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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - [PowerPC] inefficient codegen for select with negative constant"
href="https://bugs.llvm.org/show_bug.cgi?id=32105">32105</a>
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<th>Summary</th>
<td>[PowerPC] inefficient codegen for select with negative constant
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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>All
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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>Backend: PowerPC
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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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</tr>
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<th>CC</th>
<td>llvm-bugs@lists.llvm.org
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<p>
<div>
<pre>This is a simpler example than:
<a href="https://reviews.llvm.org/D30502">https://reviews.llvm.org/D30502</a>
define i32 @sel_with_negative_constant(i1 %cond) {
%sel = select i1 %cond, i32 -32, i32 2
ret i32 %sel
}
...the extension to i64 return type seems to make the simple -32 constant turn
into:
$ ./llc -o - ppcshl.ll -mtriple=powerpc64le
...
lis 4, 2047 ; 0x07FF (top 5 bits are clear)
andi. 3, 3, 1
ori 3, 4, 65535 0xFFFF
li 4, 2
sldi 3, 3, 5 ; 0x00000000FFFFFFE0 (-32 with top 32 bits cleared?)
isel 3, 3, 4, 1
blr
I'm working on DAG patches that would eliminate the isel for
select-of-constants, but the extension to i64 for negative constants seems to
be interfering on PPC64. See:
<a href="https://reviews.llvm.org/D30180">https://reviews.llvm.org/D30180</a>
...tests with -1 should have folded to almost nothing.</pre>
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