third_party/LLVM/docs/HowToSubmitABug.html - SwiftShader - Git at Google

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 <head>
   <title>How to submit an LLVM bug report</title>
   <link rel="stylesheet" href="llvm.css" type="text/css">
 </head>
 <body>

 <h1>
   How to submit an LLVM bug report
 </h1>

 <table class="layout" style="width: 90%" >
 <tr class="layout">
   <td class="left">
 <ol>
   <li><a href="#introduction">Introduction - Got bugs?</a></li>
   <li><a href="#crashers">Crashing Bugs</a>
     <ul>
     <li><a href="#front-end">Front-end bugs</a>
     <li><a href="#ct_optimizer">Compile-time optimization bugs</a>
     <li><a href="#ct_codegen">Code generator bugs</a>
     </ul></li>
   <li><a href="#miscompilations">Miscompilations</a></li>
   <li><a href="#codegen">Incorrect code generation (JIT and LLC)</a></li>
 </ol>
 <div class="doc_author">
   <p>Written by <a href="mailto:sabre@nondot.org">Chris Lattner</a> and
                 <a href="http://misha.brukman.net">Misha Brukman</a></p>
 </div>
 </td>
 <td class="right">
   <img src="img/Debugging.gif" alt="Debugging" width="444" height="314">
 </td>
 </tr>
 </table>

 <!-- *********************************************************************** -->
 <h2>
   <a name="introduction">Introduction - Got bugs?</a>
 </h2>
 <!-- *********************************************************************** -->

 <div>

 <p>If you're working with LLVM and run into a bug, we definitely want to know
 about it.  This document describes what you can do to increase the odds of
 getting it fixed quickly.</p>

 <p>Basically you have to do two things at a minimum.  First, decide whether the
 bug <a href="#crashers">crashes the compiler</a> (or an LLVM pass), or if the
 compiler is <a href="#miscompilations">miscompiling</a> the program (i.e., the
 compiler successfully produces an executable, but it doesn't run right).  Based
 on
 what type of bug it is, follow the instructions in the linked section to narrow
 down the bug so that the person who fixes it will be able to find the problem
 more easily.</p>

 <p>Once you have a reduced test-case, go to <a
 href="http://llvm.org/bugs/enter_bug.cgi">the LLVM Bug Tracking
 System</a> and fill out the form with the necessary details (note that you don't
 need to pick a category, just use the "new-bugs" category if you're not sure).
 The bug description should contain the following
 information:</p>

 <ul>
   <li>All information necessary to reproduce the problem.</li>
   <li>The reduced test-case that triggers the bug.</li>
   <li>The location where you obtained LLVM (if not from our Subversion
   repository).</li>
 </ul>

 <p>Thanks for helping us make LLVM better!</p>

 </div>

 <!-- *********************************************************************** -->
 <h2>
   <a name="crashers">Crashing Bugs</a>
 </h2>
 <!-- *********************************************************************** -->

 <div>

 <p>More often than not, bugs in the compiler cause it to crash&mdash;often due
 to an assertion failure of some sort. The most important
 piece of the puzzle is to figure out if it is crashing in the GCC front-end
 or if it is one of the LLVM libraries (e.g. the optimizer or code generator)
 that has problems.</p>

 <p>To figure out which component is crashing (the front-end,
 optimizer or code generator), run the
 <tt><b>llvm-gcc</b></tt> command line as you were when the crash occurred, but
 with the following extra command line options:</p>

 <ul>
   <li><tt><b>-O0 -emit-llvm</b></tt>: If <tt>llvm-gcc</tt> still crashes when
   passed these options (which disable the optimizer and code generator), then
   the crash is in the front-end.  Jump ahead to the section on <a
   href="#front-end">front-end bugs</a>.</li>

   <li><tt><b>-emit-llvm</b></tt>: If <tt>llvm-gcc</tt> crashes with this option
   (which disables the code generator), you found an optimizer bug.  Jump ahead
   to <a href="#ct_optimizer"> compile-time optimization bugs</a>.</li>

   <li>Otherwise, you have a code generator crash.  Jump ahead to <a
   href="#ct_codegen">code generator bugs</a>.</li>

