[glibc/release/2.26/master] aarch64, falkor: Ignore prefetcher tagging for smaller copies

[Wilco Dijkstra <wilco at sourceware dot org>]

https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=d3c05bfffa65b39ba64d62e24ed4a6c118fab3ef

commit d3c05bfffa65b39ba64d62e24ed4a6c118fab3ef
Author: Siddhesh Poyarekar <siddhesh@sourceware.org>
Date:   Fri May 11 00:11:52 2018 +0530

    aarch64,falkor: Ignore prefetcher tagging for smaller copies
    
    For smaller and medium sized copies, the effect of hardware
    prefetching are not as dominant as instruction level parallelism.
    Hence it makes more sense to load data into multiple registers than to
    try and route them to the same prefetch unit.  This is also the case
    for the loop exit where we are unable to latch on to the same prefetch
    unit anyway so it makes more sense to have data loaded in parallel.
    
    The performance results are a bit mixed with memcpy-random, with
    numbers jumping between -1% and +3%, i.e. the numbers don't seem
    repeatable.  memcpy-walk sees a 70% improvement (i.e. > 2x) for 128
    bytes and that improvement reduces down as the impact of the tail copy
    decreases in comparison to the loop.
    
    	* sysdeps/aarch64/multiarch/memcpy_falkor.S (__memcpy_falkor):
    	Use multiple registers to copy data in loop tail.
    
    (cherry picked from commit db725a458e1cb0e17204daa543744faf08bb2e06)

Diff:
---
 ChangeLog                                 |  5 +++
 sysdeps/aarch64/multiarch/memcpy_falkor.S | 68 +++++++++++++++++++------------
 2 files changed, 46 insertions(+), 27 deletions(-)

diff --git a/ChangeLog b/ChangeLog
index e9557b8..65b46ef 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,10 @@
 2019-09-06  Siddhesh Poyarekar  <siddhesh@sourceware.org>
 
+	* sysdeps/aarch64/multiarch/memcpy_falkor.S (__memcpy_falkor):
+	Use multiple registers to copy data in loop tail.
+
+2019-09-06  Siddhesh Poyarekar  <siddhesh@sourceware.org>
+
 	* sysdeps/aarch64/strncmp.S (strncmp): Use lsr instead of
 	mov + lsr.
 
diff --git a/sysdeps/aarch64/multiarch/memcpy_falkor.S b/sysdeps/aarch64/multiarch/memcpy_falkor.S
index dea4f22..3b8601f 100644
--- a/sysdeps/aarch64/multiarch/memcpy_falkor.S
+++ b/sysdeps/aarch64/multiarch/memcpy_falkor.S
@@ -35,6 +35,20 @@
 #define A_hw	w7
 #define tmp1	x14
 
+#define B_l	x8
+#define B_lw	w8
+#define B_h	x9
+#define C_l	x10
+#define C_h	x11
+#define D_l	x12
+#define D_h	x13
+#define E_l	dst
+#define E_h	tmp1
+#define F_l	src
+#define F_h	count
+#define G_l	srcend
+#define G_h	x15
+
 /* Copies are split into 3 main cases:
 
    1. Small copies of up to 32 bytes
@@ -74,21 +88,21 @@ ENTRY_ALIGN (__memcpy_falkor, 6)
 	/* Medium copies: 33..128 bytes.  */
 	sub	tmp1, count, 1
 	ldp	A_l, A_h, [src, 16]
-	stp	A_l, A_h, [dstin, 16]
+	ldp	B_l, B_h, [srcend, -32]
+	ldp	C_l, C_h, [srcend, -16]
 	tbz	tmp1, 6, 1f
-	ldp	A_l, A_h, [src, 32]
-	stp	A_l, A_h, [dstin, 32]
-	ldp	A_l, A_h, [src, 48]
-	stp	A_l, A_h, [dstin, 48]
-	ldp	A_l, A_h, [srcend, -64]
-	stp	A_l, A_h, [dstend, -64]
-	ldp	A_l, A_h, [srcend, -48]
-	stp	A_l, A_h, [dstend, -48]
+	ldp	D_l, D_h, [src, 32]
+	ldp	E_l, E_h, [src, 48]
+	stp	D_l, D_h, [dstin, 32]
+	stp	E_l, E_h, [dstin, 48]
+	ldp	F_l, F_h, [srcend, -64]
+	ldp	G_l, G_h, [srcend, -48]
+	stp	F_l, F_h, [dstend, -64]
+	stp	G_l, G_h, [dstend, -48]
 1:
-	ldp	A_l, A_h, [srcend, -32]
-	stp	A_l, A_h, [dstend, -32]
-	ldp	A_l, A_h, [srcend, -16]
-	stp	A_l, A_h, [dstend, -16]
+	stp	A_l, A_h, [dstin, 16]
+	stp	B_l, B_h, [dstend, -32]
+	stp	C_l, C_h, [dstend, -16]
 	ret
 
 	.p2align 4
@@ -98,36 +112,36 @@ L(copy32):
 	cmp	count, 16
 	b.lo	1f
 	ldp	A_l, A_h, [src]
+	ldp	B_l, B_h, [srcend, -16]
 	stp	A_l, A_h, [dstin]
-	ldp	A_l, A_h, [srcend, -16]
-	stp	A_l, A_h, [dstend, -16]
+	stp	B_l, B_h, [dstend, -16]
 	ret
 	.p2align 4
 1:
 	/* 8-15 */
 	tbz	count, 3, 1f
 	ldr	A_l, [src]
+	ldr	B_l, [srcend, -8]
 	str	A_l, [dstin]
-	ldr	A_l, [srcend, -8]
-	str	A_l, [dstend, -8]
+	str	B_l, [dstend, -8]
 	ret
 	.p2align 4
 1:
 	/* 4-7 */
 	tbz	count, 2, 1f
 	ldr	A_lw, [src]
+	ldr	B_lw, [srcend, -4]
 	str	A_lw, [dstin]
-	ldr	A_lw, [srcend, -4]
-	str	A_lw, [dstend, -4]
+	str	B_lw, [dstend, -4]
 	ret
 	.p2align 4
 1:
 	/* 2-3 */
 	tbz	count, 1, 1f
 	ldrh	A_lw, [src]
+	ldrh	B_lw, [srcend, -2]
 	strh	A_lw, [dstin]
-	ldrh	A_lw, [srcend, -2]
-	strh	A_lw, [dstend, -2]
+	strh	B_lw, [dstend, -2]
 	ret
 	.p2align 4
 1:
@@ -171,12 +185,12 @@ L(loop64):
 L(last64):
 	ldp	A_l, A_h, [srcend, -64]
 	stnp	A_l, A_h, [dstend, -64]
-	ldp	A_l, A_h, [srcend, -48]
-	stnp	A_l, A_h, [dstend, -48]
-	ldp	A_l, A_h, [srcend, -32]
-	stnp	A_l, A_h, [dstend, -32]
-	ldp	A_l, A_h, [srcend, -16]
-	stnp	A_l, A_h, [dstend, -16]
+	ldp	B_l, B_h, [srcend, -48]
+	stnp	B_l, B_h, [dstend, -48]
+	ldp	C_l, C_h, [srcend, -32]
+	stnp	C_l, C_h, [dstend, -32]
+	ldp	D_l, D_h, [srcend, -16]
+	stnp	D_l, D_h, [dstend, -16]
 	ret
 
 END (__memcpy_falkor)