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update this for llvm-gcc4
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@34566 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner
parent
438d71eea4
commit
1a5ed97f35
@ -19,9 +19,8 @@
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<li><a href="#crashers">Crashing Bugs</a>
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<ul>
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<li><a href="#front-end">Front-end bugs</a>
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<li><a href="#gccas">GCCAS bugs</a>
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<li><a href="#gccld">GCCLD bugs</a>
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<li><a href="#passes">Bugs in LLVM passes</a>
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<li><a href="#ct_optimizer">Compile-time optimization bugs</a>
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<li><a href="#ct_codegen">Code generator bugs</a>
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</ul></li>
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<li><a href="#miscompilations">Miscompilations</a></li>
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<li><a href="#codegen">Incorrect code generation (JIT and LLC)</a></li>
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@ -51,15 +50,18 @@ getting it fixed quickly.</p>
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<p>Basically you have to do two things at a minimum. First, decide whether the
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bug <a href="#crashers">crashes the compiler</a> (or an LLVM pass), or if the
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compiler is <a href="#miscompilations">miscompiling</a> the program. Based on
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compiler is <a href="#miscompilations">miscompiling</a> the program (i.e., the
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compiler successfully produces an executable, but it doesn't run right). Based
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on
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what type of bug it is, follow the instructions in the linked section to narrow
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down the bug so that the person who fixes it will be able to find the problem
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more easily.</p>
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<p>Once you have a reduced test-case, go to <a
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href="http://llvm.org/bugs/enter_bug.cgi">the LLVM Bug Tracking
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System</a>, select the category in which the bug falls, and fill out the form
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with the necessary details. The bug description should contain the following
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System</a> and fill out the form with the necessary details (note that you don't
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need to pick a catagory, just use the "new-bugs" catagory if you're not sure).
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The bug description should contain the following
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information:</p>
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<ul>
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@ -81,35 +83,29 @@ information:</p>
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<div class="doc_text">
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<p>More often than not, bugs in the compiler cause it to crash—often due to an
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assertion failure of some sort. If you are running <tt><b>opt</b></tt>
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directly, and something crashes, jump to the section on
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<a href="#passes">bugs in LLVM passes</a>. Otherwise, the most important
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piece of the puzzle is to figure out if it is the GCC-based front-end that is
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buggy or if it's one of the LLVM tools that has problems.</p>
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<p>More often than not, bugs in the compiler cause it to crash—often due
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to an assertion failure of some sort. The most important
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piece of the puzzle is to figure out if it is crashing in the GCC front-end
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or if it is one of the LLVM libraries (e.g. the optimizer or code generator)
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that has problems.</p>
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<p>To figure out which program is crashing (the front-end,
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<tt><b>gccas</b></tt>, or <tt><b>gccld</b></tt>), run the
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<p>To figure out which component is crashing (the front-end,
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optimizer or code generator), run the
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<tt><b>llvm-gcc</b></tt> command line as you were when the crash occurred, but
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add a <tt>-v</tt> option to the command line. The compiler will print out a
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bunch of stuff, and should end with telling you that one of
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<tt><b>cc1</b>/<b>cc1plus</b></tt>, <tt><b>gccas</b></tt>, or
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<tt><b>gccld</b></tt> crashed.</p>
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with the following extra command line options:</p>
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<ul>
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<li><tt><b>-O0 -emit-llvm</b></tt>: If <tt>llvm-gcc</tt> still crashes when
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passed these options (which disable the optimizer and code generator), then
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the crash is in the front-end. Jump ahead to the section on <a
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href="#front-end">front-end bugs</a>.</li>
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<li>If <tt><b>cc1</b></tt> or <tt><b>cc1plus</b></tt> crashed, you found a
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problem with the front-end.