 </ul>

 <!-- ======================================================================= -->
 <h3>
   <a name="front-end">Front-end bugs</a>
 </h3>

 <div>

 <p>If the problem is in the front-end, you should re-run the same
 <tt>llvm-gcc</tt> command that resulted in the crash, but add the
 <tt>-save-temps</tt> option.  The compiler will crash again, but it will leave
 behind a <tt><i>foo</i>.i</tt> file (containing preprocessed C source code) and
 possibly <tt><i>foo</i>.s</tt> for each
 compiled <tt><i>foo</i>.c</tt> file. Send us the <tt><i>foo</i>.i</tt> file,
 along with the options you passed to llvm-gcc, and a brief description of the
 error it caused.</p>

 <p>The <a href="http://delta.tigris.org/">delta</a> tool helps to reduce the
 preprocessed file down to the smallest amount of code that still replicates the
 problem. You're encouraged to use delta to reduce the code to make the
 developers' lives easier. <a
 href="http://gcc.gnu.org/wiki/A_guide_to_testcase_reduction">This website</a>
 has instructions on the best way to use delta.</p>

 </div>

 <!-- ======================================================================= -->
 <h3>
   <a name="ct_optimizer">Compile-time optimization bugs</a>
 </h3>

 <div>

 <p>If you find that a bug crashes in the optimizer, compile your test-case to a
 <tt>.bc</tt> file by passing "<tt><b>-emit-llvm -O0 -c -o foo.bc</b></tt>".
 Then run:</p>

 <div class="doc_code">
 <p><tt><b>opt</b> -std-compile-opts -debug-pass=Arguments foo.bc
     -disable-output</tt></p>
 </div>

 <p>This command should do two things: it should print out a list of passes, and
 then it should crash in the same way as llvm-gcc.  If it doesn't crash, please
 follow the instructions for a <a href="#front-end">front-end bug</a>.</p>

 <p>If this does crash, then you should be able to debug this with the following
 bugpoint command:</p>

 <div class="doc_code">
 <p><tt><b>bugpoint</b> foo.bc &lt;list of passes printed by
 <b>opt</b>&gt;</tt></p>
 </div>

 <p>Please run this, then file a bug with the instructions and reduced .bc files
 that bugpoint emits.  If something goes wrong with bugpoint, please submit the
 "foo.bc" file and the list of passes printed by <b>opt</b>.</p>

 </div>

 <!-- ======================================================================= -->
 <h3>
   <a name="ct_codegen">Code generator bugs</a>
 </h3>

 <div>

 <p>If you find a bug that crashes llvm-gcc in the code generator, compile your
 source file to a .bc file by passing "<tt><b>-emit-llvm -c -o foo.bc</b></tt>"
 to llvm-gcc (in addition to the options you already pass).  Once your have
 foo.bc, one of the following commands should fail:</p>

 <ol>
 <li><tt><b>llc</b> foo.bc</tt></li>
 <li><tt><b>llc</b> foo.bc -relocation-model=pic</tt></li>
 <li><tt><b>llc</b> foo.bc -relocation-model=static</tt></li>
 </ol>

 <p>If none of these crash, please follow the instructions for a
 <a href="#front-end">front-end bug</a>.  If one of these do crash, you should
 be able to reduce this with one of the following bugpoint command lines (use
 the one corresponding to the command above that failed):</p>

 <ol>
 <li><tt><b>bugpoint</b> -run-llc foo.bc</tt></li>
 <li><tt><b>bugpoint</b> -run-llc foo.bc --tool-args
            -relocation-model=pic</tt></li>
 <li><tt><b>bugpoint</b> -run-llc foo.bc --tool-args
            -relocation-model=static</tt></li>
 </ol>

 <p>Please run this, then file a bug with the instructions and reduced .bc file
 that bugpoint emits.  If something goes wrong with bugpoint, please submit the
 "foo.bc" file and the option that llc crashes with.</p>

 </div>

 </div>

 <!-- *********************************************************************** -->
 <h2>
   <a name="miscompilations">Miscompilations</a>
 </h2>
 <!-- *********************************************************************** -->

