014 <div class="doc_text">
2018 <li><tt>BasicBlock(const std::string &Name = "", </tt><tt><a
2019 href="#Function">Function</a> *Parent = 0)</tt>
2021 <p>The <tt>BasicBlock</tt> constructor is used to create new basic blocks for
2022 insertion into a function. The constructor optionally takes a name for the new
2023 block, and a <a href="#Function"><tt>Function</tt></a> to insert it into. If
2024 the <tt>Parent</tt> parameter is specified, the new <tt>BasicBlock</tt> is
2025 automatically inserted at the end of the specified <a
2026 href="#Function"><tt>Function</tt></a>, if not specified, the BasicBlock must be
2027 manually inserted into the <a href="#Function"><tt>Function</tt></a>.</p></li>
2029 <li><tt>BasicBlock::iterator</tt> - Typedef for instruction list iterator<br>
2030 <tt>BasicBlock::const_iterator</tt> - Typedef for const_iterator.<br>
2031 <tt>begin()</tt>, <tt>end()</tt>, <tt>front()</tt>, <tt>back()</tt>,
2032 <tt>size()</tt>, <tt>empty()</tt>
2033 STL-style functions for accessing the instruction list.
2035 <p>These methods and typedefs are forwarding functions that have the same
2036 semantics as the standard library methods of the same names. These methods
2037 expose the underlying instruction list of a basic block in a way that is easy to
2038 manipulate. To get the full complement of container operations (including
2039 operations to update the list), you must use the <tt>getInstList()</tt>
2042 <li><tt>BasicBlock::InstListType &getInstList()</tt>
2044 <p>This method is used to get access to the underlying container that actually
2045 holds the Instructions. This method must be used when there isn't a forwarding
2046 function in the <tt>BasicBlock</tt> class for the operation that you would like
2047 to perform. Because there are no forwarding functions for "updating"
2048 operations, you need to use this if you want to update the contents of a
2049 <tt>BasicBlock</tt>.</p></li>
2051 <li><tt><a href="#Function">Function</a> *getParent()</tt>
2053 <p> Returns a pointer to <a href="#Function"><tt>Function</tt></a> the block is
2054 embedded into, or a null pointer if it is homeless.</p></li>
2056 <li><tt><a href="#TerminatorInst">TerminatorInst</a> *getTerminator()</tt>
2058 <p> Returns a pointer to the terminator instruction that appears at the end of
2059 the <tt>BasicBlock</tt>. If there is no terminator instruction, or if the last
2060 instruction in the block is not a terminator, then a null pointer is
2067 <!-- ======================================================================= -->
2068 <div class="doc_subsection">
2069 <a name="GlobalValue">The <tt>GlobalValue</tt> class</a>
2072 <div class="doc_text">
2075 href="/doxygen/GlobalValue_8h-source.html">llvm/GlobalValue.h</a>"</tt><br>
2076 doxygen info: <a href="/doxygen/classllvm_1_1GlobalValue.html">GlobalValue
2078 Superclasses: <a href="#Constant"><tt>Constant</tt></a>,
2079 <a href="#User"><tt>User</tt></a>, <a href="#Value"><tt>Value</tt></a></p>
2081 <p>Global values (<a href="#GlobalVariable"><tt>GlobalVariable</tt></a>s or <a
2082 href="#Function"><tt>Function</tt></a>s) are the only LLVM values that are
2083 visible in the bodies of all <a href="#Function"><tt>Function</tt></a>s.
