https://llvm.org/bugs/show_bug.cgi?id=31364
Bug ID: 31364
Summary: [x86] Bad lowering of _mm_shuffle_epi8
Product: libraries
Version: trunk
Hardware: PC
OS: Windows NT
Status: NEW
Severity: normal
Priority: P
Component: Backend: X86
Assignee: unassignedb...@nondot.org
Reporter: efrie...@codeaurora.org
CC: craig.top...@gmail.com, llvm-bugs@lists.llvm.org,
llvm-...@redking.me.uk
Classification: Unclassified
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.
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