[glibc/release/2.29/master] AArch64: Improve backwards memmove performance

[Wilco Dijkstra]

https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=64458aabeb7f6d15b389cb49b9faf4925db354fa

commit 64458aabeb7f6d15b389cb49b9faf4925db354fa
Author: Wilco Dijkstra <wdijkstr@arm.com>
Date:   Fri Aug 28 17:51:40 2020 +0100

    AArch64: Improve backwards memmove performance
    
    On some microarchitectures performance of the backwards memmove improves if
    the stores use STR with decreasing addresses.  So change the memmove loop
    in memcpy_advsimd.S to use 2x STR rather than STP.
    
    Reviewed-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>
    (cherry picked from commit bd394d131c10c9ec22c6424197b79410042eed99)

Diff:
---
 sysdeps/aarch64/multiarch/memcpy_advsimd.S | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/sysdeps/aarch64/multiarch/memcpy_advsimd.S b/sysdeps/aarch64/multiarch/memcpy_advsimd.S
index d4ba747777..48bb6d7ca4 100644
--- a/sysdeps/aarch64/multiarch/memcpy_advsimd.S
+++ b/sysdeps/aarch64/multiarch/memcpy_advsimd.S
@@ -223,12 +223,13 @@ L(copy_long_backwards):
 	b.ls	L(copy64_from_start)
 
 L(loop64_backwards):
-	stp	A_q, B_q, [dstend, -32]
+	str	B_q, [dstend, -16]
+	str	A_q, [dstend, -32]
 	ldp	A_q, B_q, [srcend, -96]
-	stp	C_q, D_q, [dstend, -64]
+	str	D_q, [dstend, -48]
+	str	C_q, [dstend, -64]!
 	ldp	C_q, D_q, [srcend, -128]
 	sub	srcend, srcend, 64
-	sub	dstend, dstend, 64
 	subs	count, count, 64
 	b.hi	L(loop64_backwards)