docs/Bugpoint.html - fp2-dev/platform/external/llvm - Gitiles

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   <title>LLVM bugpoint tool: design and usage</title>
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 </head>

 <h1>
   LLVM bugpoint tool: design and usage
 </h1>

 <ul>
   <li><a href="#desc">Description</a></li>
   <li><a href="#design">Design Philosophy</a>
   <ul>
     <li><a href="#autoselect">Automatic Debugger Selection</a></li>
     <li><a href="#crashdebug">Crash debugger</a></li>
     <li><a href="#codegendebug">Code generator debugger</a></li>
     <li><a href="#miscompilationdebug">Miscompilation debugger</a></li>
   </ul></li>
   <li><a href="#advice">Advice for using <tt>bugpoint</tt></a></li>
   <li><a href="#notEnough">What to do when <tt>bugpoint</tt> isn't enough</a></li>
 </ul>

 <div class="doc_author">
 <p>Written by <a href="mailto:sabre@nondot.org">Chris Lattner</a></p>
 </div>

 <!-- *********************************************************************** -->
 <h2>
 <a name="desc">Description</a>
 </h2>
 <!-- *********************************************************************** -->

 <div>

 <p><tt>bugpoint</tt> narrows down the source of problems in LLVM tools and
 passes.  It can be used to debug three types of failures: optimizer crashes,
 miscompilations by optimizers, or bad native code generation (including problems
 in the static and JIT compilers).  It aims to reduce large test cases to small,
 useful ones.  For example, if <tt>opt</tt> crashes while optimizing a
 file, it will identify the optimization (or combination of optimizations) that
 causes the crash, and reduce the file down to a small example which triggers the
 crash.</p>

 <p>For detailed case scenarios, such as debugging <tt>opt</tt>, or one of the
 LLVM code generators, see <a href="HowToSubmitABug.html">How To Submit a Bug
 Report document</a>.</p>

 </div>

 <!-- *********************************************************************** -->
 <h2>
 <a name="design">Design Philosophy</a>
 </h2>
 <!-- *********************************************************************** -->

 <div>

 <p><tt>bugpoint</tt> is designed to be a useful tool without requiring any
 hooks into the LLVM infrastructure at all.  It works with any and all LLVM
 passes and code generators, and does not need to "know" how they work.  Because
 of this, it may appear to do stupid things or miss obvious
 simplifications.  <tt>bugpoint</tt> is also designed to trade off programmer
 time for computer time in the compiler-debugging process; consequently, it may
 take a long period of (unattended) time to reduce a test case, but we feel it
 is still worth it. Note that <tt>bugpoint</tt> is generally very quick unless
 debugging a miscompilation where each test of the program (which requires
 executing it) takes a long time.</p>

 <!-- ======================================================================= -->
 <h3>
   <a name="autoselect">Automatic Debugger Selection</a>
 </h3>

 <div>

 <p><tt>bugpoint</tt> reads each <tt>.bc</tt> or <tt>.ll</tt> file specified on
 the command line and links them together into a single module, called the test
 program.  If any LLVM passes are specified on the command line, it runs these
 passes on the test program.  If any of the passes crash, or if they produce
 malformed output (which causes the verifier to abort), <tt>bugpoint</tt> starts
 the <a href="#crashdebug">crash debugger</a>.</p>

 <p>Otherwise, if the <tt>-output</tt> option was not specified,
 <tt>bugpoint</tt> runs the test program with the C backend (which is assumed to
 generate good code) to generate a reference output.  Once <tt>bugpoint</tt> has
 a reference output for the test program, it tries executing it with the
 selected code generator.  If the selected code generator crashes,
 <tt>bugpoint</tt> starts the <a href="#crashdebug">crash debugger</a> on the
 code generator.  Otherwise, if the resulting output differs from the reference
 output, it assumes the difference resulted from a code generator failure, and
 starts the <a href="#codegendebug">code generator debugger</a>.</p>

 <p>Finally, if the output of the selected code generator matches the reference
 output, <tt>bugpoint</tt> runs the test program after all of the LLVM passes
 have been applied to it.  If its output differs from the reference output, it
 assumes the difference resulted from a failure in one of the LLVM passes, and
 enters the <a href="#miscompilationdebug">miscompilation debugger</a>.
 Otherwise, there is no problem <tt>bugpoint</tt> can debug.</p>