 <div>

 <p>If llvm-gcc successfully produces an executable, but that executable doesn't
 run right, this is either a bug in the code or a bug in the
 compiler.  The first thing to check is to make sure it is not using undefined
 behavior (e.g. reading a variable before it is defined).  In particular, check
 to see if the program <a href="http://valgrind.org/">valgrind</a>s clean,
 passes purify, or some other memory checker tool.  Many of the "LLVM bugs" that
 we have chased down ended up being bugs in the program being compiled, not
  LLVM.</p>

 <p>Once you determine that the program itself is not buggy, you should choose
 which code generator you wish to compile the program with (e.g. C backend, the
 JIT, or LLC) and optionally a series of LLVM passes to run.  For example:</p>

 <div class="doc_code">
 <p><tt>
 <b>bugpoint</b> -run-cbe [... optzn passes ...] file-to-test.bc --args -- [program arguments]</tt></p>
 </div>

 <p><tt>bugpoint</tt> will try to narrow down your list of passes to the one pass
 that causes an error, and simplify the bitcode file as much as it can to assist
 you. It will print a message letting you know how to reproduce the resulting
 error.</p>

 </div>

 <!-- *********************************************************************** -->
 <h2>
   <a name="codegen">Incorrect code generation</a>
 </h2>
 <!-- *********************************************************************** -->

 <div>

 <p>Similarly to debugging incorrect compilation by mis-behaving passes, you can
 debug incorrect code generation by either LLC or the JIT, using
 <tt>bugpoint</tt>. The process <tt>bugpoint</tt> follows in this case is to try
 to narrow the code down to a function that is miscompiled by one or the other
 method, but since for correctness, the entire program must be run,
 <tt>bugpoint</tt> will compile the code it deems to not be affected with the C
 Backend, and then link in the shared object it generates.</p>

 <p>To debug the JIT:</p>

 <div class="doc_code">
 <pre>
 bugpoint -run-jit -output=[correct output file] [bitcode file]  \
          --tool-args -- [arguments to pass to lli]              \
          --args -- [program arguments]
 </pre>
 </div>

 <p>Similarly, to debug the LLC, one would run:</p>

 <div class="doc_code">
 <pre>
 bugpoint -run-llc -output=[correct output file] [bitcode file]  \
          --tool-args -- [arguments to pass to llc]              \
          --args -- [program arguments]
 </pre>
 </div>

 <p><b>Special note:</b> if you are debugging MultiSource or SPEC tests that
 already exist in the <tt>llvm/test</tt> hierarchy, there is an easier way to
 debug the JIT, LLC, and CBE, using the pre-written Makefile targets, which
 will pass the program options specified in the Makefiles:</p>

 <div class="doc_code">
 <p><tt>
 cd llvm/test/../../program<br>
 make bugpoint-jit
 </tt></p>
 </div>

 <p>At the end of a successful <tt>bugpoint</tt> run, you will be presented
 with two bitcode files: a <em>safe</em> file which can be compiled with the C
 backend and the <em>test</em> file which either LLC or the JIT
 mis-codegenerates, and thus causes the error.</p>

 <p>To reproduce the error that <tt>bugpoint</tt> found, it is sufficient to do
 the following:</p>

 <ol>

 <li><p>Regenerate the shared object from the safe bitcode file:</p>

 <div class="doc_code">
 <p><tt>
 <b>llc</b> -march=c safe.bc -o safe.c<br>
 <b>gcc</b> -shared safe.c -o safe.so
 </tt></p>
 </div></li>

 <li><p>If debugging LLC, compile test bitcode native and link with the shared
     object:</p>

 <div class="doc_code">
 <p><tt>
 <b>llc</b> test.bc -o test.s<br>
 <b>gcc</b> test.s safe.so -o test.llc<br>
 ./test.llc [program options]
 </tt></p>
 </div></li>

 <li><p>If debugging the JIT, load the shared object and supply the test
     bitcode:</p>

 <div class="doc_code">
 <p><tt><b>lli</b> -load=safe.so test.bc [program options]</tt></p>
 </div></li>

 </ol>

 </div>

 <!-- *********************************************************************** -->
 <hr>
 <address>
   <a href="http://jigsaw.w3.org/css-validator/check/referer"><img
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   src="http://www.w3.org/Icons/valid-html401-blue" alt="Valid HTML 4.01"></a>

