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10 <div class="doc_title">
11 LLVM Programmer's Manual
15 <li><a href="#introduction">Introduction</a></li>
16 <li><a href="#general">General Information</a>
18 <li><a href="#stl">The C++ Standard Template Library</a></li>
20 <li>The <tt>-time-passes</tt> option</li>
21 <li>How to use the LLVM Makefile system</li>
22 <li>How to write a regression test</li>
27 <li><a href="#apis">Important and useful LLVM APIs</a>
29 <li><a href="#isa">The <tt>isa<></tt>, <tt>cast<></tt>
30 and <tt>dyn_cast<></tt> templates</a> </li>
31 <li><a href="#DEBUG">The <tt>DEBUG()</tt> macro & <tt>-debug</tt>
34 <li><a href="#DEBUG_TYPE">Fine grained debug info with <tt>DEBUG_TYPE</tt>
35 and the <tt>-debug-only</tt> option</a> </li>
38 <li><a href="#Statistic">The <tt>Statistic</tt> template & <tt>-stats</tt>
41 <li>The <tt>InstVisitor</tt> template
42 <li>The general graph API
46 <li><a href="#common">Helpful Hints for Common Operations</a>
48 <li><a href="#inspection">Basic Inspection and Traversal Routines</a>
50 <li><a href="#iterate_function">Iterating over the <tt>BasicBlock</tt>s
51 in a <tt>Function</tt></a> </li>
52 <li><a href="#iterate_basicblock">Iterating over the <tt>Instruction</tt>s
53 in a <tt>BasicBlock</tt></a> </li>
54 <li><a href="#iterate_institer">Iterating over the <tt>Instruction</tt>s
55 in a <tt>Function</tt></a> </li>
56 <li><a href="#iterate_convert">Turning an iterator into a
57 class pointer</a> </li>
58 <li><a href="#iterate_complex">Finding call sites: a more
59 complex example</a> </li>
60 <li><a href="#calls_and_invokes">Treating calls and invokes
61 the same way</a> </li>
62 <li><a href="#iterate_chains">Iterating over def-use &
63 use-def chains</a> </li>
66 <li><a href="#simplechanges">Making simple changes</a>
68 <li><a href="#schanges_creating">Creating and inserting new
69 <tt>Instruction</tt>s</a> </li>
70 <li><a href="#schanges_deleting">Deleting <tt>Instruction</tt>s</a> </li>
71 <li><a href="#schanges_replacing">Replacing an <tt>Instruction</tt>
72 with another <tt>Value</tt></a> </li>
76 <li>Working with the Control Flow Graph
78 <li>Accessing predecessors and successors of a <tt>BasicBlock</tt>
85 <li><a href="#coreclasses">The Core LLVM Class Hierarchy Reference</a>
87 <li><a href="#Value">The <tt>Value</tt> class</a>
89 <li><a href="#User">The <tt>User</tt> class</a>
91 <li><a href="#Instruction">The <tt>Instruction</tt> class</a>
93 <li><a href="#GetElementPtrInst">The <tt>GetElementPtrInst</tt> class</a></li>
96 <li><a href="#Module">The <tt>Module</tt> class</a></li>
97 <li><a href="#Constant">The <tt>Constant</tt> class</a>
99 <li><a href="#GlobalValue">The <tt>GlobalValue</tt> class</a>
101 <li><a href="#BasicBlock">The <tt>BasicBlock</tt>class</a></li>
102 <li><a href="#Function">The <tt>Function</tt> class</a></li>
103 <li><a href="#GlobalVariable">The <tt>GlobalVariable</tt> class</a></li>
110 <li><a href="#Type">The <tt>Type</tt> class</a> </li>
111 <li><a href="#Argument">The <tt>Argument</tt> class</a></li>
116 <li><a href="#SymbolTable">The <tt>SymbolTable</tt> class </a></li>
117 <li>The <tt>ilist</tt> and <tt>iplist</tt> classes
119 <li>Creating, inserting, moving and deleting from LLVM lists </li>
122 <li>Important iterator invalidation semantics to be aware of.</li>
125 <div class="doc_author">
126 <p>Written by <a href="mailto:sabre@nondot.org">Chris Lattner</a>,
127 <a href="mailto:dhurjati@cs.uiuc.edu">Dinakar Dhurjati</a>,
128 <a href="mailto:jstanley@cs.uiuc.edu">Joel Stanley</a>, and
129 <a href="mailto:rspencer@x10sys.com">Reid Spencer</a></p>
132 <!-- *********************************************************************** -->
133 <div class="doc_section">
134 <a name="introduction">Introduction </a>
136 <!-- *********************************************************************** -->
138 <div class="doc_text">
140 <p>This document is meant to highlight some of the important classes and
141 interfaces available in the LLVM source-base. This manual is not
142 intended to explain what LLVM is, how it works, and what LLVM code looks
143 like. It assumes that you know the basics of LLVM and are interested
144 in writing transformations or otherwise analyzing or manipulating the
147 <p>This document should get you oriented so that you can find your
148 way in the continuously growing source code that makes up the LLVM
149 infrastructure. Note that this manual is not intended to serve as a
150 replacement for reading the source code, so if you think there should be
151 a method in one of these classes to do something, but it's not listed,
152 check the source. Links to the <a href="/doxygen/">doxygen</a> sources
153 are provided to make this as easy as possible.</p>
155 <p>The first section of this document describes general information that is
156 useful to know when working in the LLVM infrastructure, and the second describes
157 the Core LLVM classes. In the future this manual will be extended with
158 information describing how to use extension libraries, such as dominator
159 information, CFG traversal routines, and useful utilities like the <tt><a
160 href="/doxygen/InstVisitor_8h-source.html">InstVisitor</a></tt> template.</p>
164 <!-- *********************************************************************** -->
165 <div class="doc_section">
166 <a name="general">General Information</a>
168 <!-- *********************************************************************** -->
170 <div class="doc_text">
172 <p>This section contains general information that is useful if you are working
173 in the LLVM source-base, but that isn't specific to any particular API.</p>
177 <!-- ======================================================================= -->
178 <div class="doc_subsection">
179 <a name="stl">The C++ Standard Template Library</a>
182 <div class="doc_text">
184 <p>LLVM makes heavy use of the C++ Standard Template Library (STL),
185 perhaps much more than you are used to, or have seen before. Because of
186 this, you might want to do a little background reading in the
187 techniques used and capabilities of the library. There are many good
188 pages that discuss the STL, and several books on the subject that you
189 can get, so it will not be discussed in this document.</p>
191 <p>Here are some useful links:</p>
195 <li><a href="http://www.dinkumware.com/refxcpp.html">Dinkumware C++ Library
196 reference</a> - an excellent reference for the STL and other parts of the
197 standard C++ library.</li>
199 <li><a href="http://www.tempest-sw.com/cpp/">C++ In a Nutshell</a> - This is an
200 O'Reilly book in the making. It has a decent
202 Reference that rivals Dinkumware's, and is unfortunately no longer free since the book has been
205 <li><a href="http://www.parashift.com/c++-faq-lite/">C++ Frequently Asked
208 <li><a href="http://www.sgi.com/tech/stl/">SGI's STL Programmer's Guide</a> -
210 href="http://www.sgi.com/tech/stl/stl_introduction.html">Introduction to the
213 <li><a href="http://www.research.att.com/%7Ebs/C++.html">Bjarne Stroustrup's C++
216 <li><a href="http://64.78.49.204/">
217 Bruce Eckel's Thinking in C++, 2nd ed. Volume 2 Revision 4.0 (even better, get
222 <p>You are also encouraged to take a look at the <a
223 href="CodingStandards.html">LLVM Coding Standards</a> guide which focuses on how
224 to write maintainable code more than where to put your curly braces.</p>
228 <!-- ======================================================================= -->
229 <div class="doc_subsection">
230 <a name="stl">Other useful references</a>
233 <div class="doc_text">
236 <li><a href="http://www.psc.edu/%7Esemke/cvs_branches.html">CVS
237 Branch and Tag Primer</a></li>
238 <li><a href="http://www.fortran-2000.com/ArnaudRecipes/sharedlib.html">Using
239 static and shared libraries across platforms</a></li>
244 <!-- *********************************************************************** -->
245 <div class="doc_section">
246 <a name="apis">Important and useful LLVM APIs</a>
248 <!-- *********************************************************************** -->
250 <div class="doc_text">
252 <p>Here we highlight some LLVM APIs that are generally useful and good to
253 know about when writing transformations.</p>
257 <!-- ======================================================================= -->
258 <div class="doc_subsection">
259 <a name="isa">The isa<>, cast<> and dyn_cast<> templates</a>
262 <div class="doc_text">
264 <p>The LLVM source-base makes extensive use of a custom form of RTTI.
265 These templates have many similarities to the C++ <tt>dynamic_cast<></tt>
266 operator, but they don't have some drawbacks (primarily stemming from
267 the fact that <tt>dynamic_cast<></tt> only works on classes that
268 have a v-table). Because they are used so often, you must know what they
269 do and how they work. All of these templates are defined in the <a
270 href="/doxygen/Casting_8h-source.html"><tt>Support/Casting.h</tt></a>
271 file (note that you very rarely have to include this file directly).</p>
274 <dt><tt>isa<></tt>: </dt>
276 <dd>The <tt>isa<></tt> operator works exactly like the Java
277 "<tt>instanceof</tt>" operator. It returns true or false depending on whether
278 a reference or pointer points to an instance of the specified class. This can
279 be very useful for constraint checking of various sorts (example below).</dd>
281 <dt><tt>cast<></tt>: </dt>
283 <dd>The <tt>cast<></tt> operator is a "checked cast" operation. It
284 converts a pointer or reference from a base class to a derived cast, causing
285 an assertion failure if it is not really an instance of the right type. This
286 should be used in cases where you have some information that makes you believe
287 that something is of the right type. An example of the <tt>isa<></tt>
288 and <tt>cast<></tt> template is:
291 static bool isLoopInvariant(const <a href="#Value">Value</a> *V, const Loop *L) {
292 if (isa<<a href="#Constant">Constant</a>>(V) || isa<<a href="#Argument">Argument</a>>(V) || isa<<a href="#GlobalValue">GlobalValue</a>>(V))
295 <i>// Otherwise, it must be an instruction...</i>
296 return !L->contains(cast<<a href="#Instruction">Instruction</a>>(V)->getParent());
299 <p>Note that you should <b>not</b> use an <tt>isa<></tt> test followed
300 by a <tt>cast<></tt>, for that use the <tt>dyn_cast<></tt>
305 <dt><tt>dyn_cast<></tt>:</dt>
307 <dd>The <tt>dyn_cast<></tt> operator is a "checking cast" operation. It
308 checks to see if the operand is of the specified type, and if so, returns a
309 pointer to it (this operator does not work with references). If the operand is
310 not of the correct type, a null pointer is returned. Thus, this works very
311 much like the <tt>dynamic_cast</tt> operator in C++, and should be used in the
312 same circumstances. Typically, the <tt>dyn_cast<></tt> operator is used
313 in an <tt>if</tt> statement or some other flow control statement like this:
316 if (<a href="#AllocationInst">AllocationInst</a> *AI = dyn_cast<<a href="#AllocationInst">AllocationInst</a>>(Val)) {
321 <p> This form of the <tt>if</tt> statement effectively combines together a
322 call to <tt>isa<></tt> and a call to <tt>cast<></tt> into one
323 statement, which is very convenient.</p>
325 <p> Another common example is:</p>
328 <i>// Loop over all of the phi nodes in a basic block</i>
329 BasicBlock::iterator BBI = BB->begin();
330 for (; <a href="#PhiNode">PHINode</a> *PN = dyn_cast<<a href="#PHINode">PHINode</a>>(BBI); ++BBI)
331 std::cerr << *PN;
334 <p>Note that the <tt>dyn_cast<></tt> operator, like C++'s
335 <tt>dynamic_cast</tt> or Java's <tt>instanceof</tt> operator, can be abused.