2084 Because they are visible at global scope, they are also subject to linking with
2085 other globals defined in different translation units. To control the linking
2086 process, <tt>GlobalValue</tt>s know their linkage rules. Specifically,
2087 <tt>GlobalValue</tt>s know whether they have internal or external linkage, as
2088 defined by the <tt>LinkageTypes</tt> enumeration.</p>
2090 <p>If a <tt>GlobalValue</tt> has internal linkage (equivalent to being
2091 <tt>static</tt> in C), it is not visible to code outside the current translation
2092 unit, and does not participate in linking. If it has external linkage, it is
2093 visible to external code, and does participate in linking. In addition to
2094 linkage information, <tt>GlobalValue</tt>s keep track of which <a
2095 href="#Module"><tt>Module</tt></a> they are currently part of.</p>
2097 <p>Because <tt>GlobalValue</tt>s are memory objects, they are always referred to
2098 by their <b>address</b>. As such, the <a href="#Type"><tt>Type</tt></a> of a
2099 global is always a pointer to its contents. It is important to remember this
2100 when using the <tt>GetElementPtrInst</tt> instruction because this pointer must
2101 be dereferenced first. For example, if you have a <tt>GlobalVariable</tt> (a
2102 subclass of <tt>GlobalValue)</tt> that is an array of 24 ints, type <tt>[24 x
2103 i32]</tt>, then the <tt>GlobalVariable</tt> is a pointer to that array. Although
2104 the address of the first element of this array and the value of the
2105 <tt>GlobalVariable</tt> are the same, they have different types. The
2106 <tt>GlobalVariable</tt>'s type is <tt>[24 x i32]</tt>. The first element's type
2107 is <tt>i32.</tt> Because of this, accessing a global value requires you to
2108 dereference the pointer with <tt>GetElementPtrInst</tt> first, then its elements
2109 can be accessed. This is explained in the <a href="LangRef.html#globalvars">LLVM
2110 Language Reference Manual</a>.</p>
2114 <!-- _______________________________________________________________________ -->
2115 <div class="doc_subsubsection">
2116 <a name="m_GlobalValue">Important Public Members of the <tt>GlobalValue</tt>
2120 <div class="doc_text">
2123 <li><tt>bool hasInternalLinkage() const</tt><br>
2124 <tt>bool hasExternalLinkage() const</tt><br>
2125 <tt>void setInternalLinkage(bool HasInternalLinkage)</tt>
2126 <p> These methods manipulate the linkage characteristics of the <tt>GlobalValue</tt>.</p>
2129 <li><tt><a href="#Module">Module</a> *getParent()</tt>
2130 <p> This returns the <a href="#Module"><tt>Module</tt></a> that the
2131 GlobalValue is currently embedded into.</p></li>
2136 <!-- ======================================================================= -->
2137 <div class="doc_subsection">
2138 <a name="Function">The <tt>Function</tt> class</a>
2141 <div class="doc_text">
2144 href="/doxygen/Function_8h-source.html">llvm/Function.h</a>"</tt><br> doxygen
2145 info: <a href="/doxygen/classllvm_1_1Function.html">Function Class</a><br>
2146 Superclasses: <a href="#GlobalValue"><tt>GlobalValue</tt></a>,
2147 <a href="#Constant"><tt>Constant</tt></a>,
2148 <a href="#User"><tt>User</tt></a>,
2149 <a href="#Value"><tt>Value</tt></a></p>
2151 <p>The <tt>Function</tt> class represents a single procedure in LLVM. It is
2152 actually one of the more complex classes in the LLVM heirarchy because it must
2153 keep track of a large amount of data. The <tt>Function</tt> class keeps track
2154 of a list of <a href="#BasicBlock"><tt>BasicBlock</tt></a>s, a list of formal
2155 <a href="#Argument"><tt>Argument</tt></a>s, and a
2156 <a href="#SymbolTable"><tt>SymbolTable</tt></a>.</p>
2158 <p>The list of <a href="#BasicBlock"><tt>BasicBlock</tt></a>s is the most
2159 commonly used part of <tt>Function</tt> objects. The list imposes an implicit
2160 ordering of the blocks in the function, which indicate how the code will be
2161 layed out by the backend. Additionally, the first <a
2162 href="#BasicBlock"><tt>BasicBlock</tt></a> is the implicit entry node for the
