cmd/compile: deduplicate instructions when rewrite func results

cmd/compile: deduplicate instructions when rewrite func results

After CL 628075, do not rely on the memory arg of an OpLocalAddr.

Fixes #74788

Change-Id: I4e893241e3949bb8f2d93c8b88cc102e155b725d
Reviewed-on: https://go-review.googlesource.com/c/go/+/691275
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: David Chase <drchase@google.com>
Reviewed-by: Jorropo <jorropo.pgm@gmail.com>
Reviewed-by: Mark Freeman <mark@golang.org>