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glibc/SOURCES/glibc-RHEL-15696-88.patch

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From a6fbf4d51e9ba8063c4f8331564892ead9c67344 Mon Sep 17 00:00:00 2001
From: Noah Goldstein <goldstein.w.n@gmail.com>
Date: Wed, 23 Mar 2022 16:57:16 -0500
Subject: [PATCH] x86: Code cleanup in strchr-avx2 and comment justifying
branch
Content-type: text/plain; charset=UTF-8
Small code cleanup for size: -53 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 Original / New: 1.00
Reviewed-by: H.J. Lu <hjl.tools@gmail.com>
---
sysdeps/x86_64/multiarch/strchr-avx2.S | 204 +++++++++++++------------
1 file changed, 107 insertions(+), 97 deletions(-)
diff --git a/sysdeps/x86_64/multiarch/strchr-avx2.S b/sysdeps/x86_64/multiarch/strchr-avx2.S
index 5884726b..89dd2bf7 100644
--- a/sysdeps/x86_64/multiarch/strchr-avx2.S
+++ b/sysdeps/x86_64/multiarch/strchr-avx2.S
@@ -48,13 +48,13 @@
# define PAGE_SIZE 4096
.section SECTION(.text),"ax",@progbits
-ENTRY (STRCHR)
+ENTRY_P2ALIGN (STRCHR, 5)
/* Broadcast CHAR to YMM0. */
vmovd %esi, %xmm0
movl %edi, %eax
andl $(PAGE_SIZE - 1), %eax
VPBROADCAST %xmm0, %ymm0
- vpxor %xmm9, %xmm9, %xmm9
+ vpxor %xmm1, %xmm1, %xmm1
/* Check if we cross page boundary with one vector load. */
cmpl $(PAGE_SIZE - VEC_SIZE), %eax
@@ -62,37 +62,29 @@ ENTRY (STRCHR)
/* Check the first VEC_SIZE bytes. Search for both CHAR and the
null byte. */
- vmovdqu (%rdi), %ymm8
- VPCMPEQ %ymm8, %ymm0, %ymm1
- VPCMPEQ %ymm8, %ymm9, %ymm2
- vpor %ymm1, %ymm2, %ymm1
- vpmovmskb %ymm1, %eax
+ vmovdqu (%rdi), %ymm2
+ VPCMPEQ %ymm2, %ymm0, %ymm3
+ VPCMPEQ %ymm2, %ymm1, %ymm2
+ vpor %ymm3, %ymm2, %ymm3
+ vpmovmskb %ymm3, %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_REG
- jne L(zero)
-# endif
- addq %rdi, %rax
- VZEROUPPER_RETURN
-
- /* .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_x4):
- tzcntl %eax, %eax
- addq $(VEC_SIZE * 3 + 1), %rdi
-# ifndef USE_AS_STRCHRNUL
- /* Found CHAR or the null byte. */
+ /* Found CHAR or the null byte. */
cmp (%rdi, %rax), %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
addq %rdi, %rax
- VZEROUPPER_RETURN
+L(return_vzeroupper):
+ ZERO_UPPER_VEC_REGISTERS_RETURN
# ifndef USE_AS_STRCHRNUL
L(zero):
@@ -103,7 +95,8 @@ L(zero):
.p2align 4
L(first_vec_x1):
- tzcntl %eax, %eax
+ /* Use bsf to save code size. */
+ bsfl %eax, %eax
incq %rdi
# ifndef USE_AS_STRCHRNUL
/* Found CHAR or the null byte. */
@@ -113,9 +106,10 @@ L(first_vec_x1):
addq %rdi, %rax
VZEROUPPER_RETURN
- .p2align 4
+ .p2align 4,, 10
L(first_vec_x2):
- tzcntl %eax, %eax
+ /* Use bsf to save code size. */
+ bsfl %eax, %eax
addq $(VEC_SIZE + 1), %rdi
# ifndef USE_AS_STRCHRNUL
/* Found CHAR or the null byte. */
@@ -125,9 +119,10 @@ L(first_vec_x2):
addq %rdi, %rax
VZEROUPPER_RETURN
- .p2align 4
+ .p2align 4,, 8
L(first_vec_x3):
- tzcntl %eax, %eax
+ /* Use bsf to save code size. */
+ bsfl %eax, %eax
addq $(VEC_SIZE * 2 + 1), %rdi
