cmd/compile: Implement LoweredZeroLoop with LSX Instruction on loong64

cmd/compile: Implement LoweredZeroLoop with LSX Instruction on loong64

goos: linux
goarch: loong64
pkg: runtime
cpu: Loongson-3A6000 @ 2500.00MHz
                   |   old.txt    |               new.txt               |
                   |    sec/op    |   sec/op     vs base                |
ClearFat256           6.406n ± 0%   3.329n ± 1%  -48.03% (p=0.000 n=10)
ClearFat512          12.810n ± 0%   7.607n ± 0%  -40.62% (p=0.000 n=10)
ClearFat1024          25.62n ± 0%   14.01n ± 0%  -45.32% (p=0.000 n=10)
ClearFat1032          26.02n ± 0%   14.28n ± 0%  -45.14% (p=0.000 n=10)
ClearFat1040          26.02n ± 0%   14.41n ± 0%  -44.62% (p=0.000 n=10)
MemclrKnownSize192    4.804n ± 0%   2.827n ± 0%  -41.15% (p=0.000 n=10)
MemclrKnownSize248    6.561n ± 0%   4.371n ± 0%  -33.38% (p=0.000 n=10)
MemclrKnownSize256    6.406n ± 0%   3.335n ± 0%  -47.94% (p=0.000 n=10)
geomean               11.41n        6.453n       -43.45%

goos: linux
goarch: loong64
pkg: runtime
cpu: Loongson-3C5000 @ 2200.00MHz
                   |   old.txt    |               new.txt               |
                   |    sec/op    |   sec/op     vs base                |
ClearFat256          14.570n ± 0%   7.284n ± 0%  -50.01% (p=0.000 n=10)
ClearFat512           29.13n ± 0%   14.57n ± 0%  -49.98% (p=0.000 n=10)
ClearFat1024          58.26n ± 0%   29.15n ± 0%  -49.97% (p=0.000 n=10)
ClearFat1032          58.73n ± 0%   29.15n ± 0%  -50.36% (p=0.000 n=10)
ClearFat1040          59.18n ± 0%   29.26n ± 0%  -50.56% (p=0.000 n=10)
MemclrKnownSize192   10.930n ± 0%   5.466n ± 0%  -49.99% (p=0.000 n=10)
MemclrKnownSize248   14.110n ± 0%   6.772n ± 0%  -52.01% (p=0.000 n=10)
MemclrKnownSize256   14.570n ± 0%   7.285n ± 0%  -50.00% (p=0.000 n=10)
geomean               25.75n        12.78n       -50.36%

Change-Id: I88d7b6ae2f6fc3f095979f24fb83ff42a9d2d42e
Reviewed-on: https://go-review.googlesource.com/c/go/+/720940
Reviewed-by: Meidan Li <limeidan@loongson.cn>
Reviewed-by: Mark Freeman <markfreeman@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: sophie zhao <zhaoxiaolin@loongson.cn>
Reviewed-by: Keith Randall <khr@golang.org>
Reviewed-by: Keith Randall <khr@google.com>