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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><!--
19 <li>The <tt>-time-passes</tt> option
20 <li>How to use the LLVM Makefile system
21 <li>How to write a regression test
25 <li><a href="#apis">Important and useful LLVM APIs</a>
27 <li><a href="#isa">The <tt>isa<></tt>, <tt>cast<></tt>
28 and <tt>dyn_cast<></tt> templates</a> </li>
29 <li><a href="#DEBUG">The <tt>DEBUG()</tt> macro & <tt>-debug</tt>
32 <li><a href="#DEBUG_TYPE">Fine grained debug info with <tt>DEBUG_TYPE</tt>
33 and the <tt>-debug-only</tt> option</a> </li>
36 <li><a href="#Statistic">The <tt>Statistic</tt> template & <tt>-stats</tt>
38 <li>The <tt>InstVisitor</tt> template
39 <li>The general graph API
43 <li><a href="#common">Helpful Hints for Common Operations</a>
45 <li><a href="#inspection">Basic Inspection and Traversal Routines</a>
47 <li><a href="#iterate_function">Iterating over the <tt>BasicBlock</tt>s
48 in a <tt>Function</tt></a> </li>
49 <li><a href="#iterate_basicblock">Iterating over the <tt>Instruction</tt>s
50 in a <tt>BasicBlock</tt></a> </li>
51 <li><a href="#iterate_institer">Iterating over the <tt>Instruction</tt>s
52 in a <tt>Function</tt></a> </li>
53 <li><a href="#iterate_convert">Turning an iterator into a
54 class pointer</a> </li>
55 <li><a href="#iterate_complex">Finding call sites: a more
56 complex example</a> </li>
57 <li><a href="#calls_and_invokes">Treating calls and invokes
58 the same way</a> </li>
59 <li><a href="#iterate_chains">Iterating over def-use &
60 use-def chains</a> </li>
63 <li><a href="#simplechanges">Making simple changes</a>
65 <li><a href="#schanges_creating">Creating and inserting new
66 <tt>Instruction</tt>s</a> </li>
67 <li><a href="#schanges_deleting">Deleting <tt>Instruction</tt>s</a> </li>
68 <li><a href="#schanges_replacing">Replacing an <tt>Instruction</tt>
69 with another <tt>Value</tt></a> </li>
72 <li>Working with the Control Flow Graph
74 <li>Accessing predecessors and successors of a <tt>BasicBlock</tt>
81 <li><a href="#coreclasses">The Core LLVM Class Hierarchy Reference</a>
83 <li><a href="#Value">The <tt>Value</tt> class</a>
85 <li><a href="#User">The <tt>User</tt> class</a>
87 <li><a href="#Instruction">The <tt>Instruction</tt> class</a>
89 <li><a href="#GetElementPtrInst">The <tt>GetElementPtrInst</tt>
92 <li><a href="#GlobalValue">The <tt>GlobalValue</tt> class</a>
94 <li><a href="#BasicBlock">The <tt>BasicBlock</tt>class</a></li>
95 <li><a href="#Function">The <tt>Function</tt> class</a></li>
96 <li><a href="#GlobalVariable">The <tt>GlobalVariable</tt>
99 <li><a href="#Module">The <tt>Module</tt> class</a></li>
100 <li><a href="#Constant">The <tt>Constant</tt> class</a>
110 <li><a href="#Type">The <tt>Type</tt> class</a> </li>
111 <li><a href="#Argument">The <tt>Argument</tt> class</a> </li>
114 <li>The <tt>SymbolTable</tt> class </li>
115 <li>The <tt>ilist</tt> and <tt>iplist</tt> classes
117 <li>Creating, inserting, moving and deleting from LLVM lists </li>
120 <li>Important iterator invalidation semantics to be aware of </li>
125 <div class="doc_text">
126 <p><b>Written by <a href="mailto:sabre@nondot.org">Chris Lattner</a>,
127 <a href="mailto:dhurjati@cs.uiuc.edu">Dinakar Dhurjati</a>, and <a
128 href="mailto:jstanley@cs.uiuc.edu">Joel Stanley</a></b></p>
131 <!-- *********************************************************************** -->
132 <div class="doc_section">
133 <a name="introduction">Introduction </a>
135 <!-- *********************************************************************** -->
137 <div class="doc_text">
139 <p>This document is meant to highlight some of the important classes and
140 interfaces available in the LLVM source-base. This manual is not
141 intended to explain what LLVM is, how it works, and what LLVM code looks
142 like. It assumes that you know the basics of LLVM and are interested
143 in writing transformations or otherwise analyzing or manipulating the
146 <p>This document should get you oriented so that you can find your
147 way in the continuously growing source code that makes up the LLVM
148 infrastructure. Note that this manual is not intended to serve as a
149 replacement for reading the source code, so if you think there should be
150 a method in one of these classes to do something, but it's not listed,
151 check the source. Links to the <a href="/doxygen/">doxygen</a> sources
152 are provided to make this as easy as possible.</p>
154 <p>The first section of this document describes general information that is
155 useful to know when working in the LLVM infrastructure, and the second describes
156 the Core LLVM classes. In the future this manual will be extended with
157 information describing how to use extension libraries, such as dominator
158 information, CFG traversal routines, and useful utilities like the <tt><a
159 href="/doxygen/InstVisitor_8h-source.html">InstVisitor</a></tt> template.</p>
163 <!-- *********************************************************************** -->
164 <div class="doc_section">
165 <a name="general">General Information</a>
167 <!-- *********************************************************************** -->
169 <div class="doc_text">
171 <p>This section contains general information that is useful if you are working
172 in the LLVM source-base, but that isn't specific to any particular API.</p>
176 <!-- ======================================================================= -->
177 <div class="doc_subsection">
178 <a name="stl">The C++ Standard Template Library</a>
181 <div class="doc_text">
183 <p>LLVM makes heavy use of the C++ Standard Template Library (STL),
184 perhaps much more than you are used to, or have seen before. Because of
185 this, you might want to do a little background reading in the
186 techniques used and capabilities of the library. There are many good
187 pages that discuss the STL, and several books on the subject that you
188 can get, so it will not be discussed in this document.</p>
190 <p>Here are some useful links:</p>
194 <li><a href="http://www.dinkumware.com/refxcpp.html">Dinkumware C++ Library
195 reference</a> - an excellent reference for the STL and other parts of the
196 standard C++ library.</li>
198 <li><a href="http://www.tempest-sw.com/cpp/">C++ In a Nutshell</a> - This is an
199 O'Reilly book in the making. It has a decent <a
200 href="http://www.tempest-sw.com/cpp/ch13-libref.html">Standard Library
201 Reference</a> that rivals Dinkumware's, and is actually free until the book is
204 <li><a href="http://www.parashift.com/c++-faq-lite/">C++ Frequently Asked
207 <li><a href="http://www.sgi.com/tech/stl/">SGI's STL Programmer's Guide</a> -
209 href="http://www.sgi.com/tech/stl/stl_introduction.html">Introduction to the
212 <li><a href="http://www.research.att.com/%7Ebs/C++.html">Bjarne Stroustrup's C++
217 <p>You are also encouraged to take a look at the <a
218 href="CodingStandards.html">LLVM Coding Standards</a> guide which focuses on how
219 to write maintainable code more than where to put your curly braces.</p>
223 <!-- ======================================================================= -->
224 <div class="doc_subsection">
225 <a name="stl">Other useful references</a>
228 <div class="doc_text">
230 <p>LLVM is currently using CVS as its source versioning system. You may find
231 this reference handy:</p>
234 <li><a href="http://www.psc.edu/%7Esemke/cvs_branches.html">CVS
235 Branch and Tag Primer</a></li>
240 <!-- *********************************************************************** -->
241 <div class="doc_section">
242 <a name="apis">Important and useful LLVM APIs</a>
244 <!-- *********************************************************************** -->
246 <div class="doc_text">
248 <p>Here we highlight some LLVM APIs that are generally useful and good to
249 know about when writing transformations.</p>
253 <!-- ======================================================================= -->
254 <div class="doc_subsection">
255 <a name="isa">The isa<>, cast<> and dyn_cast<> templates</a>
258 <div class="doc_text">
260 <p>The LLVM source-base makes extensive use of a custom form of RTTI.
261 These templates have many similarities to the C++ <tt>dynamic_cast<></tt>
262 operator, but they don't have some drawbacks (primarily stemming from
263 the fact that <tt>dynamic_cast<></tt> only works on classes that
264 have a v-table). Because they are used so often, you must know what they
265 do and how they work. All of these templates are defined in the <a
266 href="/doxygen/Casting_8h-source.html"><tt>Support/Casting.h</tt></a>
267 file (note that you very rarely have to include this file directly).</p>
270 <dt><tt>isa<></tt>: </dt>
272 <dd>The <tt>isa<></tt> operator works exactly like the Java
273 "<tt>instanceof</tt>" operator. It returns true or false depending on whether
274 a reference or pointer points to an instance of the specified class. This can
275 be very useful for constraint checking of various sorts (example below).</dd>
277 <dt><tt>cast<></tt>: </dt>
279 <dd>The <tt>cast<></tt> operator is a "checked cast" operation. It
280 converts a pointer or reference from a base class to a derived cast, causing
281 an assertion failure if it is not really an instance of the right type. This
282 should be used in cases where you have some information that makes you believe
283 that something is of the right type. An example of the <tt>isa<></tt>
284 and <tt>cast<></tt> template is:
286 <pre>static bool isLoopInvariant(const <a href="#Value">Value</a> *V, const
287 Loop *L) {<br> if (isa<<a href="#Constant">Constant</a>>(V) || isa<<a
288 href="#Argument">Argument</a>>(V) || isa<<a
289 href="#GlobalValue">GlobalValue</a>>(V))<br> return true;<br><br> <i>//
290 Otherwise, it must be an instruction...</i><br> return
291 !L->contains(cast<<a
292 href="#Instruction">Instruction</a>>(V)->getParent());<br></pre>
294 <p>Note that you should <b>not</b> use an <tt>isa<></tt> test followed
295 by a <tt>cast<></tt>, for that use the <tt>dyn_cast<></tt>
300 <dt><tt>dyn_cast<></tt>:</dt>
302 <dd>The <tt>dyn_cast<></tt> operator is a "checking cast" operation. It
303 checks to see if the operand is of the specified type, and if so, returns a
304 pointer to it (this operator does not work with references). If the operand is
305 not of the correct type, a null pointer is returned. Thus, this works very
306 much like the <tt>dynamic_cast</tt> operator in C++, and should be used in the
307 same circumstances. Typically, the <tt>dyn_cast<></tt> operator is used
308 in an <tt>if</tt> statement or some other flow control statement like this:
310 <pre> if (<a href="#AllocationInst">AllocationInst</a> *AI = dyn_cast<<a
311 href="#AllocationInst">AllocationInst</a>>(Val)) {<br> ...<br> }<br></pre>
313 <p> This form of the <tt>if</tt> statement effectively combines together a
314 call to <tt>isa<></tt> and a call to <tt>cast<></tt> into one
315 statement, which is very convenient.</p>
317 <p> Another common example is:</p>
319 <pre> <i>// Loop over all of the phi nodes in a basic block</i><br>
320 BasicBlock::iterator BBI = BB->begin();<br> for (; <a
321 href="#PhiNode">PHINode</a> *PN = dyn_cast<<a
322 href="#PHINode">PHINode</a>>(BBI); ++BBI)<br> cerr << *PN;<br></pre>
324 <p>Note that the <tt>dyn_cast<></tt> operator, like C++'s
325 <tt>dynamic_cast</tt> or Java's <tt>instanceof</tt> operator, can be abused.
