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5 <title>How to submit an LLVM bug report</title>
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Chris Lattner8b6be362003-05-21 22:21:07 +00009
Misha Brukman94082392003-10-31 18:37:20 +000010<div class="doc_title">
11 How to submit an LLVM bug report
12</div>
Chris Lattner8b6be362003-05-21 22:21:07 +000013
Misha Brukman94082392003-10-31 18:37:20 +000014<table border="0" width="100%">
15<tr>
16<td valign="top">
17
Chris Lattner8b6be362003-05-21 22:21:07 +000018<ol>
Misha Brukman94082392003-10-31 18:37:20 +000019 <li><a href="#introduction">Introduction - Got bugs?</a></li>
Chris Lattner8b6be362003-05-21 22:21:07 +000020 <li><a href="#crashers">Crashing Bugs</a>
21 <ul>
22 <li><a href="#front-end">Front-end bugs</a>
23 <li><a href="#gccas">GCCAS bugs</a>
24 <li><a href="#gccld">GCCLD bugs</a>
25 <li><a href="#passes">Bugs in LLVM passes</a>
Misha Brukman94082392003-10-31 18:37:20 +000026 </ul></li>
27 <li><a href="#miscompilations">Miscompilations</a></li>
28 <li><a href="#codegen">Incorrect code generation (JIT and LLC)</a></li>
Chris Lattner8b6be362003-05-21 22:21:07 +000029
Misha Brukman94082392003-10-31 18:37:20 +000030</ol>
31
Misha Brukman637cab02004-01-15 19:03:47 +000032<div class="doc_text">
33 <p><b>Written by <a href="mailto:sabre@nondot.org">Chris Lattner</a> and
34 <a href="http://misha.brukman.net">Misha Brukman</a></b></p>
35</div>
Misha Brukman94082392003-10-31 18:37:20 +000036
37</td>
38<td align="right">
Misha Brukman637cab02004-01-15 19:03:47 +000039 <img src="Debugging.gif" alt="Debugging" width="444" height="314">
Misha Brukman94082392003-10-31 18:37:20 +000040</td>
41</tr>
Chris Lattner8b6be362003-05-21 22:21:07 +000042</table>
43
Chris Lattner8b6be362003-05-21 22:21:07 +000044<!-- *********************************************************************** -->
Misha Brukman94082392003-10-31 18:37:20 +000045<div class="doc_section">
46 <a name="introduction">Introduction - Got bugs?</a>
47</div>
Chris Lattner8b6be362003-05-21 22:21:07 +000048<!-- *********************************************************************** -->
49
Misha Brukman94082392003-10-31 18:37:20 +000050<div class="doc_text">
Chris Lattner8b6be362003-05-21 22:21:07 +000051
Misha Brukman94082392003-10-31 18:37:20 +000052<p>If you're working with LLVM and run into a bug, we definitely want to know
53about it. This document describes what you can do to increase the odds of
54getting it fixed quickly.</p>
55
56<p>Basically you have to do two things at a minimum. First, decide whether the
57bug <a href="#crashers">crashes the compiler</a> (or an LLVM pass), or if the
Chris Lattner8b6be362003-05-21 22:21:07 +000058compiler is <a href="#miscompilations">miscompiling</a> the program. Based on
59what type of bug it is, follow the instructions in the linked section to narrow
60down the bug so that the person who fixes it will be able to find the problem
Misha Brukman94082392003-10-31 18:37:20 +000061more easily.</p>
Chris Lattner8b6be362003-05-21 22:21:07 +000062
Misha Brukman94082392003-10-31 18:37:20 +000063<p>Once you have a reduced test-case, go to <a
64href="http://llvm.cs.uiuc.edu/bugs/enter_bug.cgi">the LLVM Bug Tracking
65System</a>, select the category in which the bug falls, and fill out the form
66with the necessary details. The bug description should contain the following
67information:</p>
68
John Criswell4d37c7b2003-10-22 15:06:11 +000069<ul>
Misha Brukmanafac73e2003-10-22 17:01:44 +000070 <li>All information necessary to reproduce the problem.</li>
71 <li>The reduced test-case that triggers the bug.</li>
72 <li>The location where you obtained LLVM (if not from our CVS
73 repository).</li>
John Criswell4d37c7b2003-10-22 15:06:11 +000074</ul>
75
Misha Brukman94082392003-10-31 18:37:20 +000076<p>Thanks for helping us make LLVM better!</p>
