[dev.ssa] cmd/compile/internal/ssa: OCHECKNIL is a statement, not an expression

Change-Id: I5a683f532a5a0b2bc862d80c871e8dc6721016fc
Reviewed-on: https://go-review.googlesource.com/14534Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

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

@@ -772,6 +772,10 @@ func (s *state) stmt(n *Node) {
 		b.AddEdgeTo(bNext)
 		s.startBlock(bNext)
 
+	case OCHECKNIL:
+		p := s.expr(n.Left)
+		s.nilCheck(p)
+
 	default:
 		s.Unimplementedf("unhandled stmt %s", opnames[n.Op])
 	}
@@ -1661,11 +1665,6 @@ func (s *state) expr(n *Node) *ssa.Value {
 	case OADDR:
 		return s.addr(n.Left)
 
-	case OCHECKNIL:
-		p := s.expr(n.Left)
-		s.nilCheck(p)
-		return p
-
 	case OINDREG:
 		if int(n.Reg) != Thearch.REGSP {
 			s.Unimplementedf("OINDREG of non-SP register %s in expr: %v", obj.Rconv(int(n.Reg)), n)