326 In particular you should not use big chained <tt>if/then/else</tt> blocks to
327 check for lots of different variants of classes. If you find yourself
328 wanting to do this, it is much cleaner and more efficient to use the
329 InstVisitor class to dispatch over the instruction type directly.</p>
333 <dt><tt>cast_or_null<></tt>: </dt>
335 <dd>The <tt>cast_or_null<></tt> operator works just like the
336 <tt>cast<></tt> operator, except that it allows for a null pointer as
337 an argument (which it then propagates). This can sometimes be useful,
338 allowing you to combine several null checks into one.</dd>
340 <dt><tt>dyn_cast_or_null<></tt>: </dt>
342 <dd>The <tt>dyn_cast_or_null<></tt> operator works just like the
343 <tt>dyn_cast<></tt> operator, except that it allows for a null pointer
344 as an argument (which it then propagates). This can sometimes be useful,
345 allowing you to combine several null checks into one.</dd>
349 <p>These five templates can be used with any classes, whether they have a
350 v-table or not. To add support for these templates, you simply need to add
351 <tt>classof</tt> static methods to the class you are interested casting
352 to. Describing this is currently outside the scope of this document, but there
353 are lots of examples in the LLVM source base.</p>
357 <!-- ======================================================================= -->
358 <div class="doc_subsection">
359 <a name="DEBUG">The <tt>DEBUG()</tt> macro & <tt>-debug</tt> option</a>
362 <div class="doc_text">
364 <p>Often when working on your pass you will put a bunch of debugging printouts
365 and other code into your pass. After you get it working, you want to remove
366 it... but you may need it again in the future (to work out new bugs that you run
369 <p> Naturally, because of this, you don't want to delete the debug printouts,
370 but you don't want them to always be noisy. A standard compromise is to comment
371 them out, allowing you to enable them if you need them in the future.</p>
373 <p>The "<tt><a href="/doxygen/Debug_8h-source.html">Support/Debug.h</a></tt>"
374 file provides a macro named <tt>DEBUG()</tt> that is a much nicer solution to
375 this problem. Basically, you can put arbitrary code into the argument of the
376 <tt>DEBUG</tt> macro, and it is only executed if '<tt>opt</tt>' (or any other
377 tool) is run with the '<tt>-debug</tt>' command line argument:</p>
379 <pre> ... <br> DEBUG(std::cerr << "I am here!\n");<br> ...<br></pre>
381 <p>Then you can run your pass like this:</p>
383 <pre> $ opt < a.bc > /dev/null -mypass<br> <no output><br> $ opt < a.bc > /dev/null -mypass -debug<br> I am here!<br> $<br></pre>
385 <p>Using the <tt>DEBUG()</tt> macro instead of a home-brewed solution allows you
386 to not have to create "yet another" command line option for the debug output for
387 your pass. Note that <tt>DEBUG()</tt> macros are disabled for optimized builds,
388 so they do not cause a performance impact at all (for the same reason, they
389 should also not contain side-effects!).</p>
391 <p>One additional nice thing about the <tt>DEBUG()</tt> macro is that you can
392 enable or disable it directly in gdb. Just use "<tt>set DebugFlag=0</tt>" or
393 "<tt>set DebugFlag=1</tt>" from the gdb if the program is running. If the
394 program hasn't been started yet, you can always just run it with
399 <!-- _______________________________________________________________________ -->
400 <div class="doc_subsubsection">
401 <a name="DEBUG_TYPE">Fine grained debug info with <tt>DEBUG_TYPE()</tt> and
402 the <tt>-debug-only</tt> option</a>
405 <div class="doc_text">
407 <p>Sometimes you may find yourself in a situation where enabling <tt>-debug</tt>
408 just turns on <b>too much</b> information (such as when working on the code
409 generator). If you want to enable debug information with more fine-grained
410 control, you define the <tt>DEBUG_TYPE</tt> macro and the <tt>-debug</tt> only
411 option as follows:</p>
413 <pre> ...<br> DEBUG(std::cerr << "No debug type\n");<br> #undef DEBUG_TYPE<br> #define DEBUG_TYPE "foo"<br> DEBUG(std::cerr << "'foo' debug type\n");<br> #undef DEBUG_TYPE<br> #define DEBUG_TYPE "bar"<br> DEBUG(std::cerr << "'bar' debug type\n");<br> #undef DEBUG_TYPE<br> #define DEBUG_TYPE ""<br> DEBUG(std::cerr << "No debug type (2)\n");<br> ...<br></pre>
415 <p>Then you can run your pass like this:</p>
417 <pre> $ opt < a.bc > /dev/null -mypass<br> <no output><br> $ opt < a.bc > /dev/null -mypass -debug<br> No debug type<br> 'foo' debug type<br> 'bar' debug type<br> No debug type (2)<br> $ opt < a.bc > /dev/null -mypass -debug-only=foo<br> 'foo' debug type<br> $ opt < a.bc > /dev/null -mypass -debug-only=bar<br> 'bar' debug type<br> $<br></pre>
419 <p>Of course, in practice, you should only set <tt>DEBUG_TYPE</tt> at the top of
420 a file, to specify the debug type for the entire module (if you do this before
421 you <tt>#include "Support/Debug.h"</tt>, you don't have to insert the ugly
422 <tt>#undef</tt>'s). Also, you should use names more meaningful than "foo" and
423 "bar", because there is no system in place to ensure that names do not
424 conflict. If two different modules use the same string, they will all be turned
425 on when the name is specified. This allows, for example, all debug information
426 for instruction scheduling to be enabled with <tt>-debug-type=InstrSched</tt>,
427 even if the source lives in multiple files.</p>
431 <!-- ======================================================================= -->
432 <div class="doc_subsection">
433 <a name="Statistic">The <tt>Statistic</tt> template & <tt>-stats</tt>
437 <div class="doc_text">
440 href="/doxygen/Statistic_8h-source.html">Support/Statistic.h</a></tt>" file
441 provides a template named <tt>Statistic</tt> that is used as a unified way to
442 keep track of what the LLVM compiler is doing and how effective various
443 optimizations are. It is useful to see what optimizations are contributing to
444 making a particular program run faster.</p>
446 <p>Often you may run your pass on some big program, and you're interested to see
447 how many times it makes a certain transformation. Although you can do this with
448 hand inspection, or some ad-hoc method, this is a real pain and not very useful
449 for big programs. Using the <tt>Statistic</tt> template makes it very easy to
450 keep track of this information, and the calculated information is presented in a
451 uniform manner with the rest of the passes being executed.</p>
453 <p>There are many examples of <tt>Statistic</tt> uses, but the basics of using
454 it are as follows:</p>
457 <li>Define your statistic like this:
458 <pre>static Statistic<> NumXForms("mypassname", "The # of times I did stuff");<br></pre>
460 <p>The <tt>Statistic</tt> template can emulate just about any data-type,
461 but if you do not specify a template argument, it defaults to acting like
462 an unsigned int counter (this is usually what you want).</p></li>
464 <li>Whenever you make a transformation, bump the counter:
465 <pre> ++NumXForms; // I did stuff<br></pre>
469 <p>That's all you have to do. To get '<tt>opt</tt>' to print out the
470 statistics gathered, use the '<tt>-stats</tt>' option:</p>
472 <pre> $ opt -stats -mypassname < program.bc > /dev/null<br> ... statistic output ...<br></pre>
474 <p> When running <tt>gccas</tt> on a C file from the SPEC benchmark
475 suite, it gives a report that looks like this:</p>
477 <pre> 7646 bytecodewriter - Number of normal instructions<br> 725 bytecodewriter - Number of oversized instructions<br> 129996 bytecodewriter - Number of bytecode bytes written<br> 2817 raise - Number of insts DCEd or constprop'd<br> 3213 raise - Number of cast-of-self removed<br> 5046 raise - Number of expression trees converted<br> 75 raise - Number of other getelementptr's formed<br> 138 raise - Number of load/store peepholes<br> 42 deadtypeelim - Number of unused typenames removed from symtab<br> 392 funcresolve - Number of varargs functions resolved<br> 27 globaldce - Number of global variables removed<br> 2 adce - Number of basic blocks removed<br> 134 cee - Number of branches revectored<br> 49 cee - Number of setcc instruction eliminated<br> 532 gcse - Number of loads removed<br> 2919 gcse - Number of instructions removed<br> 86 indvars - Number of canonical indvars added<br> 87 indvars - Number of aux indvars removed<br> 25 instcombine - Number of dead inst eliminate<br> 434 instcombine - Number of insts combined<br> 248 licm - Number of load insts hoisted<br> 1298 licm - Number of insts hoisted to a loop pre-header<br> 3 licm - Number of insts hoisted to multiple loop preds (bad, no loop pre-header)<br> 75 mem2reg - Number of alloca's promoted<br> 1444 cfgsimplify - Number of blocks simplified<br></pre>
