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'Pass' should now not be derived from by clients. Instead, they should derive

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from ModulePass.  Instead of implementing Pass::run, then should implement
ModulePass::runOnModule.

llvm-svn: 16430
This commit is contained in:
Chris Lattner 2004-09-20 04:36:29 +00:00
parent 046d7d920a
commit aef2bbf942
1 changed files with 30 additions and 27 deletions
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57
docs/WritingAnLLVMPass.html
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@ -23,9 +23,9 @@
<li><a href="#passtype">Pass classes and requirements</a>
<ul>
<li><a href="#ImmutablePass">The <tt>ImmutablePass</tt> class</a></li>
<li><a href="#Pass">The <tt>Pass</tt> class</a>
<li><a href="#ModulePass">The <tt>ModulePass</tt> class</a>
<ul>
<li><a href="#run">The <tt>run</tt> method</a></li>
<li><a href="#runOnModule">The <tt>runOnModule</tt> method</a></li>
</ul></li>
<li><a href="#CallGraphSCCPass">The <tt>CallGraphSCCPass</tt> class</a>
<ul>
@ -89,7 +89,7 @@
<li><a href="#future">Future extensions planned</a>
<ul>
<li><a href="#SMP">Multithreaded LLVM</a></li>
<li><a href="#PassFunctionPass"><tt>Pass</tt>es requiring
<li><a href="#PassFunctionPass"><tt>ModulePass</tt>es requiring
<tt>FunctionPass</tt>es</a></li>
</ul></li>
</ol>
@ -115,9 +115,10 @@ above all, a structuring technique for compiler code.</p>
<p>All LLVM passes are subclasses of the <tt><a
href="http://llvm.cs.uiuc.edu/doxygen/classllvm_1_1Pass.html">Pass</a></tt>
class, which implement functionality by overriding virtual methods inherited
from <tt>Pass</tt>. Depending on how your pass works, you may be able to
inherit from the <tt><a href="#CallGraphSCCPass">CallGraphSCCPass</a></tt>,
<tt><a href="#FunctionPass">FunctionPass</a></tt>, or <tt><a
from <tt>Pass</tt>. Depending on how your pass works, you should inherit from
the <tt><a href="#ModulePass">ModulePass</a></tt>, <tt><a
href="#CallGraphSCCPass">CallGraphSCCPass</a></tt>, <tt><a
href="#FunctionPass">FunctionPass</a></tt>, or <tt><a
href="#BasicBlockPass">BasicBlockPass</a></tt> classes, which gives the system
more information about what your pass does, and how it can be combined with
other passes. One of the main features of the LLVM Pass Framework is that it
@ -435,37 +436,38 @@ invalidated, and are never "run".</p>
<!-- ======================================================================= -->
<div class="doc_subsection">
<a name="Pass">The <tt>Pass</tt> class</a>
<a name="ModulePass">The <tt>ModulePass</tt> class</a>
</div>
<div class="doc_text">
<p>The "<tt><a
href="http://llvm.cs.uiuc.edu/doxygen/classllvm_1_1Pass.html">Pass</a></tt>"
href="http://llvm.cs.uiuc.edu/doxygen/classllvm_1_1ModulePass.html">ModulePass</a></tt>"
class is the most general of all superclasses that you can use. Deriving from
<tt>Pass</tt> indicates that your pass uses the entire program as a unit,
<tt>ModulePass</tt> indicates that your pass uses the entire program as a unit,
refering to function bodies in no predictable order, or adding and removing
functions. Because nothing is known about the behavior of direct <tt>Pass</tt>
functions. Because nothing is known about the behavior of <tt>ModulePass</tt>
subclasses, no optimization can be done for their execution.</p>
<p>To write a correct <tt>Pass</tt> subclass, derive from <tt>Pass</tt> and
overload the <tt>run</tt> method with the following signature:</p>
<p>To write a correct <tt>ModulePass</tt> subclass, derive from
<tt>ModulePass</tt> and overload the <tt>runOnModule</tt> method with the
following signature:</p>
</div>
<!-- _______________________________________________________________________ -->
<div class="doc_subsubsection">
<a name="run">The <tt>run</tt> method</a>
<a name="runOnModule">The <tt>runOnModule</tt> method</a>
</div>
<div class="doc_text">
<pre>
<b>virtual bool</b> run(Module &amp;M) = 0;
<b>virtual bool</b> runOnModule(Module &amp;M) = 0;
</pre>
<p>The <tt>run</tt> method performs the interesting work of the pass, and should
return true if the module was modified by the transformation, false
<p>The <tt>runOnModule</tt> method performs the interesting work of the pass,
and should return true if the module was modified by the transformation, false
otherwise.</p>
</div>
@ -585,7 +587,7 @@ program being compiled.</p>
<div class="doc_text">
<p>In contrast to direct <tt>Pass</tt> subclasses, direct <tt><a
<p>In contrast to <tt>ModulePass</tt> subclasses, <tt><a
href="http://llvm.cs.uiuc.edu/doxygen/classllvm_1_1Pass.html">FunctionPass</a></tt>
subclasses do have a predictable, local behavior that can be expected by the
system. All <tt>FunctionPass</tt> execute on each function in the program
@ -1538,23 +1540,24 @@ Despite that, we have kept the LLVM passes SMP ready, and you should too.</p>
<!-- _______________________________________________________________________ -->
<div class="doc_subsubsection">
<a name="PassFunctionPass"><tt>Pass</tt>es requiring <tt>FunctionPass</tt>es</a>
<a name="PassFunctionPass"><tt>ModulePass</tt>es requiring <tt>FunctionPass</tt>es</a>
</div>
<div class="doc_text">
<p>Currently it is illegal for a <a href="#Pass"><tt>Pass</tt></a> to require a
<a href="#FunctionPass"><tt>FunctionPass</tt></a>. This is because there is
only one instance of the <a href="#FunctionPass"><tt>FunctionPass</tt></a>
object ever created, thus nowhere to store information for all of the functions
in the program at the same time. Although this has come up a couple of times
before, this has always been worked around by factoring one big complicated pass
into a global and an interprocedural part, both of which are distinct. In the
future, it would be nice to have this though.</p>
<p>Currently it is illegal for a <a href="#ModulePass"><tt>ModulePass</tt></a>
to require a <a href="#FunctionPass"><tt>FunctionPass</tt></a>. This is because
there is only one instance of the <a
href="#FunctionPass"><tt>FunctionPass</tt></a> object ever created, thus nowhere
to store information for all of the functions in the program at the same time.
Although this has come up a couple of times before, this has always been worked
around by factoring one big complicated pass into a global and an
interprocedural part, both of which are distinct. In the future, it would be
nice to have this though.</p>
<p>Note that it is no problem for a <a
href="#FunctionPass"><tt>FunctionPass</tt></a> to require the results of a <a
href="#Pass"><tt>Pass</tt></a>, only the other way around.</p>
href="#ModulePass"><tt>ModulePass</tt></a>, only the other way around.</p>
</div>