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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - [InstCombine] Select based on sign bit condition not canonicalized"
href="https://bugs.llvm.org/show_bug.cgi?id=44521">44521</a>
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<th>Summary</th>
<td>[InstCombine] Select based on sign bit condition not canonicalized
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<th>Product</th>
<td>libraries
</td>
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<tr>
<th>Version</th>
<td>trunk
</td>
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<th>Hardware</th>
<td>All
</td>
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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>nikita.ppv@gmail.com
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<th>CC</th>
<td>llvm-bugs@lists.llvm.org
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<p>
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<pre>The following stay invariant under -instcombine:
define i8 @sign_select_scalar_sgt(i8 %cond, i8 %tval, i8 %fval) {
%cmp = icmp sgt i8 %cond, -1
%res = select i1 %cmp, i8 %fval, i8 %tval
ret i8 %res
}
define i8 @sign_select_scalar_slt(i8 %cond, i8 %tval, i8 %fval) {
%cmp = icmp slt i8 %cond, 0
%res = select i1 %cmp, i8 %tval, i8 %fval
ret i8 %res
}
define <4 x i8> @sign_select_vec_sgt(<4 x i8> %cond, <4 x i8> %tval, <4 x i8>
%fval) {
%cmp = icmp sgt <4 x i8> %cond, <i8 -1, i8 -1, i8 -1, i8 -1>
%res = select <4 x i1> %cmp, <4 x i8> %fval, <4 x i8> %tval
ret <4 x i8> %res
}
define <4 x i8> @sign_select_vec_slt(<4 x i8> %cond, <4 x i8> %tval, <4 x i8>
%fval) {
%cmp = icmp slt <4 x i8> %cond, zeroinitializer
%res = select <4 x i1> %cmp, <4 x i8> %tval, <4 x i8> %fval
ret <4 x i8> %res
}
I would expect that this gets canonicalized one way or another (<0 probably).
Noticed this when some InstCombine worklist order changes resulted in the above
patterns getting flipped in places.</pre>
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