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<base href="https://llvm.org/bugs/" />
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<body><table border="1" cellspacing="0" cellpadding="8">
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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - [x86] Bad lowering of _mm_shuffle_epi8"
href="https://llvm.org/bugs/show_bug.cgi?id=31364">31364</a>
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<th>Summary</th>
<td>[x86] Bad lowering of _mm_shuffle_epi8
</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>
<tr>
<th>OS</th>
<td>Windows NT
</td>
</tr>
<tr>
<th>Status</th>
<td>NEW
</td>
</tr>
<tr>
<th>Severity</th>
<td>normal
</td>
</tr>
<tr>
<th>Priority</th>
<td>P
</td>
</tr>
<tr>
<th>Component</th>
<td>Backend: X86
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>efriedma@codeaurora.org
</td>
</tr>
<tr>
<th>CC</th>
<td>craig.topper@gmail.com, llvm-bugs@lists.llvm.org, llvm-dev@redking.me.uk
</td>
</tr>
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<th>Classification</th>
<td>Unclassified
</td>
</tr></table>
<p>
<div>
<pre>Testcase:
#include <immintrin.h>
__m128i pshufb_const(char *a, char *b) {
const __m128i x = _mm_insert_epi8(_mm_insert_epi8(_mm_setzero_si128(), *a,
0), *b, 1);
__m128i m = _mm_set_epi8(0, 0, 0, 1, 1, 1, 1, 1, 3, 1, 1, 1, 1, 1, 1, 1);
return _mm_shuffle_epi8(x, m);
}
__m128i pshufb_var(char *a, char *b, __m128i m) {
const __m128i x = _mm_insert_epi8(_mm_insert_epi8(_mm_setzero_si128(), *a,
0), *b, 1);
return _mm_shuffle_epi8(x, m);
}
Generated code for pshufb_const (clang -O2 -mavx):
movzbl (%rsi), %eax
vmovd %eax, %xmm0
vpinsrb $1, %eax, %xmm0, %xmm0
vpinsrb $2, %eax, %xmm0, %xmm0
vpinsrb $3, %eax, %xmm0, %xmm0
vpinsrb $4, %eax, %xmm0, %xmm0
vpinsrb $5, %eax, %xmm0, %xmm0
vpinsrb $6, %eax, %xmm0, %xmm0
xorl %ecx, %ecx
vpinsrb $7, %ecx, %xmm0, %xmm0
vpinsrb $8, %eax, %xmm0, %xmm0
vpinsrb $9, %eax, %xmm0, %xmm0
vpinsrb $10, %eax, %xmm0, %xmm0
vpinsrb $11, %eax, %xmm0, %xmm0
vpinsrb $12, %eax, %xmm0, %xmm0
movzbl (%rdi), %eax
vpinsrb $13, %eax, %xmm0, %xmm0
vpinsrb $14, %eax, %xmm0, %xmm0
vpinsrb $15, %eax, %xmm0, %xmm0
retq
Generated code for pshufb_var (clang -O2 -mavx):
vpxor %xmm1, %xmm1, %xmm1
vpinsrb $0, (%rdi), %xmm1, %xmm1
vpinsrb $1, (%rsi), %xmm1, %xmm1
vpshufb %xmm0, %xmm1, %xmm0
retq
SelectionDAG is throwing away the shuffle in favor of a BUILD_VECTOR, and
failing to recover in a reasonable manner later on.</pre>
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