2163 <tt>Function</tt>. It is not legal in LLVM to explicitly branch to this initial
2164 block. There are no implicit exit nodes, and in fact there may be multiple exit
2165 nodes from a single <tt>Function</tt>. If the <a
2166 href="#BasicBlock"><tt>BasicBlock</tt></a> list is empty, this indicates that
2167 the <tt>Function</tt> is actually a function declaration: the actual body of the
2168 function hasn't been linked in yet.</p>
2170 <p>In addition to a list of <a href="#BasicBlock"><tt>BasicBlock</tt></a>s, the
2171 <tt>Function</tt> class also keeps track of the list of formal <a
2172 href="#Argument"><tt>Argument</tt></a>s that the function receives. This
2173 container manages the lifetime of the <a href="#Argument"><tt>Argument</tt></a>
2174 nodes, just like the <a href="#BasicBlock"><tt>BasicBlock</tt></a> list does for
2175 the <a href="#BasicBlock"><tt>BasicBlock</tt></a>s.</p>
2177 <p>The <a href="#SymbolTable"><tt>SymbolTable</tt></a> is a very rarely used
2178 LLVM feature that is only used when you have to look up a value by name. Aside
2179 from that, the <a href="#SymbolTable"><tt>SymbolTable</tt></a> is used
2180 internally to make sure that there are not conflicts between the names of <a
2181 href="#Instruction"><tt>Instruction</tt></a>s, <a
2182 href="#BasicBlock"><tt>BasicBlock</tt></a>s, or <a
2183 href="#Argument"><tt>Argument</tt></a>s in the function body.</p>
2185 <p>Note that <tt>Function</tt> is a <a href="#GlobalValue">GlobalValue</a>
2186 and therefore also a <a href="#Constant">Constant</a>. The value of the function
2187 is its address (after linking) which is guaranteed to be constant.</p>
2190 <!-- _______________________________________________________________________ -->
2191 <div class="doc_subsubsection">
2192 <a name="m_Function">Important Public Members of the <tt>Function</tt>
2196 <div class="doc_text">
2199 <li><tt>Function(const </tt><tt><a href="#FunctionType">FunctionType</a>
2200 *Ty, LinkageTypes Linkage, const std::string &N = "", Module* Parent = 0)</tt>
2202 <p>Constructor used when you need to create new <tt>Function</tt>s to add
2203 the the program. The constructor must specify the type of the function to
2204 create and what type of linkage the function should have. The <a
2205 href="#FunctionType"><tt>FunctionType</tt></a> argument
2206 specifies the formal arguments and return value for the function. The same
2207 <a href="#FunctionTypel"><tt>FunctionType</tt></a> value can be used to
2208 create multiple functions. The <tt>Parent</tt> argument specifies the Module
2209 in which the function is defined. If this argument is provided, the function
2210 will automatically be inserted into that module's list of
2213 <li><tt>bool isExternal()</tt>
2215 <p>Return whether or not the <tt>Function</tt> has a body defined. If the
2216 function is "external", it does not have a body, and thus must be resolved
2217 by linking with a function defined in a different translation unit.</p></li>
2219 <li><tt>Function::iterator</tt> - Typedef for basic block list iterator<br>
2220 <tt>Function::const_iterator</tt> - Typedef for const_iterator.<br>
2222 <tt>begin()</tt>, <tt>end()</tt>
2223 <tt>size()</tt>, <tt>empty()</tt>
2225 <p>These are forwarding methods that make it easy to access the contents of
2226 a <tt>Function</tt> object's <a href="#BasicBlock"><tt>BasicBlock</tt></a>
2229 <li><tt>Function::BasicBlockListType &getBasicBlockList()</tt>
2231 <p>Returns the list of <a href="#BasicBlock"><tt>BasicBlock</tt></a>s. This
2232 is necessary to use when you need to update the list or perform a complex
2233 action that doesn't have a forwarding method.</p></li>
2235 <li><tt>Function::arg_iterator</tt> - Typedef for the argument list
2237 <tt>Function::const_arg_iterator</tt> - Typedef for const_iterator.<br>
2239 <tt>arg_begin()</tt>, <tt>arg_end()</tt>
2240 <tt>arg_size()</tt>, <tt>arg_empty()</tt>
2242 <p>These are forwarding methods that make it easy to access the contents of
