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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>
86 <li><a href="#advanced">Advanced Topics</a>
88 <li><a href="#SymbolTable">The <tt>SymbolTable</tt> class </a></li>
91 <li><a href="#coreclasses">The Core LLVM Class Hierarchy Reference</a>
93 <li><a href="#Value">The <tt>Value</tt> class</a>
95 <li><a href="#User">The <tt>User</tt> class</a>
97 <li><a href="#Instruction">The <tt>Instruction</tt> class</a>
99 <li><a href="#GetElementPtrInst">The <tt>GetElementPtrInst</tt> class</a></li>
102 <li><a href="#Module">The <tt>Module</tt> class</a></li>
103 <li><a href="#Constant">The <tt>Constant</tt> class</a>
105 <li><a href="#GlobalValue">The <tt>GlobalValue</tt> class</a>
107 <li><a href="#BasicBlock">The <tt>BasicBlock</tt>class</a></li>
108 <li><a href="#Function">The <tt>Function</tt> class</a></li>
109 <li><a href="#GlobalVariable">The <tt>GlobalVariable</tt> class</a></li>
116 <li><a href="#Type">The <tt>Type</tt> class</a> </li>
117 <li><a href="#Argument">The <tt>Argument</tt> class</a></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://64.78.49.204/">
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());
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>Note that the <tt>dyn_cast<></tt> operator, like C++'s
326 <tt>dynamic_cast</tt> or Java's <tt>instanceof</tt> operator, can be abused.
327 In particular you should not use big chained <tt>if/then/else</tt> blocks to
328 check for lots of different variants of classes. If you find yourself
329 wanting to do this, it is much cleaner and more efficient to use the
330 <tt>InstVisitor</tt> class to dispatch over the instruction type directly.</p>
334 <dt><tt>cast_or_null<></tt>: </dt>
336 <dd>The <tt>cast_or_null<></tt> operator works just like the
337 <tt>cast<></tt> operator, except that it allows for a null pointer as
338 an argument (which it then propagates). This can sometimes be useful,
339 allowing you to combine several null checks into one.</dd>
341 <dt><tt>dyn_cast_or_null<></tt>: </dt>
343 <dd>The <tt>dyn_cast_or_null<></tt> operator works just like the
344 <tt>dyn_cast<></tt> operator, except that it allows for a null pointer
345 as an argument (which it then propagates). This can sometimes be useful,
346 allowing you to combine several null checks into one.</dd>
350 <p>These five templates can be used with any classes, whether they have a
351 v-table or not. To add support for these templates, you simply need to add
352 <tt>classof</tt> static methods to the class you are interested casting
353 to. Describing this is currently outside the scope of this document, but there
354 are lots of examples in the LLVM source base.</p>
358 <!-- ======================================================================= -->
359 <div class="doc_subsection">
360 <a name="DEBUG">The <tt>DEBUG()</tt> macro & <tt>-debug</tt> option</a>
363 <div class="doc_text">
365 <p>Often when working on your pass you will put a bunch of debugging printouts
366 and other code into your pass. After you get it working, you want to remove
367 it... but you may need it again in the future (to work out new bugs that you run
370 <p> Naturally, because of this, you don't want to delete the debug printouts,
371 but you don't want them to always be noisy. A standard compromise is to comment
372 them out, allowing you to enable them if you need them in the future.</p>
374 <p>The "<tt><a href="/doxygen/Debug_8h-source.html">Support/Debug.h</a></tt>"
375 file provides a macro named <tt>DEBUG()</tt> that is a much nicer solution to
376 this problem. Basically, you can put arbitrary code into the argument of the
377 <tt>DEBUG</tt> macro, and it is only executed if '<tt>opt</tt>' (or any other
378 tool) is run with the '<tt>-debug</tt>' command line argument:</p>
380 <pre> ... <br> DEBUG(std::cerr << "I am here!\n");<br> ...<br></pre>
382 <p>Then you can run your pass like this:</p>
384 <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>
386 <p>Using the <tt>DEBUG()</tt> macro instead of a home-brewed solution allows you
387 to not have to create "yet another" command line option for the debug output for
388 your pass. Note that <tt>DEBUG()</tt> macros are disabled for optimized builds,
389 so they do not cause a performance impact at all (for the same reason, they
390 should also not contain side-effects!).</p>
392 <p>One additional nice thing about the <tt>DEBUG()</tt> macro is that you can
393 enable or disable it directly in gdb. Just use "<tt>set DebugFlag=0</tt>" or
394 "<tt>set DebugFlag=1</tt>" from the gdb if the program is running. If the
395 program hasn't been started yet, you can always just run it with
400 <!-- _______________________________________________________________________ -->
401 <div class="doc_subsubsection">
402 <a name="DEBUG_TYPE">Fine grained debug info with <tt>DEBUG_TYPE()</tt> and
403 the <tt>-debug-only</tt> option</a>
406 <div class="doc_text">
408 <p>Sometimes you may find yourself in a situation where enabling <tt>-debug</tt>
409 just turns on <b>too much</b> information (such as when working on the code
410 generator). If you want to enable debug information with more fine-grained
411 control, you define the <tt>DEBUG_TYPE</tt> macro and the <tt>-debug</tt> only
412 option as follows:</p>
414 <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>
416 <p>Then you can run your pass like this:</p>
418 <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>
420 <p>Of course, in practice, you should only set <tt>DEBUG_TYPE</tt> at the top of
421 a file, to specify the debug type for the entire module (if you do this before
422 you <tt>#include "Support/Debug.h"</tt>, you don't have to insert the ugly
423 <tt>#undef</tt>'s). Also, you should use names more meaningful than "foo" and
424 "bar", because there is no system in place to ensure that names do not
425 conflict. If two different modules use the same string, they will all be turned
426 on when the name is specified. This allows, for example, all debug information
427 for instruction scheduling to be enabled with <tt>-debug-type=InstrSched</tt>,
428 even if the source lives in multiple files.</p>
432 <!-- ======================================================================= -->
433 <div class="doc_subsection">
434 <a name="Statistic">The <tt>Statistic</tt> template & <tt>-stats</tt>
438 <div class="doc_text">
441 href="/doxygen/Statistic_8h-source.html">Support/Statistic.h</a></tt>" file
442 provides a template named <tt>Statistic</tt> that is used as a unified way to
443 keep track of what the LLVM compiler is doing and how effective various
444 optimizations are. It is useful to see what optimizations are contributing to
445 making a particular program run faster.</p>
447 <p>Often you may run your pass on some big program, and you're interested to see
448 how many times it makes a certain transformation. Although you can do this with
449 hand inspection, or some ad-hoc method, this is a real pain and not very useful
450 for big programs. Using the <tt>Statistic</tt> template makes it very easy to
451 keep track of this information, and the calculated information is presented in a
452 uniform manner with the rest of the passes being executed.</p>
454 <p>There are many examples of <tt>Statistic</tt> uses, but the basics of using
455 it are as follows:</p>
458 <li>Define your statistic like this:
459 <pre>static Statistic<> NumXForms("mypassname", "The # of times I did stuff");<br></pre>
461 <p>The <tt>Statistic</tt> template can emulate just about any data-type,
462 but if you do not specify a template argument, it defaults to acting like
463 an unsigned int counter (this is usually what you want).</p></li>
465 <li>Whenever you make a transformation, bump the counter:
466 <pre> ++NumXForms; // I did stuff<br></pre>
470 <p>That's all you have to do. To get '<tt>opt</tt>' to print out the
471 statistics gathered, use the '<tt>-stats</tt>' option:</p>
473 <pre> $ opt -stats -mypassname < program.bc > /dev/null<br> ... statistic output ...<br></pre>
475 <p> When running <tt>gccas</tt> on a C file from the SPEC benchmark
476 suite, it gives a report that looks like this:</p>
478 <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>
480 <p>Obviously, with so many optimizations, having a unified framework for this
481 stuff is very nice. Making your pass fit well into the framework makes it more
482 maintainable and useful.</p>
486 <!-- *********************************************************************** -->
487 <div class="doc_section">
488 <a name="common">Helpful Hints for Common Operations</a>
490 <!-- *********************************************************************** -->
492 <div class="doc_text">
494 <p>This section describes how to perform some very simple transformations of
495 LLVM code. This is meant to give examples of common idioms used, showing the
496 practical side of LLVM transformations. <p> Because this is a "how-to" section,
497 you should also read about the main classes that you will be working with. The
498 <a href="#coreclasses">Core LLVM Class Hierarchy Reference</a> contains details
499 and descriptions of the main classes that you should know about.</p>
503 <!-- NOTE: this section should be heavy on example code -->
504 <!-- ======================================================================= -->
505 <div class="doc_subsection">
506 <a name="inspection">Basic Inspection and Traversal Routines</a>
509 <div class="doc_text">
511 <p>The LLVM compiler infrastructure have many different data structures that may
512 be traversed. Following the example of the C++ standard template library, the
513 techniques used to traverse these various data structures are all basically the
514 same. For a enumerable sequence of values, the <tt>XXXbegin()</tt> function (or
515 method) returns an iterator to the start of the sequence, the <tt>XXXend()</tt>
516 function returns an iterator pointing to one past the last valid element of the
517 sequence, and there is some <tt>XXXiterator</tt> data type that is common
518 between the two operations.</p>
520 <p>Because the pattern for iteration is common across many different aspects of
521 the program representation, the standard template library algorithms may be used
522 on them, and it is easier to remember how to iterate. First we show a few common
523 examples of the data structures that need to be traversed. Other data
524 structures are traversed in very similar ways.</p>
528 <!-- _______________________________________________________________________ -->
529 <div class="doc_subsubsection">
530 <a name="iterate_function">Iterating over the </a><a
531 href="#BasicBlock"><tt>BasicBlock</tt></a>s in a <a
532 href="#Function"><tt>Function</tt></a>
535 <div class="doc_text">
537 <p>It's quite common to have a <tt>Function</tt> instance that you'd like to
538 transform in some way; in particular, you'd like to manipulate its
539 <tt>BasicBlock</tt>s. To facilitate this, you'll need to iterate over all of
540 the <tt>BasicBlock</tt>s that constitute the <tt>Function</tt>. The following is
541 an example that prints the name of a <tt>BasicBlock</tt> and the number of
542 <tt>Instruction</tt>s it contains:</p>
544 <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>
546 <p>Note that i can be used as if it were a pointer for the purposes of
547 invoking member functions of the <tt>Instruction</tt> class. This is
548 because the indirection operator is overloaded for the iterator
549 classes. In the above code, the expression <tt>i->size()</tt> is
550 exactly equivalent to <tt>(*i).size()</tt> just like you'd expect.</p>
554 <!-- _______________________________________________________________________ -->
555 <div class="doc_subsubsection">
556 <a name="iterate_basicblock">Iterating over the </a><a
557 href="#Instruction"><tt>Instruction</tt></a>s in a <a
558 href="#BasicBlock"><tt>BasicBlock</tt></a>
561 <div class="doc_text">
563 <p>Just like when dealing with <tt>BasicBlock</tt>s in <tt>Function</tt>s, it's
564 easy to iterate over the individual instructions that make up
565 <tt>BasicBlock</tt>s. Here's a code snippet that prints out each instruction in
566 a <tt>BasicBlock</tt>:</p>
569 // blk is a pointer to a BasicBlock instance
570 for (BasicBlock::iterator i = blk->begin(), e = blk->end(); i != e; ++i)
571 // the next statement works since operator<<(ostream&,...)