 </div>

 <!-- ======================================================================= -->
 <h3>
   <a name="crashdebug">Crash debugger</a>
 </h3>

 <div>

 <p>If an optimizer or code generator crashes, <tt>bugpoint</tt> will try as hard
 as it can to reduce the list of passes (for optimizer crashes) and the size of
 the test program.  First, <tt>bugpoint</tt> figures out which combination of
 optimizer passes triggers the bug. This is useful when debugging a problem
 exposed by <tt>opt</tt>, for example, because it runs over 38 passes.</p>

 <p>Next, <tt>bugpoint</tt> tries removing functions from the test program, to
 reduce its size.  Usually it is able to reduce a test program to a single
 function, when debugging intraprocedural optimizations.  Once the number of
 functions has been reduced, it attempts to delete various edges in the control
 flow graph, to reduce the size of the function as much as possible.  Finally,
 <tt>bugpoint</tt> deletes any individual LLVM instructions whose absence does
 not eliminate the failure.  At the end, <tt>bugpoint</tt> should tell you what
 passes crash, give you a bitcode file, and give you instructions on how to
 reproduce the failure with <tt>opt</tt> or <tt>llc</tt>.</p>

 </div>

 <!-- ======================================================================= -->
 <h3>
   <a name="codegendebug">Code generator debugger</a>
 </h3>

 <div>

 <p>The code generator debugger attempts to narrow down the amount of code that
 is being miscompiled by the selected code generator.  To do this, it takes the
 test program and partitions it into two pieces: one piece which it compiles
 with the C backend (into a shared object), and one piece which it runs with
 either the JIT or the static LLC compiler.  It uses several techniques to
 reduce the amount of code pushed through the LLVM code generator, to reduce the
 potential scope of the problem.  After it is finished, it emits two bitcode
 files (called "test" [to be compiled with the code generator] and "safe" [to be
 compiled with the C backend], respectively), and instructions for reproducing
 the problem.  The code generator debugger assumes that the C backend produces
 good code.</p>

 </div>

 <!-- ======================================================================= -->
 <h3>
   <a name="miscompilationdebug">Miscompilation debugger</a>
 </h3>

 <div>

 <p>The miscompilation debugger works similarly to the code generator debugger.
 It works by splitting the test program into two pieces, running the
 optimizations specified on one piece, linking the two pieces back together, and
 then executing the result.  It attempts to narrow down the list of passes to
 the one (or few) which are causing the miscompilation, then reduce the portion
 of the test program which is being miscompiled.  The miscompilation debugger
 assumes that the selected code generator is working properly.</p>

 </div>

 </div>

 <!-- *********************************************************************** -->
 <h2>
   <a name="advice">Advice for using bugpoint</a>
 </h2>
 <!-- *********************************************************************** -->

 <div>

 <tt>bugpoint</tt> can be a remarkably useful tool, but it sometimes works in
 non-obvious ways.  Here are some hints and tips:<p>

 <ol>
 <li>In the code generator and miscompilation debuggers, <tt>bugpoint</tt> only
     works with programs that have deterministic output.  Thus, if the program
     outputs <tt>argv[0]</tt>, the date, time, or any other "random" data,
     <tt>bugpoint</tt> may misinterpret differences in these data, when output,
     as the result of a miscompilation.  Programs should be temporarily modified
     to disable outputs that are likely to vary from run to run.

 <li>In the code generator and miscompilation debuggers, debugging will go
     faster if you manually modify the program or its inputs to reduce the
     runtime, but still exhibit the problem.

 <li><tt>bugpoint</tt> is extremely useful when working on a new optimization:
     it helps track down regressions quickly.  To avoid having to relink
     <tt>bugpoint</tt> every time you change your optimization however, have
     <tt>bugpoint</tt> dynamically load your optimization with the
     <tt>-load</tt> option.

 <li><p><tt>bugpoint</tt> can generate a lot of output and run for a long period
     of time.  It is often useful to capture the output of the program to file.
     For example, in the C shell, you can run:</p>

 <div class="doc_code">
 <p><tt>bugpoint  ... |&amp; tee bugpoint.log</tt></p>
 </div>

     <p>to get a copy of <tt>bugpoint</tt>'s output in the file
     <tt>bugpoint.log</tt>, as well as on your terminal.</p>

 <li><tt>bugpoint</tt> cannot debug problems with the LLVM linker. If
     <tt>bugpoint</tt> crashes before you see its "All input ok" message,
     you might try <tt>llvm-link -v</tt> on the same set of input files. If
     that also crashes, you may be experiencing a linker bug.