336 In particular you should not use big chained <tt>if/then/else</tt> blocks to
337 check for lots of different variants of classes. If you find yourself
338 wanting to do this, it is much cleaner and more efficient to use the
339 InstVisitor class to dispatch over the instruction type directly.</p>
343 <dt><tt>cast_or_null<></tt>: </dt>
345 <dd>The <tt>cast_or_null<></tt> operator works just like the
346 <tt>cast<></tt> operator, except that it allows for a null pointer as
347 an argument (which it then propagates). This can sometimes be useful,
348 allowing you to combine several null checks into one.</dd>
350 <dt><tt>dyn_cast_or_null<></tt>: </dt>
352 <dd>The <tt>dyn_cast_or_null<></tt> operator works just like the
353 <tt>dyn_cast<></tt> operator, except that it allows for a null pointer
354 as an argument (which it then propagates). This can sometimes be useful,
355 allowing you to combine several null checks into one.</dd>
359 <p>These five templates can be used with any classes, whether they have a
360 v-table or not. To add support for these templates, you simply need to add
361 <tt>classof</tt> static methods to the class you are interested casting
362 to. Describing this is currently outside the scope of this document, but there
363 are lots of examples in the LLVM source base.</p>
367 <!-- ======================================================================= -->
368 <div class="doc_subsection">
369 <a name="DEBUG">The <tt>DEBUG()</tt> macro & <tt>-debug</tt> option</a>
372 <div class="doc_text">
374 <p>Often when working on your pass you will put a bunch of debugging printouts
375 and other code into your pass. After you get it working, you want to remove
376 it... but you may need it again in the future (to work out new bugs that you run
379 <p> Naturally, because of this, you don't want to delete the debug printouts,
380 but you don't want them to always be noisy. A standard compromise is to comment
381 them out, allowing you to enable them if you need them in the future.</p>
383 <p>The "<tt><a href="/doxygen/Debug_8h-source.html">Support/Debug.h</a></tt>"
384 file provides a macro named <tt>DEBUG()</tt> that is a much nicer solution to
385 this problem. Basically, you can put arbitrary code into the argument of the
386 <tt>DEBUG</tt> macro, and it is only executed if '<tt>opt</tt>' (or any other
387 tool) is run with the '<tt>-debug</tt>' command line argument:</p>
389 <pre> ... <br> DEBUG(std::cerr << "I am here!\n");<br> ...<br></pre>
391 <p>Then you can run your pass like this:</p>
393 <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>
395 <p>Using the <tt>DEBUG()</tt> macro instead of a home-brewed solution allows you
396 to not have to create "yet another" command line option for the debug output for
397 your pass. Note that <tt>DEBUG()</tt> macros are disabled for optimized builds,
398 so they do not cause a performance impact at all (for the same reason, they
399 should also not contain side-effects!).</p>
401 <p>One additional nice thing about the <tt>DEBUG()</tt> macro is that you can
402 enable or disable it directly in gdb. Just use "<tt>set DebugFlag=0</tt>" or
403 "<tt>set DebugFlag=1</tt>" from the gdb if the program is running. If the
404 program hasn't been started yet, you can always just run it with
409 <!-- _______________________________________________________________________ -->
410 <div class="doc_subsubsection">
411 <a name="DEBUG_TYPE">Fine grained debug info with <tt>DEBUG_TYPE()</tt> and
412 the <tt>-debug-only</tt> option</a>
415 <div class="doc_text">
417 <p>Sometimes you may find yourself in a situation where enabling <tt>-debug</tt>
418 just turns on <b>too much</b> information (such as when working on the code
419 generator). If you want to enable debug information with more fine-grained
420 control, you define the <tt>DEBUG_TYPE</tt> macro and the <tt>-debug</tt> only
421 option as follows:</p>
423 <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>
425 <p>Then you can run your pass like this:</p>
427 <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>
429 <p>Of course, in practice, you should only set <tt>DEBUG_TYPE</tt> at the top of
430 a file, to specify the debug type for the entire module (if you do this before
431 you <tt>#include "Support/Debug.h"</tt>, you don't have to insert the ugly
432 <tt>#undef</tt>'s). Also, you should use names more meaningful than "foo" and
433 "bar", because there is no system in place to ensure that names do not
434 conflict. If two different modules use the same string, they will all be turned
435 on when the name is specified. This allows, for example, all debug information
436 for instruction scheduling to be enabled with <tt>-debug-type=InstrSched</tt>,
437 even if the source lives in multiple files.</p>
441 <!-- ======================================================================= -->
442 <div class="doc_subsection">
443 <a name="Statistic">The <tt>Statistic</tt> template & <tt>-stats</tt>
447 <div class="doc_text">
450 href="/doxygen/Statistic_8h-source.html">Support/Statistic.h</a></tt>" file
451 provides a template named <tt>Statistic</tt> that is used as a unified way to
452 keep track of what the LLVM compiler is doing and how effective various
453 optimizations are. It is useful to see what optimizations are contributing to
454 making a particular program run faster.</p>
456 <p>Often you may run your pass on some big program, and you're interested to see
457 how many times it makes a certain transformation. Although you can do this with
458 hand inspection, or some ad-hoc method, this is a real pain and not very useful
459 for big programs. Using the <tt>Statistic</tt> template makes it very easy to
460 keep track of this information, and the calculated information is presented in a
461 uniform manner with the rest of the passes being executed.</p>
463 <p>There are many examples of <tt>Statistic</tt> uses, but the basics of using
464 it are as follows:</p>
467 <li>Define your statistic like this:
468 <pre>static Statistic<> NumXForms("mypassname", "The # of times I did stuff");<br></pre>
470 <p>The <tt>Statistic</tt> template can emulate just about any data-type,
471 but if you do not specify a template argument, it defaults to acting like
472 an unsigned int counter (this is usually what you want).</p></li>
474 <li>Whenever you make a transformation, bump the counter:
475 <pre> ++NumXForms; // I did stuff<br></pre>
479 <p>That's all you have to do. To get '<tt>opt</tt>' to print out the
480 statistics gathered, use the '<tt>-stats</tt>' option:</p>
482 <pre> $ opt -stats -mypassname < program.bc > /dev/null<br> ... statistic output ...<br></pre>
484 <p> When running <tt>gccas</tt> on a C file from the SPEC benchmark
485 suite, it gives a report that looks like this:</p>
487 <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>
489 <p>Obviously, with so many optimizations, having a unified framework for this
490 stuff is very nice. Making your pass fit well into the framework makes it more
491 maintainable and useful.</p>
495 <!-- *********************************************************************** -->
496 <div class="doc_section">
497 <a name="common">Helpful Hints for Common Operations</a>
499 <!-- *********************************************************************** -->
501 <div class="doc_text">
503 <p>This section describes how to perform some very simple transformations of
504 LLVM code. This is meant to give examples of common idioms used, showing the
505 practical side of LLVM transformations. <p> Because this is a "how-to" section,
506 you should also read about the main classes that you will be working with. The
507 <a href="#coreclasses">Core LLVM Class Hierarchy Reference</a> contains details
508 and descriptions of the main classes that you should know about.</p>
512 <!-- NOTE: this section should be heavy on example code -->
513 <!-- ======================================================================= -->
514 <div class="doc_subsection">
515 <a name="inspection">Basic Inspection and Traversal Routines</a>
518 <div class="doc_text">
520 <p>The LLVM compiler infrastructure have many different data structures that may
521 be traversed. Following the example of the C++ standard template library, the
522 techniques used to traverse these various data structures are all basically the
523 same. For a enumerable sequence of values, the <tt>XXXbegin()</tt> function (or
524 method) returns an iterator to the start of the sequence, the <tt>XXXend()</tt>
525 function returns an iterator pointing to one past the last valid element of the
526 sequence, and there is some <tt>XXXiterator</tt> data type that is common
527 between the two operations.</p>
529 <p>Because the pattern for iteration is common across many different aspects of
530 the program representation, the standard template library algorithms may be used
531 on them, and it is easier to remember how to iterate. First we show a few common
532 examples of the data structures that need to be traversed. Other data
533 structures are traversed in very similar ways.</p>
537 <!-- _______________________________________________________________________ -->
538 <div class="doc_subsubsection">
539 <a name="iterate_function">Iterating over the </a><a
540 href="#BasicBlock"><tt>BasicBlock</tt></a>s in a <a
541 href="#Function"><tt>Function</tt></a>
544 <div class="doc_text">
546 <p>It's quite common to have a <tt>Function</tt> instance that you'd like to
547 transform in some way; in particular, you'd like to manipulate its
548 <tt>BasicBlock</tt>s. To facilitate this, you'll need to iterate over all of
549 the <tt>BasicBlock</tt>s that constitute the <tt>Function</tt>. The following is
550 an example that prints the name of a <tt>BasicBlock</tt> and the number of
551 <tt>Instruction</tt>s it contains:</p>
553 <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>
555 <p>Note that i can be used as if it were a pointer for the purposes of
556 invoking member functions of the <tt>Instruction</tt> class. This is
557 because the indirection operator is overloaded for the iterator
558 classes. In the above code, the expression <tt>i->size()</tt> is
559 exactly equivalent to <tt>(*i).size()</tt> just like you'd expect.</p>
563 <!-- _______________________________________________________________________ -->
564 <div class="doc_subsubsection">
565 <a name="iterate_basicblock">Iterating over the </a><a
566 href="#Instruction"><tt>Instruction</tt></a>s in a <a
567 href="#BasicBlock"><tt>BasicBlock</tt></a>
570 <div class="doc_text">
572 <p>Just like when dealing with <tt>BasicBlock</tt>s in <tt>Function</tt>s, it's
573 easy to iterate over the individual instructions that make up
574 <tt>BasicBlock</tt>s. Here's a code snippet that prints out each instruction in
575 a <tt>BasicBlock</tt>:</p>
577 <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>
579 <p>However, this isn't really the best way to print out the contents of a
580 <tt>BasicBlock</tt>! Since the ostream operators are overloaded for virtually
581 anything you'll care about, you could have just invoked the print routine on the
582 basic block itself: <tt>cerr << *blk << "\n";</tt>.</p>
584 <p>Note that currently operator<< is implemented for <tt>Value*</tt>, so
585 it will print out the contents of the pointer, instead of the pointer value you
586 might expect. This is a deprecated interface that will be removed in the
587 future, so it's best not to depend on it. To print out the pointer value for
588 now, you must cast to <tt>void*</tt>.</p>
592 <!-- _______________________________________________________________________ -->
593 <div class="doc_subsubsection">
594 <a name="iterate_institer">Iterating over the </a><a
595 href="#Instruction"><tt>Instruction</tt></a>s in a <a
596 href="#Function"><tt>Function</tt></a>
599 <div class="doc_text">
601 <p>If you're finding that you commonly iterate over a <tt>Function</tt>'s
602 <tt>BasicBlock</tt>s and then that <tt>BasicBlock</tt>'s <tt>Instruction</tt>s,
603 <tt>InstIterator</tt> should be used instead. You'll need to include <a
604 href="/doxygen/InstIterator_8h-source.html"><tt>llvm/Support/InstIterator.h</tt></a>,
605 and then instantiate <tt>InstIterator</tt>s explicitly in your code. Here's a
606 small example that shows how to dump all instructions in a function to the standard error stream:<p>
608 <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>
609 Easy, isn't it? You can also use <tt>InstIterator</tt>s to fill a
610 worklist with its initial contents. For example, if you wanted to
611 initialize a worklist to contain all instructions in a <tt>Function</tt>
612 F, all you would need to do is something like:
613 <pre>std::set<Instruction*> worklist;<br>worklist.insert(inst_begin(F), inst_end(F));<br></pre>
615 <p>The STL set <tt>worklist</tt> would now contain all instructions in the
616 <tt>Function</tt> pointed to by F.</p>
620 <!-- _______________________________________________________________________ -->
621 <div class="doc_subsubsection">
622 <a name="iterate_convert">Turning an iterator into a class pointer (and
626 <div class="doc_text">
628 <p>Sometimes, it'll be useful to grab a reference (or pointer) to a class
629 instance when all you've got at hand is an iterator. Well, extracting
630 a reference or a pointer from an iterator is very straight-forward.
