https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105072
Bug ID: 105072
Summary: Miss optimization for pmovzxbq.
Product: gcc
Version: 12.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: target
Assignee: unassigned at gcc dot gnu.org
Reporter: crazylht at gmail dot com
Target Milestone: ---
This is quoted from PR105066:
It's also essential that these loads fold efficiently into memory source
operands for PMOVZX; pmovzxbq is one of the major use-cases for a 16-bit load.
That may be a separate bug, IDK
https://godbolt.org/z/3a9T55n3q shows _mm_cvtepu8_epi32(_mm_loadu_si32(p)) does
fold a 32-bit memory source operand nicely to pmovzxbd (%rdi), %xmm0 which can
micro-fuse into a single uop on Intel CPUs (for the 128-bit destination
version, not YMM), but disaster with 16-bit loads:
__m128i pmovzxbq(void *p){
return _mm_cvtepu8_epi64(_mm_loadu_si16(p));
}
pmovzxbq(void*): # -O3 -msse4.1 -mtune=haswell
pxor %xmm0, %xmm0 # 1 uop
pinsrw $0, (%rdi), %xmm0 # 2 uops, one for shuffle port
pmovzxbq %xmm0, %xmm0 # 1 uop for the same shuffle port
ret
(_mm_cvtepu8_epi64 requires SSE4.1 so there's no interaction with the
-mno-sse4.1 implementation of the load.)
