cmd/compile: add prefetch intrinsic support on loong64

This CL enables intrinsic support to emit the following prefetch
instructions for loong64 platform:
  1.Prefetch - prefetches data from memory address to cache;
  2.PrefetchStreamed - prefetches data from memory address, with a
    hint that this data is being streamed.

Benchmarks picked from go/test/bench/garbage
Parameters tested with:
GOMAXPROCS=8
tree2 -heapsize=1000000000 -cpus=8
tree -n=18
parser
peano

Benchmarks Loongson-3A6000-HV @ 2500.00MHz:
         |   bench.old   |              bench.new               |
         |    sec/op     |    sec/op      vs base               |
Tree2-8    1238.2µ ± 24%   999.9µ ± 453%       ~ (p=0.089 n=10)
Tree-8      277.4m ±  1%   275.5m ±   1%       ~ (p=0.063 n=10)
Parser-8     3.564 ±  0%    3.509 ±   1%  -1.56% (p=0.000 n=10)
Peano-8     39.12m ±  2%   38.85m ±   2%       ~ (p=0.353 n=10)
geomean     83.19m         78.28m         -5.90%

Change-Id: I59e9aa4f609a106d4f70706e6d6d1fe6738ab72a
Reviewed-on: https://go-review.googlesource.com/c/go/+/671876
Reviewed-by: Michael Knyszek <mknyszek@google.com>
Reviewed-by: Meidan Li <limeidan@loongson.cn>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: sophie zhao <zhaoxiaolin@loongson.cn>
Reviewed-by: Cherry Mui <cherryyz@google.com>

0 files changed, 0 insertions, 0 deletions