479 <p>Obviously, with so many optimizations, having a unified framework for this
480 stuff is very nice. Making your pass fit well into the framework makes it more
481 maintainable and useful.</p>
485 <!-- *********************************************************************** -->
486 <div class="doc_section">
487 <a name="common">Helpful Hints for Common Operations</a>
489 <!-- *********************************************************************** -->
491 <div class="doc_text">
493 <p>This section describes how to perform some very simple transformations of
494 LLVM code. This is meant to give examples of common idioms used, showing the
495 practical side of LLVM transformations. <p> Because this is a "how-to" section,
496 you should also read about the main classes that you will be working with. The
497 <a href="#coreclasses">Core LLVM Class Hierarchy Reference</a> contains details
498 and descriptions of the main classes that you should know about.</p>
502 <!-- NOTE: this section should be heavy on example code -->
503 <!-- ======================================================================= -->
504 <div class="doc_subsection">
505 <a name="inspection">Basic Inspection and Traversal Routines</a>
508 <div class="doc_text">
510 <p>The LLVM compiler infrastructure have many different data structures that may
511 be traversed. Following the example of the C++ standard template library, the
512 techniques used to traverse these various data structures are all basically the
513 same. For a enumerable sequence of values, the <tt>XXXbegin()</tt> function (or
514 method) returns an iterator to the start of the sequence, the <tt>XXXend()</tt>
515 function returns an iterator pointing to one past the last valid element of the
516 sequence, and there is some <tt>XXXiterator</tt> data type that is common
517 between the two operations.</p>
519 <p>Because the pattern for iteration is common across many different aspects of
520 the program representation, the standard template library algorithms may be used
521 on them, and it is easier to remember how to iterate. First we show a few common
522 examples of the data structures that need to be traversed. Other data
523 structures are traversed in very similar ways.</p>
527 <!-- _______________________________________________________________________ -->
528 <div class="subsubsection">
529 <a name="iterate_function">Iterating over the </a><a
530 href="#BasicBlock"><tt>BasicBlock</tt></a>s in a <a
531 href="#Function"><tt>Function</tt></a>
534 <div class="doc_text">
536 <p>It's quite common to have a <tt>Function</tt> instance that you'd like to
537 transform in some way; in particular, you'd like to manipulate its
538 <tt>BasicBlock</tt>s. To facilitate this, you'll need to iterate over all of
539 the <tt>BasicBlock</tt>s that constitute the <tt>Function</tt>. The following is
540 an example that prints the name of a <tt>BasicBlock</tt> and the number of
541 <tt>Instruction</tt>s it contains:</p>
543 <pre> // func is a pointer to a Function instance<br> for (Function::iterator i = func->begin(), e = func->end(); i != e; ++i) {<br><br> // print out the name of the basic block if it has one, and then the<br> // number of instructions that it contains<br><br> cerr << "Basic block (name=" << i->getName() << ") has " <br> << i->size() << " instructions.\n";<br> }<br></pre>
545 <p>Note that i can be used as if it were a pointer for the purposes of
546 invoking member functions of the <tt>Instruction</tt> class. This is
547 because the indirection operator is overloaded for the iterator
548 classes. In the above code, the expression <tt>i->size()</tt> is
549 exactly equivalent to <tt>(*i).size()</tt> just like you'd expect.</p>
553 <!-- _______________________________________________________________________ -->
554 <div class="subsubsection">
555 <a name="iterate_basicblock">Iterating over the </a><a
556 href="#Instruction"><tt>Instruction</tt></a>s in a <a
557 href="#BasicBlock"><tt>BasicBlock</tt></a>
560 <div class="doc_text">
562 <p>Just like when dealing with <tt>BasicBlock</tt>s in <tt>Function</tt>s, it's
563 easy to iterate over the individual instructions that make up
564 <tt>BasicBlock</tt>s. Here's a code snippet that prints out each instruction in
565 a <tt>BasicBlock</tt>:</p>
567 <pre> // blk is a pointer to a BasicBlock instance<br> for (BasicBlock::iterator i = blk->begin(), e = blk->end(); i != e; ++i)<br> // the next statement works since operator<<(ostream&,...) <br> // is overloaded for Instruction&<br> cerr << *i << "\n";<br></pre>
569 <p>However, this isn't really the best way to print out the contents of a
570 <tt>BasicBlock</tt>! Since the ostream operators are overloaded for virtually
571 anything you'll care about, you could have just invoked the print routine on the
572 basic block itself: <tt>cerr << *blk << "\n";</tt>.</p>
574 <p>Note that currently operator<< is implemented for <tt>Value*</tt>, so
575 it will print out the contents of the pointer, instead of the pointer value you
576 might expect. This is a deprecated interface that will be removed in the
577 future, so it's best not to depend on it. To print out the pointer value for
578 now, you must cast to <tt>void*</tt>.</p>
582 <!-- _______________________________________________________________________ -->
583 <div class="subsubsection">
584 <a name="iterate_institer">Iterating over the </a><a
585 href="#Instruction"><tt>Instruction</tt></a>s in a <a
586 href="#Function"><tt>Function</tt></a>
589 <div class="doc_text">
591 <p>If you're finding that you commonly iterate over a <tt>Function</tt>'s
592 <tt>BasicBlock</tt>s and then that <tt>BasicBlock</tt>'s <tt>Instruction</tt>s,
593 <tt>InstIterator</tt> should be used instead. You'll need to include <a
594 href="/doxygen/InstIterator_8h-source.html"><tt>llvm/Support/InstIterator.h</tt></a>,
595 and then instantiate <tt>InstIterator</tt>s explicitly in your code. Here's a
596 small example that shows how to dump all instructions in a function to stderr
597 (<b>Note:</b> Dereferencing an <tt>InstIterator</tt> yields an
598 <tt>Instruction*</tt>, <i>not</i> an <tt>Instruction&</tt>!):</p>
600 <pre>#include "<a href="/doxygen/InstIterator_8h-source.html">llvm/Support/InstIterator.h</a>"<br>...<br>// Suppose F is a ptr to a function<br>for (inst_iterator i = inst_begin(F), e = inst_end(F); i != e; ++i)<br> cerr << **i << "\n";<br></pre>
601 Easy, isn't it? You can also use <tt>InstIterator</tt>s to fill a
602 worklist with its initial contents. For example, if you wanted to
603 initialize a worklist to contain all instructions in a <tt>Function</tt>
604 F, all you would need to do is something like:
605 <pre>std::set<Instruction*> worklist;<br>worklist.insert(inst_begin(F), inst_end(F));<br></pre>
607 <p>The STL set <tt>worklist</tt> would now contain all instructions in the
608 <tt>Function</tt> pointed to by F.</p>
612 <!-- _______________________________________________________________________ -->
613 <div class="doc_subsubsection">
614 <a name="iterate_convert">Turning an iterator into a class pointer (and
618 <div class="doc_text">
620 <p>Sometimes, it'll be useful to grab a reference (or pointer) to a class
621 instance when all you've got at hand is an iterator. Well, extracting
622 a reference or a pointer from an iterator is very straightforward.
623 Assuming that <tt>i</tt> is a <tt>BasicBlock::iterator</tt> and <tt>j</tt>
624 is a <tt>BasicBlock::const_iterator</tt>:</p>
626 <pre> Instruction& inst = *i; // grab reference to instruction reference<br> Instruction* pinst = &*i; // grab pointer to instruction reference<br> const Instruction& inst = *j;<br></pre>
628 <p>However, the iterators you'll be working with in the LLVM framework are
629 special: they will automatically convert to a ptr-to-instance type whenever they
630 need to. Instead of dereferencing the iterator and then taking the address of
631 the result, you can simply assign the iterator to the proper pointer type and
632 you get the dereference and address-of operation as a result of the assignment
633 (behind the scenes, this is a result of overloading casting mechanisms). Thus
634 the last line of the last example,</p>
636 <pre>Instruction* pinst = &*i;</pre>
638 <p>is semantically equivalent to</p>
640 <pre>Instruction* pinst = i;</pre>
642 <p>It's also possible to turn a class pointer into the corresponding iterator.
