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<base href="https://llvm.org/bugs/" />
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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - [InstCombine] reduce insertelements of constants to shufflevector"
href="https://llvm.org/bugs/show_bug.cgi?id=29124">29124</a>
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<th>Summary</th>
<td>[InstCombine] reduce insertelements of constants to shufflevector
</td>
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<th>Product</th>
<td>libraries
</td>
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<th>Version</th>
<td>trunk
</td>
</tr>
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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>Scalar Optimizations
</td>
</tr>
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
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</tr>
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<th>Reporter</th>
<td>spatel+llvm@rotateright.com
</td>
</tr>
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<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
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<th>Classification</th>
<td>Unclassified
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</tr></table>
<p>
<div>
<pre>If we're inserting more than one constant into a vector:
define <4 x float> @foo(<4 x float> %x) {
%ins1 = insertelement <4 x float> %x, float 1.0, i32 1
%ins2 = insertelement <4 x float> %ins1, float 2.0, i32 2
ret <4 x float> %ins2
}
InstCombine could reduce that to a shufflevector:
define <4 x float> @goo(<4 x float> %x) {
%shuf = shufflevector <4 x float> %x, <4 x float> <float undef, float 1.0,
float 2.0, float undef>, <4 x i32><i32 0, i32 5, i32 6, i32 3>
ret <4 x float> %shuf
}
This can improve codegen (possibly a separate bug that the backend doesn't do
this too?):
$ ./llc -o - min.ll -mattr=avx
LCPI0_0:
.long 1065353216 ## float 1
LCPI0_1:
.long 1073741824 ## float 2
## BB#0:
vinsertps $16, LCPI0_0(%rip), %xmm0, %xmm0
vinsertps $32, LCPI0_1(%rip), %xmm0, %xmm0
retq
LCPI1_0:
.space 4
.long 1065353216 ## float 1
.long 1073741824 ## float 2
.space 4
## BB#0:
vblendps $6, LCPI1_0(%rip), %xmm0, %xmm0
retq</pre>
</div>
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