# ifndef USE_AS_STRCHRNUL
/* Found CHAR or the null byte. */
@@ -137,6 +132,21 @@ L(first_vec_x3):
addq %rdi, %rax
VZEROUPPER_RETURN
+ .p2align 4,, 10
+L(first_vec_x4):
+ /* Use bsf to save code size. */
+ bsfl %eax, %eax
+ addq $(VEC_SIZE * 3 + 1), %rdi
+# ifndef USE_AS_STRCHRNUL
+ /* Found CHAR or the null byte. */
+ cmp (%rdi, %rax), %CHAR_REG
+ jne L(zero)
+# endif
+ addq %rdi, %rax
+ VZEROUPPER_RETURN
+
+
+
.p2align 4
L(aligned_more):
/* Align data to VEC_SIZE - 1. This is the same number of
@@ -146,90 +156,92 @@ L(aligned_more):
L(cross_page_continue):
/* Check the next 4 * VEC_SIZE. Only one VEC_SIZE at a time
since data is only aligned to VEC_SIZE. */
- vmovdqa 1(%rdi), %ymm8
- VPCMPEQ %ymm8, %ymm0, %ymm1
- VPCMPEQ %ymm8, %ymm9, %ymm2
- vpor %ymm1, %ymm2, %ymm1
- vpmovmskb %ymm1, %eax
+ vmovdqa 1(%rdi), %ymm2
+ VPCMPEQ %ymm2, %ymm0, %ymm3
+ VPCMPEQ %ymm2, %ymm1, %ymm2
+ vpor %ymm3, %ymm2, %ymm3
+ vpmovmskb %ymm3, %eax
testl %eax, %eax
jnz L(first_vec_x1)
- vmovdqa (VEC_SIZE + 1)(%rdi), %ymm8
- VPCMPEQ %ymm8, %ymm0, %ymm1
- VPCMPEQ %ymm8, %ymm9, %ymm2
- vpor %ymm1, %ymm2, %ymm1
- vpmovmskb %ymm1, %eax
+ vmovdqa (VEC_SIZE + 1)(%rdi), %ymm2
+ VPCMPEQ %ymm2, %ymm0, %ymm3
+ VPCMPEQ %ymm2, %ymm1, %ymm2
+ vpor %ymm3, %ymm2, %ymm3
+ vpmovmskb %ymm3, %eax
testl %eax, %eax
jnz L(first_vec_x2)
- vmovdqa (VEC_SIZE * 2 + 1)(%rdi), %ymm8
- VPCMPEQ %ymm8, %ymm0, %ymm1
- VPCMPEQ %ymm8, %ymm9, %ymm2
- vpor %ymm1, %ymm2, %ymm1
- vpmovmskb %ymm1, %eax
+ vmovdqa (VEC_SIZE * 2 + 1)(%rdi), %ymm2
+ VPCMPEQ %ymm2, %ymm0, %ymm3
+ VPCMPEQ %ymm2, %ymm1, %ymm2
+ vpor %ymm3, %ymm2, %ymm3
+ vpmovmskb %ymm3, %eax
testl %eax, %eax
jnz L(first_vec_x3)
- vmovdqa (VEC_SIZE * 3 + 1)(%rdi), %ymm8
- VPCMPEQ %ymm8, %ymm0, %ymm1
- VPCMPEQ %ymm8, %ymm9, %ymm2
- vpor %ymm1, %ymm2, %ymm1
- vpmovmskb %ymm1, %eax
+ vmovdqa (VEC_SIZE * 3 + 1)(%rdi), %ymm2
+ VPCMPEQ %ymm2, %ymm0, %ymm3
+ VPCMPEQ %ymm2, %ymm1, %ymm2
+ vpor %ymm3, %ymm2, %ymm3
+ vpmovmskb %ymm3, %eax
testl %eax, %eax
jnz L(first_vec_x4)
- /* Align data to VEC_SIZE * 4 - 1. */
- addq $(VEC_SIZE * 4 + 1), %rdi
- andq $-(VEC_SIZE * 4), %rdi
+ /* Align data to VEC_SIZE * 4 - 1. */
+ incq %rdi
+ orq $(VEC_SIZE * 4 - 1), %rdi
.p2align 4
L(loop_4x_vec):
/* Compare 4 * VEC at a time forward. */
- vmovdqa (%rdi), %ymm5
- vmovdqa (VEC_SIZE)(%rdi), %ymm6
- vmovdqa (VEC_SIZE * 2)(%rdi), %ymm7
- vmovdqa (VEC_SIZE * 3)(%rdi), %ymm8
+ vmovdqa 1(%rdi), %ymm6
+ vmovdqa (VEC_SIZE + 1)(%rdi), %ymm7
/* Leaves only CHARS matching esi as 0. */
- vpxor %ymm5, %ymm0, %ymm1
vpxor %ymm6, %ymm0, %ymm2
vpxor %ymm7, %ymm0, %ymm3
- vpxor %ymm8, %ymm0, %ymm4
- VPMINU %ymm1, %ymm5, %ymm1
VPMINU %ymm2, %ymm6, %ymm2
VPMINU %ymm3, %ymm7, %ymm3
- VPMINU %ymm4, %ymm8, %ymm4
- VPMINU %ymm1, %ymm2, %ymm5
- VPMINU %ymm3, %ymm4, %ymm6
+ vmovdqa (VEC_SIZE * 2 + 1)(%rdi), %ymm6
+ vmovdqa (VEC_SIZE * 3 + 1)(%rdi), %ymm7
+
+ vpxor %ymm6, %ymm0, %ymm4
+ vpxor %ymm7, %ymm0, %ymm5
+
