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glibc/SOURCES/glibc-RHEL-15696-89.patch

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From ec285ea90415458225623ddc0492ae3f705af043 Mon Sep 17 00:00:00 2001
From: Noah Goldstein <goldstein.w.n@gmail.com>
Date: Wed, 23 Mar 2022 16:57:18 -0500
Subject: [PATCH] x86: Code cleanup in strchr-evex and comment justifying
branch
Content-type: text/plain; charset=UTF-8
Small code cleanup for size: -81 bytes.
Add comment justifying using a branch to do NULL/non-null return.
All string/memory tests pass and no regressions in benchtests.
geometric_mean(N=20) of all benchmarks New / Original: .985
Reviewed-by: H.J. Lu <hjl.tools@gmail.com>
---
sysdeps/x86_64/multiarch/strchr-evex.S | 146 ++++++++++++++-----------
1 file changed, 80 insertions(+), 66 deletions(-)
diff --git a/sysdeps/x86_64/multiarch/strchr-evex.S b/sysdeps/x86_64/multiarch/strchr-evex.S
index 7f9d4ee4..0b49e0ac 100644
--- a/sysdeps/x86_64/multiarch/strchr-evex.S
+++ b/sysdeps/x86_64/multiarch/strchr-evex.S
@@ -30,6 +30,7 @@
# ifdef USE_AS_WCSCHR
# define VPBROADCAST vpbroadcastd
# define VPCMP vpcmpd
+# define VPTESTN vptestnmd
# define VPMINU vpminud
# define CHAR_REG esi
# define SHIFT_REG ecx
@@ -37,6 +38,7 @@
# else
# define VPBROADCAST vpbroadcastb
# define VPCMP vpcmpb
+# define VPTESTN vptestnmb
# define VPMINU vpminub
# define CHAR_REG sil
# define SHIFT_REG edx
@@ -61,13 +63,11 @@
# define CHAR_PER_VEC (VEC_SIZE / CHAR_SIZE)
.section .text.evex,"ax",@progbits
-ENTRY (STRCHR)
+ENTRY_P2ALIGN (STRCHR, 5)
/* Broadcast CHAR to YMM0. */
VPBROADCAST %esi, %YMM0
movl %edi, %eax
andl $(PAGE_SIZE - 1), %eax
- vpxorq %XMMZERO, %XMMZERO, %XMMZERO
-
/* Check if we cross page boundary with one vector load.
Otherwise it is safe to use an unaligned load. */
cmpl $(PAGE_SIZE - VEC_SIZE), %eax
@@ -81,49 +81,35 @@ ENTRY (STRCHR)
vpxorq %YMM1, %YMM0, %YMM2
VPMINU %YMM2, %YMM1, %YMM2
/* Each bit in K0 represents a CHAR or a null byte in YMM1. */
- VPCMP $0, %YMMZERO, %YMM2, %k0
+ VPTESTN %YMM2, %YMM2, %k0
kmovd %k0, %eax
testl %eax, %eax
jz L(aligned_more)
tzcntl %eax, %eax
+# ifndef USE_AS_STRCHRNUL
+ /* Found CHAR or the null byte. */
+ cmp (%rdi, %rax, CHAR_SIZE), %CHAR_REG
+ /* NB: Use a branch instead of cmovcc here. The expectation is
+ that with strchr the user will branch based on input being
+ null. Since this branch will be 100% predictive of the user
+ branch a branch miss here should save what otherwise would
+ be branch miss in the user code. Otherwise using a branch 1)
+ saves code size and 2) is faster in highly predictable
+ environments. */
+ jne L(zero)
+# endif
# ifdef USE_AS_WCSCHR
/* NB: Multiply wchar_t count by 4 to get the number of bytes.