 <li><tt>bugpoint</tt> is useful for proactively finding bugs in LLVM.
     Invoking <tt>bugpoint</tt> with the <tt>-find-bugs</tt> option will cause
     the list of specified optimizations to be randomized and applied to the
     program. This process will repeat until a bug is found or the user
     kills <tt>bugpoint</tt>.
 </ol>

 </div>
 <!-- *********************************************************************** -->
 <h2>
   <a name="notEnough">What to do when bugpoint isn't enough</a>
 </h2>
 <!-- *********************************************************************** -->

 <div>

 <p>Sometimes, <tt>bugpoint</tt> is not enough. In particular, InstCombine and
 TargetLowering both have visitor structured code with lots of potential
 transformations.  If the process of using bugpoint has left you with
 still too much code to figure out and the problem seems
 to be in instcombine, the following steps may help.  These same techniques
 are useful with TargetLowering as well.</p>

 <p>Turn on <tt>-debug-only=instcombine</tt> and see which transformations
 within instcombine are firing by selecting out lines with "<tt>IC</tt>"
 in them.</p>

 <p>At this point, you have a decision to make.  Is the number
 of transformations small enough to step through them using a debugger?
 If so, then try that.</p>

 <p>If there are too many transformations, then a source modification
 approach may be helpful.
 In this approach, you can modify the source code of instcombine
 to disable just those transformations that are being performed on your
 test input and perform a binary search over the set of transformations.
 One set of places to modify are the "<tt>visit*</tt>" methods of
 <tt>InstCombiner</tt> (<I>e.g.</I> <tt>visitICmpInst</tt>) by adding a
 "<tt>return false</tt>" as the first line of the method.</p>

 <p>If that still doesn't remove enough, then change the caller of
 <tt>InstCombiner::DoOneIteration</tt>, <tt>InstCombiner::runOnFunction</tt>
 to limit the number of iterations.</p>

 <p>You may also find it useful to use "<tt>-stats</tt>" now to see what parts
 of instcombine are firing.  This can guide where to put additional reporting
 code.</p>

 <p>At this point, if the amount of transformations is still too large, then
 inserting code to limit whether or not to execute the body of the code
 in the visit function can be helpful.  Add a static counter which is
 incremented on every invocation of the function.  Then add code which
 simply returns false on desired ranges.  For example:</p>

 <div class="doc_code">
 <p><tt>static int calledCount = 0;</tt></p>
 <p><tt>calledCount++;</tt></p>
 <p><tt>DEBUG(if (calledCount &lt; 212) return false);</tt></p>
 <p><tt>DEBUG(if (calledCount &gt; 217) return false);</tt></p>
 <p><tt>DEBUG(if (calledCount == 213) return false);</tt></p>
 <p><tt>DEBUG(if (calledCount == 214) return false);</tt></p>
 <p><tt>DEBUG(if (calledCount == 215) return false);</tt></p>
 <p><tt>DEBUG(if (calledCount == 216) return false);</tt></p>
 <p><tt>DEBUG(dbgs() &lt;&lt; "visitXOR calledCount: " &lt;&lt; calledCount
 	&lt;&lt; "\n");</tt></p>
 <p><tt>DEBUG(dbgs() &lt;&lt; "I: "; I->dump());</tt></p>
 </div>

 <p>could be added to <tt>visitXOR</tt> to limit <tt>visitXor</tt> to being
 applied only to calls 212 and 217. This is from an actual test case and raises
 an important point---a simple binary search may not be sufficient, as
 transformations that interact may require isolating more than one call.
 In TargetLowering, use <tt>return SDNode();</tt> instead of
 <tt>return false;</tt>.</p>

 <p>Now that that the number of transformations is down to a manageable
 number, try examining the output to see if you can figure out which
 transformations are being done.  If that can be figured out, then
 do the usual debugging.  If which code corresponds to the transformation
 being performed isn't obvious, set a breakpoint after the call count
 based disabling and step through the code.  Alternatively, you can use
 "printf" style debugging to report waypoints.</p>

