[glibc] AArch64: Optimize strcpy

[glibc] AArch64: Optimize strcpy

[Wilco Dijkstra]

https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=349e48c01e85bd96006860084e76d322e6ca02f1

commit 349e48c01e85bd96006860084e76d322e6ca02f1
Author: Wilco Dijkstra <wilco.dijkstra@arm.com>
Date:   Wed Jan 11 13:52:39 2023 +0000

    AArch64: Optimize strcpy
    
    Unroll the main loop.  Large strings are around 20% faster on modern CPUs.
    
    Reviewed-by: Szabolcs Nagy <szabolcs.nagy@arm.com>

Diff:
---
 sysdeps/aarch64/strcpy.S | 36 +++++++++++++++++++-----------------
 1 file changed, 19 insertions(+), 17 deletions(-)

diff --git a/sysdeps/aarch64/strcpy.S b/sysdeps/aarch64/strcpy.S
index bc14dd9f79..8b045a92c2 100644
--- a/sysdeps/aarch64/strcpy.S
+++ b/sysdeps/aarch64/strcpy.S
@@ -30,7 +30,6 @@
  * MTE compatible.
  */
 
-/* Arguments and results.  */
 #define dstin		x0
 #define srcin		x1
 #define result		x0
@@ -76,14 +75,14 @@ ENTRY (STRCPY)
 	ld1	{vdata.16b}, [src]
 	cmeq	vhas_nul.16b, vdata.16b, 0
 	lsl	shift, srcin, 2
-	shrn	vend.8b, vhas_nul.8h, 4		/* 128->64 */
+	shrn	vend.8b, vhas_nul.8h, 4
 	fmov	synd, dend
 	lsr	synd, synd, shift
 	cbnz	synd, L(tail)
 
 	ldr	dataq, [src, 16]!
 	cmeq	vhas_nul.16b, vdata.16b, 0
-	shrn	vend.8b, vhas_nul.8h, 4		/* 128->64 */
+	shrn	vend.8b, vhas_nul.8h, 4
 	fmov	synd, dend
 	cbz	synd, L(start_loop)
 
@@ -102,13 +101,10 @@ ENTRY (STRCPY)
 	IFSTPCPY (add result, dstin, len)
 	ret
 
-	.p2align 4,,8
 L(tail):
 	rbit	synd, synd
 	clz	len, synd
 	lsr	len, len, 2
-
-	.p2align 4
 L(less16):
 	tbz	len, 3, L(less8)
 	sub	tmp, len, 7
@@ -141,31 +137,37 @@ L(zerobyte):
 
 	.p2align 4
 L(start_loop):
-	sub	len, src, srcin
+	sub	tmp, srcin, dstin
 	ldr	dataq2, [srcin]
-	add	dst, dstin, len
+	sub	dst, src, tmp
 	str	dataq2, [dstin]
-
-	.p2align 5
 L(loop):
-	str	dataq, [dst], 16
-	ldr	dataq, [src, 16]!
+	str	dataq, [dst], 32
+	ldr	dataq, [src, 16]
+	cmeq	vhas_nul.16b, vdata.16b, 0
+	umaxp	vend.16b, vhas_nul.16b, vhas_nul.16b
+	fmov	synd, dend
+	cbnz	synd, L(loopend)
+	str	dataq, [dst, -16]
+	ldr	dataq, [src, 32]!
 	cmeq	vhas_nul.16b, vdata.16b, 0
 	umaxp	vend.16b, vhas_nul.16b, vhas_nul.16b
 	fmov	synd, dend
 	cbz	synd, L(loop)
-
+	add	dst, dst, 16
+L(loopend):
 	shrn	vend.8b, vhas_nul.8h, 4		/* 128->64 */
 	fmov	synd, dend
+	sub	dst, dst, 31
 #ifndef __AARCH64EB__
 	rbit	synd, synd
 #endif
 	clz	len, synd
 	lsr	len, len, 2
-	sub	tmp, len, 15
-	ldr	dataq, [src, tmp]
-	str	dataq, [dst, tmp]
-	IFSTPCPY (add result, dst, len)
+	add	dst, dst, len
+	ldr	dataq, [dst, tmp]
+	str	dataq, [dst]
+	IFSTPCPY (add result, dst, 15)
 	ret
 
 END (STRCPY)