<ul>
<li><a href="#isa">The <tt>isa<></tt>, <tt>cast<></tt>
and <tt>dyn_cast<></tt> templates</a> </li>
- <li><a href="#DEBUG">The <tt>DEBUG()</tt> macro & <tt>-debug</tt>
+ <li><a href="#DEBUG">The <tt>DEBUG()</tt> macro and <tt>-debug</tt>
option</a>
<ul>
<li><a href="#DEBUG_TYPE">Fine grained debug info with <tt>DEBUG_TYPE</tt>
<li>The <tt>InstVisitor</tt> template
<li>The general graph API
-->
+ <li><a href="#ViewGraph">Viewing graphs while debugging code</a></li>
</ul>
</li>
<li><a href="#common">Helpful Hints for Common Operations</a>
<!-- ======================================================================= -->
<div class="doc_subsection">
- <a name="isa">The isa<>, cast<> and dyn_cast<> templates</a>
+ <a name="isa">The <tt>isa<></tt>, <tt>cast<></tt> and
+ <tt>dyn_cast<></tt> templates</a>
</div>
<div class="doc_text">
<dl>
<dt><tt>isa<></tt>: </dt>
- <dd>The <tt>isa<></tt> operator works exactly like the Java
+ <dd><p>The <tt>isa<></tt> operator works exactly like the Java
"<tt>instanceof</tt>" operator. It returns true or false depending on whether
a reference or pointer points to an instance of the specified class. This can
- be very useful for constraint checking of various sorts (example below).</dd>
+ be very useful for constraint checking of various sorts (example below).</p>
+ </dd>
<dt><tt>cast<></tt>: </dt>
- <dd>The <tt>cast<></tt> operator is a "checked cast" operation. It
+ <dd><p>The <tt>cast<></tt> operator is a "checked cast" operation. It
converts a pointer or reference from a base class to a derived cast, causing
an assertion failure if it is not really an instance of the right type. This
should be used in cases where you have some information that makes you believe
that something is of the right type. An example of the <tt>isa<></tt>
- and <tt>cast<></tt> template is:
+ and <tt>cast<></tt> template is:</p>
- <pre>
- static bool isLoopInvariant(const <a href="#Value">Value</a> *V, const Loop *L) {
- if (isa<<a href="#Constant">Constant</a>>(V) || isa<<a href="#Argument">Argument</a>>(V) || isa<<a href="#GlobalValue">GlobalValue</a>>(V))
- return true;
+<div class="doc_code">
+<pre>
+static bool isLoopInvariant(const <a href="#Value">Value</a> *V, const Loop *L) {
+ if (isa<<a href="#Constant">Constant</a>>(V) || isa<<a href="#Argument">Argument</a>>(V) || isa<<a href="#GlobalValue">GlobalValue</a>>(V))
+ return true;
- <i>// Otherwise, it must be an instruction...</i>
- return !L->contains(cast<<a href="#Instruction">Instruction</a>>(V)->getParent());
- }
- </pre>
+ // <i>Otherwise, it must be an instruction...</i>
+ return !L->contains(cast<<a href="#Instruction">Instruction</a>>(V)->getParent());
+}
+</pre>
+</div>
<p>Note that you should <b>not</b> use an <tt>isa<></tt> test followed
by a <tt>cast<></tt>, for that use the <tt>dyn_cast<></tt>
<dt><tt>dyn_cast<></tt>:</dt>
- <dd>The <tt>dyn_cast<></tt> operator is a "checking cast" operation. It
- checks to see if the operand is of the specified type, and if so, returns a
+ <dd><p>The <tt>dyn_cast<></tt> operator is a "checking cast" operation.
+ It checks to see if the operand is of the specified type, and if so, returns a
pointer to it (this operator does not work with references). If the operand is
not of the correct type, a null pointer is returned. Thus, this works very
- much like the <tt>dynamic_cast</tt> operator in C++, and should be used in the
- same circumstances. Typically, the <tt>dyn_cast<></tt> operator is used
- in an <tt>if</tt> statement or some other flow control statement like this:
-
- <pre>
- if (<a href="#AllocationInst">AllocationInst</a> *AI = dyn_cast<<a href="#AllocationInst">AllocationInst</a>>(Val)) {
- ...
- }
- </pre>
+ much like the <tt>dynamic_cast<></tt> operator in C++, and should be
+ used in the same circumstances. Typically, the <tt>dyn_cast<></tt>
+ operator is used in an <tt>if</tt> statement or some other flow control
+ statement like this:</p>
+
+<div class="doc_code">
+<pre>
+if (<a href="#AllocationInst">AllocationInst</a> *AI = dyn_cast<<a href="#AllocationInst">AllocationInst</a>>(Val)) {
+ // <i>...</i>
+}
+</pre>
+</div>
- <p> This form of the <tt>if</tt> statement effectively combines together a
- call to <tt>isa<></tt> and a call to <tt>cast<></tt> into one
- statement, which is very convenient.</p>
+ <p>This form of the <tt>if</tt> statement effectively combines together a call
+ to <tt>isa<></tt> and a call to <tt>cast<></tt> into one
+ statement, which is very convenient.</p>
-
<p>Note that the <tt>dyn_cast<></tt> operator, like C++'s
- <tt>dynamic_cast</tt> or Java's <tt>instanceof</tt> operator, can be abused.