 </div>

 <!-- *********************************************************************** -->

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 </body>
 </html>
	<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"
	"http://www.w3.org/TR/html4/strict.dtd">
	<html>
	<head>
	<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
	<title>LLVM bugpoint tool: design and usage</title>
	<link rel="stylesheet" href="_static/llvm.css" type="text/css">
	</head>

	<h1>
	LLVM bugpoint tool: design and usage
	</h1>

	<ul>
	<li><a href="#desc">Description</a></li>
	<li><a href="#design">Design Philosophy</a>
	<ul>
	<li><a href="#autoselect">Automatic Debugger Selection</a></li>
	<li><a href="#crashdebug">Crash debugger</a></li>
	<li><a href="#codegendebug">Code generator debugger</a></li>
	<li><a href="#miscompilationdebug">Miscompilation debugger</a></li>
	</ul></li>
	<li><a href="#advice">Advice for using <tt>bugpoint</tt></a></li>
	<li><a href="#notEnough">What to do when <tt>bugpoint</tt> isn't enough</a></li>
	</ul>

	<div class="doc_author">
	<p>Written by <a href="mailto:sabre@nondot.org">Chris Lattner</a></p>
	</div>

	<!-- *********************************************************************** -->
	<h2>
	<a name="desc">Description</a>
	</h2>
	<!-- *********************************************************************** -->

	<div>

	<p><tt>bugpoint</tt> narrows down the source of problems in LLVM tools and
	passes. It can be used to debug three types of failures: optimizer crashes,
	miscompilations by optimizers, or bad native code generation (including problems
	in the static and JIT compilers). It aims to reduce large test cases to small,
	useful ones. For example, if <tt>opt</tt> crashes while optimizing a
	file, it will identify the optimization (or combination of optimizations) that
	causes the crash, and reduce the file down to a small example which triggers the
	crash.</p>

	<p>For detailed case scenarios, such as debugging <tt>opt</tt>, or one of the
	LLVM code generators, see <a href="HowToSubmitABug.html">How To Submit a Bug
	Report document</a>.</p>

	</div>

	<!-- *********************************************************************** -->
	<h2>
	<a name="design">Design Philosophy</a>
	</h2>
	<!-- *********************************************************************** -->

	<div>

	<p><tt>bugpoint</tt> is designed to be a useful tool without requiring any
	hooks into the LLVM infrastructure at all. It works with any and all LLVM
	passes and code generators, and does not need to "know" how they work. Because
	of this, it may appear to do stupid things or miss obvious
	simplifications. <tt>bugpoint</tt> is also designed to trade off programmer
	time for computer time in the compiler-debugging process; consequently, it may
	take a long period of (unattended) time to reduce a test case, but we feel it
	is still worth it. Note that <tt>bugpoint</tt> is generally very quick unless
	debugging a miscompilation where each test of the program (which requires
	executing it) takes a long time.</p>

	<!-- ======================================================================= -->
	<h3>
	<a name="autoselect">Automatic Debugger Selection</a>
	</h3>

	<div>

	<p><tt>bugpoint</tt> reads each <tt>.bc</tt> or <tt>.ll</tt> file specified on
	the command line and links them together into a single module, called the test
	program. If any LLVM passes are specified on the command line, it runs these
	passes on the test program. If any of the passes crash, or if they produce
	malformed output (which causes the verifier to abort), <tt>bugpoint</tt> starts
	the <a href="#crashdebug">crash debugger</a>.</p>

	<p>Otherwise, if the <tt>-output</tt> option was not specified,
	<tt>bugpoint</tt> runs the test program with the C backend (which is assumed to
	generate good code) to generate a reference output. Once <tt>bugpoint</tt> has
	a reference output for the test program, it tries executing it with the
	selected code generator. If the selected code generator crashes,
	<tt>bugpoint</tt> starts the <a href="#crashdebug">crash debugger</a> on the
	code generator. Otherwise, if the resulting output differs from the reference
	output, it assumes the difference resulted from a code generator failure, and
	starts the <a href="#codegendebug">code generator debugger</a>.</p>

	<p>Finally, if the output of the selected code generator matches the reference
	output, <tt>bugpoint</tt> runs the test program after all of the LLVM passes
	have been applied to it. If its output differs from the reference output, it
	assumes the difference resulted from a failure in one of the LLVM passes, and
	enters the <a href="#miscompilationdebug">miscompilation debugger</a>.
	Otherwise, there is no problem <tt>bugpoint</tt> can debug.</p>