631 Assuming that <tt>i</tt> is a <tt>BasicBlock::iterator</tt> and <tt>j</tt>
632 is a <tt>BasicBlock::const_iterator</tt>:</p>
634 <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>
636 <p>However, the iterators you'll be working with in the LLVM framework are
637 special: they will automatically convert to a ptr-to-instance type whenever they
638 need to. Instead of dereferencing the iterator and then taking the address of
639 the result, you can simply assign the iterator to the proper pointer type and
640 you get the dereference and address-of operation as a result of the assignment
641 (behind the scenes, this is a result of overloading casting mechanisms). Thus
642 the last line of the last example,</p>
644 <pre>Instruction* pinst = &*i;</pre>
646 <p>is semantically equivalent to</p>
648 <pre>Instruction* pinst = i;</pre>
650 <p>It's also possible to turn a class pointer into the corresponding iterator,
651 and this is a constant time operation (very efficient). The following code
652 snippet illustrates use of the conversion constructors provided by LLVM
653 iterators. By using these, you can explicitly grab the iterator of something
654 without actually obtaining it via iteration over some structure:</p>
656 <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>
660 <!--_______________________________________________________________________-->
661 <div class="doc_subsubsection">
662 <a name="iterate_complex">Finding call sites: a slightly more complex
666 <div class="doc_text">
668 <p>Say that you're writing a FunctionPass and would like to count all the
669 locations in the entire module (that is, across every <tt>Function</tt>) where a
670 certain function (i.e., some <tt>Function</tt>*) is already in scope. As you'll
671 learn later, you may want to use an <tt>InstVisitor</tt> to accomplish this in a
672 much more straight-forward manner, but this example will allow us to explore how
673 you'd do it if you didn't have <tt>InstVisitor</tt> around. In pseudocode, this
674 is what we want to do:</p>
676 <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>
678 <p>And the actual code is (remember, since we're writing a
679 <tt>FunctionPass</tt>, our <tt>FunctionPass</tt>-derived class simply has to
680 override the <tt>runOnFunction</tt> method...):</p>
682 <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
683 href="#CallInst">CallInst</a>* callInst = <a href="#isa">dyn_cast</a><<a
684 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>
688 <!--_______________________________________________________________________-->
689 <div class="doc_subsubsection">
690 <a name="calls_and_invokes">Treating calls and invokes the same way</a>
693 <div class="doc_text">
695 <p>You may have noticed that the previous example was a bit oversimplified in
696 that it did not deal with call sites generated by 'invoke' instructions. In
697 this, and in other situations, you may find that you want to treat
698 <tt>CallInst</tt>s and <tt>InvokeInst</tt>s the same way, even though their
699 most-specific common base class is <tt>Instruction</tt>, which includes lots of
700 less closely-related things. For these cases, LLVM provides a handy wrapper
702 href="http://llvm.cs.uiuc.edu/doxygen/classllvm_1_1CallSite.html"><tt>CallSite</tt></a>.
703 It is essentially a wrapper around an <tt>Instruction</tt> pointer, with some
704 methods that provide functionality common to <tt>CallInst</tt>s and
705 <tt>InvokeInst</tt>s.</p>
707 <p>This class has "value semantics": it should be passed by value, not by
708 reference and it should not be dynamically allocated or deallocated using
709 <tt>operator new</tt> or <tt>operator delete</tt>. It is efficiently copyable,
710 assignable and constructable, with costs equivalents to that of a bare pointer.
711 If you look at its definition, it has only a single pointer member.</p>
715 <!--_______________________________________________________________________-->
716 <div class="doc_subsubsection">
717 <a name="iterate_chains">Iterating over def-use & use-def chains</a>
720 <div class="doc_text">
722 <p>Frequently, we might have an instance of the <a
723 href="/doxygen/structllvm_1_1Value.html">Value Class</a> and we want to
724 determine which <tt>User</tt>s use the <tt>Value</tt>. The list of all
725 <tt>User</tt>s of a particular <tt>Value</tt> is called a <i>def-use</i> chain.
726 For example, let's say we have a <tt>Function*</tt> named <tt>F</tt> to a
727 particular function <tt>foo</tt>. Finding all of the instructions that
728 <i>use</i> <tt>foo</tt> is as simple as iterating over the <i>def-use</i> chain
731 <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>
733 <p>Alternately, it's common to have an instance of the <a
734 href="/doxygen/classllvm_1_1User.html">User Class</a> and need to know what
735 <tt>Value</tt>s are used by it. The list of all <tt>Value</tt>s used by a
736 <tt>User</tt> is known as a <i>use-def</i> chain. Instances of class
737 <tt>Instruction</tt> are common <tt>User</tt>s, so we might want to iterate over
738 all of the values that a particular instruction uses (that is, the operands of
739 the particular <tt>Instruction</tt>):</p>
741 <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>
744 def-use chains ("finding all users of"): Value::use_begin/use_end
745 use-def chains ("finding all values used"): User::op_begin/op_end [op=operand]
750 <!-- ======================================================================= -->
751 <div class="doc_subsection">
752 <a name="simplechanges">Making simple changes</a>
755 <div class="doc_text">
757 <p>There are some primitive transformation operations present in the LLVM
758 infrastructure that are worth knowing about. When performing
759 transformations, it's fairly common to manipulate the contents of basic
760 blocks. This section describes some of the common methods for doing so
761 and gives example code.</p>
765 <!--_______________________________________________________________________-->
766 <div class="doc_subsubsection">
767 <a name="schanges_creating">Creating and inserting new
768 <tt>Instruction</tt>s</a>
771 <div class="doc_text">
773 <p><i>Instantiating Instructions</i></p>
775 <p>Creation of <tt>Instruction</tt>s is straight-forward: simply call the
776 constructor for the kind of instruction to instantiate and provide the necessary
777 parameters. For example, an <tt>AllocaInst</tt> only <i>requires</i> a
778 (const-ptr-to) <tt>Type</tt>. Thus:</p>
780 <pre>AllocaInst* ai = new AllocaInst(Type::IntTy);</pre>
782 <p>will create an <tt>AllocaInst</tt> instance that represents the allocation of
783 one integer in the current stack frame, at runtime. Each <tt>Instruction</tt>
784 subclass is likely to have varying default parameters which change the semantics
785 of the instruction, so refer to the <a
786 href="/doxygen/classllvm_1_1Instruction.html">doxygen documentation for the subclass of
787 Instruction</a> that you're interested in instantiating.</p>
789 <p><i>Naming values</i></p>
791 <p>It is very useful to name the values of instructions when you're able to, as
792 this facilitates the debugging of your transformations. If you end up looking
793 at generated LLVM machine code, you definitely want to have logical names
794 associated with the results of instructions! By supplying a value for the
795 <tt>Name</tt> (default) parameter of the <tt>Instruction</tt> constructor, you
796 associate a logical name with the result of the instruction's execution at
797 runtime. For example, say that I'm writing a transformation that dynamically
798 allocates space for an integer on the stack, and that integer is going to be
799 used as some kind of index by some other code. To accomplish this, I place an
800 <tt>AllocaInst</tt> at the first point in the first <tt>BasicBlock</tt> of some
801 <tt>Function</tt>, and I'm intending to use it within the same
802 <tt>Function</tt>. I might do:</p>
804 <pre>AllocaInst* pa = new AllocaInst(Type::IntTy, 0, "indexLoc");</pre>
806 <p>where <tt>indexLoc</tt> is now the logical name of the instruction's
807 execution value, which is a pointer to an integer on the runtime stack.</p>
809 <p><i>Inserting instructions</i></p>
811 <p>There are essentially two ways to insert an <tt>Instruction</tt>
812 into an existing sequence of instructions that form a <tt>BasicBlock</tt>:</p>
815 <li>Insertion into an explicit instruction list
817 <p>Given a <tt>BasicBlock* pb</tt>, an <tt>Instruction* pi</tt> within that
818 <tt>BasicBlock</tt>, and a newly-created instruction we wish to insert
819 before <tt>*pi</tt>, we do the following: </p>
821 <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>
823 <p>Appending to the end of a <tt>BasicBlock</tt> is so common that
824 the <tt>Instruction</tt> class and <tt>Instruction</tt>-derived
825 classes provide constructors which take a pointer to a
826 <tt>BasicBlock</tt> to be appended to. For example code that