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Jump ahead to the section on <a href="#front-end">front-end bugs</a>.</li>
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<li><tt><b>-emit-llvm</b></tt>: If <tt>llvm-gcc</tt> crashes with this option
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(which disables the code generator), you found an optimizer bug. Jump ahead
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to <a href="#ct_optimizer"> compile-time optimization bugs</a>.</li>
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<li>If <tt><b>gccas</b></tt> crashed, you found a bug in <a href="#gccas">one
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of the passes in <tt><b>gccas</b></tt></a>.</li>
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<li>If <tt><b>gccld</b></tt> crashed, you found a bug in <a href="#gccld">one
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of the passes in <tt><b>gccld</b></tt></a>.</li>
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<li>Otherwise, something really weird happened. Email the list with what you
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have at this point.</li>
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<li>Otherwise, you have a code generator crash. Jump ahead to <a
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href="#ct_codegen">code generator bugs</a>.</li>
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</ul>
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@ -126,9 +122,10 @@ bunch of stuff, and should end with telling you that one of
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<tt>llvm-gcc</tt> command that resulted in the crash, but add the
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<tt>-save-temps</tt> option. The compiler will crash again, but it will leave
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behind a <tt><i>foo</i>.i</tt> file (containing preprocessed C source code) and
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possibly <tt><i>foo</i>.s</tt> (containing LLVM assembly code) for each
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possibly <tt><i>foo</i>.s</tt> for each
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compiled <tt><i>foo</i>.c</tt> file. Send us the <tt><i>foo</i>.i</tt> file,
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along with a brief description of the error it caused.</p>
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along with the options you passed to llvm-gcc, and a brief description of the
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error it caused.</p>
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<p>The <a href="http://delta.tigris.org/">delta</a> tool helps to reduce the
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preprocessed file down to the smallest amount of code that still replicates the
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@ -141,81 +138,72 @@ has instructions on the best way to use delta.</p>
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<!-- ======================================================================= -->
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<div class="doc_subsection">
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<a name="gccas">GCCAS bugs</a>
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<a name="ct_optimizer">Compile-time optimization bugs</a>
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</div>
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<div class="doc_text">
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<p>If you find that a bug crashes in the <tt><b>gccas</b></tt> stage of
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compilation, compile your test-case to a <tt>.s</tt> file with the
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<tt>-save-temps</tt> option to <tt><b>llvm-gcc</b></tt>. Then run:</p>
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<p>If you find that a bug crashes in the optimizer, compile your test-case to a
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<tt>.bc</tt> file by passing "<tt><b>-emit-llvm -O0 -c -o foo.bc</b></tt>".
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Then run:</p>
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<div class="doc_code">
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<p><tt><b>gccas</b> -debug-pass=Arguments < /dev/null -o - > /dev/null</tt></p>
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<p><tt><b>opt</b> -std-compile-opts -debug-pass=Arguments foo.bc
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-disable-output</tt></p>
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</div>
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<p>... which will print a list of arguments, indicating the list of passes that
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<tt><b>gccas</b></tt> runs. Once you have the input file and the list of
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passes, go to the section on <a href="#passes">debugging bugs in LLVM
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passes</a>.</p>
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<p>This command should do two things: it should print out a list of passes, and
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then it should crash in the same was as llvm-gcc. If it doesn't crash, please
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follow the instructions for a <a href="#front-end">front-end bug</a>.</p>
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<p>If this does crash, then you should be able to debug this with the following
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bugpoint command:</p>
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<div class="doc_code">
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<p><tt><b>bugpoint</b> foo.bc <list of passes printed by
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<b>opt</b>></tt></p>
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</div>
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<p>Please run this, then file a bug with the instructions and reduced .bc files
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that bugpoint emits. If something goes wrong with bugpoint, please submit the
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"foo.bc" file and the list of passes printed by <b>opt</b>.</p>
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</div>
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<!-- ======================================================================= -->
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<div class="doc_subsection">
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<a name="gccld">GCCLD bugs</a>
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<a name="ct_codegen">Code generator bugs</a>
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</div>
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<div class="doc_text">
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<p>If you find that a bug crashes in the <tt><b>gccld</b></tt> stage of
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compilation, gather all of the <tt>.o</tt> bytecode files and libraries that are
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being linked together (the "<tt><b>llvm-gcc</b> -v</tt>" output should include
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the full list of objects linked). Then run:</p>
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<p>If you find a bug that crashes llvm-gcc in the code generator, compile your
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source file to a .bc file by passing "<tt><b>-emit-llvm -c -o foo.bc</b></tt>"
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to llvm-gcc (in addition to the options you already pass). Once your have
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foo.bc, one of the following commands should fail:</p>