Chris Lattner8b6be362003-05-21 22:21:07 +000077
Misha Brukman94082392003-10-31 18:37:20 +000078</div>
Chris Lattner8b6be362003-05-21 22:21:07 +000079
80<!-- *********************************************************************** -->
Misha Brukman94082392003-10-31 18:37:20 +000081<div class="doc_section">
82 <a name="crashers">Crashing Bugs</a>
83</div>
Chris Lattner8b6be362003-05-21 22:21:07 +000084<!-- *********************************************************************** -->
85
Misha Brukman94082392003-10-31 18:37:20 +000086<div class="doc_text">
87
88<p>More often than not, bugs in the compiler cause it to crash - often due to an
Chris Lattner8b6be362003-05-21 22:21:07 +000089assertion failure of some sort. If you are running <tt><b>opt</b></tt> or
90<tt><b>analyze</b></tt> directly, and something crashes, jump to the section on
91<a href="#passes">bugs in LLVM passes</a>. Otherwise, the most important
92piece of the puzzle is to figure out if it is the GCC-based front-end that is
Misha Brukman94082392003-10-31 18:37:20 +000093buggy or if it's one of the LLVM tools that has problems.</p>
Chris Lattner8b6be362003-05-21 22:21:07 +000094
Misha Brukman94082392003-10-31 18:37:20 +000095<p>To figure out which program is crashing (the front-end,
96<tt><b>gccas</b></tt>, or <tt><b>gccld</b></tt>), run the
97<tt><b>llvm-gcc</b></tt> command line as you were when the crash occurred, but
98add a <tt>-v</tt> option to the command line. The compiler will print out a
John Criswell79926912004-03-12 20:42:16 +000099bunch of stuff, and should end with telling you that one of
100<tt><b>cc1</b>/<b>cc1plus</b></tt>, <tt><b>gccas</b></tt>, or
101<tt><b>gccld</b></tt> crashed.</p>
Chris Lattner8b6be362003-05-21 22:21:07 +0000102
103<ul>
Chris Lattner8b6be362003-05-21 22:21:07 +0000104
John Criswell79926912004-03-12 20:42:16 +0000105 <li>If <tt><b>cc1</b></tt> or <tt><b>cc1plus</b></tt> crashed, you found a
106 problem with the front-end.
Misha Brukman94082392003-10-31 18:37:20 +0000107 Jump ahead to the section on <a href="#front-end">front-end bugs</a>.</li>
108
109 <li>If <tt><b>gccas</b></tt> crashed, you found a bug in <a href="#gccas">one
110 of the passes in <tt><b>gccas</b></tt></a>.</li>
111
112 <li>If <tt><b>gccld</b></tt> crashed, you found a bug in <a href="#gccld">one
113 of the passes in <tt><b>gccld</b></tt></a>.</li>
114
115 <li>Otherwise, something really weird happened. Email the list with what you
116 have at this point.</li>
117
118</ul>
119
120</div>
Chris Lattner8b6be362003-05-21 22:21:07 +0000121
122<!-- ======================================================================= -->
Misha Brukman94082392003-10-31 18:37:20 +0000123<div class="doc_subsection">
124 <a name="front-end">Front-end bugs</a>
125</div>
Chris Lattner8b6be362003-05-21 22:21:07 +0000126
Misha Brukman94082392003-10-31 18:37:20 +0000127<div class="doc_text">
128
129<p>If the problem is in the front-end, you should re-run the same
Brian Gaekeeefe9792003-05-23 21:03:50 +0000130<tt>llvm-gcc</tt> command that resulted in the crash, but add the
Misha Brukman94082392003-10-31 18:37:20 +0000131<tt>-save-temps</tt> option. The compiler will crash again, but it will leave
132behind a <tt><i>foo</i>.i</tt> file (containing preprocessed C source code) and
133possibly <tt><i>foo</i>.s</tt> (containing LLVM assembly code), for each
134compiled <tt><i>foo</i>.c</tt> file. Send us the <tt><i>foo</i>.i</tt> file,
135along with a brief description of the error it caused.</p>
136
137</div>
Chris Lattner8b6be362003-05-21 22:21:07 +0000138
139<!-- ======================================================================= -->
Misha Brukman94082392003-10-31 18:37:20 +0000140<div class="doc_subsection">
141 <a name="gccas">GCCAS bugs</a>
142</div>
