How to submit an LLVM bug report
</div>
-<div>
-
-<table border="0" width="100%">
-<tr>
-<td valign="top">
-
+<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="#gccas">GCCAS bugs</a>
- <li><a href="#gccld">GCCLD bugs</a>
- <li><a href="#passes">Bugs in LLVM passes</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>
-
-
<p><b>Written by <a href="mailto:sabre@nondot.org">Chris Lattner</a> and
- <a href="http://misha.brukman.net">Misha Brukman</a></b></p>
-
+<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 align="right">
- <img src="Debugging.gif" width="444" height="314">
+<td class="right">
+ <img src="img/Debugging.gif" alt="Debugging" width="444" height="314">
</td>
</tr>
</table>
<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. Based on
+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.cs.uiuc.edu/bugs/enter_bug.cgi">the LLVM Bug Tracking
-System</a>, select the category in which the bug falls, and fill out the form
-with the necessary details. The bug description should contain the following
+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 catagory, just use the "new-bugs" catagory 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 CVS
+ <li>The location where you obtained LLVM (if not from our Subversion
repository).</li>
</ul>
<div class="doc_text">
-<p>More often than not, bugs in the compiler cause it to crash - often due to an
-assertion failure of some sort. If you are running <tt><b>opt</b></tt> or
-<tt><b>analyze</b></tt> directly, and something crashes, jump to the section on
-<a href="#passes">bugs in LLVM passes</a>. Otherwise, the most important
-piece of the puzzle is to figure out if it is the GCC-based front-end that is
-buggy or if it's one of the LLVM tools that has problems.</p>
+<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 program is crashing (the front-end,
-<tt><b>gccas</b></tt>, or <tt><b>gccld</b></tt>), run the
+<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
-add a <tt>-v</tt> option to the command line. The compiler will print out a
-bunch of stuff, and should end with telling you that one of <tt><b>cc1</b></tt>,
-<tt><b>gccas</b></tt>, or <tt><b>gccld</b></tt> crashed.</p>
+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>If <tt><b>cc1</b></tt> crashed, you found a problem with 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>If <tt><b>gccas</b></tt> crashed, you found a bug in <a href="#gccas">one
- of the passes in <tt><b>gccas</b></tt></a>.</li>
-
- <li>If <tt><b>gccld</b></tt> crashed, you found a bug in <a href="#gccld">one
- of the passes in <tt><b>gccld</b></tt></a>.</li>
-
- <li>Otherwise, something really weird happened. Email the list with what you
- have at this point.</li>
+ <li>Otherwise, you have a code generator crash. Jump ahead to <a
+ href="#ct_codegen">code generator bugs</a>.</li>
</ul>
<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> (containing LLVM assembly code), for each
+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 a brief description of the error it caused.</p>
+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>
<!-- ======================================================================= -->
<div class="doc_subsection">
- <a name="gccas">GCCAS bugs</a>
+ <a name="ct_optimizer">Compile-time optimization bugs</a>
</div>
<div class="doc_text">
-<p>If you find that a bug crashes in the <tt><b>gccas</b></tt> stage of
-compilation, compile your test-case to a <tt>.s</tt> file with the
-<tt>-save-temps</tt> option to <tt><b>llvm-gcc</b></tt>. Then run:</p>
-
-<pre>
- <b>gccas</b> -debug-pass=Arguments < /dev/null -o - > /dev/null
-</pre>
-
-<p>... which will print a list of arguments, indicating the list of passes that
-<tt><b>gccas</b></tt> runs. Once you have the input file and the list of
-passes, go to the section on <a href="#passes">debugging bugs in LLVM
-passes</a>.</p>
-
-</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_subsection">
- <a name="gccld">GCCLD bugs</a>
+<div class="doc_code">
+<p><tt><b>opt</b> -std-compile-opts -debug-pass=Arguments foo.bc
+ -disable-output</tt></p>
</div>
-<div class="doc_text">
+<p>This command should do two things: it should print out a list of passes, and
+then it should crash in the same was 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 you find that a bug crashes in the <tt><b>gccld</b></tt> stage of
-compilation, gather all of the <tt>.o</tt> bytecode files and libraries that are
-being linked together (the "<tt><b>llvm-gcc</b> -v</tt>" output should include
-the full list of objects linked). Then run:</p>
