func mapKeyArg(fast int, n, key ir.Node, assigned bool) ir.Node {
	if fast == mapslow {
		// standard version takes key by reference.
		// orderState.expr made sure key is addressable.
		return typecheck.NodAddr(key)
	}
	if assigned {
		// mapassign does distinguish pointer vs. integer key.
		return key
	}
	// mapaccess and mapdelete don't distinguish pointer vs. integer key.
	switch fast {
	case mapfast32ptr:

		return n
	}
	if l.Type().IsArray() {
		if !ir.IsAddressable(n.X) {
			base.Errorf("invalid operation %v (slice of unaddressable value)", n)
			n.SetType(nil)
			return n
		}

		addr := NodAddr(n.X)
		addr.SetImplicit(true)
		n.X = Expr(addr)
		l = n.X
	}
	t := l.Type()
	var tp *types.Type
	if t.IsString() {
		if hasmax {
			base.Errorf("invalid operation %v (3-index slice of string)", n)

		types.CalcSize(tt)
		rcvr := f2.Type.Recv().Type
		if !types.Identical(rcvr, tt) {
			if rcvr.IsPtr() && types.Identical(rcvr.Elem(), tt) {
				checklvalue(n.X, "call pointer method on")
				addr := NodAddr(n.X)
				addr.SetImplicit(true)
				n.X = typecheck(addr, ctxType|ctxExpr)
			} else if tt.IsPtr() && (!rcvr.IsPtr() || rcvr.IsPtr() && rcvr.Elem().NotInHeap()) && types.Identical(tt.Elem(), rcvr) {

			base.Fatalf("mapKeyTemp: key type is not sufficiently aligned, kt=%v nt=%v", kt, nt)
		}
		tmp := o.newTemp(kt, true)
		// *(*nt)(&tmp) = n
		var e ir.Node = typecheck.NodAddr(tmp)
		e = ir.NewConvExpr(pos, ir.OCONVNOP, nt.PtrTo(), e)
		e = ir.NewStarExpr(pos, e)
		o.append(ir.NewAssignStmt(pos, e, n))
		return tmp
	}
}