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<html><head><title>How to submit an LLVM bug report</title></head>
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<tr><td> <font size=+3 color="#EEEEFF" face="Georgia,Palatino,Times,Roman"><b>How to submit an LLVM bug report</b></font></td>
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<li><a href="#introduction">Introduction - Got bugs?</a>
<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>
</ul>
<li><a href="#miscompilations">Miscompilations</a>
<p><b>Written by <a href="mailto:sabre@nondot.org">Chris Lattner</a></b><p>
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<a name="introduction">Introduction - Got bugs?
</b></font></td></tr></table><ul>
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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>
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
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>
Once you have a reduced test-case, email information about the bug to: <a
href="mailto:llvmbugs@cs.uiuc.edu">llvmbugs@cs.uiuc.edu</a>. This should
include all of the information necessary to reproduce the problem, including
where you got the LLVM tree from (if you're not working out of CVS).<p>
Thanks for helping us make LLVM better!<p>
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<a name="crashers">Crashing Bugs
</b></font></td></tr></table><ul>
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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>
To figure out which program is crashing (the front-end, <tt><b>gccas</b></tt>,
or <tt><b>gccld</b></tt>), 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>
<ul>
<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>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>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>Otherwise, something really weird happened. Email the list with what you
have at this point.
</ul><p>
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<font color="#EEEEFF" face="Georgia,Palatino"><b>
<a name="front-end">Front-end bugs
</b></font></td></tr></table><ul>
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> (containing LLVM
assembly code), 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>
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<font color="#EEEEFF" face="Georgia,Palatino"><b>
<a name="gccas">GCCAS bugs
</b></font></td></tr></table><ul>
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>
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<tr><td> </td><td width="100%">
<font color="#EEEEFF" face="Georgia,Palatino"><b>
<a name="gccld">GCCLD bugs
</b></font></td></tr></table><ul>
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>
<pre>
<b>as</b> < /dev/null > null.bc
<b>gccld</b> -debug-pass=Arguments null.bc
</pre><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>
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</ul><table width="100%" bgcolor="#441188" border=0 cellpadding=4 cellspacing=0>
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<font color="#EEEEFF" face="Georgia,Palatino"><b>
<a name="passes">Bugs in LLVM passes
</b></font></td></tr></table><ul>
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>
<pre>
<b>bugpoint</b> <input files> <list of passes>
</pre><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>
<pre>
...
Emitted bytecode to 'bugpoint-reduced-simplified.bc'
*** You can reproduce the problem with: opt bugpoint-reduced-simplified.bc -licm
</pre><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>
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<tr><td align=center><font color="#EEEEFF" size=+2 face="Georgia,Palatino"><b>
<a name="miscompilations">Miscompilations
</b></font></td></tr></table><ul>
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Fortunately we haven't had to many miscompilations. Because of this, this
section is a TODO. Basically, use bugpoint to track down the problem.<p>
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</ul>
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<address><a href="mailto:sabre@nondot.org">Chris Lattner</a></address>
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Last modified: Fri May 23 09:48:53 CDT 2003
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