572 // is overloaded for Instruction&
573 std::cerr << *i << "\n";
576 <p>However, this isn't really the best way to print out the contents of a
577 <tt>BasicBlock</tt>! Since the ostream operators are overloaded for virtually
578 anything you'll care about, you could have just invoked the print routine on the
579 basic block itself: <tt>std::cerr << *blk << "\n";</tt>.</p>
583 <!-- _______________________________________________________________________ -->
584 <div class="doc_subsubsection">
585 <a name="iterate_institer">Iterating over the </a><a
586 href="#Instruction"><tt>Instruction</tt></a>s in a <a
587 href="#Function"><tt>Function</tt></a>
590 <div class="doc_text">
592 <p>If you're finding that you commonly iterate over a <tt>Function</tt>'s
593 <tt>BasicBlock</tt>s and then that <tt>BasicBlock</tt>'s <tt>Instruction</tt>s,
594 <tt>InstIterator</tt> should be used instead. You'll need to include <a
595 href="/doxygen/InstIterator_8h-source.html"><tt>llvm/Support/InstIterator.h</tt></a>,
596 and then instantiate <tt>InstIterator</tt>s explicitly in your code. Here's a
597 small example that shows how to dump all instructions in a function to the standard error stream:<p>
599 <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>
600 Easy, isn't it? You can also use <tt>InstIterator</tt>s to fill a
601 worklist with its initial contents. For example, if you wanted to
602 initialize a worklist to contain all instructions in a <tt>Function</tt>
603 F, all you would need to do is something like:
604 <pre>std::set<Instruction*> worklist;<br>worklist.insert(inst_begin(F), inst_end(F));<br></pre>
606 <p>The STL set <tt>worklist</tt> would now contain all instructions in the
607 <tt>Function</tt> pointed to by F.</p>
611 <!-- _______________________________________________________________________ -->
612 <div class="doc_subsubsection">
613 <a name="iterate_convert">Turning an iterator into a class pointer (and
617 <div class="doc_text">
619 <p>Sometimes, it'll be useful to grab a reference (or pointer) to a class
620 instance when all you've got at hand is an iterator. Well, extracting
621 a reference or a pointer from an iterator is very straight-forward.
622 Assuming that <tt>i</tt> is a <tt>BasicBlock::iterator</tt> and <tt>j</tt>
623 is a <tt>BasicBlock::const_iterator</tt>:</p>
625 <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>
627 <p>However, the iterators you'll be working with in the LLVM framework are
628 special: they will automatically convert to a ptr-to-instance type whenever they
629 need to. Instead of dereferencing the iterator and then taking the address of
630 the result, you can simply assign the iterator to the proper pointer type and
631 you get the dereference and address-of operation as a result of the assignment
632 (behind the scenes, this is a result of overloading casting mechanisms). Thus
633 the last line of the last example,</p>
635 <pre>Instruction* pinst = &*i;</pre>
637 <p>is semantically equivalent to</p>
639 <pre>Instruction* pinst = i;</pre>
641 <p>It's also possible to turn a class pointer into the corresponding iterator,
642 and this is a constant time operation (very efficient). The following code
643 snippet illustrates use of the conversion constructors provided by LLVM
644 iterators. By using these, you can explicitly grab the iterator of something
645 without actually obtaining it via iteration over some structure:</p>
647 <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>
651 <!--_______________________________________________________________________-->
652 <div class="doc_subsubsection">
653 <a name="iterate_complex">Finding call sites: a slightly more complex
657 <div class="doc_text">
659 <p>Say that you're writing a FunctionPass and would like to count all the
660 locations in the entire module (that is, across every <tt>Function</tt>) where a
661 certain function (i.e., some <tt>Function</tt>*) is already in scope. As you'll
662 learn later, you may want to use an <tt>InstVisitor</tt> to accomplish this in a
663 much more straight-forward manner, but this example will allow us to explore how
664 you'd do it if you didn't have <tt>InstVisitor</tt> around. In pseudocode, this
665 is what we want to do:</p>
667 <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>
669 <p>And the actual code is (remember, since we're writing a
670 <tt>FunctionPass</tt>, our <tt>FunctionPass</tt>-derived class simply has to
671 override the <tt>runOnFunction</tt> method...):</p>
673 <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
674 href="#CallInst">CallInst</a>* callInst = <a href="#isa">dyn_cast</a><<a
675 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>
679 <!--_______________________________________________________________________-->
680 <div class="doc_subsubsection">
681 <a name="calls_and_invokes">Treating calls and invokes the same way</a>
684 <div class="doc_text">
686 <p>You may have noticed that the previous example was a bit oversimplified in
687 that it did not deal with call sites generated by 'invoke' instructions. In
688 this, and in other situations, you may find that you want to treat
689 <tt>CallInst</tt>s and <tt>InvokeInst</tt>s the same way, even though their
690 most-specific common base class is <tt>Instruction</tt>, which includes lots of
691 less closely-related things. For these cases, LLVM provides a handy wrapper
693 href="http://llvm.cs.uiuc.edu/doxygen/classllvm_1_1CallSite.html"><tt>CallSite</tt></a>.
694 It is essentially a wrapper around an <tt>Instruction</tt> pointer, with some
695 methods that provide functionality common to <tt>CallInst</tt>s and
696 <tt>InvokeInst</tt>s.</p>
698 <p>This class has "value semantics": it should be passed by value, not by
699 reference and it should not be dynamically allocated or deallocated using
700 <tt>operator new</tt> or <tt>operator delete</tt>. It is efficiently copyable,
701 assignable and constructable, with costs equivalents to that of a bare pointer.
702 If you look at its definition, it has only a single pointer member.</p>
706 <!--_______________________________________________________________________-->
707 <div class="doc_subsubsection">
708 <a name="iterate_chains">Iterating over def-use & use-def chains</a>
711 <div class="doc_text">
713 <p>Frequently, we might have an instance of the <a
714 href="/doxygen/structllvm_1_1Value.html">Value Class</a> and we want to
715 determine which <tt>User</tt>s use the <tt>Value</tt>. The list of all
716 <tt>User</tt>s of a particular <tt>Value</tt> is called a <i>def-use</i> chain.
