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[RFC] Improve rawmemchr implementation.


On Mon, Sep 02, 2013 at 11:55:30AM +0200, OndÅej BÃlka wrote:
> Ping,
> 
> I noticed that we use strong alias instead of weak, is that intentional?
> 
> strong_alias (rawmemchr, __rawmemchr)
> 



Hi,

I used evolver to optimize my rawmemchr, for most architectures a better
scheduling given us extra 2%.
There is catch that on bulldozer a loop is slower than original so if we
want this speedup we need to introduce again ifunc

http://kam.mff.cuni.cz/~ondra/benchmark_string/rawmemchr_profile.html
http://kam.mff.cuni.cz/~ondra/benchmark_string/rawmemchr_profile230913.tar.bz2

diff --git a/sysdeps/x86_64/rawmemchr.S b/sysdeps/x86_64/rawmemchr.S
index f4d5591..29419c9 100644
--- a/sysdeps/x86_64/rawmemchr.S
+++ b/sysdeps/x86_64/rawmemchr.S
@@ -1,7 +1,6 @@
-/* fast SSE2 memchr with 64 byte loop and pmaxub instruction using
+/* fast SSE2 rawmemchr
 
-   Copyright (C) 2011-2013 Free Software Foundation, Inc.
-   Contributed by Intel Corporation.
+   Copyright (C) 2013 Free Software Foundation, Inc.
    This file is part of the GNU C Library.
 
    The GNU C Library is free software; you can redistribute it and/or
@@ -20,186 +19,107 @@
 
 #include <sysdep.h>
 
+#define ALIGN(n) .p2align n
+
 	.text
 ENTRY (rawmemchr)
-	movd	%rsi, %xmm1
-	mov	%rdi, %rcx
-
-	punpcklbw %xmm1, %xmm1
+	movd	%esi, %xmm1
+	movq	%rdi, %rax
+	andl	$4095, %eax
 	punpcklbw %xmm1, %xmm1
-
-	and	$63, %rcx
+	cmpl	$4032, %eax
+	punpcklwd %xmm1, %xmm1
 	pshufd	$0, %xmm1, %xmm1
-
-	cmp	$48, %rcx
-	ja	L(crosscache)
-
+	jg	L(cross_page)
 	movdqu	(%rdi), %xmm0
 	pcmpeqb	%xmm1, %xmm0
-/* Check if there is a match.  */
-	pmovmskb %xmm0, %eax
-	test	%eax, %eax
-
-	jnz	L(matches)
-	add	$16, %rdi
-	and	$-16, %rdi
-	jmp	L(loop_prolog)
-
-	.p2align 4
-L(crosscache):
-	and	$15, %rcx
-	and	$-16, %rdi
-	movdqa	(%rdi), %xmm0
-
-	pcmpeqb	%xmm1, %xmm0
-/* Check if there is a match.  */
 	pmovmskb %xmm0, %eax
-/* Remove the leading bytes.  */
-	sar	%cl, %eax
 	test	%eax, %eax
-	je	L(unaligned_no_match)
-/* Check which byte is a match.  */
-	bsf	%eax, %eax
-
-	add	%rdi, %rax
-	add	%rcx, %rax
+	je	L(next_48_bytes)
+	bsf	%ax, %ax
+	addq	%rdi, %rax
 	ret
 
-	.p2align 4
-L(unaligned_no_match):
-	add	$16, %rdi
-
-	.p2align 4
-L(loop_prolog):
-	movdqa	(%rdi), %xmm0
-	pcmpeqb	%xmm1, %xmm0
-	pmovmskb %xmm0, %eax
-	test	%eax, %eax
-	jnz	L(matches)
-
-	movdqa	16(%rdi), %xmm2
-	pcmpeqb	%xmm1, %xmm2
-	pmovmskb %xmm2, %eax
-	test	%eax, %eax
-	jnz	L(matches16)
-
-	movdqa	32(%rdi), %xmm3
+L(next_48_bytes):
+	movdqu	48(%rdi), %xmm4
+	movdqu	32(%rdi), %xmm3
 	pcmpeqb	%xmm1, %xmm3
-	pmovmskb %xmm3, %eax
-	test	%eax, %eax
-	jnz	L(matches32)
-
-	movdqa	48(%rdi), %xmm4
 	pcmpeqb	%xmm1, %xmm4
-	add	$64, %rdi
-	pmovmskb %xmm4, %eax
-	test	%eax, %eax
-	jnz	L(matches0)
-
-	test	$0x3f, %rdi
-	jz	L(align64_loop)
+	pmovmskb %xmm4, %ecx
+	movdqu	16(%rdi), %xmm2
+	pmovmskb %xmm3, %eax
+	salq	$32, %rcx
+	pcmpeqb	%xmm1, %xmm2
+	salq	$16, %rax
+	pmovmskb %xmm2, %edx
+	orq	%rdx, %rax
+	orq	%rcx, %rax
+	je	L(loop_start)
+	bsfq	%rax, %rax
+	lea	16(%rdi, %rax), %rax
+	ret
 
