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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - Missing Verifier check for debug info intrinsics that precede their SSA operands"
href="https://llvm.org/bugs/show_bug.cgi?id=27273">27273</a>
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<th>Summary</th>
<td>Missing Verifier check for debug info intrinsics that precede their SSA operands
</td>
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<th>Product</th>
<td>libraries
</td>
</tr>
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<th>Version</th>
<td>trunk
</td>
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<th>Hardware</th>
<td>PC
</td>
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<th>OS</th>
<td>All
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<th>Status</th>
<td>NEW
</td>
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<th>Severity</th>
<td>normal
</td>
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<th>Priority</th>
<td>P
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<th>Component</th>
<td>Core LLVM classes
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
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<th>Reporter</th>
<td>dexonsmith@apple.com
</td>
</tr>
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<th>CC</th>
<td>aprantl@apple.com, llvm-bugs@lists.llvm.org
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<th>Classification</th>
<td>Unclassified
</td>
</tr></table>
<p>
<div>
<pre>r265631, reverted in r265637, uncovered a bug in -reassociate that breaks the
order of @llvm.dbg.value instructions compared to the SSA values they
reference.
The current Verifier check doesn't look through the
MetadataAsValue/LocalAsMetadata operands that debug info intrinsics use, such
as `metadata i32 %x` in:
--
call void @llvm.dbg.value(metadata i32 %x, ...)
%x = add i32 0, %arg
--
As a result, we need a hack in llvm::MapMetadata to return `!{}` instead of
`null` when RF_IgnoreMissingLocals is turned off to prevent a crash in
llvm::RemapInstruction.
We should add a verifier check; fix the bugs; write an upgrade to drop invalid
instructions and commit the verifier check; and then fix llvm::MapMetadata to
ignore RF_IgnoreMissingLocals (as r265631 tried to do).
There's a more complete write-up of the issue on llvm-commits (in the reply to
r265631):
<a href="http://lists.llvm.org/pipermail/llvm-commits/Week-of-Mon-20160404/345617.html">http://lists.llvm.org/pipermail/llvm-commits/Week-of-Mon-20160404/345617.html</a>
For now I'm going to push forward with a modified version of r265631 that
documents what's going on. I'll add a comment with the revision.</pre>
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