2243 a <tt>Function</tt> object's <a href="#Argument"><tt>Argument</tt></a>
2246 <li><tt>Function::ArgumentListType &getArgumentList()</tt>
2248 <p>Returns the list of <a href="#Argument"><tt>Argument</tt></a>s. This is
2249 necessary to use when you need to update the list or perform a complex
2250 action that doesn't have a forwarding method.</p></li>
2252 <li><tt><a href="#BasicBlock">BasicBlock</a> &getEntryBlock()</tt>
2254 <p>Returns the entry <a href="#BasicBlock"><tt>BasicBlock</tt></a> for the
2255 function. Because the entry block for the function is always the first
2256 block, this returns the first block of the <tt>Function</tt>.</p></li>
2258 <li><tt><a href="#Type">Type</a> *getReturnType()</tt><br>
2259 <tt><a href="#FunctionType">FunctionType</a> *getFunctionType()</tt>
2261 <p>This traverses the <a href="#Type"><tt>Type</tt></a> of the
2262 <tt>Function</tt> and returns the return type of the function, or the <a
2263 href="#FunctionType"><tt>FunctionType</tt></a> of the actual
2266 <li><tt><a href="#SymbolTable">SymbolTable</a> *getSymbolTable()</tt>
2268 <p> Return a pointer to the <a href="#SymbolTable"><tt>SymbolTable</tt></a>
2269 for this <tt>Function</tt>.</p></li>
2274 <!-- ======================================================================= -->
2275 <div class="doc_subsection">
2276 <a name="GlobalVariable">The <tt>GlobalVariable</tt> class</a>
2279 <div class="doc_text">
2282 href="/doxygen/GlobalVariable_8h-source.html">llvm/GlobalVariable.h</a>"</tt>
2284 doxygen info: <a href="/doxygen/classllvm_1_1GlobalVariable.html">GlobalVariable
2286 Superclasses: <a href="#GlobalValue"><tt>GlobalValue</tt></a>,
2287 <a href="#Constant"><tt>Constant</tt></a>,
2288 <a href="#User"><tt>User</tt></a>,
2289 <a href="#Value"><tt>Value</tt></a></p>
2291 <p>Global variables are represented with the (suprise suprise)
2292 <tt>GlobalVariable</tt> class. Like functions, <tt>GlobalVariable</tt>s are also
2293 subclasses of <a href="#GlobalValue"><tt>GlobalValue</tt></a>, and as such are
2294 always referenced by their address (global values must live in memory, so their
2295 "name" refers to their constant address). See
2296 <a href="#GlobalValue"><tt>GlobalValue</tt></a> for more on this. Global
2297 variables may have an initial value (which must be a
2298 <a href="#Constant"><tt>Constant</tt></a>), and if they have an initializer,
2299 they may be marked as "constant" themselves (indicating that their contents
2300 never change at runtime).</p>
2303 <!-- _______________________________________________________________________ -->
2304 <div class="doc_subsubsection">
2305 <a name="m_GlobalVariable">Important Public Members of the
2306 <tt>GlobalVariable</tt> class</a>
2309 <div class="doc_text">
2312 <li><tt>GlobalVariable(const </tt><tt><a href="#Type">Type</a> *Ty, bool
2313 isConstant, LinkageTypes& Linkage, <a href="#Constant">Constant</a>
2314 *Initializer = 0, const std::string &Name = "", Module* Parent = 0)</tt>
2316 <p>Create a new global variable of the specified type. If
2317 <tt>isConstant</tt> is true then the global variable will be marked as
2318 unchanging for the program. The Linkage parameter specifies the type of
2319 linkage (internal, external, weak, linkonce, appending) for the variable. If
2320 the linkage is InternalLinkage, WeakLinkage, or LinkOnceLinkage, then
2321 the resultant global variable will have internal linkage. AppendingLinkage
2322 concatenates together all instances (in different translation units) of the
2323 variable into a single variable but is only applicable to arrays. See
2324 the <a href="LangRef.html#modulestructure">LLVM Language Reference</a> for
2325 further details on linkage types. Optionally an initializer, a name, and the
2326 module to put the variable into may be specified for the global variable as
2329 <li><tt>bool isConstant() const</tt>
2331 <p>Returns true if this is a global variable that is known not to
