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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>
26 <li><a href="#apis">Important and useful LLVM APIs</a>
28 <li><a href="#isa">The <tt>isa<></tt>, <tt>cast<></tt>
29 and <tt>dyn_cast<></tt> templates</a> </li>
30 <li><a href="#DEBUG">The <tt>DEBUG()</tt> macro & <tt>-debug</tt>
33 <li><a href="#DEBUG_TYPE">Fine grained debug info with <tt>DEBUG_TYPE</tt>
34 and the <tt>-debug-only</tt> option</a> </li>
37 <li><a href="#Statistic">The <tt>Statistic</tt> template & <tt>-stats</tt>
40 <li>The <tt>InstVisitor</tt> template
41 <li>The general graph API
45 <li><a href="#common">Helpful Hints for Common Operations</a>
47 <li><a href="#inspection">Basic Inspection and Traversal Routines</a>
49 <li><a href="#iterate_function">Iterating over the <tt>BasicBlock</tt>s
50 in a <tt>Function</tt></a> </li>
51 <li><a href="#iterate_basicblock">Iterating over the <tt>Instruction</tt>s
52 in a <tt>BasicBlock</tt></a> </li>
53 <li><a href="#iterate_institer">Iterating over the <tt>Instruction</tt>s
54 in a <tt>Function</tt></a> </li>
55 <li><a href="#iterate_convert">Turning an iterator into a
56 class pointer</a> </li>
57 <li><a href="#iterate_complex">Finding call sites: a more
58 complex example</a> </li>
59 <li><a href="#calls_and_invokes">Treating calls and invokes
60 the same way</a> </li>
61 <li><a href="#iterate_chains">Iterating over def-use &
62 use-def chains</a> </li>
65 <li><a href="#simplechanges">Making simple changes</a>
67 <li><a href="#schanges_creating">Creating and inserting new
68 <tt>Instruction</tt>s</a> </li>
69 <li><a href="#schanges_deleting">Deleting <tt>Instruction</tt>s</a> </li>
70 <li><a href="#schanges_replacing">Replacing an <tt>Instruction</tt>
71 with another <tt>Value</tt></a> </li>
75 <li>Working with the Control Flow Graph
77 <li>Accessing predecessors and successors of a <tt>BasicBlock</tt>
84 <li><a href="#coreclasses">The Core LLVM Class Hierarchy Reference</a>
86 <li><a href="#Value">The <tt>Value</tt> class</a>
88 <li><a href="#User">The <tt>User</tt> class</a>
90 <li><a href="#Instruction">The <tt>Instruction</tt> class</a>
92 <li><a href="#GetElementPtrInst">The <tt>GetElementPtrInst</tt> class</a></li>
95 <li><a href="#Module">The <tt>Module</tt> class</a></li>
96 <li><a href="#Constant">The <tt>Constant</tt> class</a>
98 <li><a href="#GlobalValue">The <tt>GlobalValue</tt> class</a>
100 <li><a href="#BasicBlock">The <tt>BasicBlock</tt>class</a></li>
101 <li><a href="#Function">The <tt>Function</tt> class</a></li>
102 <li><a href="#GlobalVariable">The <tt>GlobalVariable</tt> class</a></li>
109 <li><a href="#Type">The <tt>Type</tt> class</a> </li>
110 <li><a href="#Argument">The <tt>Argument</tt> class</a></li>
115 <li><a href="#SymbolTable">The <tt>SymbolTable</tt> class </a></li>
116 <li>The <tt>ilist</tt> and <tt>iplist</tt> classes
118 <li>Creating, inserting, moving and deleting from LLVM lists </li>
121 <li>Important iterator invalidation semantics to be aware of.</li>
124 <div class="doc_author">
125 <p>Written by <a href="mailto:sabre@nondot.org">Chris Lattner</a>,
126 <a href="mailto:dhurjati@cs.uiuc.edu">Dinakar Dhurjati</a>,
127 <a href="mailto:jstanley@cs.uiuc.edu">Joel Stanley</a>, and
128 <a href="mailto:rspencer@x10sys.com">Reid Spencer</a></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
201 Reference that rivals Dinkumware's, and is unfortunately no longer free since the book has been
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++
215 <li><a href="http://www.linux.com.cn/Bruce_Eckel/TICPPv2/Contents.htm">
216 Bruce Eckel's Thinking in C++, 2nd ed. Volume 2 Revision 4.0 (even better, get
221 <p>You are also encouraged to take a look at the <a
222 href="CodingStandards.html">LLVM Coding Standards</a> guide which focuses on how
223 to write maintainable code more than where to put your curly braces.</p>
227 <!-- ======================================================================= -->
228 <div class="doc_subsection">
229 <a name="stl">Other useful references</a>
232 <div class="doc_text">
235 <li><a href="http://www.psc.edu/%7Esemke/cvs_branches.html">CVS
236 Branch and Tag Primer</a></li>
237 <li><a href="http://www.fortran-2000.com/ArnaudRecipes/sharedlib.html">Using
238 static and shared libraries across platforms</a></li>
243 <!-- *********************************************************************** -->
244 <div class="doc_section">
245 <a name="apis">Important and useful LLVM APIs</a>
247 <!-- *********************************************************************** -->
249 <div class="doc_text">
251 <p>Here we highlight some LLVM APIs that are generally useful and good to
252 know about when writing transformations.</p>
256 <!-- ======================================================================= -->
257 <div class="doc_subsection">
258 <a name="isa">The isa<>, cast<> and dyn_cast<> templates</a>
261 <div class="doc_text">
263 <p>The LLVM source-base makes extensive use of a custom form of RTTI.
264 These templates have many similarities to the C++ <tt>dynamic_cast<></tt>
265 operator, but they don't have some drawbacks (primarily stemming from
266 the fact that <tt>dynamic_cast<></tt> only works on classes that
267 have a v-table). Because they are used so often, you must know what they
268 do and how they work. All of these templates are defined in the <a
269 href="/doxygen/Casting_8h-source.html"><tt>Support/Casting.h</tt></a>
270 file (note that you very rarely have to include this file directly).</p>
273 <dt><tt>isa<></tt>: </dt>
275 <dd>The <tt>isa<></tt> operator works exactly like the Java
276 "<tt>instanceof</tt>" operator. It returns true or false depending on whether
277 a reference or pointer points to an instance of the specified class. This can
278 be very useful for constraint checking of various sorts (example below).</dd>
280 <dt><tt>cast<></tt>: </dt>
282 <dd>The <tt>cast<></tt> operator is a "checked cast" operation. It
283 converts a pointer or reference from a base class to a derived cast, causing
284 an assertion failure if it is not really an instance of the right type. This
285 should be used in cases where you have some information that makes you believe
286 that something is of the right type. An example of the <tt>isa<></tt>
287 and <tt>cast<></tt> template is:
290 static bool isLoopInvariant(const <a href="#Value">Value</a> *V, const Loop *L) {
291 if (isa<<a href="#Constant">Constant</a>>(V) || isa<<a href="#Argument">Argument</a>>(V) || isa<<a href="#GlobalValue">GlobalValue</a>>(V))
294 <i>// Otherwise, it must be an instruction...</i>
295 return !L->contains(cast<<a href="#Instruction">Instruction</a>>(V)->getParent());
298 <p>Note that you should <b>not</b> use an <tt>isa<></tt> test followed
299 by a <tt>cast<></tt>, for that use the <tt>dyn_cast<></tt>
304 <dt><tt>dyn_cast<></tt>:</dt>
306 <dd>The <tt>dyn_cast<></tt> operator is a "checking cast" operation. It
307 checks to see if the operand is of the specified type, and if so, returns a
308 pointer to it (this operator does not work with references). If the operand is
309 not of the correct type, a null pointer is returned. Thus, this works very
310 much like the <tt>dynamic_cast</tt> operator in C++, and should be used in the
311 same circumstances. Typically, the <tt>dyn_cast<></tt> operator is used
312 in an <tt>if</tt> statement or some other flow control statement like this:
315 if (<a href="#AllocationInst">AllocationInst</a> *AI = dyn_cast<<a href="#AllocationInst">AllocationInst</a>>(Val)) {
320 <p> This form of the <tt>if</tt> statement effectively combines together a
321 call to <tt>isa<></tt> and a call to <tt>cast<></tt> into one
322 statement, which is very convenient.</p>
324 <p> Another common example is:</p>
327 <i>// Loop over all of the phi nodes in a basic block</i>
328 BasicBlock::iterator BBI = BB->begin();
329 for (; <a href="#PhiNode">PHINode</a> *PN = dyn_cast<<a href="#PHINode">PHINode</a>>(BBI); ++BBI)
330 std::cerr << *PN;
333 <p>Note that the <tt>dyn_cast<></tt> operator, like C++'s
334 <tt>dynamic_cast</tt> or Java's <tt>instanceof</tt> operator, can be abused.
