[dev.ssa] cmd/compile/internal/ssa: add more critical edges

Add blocks to remove critical edges, even when it looks like
there's no phi that requires it.  Regalloc still likes to have
critical-edge-free graphs for other reasons.

Change-Id: I69f8eaecbc5d79ab9f2a257c2e289d60b18e43c8
Reviewed-on: https://go-review.googlesource.com/13933
Reviewed-by: Josh Bleecher Snyder <josharian@gmail.com>

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

@@ -99,9 +99,6 @@ func checkFunc(f *Func) {
 			if !b.Control.Type.IsMemory() {
 				f.Fatalf("call block %s has non-memory control value %s", b, b.Control.LongString())
 			}
-			if b.Succs[1].Kind != BlockExit {
-				f.Fatalf("exception edge from call block %s does not go to exit but %s", b, b.Succs[1])
-			}
 		}
 		if len(b.Succs) > 2 && b.Likely != BranchUnknown {
 			f.Fatalf("likeliness prediction %d for block %s with %d successors: %s", b.Likely, b, len(b.Succs))

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

@@ -13,19 +13,6 @@ func critical(f *Func) {
 			continue
 		}
 
-		// decide if we need to split edges coming into b.
-		hasphi := false
-		for _, v := range b.Values {
-			if v.Op == OpPhi && v.Type != TypeMem {
-				hasphi = true
-				break
-			}
-		}
-		if !hasphi {
-			// no splitting needed
-			continue
-		}
-
 		// split input edges coming from multi-output blocks.
 		for i, c := range b.Preds {
 			if c.Kind == BlockPlain {