- In particular you should not use big chained <tt>if/then/else</tt> blocks to
- check for lots of different variants of classes. If you find yourself
- wanting to do this, it is much cleaner and more efficient to use the
- <tt>InstVisitor</tt> class to dispatch over the instruction type directly.</p>
+ <p>Note that the <tt>dyn_cast<></tt> operator, like C++'s
+ <tt>dynamic_cast<></tt> or Java's <tt>instanceof</tt> operator, can be
+ abused. In particular, you should not use big chained <tt>if/then/else</tt>
+ blocks to check for lots of different variants of classes. If you find
+ yourself wanting to do this, it is much cleaner and more efficient to use the
+ <tt>InstVisitor</tt> class to dispatch over the instruction type directly.</p>
- </dd>
+ </dd>
- <dt><tt>cast_or_null<></tt>: </dt>
-
- <dd>The <tt>cast_or_null<></tt> operator works just like the
- <tt>cast<></tt> operator, except that it allows for a null pointer as
- an argument (which it then propagates). This can sometimes be useful,
- allowing you to combine several null checks into one.</dd>
+ <dt><tt>cast_or_null<></tt>: </dt>
+
+ <dd><p>The <tt>cast_or_null<></tt> operator works just like the
+ <tt>cast<></tt> operator, except that it allows for a null pointer as an
+ argument (which it then propagates). This can sometimes be useful, allowing
+ you to combine several null checks into one.</p></dd>
- <dt><tt>dyn_cast_or_null<></tt>: </dt>
+ <dt><tt>dyn_cast_or_null<></tt>: </dt>
- <dd>The <tt>dyn_cast_or_null<></tt> operator works just like the
- <tt>dyn_cast<></tt> operator, except that it allows for a null pointer
- as an argument (which it then propagates). This can sometimes be useful,
- allowing you to combine several null checks into one.</dd>
+ <dd><p>The <tt>dyn_cast_or_null<></tt> operator works just like the
+ <tt>dyn_cast<></tt> operator, except that it allows for a null pointer
+ as an argument (which it then propagates). This can sometimes be useful,
+ allowing you to combine several null checks into one.</p></dd>
- </dl>
+</dl>
<p>These five templates can be used with any classes, whether they have a
v-table or not. To add support for these templates, you simply need to add
<!-- ======================================================================= -->
<div class="doc_subsection">
- <a name="DEBUG">The <tt>DEBUG()</tt> macro & <tt>-debug</tt> option</a>
+ <a name="DEBUG">The <tt>DEBUG()</tt> macro and <tt>-debug</tt> option</a>
</div>
<div class="doc_text">
<p>Often when working on your pass you will put a bunch of debugging printouts
and other code into your pass. After you get it working, you want to remove
-it... but you may need it again in the future (to work out new bugs that you run
+it, but you may need it again in the future (to work out new bugs that you run
across).</p>
<p> Naturally, because of this, you don't want to delete the debug printouts,
<tt>DEBUG</tt> macro, and it is only executed if '<tt>opt</tt>' (or any other
tool) is run with the '<tt>-debug</tt>' command line argument:</p>
- <pre> ... <br> DEBUG(std::cerr << "I am here!\n");<br> ...<br></pre>
+<div class="doc_code">
+<pre>
+DEBUG(std::cerr << "I am here!\n");
+</pre>
+</div>
<p>Then you can run your pass like this:</p>
- <pre> $ opt < a.bc > /dev/null -mypass<br> <no output><br> $ opt < a.bc > /dev/null -mypass -debug<br> I am here!<br> $<br></pre>
+<div class="doc_code">
+<pre>
+$ opt < a.bc > /dev/null -mypass
+<i><no output></i>
+$ opt < a.bc > /dev/null -mypass -debug
+I am here!