Chris Lattner8b6be362003-05-21 22:21:07 +0000143
Misha Brukman94082392003-10-31 18:37:20 +0000144<div class="doc_text">
145
146<p>If you find that a bug crashes in the <tt><b>gccas</b></tt> stage of
Brian Gaekeeefe9792003-05-23 21:03:50 +0000147compilation, compile your test-case to a <tt>.s</tt> file with the
Misha Brukman94082392003-10-31 18:37:20 +0000148<tt>-save-temps</tt> option to <tt><b>llvm-gcc</b></tt>. Then run:</p>
Chris Lattner8b6be362003-05-21 22:21:07 +0000149
150<pre>
151 <b>gccas</b> -debug-pass=Arguments &lt; /dev/null -o - &gt; /dev/null
Misha Brukman94082392003-10-31 18:37:20 +0000152</pre>
Chris Lattner8b6be362003-05-21 22:21:07 +0000153
Misha Brukman94082392003-10-31 18:37:20 +0000154<p>... which will print a list of arguments, indicating the list of passes that
Chris Lattner8b6be362003-05-21 22:21:07 +0000155<tt><b>gccas</b></tt> runs. Once you have the input file and the list of
156passes, go to the section on <a href="#passes">debugging bugs in LLVM
Misha Brukman94082392003-10-31 18:37:20 +0000157passes</a>.</p>
Chris Lattner8b6be362003-05-21 22:21:07 +0000158
Misha Brukman94082392003-10-31 18:37:20 +0000159</div>
Chris Lattner8b6be362003-05-21 22:21:07 +0000160
161<!-- ======================================================================= -->
Misha Brukman94082392003-10-31 18:37:20 +0000162<div class="doc_subsection">
163 <a name="gccld">GCCLD bugs</a>
164</div>
Chris Lattner8b6be362003-05-21 22:21:07 +0000165
Misha Brukman94082392003-10-31 18:37:20 +0000166<div class="doc_text">
167
168<p>If you find that a bug crashes in the <tt><b>gccld</b></tt> stage of
Chris Lattner8b6be362003-05-21 22:21:07 +0000169compilation, gather all of the <tt>.o</tt> bytecode files and libraries that are
170being linked together (the "<tt><b>llvm-gcc</b> -v</tt>" output should include
Misha Brukman94082392003-10-31 18:37:20 +0000171the full list of objects linked). Then run:</p>
Chris Lattner8b6be362003-05-21 22:21:07 +0000172
173<pre>
Misha Brukmanf1d01fb2003-09-17 18:51:47 +0000174 <b>llvm-as</b> &lt; /dev/null &gt; null.bc
Chris Lattnerddaf5002003-05-23 14:49:32 +0000175 <b>gccld</b> -debug-pass=Arguments null.bc
Chris Lattner8b6be362003-05-21 22:21:07 +0000176</pre><p>
177
Misha Brukman94082392003-10-31 18:37:20 +0000178<p>... which will print a list of arguments, indicating the list of passes that
Chris Lattner8b6be362003-05-21 22:21:07 +0000179<tt><b>gccld</b></tt> runs. Once you have the input files and the list of
180passes, go to the section on <a href="#passes">debugging bugs in LLVM
Misha Brukman94082392003-10-31 18:37:20 +0000181passes</a>.</p>
182
183</div>
Chris Lattner8b6be362003-05-21 22:21:07 +0000184
185<!-- ======================================================================= -->
Misha Brukman94082392003-10-31 18:37:20 +0000186<div class="doc_subsection">
187 <a name="passes">Bugs in LLVM passes</a>
188</div>
Chris Lattner8b6be362003-05-21 22:21:07 +0000189
Misha Brukman94082392003-10-31 18:37:20 +0000190<div class="doc_text">
191
192<p>At this point, you should have some number of LLVM assembly files or bytecode
Chris Lattner8b6be362003-05-21 22:21:07 +0000193files and a list of passes which crash when run on the specified input. In
194order to reduce the list of passes (which is probably large) and the input to
Misha Brukman94082392003-10-31 18:37:20 +0000195something tractable, use the <tt><b>bugpoint</b></tt> tool as follows:</p>
Chris Lattner8b6be362003-05-21 22:21:07 +0000196
197<pre>
198 <b>bugpoint</b> &lt;input files&gt; &lt;list of passes&gt;
199</pre><p>
200
Misha Brukman94082392003-10-31 18:37:20 +0000201<p><tt><b>bugpoint</b></tt> will print a bunch of output as it reduces the
202test-case, but it should eventually print something like this:</p>
Chris Lattner8b6be362003-05-21 22:21:07 +0000203
204<pre>
205 ...
