cmd/compile: sparse conditional constant propagation
sparse conditional constant propagation can discover optimization
opportunities that cannot be found by just combining constant folding
and constant propagation and dead code elimination separately.
This is a re-submit of PR#59575, which fix a broken dominance relationship caught by ssacheck
Updates https://github.com/golang/go/issues/59399
Change-Id: I57482dee38f8e80a610aed4f64295e60c38b7a47
GitHub-Last-Rev:
830016f24e3a5320c6c127a48ab7c84e2fc672eb
GitHub-Pull-Request: golang/go#60469
Reviewed-on: https://go-review.googlesource.com/c/go/+/498795
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Keith Randall <khr@google.com>
Reviewed-by: Heschi Kreinick <heschi@google.com>
Reviewed-by: Keith Randall <khr@golang.org>