643 Usually, this conversion is quite inexpensive. The following code snippet
644 illustrates use of the conversion constructors provided by LLVM iterators. By
645 using these, you can explicitly grab the iterator of something without actually
646 obtaining it via iteration over some structure:</p>
648 <pre>void printNextInstruction(Instruction* inst) {<br> BasicBlock::iterator it(inst);<br> ++it; // after this line, it refers to the instruction after *inst.<br> if (it != inst->getParent()->end()) cerr << *it << "\n";<br>}<br></pre>
650 <p>Of course, this example is strictly pedagogical, because it'd be much
651 better to explicitly grab the next instruction directly from inst.</p>
655 <!--_______________________________________________________________________-->
656 <div class="doc_subsubsection">
657 <a name="iterate_complex">Finding call sites: a slightly more complex
661 <div class="doc_text">
663 <p>Say that you're writing a FunctionPass and would like to count all the
664 locations in the entire module (that is, across every <tt>Function</tt>) where a
665 certain function (i.e., some <tt>Function</tt>*) is already in scope. As you'll
666 learn later, you may want to use an <tt>InstVisitor</tt> to accomplish this in a
667 much more straightforward manner, but this example will allow us to explore how
668 you'd do it if you didn't have <tt>InstVisitor</tt> around. In pseudocode, this
669 is what we want to do:</p>
671 <pre>initialize callCounter to zero<br>for each Function f in the Module<br> for each BasicBlock b in f<br> for each Instruction i in b<br> if (i is a CallInst and calls the given function)<br> increment callCounter<br></pre>
673 <p>And the actual code is (remember, since we're writing a
674 <tt>FunctionPass</tt>, our <tt>FunctionPass</tt>-derived class simply has to
675 override the <tt>runOnFunction</tt> method...):</p>
677 <pre>Function* targetFunc = ...;<br><br>class OurFunctionPass : public FunctionPass {<br> public:<br> OurFunctionPass(): callCounter(0) { }<br><br> virtual runOnFunction(Function& F) {<br> for (Function::iterator b = F.begin(), be = F.end(); b != be; ++b) {<br> for (BasicBlock::iterator i = b->begin(); ie = b->end(); i != ie; ++i) {<br> if (<a
678 href="#CallInst">CallInst</a>* callInst = <a href="#isa">dyn_cast</a><<a
679 href="#CallInst">CallInst</a>>(&*i)) {<br> // we know we've encountered a call instruction, so we<br> // need to determine if it's a call to the<br> // function pointed to by m_func or not.<br> <br> if (callInst->getCalledFunction() == targetFunc)<br> ++callCounter;<br> }<br> }<br> }<br> <br> private:<br> unsigned callCounter;<br>};<br></pre>
683 <!--_______________________________________________________________________-->
684 <div class="doc_subsubsection">
685 <a name="calls_and_invokes">Treating calls and invokes the same way</a>
688 <div class="doc_text">
690 <p>You may have noticed that the previous example was a bit oversimplified in
691 that it did not deal with call sites generated by 'invoke' instructions. In
692 this, and in other situations, you may find that you want to treat
693 <tt>CallInst</tt>s and <tt>InvokeInst</tt>s the same way, even though their
694 most-specific common base class is <tt>Instruction</tt>, which includes lots of
695 less closely-related things. For these cases, LLVM provides a handy wrapper
697 href="http://llvm.cs.uiuc.edu/doxygen/classCallSite.html"><tt>CallSite
698 </tt></a>. It is essentially a wrapper around an <tt>Instruction</tt> pointer,
699 with some methods that provide functionality common to <tt>CallInst</tt>s and
700 <tt>InvokeInst</tt>s.</p>
702 <p>This class is supposed to have "value semantics". So it should be passed by
703 value, not by reference; it should not be dynamically allocated or deallocated
704 using <tt>operator new</tt> or <tt>operator delete</tt>. It is efficiently
705 copyable, assignable and constructable, with costs equivalents to that of a bare
706 pointer. (You will notice, if you look at its definition, that it has only a
707 single data member.)</p>
711 <!--_______________________________________________________________________-->
712 <div class="doc_subsubsection">
713 <a name="iterate_chains">Iterating over def-use & use-def chains</a>
716 <div class="doc_text">
718 <p>Frequently, we might have an instance of the <a
719 href="/doxygen/classValue.html">Value Class</a> and we want to determine which
720 <tt>User</tt>s use the <tt>Value</tt>. The list of all <tt>User</tt>s of a
721 particular <tt>Value</tt> is called a <i>def-use</i> chain. For example, let's
722 say we have a <tt>Function*</tt> named <tt>F</tt> to a particular function
723 <tt>foo</tt>. Finding all of the instructions that <i>use</i> <tt>foo</tt> is as
724 simple as iterating over the <i>def-use</i> chain of <tt>F</tt>:</p>
726 <pre>Function* F = ...;<br><br>for (Value::use_iterator i = F->use_begin(), e = F->use_end(); i != e; ++i) {<br> if (Instruction *Inst = dyn_cast<Instruction>(*i)) {<br> cerr << "F is used in instruction:\n";<br> cerr << *Inst << "\n";<br> }<br>}<br></pre>
728 <p>Alternately, it's common to have an instance of the <a
729 href="/doxygen/classUser.html">User Class</a> and need to know what
730 <tt>Value</tt>s are used by it. The list of all <tt>Value</tt>s used by a
731 <tt>User</tt> is known as a <i>use-def</i> chain. Instances of class
732 <tt>Instruction</tt> are common <tt>User</tt>s, so we might want to iterate over
733 all of the values that a particular instruction uses (that is, the operands of
734 the particular <tt>Instruction</tt>):</p>
736 <pre>Instruction* pi = ...;<br><br>for (User::op_iterator i = pi->op_begin(), e = pi->op_end(); i != e; ++i) {<br> Value* v = *i;<br> ...<br>}<br></pre>
739 def-use chains ("finding all users of"): Value::use_begin/use_end
740 use-def chains ("finding all values used"): User::op_begin/op_end [op=operand]
745 <!-- ======================================================================= -->
746 <div class="doc_subsection">
747 <a name="simplechanges">Making simple changes</a>
750 <div class="doc_text">
752 <p>There are some primitive transformation operations present in the LLVM
753 infrastructure that are worth knowing about. When performing
754 transformations, it's fairly common to manipulate the contents of basic
755 blocks. This section describes some of the common methods for doing so
756 and gives example code.</p>
760 <!--_______________________________________________________________________-->
761 <div class="doc_subsubsection">
762 <a name="schanges_creating">Creating and inserting new
763 <tt>Instruction</tt>s</a>
766 <div class="doc_text">
768 <p><i>Instantiating Instructions</i></p>
770 <p>Creation of <tt>Instruction</tt>s is straightforward: simply call the
771 constructor for the kind of instruction to instantiate and provide the necessary
772 parameters. For example, an <tt>AllocaInst</tt> only <i>requires</i> a
773 (const-ptr-to) <tt>Type</tt>. Thus:</p>
775 <pre>AllocaInst* ai = new AllocaInst(Type::IntTy);</pre>
777 <p>will create an <tt>AllocaInst</tt> instance that represents the allocation of
778 one integer in the current stack frame, at runtime. Each <tt>Instruction</tt>
779 subclass is likely to have varying default parameters which change the semantics
780 of the instruction, so refer to the <a
781 href="/doxygen/classInstruction.html">doxygen documentation for the subclass of
782 Instruction</a> that you're interested in instantiating.</p>
784 <p><i>Naming values</i></p>
786 <p>It is very useful to name the values of instructions when you're able to, as
787 this facilitates the debugging of your transformations. If you end up looking
788 at generated LLVM machine code, you definitely want to have logical names
789 associated with the results of instructions! By supplying a value for the
790 <tt>Name</tt> (default) parameter of the <tt>Instruction</tt> constructor, you
791 associate a logical name with the result of the instruction's execution at
792 runtime. For example, say that I'm writing a transformation that dynamically
793 allocates space for an integer on the stack, and that integer is going to be
794 used as some kind of index by some other code. To accomplish this, I place an
795 <tt>AllocaInst</tt> at the first point in the first <tt>BasicBlock</tt> of some
796 <tt>Function</tt>, and I'm intending to use it within the same
797 <tt>Function</tt>. I might do:</p>
799 <pre>AllocaInst* pa = new AllocaInst(Type::IntTy, 0, "indexLoc");</pre>
801 <p>where <tt>indexLoc</tt> is now the logical name of the instruction's
802 execution value, which is a pointer to an integer on the runtime stack.</p>
804 <p><i>Inserting instructions</i></p>
806 <p>There are essentially two ways to insert an <tt>Instruction</tt>
807 into an existing sequence of instructions that form a <tt>BasicBlock</tt>:</p>
810 <li>Insertion into an explicit instruction list
812 <p>Given a <tt>BasicBlock* pb</tt>, an <tt>Instruction* pi</tt> within that
813 <tt>BasicBlock</tt>, and a newly-created instruction we wish to insert
814 before <tt>*pi</tt>, we do the following: </p>
816 <pre> BasicBlock *pb = ...;<br> Instruction *pi = ...;<br> Instruction *newInst = new Instruction(...);<br> pb->getInstList().insert(pi, newInst); // inserts newInst before pi in pb<br></pre></li>
818 <li>Insertion into an implicit instruction list
820 <p><tt>Instruction</tt> instances that are already in <tt>BasicBlock</tt>s
821 are implicitly associated with an existing instruction list: the instruction
822 list of the enclosing basic block. Thus, we could have accomplished the same
823 thing as the above code without being given a <tt>BasicBlock</tt> by doing:
826 <pre> Instruction *pi = ...;<br> Instruction *newInst = new Instruction(...);<br> pi->getParent()->getInstList().insert(pi, newInst);<br></pre>
828 <p>In fact, this sequence of steps occurs so frequently that the
829 <tt>Instruction</tt> class and <tt>Instruction</tt>-derived classes provide
830 constructors which take (as a default parameter) a pointer to an
831 <tt>Instruction</tt> which the newly-created <tt>Instruction</tt> should
832 precede. That is, <tt>Instruction</tt> constructors are capable of
833 inserting the newly-created instance into the <tt>BasicBlock</tt> of a
834 provided instruction, immediately before that instruction. Using an
835 <tt>Instruction</tt> constructor with a <tt>insertBefore</tt> (default)
836 parameter, the above code becomes:</p>
838 <pre>Instruction* pi = ...;<br>Instruction* newInst = new Instruction(..., pi);<br></pre>
840 <p>which is much cleaner, especially if you're creating a lot of
841 instructions and adding them to <tt>BasicBlock</tt>s.</p></li>
846 <!--_______________________________________________________________________-->
847 <div class="doc_subsubsection">
848 <a name="schanges_deleting">Deleting <tt>Instruction</tt>s</a>
851 <div class="doc_text">
853 <p>Deleting an instruction from an existing sequence of instructions that form a
854 <a href="#BasicBlock"><tt>BasicBlock</tt></a> is very straightforward. First,
855 you must have a pointer to the instruction that you wish to delete. Second, you
856 need to obtain the pointer to that instruction's basic block. You use the
857 pointer to the basic block to get its list of instructions and then use the
858 erase function to remove your instruction. For example:</p>
860 <pre> <a href="#Instruction">Instruction</a> *I = .. ;<br> <a
861 href="#BasicBlock">BasicBlock</a> *BB = I->getParent();<br> BB->getInstList().erase(I);<br></pre>
865 <!--_______________________________________________________________________-->
866 <div class="doc_subsubsection">
867 <a name="schanges_replacing">Replacing an <tt>Instruction</tt> with another
871 <div class="doc_text">
873 <p><i>Replacing individual instructions</i></p>
875 <p>Including "<a href="/doxygen/BasicBlockUtils_8h-source.html">llvm/Transforms/Utils/BasicBlockUtils.h</a>"
876 permits use of two very useful replace functions: <tt>ReplaceInstWithValue</tt>
877 and <tt>ReplaceInstWithInst</tt>.</p>
879 <h4><a name="schanges_deleting">Deleting <tt>Instruction</tt>s</a></h4>
882 <li><tt>ReplaceInstWithValue</tt>
884 <p>This function replaces all uses (within a basic block) of a given
885 instruction with a value, and then removes the original instruction. The
886 following example illustrates the replacement of the result of a particular
887 <tt>AllocaInst</tt> that allocates memory for a single integer with an null