   <a href="mailto:sabre@nondot.org">Chris Lattner</a><br>
   <a href="http://llvm.org/">The LLVM Compiler Infrastructure</a>
   <br>
   Last modified: $Date: 2011-06-07 16:03:13 -0400 (Tue, 07 Jun 2011) $
 </address>

 </body>
 </html>
	<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"
	"http://www.w3.org/TR/html4/strict.dtd">
	<html>
	<head>
	<title>How to submit an LLVM bug report</title>
	<link rel="stylesheet" href="llvm.css" type="text/css">
	</head>
	<body>

	<h1>
	How to submit an LLVM bug report
	</h1>

	<table class="layout" style="width: 90%" >
	<tr class="layout">
	<td class="left">
	<ol>
	<li><a href="#introduction">Introduction - Got bugs?</a></li>
	<li><a href="#crashers">Crashing Bugs</a>
	<ul>
	<li><a href="#front-end">Front-end bugs</a>
	<li><a href="#ct_optimizer">Compile-time optimization bugs</a>
	<li><a href="#ct_codegen">Code generator bugs</a>
	</ul></li>
	<li><a href="#miscompilations">Miscompilations</a></li>
	<li><a href="#codegen">Incorrect code generation (JIT and LLC)</a></li>
	</ol>
	<div class="doc_author">
	<p>Written by <a href="mailto:sabre@nondot.org">Chris Lattner</a> and
	<a href="http://misha.brukman.net">Misha Brukman</a></p>
	</div>
	</td>
	<td class="right">
	<img src="img/Debugging.gif" alt="Debugging" width="444" height="314">
	</td>
	</tr>
	</table>

	<!-- *********************************************************************** -->
	<h2>
	<a name="introduction">Introduction - Got bugs?</a>
	</h2>
	<!-- *********************************************************************** -->

	<div>

	<p>If you're working with LLVM and run into a bug, we definitely want to know
	about it. This document describes what you can do to increase the odds of
	getting it fixed quickly.</p>

	<p>Basically you have to do two things at a minimum. First, decide whether the
	bug <a href="#crashers">crashes the compiler</a> (or an LLVM pass), or if the
	compiler is <a href="#miscompilations">miscompiling</a> the program (i.e., the
	compiler successfully produces an executable, but it doesn't run right). Based
	on
	what type of bug it is, follow the instructions in the linked section to narrow
	down the bug so that the person who fixes it will be able to find the problem
	more easily.</p>

	<p>Once you have a reduced test-case, go to <a
	href="http://llvm.org/bugs/enter_bug.cgi">the LLVM Bug Tracking
	System</a> and fill out the form with the necessary details (note that you don't
	need to pick a category, just use the "new-bugs" category if you're not sure).
	The bug description should contain the following
	information:</p>

	<ul>
	<li>All information necessary to reproduce the problem.</li>
	<li>The reduced test-case that triggers the bug.</li>
	<li>The location where you obtained LLVM (if not from our Subversion
	repository).</li>
	</ul>

	<p>Thanks for helping us make LLVM better!</p>

	</div>

	<!-- *********************************************************************** -->
	<h2>
	<a name="crashers">Crashing Bugs</a>
	</h2>
	<!-- *********************************************************************** -->

	<div>

	<p>More often than not, bugs in the compiler cause it to crash—often due
	to an assertion failure of some sort. The most important
	piece of the puzzle is to figure out if it is crashing in the GCC front-end
	or if it is one of the LLVM libraries (e.g. the optimizer or code generator)
	that has problems.</p>

	<p>To figure out which component is crashing (the front-end,
	optimizer or code generator), run the
	<tt><b>llvm-gcc</b></tt> command line as you were when the crash occurred, but
	with the following extra command line options:</p>

	<ul>
	<li><tt><b>-O0 -emit-llvm</b></tt>: If <tt>llvm-gcc</tt> still crashes when
	passed these options (which disable the optimizer and code generator), then
	the crash is in the front-end. Jump ahead to the section on <a
	href="#front-end">front-end bugs</a>.</li>

	<li><tt><b>-emit-llvm</b></tt>: If <tt>llvm-gcc</tt> crashes with this option
	(which disables the code generator), you found an optimizer bug. Jump ahead
	to <a href="#ct_optimizer"> compile-time optimization bugs</a>.</li>

