cmd/compile: in prove, make addRestrictions more generic

addRestrictions was taking a branch parameter, binding its logic
to that of addBranchRestrictions. Since we will need to use it
for updating the facts table for induction variables, refactor it
to remove the branch parameter.

Passes toolstash -cmp.

Change-Id: Iaaec350a8becd1919d03d8574ffd1bbbd906d068
Reviewed-on: https://go-review.googlesource.com/104036
Run-TryBot: Giovanni Bajo <rasky@develer.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Austin Clements <austin@google.com>

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

@@ -653,27 +653,34 @@ func getBranch(sdom SparseTree, p *Block, b *Block) branch {
 // branching from Block b in direction br.
 func addBranchRestrictions(ft *factsTable, b *Block, br branch) {
 	c := b.Control
-	addRestrictions(b, ft, boolean, nil, c, lt|gt, br)
+	switch br {
+	case negative:
+		addRestrictions(b, ft, boolean, nil, c, eq)
+	case positive:
+		addRestrictions(b, ft, boolean, nil, c, lt|gt)
+	default:
+		panic("unknown branch")
+	}
 	if tr, has := domainRelationTable[b.Control.Op]; has {
 		// When we branched from parent we learned a new set of
 		// restrictions. Update the factsTable accordingly.
-		addRestrictions(b, ft, tr.d, c.Args[0], c.Args[1], tr.r, br)
+		switch br {
+		case negative:
+			addRestrictions(b, ft, tr.d, c.Args[0], c.Args[1], tr.r^(lt|gt|eq))
+		case positive:
+			addRestrictions(b, ft, tr.d, c.Args[0], c.Args[1], tr.r)
+		}
 	}
-
 }
 
 // addRestrictions updates restrictions from the immediate
-// dominating block (p) using r. r is adjusted according to the branch taken.
-func addRestrictions(parent *Block, ft *factsTable, t domain, v, w *Value, r relation, branch branch) {
-	if t == 0 || branch == unknown {
-		// Trivial case: nothing to do, or branch unknown.
+// dominating block (p) using r.
+func addRestrictions(parent *Block, ft *factsTable, t domain, v, w *Value, r relation) {
+	if t == 0 {
+		// Trivial case: nothing to do.
 		// Shoult not happen, but just in case.
 		return
 	}
-	if branch == negative {
-		// Negative branch taken, complement the relations.
-		r = (lt | eq | gt) ^ r
-	}
 	for i := domain(1); i <= t; i <<= 1 {
 		if t&i == 0 {
 			continue