717 For example, let's say we have a <tt>Function*</tt> named <tt>F</tt> to a
718 particular function <tt>foo</tt>. Finding all of the instructions that
719 <i>use</i> <tt>foo</tt> is as simple as iterating over the <i>def-use</i> chain
722 <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>
724 <p>Alternately, it's common to have an instance of the <a
725 href="/doxygen/classllvm_1_1User.html">User Class</a> and need to know what
726 <tt>Value</tt>s are used by it. The list of all <tt>Value</tt>s used by a
727 <tt>User</tt> is known as a <i>use-def</i> chain. Instances of class
728 <tt>Instruction</tt> are common <tt>User</tt>s, so we might want to iterate over
729 all of the values that a particular instruction uses (that is, the operands of
730 the particular <tt>Instruction</tt>):</p>
732 <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>
735 def-use chains ("finding all users of"): Value::use_begin/use_end
736 use-def chains ("finding all values used"): User::op_begin/op_end [op=operand]
741 <!-- ======================================================================= -->
742 <div class="doc_subsection">
743 <a name="simplechanges">Making simple changes</a>
746 <div class="doc_text">
748 <p>There are some primitive transformation operations present in the LLVM
749 infrastructure that are worth knowing about. When performing
750 transformations, it's fairly common to manipulate the contents of basic
751 blocks. This section describes some of the common methods for doing so
752 and gives example code.</p>
756 <!--_______________________________________________________________________-->
757 <div class="doc_subsubsection">
758 <a name="schanges_creating">Creating and inserting new
759 <tt>Instruction</tt>s</a>
762 <div class="doc_text">
764 <p><i>Instantiating Instructions</i></p>
766 <p>Creation of <tt>Instruction</tt>s is straight-forward: simply call the
767 constructor for the kind of instruction to instantiate and provide the necessary
768 parameters. For example, an <tt>AllocaInst</tt> only <i>requires</i> a
769 (const-ptr-to) <tt>Type</tt>. Thus:</p>
771 <pre>AllocaInst* ai = new AllocaInst(Type::IntTy);</pre>
773 <p>will create an <tt>AllocaInst</tt> instance that represents the allocation of
774 one integer in the current stack frame, at runtime. Each <tt>Instruction</tt>
775 subclass is likely to have varying default parameters which change the semantics
776 of the instruction, so refer to the <a
777 href="/doxygen/classllvm_1_1Instruction.html">doxygen documentation for the subclass of
778 Instruction</a> that you're interested in instantiating.</p>
780 <p><i>Naming values</i></p>
782 <p>It is very useful to name the values of instructions when you're able to, as
783 this facilitates the debugging of your transformations. If you end up looking
784 at generated LLVM machine code, you definitely want to have logical names
785 associated with the results of instructions! By supplying a value for the
786 <tt>Name</tt> (default) parameter of the <tt>Instruction</tt> constructor, you
787 associate a logical name with the result of the instruction's execution at
788 runtime. For example, say that I'm writing a transformation that dynamically
789 allocates space for an integer on the stack, and that integer is going to be
790 used as some kind of index by some other code. To accomplish this, I place an
791 <tt>AllocaInst</tt> at the first point in the first <tt>BasicBlock</tt> of some
792 <tt>Function</tt>, and I'm intending to use it within the same
793 <tt>Function</tt>. I might do:</p>
795 <pre>AllocaInst* pa = new AllocaInst(Type::IntTy, 0, "indexLoc");</pre>
797 <p>where <tt>indexLoc</tt> is now the logical name of the instruction's
798 execution value, which is a pointer to an integer on the runtime stack.</p>
800 <p><i>Inserting instructions</i></p>
802 <p>There are essentially two ways to insert an <tt>Instruction</tt>
803 into an existing sequence of instructions that form a <tt>BasicBlock</tt>:</p>
806 <li>Insertion into an explicit instruction list
808 <p>Given a <tt>BasicBlock* pb</tt>, an <tt>Instruction* pi</tt> within that
809 <tt>BasicBlock</tt>, and a newly-created instruction we wish to insert
810 before <tt>*pi</tt>, we do the following: </p>
812 <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>
814 <p>Appending to the end of a <tt>BasicBlock</tt> is so common that
815 the <tt>Instruction</tt> class and <tt>Instruction</tt>-derived
816 classes provide constructors which take a pointer to a
817 <tt>BasicBlock</tt> to be appended to. For example code that
820 <pre> BasicBlock *pb = ...;<br> Instruction *newInst = new Instruction(...);<br> pb->getInstList().push_back(newInst); // appends newInst to pb<br></pre>
824 <pre> BasicBlock *pb = ...;<br> Instruction *newInst = new Instruction(..., pb);<br></pre>
826 <p>which is much cleaner, especially if you are creating
827 long instruction streams.</p></li>
829 <li>Insertion into an implicit instruction list
831 <p><tt>Instruction</tt> instances that are already in <tt>BasicBlock</tt>s
832 are implicitly associated with an existing instruction list: the instruction
833 list of the enclosing basic block. Thus, we could have accomplished the same
834 thing as the above code without being given a <tt>BasicBlock</tt> by doing:
837 <pre> Instruction *pi = ...;<br> Instruction *newInst = new Instruction(...);<br> pi->getParent()->getInstList().insert(pi, newInst);<br></pre>
839 <p>In fact, this sequence of steps occurs so frequently that the
840 <tt>Instruction</tt> class and <tt>Instruction</tt>-derived classes provide
841 constructors which take (as a default parameter) a pointer to an
842 <tt>Instruction</tt> which the newly-created <tt>Instruction</tt> should
843 precede. That is, <tt>Instruction</tt> constructors are capable of
844 inserting the newly-created instance into the <tt>BasicBlock</tt> of a
845 provided instruction, immediately before that instruction. Using an
846 <tt>Instruction</tt> constructor with a <tt>insertBefore</tt> (default)
847 parameter, the above code becomes:</p>
849 <pre>Instruction* pi = ...;<br>Instruction* newInst = new Instruction(..., pi);<br></pre>
851 <p>which is much cleaner, especially if you're creating a lot of
852 instructions and adding them to <tt>BasicBlock</tt>s.</p></li>
857 <!--_______________________________________________________________________-->
858 <div class="doc_subsubsection">
859 <a name="schanges_deleting">Deleting <tt>Instruction</tt>s</a>
862 <div class="doc_text">
864 <p>Deleting an instruction from an existing sequence of instructions that form a
865 <a href="#BasicBlock"><tt>BasicBlock</tt></a> is very straight-forward. First,
866 you must have a pointer to the instruction that you wish to delete. Second, you
867 need to obtain the pointer to that instruction's basic block. You use the
868 pointer to the basic block to get its list of instructions and then use the
869 erase function to remove your instruction. For example:</p>
871 <pre> <a href="#Instruction">Instruction</a> *I = .. ;<br> <a
872 href="#BasicBlock">BasicBlock</a> *BB = I->getParent();<br> BB->getInstList().erase(I);<br></pre>
876 <!--_______________________________________________________________________-->
877 <div class="doc_subsubsection">
878 <a name="schanges_replacing">Replacing an <tt>Instruction</tt> with another
882 <div class="doc_text">
884 <p><i>Replacing individual instructions</i></p>
886 <p>Including "<a href="/doxygen/BasicBlockUtils_8h-source.html">llvm/Transforms/Utils/BasicBlockUtils.h</a>"
887 permits use of two very useful replace functions: <tt>ReplaceInstWithValue</tt>
888 and <tt>ReplaceInstWithInst</tt>.</p>
890 <h4><a name="schanges_deleting">Deleting <tt>Instruction</tt>s</a></h4>
893 <li><tt>ReplaceInstWithValue</tt>
895 <p>This function replaces all uses (within a basic block) of a given
896 instruction with a value, and then removes the original instruction. The
897 following example illustrates the replacement of the result of a particular
898 <tt>AllocaInst</tt> that allocates memory for a single integer with a null
899 pointer to an integer.</p>
901 <pre>AllocaInst* instToReplace = ...;<br>BasicBlock::iterator ii(instToReplace);<br>ReplaceInstWithValue(instToReplace->getParent()->getInstList(), ii,<br> Constant::getNullValue(PointerType::get(Type::IntTy)));<br></pre></li>
903 <li><tt>ReplaceInstWithInst</tt>
905 <p>This function replaces a particular instruction with another
906 instruction. The following example illustrates the replacement of one
907 <tt>AllocaInst</tt> with another.</p>
909 <pre>AllocaInst* instToReplace = ...;<br>BasicBlock::iterator ii(instToReplace);<br>ReplaceInstWithInst(instToReplace->getParent()->getInstList(), ii,<br> new AllocaInst(Type::IntTy, 0, "ptrToReplacedInt"));<br></pre></li>
912 <p><i>Replacing multiple uses of <tt>User</tt>s and <tt>Value</tt>s</i></p>
914 <p>You can use <tt>Value::replaceAllUsesWith</tt> and
915 <tt>User::replaceUsesOfWith</tt> to change more than one use at a time. See the
916 doxygen documentation for the <a href="/doxygen/structllvm_1_1Value.html">Value Class</a>
917 and <a href="/doxygen/classllvm_1_1User.html">User Class</a>, respectively, for more
920 <!-- Value::replaceAllUsesWith User::replaceUsesOfWith Point out:
921 include/llvm/Transforms/Utils/ especially BasicBlockUtils.h with:
922 ReplaceInstWithValue, ReplaceInstWithInst -->
926 <!-- *********************************************************************** -->
927 <div class="doc_section">
928 <a name="advanced">Advanced Topics</a>
930 <!-- *********************************************************************** -->
932 <div class="doc_text">
938 <!-- ======================================================================= -->
939 <div class="doc_subsection">
940 <a name="SymbolTable">The <tt>SymbolTable</tt> class</a>
942 <div class="doc_text">
943 <p>This class provides a symbol table that the <a
944 href="#Function"><tt>Function</tt></a> and <a href="#Module">
945 <tt>Module</tt></a> classes use for naming definitions. The symbol table can
946 provide a name for any <a href="#Value"><tt>Value</tt></a> or <a
947 href="#Type"><tt>Type</tt></a>. <tt>SymbolTable</tt> is an abstract data
948 type. It hides the data it contains and provides access to it through a
949 controlled interface.</p>
951 <p>Note that the symbol table class is should not be directly accessed by most
952 clients. It should only be used when iteration over the symbol table names
953 themselves are required, which is very special purpose. Note that not all LLVM
954 <a href="#Value">Value</a>s have names, and those without names (i.e. they have
955 an empty name) do not exist in the symbol table.
958 <p>To use the <tt>SymbolTable</tt> well, you need to understand the
959 structure of the information it holds. The class contains two
960 <tt>std::map</tt> objects. The first, <tt>pmap</tt>, is a map of
961 <tt>Type*</tt> to maps of name (<tt>std::string</tt>) to <tt>Value*</tt>.
