From ac23759b655ceac1bd18b71f45bb1743826f0bed Mon Sep 17 00:00:00 2001
From: Noah Goldstein <goldstein.w.n@gmail.com>
Date: Fri, 25 Mar 2022 17:13:33 -0500
Subject: [PATCH] x86: Small improvements for wcslen
Just a few QOL changes.
1. Prefer `add` > `lea` as it has high execution units it can run
on.
2. Don't break macro-fusion between `test` and `jcc`
3. Reduce code size by removing gratuitous padding bytes (-90
bytes).
geometric_mean(N=20) of all benchmarks New / Original: 0.959
All string/memory tests pass.
Reviewed-by: H.J. Lu <hjl.tools@gmail.com>
(cherry picked from commit 244b415d386487521882debb845a040a4758cb18)
---
sysdeps/x86_64/wcslen.S | 86 ++++++++++++++++++++---------------------
1 file changed, 41 insertions(+), 45 deletions(-)
diff --git a/sysdeps/x86_64/wcslen.S b/sysdeps/x86_64/wcslen.S
index 9f5f7232..254bb030 100644
--- a/sysdeps/x86_64/wcslen.S
+++ b/sysdeps/x86_64/wcslen.S
@@ -41,82 +41,82 @@ ENTRY (__wcslen)
pxor %xmm0, %xmm0
lea 32(%rdi), %rax
- lea 16(%rdi), %rcx
+ addq $16, %rdi
and $-16, %rax
pcmpeqd (%rax), %xmm0
pmovmskb %xmm0, %edx
pxor %xmm1, %xmm1
+ addq $16, %rax
test %edx, %edx
- lea 16(%rax), %rax
jnz L(exit)
pcmpeqd (%rax), %xmm1
pmovmskb %xmm1, %edx
pxor %xmm2, %xmm2
+ addq $16, %rax
test %edx, %edx
- lea 16(%rax), %rax
jnz L(exit)
pcmpeqd (%rax), %xmm2
pmovmskb %xmm2, %edx
pxor %xmm3, %xmm3
+ addq $16, %rax
test %edx, %edx
- lea 16(%rax), %rax
jnz L(exit)
pcmpeqd (%rax), %xmm3
pmovmskb %xmm3, %edx
+ addq $16, %rax
test %edx, %edx
- lea 16(%rax), %rax
jnz L(exit)
pcmpeqd (%rax), %xmm0
pmovmskb %xmm0, %edx
+ addq $16, %rax
test %edx, %edx
- lea 16(%rax), %rax
jnz L(exit)
pcmpeqd (%rax), %xmm1
pmovmskb %xmm1, %edx
+ addq $16, %rax
test %edx, %edx
- lea 16(%rax), %rax
jnz L(exit)
pcmpeqd (%rax), %xmm2
pmovmskb %xmm2, %edx
+ addq $16, %rax
test %edx, %edx
- lea 16(%rax), %rax
jnz L(exit)
pcmpeqd (%rax), %xmm3
pmovmskb %xmm3, %edx
+ addq $16, %rax
test %edx, %edx
- lea 16(%rax), %rax
jnz L(exit)
pcmpeqd (%rax), %xmm0
pmovmskb %xmm0, %edx
+ addq $16, %rax
test %edx, %edx
- lea 16(%rax), %rax
jnz L(exit)
pcmpeqd (%rax), %xmm1
pmovmskb %xmm1, %edx
+ addq $16, %rax
test %edx, %edx
- lea 16(%rax), %rax
jnz L(exit)
pcmpeqd (%rax), %xmm2
pmovmskb %xmm2, %edx
+ addq $16, %rax
test %edx, %edx
- lea 16(%rax), %rax
jnz L(exit)
pcmpeqd (%rax), %xmm3
pmovmskb %xmm3, %edx
+ addq $16, %rax
test %edx, %edx
- lea 16(%rax), %rax
jnz L(exit)
and $-0x40, %rax
@@ -133,104 +133,100 @@ L(aligned_64_loop):
pminub %xmm0, %xmm2
pcmpeqd %xmm3, %xmm2
pmovmskb %xmm2, %edx
+ addq $64, %rax
test %edx, %edx
- lea 64(%rax), %rax
jz L(aligned_64_loop)
pcmpeqd -64(%rax), %xmm3
pmovmskb %xmm3, %edx
+ addq $48, %rdi
test %edx, %edx
- lea 48(%rcx), %rcx
jnz L(exit)
pcmpeqd %xmm1, %xmm3
pmovmskb %xmm3, %edx
+ addq $-16, %rdi
test %edx, %edx
- lea -16(%rcx), %rcx
jnz L(exit)
pcmpeqd -32(%rax), %xmm3
pmovmskb %xmm3, %edx
+ addq $-16, %rdi
test %edx, %edx
- lea -16(%rcx), %rcx
jnz L(exit)
pcmpeqd %xmm6, %xmm3
pmovmskb %xmm3, %edx
+ addq $-16, %rdi
test %edx, %edx
- lea -16(%rcx), %rcx
- jnz L(exit)
-
- jmp L(aligned_64_loop)
+ jz L(aligned_64_loop)
.p2align 4
L(exit):
- sub %rcx, %rax
+ sub %rdi, %rax
shr $2, %rax
test %dl, %dl
jz L(exit_high)
- mov %dl, %cl
- and $15, %cl
+ andl $15, %edx
jz L(exit_1)
ret
- .p2align 4
+ /* No align here. Naturally aligned % 16 == 1. */
L(exit_high):
- mov %dh, %ch
- and $15, %ch
+ andl $(15 << 8), %edx
jz L(exit_3)
add $2, %rax
ret
- .p2align 4
+ .p2align 3
L(exit_1):
add $1, %rax
ret
- .p2align 4
+ .p2align 3
L(exit_3):
add $3, %rax
ret
- .p2align 4
+ .p2align 3
L(exit_tail0):
- xor %rax, %rax
+ xorl %eax, %eax
ret
- .p2align 4
+ .p2align 3
L(exit_tail1):
- mov $1, %rax
+ movl $1, %eax
ret
- .p2align 4
+ .p2align 3
L(exit_tail2):
- mov $2, %rax
+ movl $2, %eax
ret
- .p2align 4
+ .p2align 3
L(exit_tail3):
- mov $3, %rax
+ movl $3, %eax
ret
- .p2align 4
+ .p2align 3
L(exit_tail4):
- mov $4, %rax
+ movl $4, %eax
ret
- .p2align 4
+ .p2align 3
L(exit_tail5):
- mov $5, %rax
+ movl $5, %eax
ret
- .p2align 4
+ .p2align 3
L(exit_tail6):
- mov $6, %rax
+ movl $6, %eax
ret
- .p2align 4
+ .p2align 3
L(exit_tail7):
- mov $7, %rax
+ movl $7, %eax
ret
END (__wcslen)
--
GitLab