335 In particular you should not use big chained <tt>if/then/else</tt> blocks to
336 check for lots of different variants of classes. If you find yourself
337 wanting to do this, it is much cleaner and more efficient to use the
338 InstVisitor class to dispatch over the instruction type directly.</p>
342 <dt><tt>cast_or_null<></tt>: </dt>
344 <dd>The <tt>cast_or_null<></tt> operator works just like the
345 <tt>cast<></tt> operator, except that it allows for a null pointer as
346 an argument (which it then propagates). This can sometimes be useful,
347 allowing you to combine several null checks into one.</dd>
349 <dt><tt>dyn_cast_or_null<></tt>: </dt>
351 <dd>The <tt>dyn_cast_or_null<></tt> operator works just like the
352 <tt>dyn_cast<></tt> operator, except that it allows for a null pointer
353 as an argument (which it then propagates). This can sometimes be useful,
354 allowing you to combine several null checks into one.</dd>
358 <p>These five templates can be used with any classes, whether they have a
359 v-table or not. To add support for these templates, you simply need to add
360 <tt>classof</tt> static methods to the class you are interested casting
361 to. Describing this is currently outside the scope of this document, but there
362 are lots of examples in the LLVM source base.</p>
366 <!-- ======================================================================= -->
367 <div class="doc_subsection">
368 <a name="DEBUG">The <tt>DEBUG()</tt> macro & <tt>-debug</tt> option</a>
371 <div class="doc_text">
373 <p>Often when working on your pass you will put a bunch of debugging printouts
374 and other code into your pass. After you get it working, you want to remove
375 it... but you may need it again in the future (to work out new bugs that you run
378 <p> Naturally, because of this, you don't want to delete the debug printouts,
379 but you don't want them to always be noisy. A standard compromise is to comment
380 them out, allowing you to enable them if you need them in the future.</p>
382 <p>The "<tt><a href="/doxygen/Debug_8h-source.html">Support/Debug.h</a></tt>"
383 file provides a macro named <tt>DEBUG()</tt> that is a much nicer solution to
384 this problem. Basically, you can put arbitrary code into the argument of the
385 <tt>DEBUG</tt> macro, and it is only executed if '<tt>opt</tt>' (or any other
386 tool) is run with the '<tt>-debug</tt>' command line argument:</p>
388 <pre> ... <br> DEBUG(std::cerr << "I am here!\n");<br> ...<br></pre>
390 <p>Then you can run your pass like this:</p>
392 <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>
394 <p>Using the <tt>DEBUG()</tt> macro instead of a home-brewed solution allows you
395 to not have to create "yet another" command line option for the debug output for
396 your pass. Note that <tt>DEBUG()</tt> macros are disabled for optimized builds,
397 so they do not cause a performance impact at all (for the same reason, they
398 should also not contain side-effects!).</p>
400 <p>One additional nice thing about the <tt>DEBUG()</tt> macro is that you can
401 enable or disable it directly in gdb. Just use "<tt>set DebugFlag=0</tt>" or
402 "<tt>set DebugFlag=1</tt>" from the gdb if the program is running. If the
403 program hasn't been started yet, you can always just run it with
408 <!-- _______________________________________________________________________ -->
409 <div class="doc_subsubsection">
410 <a name="DEBUG_TYPE">Fine grained debug info with <tt>DEBUG_TYPE()</tt> and
411 the <tt>-debug-only</tt> option</a>
414 <div class="doc_text">
416 <p>Sometimes you may find yourself in a situation where enabling <tt>-debug</tt>
417 just turns on <b>too much</b> information (such as when working on the code
418 generator). If you want to enable debug information with more fine-grained
419 control, you define the <tt>DEBUG_TYPE</tt> macro and the <tt>-debug</tt> only
420 option as follows:</p>
422 <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>
424 <p>Then you can run your pass like this:</p>
426 <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>
428 <p>Of course, in practice, you should only set <tt>DEBUG_TYPE</tt> at the top of
429 a file, to specify the debug type for the entire module (if you do this before
430 you <tt>#include "Support/Debug.h"</tt>, you don't have to insert the ugly
431 <tt>#undef</tt>'s). Also, you should use names more meaningful than "foo" and
432 "bar", because there is no system in place to ensure that names do not
433 conflict. If two different modules use the same string, they will all be turned
434 on when the name is specified. This allows, for example, all debug information
435 for instruction scheduling to be enabled with <tt>-debug-type=InstrSched</tt>,
436 even if the source lives in multiple files.</p>
440 <!-- ======================================================================= -->
441 <div class="doc_subsection">
442 <a name="Statistic">The <tt>Statistic</tt> template & <tt>-stats</tt>
446 <div class="doc_text">
449 href="/doxygen/Statistic_8h-source.html">Support/Statistic.h</a></tt>" file
450 provides a template named <tt>Statistic</tt> that is used as a unified way to
451 keep track of what the LLVM compiler is doing and how effective various
452 optimizations are. It is useful to see what optimizations are contributing to
453 making a particular program run faster.</p>
455 <p>Often you may run your pass on some big program, and you're interested to see
456 how many times it makes a certain transformation. Although you can do this with
457 hand inspection, or some ad-hoc method, this is a real pain and not very useful
458 for big programs. Using the <tt>Statistic</tt> template makes it very easy to
459 keep track of this information, and the calculated information is presented in a
460 uniform manner with the rest of the passes being executed.</p>
462 <p>There are many examples of <tt>Statistic</tt> uses, but the basics of using
463 it are as follows:</p>
466 <li>Define your statistic like this:
467 <pre>static Statistic<> NumXForms("mypassname", "The # of times I did stuff");<br></pre>
469 <p>The <tt>Statistic</tt> template can emulate just about any data-type,
470 but if you do not specify a template argument, it defaults to acting like
471 an unsigned int counter (this is usually what you want).</p></li>
473 <li>Whenever you make a transformation, bump the counter:
474 <pre> ++NumXForms; // I did stuff<br></pre>
478 <p>That's all you have to do. To get '<tt>opt</tt>' to print out the
479 statistics gathered, use the '<tt>-stats</tt>' option:</p>
481 <pre> $ opt -stats -mypassname < program.bc > /dev/null<br> ... statistic output ...<br></pre>
483 <p> When running <tt>gccas</tt> on a C file from the SPEC benchmark
484 suite, it gives a report that looks like this:</p>
486 <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>
488 <p>Obviously, with so many optimizations, having a unified framework for this
489 stuff is very nice. Making your pass fit well into the framework makes it more
490 maintainable and useful.</p>
494 <!-- *********************************************************************** -->
495 <div class="doc_section">
496 <a name="common">Helpful Hints for Common Operations</a>
498 <!-- *********************************************************************** -->
500 <div class="doc_text">
502 <p>This section describes how to perform some very simple transformations of
503 LLVM code. This is meant to give examples of common idioms used, showing the
504 practical side of LLVM transformations. <p> Because this is a "how-to" section,
505 you should also read about the main classes that you will be working with. The
506 <a href="#coreclasses">Core LLVM Class Hierarchy Reference</a> contains details
507 and descriptions of the main classes that you should know about.</p>
511 <!-- NOTE: this section should be heavy on example code -->
512 <!-- ======================================================================= -->
513 <div class="doc_subsection">
514 <a name="inspection">Basic Inspection and Traversal Routines</a>
517 <div class="doc_text">
519 <p>The LLVM compiler infrastructure have many different data structures that may
520 be traversed. Following the example of the C++ standard template library, the
521 techniques used to traverse these various data structures are all basically the
522 same. For a enumerable sequence of values, the <tt>XXXbegin()</tt> function (or
523 method) returns an iterator to the start of the sequence, the <tt>XXXend()</tt>
524 function returns an iterator pointing to one past the last valid element of the
525 sequence, and there is some <tt>XXXiterator</tt> data type that is common
526 between the two operations.</p>
528 <p>Because the pattern for iteration is common across many different aspects of
529 the program representation, the standard template library algorithms may be used
530 on them, and it is easier to remember how to iterate. First we show a few common
531 examples of the data structures that need to be traversed. Other data
532 structures are traversed in very similar ways.</p>
536 <!-- _______________________________________________________________________ -->
537 <div class="doc_subsubsection">
538 <a name="iterate_function">Iterating over the </a><a
539 href="#BasicBlock"><tt>BasicBlock</tt></a>s in a <a
540 href="#Function"><tt>Function</tt></a>
543 <div class="doc_text">
545 <p>It's quite common to have a <tt>Function</tt> instance that you'd like to
546 transform in some way; in particular, you'd like to manipulate its
547 <tt>BasicBlock</tt>s. To facilitate this, you'll need to iterate over all of
548 the <tt>BasicBlock</tt>s that constitute the <tt>Function</tt>. The following is
549 an example that prints the name of a <tt>BasicBlock</tt> and the number of
550 <tt>Instruction</tt>s it contains:</p>
552 <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>
554 <p>Note that i can be used as if it were a pointer for the purposes of
555 invoking member functions of the <tt>Instruction</tt> class. This is
556 because the indirection operator is overloaded for the iterator
557 classes. In the above code, the expression <tt>i->size()</tt> is
558 exactly equivalent to <tt>(*i).size()</tt> just like you'd expect.</p>
562 <!-- _______________________________________________________________________ -->
563 <div class="doc_subsubsection">
564 <a name="iterate_basicblock">Iterating over the </a><a
565 href="#Instruction"><tt>Instruction</tt></a>s in a <a
566 href="#BasicBlock"><tt>BasicBlock</tt></a>
569 <div class="doc_text">
571 <p>Just like when dealing with <tt>BasicBlock</tt>s in <tt>Function</tt>s, it's
572 easy to iterate over the individual instructions that make up
573 <tt>BasicBlock</tt>s. Here's a code snippet that prints out each instruction in
574 a <tt>BasicBlock</tt>:</p>
576 <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>
578 <p>However, this isn't really the best way to print out the contents of a
579 <tt>BasicBlock</tt>! Since the ostream operators are overloaded for virtually
580 anything you'll care about, you could have just invoked the print routine on the
581 basic block itself: <tt>cerr << *blk << "\n";</tt>.</p>
583 <p>Note that currently operator<< is implemented for <tt>Value*</tt>, so
584 it will print out the contents of the pointer, instead of the pointer value you
585 might expect. This is a deprecated interface that will be removed in the
586 future, so it's best not to depend on it. To print out the pointer value for
587 now, you must cast to <tt>void*</tt>.</p>
591 <!-- _______________________________________________________________________ -->
592 <div class="doc_subsubsection">
593 <a name="iterate_institer">Iterating over the </a><a
594 href="#Instruction"><tt>Instruction</tt></a>s in a <a
595 href="#Function"><tt>Function</tt></a>
598 <div class="doc_text">
600 <p>If you're finding that you commonly iterate over a <tt>Function</tt>'s
601 <tt>BasicBlock</tt>s and then that <tt>BasicBlock</tt>'s <tt>Instruction</tt>s,
602 <tt>InstIterator</tt> should be used instead. You'll need to include <a
603 href="/doxygen/InstIterator_8h-source.html"><tt>llvm/Support/InstIterator.h</tt></a>,
604 and then instantiate <tt>InstIterator</tt>s explicitly in your code. Here's a
605 small example that shows how to dump all instructions in a function to the standard error stream:<p>
607 <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>
608 Easy, isn't it? You can also use <tt>InstIterator</tt>s to fill a
609 worklist with its initial contents. For example, if you wanted to
610 initialize a worklist to contain all instructions in a <tt>Function</tt>
611 F, all you would need to do is something like:
612 <pre>std::set<Instruction*> worklist;<br>worklist.insert(inst_begin(F), inst_end(F));<br></pre>
614 <p>The STL set <tt>worklist</tt> would now contain all instructions in the
615 <tt>Function</tt> pointed to by F.</p>
619 <!-- _______________________________________________________________________ -->
620 <div class="doc_subsubsection">
621 <a name="iterate_convert">Turning an iterator into a class pointer (and
625 <div class="doc_text">
627 <p>Sometimes, it'll be useful to grab a reference (or pointer) to a class
628 instance when all you've got at hand is an iterator. Well, extracting
629 a reference or a pointer from an iterator is very straight-forward.