962 The second, <tt>tmap</tt>, is a map of names to <tt>Type*</tt>. Thus, Values
963 are stored in two-dimensions and accessed by <tt>Type</tt> and name. Types,
964 however, are stored in a single dimension and accessed only by name.</p>
966 <p>The interface of this class provides three basic types of operations:
968 <li><em>Accessors</em>. Accessors provide read-only access to information
969 such as finding a value for a name with the
970 <a href="#SymbolTable_lookup">lookup</a> method.</li>
971 <li><em>Mutators</em>. Mutators allow the user to add information to the
972 <tt>SymbolTable</tt> with methods like
973 <a href="#SymbolTable_insert"><tt>insert</tt></a>.</li>
974 <li><em>Iterators</em>. Iterators allow the user to traverse the content
975 of the symbol table in well defined ways, such as the method
976 <a href="#SymbolTable_type_begin"><tt>type_begin</tt></a>.</li>
981 <dt><tt>Value* lookup(const Type* Ty, const std::string& name) const</tt>:
983 <dd>The <tt>lookup</tt> method searches the type plane given by the
984 <tt>Ty</tt> parameter for a <tt>Value</tt> with the provided <tt>name</tt>.
985 If a suitable <tt>Value</tt> is not found, null is returned.</dd>
987 <dt><tt>Type* lookupType( const std::string& name) const</tt>:</dt>
988 <dd>The <tt>lookupType</tt> method searches through the types for a
989 <tt>Type</tt> with the provided <tt>name</tt>. If a suitable <tt>Type</tt>
990 is not found, null is returned.</dd>
992 <dt><tt>bool hasTypes() const</tt>:</dt>
993 <dd>This function returns true if an entry has been made into the type
996 <dt><tt>bool isEmpty() const</tt>:</dt>
997 <dd>This function returns true if both the value and types maps are
1003 <dt><tt>void insert(Value *Val)</tt>:</dt>
1004 <dd>This method adds the provided value to the symbol table. The Value must
1005 have both a name and a type which are extracted and used to place the value
1006 in the correct type plane under the value's name.</dd>
1008 <dt><tt>void insert(const std::string& Name, Value *Val)</tt>:</dt>
1009 <dd> Inserts a constant or type into the symbol table with the specified
1010 name. There can be a many to one mapping between names and constants
1013 <dt><tt>void insert(const std::string& Name, Type *Typ)</tt>:</dt>
1014 <dd> Inserts a type into the symbol table with the specified name. There
1015 can be a many-to-one mapping between names and types. This method
1016 allows a type with an existing entry in the symbol table to get
1019 <dt><tt>void remove(Value* Val)</tt>:</dt>
1020 <dd> This method removes a named value from the symbol table. The
1021 type and name of the Value are extracted from \p N and used to
1022 lookup the Value in the correct type plane. If the Value is
1023 not in the symbol table, this method silently ignores the
1026 <dt><tt>void remove(Type* Typ)</tt>:</dt>
1027 <dd> This method removes a named type from the symbol table. The
1028 name of the type is extracted from \P T and used to look up
1029 the Type in the type map. If the Type is not in the symbol
1030 table, this method silently ignores the request.</dd>
1032 <dt><tt>Value* remove(const std::string& Name, Value *Val)</tt>:</dt>
1033 <dd> Remove a constant or type with the specified name from the
1036 <dt><tt>Type* remove(const std::string& Name, Type* T)</tt>:</dt>
1037 <dd> Remove a type with the specified name from the symbol table.
1038 Returns the removed Type.</dd>
1040 <dt><tt>Value *value_remove(const value_iterator& It)</tt>:</dt>
1041 <dd> Removes a specific value from the symbol table.
1042 Returns the removed value.</dd>
1044 <dt><tt>bool strip()</tt>:</dt>
1045 <dd> This method will strip the symbol table of its names leaving
1046 the type and values. </dd>
1048 <dt><tt>void clear()</tt>:</dt>
1049 <dd>Empty the symbol table completely.</dd>
1053 <p>The following functions describe three types of iterators you can obtain
1054 the beginning or end of the sequence for both const and non-const. It is
1055 important to keep track of the different kinds of iterators. There are
1056 three idioms worth pointing out:</p>
1058 <tr><th>Units</th><th>Iterator</th><th>Idiom</th></tr>
1060 <td align="left">Planes Of name/Value maps</td><td>PI</td>
1061 <td align="left"><pre><tt>
1062 for (SymbolTable::plane_const_iterator PI = ST.plane_begin(),
1063 PE = ST.plane_end(); PI != PE; ++PI ) {
1064 PI->first // This is the Type* of the plane
1065 PI->second // This is the SymbolTable::ValueMap of name/Value pairs
1069 <td align="left">All name/Type Pairs</td><td>TI</td>
1070 <td align="left"><pre><tt>
1071 for (SymbolTable::type_const_iterator TI = ST.type_begin(),
1072 TE = ST.type_end(); TI != TE; ++TI )
1073 TI->first // This is the name of the type
1074 TI->second // This is the Type* value associated with the name
1078 <td align="left">name/Value pairs in a plane</td><td>VI</td>
1079 <td align="left"><pre><tt>
1080 for (SymbolTable::value_const_iterator VI = ST.value_begin(SomeType),
1081 VE = ST.value_end(SomeType); VI != VE; ++VI )
1082 VI->first // This is the name of the Value
1083 VI->second // This is the Value* value associated with the name
1088 <p>Using the recommended iterator names and idioms will help you avoid
1089 making mistakes. Of particular note, make sure that whenever you use
1090 value_begin(SomeType) that you always compare the resulting iterator
1091 with value_end(SomeType) not value_end(SomeOtherType) or else you
1092 will loop infinitely.</p>
1096 <dt><tt>plane_iterator plane_begin()</tt>:</dt>
1097 <dd>Get an iterator that starts at the beginning of the type planes.
1098 The iterator will iterate over the Type/ValueMap pairs in the
1101 <dt><tt>plane_const_iterator plane_begin() const</tt>:</dt>
1102 <dd>Get a const_iterator that starts at the beginning of the type
1103 planes. The iterator will iterate over the Type/ValueMap pairs
1104 in the type planes. </dd>
1106 <dt><tt>plane_iterator plane_end()</tt>:</dt>
1107 <dd>Get an iterator at the end of the type planes. This serves as
1108 the marker for end of iteration over the type planes.</dd>
1110 <dt><tt>plane_const_iterator plane_end() const</tt>:</dt>
1111 <dd>Get a const_iterator at the end of the type planes. This serves as
1112 the marker for end of iteration over the type planes.</dd>
1114 <dt><tt>value_iterator value_begin(const Type *Typ)</tt>:</dt>
1115 <dd>Get an iterator that starts at the beginning of a type plane.
1116 The iterator will iterate over the name/value pairs in the type plane.
1117 Note: The type plane must already exist before using this.</dd>
1119 <dt><tt>value_const_iterator value_begin(const Type *Typ) const</tt>:</dt>
1120 <dd>Get a const_iterator that starts at the beginning of a type plane.
1121 The iterator will iterate over the name/value pairs in the type plane.
1122 Note: The type plane must already exist before using this.</dd>
1124 <dt><tt>value_iterator value_end(const Type *Typ)</tt>:</dt>
1125 <dd>Get an iterator to the end of a type plane. This serves as the marker
1126 for end of iteration of the type plane.
1127 Note: The type plane must already exist before using this.</dd>
1129 <dt><tt>value_const_iterator value_end(const Type *Typ) const</tt>:</dt>
1130 <dd>Get a const_iterator to the end of a type plane. This serves as the
1131 marker for end of iteration of the type plane.
