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<base href="https://bugs.llvm.org/">
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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - [InstCombine] hoist vector cast above splat as scalar cast?"
href="https://bugs.llvm.org/show_bug.cgi?id=32865">32865</a>
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<th>Summary</th>
<td>[InstCombine] hoist vector cast above splat as scalar cast?
</td>
</tr>
<tr>
<th>Product</th>
<td>libraries
</td>
</tr>
<tr>
<th>Version</th>
<td>trunk
</td>
</tr>
<tr>
<th>Hardware</th>
<td>PC
</td>
</tr>
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<th>OS</th>
<td>All
</td>
</tr>
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<th>Status</th>
<td>NEW
</td>
</tr>
<tr>
<th>Severity</th>
<td>enhancement
</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
</td>
</tr>
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<th>Reporter</th>
<td>spatel+llvm@rotateright.com
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
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<pre>Forking this off from <a class="bz_bug_link
bz_status_NEW "
title="NEW - Poor AVX code generation on 8xi1 masks"
href="show_bug.cgi?id=14657">bug 14657</a>.
One of these should be canonical:
define <8 x i32> @sext_last(i16 %x) {
%ins = insertelement <8 x i16> undef, i16 %x, i32 0
%splat = shufflevector <8 x i16> %ins, <8 x i16> undef, <8 x i32>
zeroinitializer
%sext = sext <8 x i16> %splat to <8 x i32>
ret <8 x i32> %sext
}
define <8 x i32> @sext_first(i16 %x) {
%sext = sext i16 %x to i32
%ins = insertelement <8 x i32> undef, i32 %sext, i32 0
%splat = shufflevector <8 x i32> %ins, <8 x i32> undef, <8 x i32>
zeroinitializer
ret <8 x i32> %splat
}
We may need to prepare the backend to expect the canonical pattern to avoid
regressions. Eg, with AVX1, there's a big difference in codegen:
$ ./llc -o - splatsext.ll -mattr=avx
_sext_last: ## @sext_last
vmovd %edi, %xmm0
vpshuflw $0, %xmm0, %xmm0 ## xmm0 = xmm0[0,0,0,0,4,5,6,7]
vpshufd $80, %xmm0, %xmm0 ## xmm0 = xmm0[0,0,1,1]
vpmovsxwd %xmm0, %xmm1
vpshufd $78, %xmm0, %xmm0 ## xmm0 = xmm0[2,3,0,1]
vpmovsxwd %xmm0, %xmm0
vinsertf128 $1, %xmm0, %ymm1, %ymm0
_sext_first: ## @sext_first
movswl %di, %eax
vmovd %eax, %xmm0
vpshufd $0, %xmm0, %xmm0 ## xmm0 = xmm0[0,0,0,0]
vinsertf128 $1, %xmm0, %ymm0, %ymm0</pre>
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