829 <pre> BasicBlock *pb = ...;<br> Instruction *newInst = new Instruction(...);<br> pb->getInstList().push_back(newInst); // appends newInst to pb<br></pre>
833 <pre> BasicBlock *pb = ...;<br> Instruction *newInst = new Instruction(..., pb);<br></pre>
835 <p>which is much cleaner, especially if you are creating
836 long instruction streams.</p></li>
838 <li>Insertion into an implicit instruction list
840 <p><tt>Instruction</tt> instances that are already in <tt>BasicBlock</tt>s
841 are implicitly associated with an existing instruction list: the instruction
842 list of the enclosing basic block. Thus, we could have accomplished the same
843 thing as the above code without being given a <tt>BasicBlock</tt> by doing:
846 <pre> Instruction *pi = ...;<br> Instruction *newInst = new Instruction(...);<br> pi->getParent()->getInstList().insert(pi, newInst);<br></pre>
848 <p>In fact, this sequence of steps occurs so frequently that the
849 <tt>Instruction</tt> class and <tt>Instruction</tt>-derived classes provide
850 constructors which take (as a default parameter) a pointer to an
851 <tt>Instruction</tt> which the newly-created <tt>Instruction</tt> should
852 precede. That is, <tt>Instruction</tt> constructors are capable of
853 inserting the newly-created instance into the <tt>BasicBlock</tt> of a
854 provided instruction, immediately before that instruction. Using an
855 <tt>Instruction</tt> constructor with a <tt>insertBefore</tt> (default)
856 parameter, the above code becomes:</p>
858 <pre>Instruction* pi = ...;<br>Instruction* newInst = new Instruction(..., pi);<br></pre>
860 <p>which is much cleaner, especially if you're creating a lot of
861 instructions and adding them to <tt>BasicBlock</tt>s.</p></li>
866 <!--_______________________________________________________________________-->
867 <div class="doc_subsubsection">
868 <a name="schanges_deleting">Deleting <tt>Instruction</tt>s</a>
871 <div class="doc_text">
873 <p>Deleting an instruction from an existing sequence of instructions that form a
874 <a href="#BasicBlock"><tt>BasicBlock</tt></a> is very straight-forward. First,
875 you must have a pointer to the instruction that you wish to delete. Second, you
876 need to obtain the pointer to that instruction's basic block. You use the
877 pointer to the basic block to get its list of instructions and then use the
878 erase function to remove your instruction. For example:</p>
880 <pre> <a href="#Instruction">Instruction</a> *I = .. ;<br> <a
881 href="#BasicBlock">BasicBlock</a> *BB = I->getParent();<br> BB->getInstList().erase(I);<br></pre>
885 <!--_______________________________________________________________________-->
886 <div class="doc_subsubsection">
887 <a name="schanges_replacing">Replacing an <tt>Instruction</tt> with another
891 <div class="doc_text">
893 <p><i>Replacing individual instructions</i></p>
895 <p>Including "<a href="/doxygen/BasicBlockUtils_8h-source.html">llvm/Transforms/Utils/BasicBlockUtils.h</a>"
896 permits use of two very useful replace functions: <tt>ReplaceInstWithValue</tt>
897 and <tt>ReplaceInstWithInst</tt>.</p>
899 <h4><a name="schanges_deleting">Deleting <tt>Instruction</tt>s</a></h4>
902 <li><tt>ReplaceInstWithValue</tt>
904 <p>This function replaces all uses (within a basic block) of a given
905 instruction with a value, and then removes the original instruction. The
906 following example illustrates the replacement of the result of a particular
907 <tt>AllocaInst</tt> that allocates memory for a single integer with a null
908 pointer to an integer.</p>
910 <pre>AllocaInst* instToReplace = ...;<br>BasicBlock::iterator ii(instToReplace);<br>ReplaceInstWithValue(instToReplace->getParent()->getInstList(), ii,<br> Constant::getNullValue(PointerType::get(Type::IntTy)));<br></pre></li>
912 <li><tt>ReplaceInstWithInst</tt>
914 <p>This function replaces a particular instruction with another
915 instruction. The following example illustrates the replacement of one
916 <tt>AllocaInst</tt> with another.</p>
918 <pre>AllocaInst* instToReplace = ...;<br>BasicBlock::iterator ii(instToReplace);<br>ReplaceInstWithInst(instToReplace->getParent()->getInstList(), ii,<br> new AllocaInst(Type::IntTy, 0, "ptrToReplacedInt"));<br></pre></li>
921 <p><i>Replacing multiple uses of <tt>User</tt>s and <tt>Value</tt>s</i></p>
923 <p>You can use <tt>Value::replaceAllUsesWith</tt> and
924 <tt>User::replaceUsesOfWith</tt> to change more than one use at a time. See the
925 doxygen documentation for the <a href="/doxygen/structllvm_1_1Value.html">Value Class</a>
926 and <a href="/doxygen/classllvm_1_1User.html">User Class</a>, respectively, for more
929 <!-- Value::replaceAllUsesWith User::replaceUsesOfWith Point out:
930 include/llvm/Transforms/Utils/ especially BasicBlockUtils.h with:
931 ReplaceInstWithValue, ReplaceInstWithInst -->
935 <!-- *********************************************************************** -->
936 <div class="doc_section">
937 <a name="coreclasses">The Core LLVM Class Hierarchy Reference </a>
939 <!-- *********************************************************************** -->
941 <div class="doc_text">
943 <p>The Core LLVM classes are the primary means of representing the program
944 being inspected or transformed. The core LLVM classes are defined in
945 header files in the <tt>include/llvm/</tt> directory, and implemented in
946 the <tt>lib/VMCore</tt> directory.</p>
950 <!-- ======================================================================= -->
951 <div class="doc_subsection">
952 <a name="Value">The <tt>Value</tt> class</a>
957 <p><tt>#include "<a href="/doxygen/Value_8h-source.html">llvm/Value.h</a>"</tt>
959 doxygen info: <a href="/doxygen/structllvm_1_1Value.html">Value Class</a></p>
961 <p>The <tt>Value</tt> class is the most important class in the LLVM Source
962 base. It represents a typed value that may be used (among other things) as an
963 operand to an instruction. There are many different types of <tt>Value</tt>s,
964 such as <a href="#Constant"><tt>Constant</tt></a>s,<a
965 href="#Argument"><tt>Argument</tt></a>s. Even <a
966 href="#Instruction"><tt>Instruction</tt></a>s and <a
967 href="#Function"><tt>Function</tt></a>s are <tt>Value</tt>s.</p>
969 <p>A particular <tt>Value</tt> may be used many times in the LLVM representation
970 for a program. For example, an incoming argument to a function (represented
971 with an instance of the <a href="#Argument">Argument</a> class) is "used" by
972 every instruction in the function that references the argument. To keep track
973 of this relationship, the <tt>Value</tt> class keeps a list of all of the <a
974 href="#User"><tt>User</tt></a>s that is using it (the <a
975 href="#User"><tt>User</tt></a> class is a base class for all nodes in the LLVM
976 graph that can refer to <tt>Value</tt>s). This use list is how LLVM represents
977 def-use information in the program, and is accessible through the <tt>use_</tt>*
978 methods, shown below.</p>
980 <p>Because LLVM is a typed representation, every LLVM <tt>Value</tt> is typed,
981 and this <a href="#Type">Type</a> is available through the <tt>getType()</tt>
982 method. In addition, all LLVM values can be named. The "name" of the
983 <tt>Value</tt> is a symbolic string printed in the LLVM code:</p>
985 <pre> %<b>foo</b> = add int 1, 2<br></pre>
987 <p><a name="#nameWarning">The name of this instruction is "foo".</a> <b>NOTE</b>
988 that the name of any value may be missing (an empty string), so names should
989 <b>ONLY</b> be used for debugging (making the source code easier to read,
990 debugging printouts), they should not be used to keep track of values or map
991 between them. For this purpose, use a <tt>std::map</tt> of pointers to the
992 <tt>Value</tt> itself instead.</p>
994 <p>One important aspect of LLVM is that there is no distinction between an SSA
995 variable and the operation that produces it. Because of this, any reference to
996 the value produced by an instruction (or the value available as an incoming
997 argument, for example) is represented as a direct pointer to the instance of
999 represents this value. Although this may take some getting used to, it
1000 simplifies the representation and makes it easier to manipulate.</p>
1004 <!-- _______________________________________________________________________ -->
1005 <div class="doc_subsubsection">
1006 <a name="m_Value">Important Public Members of the <tt>Value</tt> class</a>
1009 <div class="doc_text">
1012 <li><tt>Value::use_iterator</tt> - Typedef for iterator over the
1014 <tt>Value::use_const_iterator</tt> - Typedef for const_iterator over
1016 <tt>unsigned use_size()</tt> - Returns the number of users of the
1018 <tt>bool use_empty()</tt> - Returns true if there are no users.<br>
1019 <tt>use_iterator use_begin()</tt> - Get an iterator to the start of
1021 <tt>use_iterator use_end()</tt> - Get an iterator to the end of the
1023 <tt><a href="#User">User</a> *use_back()</tt> - Returns the last
1024 element in the list.