630 Assuming that <tt>i</tt> is a <tt>BasicBlock::iterator</tt> and <tt>j</tt>
631 is a <tt>BasicBlock::const_iterator</tt>:</p>
633 <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>
635 <p>However, the iterators you'll be working with in the LLVM framework are
636 special: they will automatically convert to a ptr-to-instance type whenever they
637 need to. Instead of dereferencing the iterator and then taking the address of
638 the result, you can simply assign the iterator to the proper pointer type and
639 you get the dereference and address-of operation as a result of the assignment
640 (behind the scenes, this is a result of overloading casting mechanisms). Thus
641 the last line of the last example,</p>
643 <pre>Instruction* pinst = &*i;</pre>
645 <p>is semantically equivalent to</p>
647 <pre>Instruction* pinst = i;</pre>
649 <p>It's also possible to turn a class pointer into the corresponding iterator,
650 and this is a constant time operation (very efficient). The following code
651 snippet illustrates use of the conversion constructors provided by LLVM
652 iterators. By using these, you can explicitly grab the iterator of something
653 without actually obtaining it via iteration over some structure:</p>
655 <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>
659 <!--_______________________________________________________________________-->
660 <div class="doc_subsubsection">
661 <a name="iterate_complex">Finding call sites: a slightly more complex
665 <div class="doc_text">
667 <p>Say that you're writing a FunctionPass and would like to count all the
668 locations in the entire module (that is, across every <tt>Function</tt>) where a
669 certain function (i.e., some <tt>Function</tt>*) is already in scope. As you'll
670 learn later, you may want to use an <tt>InstVisitor</tt> to accomplish this in a
671 much more straight-forward manner, but this example will allow us to explore how
672 you'd do it if you didn't have <tt>InstVisitor</tt> around. In pseudocode, this
673 is what we want to do:</p>
675 <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>
677 <p>And the actual code is (remember, since we're writing a
678 <tt>FunctionPass</tt>, our <tt>FunctionPass</tt>-derived class simply has to
679 override the <tt>runOnFunction</tt> method...):</p>
681 <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
682 href="#CallInst">CallInst</a>* callInst = <a href="#isa">dyn_cast</a><<a
683 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>
687 <!--_______________________________________________________________________-->
688 <div class="doc_subsubsection">
689 <a name="calls_and_invokes">Treating calls and invokes the same way</a>
692 <div class="doc_text">
694 <p>You may have noticed that the previous example was a bit oversimplified in
695 that it did not deal with call sites generated by 'invoke' instructions. In
696 this, and in other situations, you may find that you want to treat
697 <tt>CallInst</tt>s and <tt>InvokeInst</tt>s the same way, even though their
698 most-specific common base class is <tt>Instruction</tt>, which includes lots of
699 less closely-related things. For these cases, LLVM provides a handy wrapper
701 href="http://llvm.cs.uiuc.edu/doxygen/classllvm_1_1CallSite.html"><tt>CallSite</tt></a>.
702 It is essentially a wrapper around an <tt>Instruction</tt> pointer, with some
703 methods that provide functionality common to <tt>CallInst</tt>s and
704 <tt>InvokeInst</tt>s.</p>
706 <p>This class has "value semantics": it should be passed by value, not by
707 reference and it should not be dynamically allocated or deallocated using
708 <tt>operator new</tt> or <tt>operator delete</tt>. It is efficiently copyable,
709 assignable and constructable, with costs equivalents to that of a bare pointer.
710 If you look at its definition, it has only a single pointer member.</p>
714 <!--_______________________________________________________________________-->
715 <div class="doc_subsubsection">
716 <a name="iterate_chains">Iterating over def-use & use-def chains</a>
719 <div class="doc_text">
721 <p>Frequently, we might have an instance of the <a
722 href="/doxygen/structllvm_1_1Value.html">Value Class</a> and we want to
723 determine which <tt>User</tt>s use the <tt>Value</tt>. The list of all
724 <tt>User</tt>s of a particular <tt>Value</tt> is called a <i>def-use</i> chain.
725 For example, let's say we have a <tt>Function*</tt> named <tt>F</tt> to a
726 particular function <tt>foo</tt>. Finding all of the instructions that
727 <i>use</i> <tt>foo</tt> is as simple as iterating over the <i>def-use</i> chain
730 <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>
732 <p>Alternately, it's common to have an instance of the <a
733 href="/doxygen/classllvm_1_1User.html">User Class</a> and need to know what
734 <tt>Value</tt>s are used by it. The list of all <tt>Value</tt>s used by a
735 <tt>User</tt> is known as a <i>use-def</i> chain. Instances of class
736 <tt>Instruction</tt> are common <tt>User</tt>s, so we might want to iterate over
737 all of the values that a particular instruction uses (that is, the operands of
738 the particular <tt>Instruction</tt>):</p>
740 <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>
743 def-use chains ("finding all users of"): Value::use_begin/use_end
744 use-def chains ("finding all values used"): User::op_begin/op_end [op=operand]
749 <!-- ======================================================================= -->
750 <div class="doc_subsection">
751 <a name="simplechanges">Making simple changes</a>
754 <div class="doc_text">
756 <p>There are some primitive transformation operations present in the LLVM
757 infrastructure that are worth knowing about. When performing
758 transformations, it's fairly common to manipulate the contents of basic
759 blocks. This section describes some of the common methods for doing so
760 and gives example code.</p>
764 <!--_______________________________________________________________________-->
765 <div class="doc_subsubsection">
766 <a name="schanges_creating">Creating and inserting new
767 <tt>Instruction</tt>s</a>
770 <div class="doc_text">
772 <p><i>Instantiating Instructions</i></p>
774 <p>Creation of <tt>Instruction</tt>s is straight-forward: simply call the
775 constructor for the kind of instruction to instantiate and provide the necessary
776 parameters. For example, an <tt>AllocaInst</tt> only <i>requires</i> a
777 (const-ptr-to) <tt>Type</tt>. Thus:</p>
779 <pre>AllocaInst* ai = new AllocaInst(Type::IntTy);</pre>
781 <p>will create an <tt>AllocaInst</tt> instance that represents the allocation of
782 one integer in the current stack frame, at runtime. Each <tt>Instruction</tt>
783 subclass is likely to have varying default parameters which change the semantics
784 of the instruction, so refer to the <a
785 href="/doxygen/classllvm_1_1Instruction.html">doxygen documentation for the subclass of
786 Instruction</a> that you're interested in instantiating.</p>
788 <p><i>Naming values</i></p>
790 <p>It is very useful to name the values of instructions when you're able to, as
791 this facilitates the debugging of your transformations. If you end up looking
792 at generated LLVM machine code, you definitely want to have logical names
793 associated with the results of instructions! By supplying a value for the
794 <tt>Name</tt> (default) parameter of the <tt>Instruction</tt> constructor, you
795 associate a logical name with the result of the instruction's execution at
796 runtime. For example, say that I'm writing a transformation that dynamically
797 allocates space for an integer on the stack, and that integer is going to be
798 used as some kind of index by some other code. To accomplish this, I place an
799 <tt>AllocaInst</tt> at the first point in the first <tt>BasicBlock</tt> of some
800 <tt>Function</tt>, and I'm intending to use it within the same
801 <tt>Function</tt>. I might do:</p>
803 <pre>AllocaInst* pa = new AllocaInst(Type::IntTy, 0, "indexLoc");</pre>
805 <p>where <tt>indexLoc</tt> is now the logical name of the instruction's
806 execution value, which is a pointer to an integer on the runtime stack.</p>
808 <p><i>Inserting instructions</i></p>
810 <p>There are essentially two ways to insert an <tt>Instruction</tt>
811 into an existing sequence of instructions that form a <tt>BasicBlock</tt>:</p>
814 <li>Insertion into an explicit instruction list
816 <p>Given a <tt>BasicBlock* pb</tt>, an <tt>Instruction* pi</tt> within that
817 <tt>BasicBlock</tt>, and a newly-created instruction we wish to insert
818 before <tt>*pi</tt>, we do the following: </p>
820 <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>
822 <p>Appending to the end of a <tt>BasicBlock</tt> is so common that
823 the <tt>Instruction</tt> class and <tt>Instruction</tt>-derived
824 classes provide constructors which take a pointer to a
825 <tt>BasicBlock</tt> to be appended to. For example code that
828 <pre> BasicBlock *pb = ...;<br> Instruction *newInst = new Instruction(...);<br> pb->getInstList().push_back(newInst); // appends newInst to pb<br></pre>
832 <pre> BasicBlock *pb = ...;<br> Instruction *newInst = new Instruction(..., pb);<br></pre>
834 <p>which is much cleaner, especially if you are creating
835 long instruction streams.</p></li>
837 <li>Insertion into an implicit instruction list
839 <p><tt>Instruction</tt> instances that are already in <tt>BasicBlock</tt>s
840 are implicitly associated with an existing instruction list: the instruction
841 list of the enclosing basic block. Thus, we could have accomplished the same
842 thing as the above code without being given a <tt>BasicBlock</tt> by doing:
845 <pre> Instruction *pi = ...;<br> Instruction *newInst = new Instruction(...);<br> pi->getParent()->getInstList().insert(pi, newInst);<br></pre>
847 <p>In fact, this sequence of steps occurs so frequently that the
848 <tt>Instruction</tt> class and <tt>Instruction</tt>-derived classes provide
849 constructors which take (as a default parameter) a pointer to an
850 <tt>Instruction</tt> which the newly-created <tt>Instruction</tt> should
851 precede. That is, <tt>Instruction</tt> constructors are capable of
852 inserting the newly-created instance into the <tt>BasicBlock</tt> of a
853 provided instruction, immediately before that instruction. Using an
854 <tt>Instruction</tt> constructor with a <tt>insertBefore</tt> (default)
855 parameter, the above code becomes:</p>
857 <pre>Instruction* pi = ...;<br>Instruction* newInst = new Instruction(..., pi);<br></pre>
859 <p>which is much cleaner, especially if you're creating a lot of
860 instructions and adding them to <tt>BasicBlock</tt>s.</p></li>
865 <!--_______________________________________________________________________-->
866 <div class="doc_subsubsection">
867 <a name="schanges_deleting">Deleting <tt>Instruction</tt>s</a>
870 <div class="doc_text">
872 <p>Deleting an instruction from an existing sequence of instructions that form a
873 <a href="#BasicBlock"><tt>BasicBlock</tt></a> is very straight-forward. First,
874 you must have a pointer to the instruction that you wish to delete. Second, you
875 need to obtain the pointer to that instruction's basic block. You use the
876 pointer to the basic block to get its list of instructions and then use the
877 erase function to remove your instruction. For example:</p>
879 <pre> <a href="#Instruction">Instruction</a> *I = .. ;<br> <a
880 href="#BasicBlock">BasicBlock</a> *BB = I->getParent();<br> BB->getInstList().erase(I);<br></pre>
884 <!--_______________________________________________________________________-->
885 <div class="doc_subsubsection">
886 <a name="schanges_replacing">Replacing an <tt>Instruction</tt> with another
890 <div class="doc_text">
892 <p><i>Replacing individual instructions</i></p>
894 <p>Including "<a href="/doxygen/BasicBlockUtils_8h-source.html">llvm/Transforms/Utils/BasicBlockUtils.h</a>"
895 permits use of two very useful replace functions: <tt>ReplaceInstWithValue</tt>
896 and <tt>ReplaceInstWithInst</tt>.</p>
898 <h4><a name="schanges_deleting">Deleting <tt>Instruction</tt>s</a></h4>
901 <li><tt>ReplaceInstWithValue</tt>
903 <p>This function replaces all uses (within a basic block) of a given
904 instruction with a value, and then removes the original instruction. The
905 following example illustrates the replacement of the result of a particular
906 <tt>AllocaInst</tt> that allocates memory for a single integer with an null
907 pointer to an integer.</p>
909 <pre>AllocaInst* instToReplace = ...;<br>BasicBlock::iterator ii(instToReplace);<br>ReplaceInstWithValue(instToReplace->getParent()->getInstList(), ii,<br> Constant::getNullValue(PointerType::get(Type::IntTy)));<br></pre></li>
911 <li><tt>ReplaceInstWithInst</tt>
913 <p>This function replaces a particular instruction with another
914 instruction. The following example illustrates the replacement of one
915 <tt>AllocaInst</tt> with another.</p>
917 <pre>AllocaInst* instToReplace = ...;<br>BasicBlock::iterator ii(instToReplace);<br>ReplaceInstWithInst(instToReplace->getParent()->getInstList(), ii,<br> new AllocaInst(Type::IntTy, 0, "ptrToReplacedInt"));<br></pre></li>
920 <p><i>Replacing multiple uses of <tt>User</tt>s and <tt>Value</tt>s</i></p>
922 <p>You can use <tt>Value::replaceAllUsesWith</tt> and
923 <tt>User::replaceUsesOfWith</tt> to change more than one use at a time. See the
924 doxygen documentation for the <a href="/doxygen/structllvm_1_1Value.html">Value Class</a>
925 and <a href="/doxygen/classllvm_1_1User.html">User Class</a>, respectively, for more
928 <!-- Value::replaceAllUsesWith User::replaceUsesOfWith Point out:
929 include/llvm/Transforms/Utils/ especially BasicBlockUtils.h with:
930 ReplaceInstWithValue, ReplaceInstWithInst -->
934 <!-- *********************************************************************** -->
935 <div class="doc_section">
936 <a name="coreclasses">The Core LLVM Class Hierarchy Reference </a>
938 <!-- *********************************************************************** -->
940 <div class="doc_text">
942 <p>The Core LLVM classes are the primary means of representing the program
943 being inspected or transformed. The core LLVM classes are defined in
944 header files in the <tt>include/llvm/</tt> directory, and implemented in
945 the <tt>lib/VMCore</tt> directory.</p>
949 <!-- ======================================================================= -->
950 <div class="doc_subsection">
951 <a name="Value">The <tt>Value</tt> class</a>
956 <p><tt>#include "<a href="/doxygen/Value_8h-source.html">llvm/Value.h</a>"</tt>
958 doxygen info: <a href="/doxygen/structllvm_1_1Value.html">Value Class</a></p>
960 <p>The <tt>Value</tt> class is the most important class in the LLVM Source
961 base. It represents a typed value that may be used (among other things) as an
962 operand to an instruction. There are many different types of <tt>Value</tt>s,
963 such as <a href="#Constant"><tt>Constant</tt></a>s,<a
964 href="#Argument"><tt>Argument</tt></a>s. Even <a
965 href="#Instruction"><tt>Instruction</tt></a>s and <a
966 href="#Function"><tt>Function</tt></a>s are <tt>Value</tt>s.</p>
968 <p>A particular <tt>Value</tt> may be used many times in the LLVM representation
969 for a program. For example, an incoming argument to a function (represented
970 with an instance of the <a href="#Argument">Argument</a> class) is "used" by
971 every instruction in the function that references the argument. To keep track
972 of this relationship, the <tt>Value</tt> class keeps a list of all of the <a
973 href="#User"><tt>User</tt></a>s that is using it (the <a
974 href="#User"><tt>User</tt></a> class is a base class for all nodes in the LLVM
975 graph that can refer to <tt>Value</tt>s). This use list is how LLVM represents
976 def-use information in the program, and is accessible through the <tt>use_</tt>*
977 methods, shown below.</p>
979 <p>Because LLVM is a typed representation, every LLVM <tt>Value</tt> is typed,
980 and this <a href="#Type">Type</a> is available through the <tt>getType()</tt>
981 method. In addition, all LLVM values can be named. The "name" of the
982 <tt>Value</tt> is a symbolic string printed in the LLVM code:</p>
984 <pre> %<b>foo</b> = add int 1, 2<br></pre>
986 <p><a name="#nameWarning">The name of this instruction is "foo".</a> <b>NOTE</b>
987 that the name of any value may be missing (an empty string), so names should
988 <b>ONLY</b> be used for debugging (making the source code easier to read,
989 debugging printouts), they should not be used to keep track of values or map
990 between them. For this purpose, use a <tt>std::map</tt> of pointers to the
991 <tt>Value</tt> itself instead.</p>
993 <p>One important aspect of LLVM is that there is no distinction between an SSA
994 variable and the operation that produces it. Because of this, any reference to
995 the value produced by an instruction (or the value available as an incoming
996 argument, for example) is represented as a direct pointer to the instance of
998 represents this value. Although this may take some getting used to, it
999 simplifies the representation and makes it easier to manipulate.</p>
1003 <!-- _______________________________________________________________________ -->
1004 <div class="doc_subsubsection">
1005 <a name="m_Value">Important Public Members of the <tt>Value</tt> class</a>
1008 <div class="doc_text">
1011 <li><tt>Value::use_iterator</tt> - Typedef for iterator over the
1013 <tt>Value::use_const_iterator</tt> - Typedef for const_iterator over
1015 <tt>unsigned use_size()</tt> - Returns the number of users of the
1017 <tt>bool use_empty()</tt> - Returns true if there are no users.<br>
1018 <tt>use_iterator use_begin()</tt> - Get an iterator to the start of
1020 <tt>use_iterator use_end()</tt> - Get an iterator to the end of the
1022 <tt><a href="#User">User</a> *use_back()</tt> - Returns the last
1023 element in the list.
1024 <p> These methods are the interface to access the def-use
1025 information in LLVM. As with all other iterators in LLVM, the naming
1026 conventions follow the conventions defined by the <a href="#stl">STL</a>.</p>
1028 <li><tt><a href="#Type">Type</a> *getType() const</tt>
1029 <p>This method returns the Type of the Value.</p>
1031 <li><tt>bool hasName() const</tt><br>
1032 <tt>std::string getName() const</tt><br>
1033 <tt>void setName(const std::string &Name)</tt>
1034 <p> This family of methods is used to access and assign a name to a <tt>Value</tt>,
1035 be aware of the <a href="#nameWarning">precaution above</a>.</p>
1037 <li><tt>void replaceAllUsesWith(Value *V)</tt>
1039 <p>This method traverses the use list of a <tt>Value</tt> changing all <a
1040 href="#User"><tt>User</tt>s</a> of the current value to refer to
1041 "<tt>V</tt>" instead. For example, if you detect that an instruction always
1042 produces a constant value (for example through constant folding), you can
1043 replace all uses of the instruction with the constant like this:</p>
1045 <pre> Inst->replaceAllUsesWith(ConstVal);<br></pre>
1050 <!-- ======================================================================= -->
1051 <div class="doc_subsection">
1052 <a name="User">The <tt>User</tt> class</a>
1055 <div class="doc_text">
1058 <tt>#include "<a href="/doxygen/User_8h-source.html">llvm/User.h</a>"</tt><br>
1059 doxygen info: <a href="/doxygen/classllvm_1_1User.html">User Class</a><br>
