cmd/compile: rewrite the constant parts of the prove pass

Handles a lot more cases where constant ranges can eliminate
various (mostly bounds failure) paths.

Fixes #66826
Fixes #66692
Fixes #48213
Update #57959

TODO: remove constant logic from poset code, no longer needed.

Change-Id: Id196436fcd8a0c84c7d59c04f93bd92e26a0fd7e
Reviewed-on: https://go-review.googlesource.com/c/go/+/599096
Reviewed-by: David Chase <[email protected]>
LUCI-TryBot-Result: Go LUCI <[email protected]>
Reviewed-by: Michael Knyszek <[email protected]>

Author: randall77

src/cmd/compile/internal/ssa/func.go

@@ -796,7 +796,7 @@ func (f *Func) invalidateCFG() {
 //	base.DebugHashMatch(this function's package.name)
 //
 // for use in bug isolation.  The return value is true unless
-// environment variable GOSSAHASH is set, in which case "it depends".
+// environment variable GOCOMPILEDEBUG=gossahash=X is set, in which case "it depends on X".
 // See [base.DebugHashMatch] for more information.
 func (f *Func) DebugHashMatch() bool {
 	if !base.HasDebugHash() {