*/
leaq (%rdi, %rax, CHAR_SIZE), %rax
# else
addq %rdi, %rax
-# endif
-# ifndef USE_AS_STRCHRNUL
- /* Found CHAR or the null byte. */
- cmp (%rax), %CHAR_REG
- jne L(zero)
# endif
ret
- /* .p2align 5 helps keep performance more consistent if ENTRY()
- alignment % 32 was either 16 or 0. As well this makes the
- alignment % 32 of the loop_4x_vec fixed which makes tuning it
- easier. */
- .p2align 5
-L(first_vec_x3):
- tzcntl %eax, %eax
-# ifndef USE_AS_STRCHRNUL
- /* Found CHAR or the null byte. */
- cmp (VEC_SIZE * 3)(%rdi, %rax, CHAR_SIZE), %CHAR_REG
- jne L(zero)
-# endif
- /* NB: Multiply sizeof char type (1 or 4) to get the number of
- bytes. */
- leaq (VEC_SIZE * 3)(%rdi, %rax, CHAR_SIZE), %rax
- ret
-# ifndef USE_AS_STRCHRNUL
-L(zero):
- xorl %eax, %eax
- ret
-# endif
- .p2align 4
+ .p2align 4,, 10
L(first_vec_x4):
# ifndef USE_AS_STRCHRNUL
/* Check to see if first match was CHAR (k0) or null (k1). */
@@ -144,9 +130,18 @@ L(first_vec_x4):
leaq (VEC_SIZE * 4)(%rdi, %rax, CHAR_SIZE), %rax
ret
+# ifndef USE_AS_STRCHRNUL
+L(zero):
+ xorl %eax, %eax
+ ret
+# endif
+
+
.p2align 4
L(first_vec_x1):
- tzcntl %eax, %eax
+ /* Use bsf here to save 1-byte keeping keeping the block in 1x
+ fetch block. eax guranteed non-zero. */
+ bsfl %eax, %eax
# ifndef USE_AS_STRCHRNUL
/* Found CHAR or the null byte. */
cmp (VEC_SIZE)(%rdi, %rax, CHAR_SIZE), %CHAR_REG
@@ -158,7 +153,7 @@ L(first_vec_x1):
leaq (VEC_SIZE)(%rdi, %rax, CHAR_SIZE), %rax
ret
- .p2align 4
+ .p2align 4,, 10
L(first_vec_x2):
# ifndef USE_AS_STRCHRNUL
/* Check to see if first match was CHAR (k0) or null (k1). */
@@ -179,6 +174,21 @@ L(first_vec_x2):
leaq (VEC_SIZE * 2)(%rdi, %rax, CHAR_SIZE), %rax
ret
+ .p2align 4,, 10
+L(first_vec_x3):
+ /* Use bsf here to save 1-byte keeping keeping the block in 1x
+ fetch block. eax guranteed non-zero. */
+ bsfl %eax, %eax
+# ifndef USE_AS_STRCHRNUL
+ /* Found CHAR or the null byte. */
+ cmp (VEC_SIZE * 3)(%rdi, %rax, CHAR_SIZE), %CHAR_REG
+ jne L(zero)
+# endif
+ /* NB: Multiply sizeof char type (1 or 4) to get the number of
+ bytes. */
+ leaq (VEC_SIZE * 3)(%rdi, %rax, CHAR_SIZE), %rax
+ ret
+
.p2align 4
L(aligned_more):
/* Align data to VEC_SIZE. */
@@ -195,7 +205,7 @@ L(cross_page_continue):
vpxorq %YMM1, %YMM0, %YMM2
VPMINU %YMM2, %YMM1, %YMM2
/* Each bit in K0 represents a CHAR or a null byte in YMM1. */
- VPCMP $0, %YMMZERO, %YMM2, %k0
+ VPTESTN %YMM2, %YMM2, %k0
kmovd %k0, %eax
testl %eax, %eax
jnz L(first_vec_x1)
@@ -206,7 +216,7 @@ L(cross_page_continue):
/* Each bit in K0 represents a CHAR in YMM1. */
VPCMP $0, %YMM1, %YMM0, %k0
/* Each bit in K1 represents a CHAR in YMM1. */
- VPCMP $0, %YMM1, %YMMZERO, %k1
+ VPTESTN %YMM1, %YMM1, %k1
kortestd %k0, %k1
jnz L(first_vec_x2)
@@ -215,7 +225,7 @@ L(cross_page_continue):
vpxorq %YMM1, %YMM0, %YMM2
VPMINU %YMM2, %YMM1, %YMM2
/* Each bit in K0 represents a CHAR or a null byte in YMM1. */
- VPCMP $0, %YMMZERO, %YMM2, %k0
+ VPTESTN %YMM2, %YMM2, %k0
kmovd %k0, %eax
testl %eax, %eax
jnz L(first_vec_x3)
@@ -224,7 +234,7 @@ L(cross_page_continue):
/* Each bit in K0 represents a CHAR in YMM1. */
VPCMP $0, %YMM1, %YMM0, %k0
/* Each bit in K1 represents a CHAR in YMM1. */
