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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - [InstCombine] icmp slt 0 optimization hinders more optimization"
href="https://llvm.org/bugs/show_bug.cgi?id=28238">28238</a>
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<th>Summary</th>
<td>[InstCombine] icmp slt 0 optimization hinders more optimization
</td>
</tr>
<tr>
<th>Product</th>
<td>libraries
</td>
</tr>
<tr>
<th>Version</th>
<td>trunk
</td>
</tr>
<tr>
<th>Hardware</th>
<td>PC
</td>
</tr>
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<th>OS</th>
<td>All
</td>
</tr>
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<th>Status</th>
<td>NEW
</td>
</tr>
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<th>Severity</th>
<td>normal
</td>
</tr>
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<th>Priority</th>
<td>P
</td>
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<th>Component</th>
<td>Scalar Optimizations
</td>
</tr>
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
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<th>Reporter</th>
<td>spatel+llvm@rotateright.com
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
</tr>
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<th>Classification</th>
<td>Unclassified
</td>
</tr></table>
<p>
<div>
<pre>Spinning this off from <a class="bz_bug_link
bz_status_RESOLVED bz_closed"
title="RESOLVED FIXED - Optimizer doesn't simplify obvious contradiction"
href="show_bug.cgi?id=27869">bug 27869</a> (and may have a different solution than <a class="bz_bug_link
bz_status_NEW "
title="NEW --- - InstCombine greediness blocks subsequent optimizations"
href="show_bug.cgi?id=28221">bug
28221</a>):
int f(int i) {
return (i == 0) & (i >> 31);
}
'i' can't be 0 and have a bit set, so this should return 0.
$ ./clang -O1 sneaky_icmp.c -S -o - -emit-llvm
...
define i32 @f(i32 %i) {
%cmp = icmp eq i32 %i, 0
%conv = zext i1 %cmp to i32
%shr = ashr i32 %i, 31
%and = and i32 %conv, %shr
ret i32 %and
}</pre>
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</p>
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