1132 Note: the type plane must already exist before using this.</dd>
1134 <dt><tt>type_iterator type_begin()</tt>:</dt>
1135 <dd>Get an iterator to the start of the name/Type map.</dd>
1137 <dt><tt>type_const_iterator type_begin() cons</tt>:</dt>
1138 <dd> Get a const_iterator to the start of the name/Type map.</dd>
1140 <dt><tt>type_iterator type_end()</tt>:</dt>
1141 <dd>Get an iterator to the end of the name/Type map. This serves as the
1142 marker for end of iteration of the types.</dd>
1144 <dt><tt>type_const_iterator type_end() const</tt>:</dt>
1145 <dd>Get a const-iterator to the end of the name/Type map. This serves
1146 as the marker for end of iteration of the types.</dd>
1148 <dt><tt>plane_const_iterator find(const Type* Typ ) const</tt>:</dt>
1149 <dd>This method returns a plane_const_iterator for iteration over
1150 the type planes starting at a specific plane, given by \p Ty.</dd>
1152 <dt><tt>plane_iterator find( const Type* Typ </tt>:</dt>
1153 <dd>This method returns a plane_iterator for iteration over the
1154 type planes starting at a specific plane, given by \p Ty.</dd>
1161 <!-- *********************************************************************** -->
1162 <div class="doc_section">
1163 <a name="coreclasses">The Core LLVM Class Hierarchy Reference </a>
1165 <!-- *********************************************************************** -->
1167 <div class="doc_text">
1169 <p>The Core LLVM classes are the primary means of representing the program
1170 being inspected or transformed. The core LLVM classes are defined in
1171 header files in the <tt>include/llvm/</tt> directory, and implemented in
1172 the <tt>lib/VMCore</tt> directory.</p>
1176 <!-- ======================================================================= -->
1177 <div class="doc_subsection">
1178 <a name="Value">The <tt>Value</tt> class</a>
1183 <p><tt>#include "<a href="/doxygen/Value_8h-source.html">llvm/Value.h</a>"</tt>
1185 doxygen info: <a href="/doxygen/structllvm_1_1Value.html">Value Class</a></p>
1187 <p>The <tt>Value</tt> class is the most important class in the LLVM Source
1188 base. It represents a typed value that may be used (among other things) as an
1189 operand to an instruction. There are many different types of <tt>Value</tt>s,
1190 such as <a href="#Constant"><tt>Constant</tt></a>s,<a
1191 href="#Argument"><tt>Argument</tt></a>s. Even <a
1192 href="#Instruction"><tt>Instruction</tt></a>s and <a
1193 href="#Function"><tt>Function</tt></a>s are <tt>Value</tt>s.</p>
1195 <p>A particular <tt>Value</tt> may be used many times in the LLVM representation
1196 for a program. For example, an incoming argument to a function (represented
1197 with an instance of the <a href="#Argument">Argument</a> class) is "used" by
1198 every instruction in the function that references the argument. To keep track
1199 of this relationship, the <tt>Value</tt> class keeps a list of all of the <a
1200 href="#User"><tt>User</tt></a>s that is using it (the <a
1201 href="#User"><tt>User</tt></a> class is a base class for all nodes in the LLVM
1202 graph that can refer to <tt>Value</tt>s). This use list is how LLVM represents
1203 def-use information in the program, and is accessible through the <tt>use_</tt>*
1204 methods, shown below.</p>
1206 <p>Because LLVM is a typed representation, every LLVM <tt>Value</tt> is typed,
1207 and this <a href="#Type">Type</a> is available through the <tt>getType()</tt>
1208 method. In addition, all LLVM values can be named. The "name" of the
1209 <tt>Value</tt> is a symbolic string printed in the LLVM code:</p>
1211 <pre> %<b>foo</b> = add int 1, 2<br></pre>
1213 <p><a name="#nameWarning">The name of this instruction is "foo".</a> <b>NOTE</b>
1214 that the name of any value may be missing (an empty string), so names should
1215 <b>ONLY</b> be used for debugging (making the source code easier to read,
1216 debugging printouts), they should not be used to keep track of values or map
1217 between them. For this purpose, use a <tt>std::map</tt> of pointers to the
1218 <tt>Value</tt> itself instead.</p>
1220 <p>One important aspect of LLVM is that there is no distinction between an SSA
1221 variable and the operation that produces it. Because of this, any reference to
1222 the value produced by an instruction (or the value available as an incoming
1223 argument, for example) is represented as a direct pointer to the instance of
1225 represents this value. Although this may take some getting used to, it
1226 simplifies the representation and makes it easier to manipulate.</p>
1230 <!-- _______________________________________________________________________ -->
1231 <div class="doc_subsubsection">
1232 <a name="m_Value">Important Public Members of the <tt>Value</tt> class</a>
1235 <div class="doc_text">
1238 <li><tt>Value::use_iterator</tt> - Typedef for iterator over the
1240 <tt>Value::use_const_iterator</tt> - Typedef for const_iterator over
1242 <tt>unsigned use_size()</tt> - Returns the number of users of the
1244 <tt>bool use_empty()</tt> - Returns true if there are no users.<br>
1245 <tt>use_iterator use_begin()</tt> - Get an iterator to the start of
1247 <tt>use_iterator use_end()</tt> - Get an iterator to the end of the
1249 <tt><a href="#User">User</a> *use_back()</tt> - Returns the last
1250 element in the list.
1251 <p> These methods are the interface to access the def-use
1252 information in LLVM. As with all other iterators in LLVM, the naming
1253 conventions follow the conventions defined by the <a href="#stl">STL</a>.</p>
1255 <li><tt><a href="#Type">Type</a> *getType() const</tt>
1256 <p>This method returns the Type of the Value.</p>
1258 <li><tt>bool hasName() const</tt><br>
1259 <tt>std::string getName() const</tt><br>
1260 <tt>void setName(const std::string &Name)</tt>
1261 <p> This family of methods is used to access and assign a name to a <tt>Value</tt>,
1262 be aware of the <a href="#nameWarning">precaution above</a>.</p>
1264 <li><tt>void replaceAllUsesWith(Value *V)</tt>
1266 <p>This method traverses the use list of a <tt>Value</tt> changing all <a
1267 href="#User"><tt>User</tt>s</a> of the current value to refer to
1268 "<tt>V</tt>" instead. For example, if you detect that an instruction always
1269 produces a constant value (for example through constant folding), you can
1270 replace all uses of the instruction with the constant like this:</p>
1272 <pre> Inst->replaceAllUsesWith(ConstVal);<br></pre>
1277 <!-- ======================================================================= -->
1278 <div class="doc_subsection">
1279 <a name="User">The <tt>User</tt> class</a>
1282 <div class="doc_text">
1285 <tt>#include "<a href="/doxygen/User_8h-source.html">llvm/User.h</a>"</tt><br>
1286 doxygen info: <a href="/doxygen/classllvm_1_1User.html">User Class</a><br>
1287 Superclass: <a href="#Value"><tt>Value</tt></a></p>
1289 <p>The <tt>User</tt> class is the common base class of all LLVM nodes that may
1290 refer to <a href="#Value"><tt>Value</tt></a>s. It exposes a list of "Operands"
1291 that are all of the <a href="#Value"><tt>Value</tt></a>s that the User is
1292 referring to. The <tt>User</tt> class itself is a subclass of
1295 <p>The operands of a <tt>User</tt> point directly to the LLVM <a
1296 href="#Value"><tt>Value</tt></a> that it refers to. Because LLVM uses Static
1297 Single Assignment (SSA) form, there can only be one definition referred to,
1298 allowing this direct connection. This connection provides the use-def
1299 information in LLVM.</p>
1303 <!-- _______________________________________________________________________ -->
1304 <div class="doc_subsubsection">
1305 <a name="m_User">Important Public Members of the <tt>User</tt> class</a>
1308 <div class="doc_text">
1310 <p>The <tt>User</tt> class exposes the operand list in two ways: through
1311 an index access interface and through an iterator based interface.</p>
1314 <li><tt>Value *getOperand(unsigned i)</tt><br>
1315 <tt>unsigned getNumOperands()</tt>
1316 <p> These two methods expose the operands of the <tt>User</tt> in a
1317 convenient form for direct access.</p></li>
1319 <li><tt>User::op_iterator</tt> - Typedef for iterator over the operand
1321 <tt>op_iterator op_begin()</tt> - Get an iterator to the start of
1322 the operand list.<br>
1323 <tt>op_iterator op_end()</tt> - Get an iterator to the end of the
1325 <p> Together, these methods make up the iterator based interface to
1326 the operands of a <tt>User</tt>.</p></li>
1331 <!-- ======================================================================= -->
1332 <div class="doc_subsection">
1333 <a name="Instruction">The <tt>Instruction</tt> class</a>
1336 <div class="doc_text">
1338 <p><tt>#include "</tt><tt><a
1339 href="/doxygen/Instruction_8h-source.html">llvm/Instruction.h</a>"</tt><br>
1340 doxygen info: <a href="/doxygen/classllvm_1_1Instruction.html">Instruction Class</a><br>
1341 Superclasses: <a href="#User"><tt>User</tt></a>, <a
1342 href="#Value"><tt>Value</tt></a></p>
1344 <p>The <tt>Instruction</tt> class is the common base class for all LLVM
1345 instructions. It provides only a few methods, but is a very commonly used
1346 class. The primary data tracked by the <tt>Instruction</tt> class itself is the
1347 opcode (instruction type) and the parent <a
1348 href="#BasicBlock"><tt>BasicBlock</tt></a> the <tt>Instruction</tt> is embedded
1349 into. To represent a specific type of instruction, one of many subclasses of
1350 <tt>Instruction</tt> are used.</p>
1352 <p> Because the <tt>Instruction</tt> class subclasses the <a
1353 href="#User"><tt>User</tt></a> class, its operands can be accessed in the same
1354 way as for other <a href="#User"><tt>User</tt></a>s (with the
1355 <tt>getOperand()</tt>/<tt>getNumOperands()</tt> and
1356 <tt>op_begin()</tt>/<tt>op_end()</tt> methods).</p> <p> An important file for
1357 the <tt>Instruction</tt> class is the <tt>llvm/Instruction.def</tt> file. This
1358 file contains some meta-data about the various different types of instructions
1359 in LLVM. It describes the enum values that are used as opcodes (for example
1360 <tt>Instruction::Add</tt> and <tt>Instruction::SetLE</tt>), as well as the
1361 concrete sub-classes of <tt>Instruction</tt> that implement the instruction (for
1362 example <tt><a href="#BinaryOperator">BinaryOperator</a></tt> and <tt><a
1363 href="#SetCondInst">SetCondInst</a></tt>). Unfortunately, the use of macros in
1364 this file confuses doxygen, so these enum values don't show up correctly in the
1365 <a href="/doxygen/classllvm_1_1Instruction.html">doxygen output</a>.</p>
1369 <!-- _______________________________________________________________________ -->
1370 <div class="doc_subsubsection">
1371 <a name="m_Instruction">Important Public Members of the <tt>Instruction</tt>
1375 <div class="doc_text">
1378 <li><tt><a href="#BasicBlock">BasicBlock</a> *getParent()</tt>
1379 <p>Returns the <a href="#BasicBlock"><tt>BasicBlock</tt></a> that
1380 this <tt>Instruction</tt> is embedded into.</p></li>
1381 <li><tt>bool mayWriteToMemory()</tt>
1382 <p>Returns true if the instruction writes to memory, i.e. it is a
1383 <tt>call</tt>,<tt>free</tt>,<tt>invoke</tt>, or <tt>store</tt>.</p></li>
1384 <li><tt>unsigned getOpcode()</tt>
1385 <p>Returns the opcode for the <tt>Instruction</tt>.</p></li>
1386 <li><tt><a href="#Instruction">Instruction</a> *clone() const</tt>
1387 <p>Returns another instance of the specified instruction, identical
1388 in all ways to the original except that the instruction has no parent
1389 (ie it's not embedded into a <a href="#BasicBlock"><tt>BasicBlock</tt></a>),
1390 and it has no name</p></li>
1395 <!-- ======================================================================= -->
1396 <div class="doc_subsection">
1397 <a name="BasicBlock">The <tt>BasicBlock</tt> class</a>
1400 <div class="doc_text">
1403 href="/doxygen/BasicBlock_8h-source.html">llvm/BasicBlock.h</a>"</tt><br>
1404 doxygen info: <a href="/doxygen/structllvm_1_1BasicBlock.html">BasicBlock
1406 Superclass: <a href="#Value"><tt>Value</tt></a></p>
1408 <p>This class represents a single entry multiple exit section of the code,
1409 commonly known as a basic block by the compiler community. The
1410 <tt>BasicBlock</tt> class maintains a list of <a
1411 href="#Instruction"><tt>Instruction</tt></a>s, which form the body of the block.
