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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - [InstCombine] try to thread binop through select-of-constants"
href="https://bugs.llvm.org/show_bug.cgi?id=52406">52406</a>
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<th>Summary</th>
<td>[InstCombine] try to thread binop through select-of-constants
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<th>Product</th>
<td>libraries
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<th>Version</th>
<td>trunk
</td>
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<th>Hardware</th>
<td>PC
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<th>OS</th>
<td>All
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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>Scalar Optimizations
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
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<th>Reporter</th>
<td>spatel+llvm@rotateright.com
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<th>CC</th>
<td>llvm-bugs@lists.llvm.org
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<pre>Forking this off from <a class="bz_bug_link
bz_status_CONFIRMED "
title="CONFIRMED - [InstCombine] fold multiply and equality compare with constant"
href="show_bug.cgi?id=52402">bug 52402</a> (it doesn't involve multiplication magic):
define i8 @src(i8 %x, i1 %b) {
%t4 = and i8 %x, 8
%t7 = select i1 %b, i8 7, i8 0
%t8 = shl i8 %t4, %t7
ret i8 %t8
}
define i8 @tgt(i8 %x, i1 %b) {
%t4 = and i8 %x, 8
%r = select i1 %b, i8 0, i8 %t4
ret i8 %r
}
<a href="https://alive2.llvm.org/ce/z/zw2px6">https://alive2.llvm.org/ce/z/zw2px6</a>
It probably does not make sense in general to pull the binop into the select -
we need to be able to simplify both sides of the select to justify this. This
might involve checking if one of the select operands is an identity constant
(ConstantExpr::getBinOpIdentity).</pre>
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