cmd/internal/obj/riscv: improve register MOVB/MOVH/MOVBU/MOVHU for rva22u64
When GORISCV64 enables rva22u64, use SEXTB for MOVB, SEXTH for MOVH, ZEXTH
for MOVHU and ADDUW for MOVWU. These are single instruction alternatives
to the two instruction shift sequences that are needed otherwise.
Change-Id: Iea5e394f57e238ae8771400a87287c1ee507d44c
Reviewed-on: https://go-review.googlesource.com/c/go/+/572736 Reviewed-by: David Chase <drchase@google.com>
Run-TryBot: Joel Sing <joel@sing.id.au> Reviewed-by: Mark Ryan <markdryan@rivosinc.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
TryBot-Result: Gopher Robot <gobot@golang.org> Reviewed-by: Cherry Mui <cherryyz@google.com> Reviewed-by: M Zhuo <mengzhuo1203@gmail.com>