- VPCMP $0, %YMM1, %YMMZERO, %k1
+ VPTESTN %YMM1, %YMM1, %k1
kortestd %k0, %k1
jnz L(first_vec_x4)
@@ -265,33 +275,33 @@ L(loop_4x_vec):
VPMINU %YMM3, %YMM4, %YMM4
VPMINU %YMM2, %YMM4, %YMM4{%k4}{z}
- VPCMP $0, %YMMZERO, %YMM4, %k1
+ VPTESTN %YMM4, %YMM4, %k1
kmovd %k1, %ecx
subq $-(VEC_SIZE * 4), %rdi
testl %ecx, %ecx
jz L(loop_4x_vec)
- VPCMP $0, %YMMZERO, %YMM1, %k0
+ VPTESTN %YMM1, %YMM1, %k0
kmovd %k0, %eax
testl %eax, %eax
jnz L(last_vec_x1)
- VPCMP $0, %YMMZERO, %YMM2, %k0
+ VPTESTN %YMM2, %YMM2, %k0
kmovd %k0, %eax
testl %eax, %eax
jnz L(last_vec_x2)
- VPCMP $0, %YMMZERO, %YMM3, %k0
+ VPTESTN %YMM3, %YMM3, %k0
kmovd %k0, %eax
/* Combine YMM3 matches (eax) with YMM4 matches (ecx). */
# ifdef USE_AS_WCSCHR
sall $8, %ecx
orl %ecx, %eax
- tzcntl %eax, %eax
+ bsfl %eax, %eax
# else
salq $32, %rcx
orq %rcx, %rax
- tzcntq %rax, %rax
+ bsfq %rax, %rax
# endif
# ifndef USE_AS_STRCHRNUL
/* Check if match was CHAR or null. */
@@ -303,28 +313,28 @@ L(loop_4x_vec):
leaq (VEC_SIZE * 2)(%rdi, %rax, CHAR_SIZE), %rax
ret
-# ifndef USE_AS_STRCHRNUL
-L(zero_end):
- xorl %eax, %eax
- ret
+ .p2align 4,, 8
+L(last_vec_x1):
+ bsfl %eax, %eax
+# ifdef USE_AS_WCSCHR
+ /* NB: Multiply wchar_t count by 4 to get the number of bytes.
+ */
+ leaq (%rdi, %rax, CHAR_SIZE), %rax
+# else
+ addq %rdi, %rax
# endif
- .p2align 4
-L(last_vec_x1):
- tzcntl %eax, %eax
# ifndef USE_AS_STRCHRNUL
/* Check if match was null. */
- cmp (%rdi, %rax, CHAR_SIZE), %CHAR_REG
+ cmp (%rax), %CHAR_REG
jne L(zero_end)
# endif
- /* NB: Multiply sizeof char type (1 or 4) to get the number of
- bytes. */
- leaq (%rdi, %rax, CHAR_SIZE), %rax
+
ret
- .p2align 4
+ .p2align 4,, 8
L(last_vec_x2):
- tzcntl %eax, %eax
+ bsfl %eax, %eax
# ifndef USE_AS_STRCHRNUL
/* Check if match was null. */
cmp (VEC_SIZE)(%rdi, %rax, CHAR_SIZE), %CHAR_REG
@@ -336,7 +346,7 @@ L(last_vec_x2):
ret
/* Cold case for crossing page with first load. */
- .p2align 4
+ .p2align 4,, 8
L(cross_page_boundary):
movq %rdi, %rdx
/* Align rdi. */
@@ -346,9 +356,9 @@ L(cross_page_boundary):
vpxorq %YMM1, %YMM0, %YMM2
VPMINU %YMM2, %YMM1, %YMM2
/* Each bit in K0 represents a CHAR or a null byte in YMM1. */
- VPCMP $0, %YMMZERO, %YMM2, %k0
+ VPTESTN %YMM2, %YMM2, %k0
kmovd %k0, %eax
- /* Remove the leading bits. */
+ /* Remove the leading bits. */
# ifdef USE_AS_WCSCHR
movl %edx, %SHIFT_REG
/* NB: Divide shift count by 4 since each bit in K1 represent 4
@@ -360,20 +370,24 @@ L(cross_page_boundary):
/* If eax is zero continue. */
testl %eax, %eax
jz L(cross_page_continue)
- tzcntl %eax, %eax
-# ifndef USE_AS_STRCHRNUL
- /* Check to see if match was CHAR or null. */
- cmp (%rdx, %rax, CHAR_SIZE), %CHAR_REG
- jne L(zero_end)
-# endif
+ bsfl %eax, %eax
+
# ifdef USE_AS_WCSCHR
/* NB: Multiply wchar_t count by 4 to get the number of
bytes. */
leaq (%rdx, %rax, CHAR_SIZE), %rax
# else
addq %rdx, %rax
+# endif
+# ifndef USE_AS_STRCHRNUL
+ /* Check to see if match was CHAR or null. */
+ cmp (%rax), %CHAR_REG
+ je L(cross_page_ret)
+L(zero_end):
+ xorl %eax, %eax
+L(cross_page_ret):
# endif
ret
END (STRCHR)
-# endif
+#endif
--
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