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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - [InstCombine] Failure to simplify 2 icmp and select after rL369840"
href="https://bugs.llvm.org/show_bug.cgi?id=43261">43261</a>
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<th>Summary</th>
<td>[InstCombine] Failure to simplify 2 icmp and select after rL369840
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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>Linux
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<th>Status</th>
<td>NEW
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<th>Severity</th>
<td>enhancement
</td>
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<th>Priority</th>
<td>P
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<th>Component</th>
<td>Scalar Optimizations
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
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<th>Reporter</th>
<td>denis.bakhvalov@intel.com
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<th>CC</th>
<td>llvm-bugs@lists.llvm.org
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<p>
<div>
<pre>Before rL369840 we simplified the following case:
%tmp = add i32 %i, -3
%tmp1 = icmp ult i32 %tmp, 2
%cmp2 = icmp eq i32 %i, 5
%phitmp = zext i1 %cmp2 to i32
%tmp2 = select i1 %tmp1, i32 1, i32 %phitmp
to
%tmp = add i32 %i, -3
%0 = icmp ult i32 %tmp, 3
%tmp2 = zext i1 %0 to i32
Proof: <a href="https://rise4fun.com/Alive/dhoe">https://rise4fun.com/Alive/dhoe</a>
There were 4 steps of simplification:
step1&2: <a href="https://rise4fun.com/Alive/82o">https://rise4fun.com/Alive/82o</a>
step3&4: <a href="https://rise4fun.com/Alive/Izp">https://rise4fun.com/Alive/Izp</a>
After rL369840 we invert the first comparison (icmp ult -> ugt, as a result of
tryToReuseConstantFromSelectInComparison() ) and instcombine takes another
route.
I'm not sure if it is a duplicate of recently created bug for InstCombine.</pre>
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