go.tools/go/ssa: fix range iteration over values of pointer to named array type

LGTM=adonovan
R=adonovan
CC=golang-codereviews
https://golang.org/cl/107800045

go/ssa/builder.go

@@ -1641,7 +1641,7 @@ func (b *builder) rangeIndexed(fn *Function, x Value, tv types.Type) (k, v Value
 				X:     x,
 				Index: k,
 			}
-			instr.setType(types.NewPointer(t.Elem().(*types.Array).Elem()))
+			instr.setType(types.NewPointer(t.Elem().Underlying().(*types.Array).Elem()))
 			v = emitLoad(fn, fn.emit(instr))
 
 		case *types.Slice:

go/ssa/interp/testdata/coverage.go

@@ -642,3 +642,16 @@ func bug7840() bool {
 	// This creates a single-predecessor block with a φ-node.
 	return false && a == 0 && a == 0
 }
+
+// Regression test for range of pointer to named array type.
+func init() {
+	type intarr [3]int
+	ia := intarr{1, 2, 3}
+	var count int
+	for _, x := range &ia {
+		count += x
+	}
+	if count != 6 {
+		panic(count)
+	}
+}