llvm/docs/Bugpoint.html - toolchain/llvm-project - Gitiles

 <html>
 <title>LLVM: bugpoint tool</title>

 <body bgcolor=white>

 <center><h1>LLVM: <tt>bugpoint</tt> tool</h1></center>
 <HR>

 <h3>NAME</h3>
 <tt>bugpoint</tt>

 <h3>SYNOPSIS</h3>
 <tt>bugpoint [options] [input LLVM ll/bc files] [LLVM passes] --args &lt;program arguments&gt;...</tt>

 <img src="../img/Debugging.gif" width=444 height=314 align=right>
 <h3>DESCRIPTION</h3>

 The <tt>bugpoint</tt> tool 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><a href="gccas.html">gccas</a></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>

 <a name="designphilosophy">
 <h4>Design Philosophy</h4>

 <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>

 <a name="automaticdebuggerselection">
 <h4>Automatic Debugger Selection</h4>

 <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>

 Otherwise, if the <a href="#opt_output"><tt>-output</tt></a> 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 <a href="#opt_run-">selected</a> 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>

 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>

 <a name="crashdebug">
 <h4>Crash debugger</h4>

 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>gccas</tt>, for example, because it runs over 38 passes.<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 bytecode file, and give you instructions on how to
 reproduce the failure with <tt><a href="opt.html">opt</a></tt>, <tt><a
 href="analyze.html">analyze</a></tt>, or <tt><a href="llc.html">llc</a></tt>.<p>

 <a name="codegendebug">
 <h4>Code generator debugger</h4>

 <p>The code generator debugger attempts to narrow down the amount of code that
 is being miscompiled by the <a href="#opt_run-">selected</a> 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 bytecode 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>

 <a name="miscompilationdebug">
 <h4>Miscompilation debugger</h4>

 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>

 <a name="bugpoint notes">
 <h4>Advice for using <tt>bugpoint</tt></h4>

 <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 <a
     href="#opt_load"><tt>-load</tt></a> option.

 <li><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 type:<br>
     <tt>bugpoint  ..... |&amp; tee bugpoint.log</tt>
     <br>to get a copy of <tt>bugpoint</tt>'s output in the file
     <tt>bugpoint.log</tt>, as well as on your terminal.

 <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>If your program is <b>supposed</b> to crash, <tt>bugpoint</tt> will be
     confused. One way to deal with this is to cause bugpoint to ignore the exit
     code from your program, by giving it the <tt>-check-exit-code=false</tt>
     option.

 </ol>

 <h3>OPTIONS</h3>

 <ul>
 	<li><tt>-additional-so &lt;library&gt;</tt><br>
     Load <tt>&lt;library&gt;</tt> into the test program whenever it is run.
     This is useful if you are debugging programs which depend on non-LLVM
     libraries (such as the X or curses libraries) to run.<p>

 	<li><tt>-args &lt;program args&gt;</tt><br>
 	Pass all arguments specified after <tt>-args</tt> to the
 	test program whenever it runs.  Note that if any of
 	the <tt>&lt;program args&gt;</tt> start with a '-', you should use:
         <p>
         <tt>bugpoint &lt;bugpoint args&gt; -args -- &lt;program args&gt;</tt>
         <p>
         The "<tt>--</tt>" right after the <tt>-args</tt> option tells
         <tt>bugpoint</tt> to consider any options starting with <tt>-</tt> to be
         part of the <tt>-args</tt> option, not as options to <tt>bugpoint</tt>
         itself.<p>

 	<li><tt>-tool-args &lt;tool args&gt;</tt><br>
 	Pass all arguments specified after <tt>-tool-args</tt> to the
 	LLVM tool under test (llc, lli, etc.) whenever it runs.
 	You should use this option in the following way:
         <p>
         <tt>bugpoint &lt;bugpoint args&gt; -tool-args -- &lt;tool args&gt;</tt>
         <p>
         The "<tt>--</tt>" right after the <tt>-tool-args</tt> option tells
         <tt>bugpoint</tt> to consider any options starting with <tt>-</tt> to be
         part of the <tt>-tool-args</tt> option, not as options to
         <tt>bugpoint</tt> itself. (See <tt>-args</tt>, above.)<p>

 	<li><tt>-check-exit-code={true,false}</tt><br>
     Assume a non-zero exit code or core dump from the test program is
     a failure. Defaults to true.<p>