888 pointer to an integer.</p>
890 <pre>AllocaInst* instToReplace = ...;<br>BasicBlock::iterator ii(instToReplace);<br>ReplaceInstWithValue(instToReplace->getParent()->getInstList(), ii,<br> Constant::getNullValue(PointerType::get(Type::IntTy)));<br></pre></li>
892 <li><tt>ReplaceInstWithInst</tt>
894 <p>This function replaces a particular instruction with another
895 instruction. The following example illustrates the replacement of one
896 <tt>AllocaInst</tt> with another.</p>
898 <pre>AllocaInst* instToReplace = ...;<br>BasicBlock::iterator ii(instToReplace);<br>ReplaceInstWithInst(instToReplace->getParent()->getInstList(), ii,<br> new AllocaInst(Type::IntTy, 0, "ptrToReplacedInt"));<br></pre></li>
901 <p><i>Replacing multiple uses of <tt>User</tt>s and <tt>Value</tt>s</i></p>
903 <p>You can use <tt>Value::replaceAllUsesWith</tt> and
904 <tt>User::replaceUsesOfWith</tt> to change more than one use at a time. See the
905 doxygen documentation for the <a href="/doxygen/classValue.html">Value Class</a>
906 and <a href="/doxygen/classUser.html">User Class</a>, respectively, for more
909 <!-- Value::replaceAllUsesWith User::replaceUsesOfWith Point out:
910 include/llvm/Transforms/Utils/ especially BasicBlockUtils.h with:
911 ReplaceInstWithValue, ReplaceInstWithInst -->
915 <!-- *********************************************************************** -->
916 <div class="doc_section">
917 <a name="coreclasses">The Core LLVM Class Hierarchy Reference </a>
919 <!-- *********************************************************************** -->
921 <div class="doc_text">
923 <p>The Core LLVM classes are the primary means of representing the program
924 being inspected or transformed. The core LLVM classes are defined in
925 header files in the <tt>include/llvm/</tt> directory, and implemented in
926 the <tt>lib/VMCore</tt> directory.</p>
930 <!-- ======================================================================= -->
931 <div class="doc_subsection">
932 <a name="Value">The <tt>Value</tt> class</a>
937 <p><tt>#include "<a href="/doxygen/Value_8h-source.html">llvm/Value.h</a>"</tt>
939 doxygen info: <a href="/doxygen/classValue.html">Value Class</a></p>
941 <p>The <tt>Value</tt> class is the most important class in the LLVM Source
942 base. It represents a typed value that may be used (among other things) as an
943 operand to an instruction. There are many different types of <tt>Value</tt>s,
944 such as <a href="#Constant"><tt>Constant</tt></a>s,<a
945 href="#Argument"><tt>Argument</tt></a>s. Even <a
946 href="#Instruction"><tt>Instruction</tt></a>s and <a
947 href="#Function"><tt>Function</tt></a>s are <tt>Value</tt>s.</p>
949 <p>A particular <tt>Value</tt> may be used many times in the LLVM representation
950 for a program. For example, an incoming argument to a function (represented
951 with an instance of the <a href="#Argument">Argument</a> class) is "used" by
952 every instruction in the function that references the argument. To keep track
953 of this relationship, the <tt>Value</tt> class keeps a list of all of the <a
954 href="#User"><tt>User</tt></a>s that is using it (the <a
955 href="#User"><tt>User</tt></a> class is a base class for all nodes in the LLVM
956 graph that can refer to <tt>Value</tt>s). This use list is how LLVM represents
957 def-use information in the program, and is accessible through the <tt>use_</tt>*
958 methods, shown below.</p>
960 <p>Because LLVM is a typed representation, every LLVM <tt>Value</tt> is typed,
961 and this <a href="#Type">Type</a> is available through the <tt>getType()</tt>
962 method. In addition, all LLVM values can be named. The "name" of the
963 <tt>Value</tt> is a symbolic string printed in the LLVM code:</p>
965 <pre> %<b>foo</b> = add int 1, 2<br></pre>
967 <p><a name="#nameWarning">The name of this instruction is "foo".</a> <b>NOTE</b>
968 that the name of any value may be missing (an empty string), so names should
969 <b>ONLY</b> be used for debugging (making the source code easier to read,
970 debugging printouts), they should not be used to keep track of values or map
971 between them. For this purpose, use a <tt>std::map</tt> of pointers to the
972 <tt>Value</tt> itself instead.</p>
974 <p>One important aspect of LLVM is that there is no distinction between an SSA
975 variable and the operation that produces it. Because of this, any reference to
976 the value produced by an instruction (or the value available as an incoming
977 argument, for example) is represented as a direct pointer to the instance of
979 represents this value. Although this may take some getting used to, it
980 simplifies the representation and makes it easier to manipulate.</p>
984 <!-- _______________________________________________________________________ -->
985 <div class="doc_subsubsection">
986 <a name="m_Value">Important Public Members of the <tt>Value</tt> class</a>
989 <div class="doc_text">
992 <li><tt>Value::use_iterator</tt> - Typedef for iterator over the
994 <tt>Value::use_const_iterator</tt> - Typedef for const_iterator over
996 <tt>unsigned use_size()</tt> - Returns the number of users of the
998 <tt>bool use_empty()</tt> - Returns true if there are no users.<br>
999 <tt>use_iterator use_begin()</tt> - Get an iterator to the start of
1001 <tt>use_iterator use_end()</tt> - Get an iterator to the end of the
1003 <tt><a href="#User">User</a> *use_back()</tt> - Returns the last
1004 element in the list.
1005 <p> These methods are the interface to access the def-use
1006 information in LLVM. As with all other iterators in LLVM, the naming
1007 conventions follow the conventions defined by the <a href="#stl">STL</a>.</p>
1009 <li><tt><a href="#Type">Type</a> *getType() const</tt>
1010 <p>This method returns the Type of the Value.</p>
1012 <li><tt>bool hasName() const</tt><br>
1013 <tt>std::string getName() const</tt><br>
1014 <tt>void setName(const std::string &Name)</tt>
1015 <p> This family of methods is used to access and assign a name to a <tt>Value</tt>,
1016 be aware of the <a href="#nameWarning">precaution above</a>.</p>
1018 <li><tt>void replaceAllUsesWith(Value *V)</tt>
1020 <p>This method traverses the use list of a <tt>Value</tt> changing all <a
1021 href="#User"><tt>User</tt>s</a> of the current value to refer to
1022 "<tt>V</tt>" instead. For example, if you detect that an instruction always
1023 produces a constant value (for example through constant folding), you can
1024 replace all uses of the instruction with the constant like this:</p>
1026 <pre> Inst->replaceAllUsesWith(ConstVal);<br></pre>
1031 <!-- ======================================================================= -->
1032 <div class="doc_subsection">
1033 <a name="User">The <tt>User</tt> class</a>
1036 <div class="doc_text">
1039 <tt>#include "<a href="/doxygen/User_8h-source.html">llvm/User.h</a>"</tt><br>
1040 doxygen info: <a href="/doxygen/classUser.html">User Class</a><br>
1041 Superclass: <a href="#Value"><tt>Value</tt></a></p>
1043 <p>The <tt>User</tt> class is the common base class of all LLVM nodes that may
1044 refer to <a href="#Value"><tt>Value</tt></a>s. It exposes a list of "Operands"
1045 that are all of the <a href="#Value"><tt>Value</tt></a>s that the User is
1046 referring to. The <tt>User</tt> class itself is a subclass of
1049 <p>The operands of a <tt>User</tt> point directly to the LLVM <a
1050 href="#Value"><tt>Value</tt></a> that it refers to. Because LLVM uses Static
1051 Single Assignment (SSA) form, there can only be one definition referred to,
1052 allowing this direct connection. This connection provides the use-def
1053 information in LLVM.</p>
1057 <!-- _______________________________________________________________________ -->
1058 <div class="doc_subsubsection">
1059 <a name="m_User">Important Public Members of the <tt>User</tt> class</a>
1062 <div class="doc_text">
1064 <p>The <tt>User</tt> class exposes the operand list in two ways: through
1065 an index access interface and through an iterator based interface.</p>
1068 <li><tt>Value *getOperand(unsigned i)</tt><br>
1069 <tt>unsigned getNumOperands()</tt>
1070 <p> These two methods expose the operands of the <tt>User</tt> in a
1071 convenient form for direct access.</p></li>
1073 <li><tt>User::op_iterator</tt> - Typedef for iterator over the operand
1075 <tt>User::op_const_iterator</tt> <tt>use_iterator op_begin()</tt> -
1076 Get an iterator to the start of the operand list.<br>
1077 <tt>use_iterator op_end()</tt> - Get an iterator to the end of the
1079 <p> Together, these methods make up the iterator based interface to
1080 the operands of a <tt>User</tt>.</p></li>
1085 <!-- ======================================================================= -->
1086 <div class="doc_subsection">
1087 <a name="Instruction">The <tt>Instruction</tt> class</a>
1090 <div class="doc_text">
1092 <p><tt>#include "</tt><tt><a
1093 href="/doxygen/Instruction_8h-source.html">llvm/Instruction.h</a>"</tt><br>
1094 doxygen info: <a href="/doxygen/classInstruction.html">Instruction Class</a><br>
1095 Superclasses: <a href="#User"><tt>User</tt></a>, <a
1096 href="#Value"><tt>Value</tt></a></p>
1098 <p>The <tt>Instruction</tt> class is the common base class for all LLVM
1099 instructions. It provides only a few methods, but is a very commonly used
1100 class. The primary data tracked by the <tt>Instruction</tt> class itself is the
1101 opcode (instruction type) and the parent <a
1102 href="#BasicBlock"><tt>BasicBlock</tt></a> the <tt>Instruction</tt> is embedded
1103 into. To represent a specific type of instruction, one of many subclasses of
1104 <tt>Instruction</tt> are used.</p>
1106 <p> Because the <tt>Instruction</tt> class subclasses the <a
1107 href="#User"><tt>User</tt></a> class, its operands can be accessed in the same
1108 way as for other <a href="#User"><tt>User</tt></a>s (with the
1109 <tt>getOperand()</tt>/<tt>getNumOperands()</tt> and
1110 <tt>op_begin()</tt>/<tt>op_end()</tt> methods).</p> <p> An important file for
1111 the <tt>Instruction</tt> class is the <tt>llvm/Instruction.def</tt> file. This
1112 file contains some meta-data about the various different types of instructions
1113 in LLVM. It describes the enum values that are used as opcodes (for example
1114 <tt>Instruction::Add</tt> and <tt>Instruction::SetLE</tt>), as well as the
1115 concrete sub-classes of <tt>Instruction</tt> that implement the instruction (for
1116 example <tt><a href="#BinaryOperator">BinaryOperator</a></tt> and <tt><a
1117 href="#SetCondInst">SetCondInst</a></tt>). Unfortunately, the use of macros in
1118 this file confuses doxygen, so these enum values don't show up correctly in the
1119 <a href="/doxygen/classInstruction.html">doxygen output</a>.</p>
1123 <!-- _______________________________________________________________________ -->
1124 <div class="doc_subsubsection">
1125 <a name="m_Instruction">Important Public Members of the <tt>Instruction</tt>
1129 <div class="doc_text">
1132 <li><tt><a href="#BasicBlock">BasicBlock</a> *getParent()</tt>
1133 <p>Returns the <a href="#BasicBlock"><tt>BasicBlock</tt></a> that
1134 this <tt>Instruction</tt> is embedded into.</p></li>
1135 <li><tt>bool mayWriteToMemory()</tt>
1136 <p>Returns true if the instruction writes to memory, i.e. it is a
1137 <tt>call</tt>,<tt>free</tt>,<tt>invoke</tt>, or <tt>store</tt>.</p></li>
1138 <li><tt>unsigned getOpcode()</tt>
1139 <p>Returns the opcode for the <tt>Instruction</tt>.</p></li>
1140 <li><tt><a href="#Instruction">Instruction</a> *clone() const</tt>
1141 <p>Returns another instance of the specified instruction, identical
1142 in all ways to the original except that the instruction has no parent
1143 (ie it's not embedded into a <a href="#BasicBlock"><tt>BasicBlock</tt></a>),
1144 and it has no name</p></li>
1149 <!-- ======================================================================= -->
1150 <div class="doc_subsection">
1151 <a name="BasicBlock">The <tt>BasicBlock</tt> class</a>
1154 <div class="doc_text">
1156 <p><tt>#include "<a href="/doxygen/BasicBlock_8h-source.html">llvm/BasicBlock.h</a>"</tt><br>
1157 doxygen info: <a href="/doxygen/classBasicBlock.html">BasicBlock Class</a><br>
1158 Superclass: <a href="#Value"><tt>Value</tt></a></p>
1160 <p>This class represents a single entry multiple exit section of the code,
1161 commonly known as a basic block by the compiler community. The
1162 <tt>BasicBlock</tt> class maintains a list of <a
1163 href="#Instruction"><tt>Instruction</tt></a>s, which form the body of the block.