1060 Superclass: <a href="#Value"><tt>Value</tt></a></p>
1062 <p>The <tt>User</tt> class is the common base class of all LLVM nodes that may
1063 refer to <a href="#Value"><tt>Value</tt></a>s. It exposes a list of "Operands"
1064 that are all of the <a href="#Value"><tt>Value</tt></a>s that the User is
1065 referring to. The <tt>User</tt> class itself is a subclass of
1068 <p>The operands of a <tt>User</tt> point directly to the LLVM <a
1069 href="#Value"><tt>Value</tt></a> that it refers to. Because LLVM uses Static
1070 Single Assignment (SSA) form, there can only be one definition referred to,
1071 allowing this direct connection. This connection provides the use-def
1072 information in LLVM.</p>
1076 <!-- _______________________________________________________________________ -->
1077 <div class="doc_subsubsection">
1078 <a name="m_User">Important Public Members of the <tt>User</tt> class</a>
1081 <div class="doc_text">
1083 <p>The <tt>User</tt> class exposes the operand list in two ways: through
1084 an index access interface and through an iterator based interface.</p>
1087 <li><tt>Value *getOperand(unsigned i)</tt><br>
1088 <tt>unsigned getNumOperands()</tt>
1089 <p> These two methods expose the operands of the <tt>User</tt> in a
1090 convenient form for direct access.</p></li>
1092 <li><tt>User::op_iterator</tt> - Typedef for iterator over the operand
1094 <tt>User::op_const_iterator</tt> <tt>use_iterator op_begin()</tt> -
1095 Get an iterator to the start of the operand list.<br>
1096 <tt>use_iterator op_end()</tt> - Get an iterator to the end of the
1098 <p> Together, these methods make up the iterator based interface to
1099 the operands of a <tt>User</tt>.</p></li>
1104 <!-- ======================================================================= -->
1105 <div class="doc_subsection">
1106 <a name="Instruction">The <tt>Instruction</tt> class</a>
1109 <div class="doc_text">
1111 <p><tt>#include "</tt><tt><a
1112 href="/doxygen/Instruction_8h-source.html">llvm/Instruction.h</a>"</tt><br>
1113 doxygen info: <a href="/doxygen/classllvm_1_1Instruction.html">Instruction Class</a><br>
1114 Superclasses: <a href="#User"><tt>User</tt></a>, <a
1115 href="#Value"><tt>Value</tt></a></p>
1117 <p>The <tt>Instruction</tt> class is the common base class for all LLVM
1118 instructions. It provides only a few methods, but is a very commonly used
1119 class. The primary data tracked by the <tt>Instruction</tt> class itself is the
1120 opcode (instruction type) and the parent <a
1121 href="#BasicBlock"><tt>BasicBlock</tt></a> the <tt>Instruction</tt> is embedded
1122 into. To represent a specific type of instruction, one of many subclasses of
1123 <tt>Instruction</tt> are used.</p>
1125 <p> Because the <tt>Instruction</tt> class subclasses the <a
1126 href="#User"><tt>User</tt></a> class, its operands can be accessed in the same
1127 way as for other <a href="#User"><tt>User</tt></a>s (with the
1128 <tt>getOperand()</tt>/<tt>getNumOperands()</tt> and
1129 <tt>op_begin()</tt>/<tt>op_end()</tt> methods).</p> <p> An important file for
1130 the <tt>Instruction</tt> class is the <tt>llvm/Instruction.def</tt> file. This
1131 file contains some meta-data about the various different types of instructions
1132 in LLVM. It describes the enum values that are used as opcodes (for example
1133 <tt>Instruction::Add</tt> and <tt>Instruction::SetLE</tt>), as well as the
1134 concrete sub-classes of <tt>Instruction</tt> that implement the instruction (for
1135 example <tt><a href="#BinaryOperator">BinaryOperator</a></tt> and <tt><a
1136 href="#SetCondInst">SetCondInst</a></tt>). Unfortunately, the use of macros in
1137 this file confuses doxygen, so these enum values don't show up correctly in the
1138 <a href="/doxygen/classllvm_1_1Instruction.html">doxygen output</a>.</p>
1142 <!-- _______________________________________________________________________ -->
1143 <div class="doc_subsubsection">
1144 <a name="m_Instruction">Important Public Members of the <tt>Instruction</tt>
1148 <div class="doc_text">
1151 <li><tt><a href="#BasicBlock">BasicBlock</a> *getParent()</tt>
1152 <p>Returns the <a href="#BasicBlock"><tt>BasicBlock</tt></a> that
1153 this <tt>Instruction</tt> is embedded into.</p></li>
1154 <li><tt>bool mayWriteToMemory()</tt>
1155 <p>Returns true if the instruction writes to memory, i.e. it is a
1156 <tt>call</tt>,<tt>free</tt>,<tt>invoke</tt>, or <tt>store</tt>.</p></li>
1157 <li><tt>unsigned getOpcode()</tt>
1158 <p>Returns the opcode for the <tt>Instruction</tt>.</p></li>
1159 <li><tt><a href="#Instruction">Instruction</a> *clone() const</tt>
1160 <p>Returns another instance of the specified instruction, identical
1161 in all ways to the original except that the instruction has no parent
1162 (ie it's not embedded into a <a href="#BasicBlock"><tt>BasicBlock</tt></a>),
1163 and it has no name</p></li>
1168 <!-- ======================================================================= -->
1169 <div class="doc_subsection">
1170 <a name="BasicBlock">The <tt>BasicBlock</tt> class</a>
1173 <div class="doc_text">
1176 href="/doxygen/BasicBlock_8h-source.html">llvm/BasicBlock.h</a>"</tt><br>
1177 doxygen info: <a href="/doxygen/structllvm_1_1BasicBlock.html">BasicBlock
1179 Superclass: <a href="#Value"><tt>Value</tt></a></p>
1181 <p>This class represents a single entry multiple exit section of the code,
1182 commonly known as a basic block by the compiler community. The
1183 <tt>BasicBlock</tt> class maintains a list of <a
1184 href="#Instruction"><tt>Instruction</tt></a>s, which form the body of the block.
1185 Matching the language definition, the last element of this list of instructions
1186 is always a terminator instruction (a subclass of the <a
1187 href="#TerminatorInst"><tt>TerminatorInst</tt></a> class).</p>
1189 <p>In addition to tracking the list of instructions that make up the block, the
1190 <tt>BasicBlock</tt> class also keeps track of the <a
1191 href="#Function"><tt>Function</tt></a> that it is embedded into.</p>
1193 <p>Note that <tt>BasicBlock</tt>s themselves are <a
1194 href="#Value"><tt>Value</tt></a>s, because they are referenced by instructions
1195 like branches and can go in the switch tables. <tt>BasicBlock</tt>s have type
1200 <!-- _______________________________________________________________________ -->
1201 <div class="doc_subsubsection">
1202 <a name="m_BasicBlock">Important Public Members of the <tt>BasicBlock</tt>
1206 <div class="doc_text">
1210 <li><tt>BasicBlock(const std::string &Name = "", </tt><tt><a
1211 href="#Function">Function</a> *Parent = 0)</tt>
1213 <p>The <tt>BasicBlock</tt> constructor is used to create new basic blocks for
1214 insertion into a function. The constructor optionally takes a name for the new
1215 block, and a <a href="#Function"><tt>Function</tt></a> to insert it into. If
1216 the <tt>Parent</tt> parameter is specified, the new <tt>BasicBlock</tt> is
1217 automatically inserted at the end of the specified <a
1218 href="#Function"><tt>Function</tt></a>, if not specified, the BasicBlock must be
1219 manually inserted into the <a href="#Function"><tt>Function</tt></a>.</p></li>
1221 <li><tt>BasicBlock::iterator</tt> - Typedef for instruction list iterator<br>
1222 <tt>BasicBlock::const_iterator</tt> - Typedef for const_iterator.<br>
1223 <tt>begin()</tt>, <tt>end()</tt>, <tt>front()</tt>, <tt>back()</tt>,
1224 <tt>size()</tt>, <tt>empty()</tt>, <tt>rbegin()</tt>, <tt>rend()</tt> -
1225 STL-style functions for accessing the instruction list.
1227 <p>These methods and typedefs are forwarding functions that have the same
1228 semantics as the standard library methods of the same names. These methods
1229 expose the underlying instruction list of a basic block in a way that is easy to
1230 manipulate. To get the full complement of container operations (including
1231 operations to update the list), you must use the <tt>getInstList()</tt>
1234 <li><tt>BasicBlock::InstListType &getInstList()</tt>
1236 <p>This method is used to get access to the underlying container that actually
1237 holds the Instructions. This method must be used when there isn't a forwarding
1238 function in the <tt>BasicBlock</tt> class for the operation that you would like
1239 to perform. Because there are no forwarding functions for "updating"
1240 operations, you need to use this if you want to update the contents of a
1241 <tt>BasicBlock</tt>.</p></li>
1243 <li><tt><a href="#Function">Function</a> *getParent()</tt>
1245 <p> Returns a pointer to <a href="#Function"><tt>Function</tt></a> the block is
1246 embedded into, or a null pointer if it is homeless.</p></li>
1248 <li><tt><a href="#TerminatorInst">TerminatorInst</a> *getTerminator()</tt>
1250 <p> Returns a pointer to the terminator instruction that appears at the end of
1251 the <tt>BasicBlock</tt>. If there is no terminator instruction, or if the last
1252 instruction in the block is not a terminator, then a null pointer is
1259 <!-- ======================================================================= -->
1260 <div class="doc_subsection">
1261 <a name="GlobalValue">The <tt>GlobalValue</tt> class</a>
1264 <div class="doc_text">
1267 href="/doxygen/GlobalValue_8h-source.html">llvm/GlobalValue.h</a>"</tt><br>
1268 doxygen info: <a href="/doxygen/classllvm_1_1GlobalValue.html">GlobalValue
1270 Superclasses: <a href="#User"><tt>User</tt></a>, <a
1271 href="#Value"><tt>Value</tt></a></p>
1273 <p>Global values (<a href="#GlobalVariable"><tt>GlobalVariable</tt></a>s or <a
1274 href="#Function"><tt>Function</tt></a>s) are the only LLVM values that are
1275 visible in the bodies of all <a href="#Function"><tt>Function</tt></a>s.