+</pre>
+</div>
<p>Using the <tt>DEBUG()</tt> macro instead of a home-brewed solution allows you
to not have to create "yet another" command line option for the debug output for
control, you define the <tt>DEBUG_TYPE</tt> macro and the <tt>-debug</tt> only
option as follows:</p>
- <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>
+<div class="doc_code">
+<pre>
+DEBUG(std::cerr << "No debug type\n");
+#undef DEBUG_TYPE
+#define DEBUG_TYPE "foo"
+DEBUG(std::cerr << "'foo' debug type\n");
+#undef DEBUG_TYPE
+#define DEBUG_TYPE "bar"
+DEBUG(std::cerr << "'bar' debug type\n");
+#undef DEBUG_TYPE
+#define DEBUG_TYPE ""
+DEBUG(std::cerr << "No debug type (2)\n");
+</pre>
+</div>
<p>Then you can run your pass like this:</p>
- <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> $<br></pre>
+<div class="doc_code">
+<pre>
+$ opt < a.bc > /dev/null -mypass
+<i><no output></i>
+$ opt < a.bc > /dev/null -mypass -debug
+No debug type
+'foo' debug type
+'bar' debug type
+No debug type (2)
+$ opt < a.bc > /dev/null -mypass -debug-only=foo
+'foo' debug type
+$ opt < a.bc > /dev/null -mypass -debug-only=bar
+'bar' debug type
+</pre>
+</div>
<p>Of course, in practice, you should only set <tt>DEBUG_TYPE</tt> at the top of
a file, to specify the debug type for the entire module (if you do this before
it are as follows:</p>
<ol>
- <li>Define your statistic like this:
- <pre>static Statistic<> NumXForms("mypassname", "The # of times I did stuff");<br></pre>
+ <li><p>Define your statistic like this:</p>
+
+<div class="doc_code">
+<pre>
+static Statistic<> NumXForms("mypassname", "The # of times I did stuff");
+</pre>
+</div>
<p>The <tt>Statistic</tt> template can emulate just about any data-type,
but if you do not specify a template argument, it defaults to acting like
an unsigned int counter (this is usually what you want).</p></li>
- <li>Whenever you make a transformation, bump the counter:
- <pre> ++NumXForms; // I did stuff<br></pre>
+ <li><p>Whenever you make a transformation, bump the counter:</p>
+
+<div class="doc_code">
+<pre>
+++NumXForms; // <i>I did stuff!</i>
+</pre>
+</div>
+
</li>
</ol>
<p>That's all you have to do. To get '<tt>opt</tt>' to print out the
statistics gathered, use the '<tt>-stats</tt>' option:</p>
- <pre> $ opt -stats -mypassname < program.bc > /dev/null<br> ... statistic output ...<br></pre>
+<div class="doc_code">
+<pre>
+$ opt -stats -mypassname < program.bc > /dev/null
+<i>... statistics output ...</i>
+</pre>
+</div>
<p> When running <tt>gccas</tt> on a C file from the SPEC benchmark
suite, it gives a report that looks like this:</p>
- <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>
+<div class="doc_code">
+<pre>
+ 7646 bytecodewriter - Number of normal instructions
+ 725 bytecodewriter - Number of oversized instructions
+ 129996 bytecodewriter - Number of bytecode bytes written
+ 2817 raise - Number of insts DCEd or constprop'd
+ 3213 raise - Number of cast-of-self removed
+ 5046 raise - Number of expression trees converted
+ 75 raise - Number of other getelementptr's formed
+ 138 raise - Number of load/store peepholes
+ 42 deadtypeelim - Number of unused typenames removed from symtab
+ 392 funcresolve - Number of varargs functions resolved
+ 27 globaldce - Number of global variables removed
+ 2 adce - Number of basic blocks removed
+ 134 cee - Number of branches revectored
+ 49 cee - Number of setcc instruction eliminated
+ 532 gcse - Number of loads removed
+ 2919 gcse - Number of instructions removed
+ 86 indvars - Number of canonical indvars added
+ 87 indvars - Number of aux indvars removed
+ 25 instcombine - Number of dead inst eliminate
+ 434 instcombine - Number of insts combined
+ 248 licm - Number of load insts hoisted
+ 1298 licm - Number of insts hoisted to a loop pre-header
+ 3 licm - Number of insts hoisted to multiple loop preds (bad, no loop pre-header)
+ 75 mem2reg - Number of alloca's promoted
+ 1444 cfgsimplify - Number of blocks simplified
+</pre>
+</div>
<p>Obviously, with so many optimizations, having a unified framework for this
stuff is very nice. Making your pass fit well into the framework makes it more
</div>
+<!-- ======================================================================= -->
+<div class="doc_subsection">
+ <a name="ViewGraph">Viewing graphs while debugging code</a>
+</div>
+
+<div class="doc_text">
+
+<p>Several of the important data structures in LLVM are graphs: for example
+CFGs made out of LLVM <a href="#BasicBlock">BasicBlock</a>s, CFGs made out of
+LLVM <a href="CodeGenerator.html#machinebasicblock">MachineBasicBlock</a>s, and
+<a href="CodeGenerator.html#selectiondag_intro">Instruction Selection
+DAGs</a>. In many cases, while debugging various parts of the compiler, it is
+nice to instantly visualize these graphs.</p>
+
+<p>LLVM provides several callbacks that are available in a debug build to do
