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Diffstat (limited to 'docs/WritingAnLLVMPass.html')
| -rw-r--r-- | docs/WritingAnLLVMPass.html | 118 |
1 files changed, 69 insertions, 49 deletions
diff --git a/docs/WritingAnLLVMPass.html b/docs/WritingAnLLVMPass.html index 75426e0..adbd691 100644 --- a/docs/WritingAnLLVMPass.html +++ b/docs/WritingAnLLVMPass.html @@ -227,11 +227,13 @@ the pass itself.</p> <p>Now that we have a way to compile our new pass, we just have to write it. Start out with:</p> -<div class="doc_code"><pre> +<div class="doc_code"> +<pre> <b>#include</b> "<a href="http://llvm.org/doxygen/Pass_8h-source.html">llvm/Pass.h</a>" <b>#include</b> "<a href="http://llvm.org/doxygen/Function_8h-source.html">llvm/Function.h</a>" <b>#include</b> "<a href="http://llvm.org/doxygen/raw__ostream_8h.html">llvm/Support/raw_ostream.h</a>" -</pre></div> +</pre> +</div> <p>Which are needed because we are writing a <tt><a href="http://llvm.org/doxygen/classllvm_1_1Pass.html">Pass</a></tt>, @@ -240,53 +242,66 @@ href="http://llvm.org/doxygen/classllvm_1_1Function.html">Function</a></tt>'s, and we will be doing some printing.</p> <p>Next we have:</p> -<div class="doc_code"><pre> + +<div class="doc_code"> +<pre> <b>using namespace llvm;</b> -</pre></div> +</pre> +</div> + <p>... which is required because the functions from the include files -live in the llvm namespace. -</p> +live in the llvm namespace.</p> <p>Next we have:</p> -<div class="doc_code"><pre> +<div class="doc_code"> +<pre> <b>namespace</b> { -</pre></div> +</pre> +</div> <p>... which starts out an anonymous namespace. Anonymous namespaces are to C++ what the "<tt>static</tt>" keyword is to C (at global scope). It makes the -things declared inside of the anonymous namespace only visible to the current +things declared inside of the anonymous namespace visible only to the current file. If you're not familiar with them, consult a decent C++ book for more information.</p> <p>Next, we declare our pass itself:</p> -<div class="doc_code"><pre> +<div class="doc_code"> +<pre> <b>struct</b> Hello : <b>public</b> <a href="#FunctionPass">FunctionPass</a> { -</pre></div><p> +</pre> +</div> <p>This declares a "<tt>Hello</tt>" class that is a subclass of <tt><a href="http://llvm.org/doxygen/classllvm_1_1FunctionPass.html">FunctionPass</a></tt>. The different builtin pass subclasses are described in detail <a href="#passtype">later</a>, but for now, know that <a -href="#FunctionPass"><tt>FunctionPass</tt></a>'s operate a function at a +href="#FunctionPass"><tt>FunctionPass</tt></a>'s operate on a function at a time.</p> -<div class="doc_code"><pre> - static char ID; - Hello() : FunctionPass(ID) {} -</pre></div><p> +<div class="doc_code"> +<pre> + static char ID; + Hello() : FunctionPass(ID) {} +</pre> +</div> -<p> This declares pass identifier used by LLVM to identify pass. This allows LLVM to -avoid using expensive C++ runtime information.</p> +<p>This declares pass identifier used by LLVM to identify pass. This allows LLVM +to avoid using expensive C++ runtime information.</p> -<div class="doc_code"><pre> +<div class="doc_code"> +<pre> <b>virtual bool</b> <a href="#runOnFunction">runOnFunction</a>(Function &F) { - errs() << "<i>Hello: </i>" << F.getName() << "\n"; + errs() << "<i>Hello: </i>"; + errs().write_escaped(F.getName()) << "\n"; <b>return false</b>; } }; <i>// end of struct Hello</i> -</pre></div> +} <i>// end of anonymous namespace</i> +</pre> +</div> <p>We declare a "<a href="#runOnFunction"><tt>runOnFunction</tt></a>" method, which overloads an abstract virtual method inherited from <a @@ -294,31 +309,34 @@ href="#FunctionPass"><tt>FunctionPass</tt></a>. This is where we are supposed to do our thing, so we just print out our message with the name of each function.