1412 Matching the language definition, the last element of this list of instructions
1413 is always a terminator instruction (a subclass of the <a
1414 href="#TerminatorInst"><tt>TerminatorInst</tt></a> class).</p>
1416 <p>In addition to tracking the list of instructions that make up the block, the
1417 <tt>BasicBlock</tt> class also keeps track of the <a
1418 href="#Function"><tt>Function</tt></a> that it is embedded into.</p>
1420 <p>Note that <tt>BasicBlock</tt>s themselves are <a
1421 href="#Value"><tt>Value</tt></a>s, because they are referenced by instructions
1422 like branches and can go in the switch tables. <tt>BasicBlock</tt>s have type
1427 <!-- _______________________________________________________________________ -->
1428 <div class="doc_subsubsection">
1429 <a name="m_BasicBlock">Important Public Members of the <tt>BasicBlock</tt>
1433 <div class="doc_text">
1437 <li><tt>BasicBlock(const std::string &Name = "", </tt><tt><a
1438 href="#Function">Function</a> *Parent = 0)</tt>
1440 <p>The <tt>BasicBlock</tt> constructor is used to create new basic blocks for
1441 insertion into a function. The constructor optionally takes a name for the new
1442 block, and a <a href="#Function"><tt>Function</tt></a> to insert it into. If
1443 the <tt>Parent</tt> parameter is specified, the new <tt>BasicBlock</tt> is
1444 automatically inserted at the end of the specified <a
1445 href="#Function"><tt>Function</tt></a>, if not specified, the BasicBlock must be
1446 manually inserted into the <a href="#Function"><tt>Function</tt></a>.</p></li>
1448 <li><tt>BasicBlock::iterator</tt> - Typedef for instruction list iterator<br>
1449 <tt>BasicBlock::const_iterator</tt> - Typedef for const_iterator.<br>
1450 <tt>begin()</tt>, <tt>end()</tt>, <tt>front()</tt>, <tt>back()</tt>,
1451 <tt>size()</tt>, <tt>empty()</tt>
1452 STL-style functions for accessing the instruction list.
1454 <p>These methods and typedefs are forwarding functions that have the same
1455 semantics as the standard library methods of the same names. These methods
1456 expose the underlying instruction list of a basic block in a way that is easy to
1457 manipulate. To get the full complement of container operations (including
1458 operations to update the list), you must use the <tt>getInstList()</tt>
1461 <li><tt>BasicBlock::InstListType &getInstList()</tt>
1463 <p>This method is used to get access to the underlying container that actually
1464 holds the Instructions. This method must be used when there isn't a forwarding
1465 function in the <tt>BasicBlock</tt> class for the operation that you would like
1466 to perform. Because there are no forwarding functions for "updating"
1467 operations, you need to use this if you want to update the contents of a
1468 <tt>BasicBlock</tt>.</p></li>
1470 <li><tt><a href="#Function">Function</a> *getParent()</tt>
1472 <p> Returns a pointer to <a href="#Function"><tt>Function</tt></a> the block is
1473 embedded into, or a null pointer if it is homeless.</p></li>
1475 <li><tt><a href="#TerminatorInst">TerminatorInst</a> *getTerminator()</tt>
1477 <p> Returns a pointer to the terminator instruction that appears at the end of
1478 the <tt>BasicBlock</tt>. If there is no terminator instruction, or if the last
1479 instruction in the block is not a terminator, then a null pointer is
1486 <!-- ======================================================================= -->
1487 <div class="doc_subsection">
1488 <a name="GlobalValue">The <tt>GlobalValue</tt> class</a>
1491 <div class="doc_text">
1494 href="/doxygen/GlobalValue_8h-source.html">llvm/GlobalValue.h</a>"</tt><br>
1495 doxygen info: <a href="/doxygen/classllvm_1_1GlobalValue.html">GlobalValue
1497 Superclasses: <a href="#User"><tt>User</tt></a>, <a
1498 href="#Value"><tt>Value</tt></a></p>
1500 <p>Global values (<a href="#GlobalVariable"><tt>GlobalVariable</tt></a>s or <a
1501 href="#Function"><tt>Function</tt></a>s) are the only LLVM values that are
1502 visible in the bodies of all <a href="#Function"><tt>Function</tt></a>s.
1503 Because they are visible at global scope, they are also subject to linking with
1504 other globals defined in different translation units. To control the linking
1505 process, <tt>GlobalValue</tt>s know their linkage rules. Specifically,
1506 <tt>GlobalValue</tt>s know whether they have internal or external linkage, as
1507 defined by the <tt>LinkageTypes</tt> enumeration.</p>
1509 <p>If a <tt>GlobalValue</tt> has internal linkage (equivalent to being
1510 <tt>static</tt> in C), it is not visible to code outside the current translation
1511 unit, and does not participate in linking. If it has external linkage, it is
1512 visible to external code, and does participate in linking. In addition to
1513 linkage information, <tt>GlobalValue</tt>s keep track of which <a
1514 href="#Module"><tt>Module</tt></a> they are currently part of.</p>
1516 <p>Because <tt>GlobalValue</tt>s are memory objects, they are always referred to
1517 by their <b>address</b>. As such, the <a href="#Type"><tt>Type</tt></a> of a
1518 global is always a pointer to its contents. It is important to remember this
1519 when using the <tt>GetElementPtrInst</tt> instruction because this pointer must
1520 be dereferenced first. For example, if you have a <tt>GlobalVariable</tt> (a
1521 subclass of <tt>GlobalValue)</tt> that is an array of 24 ints, type <tt>[24 x
1522 int]</tt>, then the <tt>GlobalVariable</tt> is a pointer to that array. Although
1523 the address of the first element of this array and the value of the
1524 <tt>GlobalVariable</tt> are the same, they have different types. The
1525 <tt>GlobalVariable</tt>'s type is <tt>[24 x int]</tt>. The first element's type
1526 is <tt>int.</tt> Because of this, accessing a global value requires you to
1527 dereference the pointer with <tt>GetElementPtrInst</tt> first, then its elements
1528 can be accessed. This is explained in the <a href="LangRef.html#globalvars">LLVM
1529 Language Reference Manual</a>.</p>
1533 <!-- _______________________________________________________________________ -->
1534 <div class="doc_subsubsection">
1535 <a name="m_GlobalValue">Important Public Members of the <tt>GlobalValue</tt>
1539 <div class="doc_text">
1542 <li><tt>bool hasInternalLinkage() const</tt><br>
1543 <tt>bool hasExternalLinkage() const</tt><br>
1544 <tt>void setInternalLinkage(bool HasInternalLinkage)</tt>
1545 <p> These methods manipulate the linkage characteristics of the <tt>GlobalValue</tt>.</p>
1548 <li><tt><a href="#Module">Module</a> *getParent()</tt>
1549 <p> This returns the <a href="#Module"><tt>Module</tt></a> that the
1550 GlobalValue is currently embedded into.</p></li>
1555 <!-- ======================================================================= -->
1556 <div class="doc_subsection">
1557 <a name="Function">The <tt>Function</tt> class</a>
1560 <div class="doc_text">
1563 href="/doxygen/Function_8h-source.html">llvm/Function.h</a>"</tt><br> doxygen
1564 info: <a href="/doxygen/classllvm_1_1Function.html">Function Class</a><br>
1565 Superclasses: <a href="#GlobalValue"><tt>GlobalValue</tt></a>, <a
1566 href="#User"><tt>User</tt></a>, <a href="#Value"><tt>Value</tt></a></p>
1568 <p>The <tt>Function</tt> class represents a single procedure in LLVM. It is
1569 actually one of the more complex classes in the LLVM heirarchy because it must
1570 keep track of a large amount of data. The <tt>Function</tt> class keeps track
1571 of a list of <a href="#BasicBlock"><tt>BasicBlock</tt></a>s, a list of formal <a
1572 href="#Argument"><tt>Argument</tt></a>s, and a <a
1573 href="#SymbolTable"><tt>SymbolTable</tt></a>.</p>
1575 <p>The list of <a href="#BasicBlock"><tt>BasicBlock</tt></a>s is the most
1576 commonly used part of <tt>Function</tt> objects. The list imposes an implicit
1577 ordering of the blocks in the function, which indicate how the code will be
1578 layed out by the backend. Additionally, the first <a
1579 href="#BasicBlock"><tt>BasicBlock</tt></a> is the implicit entry node for the
1580 <tt>Function</tt>. It is not legal in LLVM to explicitly branch to this initial
1581 block. There are no implicit exit nodes, and in fact there may be multiple exit
1582 nodes from a single <tt>Function</tt>. If the <a
1583 href="#BasicBlock"><tt>BasicBlock</tt></a> list is empty, this indicates that
1584 the <tt>Function</tt> is actually a function declaration: the actual body of the
1585 function hasn't been linked in yet.</p>
1587 <p>In addition to a list of <a href="#BasicBlock"><tt>BasicBlock</tt></a>s, the
1588 <tt>Function</tt> class also keeps track of the list of formal <a
1589 href="#Argument"><tt>Argument</tt></a>s that the function receives. This
1590 container manages the lifetime of the <a href="#Argument"><tt>Argument</tt></a>
1591 nodes, just like the <a href="#BasicBlock"><tt>BasicBlock</tt></a> list does for
1592 the <a href="#BasicBlock"><tt>BasicBlock</tt></a>s.</p>
