cmd/compile: combine operations with immediate on riscv64
Replace two immediate operations with one, where possible.
Change-Id: Idc00e868155c9ca1d872aaaf70ea1f73e9eac4d6
Reviewed-on: https://go-review.googlesource.com/c/go/+/428497 Reviewed-by: Wayne Zuo <wdvxdr@golangcn.org>
TryBot-Result: Gopher Robot <gobot@golang.org>
Run-TryBot: Joel Sing <joel@sing.id.au> Reviewed-by: David Chase <drchase@google.com> Reviewed-by: Cherry Mui <cherryyz@google.com>