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<div class="doc_code">
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<p><tt><b>llvm-as</b> < /dev/null > null.bc<br>
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<b>gccld</b> -debug-pass=Arguments null.bc</tt>
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</p>
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</div>
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<ol>
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<li><tt><b>llc</b> foo.bc -f</tt></li>
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<li><tt><b>llc</b> foo.bc -f -relocation-model=pic</tt></li>
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<li><tt><b>llc</b> foo.bc -f -relocation-model=static</tt></li>
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</ol>
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<p>... which will print a list of arguments, indicating the list of passes that
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<tt><b>gccld</b></tt> runs. Once you have the input files and the list of
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passes, go to the section on <a href="#passes">debugging bugs in LLVM
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passes</a>.</p>
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<p>If none of these crash, please follow the instructions for a
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<a href="#front-end">front-end bug</a>. If one of these do crash, you should
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be able to reduce this with one of the following bugpoint command lines (use
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the one corresponding to the command above that failed):</p>
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</div>
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<ol>
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<li><tt><b>bugpoint</b> -run-llc foo.bc --tool-args</tt></li>
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<li><tt><b>bugpoint</b> -run-llc foo.bc --tool-args
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-relocation-model=pic</tt></li>
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<li><tt><b>bugpoint</b> -run-llc foo.bc --tool-args
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-relocation-model=static</tt></li>
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</ol>
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<!-- ======================================================================= -->
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<div class="doc_subsection">
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<a name="passes">Bugs in LLVM passes</a>
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</div>
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<div class="doc_text">
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<p>At this point, you should have some number of LLVM assembly files or bytecode
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files and a list of passes which crash when run on the specified input. In
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order to reduce the list of passes (which is probably large) and the input to
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something tractable, use the <tt><b>bugpoint</b></tt> tool as follows:</p>
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<div class="doc_code">
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<p><tt><b>bugpoint</b> <input files> <list of passes></tt></p>
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</div>
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<p><tt><b>bugpoint</b></tt> will print a bunch of output as it reduces the
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test-case, but it should eventually print something like this:</p>
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<div class="doc_code">
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<p><tt>
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...<br>
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Emitted bytecode to 'bugpoint-reduced-simplified.bc'<br>
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<br>
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*** You can reproduce the problem with: opt bugpoint-reduced-simplified.bc -licm<br>
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</tt></p>
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</div>
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<p>Once you complete this, please send the LLVM bytecode file and the command
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line to reproduce the problem to the llvmbugs mailing list.</p>
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<p>Please run this, then file a bug with the instructions and reduced .bc file
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that bugpoint emits. If something goes wrong with bugpoint, please submit the
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"foo.bc" file and the option that llc crashes with.</p>
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</div>
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@ -227,18 +215,14 @@ line to reproduce the problem to the llvmbugs mailing list.</p>
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<div class="doc_text">
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<p>A miscompilation occurs when a pass does not correctly transform a program,
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thus producing errors that are only noticed during execution. This is different
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from producing invalid LLVM code (i.e., code not in SSA form, using values
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before defining them, etc.) which the verifier will check for after a pass
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finishes its run.</p>
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<p>If it looks like the LLVM compiler is miscompiling a program, the very first
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thing to check is to make sure it is not using undefined behavior. In
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particular, check to see if the program <a
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href="http://valgrind.kde.org/">valgrind</a>s clean, passes purify, or some
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other memory checker tool. Many of the "LLVM bugs" that we have chased down
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ended up being bugs in the program being compiled, not LLVM.</p>
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<p>If llvm-gcc successfully produces an executable, but that executable doesn't
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run right, this is either a bug in the code or a bug in the
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compiler. The first thing to check is to make sure it is not using undefined
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behavior (e.g. reading a variable before it is defined). In particular, check
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to see if the program <a href="http://valgrind.org/">valgrind</a>s clean,
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passes purify, or some other memory checker tool. Many of the "LLVM bugs" that
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we have chased down ended up being bugs in the program being compiled, not
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LLVM.</p>
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<p>Once you determine that the program itself is not buggy, you should choose
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which code generator you wish to compile the program with (e.g. C backend, the
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