2332 be modified at runtime.</p></li>
2334 <li><tt>bool hasInitializer()</tt>
2336 <p>Returns true if this <tt>GlobalVariable</tt> has an intializer.</p></li>
2338 <li><tt><a href="#Constant">Constant</a> *getInitializer()</tt>
2340 <p>Returns the intial value for a <tt>GlobalVariable</tt>. It is not legal
2341 to call this method if there is no initializer.</p></li>
2346 <!-- ======================================================================= -->
2347 <div class="doc_subsection">
2348 <a name="Module">The <tt>Module</tt> class</a>
2351 <div class="doc_text">
2354 href="/doxygen/Module_8h-source.html">llvm/Module.h</a>"</tt><br> doxygen info:
2355 <a href="/doxygen/classllvm_1_1Module.html">Module Class</a></p>
2357 <p>The <tt>Module</tt> class represents the top level structure present in LLVM
2358 programs. An LLVM module is effectively either a translation unit of the
2359 original program or a combination of several translation units merged by the
2360 linker. The <tt>Module</tt> class keeps track of a list of <a
2361 href="#Function"><tt>Function</tt></a>s, a list of <a
2362 href="#GlobalVariable"><tt>GlobalVariable</tt></a>s, and a <a
2363 href="#SymbolTable"><tt>SymbolTable</tt></a>. Additionally, it contains a few
2364 helpful member functions that try to make common operations easy.</p>
2368 <!-- _______________________________________________________________________ -->
2369 <div class="doc_subsubsection">
2370 <a name="m_Module">Important Public Members of the <tt>Module</tt> class</a>
2373 <div class="doc_text">
2376 <li><tt>Module::Module(std::string name = "")</tt></li>
2379 <p>Constructing a <a href="#Module">Module</a> is easy. You can optionally
2380 provide a name for it (probably based on the name of the translation unit).</p>
2383 <li><tt>Module::iterator</tt> - Typedef for function list iterator<br>
2384 <tt>Module::const_iterator</tt> - Typedef for const_iterator.<br>
2386 <tt>begin()</tt>, <tt>end()</tt>
2387 <tt>size()</tt>, <tt>empty()</tt>
2389 <p>These are forwarding methods that make it easy to access the contents of
2390 a <tt>Module</tt> object's <a href="#Function"><tt>Function</tt></a>
2393 <li><tt>Module::FunctionListType &getFunctionList()</tt>
2395 <p> Returns the list of <a href="#Function"><tt>Function</tt></a>s. This is
2396 necessary to use when you need to update the list or perform a complex
2397 action that doesn't have a forwarding method.</p>
2399 <p><!-- Global Variable --></p></li>
2405 <li><tt>Module::global_iterator</tt> - Typedef for global variable list iterator<br>
2407 <tt>Module::const_global_iterator</tt> - Typedef for const_iterator.<br>
2409 <tt>global_begin()</tt>, <tt>global_end()</tt>
2410 <tt>global_size()</tt>, <tt>global_empty()</tt>
2412 <p> These are forwarding methods that make it easy to access the contents of
2413 a <tt>Module</tt> object's <a
2414 href="#GlobalVariable"><tt>GlobalVariable</tt></a> list.</p></li>
2416 <li><tt>Module::GlobalListType &getGlobalList()</tt>
2418 <p>Returns the list of <a
2419 href="#GlobalVariable"><tt>GlobalVariable</tt></a>s. This is necessary to
2420 use when you need to update the list or perform a complex action that
2421 doesn't have a forwarding method.</p>
2423 <p><!-- Symbol table stuff --> </p></li>
2429 <li><tt><a href="#SymbolTable">SymbolTable</a> *getSymbolTable()</tt>
2431 <p>Return a reference to the <a href="#SymbolTable"><tt>SymbolTable</tt></a>
2432 for this <tt>Module</tt>.</p>
2434 <p><!-- Convenience methods --></p></li>
2440 <li><tt><a href="#Function">Function</a> *getFunction(const std::string
2441 &Name, const <a href="#FunctionType">FunctionType</a> *Ty)</tt>
2443 <p>Look up the specified function in the <tt>Module</tt> <a
2444 href="#SymbolTable"><tt>SymbolTable</tt></a>. If it does not exist, return
2445 <tt>null</tt>.</p></li>
2447 <li><tt><a href="#Function">Function</a> *getOrInsertFunction(const
2448 std::string &Name, const <a href="#FunctionType">FunctionType</a> *T)</tt>