+exactly that. If you call the <tt>Function::viewCFG()</tt> method, for example,
+the current LLVM tool will pop up a window containing the CFG for the function
+where each basic block is a node in the graph, and each node contains the
+instructions in the block. Similarly, there also exists
+<tt>Function::viewCFGOnly()</tt> (does not include the instructions), the
+<tt>MachineFunction::viewCFG()</tt> and <tt>MachineFunction::viewCFGOnly()</tt>,
+and the <tt>SelectionDAG::viewGraph()</tt> methods. Within GDB, for example,
+you can usually use something like <tt>call DAG.viewGraph()</tt> to pop
+up a window. Alternatively, you can sprinkle calls to these functions in your
+code in places you want to debug.</p>
+
+<p>Getting this to work requires a small amount of configuration. On Unix
+systems with X11, install the <a href="http://www.graphviz.org">graphviz</a>
+toolkit, and make sure 'dot' and 'gv' are in your path. If you are running on
+Mac OS/X, download and install the Mac OS/X <a
+href="http://www.pixelglow.com/graphviz/">Graphviz program</a>, and add
+<tt>/Applications/Graphviz.app/Contents/MacOS/</tt> (or whereever you install
+it) to your path. Once in your system and path are set up, rerun the LLVM
+configure script and rebuild LLVM to enable this functionality.</p>
+
+<p><tt>SelectionDAG</tt> has been extended to make it easier to locate
+<i>interesting</i> nodes in large complex graphs. From gdb, if you
+<tt>call DAG.setGraphColor(<i>node</i>, "<i>color</i>")</tt>, then the
+next <tt>call DAG.viewGraph()</tt> would hilight the node in the
+specified color (choices of colors can be found at <a
+href="http://www.graphviz.org/doc/info/colors.html">Colors<a>.) More
+complex node attributes can be provided with <tt>call
+DAG.setGraphAttrs(<i>node</i>, "<i>attributes</i>")</tt> (choices can be
+found at <a href="http://www.graphviz.org/doc/info/attrs.html">Graph
+Attributes</a>.) If you want to restart and clear all the current graph
+attributes, then you can <tt>call DAG.clearGraphAttrs()</tt>. </p>
+
+</div>
+
+
<!-- *********************************************************************** -->
<div class="doc_section">
<a name="common">Helpful Hints for Common Operations</a>
an example that prints the name of a <tt>BasicBlock</tt> and the number of
<tt>Instruction</tt>s it contains:</p>
- <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>
+<div class="doc_code">
+<pre>
+// <i>func is a pointer to a Function instance</i>
+for (Function::iterator i = func->begin(), e = func->end(); i != e; ++i)
+ // <i>Print out the name of the basic block if it has one, and then the</i>
+ // <i>number of instructions that it contains</i>
+ std::cerr << "Basic block (name=" << i->getName() << ") has "
+ << i->size() << " instructions.\n";
+</pre>
+</div>
<p>Note that i can be used as if it were a pointer for the purposes of
invoking member functions of the <tt>Instruction</tt> class. This is
<tt>BasicBlock</tt>s. Here's a code snippet that prints out each instruction in
a <tt>BasicBlock</tt>:</p>
+<div class="doc_code">
<pre>
- // blk is a pointer to a BasicBlock instance
- for (BasicBlock::iterator i = blk->begin(), e = blk->end(); i != e; ++i)
- // the next statement works since operator<<(ostream&,...)
- // is overloaded for Instruction&
- std::cerr << *i << "\n";
+// <i>blk is a pointer to a BasicBlock instance</i>
+for (BasicBlock::iterator i = blk->begin(), e = blk->end(); i != e; ++i)
+ // <i>The next statement works since operator<<(ostream&,...)</i>
+ // <i>is overloaded for Instruction&</i>
+ std::cerr << *i << "\n";
</pre>
+</div>
<p>However, this isn't really the best way to print out the contents of a
<tt>BasicBlock</tt>! Since the ostream operators are overloaded for virtually
and then instantiate <tt>InstIterator</tt>s explicitly in your code. Here's a
small example that shows how to dump all instructions in a function to the standard error stream:<p>
- <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>
-Easy, isn't it? You can also use <tt>InstIterator</tt>s to fill a
+<div class="doc_code">
+<pre>
+#include "<a href="/doxygen/InstIterator_8h-source.html">llvm/Support/InstIterator.h</a>"
+
+// <i>F is a ptr to a Function instance</i>
+for (inst_iterator i = inst_begin(F), e = inst_end(F); i != e; ++i)
+ std::cerr << *i << "\n";
+</pre>
+</div>
+
+<p>Easy, isn't it? You can also use <tt>InstIterator</tt>s to fill a
worklist with its initial contents. For example, if you wanted to
initialize a worklist to contain all instructions in a <tt>Function</tt>
-F, all you would need to do is something like:
- <pre>std::set<Instruction*> worklist;<br>worklist.insert(inst_begin(F), inst_end(F));<br></pre>
+F, all you would need to do is something like:</p>
+
+<div class="doc_code">
+<pre>