+ VPMINU %ymm4, %ymm6, %ymm4
+ VPMINU %ymm5, %ymm7, %ymm5
- VPMINU %ymm5, %ymm6, %ymm6
+ VPMINU %ymm2, %ymm3, %ymm6
+ VPMINU %ymm4, %ymm5, %ymm7
- VPCMPEQ %ymm6, %ymm9, %ymm6
- vpmovmskb %ymm6, %ecx
+ VPMINU %ymm6, %ymm7, %ymm7
+
+ VPCMPEQ %ymm7, %ymm1, %ymm7
+ vpmovmskb %ymm7, %ecx
subq $-(VEC_SIZE * 4), %rdi
testl %ecx, %ecx
jz L(loop_4x_vec)
-
- VPCMPEQ %ymm1, %ymm9, %ymm1
- vpmovmskb %ymm1, %eax
+ VPCMPEQ %ymm2, %ymm1, %ymm2
+ vpmovmskb %ymm2, %eax
testl %eax, %eax
jnz L(last_vec_x0)
- VPCMPEQ %ymm5, %ymm9, %ymm2
- vpmovmskb %ymm2, %eax
+ VPCMPEQ %ymm3, %ymm1, %ymm3
+ vpmovmskb %ymm3, %eax
testl %eax, %eax
jnz L(last_vec_x1)
- VPCMPEQ %ymm3, %ymm9, %ymm3
- vpmovmskb %ymm3, %eax
+ VPCMPEQ %ymm4, %ymm1, %ymm4
+ vpmovmskb %ymm4, %eax
/* rcx has combined result from all 4 VEC. It will only be used
if the first 3 other VEC all did not contain a match. */
salq $32, %rcx
orq %rcx, %rax
tzcntq %rax, %rax
- subq $(VEC_SIZE * 2), %rdi
+ subq $(VEC_SIZE * 2 - 1), %rdi
# ifndef USE_AS_STRCHRNUL
/* Found CHAR or the null byte. */
cmp (%rdi, %rax), %CHAR_REG
@@ -239,10 +251,11 @@ L(loop_4x_vec):
VZEROUPPER_RETURN
- .p2align 4
+ .p2align 4,, 10
L(last_vec_x0):
- tzcntl %eax, %eax
- addq $-(VEC_SIZE * 4), %rdi
+ /* Use bsf to save code size. */
+ bsfl %eax, %eax
+ addq $-(VEC_SIZE * 4 - 1), %rdi
# ifndef USE_AS_STRCHRNUL
/* Found CHAR or the null byte. */
cmp (%rdi, %rax), %CHAR_REG
@@ -251,16 +264,11 @@ L(last_vec_x0):
addq %rdi, %rax
VZEROUPPER_RETURN
-# ifndef USE_AS_STRCHRNUL
-L(zero_end):
- xorl %eax, %eax
- VZEROUPPER_RETURN
-# endif
- .p2align 4
+ .p2align 4,, 10
L(last_vec_x1):
tzcntl %eax, %eax
- subq $(VEC_SIZE * 3), %rdi
+ subq $(VEC_SIZE * 3 - 1), %rdi
# ifndef USE_AS_STRCHRNUL
/* Found CHAR or the null byte. */
cmp (%rdi, %rax), %CHAR_REG
@@ -269,18 +277,23 @@ L(last_vec_x1):
addq %rdi, %rax
VZEROUPPER_RETURN
+# ifndef USE_AS_STRCHRNUL
+L(zero_end):
+ xorl %eax, %eax
+ VZEROUPPER_RETURN
+# endif
/* Cold case for crossing page with first load. */
- .p2align 4
+ .p2align 4,, 8
L(cross_page_boundary):
movq %rdi, %rdx
/* Align rdi to VEC_SIZE - 1. */
orq $(VEC_SIZE - 1), %rdi
- vmovdqa -(VEC_SIZE - 1)(%rdi), %ymm8
- VPCMPEQ %ymm8, %ymm0, %ymm1
- VPCMPEQ %ymm8, %ymm9, %ymm2
- vpor %ymm1, %ymm2, %ymm1
- vpmovmskb %ymm1, %eax
+ vmovdqa -(VEC_SIZE - 1)(%rdi), %ymm2
+ VPCMPEQ %ymm2, %ymm0, %ymm3
+ VPCMPEQ %ymm2, %ymm1, %ymm2
+ vpor %ymm3, %ymm2, %ymm3
+ vpmovmskb %ymm3, %eax
/* Remove the leading bytes. sarxl only uses bits [5:0] of COUNT
so no need to manually mod edx. */
sarxl %edx, %eax, %eax
@@ -291,13 +304,10 @@ L(cross_page_boundary):
xorl %ecx, %ecx
/* Found CHAR or the null byte. */
cmp (%rdx, %rax), %CHAR_REG
- leaq (%rdx, %rax), %rax
- cmovne %rcx, %rax
-# else
- addq %rdx, %rax
+ jne L(zero_end)
# endif
-L(return_vzeroupper):
- ZERO_UPPER_VEC_REGISTERS_RETURN
+ addq %rdx, %rax
+ VZEROUPPER_RETURN
END (STRCHR)
-# endif
+#endif
--
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