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