1025 <p> These methods are the interface to access the def-use
1026 information in LLVM. As with all other iterators in LLVM, the naming
1027 conventions follow the conventions defined by the <a href="#stl">STL</a>.</p>
1029 <li><tt><a href="#Type">Type</a> *getType() const</tt>
1030 <p>This method returns the Type of the Value.</p>
1032 <li><tt>bool hasName() const</tt><br>
1033 <tt>std::string getName() const</tt><br>
1034 <tt>void setName(const std::string &Name)</tt>
1035 <p> This family of methods is used to access and assign a name to a <tt>Value</tt>,
1036 be aware of the <a href="#nameWarning">precaution above</a>.</p>
1038 <li><tt>void replaceAllUsesWith(Value *V)</tt>
1040 <p>This method traverses the use list of a <tt>Value</tt> changing all <a
1041 href="#User"><tt>User</tt>s</a> of the current value to refer to
1042 "<tt>V</tt>" instead. For example, if you detect that an instruction always
1043 produces a constant value (for example through constant folding), you can
1044 replace all uses of the instruction with the constant like this:</p>
1046 <pre> Inst->replaceAllUsesWith(ConstVal);<br></pre>
1051 <!-- ======================================================================= -->
1052 <div class="doc_subsection">
1053 <a name="User">The <tt>User</tt> class</a>
1056 <div class="doc_text">
1059 <tt>#include "<a href="/doxygen/User_8h-source.html">llvm/User.h</a>"</tt><br>
1060 doxygen info: <a href="/doxygen/classllvm_1_1User.html">User Class</a><br>
1061 Superclass: <a href="#Value"><tt>Value</tt></a></p>
1063 <p>The <tt>User</tt> class is the common base class of all LLVM nodes that may
1064 refer to <a href="#Value"><tt>Value</tt></a>s. It exposes a list of "Operands"
1065 that are all of the <a href="#Value"><tt>Value</tt></a>s that the User is
1066 referring to. The <tt>User</tt> class itself is a subclass of
1069 <p>The operands of a <tt>User</tt> point directly to the LLVM <a
1070 href="#Value"><tt>Value</tt></a> that it refers to. Because LLVM uses Static
1071 Single Assignment (SSA) form, there can only be one definition referred to,
1072 allowing this direct connection. This connection provides the use-def
1073 information in LLVM.</p>
1077 <!-- _______________________________________________________________________ -->
1078 <div class="doc_subsubsection">
1079 <a name="m_User">Important Public Members of the <tt>User</tt> class</a>
1082 <div class="doc_text">
1084 <p>The <tt>User</tt> class exposes the operand list in two ways: through
1085 an index access interface and through an iterator based interface.</p>
1088 <li><tt>Value *getOperand(unsigned i)</tt><br>
1089 <tt>unsigned getNumOperands()</tt>
1090 <p> These two methods expose the operands of the <tt>User</tt> in a
1091 convenient form for direct access.</p></li>
1093 <li><tt>User::op_iterator</tt> - Typedef for iterator over the operand
1095 <tt>op_iterator op_begin()</tt> - Get an iterator to the start of
1096 the operand list.<br>
1097 <tt>op_iterator op_end()</tt> - Get an iterator to the end of the
1099 <p> Together, these methods make up the iterator based interface to
1100 the operands of a <tt>User</tt>.</p></li>
1105 <!-- ======================================================================= -->
1106 <div class="doc_subsection">
1107 <a name="Instruction">The <tt>Instruction</tt> class</a>
1110 <div class="doc_text">
1112 <p><tt>#include "</tt><tt><a
1113 href="/doxygen/Instruction_8h-source.html">llvm/Instruction.h</a>"</tt><br>
1114 doxygen info: <a href="/doxygen/classllvm_1_1Instruction.html">Instruction Class</a><br>
1115 Superclasses: <a href="#User"><tt>User</tt></a>, <a
1116 href="#Value"><tt>Value</tt></a></p>
1118 <p>The <tt>Instruction</tt> class is the common base class for all LLVM
1119 instructions. It provides only a few methods, but is a very commonly used
1120 class. The primary data tracked by the <tt>Instruction</tt> class itself is the
1121 opcode (instruction type) and the parent <a
1122 href="#BasicBlock"><tt>BasicBlock</tt></a> the <tt>Instruction</tt> is embedded
1123 into. To represent a specific type of instruction, one of many subclasses of
1124 <tt>Instruction</tt> are used.</p>
1126 <p> Because the <tt>Instruction</tt> class subclasses the <a
1127 href="#User"><tt>User</tt></a> class, its operands can be accessed in the same
1128 way as for other <a href="#User"><tt>User</tt></a>s (with the
1129 <tt>getOperand()</tt>/<tt>getNumOperands()</tt> and
1130 <tt>op_begin()</tt>/<tt>op_end()</tt> methods).</p> <p> An important file for
1131 the <tt>Instruction</tt> class is the <tt>llvm/Instruction.def</tt> file. This
1132 file contains some meta-data about the various different types of instructions
1133 in LLVM. It describes the enum values that are used as opcodes (for example
1134 <tt>Instruction::Add</tt> and <tt>Instruction::SetLE</tt>), as well as the
1135 concrete sub-classes of <tt>Instruction</tt> that implement the instruction (for
1136 example <tt><a href="#BinaryOperator">BinaryOperator</a></tt> and <tt><a
1137 href="#SetCondInst">SetCondInst</a></tt>). Unfortunately, the use of macros in
1138 this file confuses doxygen, so these enum values don't show up correctly in the
1139 <a href="/doxygen/classllvm_1_1Instruction.html">doxygen output</a>.</p>
1143 <!-- _______________________________________________________________________ -->
1144 <div class="doc_subsubsection">
1145 <a name="m_Instruction">Important Public Members of the <tt>Instruction</tt>
1149 <div class="doc_text">
1152 <li><tt><a href="#BasicBlock">BasicBlock</a> *getParent()</tt>
1153 <p>Returns the <a href="#BasicBlock"><tt>BasicBlock</tt></a> that
1154 this <tt>Instruction</tt> is embedded into.</p></li>
1155 <li><tt>bool mayWriteToMemory()</tt>
1156 <p>Returns true if the instruction writes to memory, i.e. it is a
1157 <tt>call</tt>,<tt>free</tt>,<tt>invoke</tt>, or <tt>store</tt>.</p></li>
1158 <li><tt>unsigned getOpcode()</tt>
1159 <p>Returns the opcode for the <tt>Instruction</tt>.</p></li>
1160 <li><tt><a href="#Instruction">Instruction</a> *clone() const</tt>
1161 <p>Returns another instance of the specified instruction, identical
1162 in all ways to the original except that the instruction has no parent
1163 (ie it's not embedded into a <a href="#BasicBlock"><tt>BasicBlock</tt></a>),
1164 and it has no name</p></li>
1169 <!-- ======================================================================= -->
1170 <div class="doc_subsection">
1171 <a name="BasicBlock">The <tt>BasicBlock</tt> class</a>
1174 <div class="doc_text">
1177 href="/doxygen/BasicBlock_8h-source.html">llvm/BasicBlock.h</a>"</tt><br>
1178 doxygen info: <a href="/doxygen/structllvm_1_1BasicBlock.html">BasicBlock
1180 Superclass: <a href="#Value"><tt>Value</tt></a></p>
1182 <p>This class represents a single entry multiple exit section of the code,
1183 commonly known as a basic block by the compiler community. The
1184 <tt>BasicBlock</tt> class maintains a list of <a
1185 href="#Instruction"><tt>Instruction</tt></a>s, which form the body of the block.
1186 Matching the language definition, the last element of this list of instructions
1187 is always a terminator instruction (a subclass of the <a
1188 href="#TerminatorInst"><tt>TerminatorInst</tt></a> class).</p>
1190 <p>In addition to tracking the list of instructions that make up the block, the
1191 <tt>BasicBlock</tt> class also keeps track of the <a
1192 href="#Function"><tt>Function</tt></a> that it is embedded into.</p>
1194 <p>Note that <tt>BasicBlock</tt>s themselves are <a
1195 href="#Value"><tt>Value</tt></a>s, because they are referenced by instructions
1196 like branches and can go in the switch tables. <tt>BasicBlock</tt>s have type
1201 <!-- _______________________________________________________________________ -->
1202 <div class="doc_subsubsection">
1203 <a name="m_BasicBlock">Important Public Members of the <tt>BasicBlock</tt>
1207 <div class="doc_text">
1211 <li><tt>BasicBlock(const std::string &Name = "", </tt><tt><a
1212 href="#Function">Function</a> *Parent = 0)</tt>
1214 <p>The <tt>BasicBlock</tt> constructor is used to create new basic blocks for
1215 insertion into a function. The constructor optionally takes a name for the new
1216 block, and a <a href="#Function"><tt>Function</tt></a> to insert it into. If
1217 the <tt>Parent</tt> parameter is specified, the new <tt>BasicBlock</tt> is
1218 automatically inserted at the end of the specified <a
1219 href="#Function"><tt>Function</tt></a>, if not specified, the BasicBlock must be
1220 manually inserted into the <a href="#Function"><tt>Function</tt></a>.</p></li>
1222 <li><tt>BasicBlock::iterator</tt> - Typedef for instruction list iterator<br>
1223 <tt>BasicBlock::const_iterator</tt> - Typedef for const_iterator.<br>
1224 <tt>begin()</tt>, <tt>end()</tt>, <tt>front()</tt>, <tt>back()</tt>,
1225 <tt>size()</tt>, <tt>empty()</tt>, <tt>rbegin()</tt>, <tt>rend()</tt> -
1226 STL-style functions for accessing the instruction list.
1228 <p>These methods and typedefs are forwarding functions that have the same
1229 semantics as the standard library methods of the same names. These methods
1230 expose the underlying instruction list of a basic block in a way that is easy to
1231 manipulate. To get the full complement of container operations (including
1232 operations to update the list), you must use the <tt>getInstList()</tt>
1235 <li><tt>BasicBlock::InstListType &getInstList()</tt>
1237 <p>This method is used to get access to the underlying container that actually
1238 holds the Instructions. This method must be used when there isn't a forwarding
1239 function in the <tt>BasicBlock</tt> class for the operation that you would like
1240 to perform. Because there are no forwarding functions for "updating"
1241 operations, you need to use this if you want to update the contents of a
1242 <tt>BasicBlock</tt>.</p></li>
1244 <li><tt><a href="#Function">Function</a> *getParent()</tt>
1246 <p> Returns a pointer to <a href="#Function"><tt>Function</tt></a> the block is
1247 embedded into, or a null pointer if it is homeless.</p></li>
1249 <li><tt><a href="#TerminatorInst">TerminatorInst</a> *getTerminator()</tt>
1251 <p> Returns a pointer to the terminator instruction that appears at the end of
1252 the <tt>BasicBlock</tt>. If there is no terminator instruction, or if the last
1253 instruction in the block is not a terminator, then a null pointer is
1260 <!-- ======================================================================= -->
1261 <div class="doc_subsection">
1262 <a name="GlobalValue">The <tt>GlobalValue</tt> class</a>
1265 <div class="doc_text">
1268 href="/doxygen/GlobalValue_8h-source.html">llvm/GlobalValue.h</a>"</tt><br>
1269 doxygen info: <a href="/doxygen/classllvm_1_1GlobalValue.html">GlobalValue
1271 Superclasses: <a href="#User"><tt>User</tt></a>, <a
1272 href="#Value"><tt>Value</tt></a></p>
1274 <p>Global values (<a href="#GlobalVariable"><tt>GlobalVariable</tt></a>s or <a
1275 href="#Function"><tt>Function</tt></a>s) are the only LLVM values that are
1276 visible in the bodies of all <a href="#Function"><tt>Function</tt></a>s.