1276 Because they are visible at global scope, they are also subject to linking with
1277 other globals defined in different translation units. To control the linking
1278 process, <tt>GlobalValue</tt>s know their linkage rules. Specifically,
1279 <tt>GlobalValue</tt>s know whether they have internal or external linkage, as
1280 defined by the <tt>LinkageTypes</tt> enumeration.</p>
1282 <p>If a <tt>GlobalValue</tt> has internal linkage (equivalent to being
1283 <tt>static</tt> in C), it is not visible to code outside the current translation
1284 unit, and does not participate in linking. If it has external linkage, it is
1285 visible to external code, and does participate in linking. In addition to
1286 linkage information, <tt>GlobalValue</tt>s keep track of which <a
1287 href="#Module"><tt>Module</tt></a> they are currently part of.</p>
1289 <p>Because <tt>GlobalValue</tt>s are memory objects, they are always referred to
1290 by their <b>address</b>. As such, the <a href="#Type"><tt>Type</tt></a> of a
1291 global is always a pointer to its contents. It is important to remember this
1292 when using the <tt>GetElementPtrInst</tt> instruction because this pointer must
1293 be dereferenced first. For example, if you have a <tt>GlobalVariable</tt> (a
1294 subclass of <tt>GlobalValue)</tt> that is an array of 24 ints, type <tt>[24 x
1295 int]</tt>, then the <tt>GlobalVariable</tt> is a pointer to that array. Although
1296 the address of the first element of this array and the value of the
1297 <tt>GlobalVariable</tt> are the same, they have different types. The
1298 <tt>GlobalVariable</tt>'s type is <tt>[24 x int]</tt>. The first element's type
1299 is <tt>int.</tt> Because of this, accessing a global value requires you to
1300 dereference the pointer with <tt>GetElementPtrInst</tt> first, then its elements
1301 can be accessed. This is explained in the <a href="LangRef.html#globalvars">LLVM
1302 Language Reference Manual</a>.</p>
1306 <!-- _______________________________________________________________________ -->
1307 <div class="doc_subsubsection">
1308 <a name="m_GlobalValue">Important Public Members of the <tt>GlobalValue</tt>
1312 <div class="doc_text">
1315 <li><tt>bool hasInternalLinkage() const</tt><br>
1316 <tt>bool hasExternalLinkage() const</tt><br>
1317 <tt>void setInternalLinkage(bool HasInternalLinkage)</tt>
1318 <p> These methods manipulate the linkage characteristics of the <tt>GlobalValue</tt>.</p>
1321 <li><tt><a href="#Module">Module</a> *getParent()</tt>
1322 <p> This returns the <a href="#Module"><tt>Module</tt></a> that the
1323 GlobalValue is currently embedded into.</p></li>
1328 <!-- ======================================================================= -->
1329 <div class="doc_subsection">
1330 <a name="Function">The <tt>Function</tt> class</a>
1333 <div class="doc_text">
1336 href="/doxygen/Function_8h-source.html">llvm/Function.h</a>"</tt><br> doxygen
1337 info: <a href="/doxygen/classllvm_1_1Function.html">Function Class</a><br>
1338 Superclasses: <a href="#GlobalValue"><tt>GlobalValue</tt></a>, <a
1339 href="#User"><tt>User</tt></a>, <a href="#Value"><tt>Value</tt></a></p>
1341 <p>The <tt>Function</tt> class represents a single procedure in LLVM. It is
1342 actually one of the more complex classes in the LLVM heirarchy because it must
1343 keep track of a large amount of data. The <tt>Function</tt> class keeps track
1344 of a list of <a href="#BasicBlock"><tt>BasicBlock</tt></a>s, a list of formal <a
1345 href="#Argument"><tt>Argument</tt></a>s, and a <a
1346 href="#SymbolTable"><tt>SymbolTable</tt></a>.</p>
1348 <p>The list of <a href="#BasicBlock"><tt>BasicBlock</tt></a>s is the most
1349 commonly used part of <tt>Function</tt> objects. The list imposes an implicit
1350 ordering of the blocks in the function, which indicate how the code will be
1351 layed out by the backend. Additionally, the first <a
1352 href="#BasicBlock"><tt>BasicBlock</tt></a> is the implicit entry node for the
1353 <tt>Function</tt>. It is not legal in LLVM to explicitly branch to this initial
1354 block. There are no implicit exit nodes, and in fact there may be multiple exit
1355 nodes from a single <tt>Function</tt>. If the <a
1356 href="#BasicBlock"><tt>BasicBlock</tt></a> list is empty, this indicates that
1357 the <tt>Function</tt> is actually a function declaration: the actual body of the
1358 function hasn't been linked in yet.</p>
1360 <p>In addition to a list of <a href="#BasicBlock"><tt>BasicBlock</tt></a>s, the
1361 <tt>Function</tt> class also keeps track of the list of formal <a
1362 href="#Argument"><tt>Argument</tt></a>s that the function receives. This
1363 container manages the lifetime of the <a href="#Argument"><tt>Argument</tt></a>
1364 nodes, just like the <a href="#BasicBlock"><tt>BasicBlock</tt></a> list does for
1365 the <a href="#BasicBlock"><tt>BasicBlock</tt></a>s.</p>
1367 <p>The <a href="#SymbolTable"><tt>SymbolTable</tt></a> is a very rarely used
1368 LLVM feature that is only used when you have to look up a value by name. Aside
1369 from that, the <a href="#SymbolTable"><tt>SymbolTable</tt></a> is used
1370 internally to make sure that there are not conflicts between the names of <a
1371 href="#Instruction"><tt>Instruction</tt></a>s, <a
1372 href="#BasicBlock"><tt>BasicBlock</tt></a>s, or <a
1373 href="#Argument"><tt>Argument</tt></a>s in the function body.</p>
1375 <p>Note that <tt>Function</tt> is a <a href="#GlobalValue">GlobalValue</a>
1376 and therefore also a <a href="#Constant">Constant</a>. The value of the function
1377 is its address (after linking) which is guaranteed to be constant.</p>
1380 <!-- _______________________________________________________________________ -->
1381 <div class="doc_subsubsection">
1382 <a name="m_Function">Important Public Members of the <tt>Function</tt>
1386 <div class="doc_text">
1389 <li><tt>Function(const </tt><tt><a href="#FunctionType">FunctionType</a>
1390 *Ty, LinkageTypes Linkage, const std::string &N = "", Module* Parent = 0)</tt>
1392 <p>Constructor used when you need to create new <tt>Function</tt>s to add
1393 the the program. The constructor must specify the type of the function to
1394 create and what type of linkage the function should have. The <a
1395 href="#FunctionType"><tt>FunctionType</tt></a> argument
1396 specifies the formal arguments and return value for the function. The same
1397 <a href="#FunctionTypel"><tt>FunctionType</tt></a> value can be used to
1398 create multiple functions. The <tt>Parent</tt> argument specifies the Module
1399 in which the function is defined. If this argument is provided, the function
1400 will automatically be inserted into that module's list of
1403 <li><tt>bool isExternal()</tt>
1405 <p>Return whether or not the <tt>Function</tt> has a body defined. If the
1406 function is "external", it does not have a body, and thus must be resolved
1407 by linking with a function defined in a different translation unit.</p></li>
1409 <li><tt>Function::iterator</tt> - Typedef for basic block list iterator<br>
1410 <tt>Function::const_iterator</tt> - Typedef for const_iterator.<br>
1412 <tt>begin()</tt>, <tt>end()</tt>, <tt>front()</tt>, <tt>back()</tt>,
1413 <tt>size()</tt>, <tt>empty()</tt>, <tt>rbegin()</tt>, <tt>rend()</tt>
1415 <p>These are forwarding methods that make it easy to access the contents of
1416 a <tt>Function</tt> object's <a href="#BasicBlock"><tt>BasicBlock</tt></a>
1419 <li><tt>Function::BasicBlockListType &getBasicBlockList()</tt>
1421 <p>Returns the list of <a href="#BasicBlock"><tt>BasicBlock</tt></a>s. This
1422 is necessary to use when you need to update the list or perform a complex
1423 action that doesn't have a forwarding method.</p></li>
1425 <li><tt>Function::aiterator</tt> - Typedef for the argument list
1427 <tt>Function::const_aiterator</tt> - Typedef for const_iterator.<br>
1429 <tt>abegin()</tt>, <tt>aend()</tt>, <tt>afront()</tt>, <tt>aback()</tt>,
1430 <tt>asize()</tt>, <tt>aempty()</tt>, <tt>arbegin()</tt>, <tt>arend()</tt>
1432 <p>These are forwarding methods that make it easy to access the contents of
1433 a <tt>Function</tt> object's <a href="#Argument"><tt>Argument</tt></a>
1436 <li><tt>Function::ArgumentListType &getArgumentList()</tt>
1438 <p>Returns the list of <a href="#Argument"><tt>Argument</tt></a>s. This is
1439 necessary to use when you need to update the list or perform a complex
1440 action that doesn't have a forwarding method.</p></li>
1442 <li><tt><a href="#BasicBlock">BasicBlock</a> &getEntryBlock()</tt>
1444 <p>Returns the entry <a href="#BasicBlock"><tt>BasicBlock</tt></a> for the
1445 function. Because the entry block for the function is always the first
1446 block, this returns the first block of the <tt>Function</tt>.</p></li>
1448 <li><tt><a href="#Type">Type</a> *getReturnType()</tt><br>
1449 <tt><a href="#FunctionType">FunctionType</a> *getFunctionType()</tt>
1451 <p>This traverses the <a href="#Type"><tt>Type</tt></a> of the
1452 <tt>Function</tt> and returns the return type of the function, or the <a
1453 href="#FunctionType"><tt>FunctionType</tt></a> of the actual
1456 <li><tt><a href="#SymbolTable">SymbolTable</a> *getSymbolTable()</tt>
1458 <p> Return a pointer to the <a href="#SymbolTable"><tt>SymbolTable</tt></a>
1459 for this <tt>Function</tt>.</p></li>
1464 <!-- ======================================================================= -->
1465 <div class="doc_subsection">
1466 <a name="GlobalVariable">The <tt>GlobalVariable</tt> class</a>
1469 <div class="doc_text">
1472 href="/doxygen/GlobalVariable_8h-source.html">llvm/GlobalVariable.h</a>"</tt>
1474 doxygen info: <a href="/doxygen/classllvm_1_1GlobalVariable.html">GlobalVariable
1475 Class</a><br> Superclasses: <a href="#GlobalValue"><tt>GlobalValue</tt></a>, <a
1476 href="#User"><tt>User</tt></a>, <a href="#Value"><tt>Value</tt></a></p>
1478 <p>Global variables are represented with the (suprise suprise)
1479 <tt>GlobalVariable</tt> class. Like functions, <tt>GlobalVariable</tt>s are also
1480 subclasses of <a href="#GlobalValue"><tt>GlobalValue</tt></a>, and as such are
1481 always referenced by their address (global values must live in memory, so their
1482 "name" refers to their address). See <a
1483 href="#GlobalValue"><tt>GlobalValue</tt></a> for more on this. Global variables
1484 may have an initial value (which must be a <a
1485 href="#Constant"><tt>Constant</tt></a>), and if they have an initializer, they
1486 may be marked as "constant" themselves (indicating that their contents never
1487 change at runtime).</p>
1491 <!-- _______________________________________________________________________ -->
1492 <div class="doc_subsubsection">
1493 <a name="m_GlobalVariable">Important Public Members of the
1494 <tt>GlobalVariable</tt> class</a>
1497 <div class="doc_text">
1500 <li><tt>GlobalVariable(const </tt><tt><a href="#Type">Type</a> *Ty, bool
1501 isConstant, LinkageTypes& Linkage, <a href="#Constant">Constant</a>
1502 *Initializer = 0, const std::string &Name = "", Module* Parent = 0)</tt>
1504 <p>Create a new global variable of the specified type. If
1505 <tt>isConstant</tt> is true then the global variable will be marked as
1506 unchanging for the program. The Linkage parameter specifies the type of
1507 linkage (internal, external, weak, linkonce, appending) for the variable. If
1508 the linkage is InternalLinkage, WeakLinkage, or LinkOnceLinkage, then
1509 the resultant global variable will have internal linkage. AppendingLinkage
1510 concatenates together all instances (in different translation units) of the
1511 variable into a single variable but is only applicable to arrays. See
1512 the <a href="LangRef.html#modulestructure">LLVM Language Reference</a> for
1513 further details on linkage types. Optionally an initializer, a name, and the