 	<li><tt>-disable-{dce,simplifycfg}</tt><br>
     Do not run the specified passes to clean up and reduce the size of the
     test program. By default, <tt>bugpoint</tt> uses these passes internally
     when attempting to reduce test programs.  If you're trying to find
     a bug in one of these passes, <tt>bugpoint</tt> may crash.<p>

 	<li> <tt>-help</tt><br>
 	Print a summary of command line options.<p>

 	<a name="opt_input"><li><tt>-input &lt;filename&gt;</tt><br>
 	Open <tt>&lt;filename&gt;</tt> and redirect the standard input of the
     test program, whenever it runs, to come from that file.
 	<p>

 	<a name="opt_load"><li> <tt>-load &lt;plugin&gt;</tt><br>
 	Load the dynamic object <tt>&lt;plugin&gt;</tt> into <tt>bugpoint</tt>
     itself.  This object should register new
 	optimization passes.  Once loaded, the object will add new command line
 	options to enable various optimizations.  To see the new complete list
 	of optimizations, use the -help and -load options together:
 	<p>
 	<tt>bugpoint -load &lt;plugin&gt; -help</tt>
 	<p>

 	<a name="opt_output"><li><tt>-output &lt;filename&gt;</tt><br>
     Whenever the test program produces output on its standard output
     stream, it should match the contents of <tt>&lt;filename&gt;</tt>
     (the "reference output"). If you do not use this option,
     <tt>bugpoint</tt> will attempt to generate a reference output by
     compiling the program with the C backend and running it.<p>

 	<li><tt>-profile-info-file &lt;filename&gt;</tt><br>
     Profile file loaded by -profile-loader.<p>

 	<a name="opt_run-"><li><tt>-run-{int,jit,llc,cbe}</tt><br>
     Whenever the test program is compiled, <tt>bugpoint</tt> should generate
     code for it using the specified code generator.  These options allow
     you to choose the interpreter, the JIT compiler, the static native
     code compiler, or the C backend, respectively.<p>
 </ul>

 <h3>EXIT STATUS</h3>

 If <tt>bugpoint</tt> succeeds in finding a problem, it will exit with 0.
 Otherwise, if an error occurs, it will exit with a non-zero value.

 <h3>SEE ALSO</h3>
 <a href="opt.html"><tt>opt</tt></a>,
 <a href="analyze.html"><tt>analyze</tt></a>

 <HR>
 Maintained by the <a href="http://llvm.cs.uiuc.edu">LLVM Team</a>.
 </body>
 </html>
	<html>
	<title>LLVM: bugpoint tool</title>

	<body bgcolor=white>

	<center><h1>LLVM: <tt>bugpoint</tt> tool</h1></center>
	<HR>

	<h3>NAME</h3>
	<tt>bugpoint</tt>

	<h3>SYNOPSIS</h3>
	<tt>bugpoint [options] [input LLVM ll/bc files] [LLVM passes] --args <program arguments>...</tt>

	<img src="../img/Debugging.gif" width=444 height=314 align=right>
	<h3>DESCRIPTION</h3>

	The <tt>bugpoint</tt> tool 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><a href="gccas.html">gccas</a></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>

	<a name="designphilosophy">
	<h4>Design Philosophy</h4>

	<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>

	<a name="automaticdebuggerselection">
	<h4>Automatic Debugger Selection</h4>

	<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>

	Otherwise, if the <a href="#opt_output"><tt>-output</tt></a> 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 <a href="#opt_run-">selected</a> 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>

	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>

	<a name="crashdebug">
	<h4>Crash debugger</h4>

	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>gccas</tt>, for example, because it runs over 38 passes.<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 bytecode file, and give you instructions on how to
	reproduce the failure with <tt><a href="opt.html">opt</a></tt>, <tt><a
	href="analyze.html">analyze</a></tt>, or <tt><a href="llc.html">llc</a></tt>.<p>

	<a name="codegendebug">
	<h4>Code generator debugger</h4>

	<p>The code generator debugger attempts to narrow down the amount of code that
	is being miscompiled by the <a href="#opt_run-">selected</a> 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 bytecode 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>

	<a name="miscompilationdebug">
	<h4>Miscompilation debugger</h4>

	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>

	<a name="bugpoint notes">
	<h4>Advice for using <tt>bugpoint</tt></h4>

	<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 <a
	href="#opt_load"><tt>-load</tt></a> option.