+std::set<Instruction*> worklist;
+worklist.insert(inst_begin(F), inst_end(F));
+</pre>
+</div>
<p>The STL set <tt>worklist</tt> would now contain all instructions in the
<tt>Function</tt> pointed to by F.</p>
Assuming that <tt>i</tt> is a <tt>BasicBlock::iterator</tt> and <tt>j</tt>
is a <tt>BasicBlock::const_iterator</tt>:</p>
- <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>
+<div class="doc_code">
+<pre>
+Instruction& inst = *i; // <i>Grab reference to instruction reference</i>
+Instruction* pinst = &*i; // <i>Grab pointer to instruction reference</i>
+const Instruction& inst = *j;
+</pre>
+</div>
<p>However, the iterators you'll be working with in the LLVM framework are
special: they will automatically convert to a ptr-to-instance type whenever they
(behind the scenes, this is a result of overloading casting mechanisms). Thus
the last line of the last example,</p>
- <pre>Instruction* pinst = &*i;</pre>
+<div class="doc_code">
+<pre>
+Instruction* pinst = &*i;
+</pre>
+</div>
<p>is semantically equivalent to</p>
- <pre>Instruction* pinst = i;</pre>
+<div class="doc_code">
+<pre>
+Instruction* pinst = i;
+</pre>
+</div>
<p>It's also possible to turn a class pointer into the corresponding iterator,
and this is a constant time operation (very efficient). The following code
iterators. By using these, you can explicitly grab the iterator of something
without actually obtaining it via iteration over some structure:</p>
- <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>
+<div class="doc_code">
+<pre>
+void printNextInstruction(Instruction* inst) {
+ BasicBlock::iterator it(inst);
+ ++it; // <i>After this line, it refers to the instruction after *inst</i>
+ if (it != inst->getParent()->end()) std::cerr << *it << "\n";
+}
+</pre>
+</div>
</div>
you'd do it if you didn't have <tt>InstVisitor</tt> around. In pseudocode, this
is what we want to do:</p>
- <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>
+<div class="doc_code">
+<pre>
+initialize callCounter to zero
+for each Function f in the Module
+ for each BasicBlock b in f
+ for each Instruction i in b
+ if (i is a CallInst and calls the given function)
+ increment callCounter
+</pre>
+</div>
-<p>And the actual code is (remember, since we're writing a
+<p>And the actual code is (remember, because we're writing a
<tt>FunctionPass</tt>, our <tt>FunctionPass</tt>-derived class simply has to
-override the <tt>runOnFunction</tt> method...):</p>
+override the <tt>runOnFunction</tt> method):</p>
- <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
- href="#CallInst">CallInst</a>* callInst = <a href="#isa">dyn_cast</a><<a
- 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>
+<div class="doc_code">
+<pre>
+Function* targetFunc = ...;
+
+class OurFunctionPass : public FunctionPass {
+ public:
+ OurFunctionPass(): callCounter(0) { }
+
+ virtual runOnFunction(Function& F) {
+ for (Function::iterator b = F.begin(), be = F.end(); b != be; ++b) {
+ for (BasicBlock::iterator i = b->begin(); ie = b->end(); i != ie; ++i) {
+ if (<a href="#CallInst">CallInst</a>* callInst = <a href="#isa">dyn_cast</a><<a
+ href="#CallInst">CallInst</a>>(&*i)) {
+ // <i>We know we've encountered a call instruction, so we</i>
+ // <i>need to determine if it's a call to the</i>
+ // <i>function pointed to by m_func or not</i>
+
+ if (callInst->getCalledFunction() == targetFunc)
+ ++callCounter;
+ }
+ }
+ }
+ }
+
+ private:
+ unsigned callCounter;
+};
+</pre>
+</div>
</div>
most-specific common base class is <tt>Instruction</tt>, which includes lots of
less closely-related things. For these cases, LLVM provides a handy wrapper
class called <a
-href="http://llvm.cs.uiuc.edu/doxygen/classllvm_1_1CallSite.html"><tt>CallSite</tt></a>.
+href="http://llvm.org/doxygen/classllvm_1_1CallSite.html"><tt>CallSite</tt></a>.
It is essentially a wrapper around an <tt>Instruction</tt> pointer, with some
methods that provide functionality common to <tt>CallInst</tt>s and
<tt>InvokeInst</tt>s.</p>
<i>use</i> <tt>foo</tt> is as simple as iterating over the <i>def-use</i> chain
of <tt>F</tt>:</p>
- <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>
+<div class="doc_code">
+<pre>
+Function* F = ...;
+
+for (Value::use_iterator i = F->use_begin(), e = F->use_end(); i != e; ++i)
+ if (Instruction *Inst = dyn_cast<Instruction>(*i)) {
+ std::cerr << "F is used in instruction:\n";
+ std::cerr << *Inst << "\n";
+ }
+</pre>
+</div>
<p>Alternately, it's common to have an instance of the <a
href="/doxygen/classllvm_1_1User.html">User Class</a> and need to know what
all of the values that a particular instruction uses (that is, the operands of
the particular <tt>Instruction</tt>):</p>
- <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>
+<div class="doc_code">
+<pre>
+Instruction* pi = ...;
+
+for (User::op_iterator i = pi->op_begin(), e = pi->op_end(); i != e; ++i) {