	</div>

	<!-- ======================================================================= -->
	<h3>
	<a name="crashdebug">Crash debugger</a>
	</h3>

	<div>

	<p>If an optimizer or code generator crashes, <tt>bugpoint</tt> will try as hard
	as it can to reduce the list of passes (for optimizer crashes) and the size of
	the test program. First, <tt>bugpoint</tt> figures out which combination of
	optimizer passes triggers the bug. This is useful when debugging a problem
	exposed by <tt>opt</tt>, for example, because it runs over 38 passes.</p>

	<p>Next, <tt>bugpoint</tt> tries removing functions from the test program, to
	reduce its size. Usually it is able to reduce a test program to a single
	function, when debugging intraprocedural optimizations. Once the number of
	functions has been reduced, it attempts to delete various edges in the control
	flow graph, to reduce the size of the function as much as possible. Finally,
	<tt>bugpoint</tt> deletes any individual LLVM instructions whose absence does
	not eliminate the failure. At the end, <tt>bugpoint</tt> should tell you what
	passes crash, give you a bitcode file, and give you instructions on how to
	reproduce the failure with <tt>opt</tt> or <tt>llc</tt>.</p>

	</div>

	<!-- ======================================================================= -->
	<h3>
	<a name="codegendebug">Code generator debugger</a>
	</h3>

	<div>

	<p>The code generator debugger attempts to narrow down the amount of code that
	is being miscompiled by the selected code generator. To do this, it takes the
	test program and partitions it into two pieces: one piece which it compiles
	with the C backend (into a shared object), and one piece which it runs with
	either the JIT or the static LLC compiler. It uses several techniques to
	reduce the amount of code pushed through the LLVM code generator, to reduce the
	potential scope of the problem. After it is finished, it emits two bitcode
	files (called "test" [to be compiled with the code generator] and "safe" [to be
	compiled with the C backend], respectively), and instructions for reproducing
	the problem. The code generator debugger assumes that the C backend produces
	good code.</p>

	</div>

	<!-- ======================================================================= -->
	<h3>
	<a name="miscompilationdebug">Miscompilation debugger</a>
	</h3>

	<div>

	<p>The miscompilation debugger works similarly to the code generator debugger.
	It works by splitting the test program into two pieces, running the
	optimizations specified on one piece, linking the two pieces back together, and
	then executing the result. It attempts to narrow down the list of passes to
	the one (or few) which are causing the miscompilation, then reduce the portion
	of the test program which is being miscompiled. The miscompilation debugger
	assumes that the selected code generator is working properly.</p>

	</div>

	</div>

	<!-- *********************************************************************** -->
	<h2>
	<a name="advice">Advice for using bugpoint</a>
	</h2>
	<!-- *********************************************************************** -->

	<div>

	<tt>bugpoint</tt> can be a remarkably useful tool, but it sometimes works in
	non-obvious ways. Here are some hints and tips:<p>

	<ol>
	<li>In the code generator and miscompilation debuggers, <tt>bugpoint</tt> only
	works with programs that have deterministic output. Thus, if the program
	outputs <tt>argv[0]</tt>, the date, time, or any other "random" data,
	<tt>bugpoint</tt> may misinterpret differences in these data, when output,
	as the result of a miscompilation. Programs should be temporarily modified
	to disable outputs that are likely to vary from run to run.

	<li>In the code generator and miscompilation debuggers, debugging will go
	faster if you manually modify the program or its inputs to reduce the
	runtime, but still exhibit the problem.

	<li><tt>bugpoint</tt> is extremely useful when working on a new optimization:
	it helps track down regressions quickly. To avoid having to relink
	<tt>bugpoint</tt> every time you change your optimization however, have
	<tt>bugpoint</tt> dynamically load your optimization with the
	<tt>-load</tt> option.

	<li><p><tt>bugpoint</tt> can generate a lot of output and run for a long period
	of time. It is often useful to capture the output of the program to file.
	For example, in the C shell, you can run:</p>

	<div class="doc_code">
	<p><tt>bugpoint ... \|& tee bugpoint.log</tt></p>
	</div>

	<p>to get a copy of <tt>bugpoint</tt>'s output in the file
	<tt>bugpoint.log</tt>, as well as on your terminal.</p>

	<li><tt>bugpoint</tt> cannot debug problems with the LLVM linker. If
	<tt>bugpoint</tt> crashes before you see its "All input ok" message,
	you might try <tt>llvm-link -v</tt> on the same set of input files. If
	that also crashes, you may be experiencing a linker bug.