206 Emitted bytecode to 'bugpoint-reduced-simplified.bc'
207
208 *** You can reproduce the problem with: opt bugpoint-reduced-simplified.bc -licm
Misha Brukman94082392003-10-31 18:37:20 +0000209</pre>
Chris Lattner8b6be362003-05-21 22:21:07 +0000210
Misha Brukman94082392003-10-31 18:37:20 +0000211<p>Once you complete this, please send the LLVM bytecode file and the command
212line to reproduce the problem to the llvmbugs mailing list.</p>
Chris Lattner8b6be362003-05-21 22:21:07 +0000213
Misha Brukman94082392003-10-31 18:37:20 +0000214</div>
Chris Lattner8b6be362003-05-21 22:21:07 +0000215
216<!-- *********************************************************************** -->
Misha Brukman94082392003-10-31 18:37:20 +0000217<div class="doc_section">
218 <a name="miscompilations">Miscompilations</a>
219</div>
Chris Lattner8b6be362003-05-21 22:21:07 +0000220<!-- *********************************************************************** -->
221
Misha Brukman94082392003-10-31 18:37:20 +0000222<div class="doc_text">
Chris Lattner8b6be362003-05-21 22:21:07 +0000223
Misha Brukman94082392003-10-31 18:37:20 +0000224<p>A miscompilation occurs when a pass does not correctly transform a program,
225thus producing errors that are only noticed during execution. This is different
226from producing invalid LLVM code (i.e., code not in SSA form, using values
227before defining them, etc.) which the verifier will check for after a pass
228finishes its run.</p>
229
230<p>To debug a miscompilation, you should choose which program you wish to run
231the output through, e.g. C backend, the JIT, or LLC, and a selection of passes,
232one of which may be causing the error, and run, for example:</p>
Misha Brukmanf1d01fb2003-09-17 18:51:47 +0000233
234<pre>
Chris Lattner18ab2b92003-10-14 20:58:07 +0000235 <b>bugpoint</b> -run-cbe [... optimization passes ...] file-to-test.bc
Misha Brukmanf1d01fb2003-09-17 18:51:47 +0000236</pre>
237
Misha Brukman94082392003-10-31 18:37:20 +0000238<p><tt>bugpoint</tt> will try to narrow down your list of passes to the one pass
Misha Brukmanf1d01fb2003-09-17 18:51:47 +0000239that causes an error, and simplify the bytecode file as much as it can to assist
240you. It will print a message letting you know how to reproduce the resulting
Misha Brukman94082392003-10-31 18:37:20 +0000241error.</p>
242
243</div>
Misha Brukmanf1d01fb2003-09-17 18:51:47 +0000244
245<!-- *********************************************************************** -->
Misha Brukman94082392003-10-31 18:37:20 +0000246<div class="doc_section">
247 <a name="codegen">Incorrect code generation</a>
248</div>
Misha Brukmanf1d01fb2003-09-17 18:51:47 +0000249<!-- *********************************************************************** -->
250
Misha Brukman94082392003-10-31 18:37:20 +0000251<div class="doc_text">
252
253<p>Similarly to debugging incorrect compilation by mis-behaving passes, you can
Misha Brukmanf1d01fb2003-09-17 18:51:47 +0000254debug incorrect code generation by either LLC or the JIT, using
255<tt>bugpoint</tt>. The process <tt>bugpoint</tt> follows in this case is to try
256to narrow the code down to a function that is miscompiled by one or the other
257method, but since for correctness, the entire program must be run,
258<tt>bugpoint</tt> will compile the code it deems to not be affected with the C