1514 module to put the variable into may be specified for the global variable as
1517 <li><tt>bool isConstant() const</tt>
1519 <p>Returns true if this is a global variable that is known not to
1520 be modified at runtime.</p></li>
1522 <li><tt>bool hasInitializer()</tt>
1524 <p>Returns true if this <tt>GlobalVariable</tt> has an intializer.</p></li>
1526 <li><tt><a href="#Constant">Constant</a> *getInitializer()</tt>
1528 <p>Returns the intial value for a <tt>GlobalVariable</tt>. It is not legal
1529 to call this method if there is no initializer.</p></li>
1534 <!-- ======================================================================= -->
1535 <div class="doc_subsection">
1536 <a name="Module">The <tt>Module</tt> class</a>
1539 <div class="doc_text">
1542 href="/doxygen/Module_8h-source.html">llvm/Module.h</a>"</tt><br> doxygen info:
1543 <a href="/doxygen/classllvm_1_1Module.html">Module Class</a></p>
1545 <p>The <tt>Module</tt> class represents the top level structure present in LLVM
1546 programs. An LLVM module is effectively either a translation unit of the
1547 original program or a combination of several translation units merged by the
1548 linker. The <tt>Module</tt> class keeps track of a list of <a
1549 href="#Function"><tt>Function</tt></a>s, a list of <a
1550 href="#GlobalVariable"><tt>GlobalVariable</tt></a>s, and a <a
1551 href="#SymbolTable"><tt>SymbolTable</tt></a>. Additionally, it contains a few
1552 helpful member functions that try to make common operations easy.</p>
1556 <!-- _______________________________________________________________________ -->
1557 <div class="doc_subsubsection">
1558 <a name="m_Module">Important Public Members of the <tt>Module</tt> class</a>
1561 <div class="doc_text">
1564 <li><tt>Module::Module(std::string name = "")</tt></li>
1567 <p>Constructing a <a href="#Module">Module</a> is easy. You can optionally
1568 provide a name for it (probably based on the name of the translation unit).</p>
1571 <li><tt>Module::iterator</tt> - Typedef for function list iterator<br>
1572 <tt>Module::const_iterator</tt> - Typedef for const_iterator.<br>
1574 <tt>begin()</tt>, <tt>end()</tt>, <tt>front()</tt>, <tt>back()</tt>,
1575 <tt>size()</tt>, <tt>empty()</tt>, <tt>rbegin()</tt>, <tt>rend()</tt>
1577 <p>These are forwarding methods that make it easy to access the contents of
1578 a <tt>Module</tt> object's <a href="#Function"><tt>Function</tt></a>
1581 <li><tt>Module::FunctionListType &getFunctionList()</tt>
1583 <p> Returns the list of <a href="#Function"><tt>Function</tt></a>s. This is
1584 necessary to use when you need to update the list or perform a complex
1585 action that doesn't have a forwarding method.</p>
1587 <p><!-- Global Variable --></p></li>
1593 <li><tt>Module::giterator</tt> - Typedef for global variable list iterator<br>
1595 <tt>Module::const_giterator</tt> - Typedef for const_iterator.<br>
1597 <tt>gbegin()</tt>, <tt>gend()</tt>, <tt>gfront()</tt>, <tt>gback()</tt>,
1598 <tt>gsize()</tt>, <tt>gempty()</tt>, <tt>grbegin()</tt>, <tt>grend()</tt>
1600 <p> These are forwarding methods that make it easy to access the contents of
1601 a <tt>Module</tt> object's <a
1602 href="#GlobalVariable"><tt>GlobalVariable</tt></a> list.</p></li>
1604 <li><tt>Module::GlobalListType &getGlobalList()</tt>
1606 <p>Returns the list of <a
1607 href="#GlobalVariable"><tt>GlobalVariable</tt></a>s. This is necessary to
1608 use when you need to update the list or perform a complex action that
1609 doesn't have a forwarding method.</p>
1611 <p><!-- Symbol table stuff --> </p></li>
1617 <li><tt><a href="#SymbolTable">SymbolTable</a> *getSymbolTable()</tt>
1619 <p>Return a reference to the <a href="#SymbolTable"><tt>SymbolTable</tt></a>
1620 for this <tt>Module</tt>.</p>
1622 <p><!-- Convenience methods --></p></li>
1628 <li><tt><a href="#Function">Function</a> *getFunction(const std::string
1629 &Name, const <a href="#FunctionType">FunctionType</a> *Ty)</tt>
1631 <p>Look up the specified function in the <tt>Module</tt> <a
1632 href="#SymbolTable"><tt>SymbolTable</tt></a>. If it does not exist, return
1633 <tt>null</tt>.</p></li>
1635 <li><tt><a href="#Function">Function</a> *getOrInsertFunction(const
1636 std::string &Name, const <a href="#FunctionType">FunctionType</a> *T)</tt>
1638 <p>Look up the specified function in the <tt>Module</tt> <a
1639 href="#SymbolTable"><tt>SymbolTable</tt></a>. If it does not exist, add an
1640 external declaration for the function and return it.</p></li>
1642 <li><tt>std::string getTypeName(const <a href="#Type">Type</a> *Ty)</tt>
1644 <p>If there is at least one entry in the <a
1645 href="#SymbolTable"><tt>SymbolTable</tt></a> for the specified <a
1646 href="#Type"><tt>Type</tt></a>, return it. Otherwise return the empty
1649 <li><tt>bool addTypeName(const std::string &Name, const <a
1650 href="#Type">Type</a> *Ty)</tt>
1652 <p>Insert an entry in the <a href="#SymbolTable"><tt>SymbolTable</tt></a>
1653 mapping <tt>Name</tt> to <tt>Ty</tt>. If there is already an entry for this
1654 name, true is returned and the <a
1655 href="#SymbolTable"><tt>SymbolTable</tt></a> is not modified.</p></li>
1660 <!-- ======================================================================= -->
1661 <div class="doc_subsection">
1662 <a name="Constant">The <tt>Constant</tt> class and subclasses</a>
1665 <div class="doc_text">
1667 <p>Constant represents a base class for different types of constants. It
1668 is subclassed by ConstantBool, ConstantInt, ConstantSInt, ConstantUInt,
1669 ConstantArray etc for representing the various types of Constants.</p>
1673 <!-- _______________________________________________________________________ -->
1674 <div class="doc_subsubsection">
1675 <a name="m_Constant">Important Public Methods</a>
1677 <div class="doc_text">
1680 <!-- _______________________________________________________________________ -->
1681 <div class="doc_subsubsection">Important Subclasses of Constant </div>
1682 <div class="doc_text">
1684 <li>ConstantSInt : This subclass of Constant represents a signed integer
1687 <li><tt>int64_t getValue() const</tt>: Returns the underlying value of
1688 this constant. </li>
1691 <li>ConstantUInt : This class represents an unsigned integer.
1693 <li><tt>uint64_t getValue() const</tt>: Returns the underlying value of
1694 this constant. </li>
1697 <li>ConstantFP : This class represents a floating point constant.
1699 <li><tt>double getValue() const</tt>: Returns the underlying value of
1700 this constant. </li>
1703 <li>ConstantBool : This represents a boolean constant.
1705 <li><tt>bool getValue() const</tt>: Returns the underlying value of this
1709 <li>ConstantArray : This represents a constant array.
1711 <li><tt>const std::vector<Use> &getValues() const</tt>: Returns
1712 a Vecotr of component constants that makeup this array. </li>
1715 <li>ConstantStruct : This represents a constant struct.
1717 <li><tt>const std::vector<Use> &getValues() const</tt>: Returns
1718 a Vector of component constants that makeup this array. </li>
1721 <li>GlobalValue : This represents either a global variable or a function. In
1722 either case, the value is a constant fixed address (after linking).
1727 <!-- ======================================================================= -->
1728 <div class="doc_subsection">
1729 <a name="Type">The <tt>Type</tt> class and Derived Types</a>
1732 <div class="doc_text">
1734 <p>Type as noted earlier is also a subclass of a Value class. Any primitive
1735 type (like int, short etc) in LLVM is an instance of Type Class. All other
1736 types are instances of subclasses of type like FunctionType, ArrayType
1737 etc. DerivedType is the interface for all such dervied types including
1738 FunctionType, ArrayType, PointerType, StructType. Types can have names. They can
1739 be recursive (StructType). There exists exactly one instance of any type
1740 structure at a time. This allows using pointer equality of Type *s for comparing
1745 <!-- _______________________________________________________________________ -->
1746 <div class="doc_subsubsection">
1747 <a name="m_Value">Important Public Methods</a>
1750 <div class="doc_text">
1754 <li><tt>bool isSigned() const</tt>: Returns whether an integral numeric type
1755 is signed. This is true for SByteTy, ShortTy, IntTy, LongTy. Note that this is
1756 not true for Float and Double. </li>
1758 <li><tt>bool isUnsigned() const</tt>: Returns whether a numeric type is
1759 unsigned. This is not quite the complement of isSigned... nonnumeric types
1760 return false as they do with isSigned. This returns true for UByteTy,
1761 UShortTy, UIntTy, and ULongTy. </li>
1763 <li><tt>bool isInteger() const</tt>: Equivalent to isSigned() || isUnsigned().</li>
1765 <li><tt>bool isIntegral() const</tt>: Returns true if this is an integral
1766 type, which is either Bool type or one of the Integer types.</li>
1768 <li><tt>bool isFloatingPoint()</tt>: Return true if this is one of the two
1769 floating point types.</li>
1771 <li><tt>isLosslesslyConvertableTo (const Type *Ty) const</tt>: Return true if
1772 this type can be converted to 'Ty' without any reinterpretation of bits. For
1773 example, uint to int or one pointer type to another.</li>
1777 <!-- _______________________________________________________________________ -->
1778 <div class="doc_subsubsection">
1779 <a name="m_Value">Important Derived Types</a>
1781 <div class="doc_text">
1783 <li>SequentialType : This is subclassed by ArrayType and PointerType
1785 <li><tt>const Type * getElementType() const</tt>: Returns the type of each
1786 of the elements in the sequential type. </li>
1789 <li>ArrayType : This is a subclass of SequentialType and defines interface for
1792 <li><tt>unsigned getNumElements() const</tt>: Returns the number of
1793 elements in the array. </li>
1796 <li>PointerType : Subclass of SequentialType for pointer types. </li>
1797 <li>StructType : subclass of DerivedTypes for struct types </li>
1798 <li>FunctionType : subclass of DerivedTypes for function types.
1800 <li><tt>bool isVarArg() const</tt>: Returns true if its a vararg
1802 <li><tt> const Type * getReturnType() const</tt>: Returns the
1803 return type of the function.</li>
1804 <li><tt>const Type * getParamType (unsigned i)</tt>: Returns
1805 the type of the ith parameter.</li>
1806 <li><tt> const unsigned getNumParams() const</tt>: Returns the
1807 number of formal parameters.</li>
1813 <!-- ======================================================================= -->
1814 <div class="doc_subsection">
1815 <a name="Argument">The <tt>Argument</tt> class</a>
1818 <div class="doc_text">
1820 <p>This subclass of Value defines the interface for incoming formal
1821 arguments to a function. A Function maitanis a list of its formal
1822 arguments. An argument has a pointer to the parent Function.</p>
1826 <!-- ======================================================================= -->
1827 <div class="doc_subsection">
1828 <a name="SymbolTable">The <tt>SymbolTable</tt> class</a>
1830 <div class="doc_text">
1831 <p>This class provides a symbol table that the
1832 <a href="#Function"><tt>Function</tt></a> and <a href="#Module">
1833 <tt>Module</tt></a> classes use for naming definitions. The symbol table can
1834 provide a name for any <a href="#Value"><tt>Value</tt></a> or
1835 <a href="#Type"><tt>Type</tt></a>. <tt>SymbolTable</tt> is an abstract data
1836 type. It hides the data it contains and provides access to it through a
1837 controlled interface.</p>
1839 <p>To use the <tt>SymbolTable</tt> well, you need to understand the
1840 structure of the information it holds. The class contains two
1841 <tt>std::map</tt> objects. The first, <tt>pmap</tt>, is a map of
1842 <tt>Type*</tt> to maps of name (<tt>std::string</tt>) to <tt>Value*</tt>.
