cmd/compile: fold negation into addition/subtraction on loong64
This change also avoid double negation, and add loong64 codegen for arithmetic tests.
Reduce the number of go toolchain instructions on loong64 as follows.
file before after Δ %
addr2line 279972 279896 -76 -0.0271%
asm 556390 556310 -80 -0.0144%
buildid 272376 272300 -76 -0.0279%
cgo 481534 481550 +16 +0.0033%
compile
2457992 2457396 -596 -0.0242%
covdata 323488 323404 -84 -0.0260%
cover 518630 518490 -140 -0.0270%
dist 340894 340814 -80 -0.0235%
distpack 282568 282484 -84 -0.0297%
doc 790224 789984 -240 -0.0304%
fix 324408 324348 -60 -0.0185%
link 704910 704666 -244 -0.0346%
nm 277220 277144 -76 -0.0274%
objdump 508026 507878 -148 -0.0291%
pack 221810 221786 -24 -0.0108%
pprof
1470284 1469880 -404 -0.0275%
test2json 254896 254852 -44 -0.0173%
trace
1100390 1100074 -316 -0.0287%
vet 781398 781142 -256 -0.0328%
go
1529668 1529128 -540 -0.0353%
gofmt 318668 318568 -100 -0.0314%
total
13795746 13792094 -3652 -0.0265%
Change-Id: I88d1f12cfc4be0e92687c48e06a57213aa484aca
Reviewed-on: https://go-review.googlesource.com/c/go/+/672555
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Cherry Mui <cherryyz@google.com>
Reviewed-by: abner chenc <chenguoqi@loongson.cn>
Reviewed-by: Michael Knyszek <mknyszek@google.com>