cmd/compile: set hiter type for map iterator in order pass

Previously the type was first set to uint8 and then corrected
later in walkrange.

Change-Id: I9e4b597710e8a5fad39dde035df85676bc8d2874
Reviewed-on: https://go-review.googlesource.com/61032
Run-TryBot: Martin Möhrmann <moehrmann@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>

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

@@ -762,8 +762,9 @@ func orderstmt(n *Node, order *Order) {
 			r := n.Right
 			n.Right = ordercopyexpr(r, r.Type, order, 0)
 
-			// n->alloc is the temp for the iterator.
-			prealloc[n] = ordertemp(types.Types[TUINT8], order, true)
+			// prealloc[n] is the temp for the iterator.
+			// hiter contains pointers and needs to be zeroed.
+			prealloc[n] = ordertemp(hiter(n.Type), order, true)
 		}
 		for i := range n.List.Slice() {
 			n.List.SetIndex(i, orderexprinplace(n.List.Index(i), order))

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

@@ -249,9 +249,8 @@ func walkrange(n *Node) *Node {
 		// we only use a once, so no copy needed.
 		ha := a
 
-		th := hiter(t)
 		hit := prealloc[n]
-		hit.Type = th
+		th := hit.Type
 		n.Left = nil
 		keysym := th.Field(0).Sym // depends on layout of iterator struct.  See reflect.go:hiter
 		valsym := th.Field(1).Sym // ditto