</p> -<div class="doc_code"><pre> - char Hello::ID = 0; -</pre></div> +<div class="doc_code"> +<pre> +char Hello::ID = 0; +</pre> +</div> -<p> We initialize pass ID here. LLVM uses ID's address to identify pass so +<p>We initialize pass ID here. LLVM uses ID's address to identify a pass, so initialization value is not important.</p> -<div class="doc_code"><pre> - static RegisterPass<Hello> X("<i>hello</i>", "<i>Hello World Pass</i>", - false /* Only looks at CFG */, - false /* Analysis Pass */); -} <i>// end of anonymous namespace</i> -</pre></div> +<div class="doc_code"> +<pre> +static RegisterPass<Hello> X("<i>hello</i>", "<i>Hello World Pass</i>", + false /* Only looks at CFG */, + false /* Analysis Pass */); +</pre> +</div> -<p>Lastly, we <a href="#registration">register our class</a> <tt>Hello</tt>, -giving it a command line -argument "<tt>hello</tt>", and a name "<tt>Hello World Pass</tt>". -Last two arguments describe its behavior. -If a pass walks CFG without modifying it then third argument is set to true. -If a pass is an analysis pass, for example dominator tree pass, then true -is supplied as fourth argument. </p> +<p>Lastly, we <a href="#registration">register our class</a> <tt>Hello</tt>, +giving it a command line argument "<tt>hello</tt>", and a name "<tt>Hello World +Pass</tt>". The last two arguments describe its behavior: if a pass walks CFG +without modifying it then the third argument is set to <tt>true</tt>; if a pass +is an analysis pass, for example dominator tree pass, then <tt>true</tt> is +supplied as the fourth argument.</p> <p>As a whole, the <tt>.cpp</tt> file looks like:</p> -<div class="doc_code"><pre> +<div class="doc_code"> +<pre> <b>#include</b> "<a href="http://llvm.org/doxygen/Pass_8h-source.html">llvm/Pass.h</a>" <b>#include</b> "<a href="http://llvm.org/doxygen/Function_8h-source.html">llvm/Function.h</a>" <b>#include</b> "<a href="http://llvm.org/doxygen/raw__ostream_8h.html">llvm/Support/raw_ostream.h</a>" @@ -332,24 +350,26 @@ is supplied as fourth argument. </p> Hello() : FunctionPass(ID) {} <b>virtual bool</b> <a href="#runOnFunction">runOnFunction</a>(Function &F) { - errs() << "<i>Hello: </i>" << F.getName() << "\n"; + errs() << "<i>Hello: </i>"; + errs().write_escaped(F.getName()) << '\n'; <b>return false</b>; } + }; - - char Hello::ID = 0; - static RegisterPass<Hello> X("hello", "Hello World Pass", false, false); } - -</pre></div> + +char Hello::ID = 0; +static RegisterPass<Hello> X("hello", "Hello World Pass", false, false); +</pre> +</div> <p>Now that it's all together, compile the file with a simple "<tt>gmake</tt>" command in the local directory and you should get a new file "<tt>Debug+Asserts/lib/Hello.so</tt>" under the top level directory of the LLVM source tree (not in the local directory). Note that everything in this file is -contained in an anonymous namespace: this reflects the fact that passes are self -contained units that do not need external interfaces (although they can have -them) to be useful.</p> +contained in an anonymous namespace — this reflects the fact that passes +are self contained units that do not need external interfaces (although they can +have them) to be useful.</p> </div> @@ -1929,7 +1949,7 @@ Despite that, we have kept the LLVM passes SMP ready, and you should too.</p> <a href="mailto:sabre@nondot.org">Chris Lattner</a><br> <a href="http://llvm.org/">The LLVM Compiler Infrastructure</a><br> - Last modified: $Date: 2011-04-23 02:30:22 +0200 (Sat, 23 Apr 2011) $ + Last modified: $Date: 2011-10-11 09:03:52 +0200 (Tue, 11 Oct 2011) $ </address> </body> |
