cmd/compile: fold constant in ADDshift op on loong64
Removes 918 instructions from the go binary on loong64.
file before after Δ
go
1633120 1632948 -172
gofmt 323470 323334 -136
asm 568024 568024 -0
cgo 488030 487890 -140
compile
2501050 2500728 -322
cover 530124 530124 -0
link 723532 723520 -12
preprofile 240568 240568 -0
vet 819392 819256 -136
Change-Id: Id4015c66b2073323b7ad257b3ed05bb99f81e9a1
Reviewed-on: https://go-review.googlesource.com/c/go/+/701655
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Keith Randall <khr@google.com>
Reviewed-by: Keith Randall <khr@golang.org>
Auto-Submit: Keith Randall <khr@golang.org>
Reviewed-by: Mark Freeman <markfreeman@google.com>