2450 <p>Look up the specified function in the <tt>Module</tt> <a
2451 href="#SymbolTable"><tt>SymbolTable</tt></a>. If it does not exist, add an
2452 external declaration for the function and return it.</p></li>
2454 <li><tt>std::string getTypeName(const <a href="#Type">Type</a> *Ty)</tt>
2456 <p>If there is at least one entry in the <a
2457 href="#SymbolTable"><tt>SymbolTable</tt></a> for the specified <a
2458 href="#Type"><tt>Type</tt></a>, return it. Otherwise return the empty
2461 <li><tt>bool addTypeName(const std::string &Name, const <a
2462 href="#Type">Type</a> *Ty)</tt>
2464 <p>Insert an entry in the <a href="#SymbolTable"><tt>SymbolTable</tt></a>
2465 mapping <tt>Name</tt> to <tt>Ty</tt>. If there is already an entry for this
2466 name, true is returned and the <a
2467 href="#SymbolTable"><tt>SymbolTable</tt></a> is not modified.</p></li>
2472 <!-- ======================================================================= -->
2473 <div class="doc_subsection">
2474 <a name="Constant">The <tt>Constant</tt> class and subclasses</a>
2477 <div class="doc_text">
2479 <p>Constant represents a base class for different types of constants. It
2480 is subclassed by ConstantInt, ConstantArray, etc. for representing
2481 the various types of Constants.</p>
2485 <!-- _______________________________________________________________________ -->
2486 <div class="doc_subsubsection">
2487 <a name="m_Constant">Important Public Methods</a>
2489 <div class="doc_text">
2492 <!-- _______________________________________________________________________ -->
2493 <div class="doc_subsubsection">Important Subclasses of Constant </div>
2494 <div class="doc_text">
2496 <li>ConstantInt : This subclass of Constant represents an integer constant of
2497 any width, including boolean (1 bit integer).
2499 <li><tt>int64_t getSExtValue() const</tt>: Returns the underlying value of
2500 this constant as a sign extended signed integer value.</li>
2501 <li><tt>uint64_t getZExtValue() const</tt>: Returns the underlying value
2502 of this constant as a zero extended unsigned integer value.</li>
2503 <li><tt>static ConstantInt* get(const Type *Ty, uint64_t Val)</tt>:
2504 Returns the ConstantInt object that represents the value provided by
2505 <tt>Val</tt> for integer type <tt>Ty</tt>.</li>
2508 <li>ConstantFP : This class represents a floating point constant.
2510 <li><tt>double getValue() const</tt>: Returns the underlying value of
2511 this constant. </li>
2515 <li><tt>bool getValue() const</tt>: Returns the underlying value of this
2519 <li>ConstantArray : This represents a constant array.
2521 <li><tt>const std::vector<Use> &getValues() const</tt>: Returns
2522 a vector of component constants that makeup this array. </li>
2525 <li>ConstantStruct : This represents a constant struct.
2527 <li><tt>const std::vector<Use> &getValues() const</tt>: Returns
2528 a vector of component constants that makeup this array. </li>
2531 <li>GlobalValue : This represents either a global variable or a function. In
2532 either case, the value is a constant fixed address (after linking).
2536 <!-- ======================================================================= -->
2537 <div class="doc_subsection">
2538 <a name="Argument">The <tt>Argument</tt> class</a>
2541 <div class="doc_text">
2543 <p>This subclass of Value defines the interface for incoming formal
2544 arguments to a function. A Function maintains a list of its formal
2545 arguments. An argument has a pointer to the parent Function.</p>
2549 <!-- *********************************************************************** -->
2552 <a href="http://jigsaw.w3.org/css-validator/check/referer"><img
2553 src="http://jigsaw.w3.org/css-validator/images/vcss" alt="Valid CSS!"></a>
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2557 <a href="mailto:dhurjati@cs.uiuc.edu">Dinakar Dhurjati</a> and
2558 <a href="mailto:sabre@nondot.org">Chris Lattner</a><br>
2559 <a href="http://llvm.org">The LLVM Compiler Infrastructure</a><br>
2560 Last modified: $Date$