[dev.ssa] cmd/compile: allow control values to be CSEd
With the separate flagalloc pass, it should be fine to
allow CSE of control values. The worst that can happen
is that the comparison gets un-CSEd by flagalloc.
Fix bug in flagalloc where flag restores were getting
clobbered by rematerialization during register allocation.
Change-Id: If476cf98b69973e8f1a8eb29441136dd12fab8ad
Reviewed-on: https://go-review.googlesource.com/17760 Reviewed-by: David Chase <drchase@google.com>
Run-TryBot: Keith Randall <khr@golang.org>