1594 <p>The <a href="#SymbolTable"><tt>SymbolTable</tt></a> is a very rarely used
1595 LLVM feature that is only used when you have to look up a value by name. Aside
1596 from that, the <a href="#SymbolTable"><tt>SymbolTable</tt></a> is used
1597 internally to make sure that there are not conflicts between the names of <a
1598 href="#Instruction"><tt>Instruction</tt></a>s, <a
1599 href="#BasicBlock"><tt>BasicBlock</tt></a>s, or <a
1600 href="#Argument"><tt>Argument</tt></a>s in the function body.</p>
1602 <p>Note that <tt>Function</tt> is a <a href="#GlobalValue">GlobalValue</a>
1603 and therefore also a <a href="#Constant">Constant</a>. The value of the function
1604 is its address (after linking) which is guaranteed to be constant.</p>
1607 <!-- _______________________________________________________________________ -->
1608 <div class="doc_subsubsection">
1609 <a name="m_Function">Important Public Members of the <tt>Function</tt>
1613 <div class="doc_text">
1616 <li><tt>Function(const </tt><tt><a href="#FunctionType">FunctionType</a>
1617 *Ty, LinkageTypes Linkage, const std::string &N = "", Module* Parent = 0)</tt>
1619 <p>Constructor used when you need to create new <tt>Function</tt>s to add
1620 the the program. The constructor must specify the type of the function to
1621 create and what type of linkage the function should have. The <a
1622 href="#FunctionType"><tt>FunctionType</tt></a> argument
1623 specifies the formal arguments and return value for the function. The same
1624 <a href="#FunctionTypel"><tt>FunctionType</tt></a> value can be used to
1625 create multiple functions. The <tt>Parent</tt> argument specifies the Module
1626 in which the function is defined. If this argument is provided, the function
1627 will automatically be inserted into that module's list of
1630 <li><tt>bool isExternal()</tt>
1632 <p>Return whether or not the <tt>Function</tt> has a body defined. If the
1633 function is "external", it does not have a body, and thus must be resolved
1634 by linking with a function defined in a different translation unit.</p></li>
1636 <li><tt>Function::iterator</tt> - Typedef for basic block list iterator<br>
1637 <tt>Function::const_iterator</tt> - Typedef for const_iterator.<br>
1639 <tt>begin()</tt>, <tt>end()</tt>
1640 <tt>size()</tt>, <tt>empty()</tt>
1642 <p>These are forwarding methods that make it easy to access the contents of
1643 a <tt>Function</tt> object's <a href="#BasicBlock"><tt>BasicBlock</tt></a>
1646 <li><tt>Function::BasicBlockListType &getBasicBlockList()</tt>
1648 <p>Returns the list of <a href="#BasicBlock"><tt>BasicBlock</tt></a>s. This
1649 is necessary to use when you need to update the list or perform a complex
1650 action that doesn't have a forwarding method.</p></li>
1652 <li><tt>Function::arg_iterator</tt> - Typedef for the argument list
1654 <tt>Function::const_arg_iterator</tt> - Typedef for const_iterator.<br>
1656 <tt>arg_begin()</tt>, <tt>arg_end()</tt>
1657 <tt>arg_size()</tt>, <tt>arg_empty()</tt>
1659 <p>These are forwarding methods that make it easy to access the contents of
1660 a <tt>Function</tt> object's <a href="#Argument"><tt>Argument</tt></a>
1663 <li><tt>Function::ArgumentListType &getArgumentList()</tt>
1665 <p>Returns the list of <a href="#Argument"><tt>Argument</tt></a>s. This is
1666 necessary to use when you need to update the list or perform a complex
1667 action that doesn't have a forwarding method.</p></li>
1669 <li><tt><a href="#BasicBlock">BasicBlock</a> &getEntryBlock()</tt>
1671 <p>Returns the entry <a href="#BasicBlock"><tt>BasicBlock</tt></a> for the
1672 function. Because the entry block for the function is always the first
1673 block, this returns the first block of the <tt>Function</tt>.</p></li>
1675 <li><tt><a href="#Type">Type</a> *getReturnType()</tt><br>
1676 <tt><a href="#FunctionType">FunctionType</a> *getFunctionType()</tt>
1678 <p>This traverses the <a href="#Type"><tt>Type</tt></a> of the
1679 <tt>Function</tt> and returns the return type of the function, or the <a
1680 href="#FunctionType"><tt>FunctionType</tt></a> of the actual
1683 <li><tt><a href="#SymbolTable">SymbolTable</a> *getSymbolTable()</tt>
1685 <p> Return a pointer to the <a href="#SymbolTable"><tt>SymbolTable</tt></a>
1686 for this <tt>Function</tt>.</p></li>
1691 <!-- ======================================================================= -->
1692 <div class="doc_subsection">
1693 <a name="GlobalVariable">The <tt>GlobalVariable</tt> class</a>
1696 <div class="doc_text">
1699 href="/doxygen/GlobalVariable_8h-source.html">llvm/GlobalVariable.h</a>"</tt>
1701 doxygen info: <a href="/doxygen/classllvm_1_1GlobalVariable.html">GlobalVariable
1702 Class</a><br> Superclasses: <a href="#GlobalValue"><tt>GlobalValue</tt></a>, <a
1703 href="#User"><tt>User</tt></a>, <a href="#Value"><tt>Value</tt></a></p>
1705 <p>Global variables are represented with the (suprise suprise)
1706 <tt>GlobalVariable</tt> class. Like functions, <tt>GlobalVariable</tt>s are also
1707 subclasses of <a href="#GlobalValue"><tt>GlobalValue</tt></a>, and as such are
1708 always referenced by their address (global values must live in memory, so their
1709 "name" refers to their address). See <a
1710 href="#GlobalValue"><tt>GlobalValue</tt></a> for more on this. Global variables
1711 may have an initial value (which must be a <a
1712 href="#Constant"><tt>Constant</tt></a>), and if they have an initializer, they
1713 may be marked as "constant" themselves (indicating that their contents never
1714 change at runtime).</p>
1718 <!-- _______________________________________________________________________ -->
1719 <div class="doc_subsubsection">
1720 <a name="m_GlobalVariable">Important Public Members of the
1721 <tt>GlobalVariable</tt> class</a>
1724 <div class="doc_text">
1727 <li><tt>GlobalVariable(const </tt><tt><a href="#Type">Type</a> *Ty, bool
1728 isConstant, LinkageTypes& Linkage, <a href="#Constant">Constant</a>
1729 *Initializer = 0, const std::string &Name = "", Module* Parent = 0)</tt>
1731 <p>Create a new global variable of the specified type. If
1732 <tt>isConstant</tt> is true then the global variable will be marked as
1733 unchanging for the program. The Linkage parameter specifies the type of
1734 linkage (internal, external, weak, linkonce, appending) for the variable. If
1735 the linkage is InternalLinkage, WeakLinkage, or LinkOnceLinkage, then
1736 the resultant global variable will have internal linkage. AppendingLinkage
1737 concatenates together all instances (in different translation units) of the
1738 variable into a single variable but is only applicable to arrays. See
1739 the <a href="LangRef.html#modulestructure">LLVM Language Reference</a> for
1740 further details on linkage types. Optionally an initializer, a name, and the
1741 module to put the variable into may be specified for the global variable as
1744 <li><tt>bool isConstant() const</tt>
1746 <p>Returns true if this is a global variable that is known not to
1747 be modified at runtime.</p></li>
1749 <li><tt>bool hasInitializer()</tt>
1751 <p>Returns true if this <tt>GlobalVariable</tt> has an intializer.</p></li>
1753 <li><tt><a href="#Constant">Constant</a> *getInitializer()</tt>
1755 <p>Returns the intial value for a <tt>GlobalVariable</tt>. It is not legal
1756 to call this method if there is no initializer.</p></li>
1761 <!-- ======================================================================= -->
1762 <div class="doc_subsection">
1763 <a name="Module">The <tt>Module</tt> class</a>
1766 <div class="doc_text">
1769 href="/doxygen/Module_8h-source.html">llvm/Module.h</a>"</tt><br> doxygen info:
1770 <a href="/doxygen/classllvm_1_1Module.html">Module Class</a></p>
1772 <p>The <tt>Module</tt> class represents the top level structure present in LLVM
1773 programs. An LLVM module is effectively either a translation unit of the
1774 original program or a combination of several translation units merged by the
1775 linker. The <tt>Module</tt> class keeps track of a list of <a
1776 href="#Function"><tt>Function</tt></a>s, a list of <a
1777 href="#GlobalVariable"><tt>GlobalVariable</tt></a>s, and a <a
1778 href="#SymbolTable"><tt>SymbolTable</tt></a>. Additionally, it contains a few
1779 helpful member functions that try to make common operations easy.</p>
1783 <!-- _______________________________________________________________________ -->
1784 <div class="doc_subsubsection">
1785 <a name="m_Module">Important Public Members of the <tt>Module</tt> class</a>
1788 <div class="doc_text">
1791 <li><tt>Module::Module(std::string name = "")</tt></li>
1794 <p>Constructing a <a href="#Module">Module</a> is easy. You can optionally
1795 provide a name for it (probably based on the name of the translation unit).</p>
1798 <li><tt>Module::iterator</tt> - Typedef for function list iterator<br>
1799 <tt>Module::const_iterator</tt> - Typedef for const_iterator.<br>
1801 <tt>begin()</tt>, <tt>end()</tt>