+ Value* v = *i;
+ // <i>...</i>
+}
+</pre>
+</div>
<!--
def-use chains ("finding all users of"): Value::use_begin/use_end
parameters. For example, an <tt>AllocaInst</tt> only <i>requires</i> a
(const-ptr-to) <tt>Type</tt>. Thus:</p>
-<pre>AllocaInst* ai = new AllocaInst(Type::IntTy);</pre>
+<div class="doc_code">
+<pre>
+AllocaInst* ai = new AllocaInst(Type::IntTy);
+</pre>
+</div>
<p>will create an <tt>AllocaInst</tt> instance that represents the allocation of
one integer in the current stack frame, at runtime. Each <tt>Instruction</tt>
<tt>Function</tt>, and I'm intending to use it within the same
<tt>Function</tt>. I might do:</p>
- <pre>AllocaInst* pa = new AllocaInst(Type::IntTy, 0, "indexLoc");</pre>
+<div class="doc_code">
+<pre>
+AllocaInst* pa = new AllocaInst(Type::IntTy, 0, "indexLoc");
+</pre>
+</div>
<p>where <tt>indexLoc</tt> is now the logical name of the instruction's
execution value, which is a pointer to an integer on the runtime stack.</p>
<tt>BasicBlock</tt>, and a newly-created instruction we wish to insert
before <tt>*pi</tt>, we do the following: </p>
- <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>
+<div class="doc_code">
+<pre>
+BasicBlock *pb = ...;
+Instruction *pi = ...;
+Instruction *newInst = new Instruction(...);
+
+pb->getInstList().insert(pi, newInst); // <i>Inserts newInst before pi in pb</i>
+</pre>
+</div>
<p>Appending to the end of a <tt>BasicBlock</tt> is so common that
the <tt>Instruction</tt> class and <tt>Instruction</tt>-derived
<tt>BasicBlock</tt> to be appended to. For example code that
looked like: </p>
- <pre> BasicBlock *pb = ...;<br> Instruction *newInst = new Instruction(...);<br> pb->getInstList().push_back(newInst); // appends newInst to pb<br></pre>
+<div class="doc_code">
+<pre>
+BasicBlock *pb = ...;
+Instruction *newInst = new Instruction(...);
+
+pb->getInstList().push_back(newInst); // <i>Appends newInst to pb</i>
+</pre>
+</div>
<p>becomes: </p>
- <pre> BasicBlock *pb = ...;<br> Instruction *newInst = new Instruction(..., pb);<br></pre>
+<div class="doc_code">
+<pre>
+BasicBlock *pb = ...;
+Instruction *newInst = new Instruction(..., pb);
+</pre>
+</div>
<p>which is much cleaner, especially if you are creating
long instruction streams.</p></li>
thing as the above code without being given a <tt>BasicBlock</tt> by doing:
</p>
- <pre> Instruction *pi = ...;<br> Instruction *newInst = new Instruction(...);<br> pi->getParent()->getInstList().insert(pi, newInst);<br></pre>
+<div class="doc_code">
+<pre>
+Instruction *pi = ...;
+Instruction *newInst = new Instruction(...);
+
+pi->getParent()->getInstList().insert(pi, newInst);
+</pre>
+</div>
<p>In fact, this sequence of steps occurs so frequently that the
<tt>Instruction</tt> class and <tt>Instruction</tt>-derived classes provide
<tt>Instruction</tt> constructor with a <tt>insertBefore</tt> (default)
parameter, the above code becomes:</p>
- <pre>Instruction* pi = ...;<br>Instruction* newInst = new Instruction(..., pi);<br></pre>
+<div class="doc_code">
+<pre>
+Instruction* pi = ...;
+Instruction* newInst = new Instruction(..., pi);
+</pre>
+</div>
<p>which is much cleaner, especially if you're creating a lot of
-instructions and adding them to <tt>BasicBlock</tt>s.</p></li>
+ instructions and adding them to <tt>BasicBlock</tt>s.</p></li>
</ul>
</div>
pointer to the basic block to get its list of instructions and then use the
erase function to remove your instruction. For example:</p>
- <pre> <a href="#Instruction">Instruction</a> *I = .. ;<br> <a
- href="#BasicBlock">BasicBlock</a> *BB = I->getParent();<br> BB->getInstList().erase(I);<br></pre>
+<div class="doc_code">
+<pre>
+<a href="#Instruction">Instruction</a> *I = .. ;
+<a href="#BasicBlock">BasicBlock</a> *BB = I->getParent();
+
+BB->getInstList().erase(I);
+</pre>
+</div>
</div>
<tt>AllocaInst</tt> that allocates memory for a single integer with a null
pointer to an integer.</p>
- <pre>AllocaInst* instToReplace = ...;<br>BasicBlock::iterator ii(instToReplace);<br>ReplaceInstWithValue(instToReplace->getParent()->getInstList(), ii,<br> Constant::getNullValue(PointerType::get(Type::IntTy)));<br></pre></li>
+<div class="doc_code">
+<pre>
+AllocaInst* instToReplace = ...;
+BasicBlock::iterator ii(instToReplace);
+
+ReplaceInstWithValue(instToReplace->getParent()->getInstList(), ii,
+ Constant::getNullValue(PointerType::get(Type::IntTy)));
+</pre></div></li>
<li><tt>ReplaceInstWithInst</tt>
instruction. The following example illustrates the replacement of one
<tt>AllocaInst</tt> with another.</p>
- <pre>AllocaInst* instToReplace = ...;<br>BasicBlock::iterator ii(instToReplace);<br>ReplaceInstWithInst(instToReplace->getParent()->getInstList(), ii,<br> new AllocaInst(Type::IntTy, 0, "ptrToReplacedInt"));<br></pre></li>
+<div class="doc_code">
+<pre>