1164 Matching the language definition, the last element of this list of instructions
1165 is always a terminator instruction (a subclass of the <a
1166 href="#TerminatorInst"><tt>TerminatorInst</tt></a> class).</p>
1168 <p>In addition to tracking the list of instructions that make up the block, the
1169 <tt>BasicBlock</tt> class also keeps track of the <a
1170 href="#Function"><tt>Function</tt></a> that it is embedded into.</p>
1172 <p>Note that <tt>BasicBlock</tt>s themselves are <a
1173 href="#Value"><tt>Value</tt></a>s, because they are referenced by instructions
1174 like branches and can go in the switch tables. <tt>BasicBlock</tt>s have type
1179 <!-- _______________________________________________________________________ -->
1180 <div class="doc_subsubsection">
1181 <a name="m_BasicBlock">Important Public Members of the <tt>BasicBlock</tt>
1185 <div class="doc_text">
1188 <li><tt>BasicBlock(const std::string &Name = "", </tt><tt><a
1189 href="#Function">Function</a> *Parent = 0)</tt>
1190 <p>The <tt>BasicBlock</tt> constructor is used to create new basic
1191 blocks for insertion into a function. The constructor optionally takes
1192 a name for the new block, and a <a href="#Function"><tt>Function</tt></a>
1193 to insert it into. If the <tt>Parent</tt> parameter is specified, the
1194 new <tt>BasicBlock</tt> is automatically inserted at the end of the
1195 specified <a href="#Function"><tt>Function</tt></a>, if not specified,
1196 the BasicBlock must be manually inserted into the <a href="#Function"><tt>Function</tt></a>.</p>
1198 <li><tt>BasicBlock::iterator</tt> - Typedef for instruction list
1200 <tt>BasicBlock::const_iterator</tt> - Typedef for const_iterator.<br>
1201 <tt>begin()</tt>, <tt>end()</tt>, <tt>front()</tt>, <tt>back()</tt>,<tt>size()</tt>,<tt>empty()</tt>,<tt>rbegin()</tt>,<tt>rend()
1202 - </tt>STL style functions for accessing the instruction list.
1203 <p> These methods and typedefs are forwarding functions that have
1204 the same semantics as the standard library methods of the same names.
1205 These methods expose the underlying instruction list of a basic block in
1206 a way that is easy to manipulate. To get the full complement of
1207 container operations (including operations to update the list), you must
1208 use the <tt>getInstList()</tt> method.</p></li>
1209 <li><tt>BasicBlock::InstListType &getInstList()</tt>
1210 <p> This method is used to get access to the underlying container
1211 that actually holds the Instructions. This method must be used when
1212 there isn't a forwarding function in the <tt>BasicBlock</tt> class for
1213 the operation that you would like to perform. Because there are no
1214 forwarding functions for "updating" operations, you need to use this if
1215 you want to update the contents of a <tt>BasicBlock</tt>.</p></li>
1216 <li><tt><a href="#Function">Function</a> *getParent()</tt>
1217 <p> Returns a pointer to <a href="#Function"><tt>Function</tt></a>
1218 the block is embedded into, or a null pointer if it is homeless.</p></li>
1219 <li><tt><a href="#TerminatorInst">TerminatorInst</a> *getTerminator()</tt>
1220 <p> Returns a pointer to the terminator instruction that appears at
1221 the end of the <tt>BasicBlock</tt>. If there is no terminator
1222 instruction, or if the last instruction in the block is not a
1223 terminator, then a null pointer is returned.</p></li>
1228 <!-- ======================================================================= -->
1229 <div class="doc_subsection">
1230 <a name="GlobalValue">The <tt>GlobalValue</tt> class</a>
1233 <div class="doc_text">
1236 href="/doxygen/GlobalValue_8h-source.html">llvm/GlobalValue.h</a>"</tt><br>
1237 doxygen info: <a href="/doxygen/classGlobalValue.html">GlobalValue Class</a><br>
1238 Superclasses: <a href="#User"><tt>User</tt></a>, <a
1239 href="#Value"><tt>Value</tt></a></p>
1241 <p>Global values (<a href="#GlobalVariable"><tt>GlobalVariable</tt></a>s or <a
1242 href="#Function"><tt>Function</tt></a>s) are the only LLVM values that are
1243 visible in the bodies of all <a href="#Function"><tt>Function</tt></a>s.
1244 Because they are visible at global scope, they are also subject to linking with
1245 other globals defined in different translation units. To control the linking
1246 process, <tt>GlobalValue</tt>s know their linkage rules. Specifically,
1247 <tt>GlobalValue</tt>s know whether they have internal or external linkage, as
1248 defined by the <tt>LinkageTypes</tt> enumerator.</p>
1250 <p>If a <tt>GlobalValue</tt> has internal linkage (equivalent to being
1251 <tt>static</tt> in C), it is not visible to code outside the current translation
1252 unit, and does not participate in linking. If it has external linkage, it is
1253 visible to external code, and does participate in linking. In addition to
1254 linkage information, <tt>GlobalValue</tt>s keep track of which <a
1255 href="#Module"><tt>Module</tt></a> they are currently part of.</p>
1257 <p>Because <tt>GlobalValue</tt>s are memory objects, they are always referred to
1258 by their <b>address</b>. As such, the <a href="#Type"><tt>Type</tt></a> of a
1259 global is always a pointer to its contents. It is important to remember this
1260 when using the <tt>GetElementPtrInst</tt> instruction because this pointer must
1261 be dereferenced first. For example, if you have a <tt>GlobalVariable</tt> (a
1262 subclass of <tt>GlobalValue)</tt> that is an array of 24 ints, type <tt>[24 x
1263 int]</tt>, then the <tt>GlobalVariable</tt> is a pointer to that array. Although
1264 the address of the first element of this array and the value of the
1265 <tt>GlobalVariable</tt> are the same, they have different types. The
1266 <tt>GlobalVariable</tt>'s type is <tt>[24 x int]</tt>. The first element's type
1267 is <tt>int.</tt> Because of this, accessing a global value requires you to
1268 dereference the pointer with <tt>GetElementPtrInst</tt> first, then its elements
1269 can be accessed. This is explained in the <a href="LangRef.html#globalvars">LLVM
1270 Language Reference Manual</a>.</p>
1274 <!-- _______________________________________________________________________ -->
1275 <div class="doc_subsubsection">
1276 <a name="m_GlobalValue">Important Public Members of the <tt>GlobalValue</tt>
1280 <div class="doc_text">
1283 <li><tt>bool hasInternalLinkage() const</tt><br>
1284 <tt>bool hasExternalLinkage() const</tt><br>
1285 <tt>void setInternalLinkage(bool HasInternalLinkage)</tt>
1286 <p> These methods manipulate the linkage characteristics of the <tt>GlobalValue</tt>.</p>
1289 <li><tt><a href="#Module">Module</a> *getParent()</tt>
1290 <p> This returns the <a href="#Module"><tt>Module</tt></a> that the
1291 GlobalValue is currently embedded into.</p></li>
1296 <!-- ======================================================================= -->
1297 <div class="doc_subsection">
1298 <a name="Function">The <tt>Function</tt> class</a>
1301 <div class="doc_text">
1304 href="/doxygen/Function_8h-source.html">llvm/Function.h</a>"</tt><br> doxygen
1305 info: <a href="/doxygen/classFunction.html">Function Class</a><br> Superclasses:
1306 <a href="#GlobalValue"><tt>GlobalValue</tt></a>, <a
1307 href="#User"><tt>User</tt></a>, <a href="#Value"><tt>Value</tt></a></p>
1309 <p>The <tt>Function</tt> class represents a single procedure in LLVM. It is
1310 actually one of the more complex classes in the LLVM heirarchy because it must
1311 keep track of a large amount of data. The <tt>Function</tt> class keeps track
1312 of a list of <a href="#BasicBlock"><tt>BasicBlock</tt></a>s, a list of formal <a
1313 href="#Argument"><tt>Argument</tt></a>s, and a <a
1314 href="#SymbolTable"><tt>SymbolTable</tt></a>.</p>
1316 <p>The list of <a href="#BasicBlock"><tt>BasicBlock</tt></a>s is the most
1317 commonly used part of <tt>Function</tt> objects. The list imposes an implicit
1318 ordering of the blocks in the function, which indicate how the code will be
1319 layed out by the backend. Additionally, the first <a
1320 href="#BasicBlock"><tt>BasicBlock</tt></a> is the implicit entry node for the
1321 <tt>Function</tt>. It is not legal in LLVM to explicitly branch to this initial
1322 block. There are no implicit exit nodes, and in fact there may be multiple exit
1323 nodes from a single <tt>Function</tt>. If the <a
1324 href="#BasicBlock"><tt>BasicBlock</tt></a> list is empty, this indicates that
1325 the <tt>Function</tt> is actually a function declaration: the actual body of the
1326 function hasn't been linked in yet.</p>
1328 <p>In addition to a list of <a href="#BasicBlock"><tt>BasicBlock</tt></a>s, the
1329 <tt>Function</tt> class also keeps track of the list of formal <a
1330 href="#Argument"><tt>Argument</tt></a>s that the function receives. This
1331 container manages the lifetime of the <a href="#Argument"><tt>Argument</tt></a>
1332 nodes, just like the <a href="#BasicBlock"><tt>BasicBlock</tt></a> list does for
1333 the <a href="#BasicBlock"><tt>BasicBlock</tt></a>s.</p>
1335 <p>The <a href="#SymbolTable"><tt>SymbolTable</tt></a> is a very rarely used
1336 LLVM feature that is only used when you have to look up a value by name. Aside
1337 from that, the <a href="#SymbolTable"><tt>SymbolTable</tt></a> is used