	<li><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 type:<br>
	<tt>bugpoint ..... \|& tee bugpoint.log</tt>
	<br>to get a copy of <tt>bugpoint</tt>'s output in the file
	<tt>bugpoint.log</tt>, as well as on your terminal.

	<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>If your program is <b>supposed</b> to crash, <tt>bugpoint</tt> will be
	confused. One way to deal with this is to cause bugpoint to ignore the exit
	code from your program, by giving it the <tt>-check-exit-code=false</tt>
	option.

	</ol>

	<h3>OPTIONS</h3>

	<ul>
	<li><tt>-additional-so <library></tt><br>
	Load <tt><library></tt> into the test program whenever it is run.
	This is useful if you are debugging programs which depend on non-LLVM
	libraries (such as the X or curses libraries) to run.<p>

	<li><tt>-args <program args></tt><br>
	Pass all arguments specified after <tt>-args</tt> to the
	test program whenever it runs. Note that if any of
	the <tt><program args></tt> start with a '-', you should use:
	<p>
	<tt>bugpoint <bugpoint args> -args -- <program args></tt>
	<p>
	The "<tt>--</tt>" right after the <tt>-args</tt> option tells
	<tt>bugpoint</tt> to consider any options starting with <tt>-</tt> to be
	part of the <tt>-args</tt> option, not as options to <tt>bugpoint</tt>
	itself.<p>

	<li><tt>-tool-args <tool args></tt><br>
	Pass all arguments specified after <tt>-tool-args</tt> to the
	LLVM tool under test (llc, lli, etc.) whenever it runs.
	You should use this option in the following way:
	<p>
	<tt>bugpoint <bugpoint args> -tool-args -- <tool args></tt>
	<p>
	The "<tt>--</tt>" right after the <tt>-tool-args</tt> option tells
	<tt>bugpoint</tt> to consider any options starting with <tt>-</tt> to be
	part of the <tt>-tool-args</tt> option, not as options to
	<tt>bugpoint</tt> itself. (See <tt>-args</tt>, above.)<p>

	<li><tt>-check-exit-code={true,false}</tt><br>
	Assume a non-zero exit code or core dump from the test program is
	a failure. Defaults to true.<p>

	<li><tt>-disable-{dce,simplifycfg}</tt><br>
	Do not run the specified passes to clean up and reduce the size of the
	test program. By default, <tt>bugpoint</tt> uses these passes internally
	when attempting to reduce test programs. If you're trying to find
	a bug in one of these passes, <tt>bugpoint</tt> may crash.<p>

	<li> <tt>-help</tt><br>
	Print a summary of command line options.<p>

	<a name="opt_input"><li><tt>-input <filename></tt><br>
	Open <tt><filename></tt> and redirect the standard input of the
	test program, whenever it runs, to come from that file.
	<p>

	<a name="opt_load"><li> <tt>-load <plugin></tt><br>
	Load the dynamic object <tt><plugin></tt> into <tt>bugpoint</tt>
	itself. This object should register new
	optimization passes. Once loaded, the object will add new command line
	options to enable various optimizations. To see the new complete list
	of optimizations, use the -help and -load options together:
	<p>
	<tt>bugpoint -load <plugin> -help</tt>
	<p>

	<a name="opt_output"><li><tt>-output <filename></tt><br>
	Whenever the test program produces output on its standard output
	stream, it should match the contents of <tt><filename></tt>
	(the "reference output"). If you do not use this option,
	<tt>bugpoint</tt> will attempt to generate a reference output by
	compiling the program with the C backend and running it.<p>

	<li><tt>-profile-info-file <filename></tt><br>
	Profile file loaded by -profile-loader.<p>

	<a name="opt_run-"><li><tt>-run-{int,jit,llc,cbe}</tt><br>
	Whenever the test program is compiled, <tt>bugpoint</tt> should generate
	code for it using the specified code generator. These options allow
	you to choose the interpreter, the JIT compiler, the static native
	code compiler, or the C backend, respectively.<p>
	</ul>

	<h3>EXIT STATUS</h3>

	If <tt>bugpoint</tt> succeeds in finding a problem, it will exit with 0.
	Otherwise, if an error occurs, it will exit with a non-zero value.

	<h3>SEE ALSO</h3>
	<a href="opt.html"><tt>opt</tt></a>,
	<a href="analyze.html"><tt>analyze</tt></a>

	<HR>
	Maintained by the <a href="http://llvm.cs.uiuc.edu">LLVM Team</a>.
	</body>
	</html>