1843 The second, <tt>tmap</tt>, is a map of names to <tt>Type*</tt>. Thus, Values
1844 are stored in two-dimensions and accessed by <tt>Type</tt> and name. Types,
1845 however, are stored in a single dimension and accessed only by name.</p>
1847 <p>The interface of this class provides three basic types of operations:
1849 <li><em>Accessors</em>. Accessors provide read-only access to information
1850 such as finding a value for a name with the
1851 <a href="#SymbolTable_lookup">lookup</a> method.</li>
1852 <li><em>Mutators</em>. Mutators allow the user to add information to the
1853 <tt>SymbolTable</tt> with methods like
1854 <a href="#SymbolTable_insert"><tt>insert</tt></a>.</li>
1855 <li><em>Iterators</em>. Iterators allow the user to traverse the content
1856 of the symbol table in well defined ways, such as the method
1857 <a href="#SymbolTable_type_begin"><tt>type_begin</tt></a>.</li>
1862 <dt><tt>Value* lookup(const Type* Ty, const std::string& name) const</tt>:
1864 <dd>The <tt>lookup</tt> method searches the type plane given by the
1865 <tt>Ty</tt> parameter for a <tt>Value</tt> with the provided <tt>name</tt>.
1866 If a suitable <tt>Value</tt> is not found, null is returned.</dd>
1868 <dt><tt>Type* lookupType( const std::string& name) const</tt>:</dt>
1869 <dd>The <tt>lookupType</tt> method searches through the types for a
1870 <tt>Type</tt> with the provided <tt>name</tt>. If a suitable <tt>Type</tt>
1871 is not found, null is returned.</dd>
1873 <dt><tt>bool hasTypes() const</tt>:</dt>
1874 <dd>This function returns true if an entry has been made into the type
1877 <dt><tt>bool isEmpty() const</tt>:</dt>
1878 <dd>This function returns true if both the value and types maps are
1881 <dt><tt>std::string get_name(const Value*) const</tt>:</dt>
1882 <dd>This function returns the name of the Value provided or the empty
1883 string if the Value is not in the symbol table.</dd>
1885 <dt><tt>std::string get_name(const Type*) const</tt>:</dt>
1886 <dd>This function returns the name of the Type provided or the empty
1887 string if the Type is not in the symbol table.</dd>
1892 <dt><tt>void insert(Value *Val)</tt>:</dt>
1893 <dd>This method adds the provided value to the symbol table. The Value must
1894 have both a name and a type which are extracted and used to place the value
1895 in the correct type plane under the value's name.</dd>
1897 <dt><tt>void insert(const std::string& Name, Value *Val)</tt>:</dt>
1898 <dd> Inserts a constant or type into the symbol table with the specified
1899 name. There can be a many to one mapping between names and constants
1902 <dt><tt>void insert(const std::string& Name, Type *Typ)</tt>:</dt>
1903 <dd> Inserts a type into the symbol table with the specified name. There
1904 can be a many-to-one mapping between names and types. This method
1905 allows a type with an existing entry in the symbol table to get
1908 <dt><tt>void remove(Value* Val)</tt>:</dt>
1909 <dd> This method removes a named value from the symbol table. The
1910 type and name of the Value are extracted from \p N and used to
1911 lookup the Value in the correct type plane. If the Value is
1912 not in the symbol table, this method silently ignores the
1915 <dt><tt>void remove(Type* Typ)</tt>:</dt>
1916 <dd> This method removes a named type from the symbol table. The
1917 name of the type is extracted from \P T and used to look up
1918 the Type in the type map. If the Type is not in the symbol
1919 table, this method silently ignores the request.</dd>
1921 <dt><tt>Value* remove(const std::string& Name, Value *Val)</tt>:</dt>
1922 <dd> Remove a constant or type with the specified name from the
1925 <dt><tt>Type* remove(const std::string& Name, Type* T)</tt>:</dt>
1926 <dd> Remove a type with the specified name from the symbol table.
1927 Returns the removed Type.</dd>
1929 <dt><tt>Value *value_remove(const value_iterator& It)</tt>:</dt>
1930 <dd> Removes a specific value from the symbol table.
1931 Returns the removed value.</dd>
1933 <dt><tt>bool strip()</tt>:</dt>
1934 <dd> This method will strip the symbol table of its names leaving
1935 the type and values. </dd>
1937 <dt><tt>void clear()</tt>:</dt>
1938 <dd>Empty the symbol table completely.</dd>
1942 <p>The following functions describe three types of iterators you can obtain
1943 the beginning or end of the sequence for both const and non-const. It is
1944 important to keep track of the different kinds of iterators. There are
1945 three idioms worth pointing out:</p>
1947 <tr><th>Units</th><th>Iterator</th><th>Idiom</th></tr>
1949 <td align="left">Planes Of name/Value maps</td><td>PI</td>
1950 <td align="left"><pre><tt>
1951 for (SymbolTable::plane_const_iterator PI = ST.plane_begin(),
1952 PE = ST.plane_end(); PI != PE; ++PI ) {
1953 PI->first // This is the Type* of the plane
1954 PI->second // This is the SymbolTable::ValueMap of name/Value pairs
1958 <td align="left">All name/Type Pairs</td><td>TI</td>
1959 <td align="left"><pre><tt>
1960 for (SymbolTable::type_const_iterator TI = ST.type_begin(),
1961 TE = ST.type_end(); TI != TE; ++TI )
1962 TI->first // This is the name of the type
1963 TI->second // This is the Type* value associated with the name
1967 <td align="left">name/Value pairs in a plane</td><td>VI</td>
1968 <td align="left"><pre><tt>
1969 for (SymbolTable::value_const_iterator VI = ST.value_begin(SomeType),
1970 VE = ST.value_end(SomeType); VI != VE; ++VI )
1971 VI->first // This is the name of the Value
1972 VI->second // This is the Value* value associated with the name
1977 <p>Using the recommended iterator names and idioms will help you avoid
1978 making mistakes. Of particular note, make sure that whenever you use
1979 value_begin(SomeType) that you always compare the resulting iterator
1980 with value_end(SomeType) not value_end(SomeOtherType) or else you
1981 will loop infinitely.</p>
1985 <dt><tt>plane_iterator plane_begin()</tt>:</dt>
1986 <dd>Get an iterator that starts at the beginning of the type planes.
1987 The iterator will iterate over the Type/ValueMap pairs in the
1990 <dt><tt>plane_const_iterator plane_begin() const</tt>:</dt>
1991 <dd>Get a const_iterator that starts at the beginning of the type
1992 planes. The iterator will iterate over the Type/ValueMap pairs
1993 in the type planes. </dd>
1995 <dt><tt>plane_iterator plane_end()</tt>:</dt>
1996 <dd>Get an iterator at the end of the type planes. This serves as
1997 the marker for end of iteration over the type planes.</dd>
1999 <dt><tt>plane_const_iterator plane_end() const</tt>:</dt>
2000 <dd>Get a const_iterator at the end of the type planes. This serves as
2001 the marker for end of iteration over the type planes.</dd>
2003 <dt><tt>value_iterator value_begin(const Type *Typ)</tt>:</dt>
2004 <dd>Get an iterator that starts at the beginning of a type plane.
2005 The iterator will iterate over the name/value pairs in the type plane.
2006 Note: The type plane must already exist before using this.</dd>
2008 <dt><tt>value_const_iterator value_begin(const Type *Typ) const</tt>:</dt>
2009 <dd>Get a const_iterator that starts at the beginning of a type plane.
2010 The iterator will iterate over the name/value pairs in the type plane.
2011 Note: The type plane must already exist before using this.</dd>
2013 <dt><tt>value_iterator value_end(const Type *Typ)</tt>:</dt>
2014 <dd>Get an iterator to the end of a type plane. This serves as the marker
2015 for end of iteration of the type plane.
2016 Note: The type plane must already exist before using this.</dd>
2018 <dt><tt>value_const_iterator value_end(const Type *Typ) const</tt>:</dt>
2019 <dd>Get a const_iterator to the end of a type plane. This serves as the
2020 marker for end of iteration of the type plane.
2021 Note: the type plane must already exist before using this.</dd>
2023 <dt><tt>type_iterator type_begin()</tt>:</dt>
2024 <dd>Get an iterator to the start of the name/Type map.</dd>
2026 <dt><tt>type_const_iterator type_begin() cons</tt>:</dt>
2027 <dd> Get a const_iterator to the start of the name/Type map.</dd>
2029 <dt><tt>type_iterator type_end()</tt>:</dt>
2030 <dd>Get an iterator to the end of the name/Type map. This serves as the
2031 marker for end of iteration of the types.</dd>
2033 <dt><tt>type_const_iterator type_end() const</tt>:</dt>
2034 <dd>Get a const-iterator to the end of the name/Type map. This serves
2035 as the marker for end of iteration of the types.</dd>
2037 <dt><tt>plane_const_iterator find(const Type* Typ ) const</tt>:</dt>
2038 <dd>This method returns a plane_const_iterator for iteration over
2039 the type planes starting at a specific plane, given by \p Ty.</dd>
2041 <dt><tt>plane_iterator find( const Type* Typ </tt>:</dt>
2042 <dd>This method returns a plane_iterator for iteration over the
2043 type planes starting at a specific plane, given by \p Ty.</dd>
2045 <dt><tt>const ValueMap* findPlane( const Type* Typ ) cons</tt>:</dt>
2046 <dd>This method returns a ValueMap* for a specific type plane. This
2047 interface is deprecated and may go away in the future.</dd>
2051 <!-- *********************************************************************** -->
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2059 <a href="mailto:dhurjati@cs.uiuc.edu">Dinakar Dhurjati</a> and
2060 <a href="mailto:sabre@nondot.org">Chris Lattner</a><br>
2061 <a href="http://llvm.cs.uiuc.edu">The LLVM Compiler Infrastructure</a><br>
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