Misha Brukman94082392003-10-31 18:37:20 +0000259Backend, and then link in the shared object it generates.</p>
Misha Brukmanf1d01fb2003-09-17 18:51:47 +0000260
Misha Brukman94082392003-10-31 18:37:20 +0000261<p>To debug the JIT:</p>
262
Misha Brukmanf1d01fb2003-09-17 18:51:47 +0000263<pre>
Chris Lattner18ab2b92003-10-14 20:58:07 +0000264 <b>bugpoint</b> -run-jit -output=[correct output file] [bytecodefile]
Misha Brukmanf1d01fb2003-09-17 18:51:47 +0000265</pre>
266
Misha Brukman94082392003-10-31 18:37:20 +0000267<p>Similarly, to debug the LLC, one would run:</p>
268
Misha Brukmanf1d01fb2003-09-17 18:51:47 +0000269<pre>
Chris Lattner18ab2b92003-10-14 20:58:07 +0000270 <b>bugpoint</b> -run-llc -output=[correct output file] [bytecodefile]
Misha Brukmanf1d01fb2003-09-17 18:51:47 +0000271</pre>
272
Misha Brukman94082392003-10-31 18:37:20 +0000273<p>At the end of a successful <tt>bugpoint</tt> run, you will be presented
Misha Brukmanf1d01fb2003-09-17 18:51:47 +0000274with two bytecode files: a <em>safe</em> file which can be compiled with the C
275backend and the <em>test</em> file which either LLC or the JIT
Misha Brukman94082392003-10-31 18:37:20 +0000276mis-codegenerates, and thus causes the error.</p>
Misha Brukmanf1d01fb2003-09-17 18:51:47 +0000277
Misha Brukman94082392003-10-31 18:37:20 +0000278<p>To reproduce the error that <tt>bugpoint</tt> found, it is sufficient to do
279the following:</p>
Misha Brukmanf1d01fb2003-09-17 18:51:47 +0000280
281<ol>
Misha Brukman94082392003-10-31 18:37:20 +0000282
Misha Brukmanf1d01fb2003-09-17 18:51:47 +0000283 <li>Regenerate the shared object from the safe bytecode file:<br>
Misha Brukman94082392003-10-31 18:37:20 +0000284
Misha Brukmanf1d01fb2003-09-17 18:51:47 +0000285<pre>
Chris Lattner036e6392004-02-14 01:07:17 +0000286 <b>llc</b> -march=c safe.bc -o safe.c<br>
Misha Brukmanf1d01fb2003-09-17 18:51:47 +0000287 <b>gcc</b> -shared safe.c -o safe.so
288</pre></li>
Misha Brukman94082392003-10-31 18:37:20 +0000289
Misha Brukmanf1d01fb2003-09-17 18:51:47 +0000290 <li>If debugging LLC, compile test bytecode native and link with the shared object:<br>
Misha Brukman94082392003-10-31 18:37:20 +0000291
Misha Brukmanf1d01fb2003-09-17 18:51:47 +0000292<pre>
293 <b>llc</b> test.bc -o test.s -f<br>
294 gcc test.s safe.so -o test.llc<br>
295 ./test.llc [program options]
296</pre></li>
Misha Brukman94082392003-10-31 18:37:20 +0000297
Misha Brukman637cab02004-01-15 19:03:47 +0000298 <li>If debugging the JIT, load the shared object and supply the test
299bytecode:
Misha Brukman94082392003-10-31 18:37:20 +0000300
Misha Brukmanf1d01fb2003-09-17 18:51:47 +0000301<pre>
302 <b>lli</b> -load=safe.so test.bc [program options]
303</pre></li>
Misha Brukman94082392003-10-31 18:37:20 +0000304
Misha Brukmanf1d01fb2003-09-17 18:51:47 +0000305</ol>
Chris Lattner8b6be362003-05-21 22:21:07 +0000306
Misha Brukman94082392003-10-31 18:37:20 +0000307</div>
308
Chris Lattner8b6be362003-05-21 22:21:07 +0000309<!-- *********************************************************************** -->
Misha Brukman94082392003-10-31 18:37:20 +0000310<hr>
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317 <a href="mailto:sabre@nondot.org">Chris Lattner</a><br>
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