cmd/compile: avoid extending when already sufficiently masked on loong64
Reduce the number of go toolchain instructions on loong64 as follows.
file before after Δ %
asm 562400 561348 -1052 -0.1871%
cgo 488268 487932 -336 -0.0688%
compile
2505750 2503710 -2040 -0.0814%
cover 525874 525506 -368 -0.0700%
link 714162 713562 -600 -0.0840%
preprofile 240250 240054 -196 -0.0816%
vet 794074 793742 -332 -0.0418%
go
1598284 1597680 -604 -0.0378%
gofmt 324126 323926 -200 -0.0617%
total
7753188 7747460 -5728 -0.0739%
Change-Id: I3406113553b0fc4947d763ab66e57e69aa98c020
Reviewed-on: https://go-review.googlesource.com/c/go/+/683615
Reviewed-by: Keith Randall <khr@golang.org>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Keith Randall <khr@google.com>
Reviewed-by: Mark Freeman <mark@golang.org>