1277 Because they are visible at global scope, they are also subject to linking with
1278 other globals defined in different translation units. To control the linking
1279 process, <tt>GlobalValue</tt>s know their linkage rules. Specifically,
1280 <tt>GlobalValue</tt>s know whether they have internal or external linkage, as
1281 defined by the <tt>LinkageTypes</tt> enumeration.</p>
1283 <p>If a <tt>GlobalValue</tt> has internal linkage (equivalent to being
1284 <tt>static</tt> in C), it is not visible to code outside the current translation
1285 unit, and does not participate in linking. If it has external linkage, it is
1286 visible to external code, and does participate in linking. In addition to
1287 linkage information, <tt>GlobalValue</tt>s keep track of which <a
1288 href="#Module"><tt>Module</tt></a> they are currently part of.</p>
1290 <p>Because <tt>GlobalValue</tt>s are memory objects, they are always referred to
1291 by their <b>address</b>. As such, the <a href="#Type"><tt>Type</tt></a> of a
1292 global is always a pointer to its contents. It is important to remember this
1293 when using the <tt>GetElementPtrInst</tt> instruction because this pointer must
1294 be dereferenced first. For example, if you have a <tt>GlobalVariable</tt> (a
1295 subclass of <tt>GlobalValue)</tt> that is an array of 24 ints, type <tt>[24 x
1296 int]</tt>, then the <tt>GlobalVariable</tt> is a pointer to that array. Although
1297 the address of the first element of this array and the value of the
1298 <tt>GlobalVariable</tt> are the same, they have different types. The
1299 <tt>GlobalVariable</tt>'s type is <tt>[24 x int]</tt>. The first element's type
1300 is <tt>int.</tt> Because of this, accessing a global value requires you to
1301 dereference the pointer with <tt>GetElementPtrInst</tt> first, then its elements
1302 can be accessed. This is explained in the <a href="LangRef.html#globalvars">LLVM
1303 Language Reference Manual</a>.</p>
1307 <!-- _______________________________________________________________________ -->
1308 <div class="doc_subsubsection">
1309 <a name="m_GlobalValue">Important Public Members of the <tt>GlobalValue</tt>
1313 <div class="doc_text">
1316 <li><tt>bool hasInternalLinkage() const</tt><br>
1317 <tt>bool hasExternalLinkage() const</tt><br>
1318 <tt>void setInternalLinkage(bool HasInternalLinkage)</tt>
1319 <p> These methods manipulate the linkage characteristics of the <tt>GlobalValue</tt>.</p>
1322 <li><tt><a href="#Module">Module</a> *getParent()</tt>
1323 <p> This returns the <a href="#Module"><tt>Module</tt></a> that the
1324 GlobalValue is currently embedded into.</p></li>
1329 <!-- ======================================================================= -->
1330 <div class="doc_subsection">
1331 <a name="Function">The <tt>Function</tt> class</a>
1334 <div class="doc_text">
1337 href="/doxygen/Function_8h-source.html">llvm/Function.h</a>"</tt><br> doxygen
1338 info: <a href="/doxygen/classllvm_1_1Function.html">Function Class</a><br>
1339 Superclasses: <a href="#GlobalValue"><tt>GlobalValue</tt></a>, <a
1340 href="#User"><tt>User</tt></a>, <a href="#Value"><tt>Value</tt></a></p>
1342 <p>The <tt>Function</tt> class represents a single procedure in LLVM. It is
1343 actually one of the more complex classes in the LLVM heirarchy because it must
1344 keep track of a large amount of data. The <tt>Function</tt> class keeps track
1345 of a list of <a href="#BasicBlock"><tt>BasicBlock</tt></a>s, a list of formal <a
1346 href="#Argument"><tt>Argument</tt></a>s, and a <a
1347 href="#SymbolTable"><tt>SymbolTable</tt></a>.</p>
1349 <p>The list of <a href="#BasicBlock"><tt>BasicBlock</tt></a>s is the most
1350 commonly used part of <tt>Function</tt> objects. The list imposes an implicit
1351 ordering of the blocks in the function, which indicate how the code will be
1352 layed out by the backend. Additionally, the first <a
1353 href="#BasicBlock"><tt>BasicBlock</tt></a> is the implicit entry node for the
1354 <tt>Function</tt>. It is not legal in LLVM to explicitly branch to this initial
1355 block. There are no implicit exit nodes, and in fact there may be multiple exit
1356 nodes from a single <tt>Function</tt>. If the <a
1357 href="#BasicBlock"><tt>BasicBlock</tt></a> list is empty, this indicates that
1358 the <tt>Function</tt> is actually a function declaration: the actual body of the
1359 function hasn't been linked in yet.</p>
1361 <p>In addition to a list of <a href="#BasicBlock"><tt>BasicBlock</tt></a>s, the
1362 <tt>Function</tt> class also keeps track of the list of formal <a
1363 href="#Argument"><tt>Argument</tt></a>s that the function receives. This
1364 container manages the lifetime of the <a href="#Argument"><tt>Argument</tt></a>
1365 nodes, just like the <a href="#BasicBlock"><tt>BasicBlock</tt></a> list does for
1366 the <a href="#BasicBlock"><tt>BasicBlock</tt></a>s.</p>
1368 <p>The <a href="#SymbolTable"><tt>SymbolTable</tt></a> is a very rarely used
1369 LLVM feature that is only used when you have to look up a value by name. Aside
1370 from that, the <a href="#SymbolTable"><tt>SymbolTable</tt></a> is used
1371 internally to make sure that there are not conflicts between the names of <a
1372 href="#Instruction"><tt>Instruction</tt></a>s, <a
1373 href="#BasicBlock"><tt>BasicBlock</tt></a>s, or <a
1374 href="#Argument"><tt>Argument</tt></a>s in the function body.</p>
1376 <p>Note that <tt>Function</tt> is a <a href="#GlobalValue">GlobalValue</a>
1377 and therefore also a <a href="#Constant">Constant</a>. The value of the function
1378 is its address (after linking) which is guaranteed to be constant.</p>
1381 <!-- _______________________________________________________________________ -->
1382 <div class="doc_subsubsection">
1383 <a name="m_Function">Important Public Members of the <tt>Function</tt>
1387 <div class="doc_text">
1390 <li><tt>Function(const </tt><tt><a href="#FunctionType">FunctionType</a>
1391 *Ty, LinkageTypes Linkage, const std::string &N = "", Module* Parent = 0)</tt>
1393 <p>Constructor used when you need to create new <tt>Function</tt>s to add
1394 the the program. The constructor must specify the type of the function to
1395 create and what type of linkage the function should have. The <a
1396 href="#FunctionType"><tt>FunctionType</tt></a> argument
1397 specifies the formal arguments and return value for the function. The same
1398 <a href="#FunctionTypel"><tt>FunctionType</tt></a> value can be used to
1399 create multiple functions. The <tt>Parent</tt> argument specifies the Module
1400 in which the function is defined. If this argument is provided, the function
1401 will automatically be inserted into that module's list of
1404 <li><tt>bool isExternal()</tt>
1406 <p>Return whether or not the <tt>Function</tt> has a body defined. If the
1407 function is "external", it does not have a body, and thus must be resolved
1408 by linking with a function defined in a different translation unit.</p></li>
1410 <li><tt>Function::iterator</tt> - Typedef for basic block list iterator<br>
1411 <tt>Function::const_iterator</tt> - Typedef for const_iterator.<br>
1413 <tt>begin()</tt>, <tt>end()</tt>, <tt>front()</tt>, <tt>back()</tt>,
1414 <tt>size()</tt>, <tt>empty()</tt>, <tt>rbegin()</tt>, <tt>rend()</tt>
1416 <p>These are forwarding methods that make it easy to access the contents of
1417 a <tt>Function</tt> object's <a href="#BasicBlock"><tt>BasicBlock</tt></a>
1420 <li><tt>Function::BasicBlockListType &getBasicBlockList()</tt>
1422 <p>Returns the list of <a href="#BasicBlock"><tt>BasicBlock</tt></a>s. This
1423 is necessary to use when you need to update the list or perform a complex
1424 action that doesn't have a forwarding method.</p></li>
1426 <li><tt>Function::aiterator</tt> - Typedef for the argument list
1428 <tt>Function::const_aiterator</tt> - Typedef for const_iterator.<br>
1430 <tt>abegin()</tt>, <tt>aend()</tt>, <tt>afront()</tt>, <tt>aback()</tt>,
1431 <tt>asize()</tt>, <tt>aempty()</tt>, <tt>arbegin()</tt>, <tt>arend()</tt>
1433 <p>These are forwarding methods that make it easy to access the contents of
1434 a <tt>Function</tt> object's <a href="#Argument"><tt>Argument</tt></a>
1437 <li><tt>Function::ArgumentListType &getArgumentList()</tt>
1439 <p>Returns the list of <a href="#Argument"><tt>Argument</tt></a>s. This is
1440 necessary to use when you need to update the list or perform a complex
1441 action that doesn't have a forwarding method.</p></li>
1443 <li><tt><a href="#BasicBlock">BasicBlock</a> &getEntryBlock()</tt>
1445 <p>Returns the entry <a href="#BasicBlock"><tt>BasicBlock</tt></a> for the
1446 function. Because the entry block for the function is always the first
1447 block, this returns the first block of the <tt>Function</tt>.</p></li>
1449 <li><tt><a href="#Type">Type</a> *getReturnType()</tt><br>
1450 <tt><a href="#FunctionType">FunctionType</a> *getFunctionType()</tt>
1452 <p>This traverses the <a href="#Type"><tt>Type</tt></a> of the
1453 <tt>Function</tt> and returns the return type of the function, or the <a
1454 href="#FunctionType"><tt>FunctionType</tt></a> of the actual
1457 <li><tt><a href="#SymbolTable">SymbolTable</a> *getSymbolTable()</tt>
1459 <p> Return a pointer to the <a href="#SymbolTable"><tt>SymbolTable</tt></a>
1460 for this <tt>Function</tt>.</p></li>
1465 <!-- ======================================================================= -->
1466 <div class="doc_subsection">
1467 <a name="GlobalVariable">The <tt>GlobalVariable</tt> class</a>
1470 <div class="doc_text">
1473 href="/doxygen/GlobalVariable_8h-source.html">llvm/GlobalVariable.h</a>"</tt>
1475 doxygen info: <a href="/doxygen/classllvm_1_1GlobalVariable.html">GlobalVariable
1476 Class</a><br> Superclasses: <a href="#GlobalValue"><tt>GlobalValue</tt></a>, <a
1477 href="#User"><tt>User</tt></a>, <a href="#Value"><tt>Value</tt></a></p>
1479 <p>Global variables are represented with the (suprise suprise)
1480 <tt>GlobalVariable</tt> class. Like functions, <tt>GlobalVariable</tt>s are also
1481 subclasses of <a href="#GlobalValue"><tt>GlobalValue</tt></a>, and as such are
1482 always referenced by their address (global values must live in memory, so their
1483 "name" refers to their address). See <a
1484 href="#GlobalValue"><tt>GlobalValue</tt></a> for more on this. Global variables
1485 may have an initial value (which must be a <a
1486 href="#Constant"><tt>Constant</tt></a>), and if they have an initializer, they
1487 may be marked as "constant" themselves (indicating that their contents never
1488 change at runtime).</p>
1492 <!-- _______________________________________________________________________ -->
1493 <div class="doc_subsubsection">
1494 <a name="m_GlobalVariable">Important Public Members of the
1495 <tt>GlobalVariable</tt> class</a>
1498 <div class="doc_text">
1501 <li><tt>GlobalVariable(const </tt><tt><a href="#Type">Type</a> *Ty, bool
1502 isConstant, LinkageTypes& Linkage, <a href="#Constant">Constant</a>