1338 internally to make sure that there are not conflicts between the names of <a
1339 href="#Instruction"><tt>Instruction</tt></a>s, <a
1340 href="#BasicBlock"><tt>BasicBlock</tt></a>s, or <a
1341 href="#Argument"><tt>Argument</tt></a>s in the function body.</p>
1345 <!-- _______________________________________________________________________ -->
1346 <div class="doc_subsubsection">
1347 <a name="m_Function">Important Public Members of the <tt>Function</tt>
1351 <div class="doc_text">
1354 <li><tt>Function(const </tt><tt><a href="#FunctionType">FunctionType</a>
1355 *Ty, bool isInternal, const std::string &N = "", Module* Parent = 0)</tt>
1357 <p>Constructor used when you need to create new <tt>Function</tt>s to add
1358 the the program. The constructor must specify the type of the function to
1359 create and whether or not it should start out with internal or external
1360 linkage. The <a href="#FunctionType"><tt>FunctionType</tt></a> argument
1361 specifies the formal arguments and return value for the function. The same
1362 <a href="#FunctionTypel"><tt>FunctionType</tt></a> value can be used to
1363 create multiple functions. The <tt>Parent</tt> argument specifies the Module
1364 in which the function is defined. If this argument is provided, the function
1365 will automatically be inserted into that module's list of
1368 <li><tt>bool isExternal()</tt>
1370 <p>Return whether or not the <tt>Function</tt> has a body defined. If the
1371 function is "external", it does not have a body, and thus must be resolved
1372 by linking with a function defined in a different translation unit.</p></li>
1374 <li><tt>Function::iterator</tt> - Typedef for basic block list iterator<br>
1375 <tt>Function::const_iterator</tt> - Typedef for const_iterator.<br>
1377 <tt>begin()</tt>, <tt>end()</tt>, <tt>front()</tt>, <tt>back()</tt>,
1378 <tt>size()</tt>, <tt>empty()</tt>, <tt>rbegin()</tt>, <tt>rend()</tt>
1380 <p>These are forwarding methods that make it easy to access the contents of
1381 a <tt>Function</tt> object's <a href="#BasicBlock"><tt>BasicBlock</tt></a>
1384 <li><tt>Function::BasicBlockListType &getBasicBlockList()</tt>
1386 <p>Returns the list of <a href="#BasicBlock"><tt>BasicBlock</tt></a>s. This
1387 is necessary to use when you need to update the list or perform a complex
1388 action that doesn't have a forwarding method.</p></li>
1390 <li><tt>Function::aiterator</tt> - Typedef for the argument list
1392 <tt>Function::const_aiterator</tt> - Typedef for const_iterator.<br>
1394 <tt>abegin()</tt>, <tt>aend()</tt>, <tt>afront()</tt>, <tt>aback()</tt>,
1395 <tt>asize()</tt>, <tt>aempty()</tt>, <tt>arbegin()</tt>, <tt>arend()</tt>
1397 <p>These are forwarding methods that make it easy to access the contents of
1398 a <tt>Function</tt> object's <a href="#Argument"><tt>Argument</tt></a>
1401 <li><tt>Function::ArgumentListType &getArgumentList()</tt>
1403 <p>Returns the list of <a href="#Argument"><tt>Argument</tt></a>s. This is
1404 necessary to use when you need to update the list or perform a complex
1405 action that doesn't have a forwarding method.</p></li>
1407 <li><tt><a href="#BasicBlock">BasicBlock</a> &getEntryBlock()</tt>
1409 <p>Returns the entry <a href="#BasicBlock"><tt>BasicBlock</tt></a> for the
1410 function. Because the entry block for the function is always the first
1411 block, this returns the first block of the <tt>Function</tt>.</p></li>
1413 <li><tt><a href="#Type">Type</a> *getReturnType()</tt><br>
1414 <tt><a href="#FunctionType">FunctionType</a> *getFunctionType()</tt>
1416 <p>This traverses the <a href="#Type"><tt>Type</tt></a> of the
1417 <tt>Function</tt> and returns the return type of the function, or the <a
1418 href="#FunctionType"><tt>FunctionType</tt></a> of the actual
1421 <li><tt><a href="#SymbolTable">SymbolTable</a> *getSymbolTable()</tt>
1423 <p> Return a pointer to the <a href="#SymbolTable"><tt>SymbolTable</tt></a>
1424 for this <tt>Function</tt>.</p></li>
1429 <!-- ======================================================================= -->
1430 <div class="doc_subsection">
1431 <a name="GlobalVariable">The <tt>GlobalVariable</tt> class</a>
1434 <div class="doc_text">
1437 href="/doxygen/GlobalVariable_8h-source.html">llvm/GlobalVariable.h</a>"</tt>
1439 doxygen info: <a href="/doxygen/classGlobalVariable.html">GlobalVariable
1440 Class</a><br> Superclasses: <a href="#GlobalValue"><tt>GlobalValue</tt></a>, <a
1441 href="#User"><tt>User</tt></a>, <a href="#Value"><tt>Value</tt></a></p>
1443 <p>Global variables are represented with the (suprise suprise)
1444 <tt>GlobalVariable</tt> class. Like functions, <tt>GlobalVariable</tt>s are also
1445 subclasses of <a href="#GlobalValue"><tt>GlobalValue</tt></a>, and as such are
1446 always referenced by their address (global values must live in memory, so their
1447 "name" refers to their address). See <a
1448 href="#GlobalValue"><tt>GlobalValue</tt></a> for more on this. Global variables
1449 may have an initial value (which must be a <a
1450 href="#Constant"><tt>Constant</tt></a>), and if they have an initializer, they
1451 may be marked as "constant" themselves (indicating that their contents never
1452 change at runtime).</p>
1456 <!-- _______________________________________________________________________ -->
1457 <div class="doc_subsubsection">
1458 <a name="m_GlobalVariable">Important Public Members of the
1459 <tt>GlobalVariable</tt> class</a>
1462 <div class="doc_text">
1465 <li><tt>GlobalVariable(const </tt><tt><a href="#Type">Type</a> *Ty, bool
1466 isConstant, LinkageTypes& Linkage, <a href="#Constant">Constant</a>
1467 *Initializer = 0, const std::string &Name = "", Module* Parent = 0)</tt>
1469 <p>Create a new global variable of the specified type. If
1470 <tt>isConstant</tt> is true then the global variable will be marked as
1471 unchanging for the program. The Linkage parameter specifies the type of
1472 linkage (internal, external, weak, linkonce, appending) for the variable. If
1473 the linkage is InternalLinkage, WeakLinkage, or LinkOnceLinkage, then
1474 the resultant global variable will have internal linkage. AppendingLinkage
1475 concatenates together all instances (in different translation units) of the
1476 variable into a single variable but is only applicable to arrays. See
1477 the <a href="LangRef.html#modulestructure">LLVM Language Reference</a> for
1478 further details on linkage types. Optionally an initializer, a name, and the
1479 module to put the variable into may be specified for the global variable as
1482 <li><tt>bool isConstant() const</tt>
1484 <p>Returns true if this is a global variable that is known not to
1485 be modified at runtime.</p></li>
1487 <li><tt>bool hasInitializer()</tt>
1489 <p>Returns true if this <tt>GlobalVariable</tt> has an intializer.</p></li>
1491 <li><tt><a href="#Constant">Constant</a> *getInitializer()</tt>
1493 <p>Returns the intial value for a <tt>GlobalVariable</tt>. It is not legal
1494 to call this method if there is no initializer.</p></li>
1499 <!-- ======================================================================= -->
1500 <div class="doc_subsection">
1501 <a name="Module">The <tt>Module</tt> class</a>
1504 <div class="doc_text">
1507 href="/doxygen/Module_8h-source.html">llvm/Module.h</a>"</tt><br> doxygen info:
1508 <a href="/doxygen/classModule.html">Module Class</a></p>
1510 <p>The <tt>Module</tt> class represents the top level structure present in LLVM
1511 programs. An LLVM module is effectively either a translation unit of the
1512 original program or a combination of several translation units merged by the
1513 linker. The <tt>Module</tt> class keeps track of a list of <a
1514 href="#Function"><tt>Function</tt></a>s, a list of <a
1515 href="#GlobalVariable"><tt>GlobalVariable</tt></a>s, and a <a
1516 href="#SymbolTable"><tt>SymbolTable</tt></a>. Additionally, it contains a few
1517 helpful member functions that try to make common operations easy.</p>
1521 <!-- _______________________________________________________________________ -->
1522 <div class="doc_subsubsection">
1523 <a name="m_Module">Important Public Members of the <tt>Module</tt> class</a>
1526 <div class="doc_text">
1529 <li><tt>Module::Module(std::string name = "")</tt></li>
1532 <p>Constructing a <a href="#Module">Module</a> is easy. You can optionally
1533 provide a name for it (probably based on the name of the translation unit).</p>
1536 <li><tt>Module::iterator</tt> - Typedef for function list iterator<br>
1537 <tt>Module::const_iterator</tt> - Typedef for const_iterator.<br>
1539 <tt>begin()</tt>, <tt>end()</tt>, <tt>front()</tt>, <tt>back()</tt>,
1540 <tt>size()</tt>, <tt>empty()</tt>, <tt>rbegin()</tt>, <tt>rend()</tt>
1542 <p>These are forwarding methods that make it easy to access the contents of
1543 a <tt>Module</tt> object's <a href="#Function"><tt>Function</tt></a>
1546 <li><tt>Module::FunctionListType &getFunctionList()</tt>
1548 <p> Returns the list of <a href="#Function"><tt>Function</tt></a>s. This is
1549 necessary to use when you need to update the list or perform a complex
1550 action that doesn't have a forwarding method.</p>
1552 <p><!-- Global Variable --></p></li>