	<li>Otherwise, you have a code generator crash. Jump ahead to <a
	href="#ct_codegen">code generator bugs</a>.</li>

	</ul>

	<!-- ======================================================================= -->
	<h3>
	<a name="front-end">Front-end bugs</a>
	</h3>

	<div>

	<p>If the problem is in the front-end, you should re-run the same
	<tt>llvm-gcc</tt> command that resulted in the crash, but add the
	<tt>-save-temps</tt> option. The compiler will crash again, but it will leave
	behind a <tt><i>foo</i>.i</tt> file (containing preprocessed C source code) and
	possibly <tt><i>foo</i>.s</tt> for each
	compiled <tt><i>foo</i>.c</tt> file. Send us the <tt><i>foo</i>.i</tt> file,
	along with the options you passed to llvm-gcc, and a brief description of the
	error it caused.</p>

	<p>The <a href="http://delta.tigris.org/">delta</a> tool helps to reduce the
	preprocessed file down to the smallest amount of code that still replicates the
	problem. You're encouraged to use delta to reduce the code to make the
	developers' lives easier. <a
	href="http://gcc.gnu.org/wiki/A_guide_to_testcase_reduction">This website</a>
	has instructions on the best way to use delta.</p>

	</div>

	<!-- ======================================================================= -->
	<h3>
	<a name="ct_optimizer">Compile-time optimization bugs</a>
	</h3>

	<div>

	<p>If you find that a bug crashes in the optimizer, compile your test-case to a
	<tt>.bc</tt> file by passing "<tt><b>-emit-llvm -O0 -c -o foo.bc</b></tt>".
	Then run:</p>

	<div class="doc_code">
	<p><tt><b>opt</b> -std-compile-opts -debug-pass=Arguments foo.bc
	-disable-output</tt></p>
	</div>

	<p>This command should do two things: it should print out a list of passes, and
	then it should crash in the same way as llvm-gcc. If it doesn't crash, please
	follow the instructions for a <a href="#front-end">front-end bug</a>.</p>

	<p>If this does crash, then you should be able to debug this with the following
	bugpoint command:</p>

	<div class="doc_code">
	<p><tt><b>bugpoint</b> foo.bc <list of passes printed by
	<b>opt</b>></tt></p>
	</div>

	<p>Please run this, then file a bug with the instructions and reduced .bc files
	that bugpoint emits. If something goes wrong with bugpoint, please submit the
	"foo.bc" file and the list of passes printed by <b>opt</b>.</p>

	</div>

	<!-- ======================================================================= -->
	<h3>
	<a name="ct_codegen">Code generator bugs</a>
	</h3>

	<div>

	<p>If you find a bug that crashes llvm-gcc in the code generator, compile your
	source file to a .bc file by passing "<tt><b>-emit-llvm -c -o foo.bc</b></tt>"
	to llvm-gcc (in addition to the options you already pass). Once your have
	foo.bc, one of the following commands should fail:</p>

	<ol>
	<li><tt><b>llc</b> foo.bc</tt></li>
	<li><tt><b>llc</b> foo.bc -relocation-model=pic</tt></li>
	<li><tt><b>llc</b> foo.bc -relocation-model=static</tt></li>
	</ol>

	<p>If none of these crash, please follow the instructions for a
	<a href="#front-end">front-end bug</a>. If one of these do crash, you should
	be able to reduce this with one of the following bugpoint command lines (use
	the one corresponding to the command above that failed):</p>

	<ol>
	<li><tt><b>bugpoint</b> -run-llc foo.bc</tt></li>
	<li><tt><b>bugpoint</b> -run-llc foo.bc --tool-args
	-relocation-model=pic</tt></li>
	<li><tt><b>bugpoint</b> -run-llc foo.bc --tool-args
	-relocation-model=static</tt></li>
	</ol>

	<p>Please run this, then file a bug with the instructions and reduced .bc file
	that bugpoint emits. If something goes wrong with bugpoint, please submit the
	"foo.bc" file and the option that llc crashes with.</p>

