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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - Assert when combining an AND of two FCMPs."
href="http://llvm.org/bugs/show_bug.cgi?id=15737">15737</a>
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<th>Summary</th>
<td>Assert when combining an AND of two FCMPs.
</td>
</tr>
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<th>Product</th>
<td>clang
</td>
</tr>
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<th>Version</th>
<td>trunk
</td>
</tr>
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<th>Hardware</th>
<td>Macintosh
</td>
</tr>
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<th>OS</th>
<td>MacOS X
</td>
</tr>
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<th>Status</th>
<td>NEW
</td>
</tr>
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<th>Severity</th>
<td>normal
</td>
</tr>
<tr>
<th>Priority</th>
<td>P
</td>
</tr>
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<th>Component</th>
<td>-New Bugs
</td>
</tr>
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<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>cameron.mcinally@nyu.edu
</td>
</tr>
<tr>
<th>CC</th>
<td>llvmbugs@cs.uiuc.edu
</td>
</tr>
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<th>Classification</th>
<td>Unclassified
</td>
</tr></table>
<p>
<div>
<pre>Created <span class=""><a href="attachment.cgi?id=10346" name="attach_10346" title="Tarball of preprocessed source, run script, and backtrace.">attachment 10346</a> <a href="attachment.cgi?id=10346&action=edit" title="Tarball of preprocessed source, run script, and backtrace.">[details]</a></span>
Tarball of preprocessed source, run script, and backtrace.
When compiling this function at -O2, Clang issues an assert:
int kung( float a, double b ) {
return (a == a) & (b == b);
}
The assert is:
Assertion failed: (getOperand(0)->getType() == getOperand(1)->getType() &&
"Both operands to FCmp instruction are not of the same type!"), function
FCmpInst, file /Users/xkrebstarx/clang/llvm/include/llvm/IR/Instructions.h,
line 1117.
We begin with a float "a" and double "b":
<span class="quote">> (fcmp oeq a, a) & (fcmp oeq b, b) </span >
After canonicalization in InstCombine, we end up with the expression:
<span class="quote">> (fcmp ord a, 0.0) & (fcmp ord b, 0.0)</span >
The bug manifest is in InstCombiner::FoldAndOfFCmps(FCmpInst *LHS, FCmpInst
*RHS), when trying to perform this transformation:
<span class="quote">> (fcmp ord x, c) & (fcmp ord y, c) -> (fcmp ord x, y)</span >
This is all fine, except that the FCmpInst constructor in the IRBuilder
requires that both operands to the new fcmp are the same type, which they are
not.</pre>
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