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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - Missing pattern in instcombine"
href="https://llvm.org/bugs/show_bug.cgi?id=30794">30794</a>
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<th>Summary</th>
<td>Missing pattern in instcombine
</td>
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<th>Product</th>
<td>new-bugs
</td>
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<th>Version</th>
<td>3.9
</td>
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<th>Hardware</th>
<td>PC
</td>
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<th>OS</th>
<td>All
</td>
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<th>Status</th>
<td>NEW
</td>
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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>new bugs
</td>
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
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<th>Reporter</th>
<td>mehdi.amini@apple.com
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
</tr>
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<th>Classification</th>
<td>Unclassified
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</tr></table>
<p>
<div>
<pre>Instcombine is turning `v < 0x4000000000000000 && v >= -0x4000000000000000`
into `v + 0x4000000000000000 > -1`.
This alone is fine, but is inhibiting other combine. For instance when v is
`sext i32 to i64`, the individual comparison are being folded away:
icmp sgt i64 (sext i32 %0 to i64 ), -4611686018427387905.
And
icmp slt i64 (sext i32 %0 to i64 ), 4611686018427387904
However if the comparison are first combined, we get this pattern:
%2 = sext i32 %0 to i64
%3 = add i64 %2, 4611686018427387904
That instcombine does not reduce further.
(See also here:
<a href="http://stackoverflow.com/questions/40203127/why-doesnt-clang-llvm-optimize-this">http://stackoverflow.com/questions/40203127/why-doesnt-clang-llvm-optimize-this</a>
)</pre>
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</p>
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