[llvm-commits] [llvm] r141655 - /llvm/trunk/docs/WritingAnLLVMPass.html
Bill Wendling
isanbard at gmail.com
Tue Oct 11 00:03:52 PDT 2011
Author: void
Date: Tue Oct 11 02:03:52 2011
New Revision: 141655
URL: http://llvm.org/viewvc/llvm-project?rev=141655&view=rev
Log:
Minor modifications to make the Hello World example resemble the Hello World
pass in the tree. Also some minor formatting changes.
PR9413
Modified:
llvm/trunk/docs/WritingAnLLVMPass.html
Modified: llvm/trunk/docs/WritingAnLLVMPass.html
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/docs/WritingAnLLVMPass.html?rev=141655&r1=141654&r2=141655&view=diff
==============================================================================
--- llvm/trunk/docs/WritingAnLLVMPass.html (original)
+++ llvm/trunk/docs/WritingAnLLVMPass.html Tue Oct 11 02:03:52 2011
@@ -227,11 +227,13 @@
<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 @@
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 @@
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 @@
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>
More information about the llvm-commits
mailing list