	</div>

	</div>

	<!-- *********************************************************************** -->
	<h2>
	<a name="miscompilations">Miscompilations</a>
	</h2>
	<!-- *********************************************************************** -->

	<div>

	<p>If llvm-gcc successfully produces an executable, but that executable doesn't
	run right, this is either a bug in the code or a bug in the
	compiler. The first thing to check is to make sure it is not using undefined
	behavior (e.g. reading a variable before it is defined). In particular, check
	to see if the program <a href="http://valgrind.org/">valgrind</a>s clean,
	passes purify, or some other memory checker tool. Many of the "LLVM bugs" that
	we have chased down ended up being bugs in the program being compiled, not
	LLVM.</p>

	<p>Once you determine that the program itself is not buggy, you should choose
	which code generator you wish to compile the program with (e.g. C backend, the
	JIT, or LLC) and optionally a series of LLVM passes to run. For example:</p>

	<div class="doc_code">
	<p><tt>
	<b>bugpoint</b> -run-cbe [... optzn passes ...] file-to-test.bc --args -- [program arguments]</tt></p>
	</div>

	<p><tt>bugpoint</tt> will try to narrow down your list of passes to the one pass
	that causes an error, and simplify the bitcode file as much as it can to assist
	you. It will print a message letting you know how to reproduce the resulting
	error.</p>

	</div>

	<!-- *********************************************************************** -->
	<h2>
	<a name="codegen">Incorrect code generation</a>
	</h2>
	<!-- *********************************************************************** -->

	<div>

	<p>Similarly to debugging incorrect compilation by mis-behaving passes, you can
	debug incorrect code generation by either LLC or the JIT, using
	<tt>bugpoint</tt>. The process <tt>bugpoint</tt> follows in this case is to try
	to narrow the code down to a function that is miscompiled by one or the other
	method, but since for correctness, the entire program must be run,
	<tt>bugpoint</tt> will compile the code it deems to not be affected with the C
	Backend, and then link in the shared object it generates.</p>

	<p>To debug the JIT:</p>

	<div class="doc_code">
	<pre>
	bugpoint -run-jit -output=[correct output file] [bitcode file] \
	--tool-args -- [arguments to pass to lli] \
	--args -- [program arguments]
	</pre>
	</div>

	<p>Similarly, to debug the LLC, one would run:</p>

	<div class="doc_code">
	<pre>
	bugpoint -run-llc -output=[correct output file] [bitcode file] \
	--tool-args -- [arguments to pass to llc] \
	--args -- [program arguments]
	</pre>
	</div>

	<p><b>Special note:</b> if you are debugging MultiSource or SPEC tests that
	already exist in the <tt>llvm/test</tt> hierarchy, there is an easier way to
	debug the JIT, LLC, and CBE, using the pre-written Makefile targets, which
	will pass the program options specified in the Makefiles:</p>

	<div class="doc_code">
	<p><tt>
	cd llvm/test/../../program<br>
	make bugpoint-jit
	</tt></p>
	</div>

	<p>At the end of a successful <tt>bugpoint</tt> run, you will be presented
	with two bitcode files: a <em>safe</em> file which can be compiled with the C
	backend and the <em>test</em> file which either LLC or the JIT
	mis-codegenerates, and thus causes the error.</p>

	<p>To reproduce the error that <tt>bugpoint</tt> found, it is sufficient to do
	the following:</p>

	<ol>

	<li><p>Regenerate the shared object from the safe bitcode file:</p>

	<div class="doc_code">
	<p><tt>
	<b>llc</b> -march=c safe.bc -o safe.c<br>
	<b>gcc</b> -shared safe.c -o safe.so
	</tt></p>
	</div></li>

	<li><p>If debugging LLC, compile test bitcode native and link with the shared
	object:</p>

	<div class="doc_code">
	<p><tt>
	<b>llc</b> test.bc -o test.s<br>
	<b>gcc</b> test.s safe.so -o test.llc<br>
	./test.llc [program options]
	</tt></p>
	</div></li>

	<li><p>If debugging the JIT, load the shared object and supply the test
	bitcode:</p>

	<div class="doc_code">
	<p><tt><b>lli</b> -load=safe.so test.bc [program options]</tt></p>
	</div></li>

	</ol>

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