cmd/internal/obj/riscv: support additional register to register moves
Add support for signed and unsigned register to register moves of various
sizes. This makes it easier to handle zero and sign extension and will allow
for further changes that improve the compiler optimisations for riscv64.
While here, change the existing register to register moves from obj.Prog
rewriting to instruction generation.
Change-Id: Id21911019b76922367a134da13c3449a84a1fb08
Reviewed-on: https://go-review.googlesource.com/c/go/+/264657
Trust: Joel Sing <joel@sing.id.au> Reviewed-by: Cherry Zhang <cherryyz@google.com>