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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - _mm_adds_epu8 and _mm_subs_epu8 with constant operand don't generate paddusb/psubusb"
href="https://bugs.llvm.org/show_bug.cgi?id=40053">40053</a>
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<th>Summary</th>
<td>_mm_adds_epu8 and _mm_subs_epu8 with constant operand don't generate paddusb/psubusb
</td>
</tr>
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<th>Product</th>
<td>libraries
</td>
</tr>
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<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
</td>
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<th>Status</th>
<td>NEW
</td>
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<th>Severity</th>
<td>enhancement
</td>
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<th>Priority</th>
<td>P
</td>
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<th>Component</th>
<td>Backend: X86
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
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<th>Reporter</th>
<td>amanieu@gmail.com
</td>
</tr>
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<th>CC</th>
<td>craig.topper@gmail.com, llvm-bugs@lists.llvm.org, llvm-dev@redking.me.uk, spatel+llvm@rotateright.com
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</tr></table>
<p>
<div>
<pre>It seems that instruction selection can't see through the transformations done
on the constants.
This is a regression from 7.0 where these intrinsics would compile to a single
instruction.
Source:
#include <emmintrin.h>
__m128i test_add(__m128i x) {
__m128i c = _mm_set1_epi8(1);
return _mm_adds_epu8(x, c);
}
__m128i test_sub(__m128i x) {
__m128i c = _mm_set1_epi8(1);
return _mm_subs_epu8(x, c);
}
Assembly (trunk):
test_add:
pcmpeqd xmm1, xmm1
movdqa xmm2, xmm0
psubb xmm2, xmm1
pcmpeqb xmm0, xmm1
por xmm0, xmm2
ret
.LCPI1_0:
.zero 16,1
test_sub:
pmaxub xmm0, xmmword ptr [rip + .LCPI1_0]
pcmpeqd xmm1, xmm1
paddb xmm0, xmm1
ret
Assembly (7.0):
.LCPI0_0:
.zero 16,1
test_add:
paddusb .LCPI0_0(%rip), %xmm0
retq
.LCPI1_0:
.zero 16,1
test_sub:
psubusb .LCPI1_0(%rip), %xmm0
retq</pre>
</div>
</p>
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