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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - [PeepholeOptimizer] foldRedundantCopy breaks if Copy is changed by TII.foldImmediate"
href="https://bugs.llvm.org/show_bug.cgi?id=43898">43898</a>
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<th>Summary</th>
<td>[PeepholeOptimizer] foldRedundantCopy breaks if Copy is changed by TII.foldImmediate
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<th>Product</th>
<td>libraries
</td>
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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>Windows NT
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<th>Status</th>
<td>NEW
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<th>Severity</th>
<td>enhancement
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<th>Priority</th>
<td>P
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<th>Component</th>
<td>Common Code Generator Code
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
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<th>Reporter</th>
<td>alex.davies@iinet.net.au
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<th>CC</th>
<td>llvm-bugs@lists.llvm.org
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<p>
<div>
<pre>For all MIs per basic block:
foldRedundantCopy tracks copy instructions and places them in DenseMap
CopyMIs.
foldImmediate tracks isMoveImm, and calls foldImmediate on uses of these.
foldImmediate is allowed to change the desc of UseMI - see
ARMBaseInstrInfo.cpp.
On seeing the description for "foldImmediate", it seems logical to optimize
copy instructions - but if you try to do so, it's only a matter of time until
compilation fails, as foldRedundantCopy does not verify that instructions in
CopyMI is still actually a copy instruction.
I figure either (1) do not call foldImmediate on COPYs, if it is recommended
that targets do not perform this optimization here, or (2) add:
if (!PrevCopy->isCopy())
return false;
to line 1410 of PeepholeOptimizer.cpp
Cheers :)</pre>
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