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x86: Move and slightly improve memset_erms

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Implementation wise:
    1. Remove the VZEROUPPER as memset_{impl}_unaligned_erms does not
       use the L(stosb) label that was previously defined.

    2. Don't give the hotpath (fallthrough) to zero size.

Code positioning wise:

Move memset_{chk}_erms to its own file.  Leaving it in between the
memset_{impl}_unaligned both adds unnecessary complexity to the
file and wastes space in a relatively hot cache section.
This commit is contained in:
Noah Goldstein 2022-06-29 16:07:05 -07:00
parent 2a1099020c
commit 4a3f29e7e4
3 changed files with 45 additions and 31 deletions
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1
sysdeps/x86_64/multiarch/Makefile
View file

@ -29,6 +29,7 @@ sysdep_routines += \
memset-avx2-unaligned-erms-rtm \
memset-avx512-no-vzeroupper \
memset-avx512-unaligned-erms \
memset-erms \
memset-evex-unaligned-erms \
memset-sse2-unaligned-erms \
rawmemchr-avx2 \

44
sysdeps/x86_64/multiarch/memset-erms.S Normal file
View file

@ -0,0 +1,44 @@
/* memset implement with rep stosb
Copyright (C) 2022 Free Software Foundation, Inc.
This file is part of the GNU C Library.
The GNU C Library is free software; you can redistribute it and/or
modify it under the terms of the GNU Lesser General Public
License as published by the Free Software Foundation; either
version 2.1 of the License, or (at your option) any later version.
The GNU C Library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public
License along with the GNU C Library; if not, see
<https://www.gnu.org/licenses/>. */
#include <sysdep.h>
#if defined USE_MULTIARCH && IS_IN (libc)
.text
ENTRY (__memset_chk_erms)
cmp %RDX_LP, %RCX_LP
jb HIDDEN_JUMPTARGET (__chk_fail)
END (__memset_chk_erms)
/* Only used to measure performance of REP STOSB. */
ENTRY (__memset_erms)
/* Skip zero length. */
test %RDX_LP, %RDX_LP
jz L(stosb_return_zero)
mov %RDX_LP, %RCX_LP
movzbl %sil, %eax
mov %RDI_LP, %RDX_LP
rep stosb
mov %RDX_LP, %RAX_LP
ret
L(stosb_return_zero):
movq %rdi, %rax
ret
END (__memset_erms)
#endif

31
sysdeps/x86_64/multiarch/memset-vec-unaligned-erms.S
View file

@ -156,37 +156,6 @@ L(entry_from_wmemset):
#if defined USE_MULTIARCH && IS_IN (libc)
END (MEMSET_SYMBOL (__memset, unaligned))
# if VEC_SIZE == 16
ENTRY (__memset_chk_erms)
cmp %RDX_LP, %RCX_LP
jb HIDDEN_JUMPTARGET (__chk_fail)
END (__memset_chk_erms)
/* Only used to measure performance of REP STOSB. */
ENTRY (__memset_erms)
/* Skip zero length. */
test %RDX_LP, %RDX_LP
jnz L(stosb)
movq %rdi, %rax
ret
# else
/* Provide a hidden symbol to debugger. */
.hidden MEMSET_SYMBOL (__memset, erms)
ENTRY (MEMSET_SYMBOL (__memset, erms))
# endif
L(stosb):
mov %RDX_LP, %RCX_LP
movzbl %sil, %eax
mov %RDI_LP, %RDX_LP
rep stosb
mov %RDX_LP, %RAX_LP
VZEROUPPER_RETURN
# if VEC_SIZE == 16
END (__memset_erms)
# else
END (MEMSET_SYMBOL (__memset, erms))
# endif
# if defined SHARED && IS_IN (libc)
ENTRY_CHK (MEMSET_CHK_SYMBOL (__memset_chk, unaligned_erms))
cmp %RDX_LP, %RCX_LP