[dev.ssa] cmd/compile: Make PPARAMOUT variables SSAable
Add writeback code to each return location which copies
the final result back to the correct stack location.
Cgo plays tricky games by taking the address of a
in f(a int) (b int) and then using that address to
modify b. So for cgo-generated Go code, disable the
SSAing of output args.
Update #14511
Change-Id: I95cba727d53699d31124eef41db0e03935862be9
Reviewed-on: https://go-review.googlesource.com/19988 Reviewed-by: Todd Neal <todd@tneal.org>
Run-TryBot: Keith Randall <khr@golang.org> Reviewed-by: Ian Lance Taylor <iant@golang.org>