+AllocaInst* instToReplace = ...;
+BasicBlock::iterator ii(instToReplace);
+
+ReplaceInstWithInst(instToReplace->getParent()->getInstList(), ii,
+ new AllocaInst(Type::IntTy, 0, "ptrToReplacedInt"));
+</pre></div></li>
</ul>
<p><i>Replacing multiple uses of <tt>User</tt>s and <tt>Value</tt>s</i></p>
to be emitted to an output .ll file:
</p>
+<div class="doc_code">
<pre>
- %mylist = type { %mylist*, int }
+%mylist = type { %mylist*, int }
</pre>
+</div>
<p>
To build this, use the following LLVM APIs:
</p>
+<div class="doc_code">
<pre>
- //<i> Create the initial outer struct.</i>
-
<a href="#PATypeHolder">PATypeHolder</a> StructTy = OpaqueType::get();
- std::vector<const Type*> Elts;
- Elts.push_back(PointerType::get(StructTy));
- Elts.push_back(Type::IntTy);
- StructType *NewSTy = StructType::get(Elts);
-
- //<i> At this point, NewSTy = "{ opaque*, int }". Tell VMCore that</i>
- //<i> the struct and the opaque type are actually the same.</i>
-
cast<OpaqueType>(StructTy.get())-><a href="#refineAbstractTypeTo">refineAbstractTypeTo</a>(NewSTy);
-
-
// <i>NewSTy is potentially invalidated, but StructTy (a <a href="#PATypeHolder">PATypeHolder</a>) is</i>
- // <i>kept up-to-date.</i>
- NewSTy = cast<StructType>(StructTy.get());
-
- // <i>Add a name for the type to the module symbol table (optional).</i>
- MyModule->addTypeName("mylist", NewSTy);
+// <i>Create the initial outer struct</i>
+<a href="#PATypeHolder">PATypeHolder</a> StructTy = OpaqueType::get();
+std::vector<const Type*> Elts;
+Elts.push_back(PointerType::get(StructTy));
+Elts.push_back(Type::IntTy);
+StructType *NewSTy = StructType::get(Elts);
+
+// <i>At this point, NewSTy = "{ opaque*, int }". Tell VMCore that</i>
+// <i>the struct and the opaque type are actually the same.</i>
+cast<OpaqueType>(StructTy.get())-><a href="#refineAbstractTypeTo">refineAbstractTypeTo</a>(NewSTy);
+
+// <i>NewSTy is potentially invalidated, but StructTy (a <a href="#PATypeHolder">PATypeHolder</a>) is</i>
+// <i>kept up-to-date</i>
+NewSTy = cast<StructType>(StructTy.get());
+
+// <i>Add a name for the type to the module symbol table (optional)</i>
+MyModule->addTypeName("mylist", NewSTy);
</pre>
+</div>
<p>
This code shows the basic approach used to build recursive types: build a
the beginning or end of the sequence for both const and non-const. It is
important to keep track of the different kinds of iterators. There are
three idioms worth pointing out:</p>
+
<table>
<tr><th>Units</th><th>Iterator</th><th>Idiom</th></tr>
<tr>
<td align="left"><pre><tt>
for (SymbolTable::plane_const_iterator PI = ST.plane_begin(),
PE = ST.plane_end(); PI != PE; ++PI ) {
- PI->first // This is the Type* of the plane
- PI->second // This is the SymbolTable::ValueMap of name/Value pairs
+ PI->first // <i>This is the Type* of the plane</i>
+ PI->second // <i>This is the SymbolTable::ValueMap of name/Value pairs</i>
+}
</tt></pre></td>
</tr>
<tr>
<td align="left">All name/Type Pairs</td><td>TI</td>
<td align="left"><pre><tt>
for (SymbolTable::type_const_iterator TI = ST.type_begin(),
- TE = ST.type_end(); TI != TE; ++TI )
- TI->first // This is the name of the type
- TI->second // This is the Type* value associated with the name
+ TE = ST.type_end(); TI != TE; ++TI ) {
+ TI->first // <i>This is the name of the type</i>
+ TI->second // <i>This is the Type* value associated with the name</i>
+}
</tt></pre></td>
</tr>
<tr>
<td align="left">name/Value pairs in a plane</td><td>VI</td>
<td align="left"><pre><tt>
for (SymbolTable::value_const_iterator VI = ST.value_begin(SomeType),
- VE = ST.value_end(SomeType); VI != VE; ++VI )
- VI->first // This is the name of the Value
- VI->second // This is the Value* value associated with the name
+ VE = ST.value_end(SomeType); VI != VE; ++VI ) {
+ VI->first // <i>This is the name of the Value</i>
+ VI->second // <i>This is the Value* value associated with the name</i>
+}
</tt></pre></td>
</tr>
</table>
method. In addition, all LLVM values can be named. The "name" of the
<tt>Value</tt> is a symbolic string printed in the LLVM code:</p>
- <pre> %<b>foo</b> = add int 1, 2<br></pre>
+<div class="doc_code">
+<pre>
+%<b>foo</b> = add int 1, 2
+</pre>
+</div>
<p><a name="#nameWarning">The name of this instruction is "foo".</a> <b>NOTE</b>
that the name of any value may be missing (an empty string), so names should
produces a constant value (for example through constant folding), you can
replace all uses of the instruction with the constant like this:</p>
- <pre> Inst->replaceAllUsesWith(ConstVal);<br></pre>
+<div class="doc_code">
+<pre>
+Inst->replaceAllUsesWith(ConstVal);
+</pre>
+</div>
+
</ul>
</div>
href="/doxygen/GlobalValue_8h-source.html">llvm/GlobalValue.h</a>"</tt><br>
doxygen info: <a href="/doxygen/classllvm_1_1GlobalValue.html">GlobalValue
Class</a><br>
-Superclasses: <a href="#User"><tt>User</tt></a>, <a
