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amd64: align memset buffers to 16 bytes before using rep stos

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Both Intel manual and Agner Fog's docs suggest aligning to 16.

See the review for benchmark results.

Reviewed by:	kib (previous version)
Sponsored by:	The FreeBSD Foundation
Differential Revision:	https://reviews.freebsd.org/D17661
This commit is contained in:
mjg 2018-11-08 15:12:36 +00:00
parent 35c107709e
commit 4f16b562cf
1 changed files with 16 additions and 2 deletions
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18
sys/amd64/amd64/support.S
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@ -515,24 +515,38 @@ END(memcpy_erms)
1256:
movq %rdi,%r9
movq %r10,%rax
testl $15,%edi
jnz 3f
1:
.if \erms == 1
rep
stosb
movq %r9,%rax
.else
movq %rcx,%rdx
shrq $3,%rcx
rep
stosq
movq %r9,%rax
andl $7,%edx
jnz 1f
jnz 2f
POP_FRAME_POINTER
ret
1:
2:
movq %r10,-8(%rdi,%rdx)
.endif
POP_FRAME_POINTER
ret
ALIGN_TEXT
3:
movq %r10,(%rdi)
movq %r10,8(%rdi)
movq %rdi,%r8
andq $15,%r8
leaq -16(%rcx,%r8),%rcx
neg %r8
leaq 16(%rdi,%r8),%rdi
jmp 1b
.endm
ENTRY(memset_std)