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x86: Shrink code size of memchr-evex.S

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This is not meant as a performance optimization. The previous code was
far to liberal in aligning targets and wasted code size unnecissarily.

The total code size saving is: 64 bytes

There are no non-negligible changes in the benchmarks.
Geometric Mean of all benchmarks New / Old: 1.000

Full xcheck passes on x86_64.
Reviewed-by: H.J. Lu <hjl.tools@gmail.com>

(cherry picked from commit 56da3fe1dd)
This commit is contained in:
Noah Goldstein 2022-06-06 21:11:34 -07:00 committed by Sunil K Pandey
parent a910d7e164
commit 3c87383a20
1 changed files with 26 additions and 22 deletions
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48
sysdeps/x86_64/multiarch/memchr-evex.S
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@ -88,7 +88,7 @@
# define PAGE_SIZE 4096
.section SECTION(.text),"ax",@progbits
ENTRY (MEMCHR)
ENTRY_P2ALIGN (MEMCHR, 6)
# ifndef USE_AS_RAWMEMCHR
/* Check for zero length. */
test %RDX_LP, %RDX_LP
@ -131,22 +131,24 @@ L(zero):
xorl %eax, %eax
ret
.p2align 5
L(first_vec_x0):
/* Check if first match was before length. */
tzcntl %eax, %eax
xorl %ecx, %ecx
cmpl %eax, %edx
leaq (%rdi, %rax, CHAR_SIZE), %rax
cmovle %rcx, %rax
ret
# else
/* NB: first_vec_x0 is 17 bytes which will leave
cross_page_boundary (which is relatively cold) close enough
to ideal alignment. So only realign L(cross_page_boundary) if
rawmemchr. */
.p2align 4
L(first_vec_x0):
/* Check if first match was before length. NB: tzcnt has false data-
dependency on destination. eax already had a data-dependency on esi
so this should have no affect here. */
tzcntl %eax, %esi
# ifdef USE_AS_WMEMCHR
leaq (%rdi, %rsi, CHAR_SIZE), %rdi
# else
addq %rsi, %rdi
# endif
xorl %eax, %eax
cmpl %esi, %edx
cmovg %rdi, %rax
ret
# endif
.p2align 4
L(cross_page_boundary):
/* Save pointer before aligning as its original value is
necessary for computer return address if byte is found or
@ -400,10 +402,14 @@ L(last_2x_vec):
L(zero_end):
ret
L(set_zero_end):
xorl %eax, %eax
ret
.p2align 4
L(first_vec_x1_check):
tzcntl %eax, %eax
/* eax must be non-zero. Use bsfl to save code size. */
bsfl %eax, %eax
/* Adjust length. */
subl $-(CHAR_PER_VEC * 4), %edx
/* Check if match within remaining length. */
@ -412,9 +418,6 @@ L(first_vec_x1_check):
/* NB: Multiply bytes by CHAR_SIZE to get the wchar_t count. */
leaq VEC_SIZE(%rdi, %rax, CHAR_SIZE), %rax
ret
L(set_zero_end):
xorl %eax, %eax
ret
.p2align 4
L(loop_4x_vec_end):
@ -464,7 +467,7 @@ L(loop_4x_vec_end):
# endif
ret
.p2align 4
.p2align 4,, 10
L(last_vec_x1_return):
tzcntl %eax, %eax
# if defined USE_AS_WMEMCHR || RET_OFFSET != 0
@ -496,6 +499,7 @@ L(last_vec_x3_return):
# endif
# ifndef USE_AS_RAWMEMCHR
.p2align 4,, 5
L(last_4x_vec_or_less_cmpeq):
VPCMP $0, (VEC_SIZE * 5)(%rdi), %YMMMATCH, %k0
kmovd %k0, %eax
@ -546,7 +550,7 @@ L(last_4x_vec):
# endif
andl %ecx, %eax
jz L(zero_end2)
tzcntl %eax, %eax
bsfl %eax, %eax
leaq (VEC_SIZE * 4)(%rdi, %rax, CHAR_SIZE), %rax
L(zero_end2):
ret
@ -562,6 +566,6 @@ L(last_vec_x3):
leaq (VEC_SIZE * 3)(%rdi, %rax, CHAR_SIZE), %rax
ret
# endif
/* 7 bytes from next cache line. */
END (MEMCHR)
#endif