1802 <tt>size()</tt>, <tt>empty()</tt>
1804 <p>These are forwarding methods that make it easy to access the contents of
1805 a <tt>Module</tt> object's <a href="#Function"><tt>Function</tt></a>
1808 <li><tt>Module::FunctionListType &getFunctionList()</tt>
1810 <p> Returns the list of <a href="#Function"><tt>Function</tt></a>s. This is
1811 necessary to use when you need to update the list or perform a complex
1812 action that doesn't have a forwarding method.</p>
1814 <p><!-- Global Variable --></p></li>
1820 <li><tt>Module::global_iterator</tt> - Typedef for global variable list iterator<br>
1822 <tt>Module::const_global_iterator</tt> - Typedef for const_iterator.<br>
1824 <tt>global_begin()</tt>, <tt>global_end()</tt>
1825 <tt>global_size()</tt>, <tt>global_empty()</tt>
1827 <p> These are forwarding methods that make it easy to access the contents of
1828 a <tt>Module</tt> object's <a
1829 href="#GlobalVariable"><tt>GlobalVariable</tt></a> list.</p></li>
1831 <li><tt>Module::GlobalListType &getGlobalList()</tt>
1833 <p>Returns the list of <a
1834 href="#GlobalVariable"><tt>GlobalVariable</tt></a>s. This is necessary to
1835 use when you need to update the list or perform a complex action that
1836 doesn't have a forwarding method.</p>
1838 <p><!-- Symbol table stuff --> </p></li>
1844 <li><tt><a href="#SymbolTable">SymbolTable</a> *getSymbolTable()</tt>
1846 <p>Return a reference to the <a href="#SymbolTable"><tt>SymbolTable</tt></a>
1847 for this <tt>Module</tt>.</p>
1849 <p><!-- Convenience methods --></p></li>
1855 <li><tt><a href="#Function">Function</a> *getFunction(const std::string
1856 &Name, const <a href="#FunctionType">FunctionType</a> *Ty)</tt>
1858 <p>Look up the specified function in the <tt>Module</tt> <a
1859 href="#SymbolTable"><tt>SymbolTable</tt></a>. If it does not exist, return
1860 <tt>null</tt>.</p></li>
1862 <li><tt><a href="#Function">Function</a> *getOrInsertFunction(const
1863 std::string &Name, const <a href="#FunctionType">FunctionType</a> *T)</tt>
1865 <p>Look up the specified function in the <tt>Module</tt> <a
1866 href="#SymbolTable"><tt>SymbolTable</tt></a>. If it does not exist, add an
1867 external declaration for the function and return it.</p></li>
1869 <li><tt>std::string getTypeName(const <a href="#Type">Type</a> *Ty)</tt>
1871 <p>If there is at least one entry in the <a
1872 href="#SymbolTable"><tt>SymbolTable</tt></a> for the specified <a
1873 href="#Type"><tt>Type</tt></a>, return it. Otherwise return the empty
1876 <li><tt>bool addTypeName(const std::string &Name, const <a
1877 href="#Type">Type</a> *Ty)</tt>
1879 <p>Insert an entry in the <a href="#SymbolTable"><tt>SymbolTable</tt></a>
1880 mapping <tt>Name</tt> to <tt>Ty</tt>. If there is already an entry for this
1881 name, true is returned and the <a
1882 href="#SymbolTable"><tt>SymbolTable</tt></a> is not modified.</p></li>
1887 <!-- ======================================================================= -->
1888 <div class="doc_subsection">
1889 <a name="Constant">The <tt>Constant</tt> class and subclasses</a>
1892 <div class="doc_text">
1894 <p>Constant represents a base class for different types of constants. It
1895 is subclassed by ConstantBool, ConstantInt, ConstantSInt, ConstantUInt,
1896 ConstantArray etc for representing the various types of Constants.</p>
1900 <!-- _______________________________________________________________________ -->
1901 <div class="doc_subsubsection">
1902 <a name="m_Constant">Important Public Methods</a>
1904 <div class="doc_text">
1907 <!-- _______________________________________________________________________ -->
1908 <div class="doc_subsubsection">Important Subclasses of Constant </div>
1909 <div class="doc_text">
1911 <li>ConstantSInt : This subclass of Constant represents a signed integer
1914 <li><tt>int64_t getValue() const</tt>: Returns the underlying value of
1915 this constant. </li>
1918 <li>ConstantUInt : This class represents an unsigned integer.
1920 <li><tt>uint64_t getValue() const</tt>: Returns the underlying value of
1921 this constant. </li>
1924 <li>ConstantFP : This class represents a floating point constant.
1926 <li><tt>double getValue() const</tt>: Returns the underlying value of
1927 this constant. </li>
1930 <li>ConstantBool : This represents a boolean constant.
1932 <li><tt>bool getValue() const</tt>: Returns the underlying value of this
1936 <li>ConstantArray : This represents a constant array.
1938 <li><tt>const std::vector<Use> &getValues() const</tt>: Returns
1939 a vector of component constants that makeup this array. </li>
1942 <li>ConstantStruct : This represents a constant struct.
1944 <li><tt>const std::vector<Use> &getValues() const</tt>: Returns
1945 a vector of component constants that makeup this array. </li>
1948 <li>GlobalValue : This represents either a global variable or a function. In
1949 either case, the value is a constant fixed address (after linking).
1954 <!-- ======================================================================= -->
1955 <div class="doc_subsection">
1956 <a name="Type">The <tt>Type</tt> class and Derived Types</a>
1959 <div class="doc_text">
1961 <p>Type as noted earlier is also a subclass of a Value class. Any primitive
1962 type (like int, short etc) in LLVM is an instance of Type Class. All other
1963 types are instances of subclasses of type like FunctionType, ArrayType
1964 etc. DerivedType is the interface for all such dervied types including
1965 FunctionType, ArrayType, PointerType, StructType. Types can have names. They can
1966 be recursive (StructType). There exists exactly one instance of any type
1967 structure at a time. This allows using pointer equality of Type *s for comparing
1972 <!-- _______________________________________________________________________ -->
1973 <div class="doc_subsubsection">
1974 <a name="m_Value">Important Public Methods</a>
1977 <div class="doc_text">
1981 <li><tt>bool isSigned() const</tt>: Returns whether an integral numeric type
1982 is signed. This is true for SByteTy, ShortTy, IntTy, LongTy. Note that this is
1983 not true for Float and Double. </li>
1985 <li><tt>bool isUnsigned() const</tt>: Returns whether a numeric type is
1986 unsigned. This is not quite the complement of isSigned... nonnumeric types
1987 return false as they do with isSigned. This returns true for UByteTy,
1988 UShortTy, UIntTy, and ULongTy. </li>
1990 <li><tt>bool isInteger() const</tt>: Equivalent to isSigned() || isUnsigned().</li>
1992 <li><tt>bool isIntegral() const</tt>: Returns true if this is an integral
1993 type, which is either Bool type or one of the Integer types.</li>
1995 <li><tt>bool isFloatingPoint()</tt>: Return true if this is one of the two
1996 floating point types.</li>
1998 <li><tt>isLosslesslyConvertableTo (const Type *Ty) const</tt>: Return true if
1999 this type can be converted to 'Ty' without any reinterpretation of bits. For
2000 example, uint to int or one pointer type to another.</li>
2004 <!-- _______________________________________________________________________ -->
2005 <div class="doc_subsubsection">
2006 <a name="m_Value">Important Derived Types</a>
2008 <div class="doc_text">
2010 <li>SequentialType : This is subclassed by ArrayType and PointerType
2012 <li><tt>const Type * getElementType() const</tt>: Returns the type of each
2013 of the elements in the sequential type. </li>
2016 <li>ArrayType : This is a subclass of SequentialType and defines interface for
2019 <li><tt>unsigned getNumElements() const</tt>: Returns the number of
2020 elements in the array. </li>
2023 <li>PointerType : Subclass of SequentialType for pointer types. </li>
2024 <li>StructType : subclass of DerivedTypes for struct types </li>
2025 <li>FunctionType : subclass of DerivedTypes for function types.
2027 <li><tt>bool isVarArg() const</tt>: Returns true if its a vararg
2029 <li><tt> const Type * getReturnType() const</tt>: Returns the
2030 return type of the function.</li>
2031 <li><tt>const Type * getParamType (unsigned i)</tt>: Returns
2032 the type of the ith parameter.</li>
2033 <li><tt> const unsigned getNumParams() const</tt>: Returns the
2034 number of formal parameters.</li>
2040 <!-- ======================================================================= -->
2041 <div class="doc_subsection">
2042 <a name="Argument">The <tt>Argument</tt> class</a>
2045 <div class="doc_text">
2047 <p>This subclass of Value defines the interface for incoming formal
2048 arguments to a function. A Function maintains a list of its formal
2049 arguments. An argument has a pointer to the parent Function.</p>
2053 <!-- *********************************************************************** -->
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2061 <a href="mailto:dhurjati@cs.uiuc.edu">Dinakar Dhurjati</a> and
2062 <a href="mailto:sabre@nondot.org">Chris Lattner</a><br>
2063 <a href="http://llvm.cs.uiuc.edu">The LLVM Compiler Infrastructure</a><br>
2064 Last modified: $Date$