-href="#Value"><tt>Value</tt></a></p>
+Superclasses: <a href="#Constant"><tt>Constant</tt></a>,
+<a href="#User"><tt>User</tt></a>, <a href="#Value"><tt>Value</tt></a></p>
<p>Global values (<a href="#GlobalVariable"><tt>GlobalVariable</tt></a>s or <a
href="#Function"><tt>Function</tt></a>s) are the only LLVM values that are
<p><tt>#include "<a
href="/doxygen/Function_8h-source.html">llvm/Function.h</a>"</tt><br> doxygen
info: <a href="/doxygen/classllvm_1_1Function.html">Function Class</a><br>
-Superclasses: <a href="#GlobalValue"><tt>GlobalValue</tt></a>, <a
-href="#User"><tt>User</tt></a>, <a href="#Value"><tt>Value</tt></a></p>
+Superclasses: <a href="#GlobalValue"><tt>GlobalValue</tt></a>,
+<a href="#Constant"><tt>Constant</tt></a>,
+<a href="#User"><tt>User</tt></a>,
+<a href="#Value"><tt>Value</tt></a></p>
<p>The <tt>Function</tt> class represents a single procedure in LLVM. It is
actually one of the more complex classes in the LLVM heirarchy because it must
keep track of a large amount of data. The <tt>Function</tt> class keeps track
-of a list of <a href="#BasicBlock"><tt>BasicBlock</tt></a>s, a list of formal <a
-href="#Argument"><tt>Argument</tt></a>s, and a <a
-href="#SymbolTable"><tt>SymbolTable</tt></a>.</p>
+of a list of <a href="#BasicBlock"><tt>BasicBlock</tt></a>s, a list of formal
+<a href="#Argument"><tt>Argument</tt></a>s, and a
+<a href="#SymbolTable"><tt>SymbolTable</tt></a>.</p>
<p>The list of <a href="#BasicBlock"><tt>BasicBlock</tt></a>s is the most
commonly used part of <tt>Function</tt> objects. The list imposes an implicit
href="/doxygen/GlobalVariable_8h-source.html">llvm/GlobalVariable.h</a>"</tt>
<br>
doxygen info: <a href="/doxygen/classllvm_1_1GlobalVariable.html">GlobalVariable
-Class</a><br> Superclasses: <a href="#GlobalValue"><tt>GlobalValue</tt></a>, <a
-href="#User"><tt>User</tt></a>, <a href="#Value"><tt>Value</tt></a></p>
+ Class</a><br>
+Superclasses: <a href="#GlobalValue"><tt>GlobalValue</tt></a>,
+<a href="#Constant"><tt>Constant</tt></a>,
+<a href="#User"><tt>User</tt></a>,
+<a href="#Value"><tt>Value</tt></a></p>
<p>Global variables are represented with the (suprise suprise)
<tt>GlobalVariable</tt> class. Like functions, <tt>GlobalVariable</tt>s are also
subclasses of <a href="#GlobalValue"><tt>GlobalValue</tt></a>, and as such are
always referenced by their address (global values must live in memory, so their
-"name" refers to their address). See <a
-href="#GlobalValue"><tt>GlobalValue</tt></a> for more on this. Global variables
-may have an initial value (which must be a <a
-href="#Constant"><tt>Constant</tt></a>), and if they have an initializer, they
-may be marked as "constant" themselves (indicating that their contents never
-change at runtime).</p>
-
+"name" refers to their constant address). See
+<a href="#GlobalValue"><tt>GlobalValue</tt></a> for more on this. Global
+variables may have an initial value (which must be a
+<a href="#Constant"><tt>Constant</tt></a>), and if they have an initializer,
+they may be marked as "constant" themselves (indicating that their contents
+never change at runtime).</p>
</div>
<!-- _______________________________________________________________________ -->
<div class="doc_text">
<p>Constant represents a base class for different types of constants. It
-is subclassed by ConstantBool, ConstantInt, ConstantSInt, ConstantUInt,
-ConstantArray etc for representing the various types of Constants.</p>
+is subclassed by ConstantBool, ConstantInt, ConstantArray etc for representing
+the various types of Constants.</p>
</div>
<div class="doc_subsubsection">Important Subclasses of Constant </div>
<div class="doc_text">
<ul>
- <li>ConstantSInt : This subclass of Constant represents a signed integer
- constant.
- <ul>
- <li><tt>int64_t getValue() const</tt>: Returns the underlying value of
- this constant. </li>
- </ul>
- </li>
- <li>ConstantUInt : This class represents an unsigned integer.
+ <li>ConstantInt : This subclass of Constant represents an integer constant.
<ul>
- <li><tt>uint64_t getValue() const</tt>: Returns the underlying value of
- this constant. </li>
+ <li><tt>int64_t getSExtValue() const</tt>: Returns the underlying value of
+ this constant as a sign extended signed integer value.</li>
+ <li><tt>uint64_t getZExtValue() const</tt>: Returns the underlying value
+ of this constant as a zero extended unsigned integer value.</li>
</ul>
</li>
<li>ConstantFP : This class represents a floating point constant.
<a href="mailto:dhurjati@cs.uiuc.edu">Dinakar Dhurjati</a> and
<a href="mailto:sabre@nondot.org">Chris Lattner</a><br>
- <a href="http://llvm.cs.uiuc.edu">The LLVM Compiler Infrastructure</a><br>
+ <a href="http://llvm.org">The LLVM Compiler Infrastructure</a><br>
Last modified: $Date$
</address>
projects / oota-llvm.git / blobdiff