1503 *Initializer = 0, const std::string &Name = "", Module* Parent = 0)</tt>
1505 <p>Create a new global variable of the specified type. If
1506 <tt>isConstant</tt> is true then the global variable will be marked as
1507 unchanging for the program. The Linkage parameter specifies the type of
1508 linkage (internal, external, weak, linkonce, appending) for the variable. If
1509 the linkage is InternalLinkage, WeakLinkage, or LinkOnceLinkage, then
1510 the resultant global variable will have internal linkage. AppendingLinkage
1511 concatenates together all instances (in different translation units) of the
1512 variable into a single variable but is only applicable to arrays. See
1513 the <a href="LangRef.html#modulestructure">LLVM Language Reference</a> for
1514 further details on linkage types. Optionally an initializer, a name, and the
1515 module to put the variable into may be specified for the global variable as
1518 <li><tt>bool isConstant() const</tt>
1520 <p>Returns true if this is a global variable that is known not to
1521 be modified at runtime.</p></li>
1523 <li><tt>bool hasInitializer()</tt>
1525 <p>Returns true if this <tt>GlobalVariable</tt> has an intializer.</p></li>
1527 <li><tt><a href="#Constant">Constant</a> *getInitializer()</tt>
1529 <p>Returns the intial value for a <tt>GlobalVariable</tt>. It is not legal
1530 to call this method if there is no initializer.</p></li>
1535 <!-- ======================================================================= -->
1536 <div class="doc_subsection">
1537 <a name="Module">The <tt>Module</tt> class</a>
1540 <div class="doc_text">
1543 href="/doxygen/Module_8h-source.html">llvm/Module.h</a>"</tt><br> doxygen info:
1544 <a href="/doxygen/classllvm_1_1Module.html">Module Class</a></p>
1546 <p>The <tt>Module</tt> class represents the top level structure present in LLVM
1547 programs. An LLVM module is effectively either a translation unit of the
1548 original program or a combination of several translation units merged by the
1549 linker. The <tt>Module</tt> class keeps track of a list of <a
1550 href="#Function"><tt>Function</tt></a>s, a list of <a
1551 href="#GlobalVariable"><tt>GlobalVariable</tt></a>s, and a <a
1552 href="#SymbolTable"><tt>SymbolTable</tt></a>. Additionally, it contains a few
1553 helpful member functions that try to make common operations easy.</p>
1557 <!-- _______________________________________________________________________ -->
1558 <div class="doc_subsubsection">
1559 <a name="m_Module">Important Public Members of the <tt>Module</tt> class</a>
1562 <div class="doc_text">
1565 <li><tt>Module::Module(std::string name = "")</tt></li>
1568 <p>Constructing a <a href="#Module">Module</a> is easy. You can optionally
1569 provide a name for it (probably based on the name of the translation unit).</p>
1572 <li><tt>Module::iterator</tt> - Typedef for function list iterator<br>
1573 <tt>Module::const_iterator</tt> - Typedef for const_iterator.<br>
1575 <tt>begin()</tt>, <tt>end()</tt>, <tt>front()</tt>, <tt>back()</tt>,
1576 <tt>size()</tt>, <tt>empty()</tt>, <tt>rbegin()</tt>, <tt>rend()</tt>
1578 <p>These are forwarding methods that make it easy to access the contents of
1579 a <tt>Module</tt> object's <a href="#Function"><tt>Function</tt></a>
1582 <li><tt>Module::FunctionListType &getFunctionList()</tt>
1584 <p> Returns the list of <a href="#Function"><tt>Function</tt></a>s. This is
1585 necessary to use when you need to update the list or perform a complex
1586 action that doesn't have a forwarding method.</p>
1588 <p><!-- Global Variable --></p></li>
1594 <li><tt>Module::giterator</tt> - Typedef for global variable list iterator<br>
1596 <tt>Module::const_giterator</tt> - Typedef for const_iterator.<br>
1598 <tt>gbegin()</tt>, <tt>gend()</tt>, <tt>gfront()</tt>, <tt>gback()</tt>,
1599 <tt>gsize()</tt>, <tt>gempty()</tt>, <tt>grbegin()</tt>, <tt>grend()</tt>
1601 <p> These are forwarding methods that make it easy to access the contents of
1602 a <tt>Module</tt> object's <a
1603 href="#GlobalVariable"><tt>GlobalVariable</tt></a> list.</p></li>
1605 <li><tt>Module::GlobalListType &getGlobalList()</tt>
1607 <p>Returns the list of <a
1608 href="#GlobalVariable"><tt>GlobalVariable</tt></a>s. This is necessary to
1609 use when you need to update the list or perform a complex action that
1610 doesn't have a forwarding method.</p>
1612 <p><!-- Symbol table stuff --> </p></li>
1618 <li><tt><a href="#SymbolTable">SymbolTable</a> *getSymbolTable()</tt>
1620 <p>Return a reference to the <a href="#SymbolTable"><tt>SymbolTable</tt></a>
1621 for this <tt>Module</tt>.</p>
1623 <p><!-- Convenience methods --></p></li>
1629 <li><tt><a href="#Function">Function</a> *getFunction(const std::string
1630 &Name, const <a href="#FunctionType">FunctionType</a> *Ty)</tt>
1632 <p>Look up the specified function in the <tt>Module</tt> <a
1633 href="#SymbolTable"><tt>SymbolTable</tt></a>. If it does not exist, return
1634 <tt>null</tt>.</p></li>
1636 <li><tt><a href="#Function">Function</a> *getOrInsertFunction(const
1637 std::string &Name, const <a href="#FunctionType">FunctionType</a> *T)</tt>
1639 <p>Look up the specified function in the <tt>Module</tt> <a
1640 href="#SymbolTable"><tt>SymbolTable</tt></a>. If it does not exist, add an
1641 external declaration for the function and return it.</p></li>
1643 <li><tt>std::string getTypeName(const <a href="#Type">Type</a> *Ty)</tt>
1645 <p>If there is at least one entry in the <a
1646 href="#SymbolTable"><tt>SymbolTable</tt></a> for the specified <a
1647 href="#Type"><tt>Type</tt></a>, return it. Otherwise return the empty
1650 <li><tt>bool addTypeName(const std::string &Name, const <a
1651 href="#Type">Type</a> *Ty)</tt>
1653 <p>Insert an entry in the <a href="#SymbolTable"><tt>SymbolTable</tt></a>
1654 mapping <tt>Name</tt> to <tt>Ty</tt>. If there is already an entry for this
1655 name, true is returned and the <a
1656 href="#SymbolTable"><tt>SymbolTable</tt></a> is not modified.</p></li>
1661 <!-- ======================================================================= -->
1662 <div class="doc_subsection">
1663 <a name="Constant">The <tt>Constant</tt> class and subclasses</a>
1666 <div class="doc_text">
1668 <p>Constant represents a base class for different types of constants. It
1669 is subclassed by ConstantBool, ConstantInt, ConstantSInt, ConstantUInt,
1670 ConstantArray etc for representing the various types of Constants.</p>
1674 <!-- _______________________________________________________________________ -->
1675 <div class="doc_subsubsection">
1676 <a name="m_Constant">Important Public Methods</a>
1678 <div class="doc_text">
1681 <!-- _______________________________________________________________________ -->
1682 <div class="doc_subsubsection">Important Subclasses of Constant </div>
1683 <div class="doc_text">
1685 <li>ConstantSInt : This subclass of Constant represents a signed integer
1688 <li><tt>int64_t getValue() const</tt>: Returns the underlying value of
1689 this constant. </li>
1692 <li>ConstantUInt : This class represents an unsigned integer.
1694 <li><tt>uint64_t getValue() const</tt>: Returns the underlying value of
1695 this constant. </li>
1698 <li>ConstantFP : This class represents a floating point constant.
1700 <li><tt>double getValue() const</tt>: Returns the underlying value of
1701 this constant. </li>
1704 <li>ConstantBool : This represents a boolean constant.
1706 <li><tt>bool getValue() const</tt>: Returns the underlying value of this
1710 <li>ConstantArray : This represents a constant array.
1712 <li><tt>const std::vector<Use> &getValues() const</tt>: Returns
1713 a vector of component constants that makeup this array. </li>
1716 <li>ConstantStruct : This represents a constant struct.
1718 <li><tt>const std::vector<Use> &getValues() const</tt>: Returns
1719 a vector of component constants that makeup this array. </li>
1722 <li>GlobalValue : This represents either a global variable or a function. In
1723 either case, the value is a constant fixed address (after linking).
1728 <!-- ======================================================================= -->
1729 <div class="doc_subsection">
1730 <a name="Type">The <tt>Type</tt> class and Derived Types</a>
1733 <div class="doc_text">
1735 <p>Type as noted earlier is also a subclass of a Value class. Any primitive
1736 type (like int, short etc) in LLVM is an instance of Type Class. All other
1737 types are instances of subclasses of type like FunctionType, ArrayType
1738 etc. DerivedType is the interface for all such dervied types including
1739 FunctionType, ArrayType, PointerType, StructType. Types can have names. They can
1740 be recursive (StructType). There exists exactly one instance of any type
1741 structure at a time. This allows using pointer equality of Type *s for comparing
1746 <!-- _______________________________________________________________________ -->
1747 <div class="doc_subsubsection">
1748 <a name="m_Value">Important Public Methods</a>
1751 <div class="doc_text">
1755 <li><tt>bool isSigned() const</tt>: Returns whether an integral numeric type
1756 is signed. This is true for SByteTy, ShortTy, IntTy, LongTy. Note that this is
1757 not true for Float and Double. </li>
1759 <li><tt>bool isUnsigned() const</tt>: Returns whether a numeric type is
1760 unsigned. This is not quite the complement of isSigned... nonnumeric types
1761 return false as they do with isSigned. This returns true for UByteTy,
1762 UShortTy, UIntTy, and ULongTy. </li>
1764 <li><tt>bool isInteger() const</tt>: Equivalent to isSigned() || isUnsigned().</li>
1766 <li><tt>bool isIntegral() const</tt>: Returns true if this is an integral
1767 type, which is either Bool type or one of the Integer types.</li>
1769 <li><tt>bool isFloatingPoint()</tt>: Return true if this is one of the two
1770 floating point types.</li>
1772 <li><tt>isLosslesslyConvertableTo (const Type *Ty) const</tt>: Return true if
1773 this type can be converted to 'Ty' without any reinterpretation of bits. For
1774 example, uint to int or one pointer type to another.</li>
1778 <!-- _______________________________________________________________________ -->
1779 <div class="doc_subsubsection">
1780 <a name="m_Value">Important Derived Types</a>
1782 <div class="doc_text">
1784 <li>SequentialType : This is subclassed by ArrayType and PointerType
1786 <li><tt>const Type * getElementType() const</tt>: Returns the type of each
1787 of the elements in the sequential type. </li>
1790 <li>ArrayType : This is a subclass of SequentialType and defines interface for
1793 <li><tt>unsigned getNumElements() const</tt>: Returns the number of
1794 elements in the array. </li>
1797 <li>PointerType : Subclass of SequentialType for pointer types. </li>
1798 <li>StructType : subclass of DerivedTypes for struct types </li>
1799 <li>FunctionType : subclass of DerivedTypes for function types.
