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AArch64: Update A64FX memset not to degrade at 16KB

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This patch updates unroll8 code so as not to degrade at the peak
performance 16KB for both FX1000 and FX700.

Inserted 2 instructions at the beginning of the unroll8 loop,
cmp and branch, are a workaround that is found heuristically.

Reviewed-by: Wilco Dijkstra <Wilco.Dijkstra@arm.com>
This commit is contained in:
Naohiro Tamura via Libc-alpha 2021-08-27 05:03:04 +00:00 committed by Szabolcs Nagy
parent 69623c0db0
commit 23777232c2
1 changed files with 8 additions and 1 deletions
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9
sysdeps/aarch64/multiarch/memset_a64fx.S
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@ -96,7 +96,14 @@ L(vl_agnostic): // VL Agnostic
L(unroll8):
sub count, count, tmp1
.p2align 4
1: st1b_unroll 0, 7
// The 2 instructions at the beginning of the following loop,
// cmp and branch, are a workaround so as not to degrade at
// the peak performance 16KB.
// It is found heuristically and the branch condition, b.ne,
// is chosen intentionally never to jump.
1: cmp xzr, xzr
b.ne 1b
st1b_unroll 0, 7
add dst, dst, tmp1
subs count, count, tmp1
b.hi 1b