glibc/SOURCES/glibc-upstream-2.34-287.patch

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2022-11-15 07:04:49 +00:00
commit 3c87383a20daff9a230439e31b778716bfed4d8b
Author: Noah Goldstein <goldstein.w.n@gmail.com>
Date: Mon Jun 6 21:11:34 2022 -0700
x86: Shrink code size of memchr-evex.S
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 56da3fe1dd075285fa8186d44b3c28e68c687e62)
diff --git a/sysdeps/x86_64/multiarch/memchr-evex.S b/sysdeps/x86_64/multiarch/memchr-evex.S
index 4d0ed6d136f099e1..68381c99a4948134 100644
--- a/sysdeps/x86_64/multiarch/memchr-evex.S
+++ b/sysdeps/x86_64/multiarch/memchr-evex.S
@@ -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
+ .p2align 4
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
+ /* 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
-# 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
# 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