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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - [x86, SSE] high elements of vectors are not ignored as expected"
href="https://llvm.org/bugs/show_bug.cgi?id=24523">24523</a>
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<th>Summary</th>
<td>[x86, SSE] high elements of vectors are not ignored as expected
</td>
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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
</td>
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<th>Status</th>
<td>NEW
</td>
</tr>
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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>Backend: X86
</td>
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
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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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<th>Classification</th>
<td>Unclassified
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</tr></table>
<p>
<div>
<pre>Noticed in <a class="bz_bug_link
bz_status_NEW "
title="NEW --- - [x86] fmax/fmin calls should be optimized and inlined"
href="show_bug.cgi?id=24475">bug 24475</a>: we're not eliminating meaningless ops on the higher
elements of vectors.
$ cat isnan.ll
define float @my_sse_isnan(float %f1) {
%v1 = insertelement <4 x float> undef, float %f1, i32 0
; this shouldn't affect anything; we only care about the low (scalar) element
%v2 = insertelement <4 x float> %v1, float 0.0, i32 1
%cmpss = tail call <4 x float> @llvm.x86.sse.cmp.ss(<4 x float> %v2, <4 x
float> %v2, i8 3)
%ext = extractelement <4 x float> %cmpss, i32 0
ret float %ext
}
$ ./llc -o - isnan.ll
...
xorps %xmm1, %xmm1
movss %xmm0, %xmm1 ## xmm1 = xmm0[0],xmm1[1,2,3]
cmpunordss %xmm1, %xmm1
movaps %xmm1, %xmm0
retq
I was expecting that to be reduced to:
cmpunordss %xmm0, %xmm0
retq</pre>
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