[dev.unified] cmd/compile/internal/walk: minor prep refactoring

Two small refactorings that will make it easier to thread through
RType parameters later. Behavior preserving, but seemed worth
separating out.

Passes toolstash -cmp.

Change-Id: I77905775015b6582bad2b32dd7700880c415893f
Reviewed-on: https://go-review.googlesource.com/c/go/+/413354
Reviewed-by: David Chase <drchase@google.com>
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>

src/cmd/compile/internal/walk/complit.go

@@ -414,9 +414,9 @@ func slicelit(ctxt initContext, n *ir.CompLitExpr, var_ ir.Node, init *ir.Nodes)
 
 func maplit(n *ir.CompLitExpr, m ir.Node, init *ir.Nodes) {
 	// make the map var
-	a := ir.NewCallExpr(base.Pos, ir.OMAKE, nil, nil)
+	args := []ir.Node{ir.TypeNode(n.Type()), ir.NewInt(n.Len + int64(len(n.List)))}
+	a := typecheck.Expr(ir.NewCallExpr(base.Pos, ir.OMAKE, nil, args)).(*ir.MakeExpr)
 	a.SetEsc(n.Esc())
-	a.Args = []ir.Node{ir.TypeNode(n.Type()), ir.NewInt(n.Len + int64(len(n.List)))}
 	appendWalkStmt(init, ir.NewAssignStmt(base.Pos, m, a))
 
 	entries := n.List

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

@@ -38,11 +38,7 @@ func cheapComputableIndex(width int64) bool {
 // the returned node.
 func walkRange(nrange *ir.RangeStmt) ir.Node {
 	if isMapClear(nrange) {
-		m := nrange.X
-		lno := ir.SetPos(m)
-		n := mapClear(m)
-		base.Pos = lno
-		return n
+		return mapClear(nrange)
 	}
 
 	nfor := ir.NewForStmt(nrange.Pos(), nil, nil, nil, nil)
@@ -360,7 +356,11 @@ func isMapClear(n *ir.RangeStmt) bool {
 }
 
 // mapClear constructs a call to runtime.mapclear for the map m.
-func mapClear(m ir.Node) ir.Node {
+func mapClear(nrange *ir.RangeStmt) ir.Node {
+	m := nrange.X
+	origPos := ir.SetPos(m)
+	defer func() { base.Pos = origPos }()
+
 	t := m.Type()
 
 	// instantiate mapclear(typ *type, hmap map[any]any)