-	movdqa	(%rdi), %xmm0
-	pcmpeqb	%xmm1, %xmm0
-	pmovmskb %xmm0, %eax
-	test	%eax, %eax
-	jnz	L(matches)
+L(loop_start):
+	andq	$-64, %rdi
 
-	movdqa	16(%rdi), %xmm2
+	ALIGN (4)
+L(loop64):
+	movdqa	64(%rdi), %xmm2
+	movdqa	80(%rdi), %xmm3
 	pcmpeqb	%xmm1, %xmm2
-	pmovmskb %xmm2, %eax
-	test	%eax, %eax
-	jnz	L(matches16)
-
-	movdqa	32(%rdi), %xmm3
+	movdqa	112(%rdi), %xmm5
+	movdqa	96(%rdi), %xmm4
+	addq	$64, %rdi
+	pcmpeqb	%xmm1, %xmm5
+	pmaxub	%xmm2, %xmm5
 	pcmpeqb	%xmm1, %xmm3
+	pcmpeqb	%xmm1, %xmm4
+	pmaxub	%xmm3, %xmm5
+	pmaxub	%xmm4, %xmm5
+	pmovmskb %xmm5, %edx
+	testl	%edx, %edx
+	je	L(loop64)
+	pmovmskb %xmm4, %esi
+	salq	$48, %rdx
+	salq	$32, %rsi
 	pmovmskb %xmm3, %eax
-	test	%eax, %eax
-	jnz	L(matches32)
+	pmovmskb %xmm2, %ecx
+	salq	$16, %rax
+	orq	%rsi, %rax
+	orq	%rcx, %rax
+	orq	%rdx, %rax
+	bsfq	%rax, %rax
+	addq	%rdi, %rax
+	ret
 
-	movdqa	48(%rdi), %xmm3
+	ALIGN (4)
+L(cross_page):
+	movq	%rdi, %rcx
+	andq	$-64, %rdi
+	movdqa	(%rdi), %xmm2
+	movdqa	16(%rdi), %xmm3
+	movdqa	48(%rdi), %xmm5
+	movdqa	32(%rdi), %xmm4
 	pcmpeqb	%xmm1, %xmm3
-	pmovmskb %xmm3, %eax
-
-	add	$64, %rdi
-	test	%eax, %eax
-	jnz	L(matches0)
-
-	and	$-64, %rdi
-
-	.p2align 4
-L(align64_loop):
-	movdqa	(%rdi), %xmm0
-	movdqa	16(%rdi), %xmm2
-	movdqa	32(%rdi), %xmm3
-	movdqa	48(%rdi), %xmm4
-
-	pcmpeqb	%xmm1, %xmm0
 	pcmpeqb	%xmm1, %xmm2
-	pcmpeqb	%xmm1, %xmm3
+	pmovmskb %xmm2, %r8d
 	pcmpeqb	%xmm1, %xmm4
-
-	pmaxub	%xmm0, %xmm3
-	pmaxub	%xmm2, %xmm4
-	pmaxub	%xmm3, %xmm4
-	pmovmskb %xmm4, %eax
-
-	add	$64, %rdi
-
-	test	%eax, %eax
-	jz	L(align64_loop)
-
-	sub	$64, %rdi
-
-	pmovmskb %xmm0, %eax
-	test	%eax, %eax
-	jnz	L(matches)
-
-	pmovmskb %xmm2, %eax
-	test	%eax, %eax
-	jnz	L(matches16)
-
-	movdqa	32(%rdi), %xmm3
-	pcmpeqb	%xmm1, %xmm3
-
-	pcmpeqb	48(%rdi), %xmm1
+	pcmpeqb	%xmm1, %xmm5
+	pmovmskb %xmm5, %edx
+	pmovmskb %xmm4, %esi
 	pmovmskb %xmm3, %eax
-	test	%eax, %eax
-	jnz	L(matches32)
-
-	pmovmskb %xmm1, %eax
-	bsf	%eax, %eax
-	lea	48(%rdi, %rax), %rax
-	ret
-
-	.p2align 4
-L(matches0):
-	bsf	%eax, %eax
-	lea	-16(%rax, %rdi), %rax
-	ret
-
-	.p2align 4
-L(matches):
-	bsf	%eax, %eax
-	add	%rdi, %rax
-	ret
-
-	.p2align 4
-L(matches16):
-	bsf	%eax, %eax
-	lea	16(%rax, %rdi), %rax
-	ret
-
-	.p2align 4
-L(matches32):
-	bsf	%eax, %eax
-	lea	32(%rax, %rdi), %rax
-	ret
-
-	.p2align 4
-L(return_null):
-	xor	%rax, %rax
-	ret
+	salq	$32, %rsi
+	salq	$16, %rax
+	salq	$48, %rdx
+	orq	%rsi, %rax
+	orq	%r8, %rax
+	orq	%rdx, %rax
+	shrq	%cl, %rax
+	testq	%rax, %rax
+	je	L(loop64)
+	bsfq	%rax, %rax
+	addq	%rcx, %rax
+	ret
 
 END (rawmemchr)
 


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