+<p>If this does crash, then you should be able to debug this with the following
+bugpoint command:</p>
-<pre>
- <b>llvm-as</b> < /dev/null > null.bc
- <b>gccld</b> -debug-pass=Arguments null.bc
-</pre><p>
+<div class="doc_code">
+<p><tt><b>bugpoint</b> foo.bc <list of passes printed by
+<b>opt</b>></tt></p>
+</div>
-<p>... which will print a list of arguments, indicating the list of passes that
-<tt><b>gccld</b></tt> runs. Once you have the input files and the list of
-passes, go to the section on <a href="#passes">debugging bugs in LLVM
-passes</a>.</p>
+<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>
<!-- ======================================================================= -->
<div class="doc_subsection">
- <a name="passes">Bugs in LLVM passes</a>
+ <a name="ct_codegen">Code generator bugs</a>
</div>
<div class="doc_text">
-<p>At this point, you should have some number of LLVM assembly files or bytecode
-files and a list of passes which crash when run on the specified input. In
-order to reduce the list of passes (which is probably large) and the input to
-something tractable, use the <tt><b>bugpoint</b></tt> tool as follows:</p>
+<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>
-<pre>
- <b>bugpoint</b> <input files> <list of passes>
-</pre><p>
+<ol>
+<li><tt><b>llc</b> foo.bc -f</tt></li>
+<li><tt><b>llc</b> foo.bc -f -relocation-model=pic</tt></li>
+<li><tt><b>llc</b> foo.bc -f -relocation-model=static</tt></li>
+<li><tt><b>llc</b> foo.bc -f -enable-eh</tt></li>
+<li><tt><b>llc</b> foo.bc -f -relocation-model=pic -enable-eh</tt></li>
+<li><tt><b>llc</b> foo.bc -f -relocation-model=static -enable-eh</tt></li>
+</ol>
-<p><tt><b>bugpoint</b></tt> will print a bunch of output as it reduces the
-test-case, but it should eventually print something like this:</p>
+<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>
-<pre>
- ...
- Emitted bytecode to 'bugpoint-reduced-simplified.bc'
-
- *** You can reproduce the problem with: opt bugpoint-reduced-simplified.bc -licm
-</pre>
+<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>
+<li><tt><b>bugpoint</b> -run-llc foo.bc --tool-args -enable-eh</tt></li>
+<li><tt><b>bugpoint</b> -run-llc foo.bc --tool-args
+ -relocation-model=pic -enable-eh</tt></li>
+<li><tt><b>bugpoint</b> -run-llc foo.bc --tool-args
+ -relocation-model=static -enable-eh</tt></li>
+</ol>
-<p>Once you complete this, please send the LLVM bytecode file and the command
-line to reproduce the problem to the llvmbugs mailing list.</p>
+<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 class="doc_text">
-<p>A miscompilation occurs when a pass does not correctly transform a program,
-thus producing errors that are only noticed during execution. This is different
-from producing invalid LLVM code (i.e., code not in SSA form, using values
-before defining them, etc.) which the verifier will check for after a pass
-finishes its run.</p>
-
-<p>To debug a miscompilation, you should choose which program you wish to run
-the output through, e.g. C backend, the JIT, or LLC, and a selection of passes,
-one of which may be causing the error, and run, for example:</p>
-
-<pre>
- <b>bugpoint</b> -run-cbe [... optimization passes ...] file-to-test.bc
-</pre>
+<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 bytecode file as much as it can to assist
+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>
<p>To debug the JIT:</p>
+<div class="doc_code">
<pre>
- <b>bugpoint</b> -run-jit -output=[correct output file] [bytecodefile]
+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>
- <b>bugpoint</b> -run-llc -output=[correct output file] [bytecodefile]
+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 bytecode files: a <em>safe</em> file which can be compiled with the C
+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>
<ol>
- <li>Regenerate the shared object from the safe bytecode file:<br>
-
-<pre>
- <b>llvm-dis</b> -c safe.bc -o safe.c<br>
- <b>gcc</b> -shared safe.c -o safe.so
-</pre></li>
-
- <li>If debugging LLC, compile test bytecode native and link with the shared object:<br>
-
-<pre>
- <b>llc</b> test.bc -o test.s -f<br>
- gcc test.s safe.so -o test.llc<br>
- ./test.llc [program options]
-</pre></li>
-
-<p>If debugging the JIT, load the shared object and supply the test
-bytecode:</p>
-
-<pre>
- <b>lli</b> -load=safe.so test.bc [program options]
-</pre></li>
+<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 -f<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>
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