	<li><tt>bugpoint</tt> is useful for proactively finding bugs in LLVM.
	Invoking <tt>bugpoint</tt> with the <tt>-find-bugs</tt> option will cause
	the list of specified optimizations to be randomized and applied to the
	program. This process will repeat until a bug is found or the user
	kills <tt>bugpoint</tt>.
	</ol>

	</div>
	<!-- *********************************************************************** -->
	<h2>
	<a name="notEnough">What to do when bugpoint isn't enough</a>
	</h2>
	<!-- *********************************************************************** -->

	<div>

	<p>Sometimes, <tt>bugpoint</tt> is not enough. In particular, InstCombine and
	TargetLowering both have visitor structured code with lots of potential
	transformations. If the process of using bugpoint has left you with
	still too much code to figure out and the problem seems
	to be in instcombine, the following steps may help. These same techniques
	are useful with TargetLowering as well.</p>

	<p>Turn on <tt>-debug-only=instcombine</tt> and see which transformations
	within instcombine are firing by selecting out lines with "<tt>IC</tt>"
	in them.</p>

	<p>At this point, you have a decision to make. Is the number
	of transformations small enough to step through them using a debugger?
	If so, then try that.</p>

	<p>If there are too many transformations, then a source modification
	approach may be helpful.
	In this approach, you can modify the source code of instcombine
	to disable just those transformations that are being performed on your
	test input and perform a binary search over the set of transformations.
	One set of places to modify are the "<tt>visit*</tt>" methods of
	<tt>InstCombiner</tt> (<I>e.g.</I> <tt>visitICmpInst</tt>) by adding a
	"<tt>return false</tt>" as the first line of the method.</p>

	<p>If that still doesn't remove enough, then change the caller of
	<tt>InstCombiner::DoOneIteration</tt>, <tt>InstCombiner::runOnFunction</tt>
	to limit the number of iterations.</p>

	<p>You may also find it useful to use "<tt>-stats</tt>" now to see what parts
	of instcombine are firing. This can guide where to put additional reporting
	code.</p>

	<p>At this point, if the amount of transformations is still too large, then
	inserting code to limit whether or not to execute the body of the code
	in the visit function can be helpful. Add a static counter which is
	incremented on every invocation of the function. Then add code which
	simply returns false on desired ranges. For example:</p>

	<div class="doc_code">
	<p><tt>static int calledCount = 0;</tt></p>
	<p><tt>calledCount++;</tt></p>
	<p><tt>DEBUG(if (calledCount < 212) return false);</tt></p>
	<p><tt>DEBUG(if (calledCount > 217) return false);</tt></p>
	<p><tt>DEBUG(if (calledCount == 213) return false);</tt></p>
	<p><tt>DEBUG(if (calledCount == 214) return false);</tt></p>
	<p><tt>DEBUG(if (calledCount == 215) return false);</tt></p>
	<p><tt>DEBUG(if (calledCount == 216) return false);</tt></p>
	<p><tt>DEBUG(dbgs() << "visitXOR calledCount: " << calledCount
	<< "\n");</tt></p>
	<p><tt>DEBUG(dbgs() << "I: "; I->dump());</tt></p>
	</div>

	<p>could be added to <tt>visitXOR</tt> to limit <tt>visitXor</tt> to being
	applied only to calls 212 and 217. This is from an actual test case and raises
	an important point---a simple binary search may not be sufficient, as
	transformations that interact may require isolating more than one call.
	In TargetLowering, use <tt>return SDNode();</tt> instead of
	<tt>return false;</tt>.</p>

	<p>Now that that the number of transformations is down to a manageable
	number, try examining the output to see if you can figure out which
	transformations are being done. If that can be figured out, then
	do the usual debugging. If which code corresponds to the transformation
	being performed isn't obvious, set a breakpoint after the call count
	based disabling and step through the code. Alternatively, you can use
	"printf" style debugging to report waypoints.</p>

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	<a href="mailto:sabre@nondot.org">Chris Lattner</a><br>
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