1558 <li><tt>Module::giterator</tt> - Typedef for global variable list iterator<br>
1560 <tt>Module::const_giterator</tt> - Typedef for const_iterator.<br>
1562 <tt>gbegin()</tt>, <tt>gend()</tt>, <tt>gfront()</tt>, <tt>gback()</tt>,
1563 <tt>gsize()</tt>, <tt>gempty()</tt>, <tt>grbegin()</tt>, <tt>grend()</tt>
1565 <p> These are forwarding methods that make it easy to access the contents of
1566 a <tt>Module</tt> object's <a
1567 href="#GlobalVariable"><tt>GlobalVariable</tt></a> list.</p></li>
1569 <li><tt>Module::GlobalListType &getGlobalList()</tt>
1571 <p>Returns the list of <a
1572 href="#GlobalVariable"><tt>GlobalVariable</tt></a>s. This is necessary to
1573 use when you need to update the list or perform a complex action that
1574 doesn't have a forwarding method.</p>
1576 <p><!-- Symbol table stuff --> </p></li>
1582 <li><tt><a href="#SymbolTable">SymbolTable</a> *getSymbolTable()</tt>
1584 <p>Return a reference to the <a href="#SymbolTable"><tt>SymbolTable</tt></a>
1585 for this <tt>Module</tt>.</p>
1587 <p><!-- Convenience methods --></p></li>
1593 <li><tt><a href="#Function">Function</a> *getFunction(const std::string
1594 &Name, const <a href="#FunctionType">FunctionType</a> *Ty)</tt>
1596 <p>Look up the specified function in the <tt>Module</tt> <a
1597 href="#SymbolTable"><tt>SymbolTable</tt></a>. If it does not exist, return
1598 <tt>null</tt>.</p></li>
1600 <li><tt><a href="#Function">Function</a> *getOrInsertFunction(const
1601 std::string &Name, const <a href="#FunctionType">FunctionType</a> *T)</tt>
1603 <p>Look up the specified function in the <tt>Module</tt> <a
1604 href="#SymbolTable"><tt>SymbolTable</tt></a>. If it does not exist, add an
1605 external declaration for the function and return it.</p></li>
1607 <li><tt>std::string getTypeName(const <a href="#Type">Type</a> *Ty)</tt>
1609 <p>If there is at least one entry in the <a
1610 href="#SymbolTable"><tt>SymbolTable</tt></a> for the specified <a
1611 href="#Type"><tt>Type</tt></a>, return it. Otherwise return the empty
1614 <li><tt>bool addTypeName(const std::string &Name, const <a
1615 href="#Type">Type</a> *Ty)</tt>
1617 <p>Insert an entry in the <a href="#SymbolTable"><tt>SymbolTable</tt></a>
1618 mapping <tt>Name</tt> to <tt>Ty</tt>. If there is already an entry for this
1619 name, true is returned and the <a
1620 href="#SymbolTable"><tt>SymbolTable</tt></a> is not modified.</p></li>
1625 <!-- ======================================================================= -->
1626 <div class="doc_subsection">
1627 <a name="Constant">The <tt>Constant</tt> class and subclasses</a>
1630 <div class="doc_text">
1632 <p>Constant represents a base class for different types of constants. It
1633 is subclassed by ConstantBool, ConstantInt, ConstantSInt, ConstantUInt,
1634 ConstantArray etc for representing the various types of Constants.</p>
1638 <!-- _______________________________________________________________________ -->
1639 <div class="doc_subsubsection">
1640 <a name="m_Value">Important Public Methods</a>
1643 <div class="doc_text">
1646 <li><tt>bool isConstantExpr()</tt>: Returns true if it is a
1648 <hr> Important Subclasses of Constant
1651 <li>ConstantSInt : This subclass of Constant represents a signed
1654 <li><tt>int64_t getValue() const</tt>: Returns the underlying value of
1655 this constant. </li>
1658 <li>ConstantUInt : This class represents an unsigned integer.
1660 <li><tt>uint64_t getValue() const</tt>: Returns the underlying value
1661 of this constant. </li>
1664 <li>ConstantFP : This class represents a floating point constant.
1666 <li><tt>double getValue() const</tt>: Returns the underlying value of
1667 this constant. </li>
1670 <li>ConstantBool : This represents a boolean constant.
1672 <li><tt>bool getValue() const</tt>: Returns the underlying value of
1673 this constant. </li>
1676 <li>ConstantArray : This represents a constant array.
1678 <li><tt>const std::vector<Use> &getValues() const</tt>:
1679 Returns a Vecotr of component constants that makeup this array. </li>
1682 <li>ConstantStruct : This represents a constant struct.
1684 <li><tt>const std::vector<Use> &getValues() const</tt>:
1685 Returns a Vecotr of component constants that makeup this array. </li>
1688 <li>ConstantPointerRef : This represents a constant pointer value
1689 that is initialized to point to a global value, which lies at a
1690 constant fixed address.
1692 <li><tt>GlobalValue *getValue()</tt>: Returns the global
1693 value to which this pointer is pointing to. </li>
1702 <!-- ======================================================================= -->
1703 <div class="doc_subsection">
1704 <a name="Type">The <tt>Type</tt> class and Derived Types</a>
1707 <div class="doc_text">
1709 <p>Type as noted earlier is also a subclass of a Value class. Any primitive
1710 type (like int, short etc) in LLVM is an instance of Type Class. All other
1711 types are instances of subclasses of type like FunctionType, ArrayType
1712 etc. DerivedType is the interface for all such dervied types including
1713 FunctionType, ArrayType, PointerType, StructType. Types can have names. They can
1714 be recursive (StructType). There exists exactly one instance of any type
1715 structure at a time. This allows using pointer equality of Type *s for comparing
1720 <!-- _______________________________________________________________________ -->
1721 <div class="doc_subsubsection">
1722 <a name="m_Value">Important Public Methods</a>
1725 <div class="doc_text">
1729 <li><tt>PrimitiveID getPrimitiveID() const</tt>: Returns the base type of the
1732 <li><tt>bool isSigned() const</tt>: Returns whether an integral numeric type
1733 is signed. This is true for SByteTy, ShortTy, IntTy, LongTy. Note that this is
1734 not true for Float and Double. </li>
1736 <li><tt>bool isUnsigned() const</tt>: Returns whether a numeric type is
1737 unsigned. This is not quite the complement of isSigned... nonnumeric types
1738 return false as they do with isSigned. This returns true for UByteTy,
1739 UShortTy, UIntTy, and ULongTy. </li>
1741 <li><tt>bool isInteger() const</tt>: Equilivent to isSigned() || isUnsigned(),
1742 but with only a single virtual function invocation.</li>
1744 <li><tt>bool isIntegral() const</tt>: Returns true if this is an integral
1745 type, which is either Bool type or one of the Integer types.</li>
1747 <li><tt>bool isFloatingPoint()</tt>: Return true if this is one of the two
1748 floating point types.</li>
1750 <li><tt>bool isRecursive() const</tt>: Returns rue if the type graph contains
1753 <li><tt>isLosslesslyConvertableTo (const Type *Ty) const</tt>: Return true if
1754 this type can be converted to 'Ty' without any reinterpretation of bits. For
1755 example, uint to int.</li>
1757 <li><tt>bool isPrimitiveType() const</tt>: Returns true if it is a primitive
1760 <li><tt>bool isDerivedType() const</tt>: Returns true if it is a derived
1763 <li><tt>const Type * getContainedType (unsigned i) const</tt>: This method is
1764 used to implement the type iterator. For derived types, this returns the types
1765 'contained' in the derived type, returning 0 when 'i' becomes invalid. This
1766 allows the user to iterate over the types in a struct, for example, really
1769 <li><tt>unsigned getNumContainedTypes() const</tt>: Return the number of types
1770 in the derived type.
1773 <p>Derived Types</p>
1776 <li>SequentialType : This is subclassed by ArrayType and PointerType
1778 <li><tt>const Type * getElementType() const</tt>: Returns the type of
1779 each of the elements in the sequential type. </li>
1782 <li>ArrayType : This is a subclass of SequentialType and defines
1783 interface for array types.
1785 <li><tt>unsigned getNumElements() const</tt>: Returns the number of
1786 elements in the array. </li>
1789 <li>PointerType : Subclass of SequentialType for pointer types. </li>
1790 <li>StructType : subclass of DerivedTypes for struct types </li>
1791 <li>FunctionType : subclass of DerivedTypes for function types.
1793 <li><tt>bool isVarArg() const</tt>: Returns true if its a vararg
1795 <li><tt> const Type * getReturnType() const</tt>: Returns the
1796 return type of the function.</li>
1797 <li><tt>const Type * getParamType (unsigned i)</tt>: Returns
1798 the type of the ith parameter.</li>
1799 <li><tt> const unsigned getNumParams() const</tt>: Returns the
1800 number of formal parameters.</li>
1809 <!-- ======================================================================= -->
1810 <div class="doc_subsection">
1811 <a name="Argument">The <tt>Argument</tt> class</a>
1814 <div class="doc_text">
1816 <p>This subclass of Value defines the interface for incoming formal
1817 arguments to a function. A Function maitanis a list of its formal
1818 arguments. An argument has a pointer to the parent Function.</p>
1822 <!-- *********************************************************************** -->
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1830 <a href="mailto:dhurjati@cs.uiuc.edu">Dinakar Dhurjati</a> and
1831 <a href="mailto:sabre@nondot.org">Chris Lattner</a><br>
1832 <a href="http://llvm.cs.uiuc.edu">The LLVM Compiler Infrastructure</a><br>
1833 Last modified: $Date$