1801 <li><tt>bool isVarArg() const</tt>: Returns true if its a vararg
1803 <li><tt> const Type * getReturnType() const</tt>: Returns the
1804 return type of the function.</li>
1805 <li><tt>const Type * getParamType (unsigned i)</tt>: Returns
1806 the type of the ith parameter.</li>
1807 <li><tt> const unsigned getNumParams() const</tt>: Returns the
1808 number of formal parameters.</li>
1814 <!-- ======================================================================= -->
1815 <div class="doc_subsection">
1816 <a name="Argument">The <tt>Argument</tt> class</a>
1819 <div class="doc_text">
1821 <p>This subclass of Value defines the interface for incoming formal
1822 arguments to a function. A Function maintains a list of its formal
1823 arguments. An argument has a pointer to the parent Function.</p>
1827 <!-- ======================================================================= -->
1828 <div class="doc_subsection">
1829 <a name="SymbolTable">The <tt>SymbolTable</tt> class</a>
1831 <div class="doc_text">
1832 <p>This class provides a symbol table that the
1833 <a href="#Function"><tt>Function</tt></a> and <a href="#Module">
1834 <tt>Module</tt></a> classes use for naming definitions. The symbol table can
1835 provide a name for any <a href="#Value"><tt>Value</tt></a> or
1836 <a href="#Type"><tt>Type</tt></a>. <tt>SymbolTable</tt> is an abstract data
1837 type. It hides the data it contains and provides access to it through a
1838 controlled interface.</p>
1840 <p>To use the <tt>SymbolTable</tt> well, you need to understand the
1841 structure of the information it holds. The class contains two
1842 <tt>std::map</tt> objects. The first, <tt>pmap</tt>, is a map of
1843 <tt>Type*</tt> to maps of name (<tt>std::string</tt>) to <tt>Value*</tt>.
1844 The second, <tt>tmap</tt>, is a map of names to <tt>Type*</tt>. Thus, Values
1845 are stored in two-dimensions and accessed by <tt>Type</tt> and name. Types,
1846 however, are stored in a single dimension and accessed only by name.</p>
1848 <p>The interface of this class provides three basic types of operations:
1850 <li><em>Accessors</em>. Accessors provide read-only access to information
1851 such as finding a value for a name with the
1852 <a href="#SymbolTable_lookup">lookup</a> method.</li>
1853 <li><em>Mutators</em>. Mutators allow the user to add information to the
1854 <tt>SymbolTable</tt> with methods like
1855 <a href="#SymbolTable_insert"><tt>insert</tt></a>.</li>
1856 <li><em>Iterators</em>. Iterators allow the user to traverse the content
1857 of the symbol table in well defined ways, such as the method
1858 <a href="#SymbolTable_type_begin"><tt>type_begin</tt></a>.</li>
1863 <dt><tt>Value* lookup(const Type* Ty, const std::string& name) const</tt>:
1865 <dd>The <tt>lookup</tt> method searches the type plane given by the
1866 <tt>Ty</tt> parameter for a <tt>Value</tt> with the provided <tt>name</tt>.
1867 If a suitable <tt>Value</tt> is not found, null is returned.</dd>
1869 <dt><tt>Type* lookupType( const std::string& name) const</tt>:</dt>
1870 <dd>The <tt>lookupType</tt> method searches through the types for a
1871 <tt>Type</tt> with the provided <tt>name</tt>. If a suitable <tt>Type</tt>
1872 is not found, null is returned.</dd>
1874 <dt><tt>bool hasTypes() const</tt>:</dt>
1875 <dd>This function returns true if an entry has been made into the type
1878 <dt><tt>bool isEmpty() const</tt>:</dt>
1879 <dd>This function returns true if both the value and types maps are
1882 <dt><tt>std::string get_name(const Value*) const</tt>:</dt>
1883 <dd>This function returns the name of the Value provided or the empty
1884 string if the Value is not in the symbol table.</dd>
1886 <dt><tt>std::string get_name(const Type*) const</tt>:</dt>
1887 <dd>This function returns the name of the Type provided or the empty
1888 string if the Type is not in the symbol table.</dd>
1893 <dt><tt>void insert(Value *Val)</tt>:</dt>
1894 <dd>This method adds the provided value to the symbol table. The Value must
1895 have both a name and a type which are extracted and used to place the value
1896 in the correct type plane under the value's name.</dd>
1898 <dt><tt>void insert(const std::string& Name, Value *Val)</tt>:</dt>
1899 <dd> Inserts a constant or type into the symbol table with the specified
1900 name. There can be a many to one mapping between names and constants
1903 <dt><tt>void insert(const std::string& Name, Type *Typ)</tt>:</dt>
1904 <dd> Inserts a type into the symbol table with the specified name. There
1905 can be a many-to-one mapping between names and types. This method
1906 allows a type with an existing entry in the symbol table to get
1909 <dt><tt>void remove(Value* Val)</tt>:</dt>
1910 <dd> This method removes a named value from the symbol table. The
1911 type and name of the Value are extracted from \p N and used to
1912 lookup the Value in the correct type plane. If the Value is
1913 not in the symbol table, this method silently ignores the
1916 <dt><tt>void remove(Type* Typ)</tt>:</dt>
1917 <dd> This method removes a named type from the symbol table. The
1918 name of the type is extracted from \P T and used to look up
1919 the Type in the type map. If the Type is not in the symbol
1920 table, this method silently ignores the request.</dd>
1922 <dt><tt>Value* remove(const std::string& Name, Value *Val)</tt>:</dt>
1923 <dd> Remove a constant or type with the specified name from the
1926 <dt><tt>Type* remove(const std::string& Name, Type* T)</tt>:</dt>
1927 <dd> Remove a type with the specified name from the symbol table.
1928 Returns the removed Type.</dd>
1930 <dt><tt>Value *value_remove(const value_iterator& It)</tt>:</dt>
1931 <dd> Removes a specific value from the symbol table.
1932 Returns the removed value.</dd>
1934 <dt><tt>bool strip()</tt>:</dt>
1935 <dd> This method will strip the symbol table of its names leaving
1936 the type and values. </dd>
1938 <dt><tt>void clear()</tt>:</dt>
1939 <dd>Empty the symbol table completely.</dd>
1943 <p>The following functions describe three types of iterators you can obtain
1944 the beginning or end of the sequence for both const and non-const. It is
1945 important to keep track of the different kinds of iterators. There are
1946 three idioms worth pointing out:</p>
1948 <tr><th>Units</th><th>Iterator</th><th>Idiom</th></tr>
1950 <td align="left">Planes Of name/Value maps</td><td>PI</td>
1951 <td align="left"><pre><tt>
1952 for (SymbolTable::plane_const_iterator PI = ST.plane_begin(),
1953 PE = ST.plane_end(); PI != PE; ++PI ) {
1954 PI->first // This is the Type* of the plane
1955 PI->second // This is the SymbolTable::ValueMap of name/Value pairs
1959 <td align="left">All name/Type Pairs</td><td>TI</td>
1960 <td align="left"><pre><tt>
1961 for (SymbolTable::type_const_iterator TI = ST.type_begin(),
1962 TE = ST.type_end(); TI != TE; ++TI )
1963 TI->first // This is the name of the type
1964 TI->second // This is the Type* value associated with the name
1968 <td align="left">name/Value pairs in a plane</td><td>VI</td>
1969 <td align="left"><pre><tt>
1970 for (SymbolTable::value_const_iterator VI = ST.value_begin(SomeType),
1971 VE = ST.value_end(SomeType); VI != VE; ++VI )
1972 VI->first // This is the name of the Value
1973 VI->second // This is the Value* value associated with the name
1978 <p>Using the recommended iterator names and idioms will help you avoid
1979 making mistakes. Of particular note, make sure that whenever you use
1980 value_begin(SomeType) that you always compare the resulting iterator
1981 with value_end(SomeType) not value_end(SomeOtherType) or else you
1982 will loop infinitely.</p>
1986 <dt><tt>plane_iterator plane_begin()</tt>:</dt>
1987 <dd>Get an iterator that starts at the beginning of the type planes.
1988 The iterator will iterate over the Type/ValueMap pairs in the
1991 <dt><tt>plane_const_iterator plane_begin() const</tt>:</dt>
1992 <dd>Get a const_iterator that starts at the beginning of the type
1993 planes. The iterator will iterate over the Type/ValueMap pairs
1994 in the type planes. </dd>
1996 <dt><tt>plane_iterator plane_end()</tt>:</dt>
1997 <dd>Get an iterator at the end of the type planes. This serves as
1998 the marker for end of iteration over the type planes.</dd>
2000 <dt><tt>plane_const_iterator plane_end() const</tt>:</dt>
2001 <dd>Get a const_iterator at the end of the type planes. This serves as
2002 the marker for end of iteration over the type planes.</dd>
2004 <dt><tt>value_iterator value_begin(const Type *Typ)</tt>:</dt>
2005 <dd>Get an iterator that starts at the beginning of a type plane.
2006 The iterator will iterate over the name/value pairs in the type plane.
2007 Note: The type plane must already exist before using this.</dd>
2009 <dt><tt>value_const_iterator value_begin(const Type *Typ) const</tt>:</dt>
2010 <dd>Get a const_iterator that starts at the beginning of a type plane.
2011 The iterator will iterate over the name/value pairs in the type plane.
2012 Note: The type plane must already exist before using this.</dd>
2014 <dt><tt>value_iterator value_end(const Type *Typ)</tt>:</dt>
2015 <dd>Get an iterator to the end of a type plane. This serves as the marker
2016 for end of iteration of the type plane.
2017 Note: The type plane must already exist before using this.</dd>
2019 <dt><tt>value_const_iterator value_end(const Type *Typ) const</tt>:</dt>
2020 <dd>Get a const_iterator to the end of a type plane. This serves as the
2021 marker for end of iteration of the type plane.
2022 Note: the type plane must already exist before using this.</dd>
2024 <dt><tt>type_iterator type_begin()</tt>:</dt>
2025 <dd>Get an iterator to the start of the name/Type map.</dd>
2027 <dt><tt>type_const_iterator type_begin() cons</tt>:</dt>
2028 <dd> Get a const_iterator to the start of the name/Type map.</dd>
2030 <dt><tt>type_iterator type_end()</tt>:</dt>
2031 <dd>Get an iterator to the end of the name/Type map. This serves as the
2032 marker for end of iteration of the types.</dd>
2034 <dt><tt>type_const_iterator type_end() const</tt>:</dt>
2035 <dd>Get a const-iterator to the end of the name/Type map. This serves
2036 as the marker for end of iteration of the types.</dd>
2038 <dt><tt>plane_const_iterator find(const Type* Typ ) const</tt>:</dt>
2039 <dd>This method returns a plane_const_iterator for iteration over
2040 the type planes starting at a specific plane, given by \p Ty.</dd>
2042 <dt><tt>plane_iterator find( const Type* Typ </tt>:</dt>
2043 <dd>This method returns a plane_iterator for iteration over the
2044 type planes starting at a specific plane, given by \p Ty.</dd>
2046 <dt><tt>const ValueMap* findPlane( const Type* Typ ) cons</tt>:</dt>
2047 <dd>This method returns a ValueMap* for a specific type plane. This
2048 interface is deprecated and may go away in the future.</dd>
2052 <!-- *********************************************************************** -->
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2060 <a href="mailto:dhurjati@cs.uiuc.edu">Dinakar Dhurjati</a> and
2061 <a href="mailto:sabre@nondot.org">Chris Lattner</a><br>
2062 <a href="http://llvm.cs.uiuc.edu">The LLVM Compiler Infrastructure</a><br>
2063 Last modified: $Date$