https://llvm.org/bugs/show_bug.cgi?id=25554
Bug ID: 25554
Summary: [x86, SSE] rematerialized existing constants
Product: libraries
Version: trunk
Hardware: PC
OS: All
Status: NEW
Severity: normal
Priority: P
Component: Backend: X86
Assignee: unassignedb...@nondot.org
Reporter: spatel+l...@rotateright.com
CC: llvm-bugs@lists.llvm.org
Classification: Unclassified
$ cat bad_vmov.c
#include <smmintrin.h>
void foo(__m128i v0, __m128i v1, int *ret) {
__m128i one0 = _mm_set_epi32(0,0,0,1);
__m128i one1 = _mm_set_epi32(0,1,0,0);
if ( _mm_testz_si128(v0, one0) ) ret[0] = 10;
if ( _mm_testz_si128(v1, one1) ) ret[1] = 20;
}
Using:
./clang -v
clang version 3.8.0 (trunk 253253)
Target: x86_64-apple-darwin15.0.0
Thread model: posix
$ ./clang -O2 -S -o - bad_vmov.c -fomit-frame-pointer -msse4.1
...
movl $1, %eax
movd %rax, %xmm2
ptest %xmm2, %xmm0
jne LBB0_2
movl $10, (%rdi)
LBB0_2:
movl $1, %eax <--- $1 was already in %eax
movd %rax, %xmm0 <--- and %xmm2 already has this value
pslldq $8, %xmm0
ptest %xmm0, %xmm1
jne LBB0_4
movl $20, 4(%rdi)
LBB0_4:
retq
--
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