base.Errorf("%v is not a top level statement", n.Sym())
		} else {
			base.Errorf("%v is not a top level statement", n.Op())
		}
		ir.Dump("nottop", n)
		return n

	case ir.OAS,
		ir.OASOP,
		ir.OAS2,
		ir.OAS2DOTTYPE,
		ir.OAS2RECV,
		ir.OAS2FUNC,
		ir.OAS2MAPR,
		ir.OCLEAR,
		ir.OCLOSE,
		ir.OCOPY,
		ir.OCALLINTER,
		ir.OCALL,
		ir.OCALLFUNC,
		ir.ODELETE,
		ir.OSEND,
		ir.OPRINT,

			fn := chanfn("selectnbrecv", 2, ch.Type())
			call := mkcall1(fn, fn.Type().ResultsTuple(), r.PtrInit(), elem, ch)
			as := ir.NewAssignListStmt(r.Pos(), ir.OAS2, []ir.Node{cond, n.Lhs[1]}, []ir.Node{call})
			r.PtrInit().Append(typecheck.Stmt(as))
		}

		r.Cond = typecheck.Expr(cond)
		r.Body = cas.Body
		r.Else = append(dflt.Init(), dflt.Body...)

func rangeAssign2(n *ir.RangeStmt, key, value ir.Node) ir.Node {
	// Use OAS2 to correctly handle assignments
	// of the form "v1, a[v1] = range".
	key = rangeConvert(n, n.Key.Type(), key, n.KeyTypeWord, n.KeySrcRType)
	value = rangeConvert(n, n.Value.Type(), value, n.ValueTypeWord, n.ValueSrcRType)
	return ir.NewAssignListStmt(n.Pos(), ir.OAS2, []ir.Node{n.Key, n.Value}, []ir.Node{key, value})
}

	}

	if !s.seenMutation {
		s.seenMutation = mayModifyPkgVar(rhs)
	}

	if allBlank(lhs) && !AnySideEffects(rhs) {
		return true // discard
	}

	// Only worry about simple "l = r" assignments. The OAS2*
	// assignments mostly necessitate dynamic execution anyway.
	if len(lhs) > 1 {
		return false
	}

	lno := ir.SetPos(n)
	defer func() { base.Pos = lno }()

	nam := lhs[0].(*ir.Name)

	OADDR:             "&",
	OADD:              "+",
	OADDSTR:           "+",
	OANDAND:           "&&",
	OANDNOT:           "&^",
	OAND:              "&",
	OAPPEND:           "append",
	OAS:               "=",
	OAS2:              "=",
	OBREAK:            "break",
	OCALL:             "function call", // not actual syntax
	OCAP:              "cap",
	OCASE:             "case",
	OCLEAR:            "clear",
	OCLOSE:            "close",

		tcAssign(n)

		// Code that creates temps does not bother to set defn, so do it here.
		if n.X.Op() == ir.ONAME && ir.IsAutoTmp(n.X) {
			n.X.Name().Defn = n
		}
		return n

	case ir.OAS2:
		tcAssignList(n.(*ir.AssignListStmt))
		return n

	case ir.OBREAK,
		ir.OCONTINUE,
		ir.ODCL,
		ir.OGOTO,
		ir.OFALL:
		return n

	case ir.OBLOCK:
		n := n.(*ir.BlockStmt)

			as := typecheck.Stmt(ir.NewAssignStmt(n.Pos(), l1, r))
			o.mapAssign(as)
			o.popTemp(t)
			return
		}

		o.mapAssign(n)
		o.popTemp(t)

	case ir.OAS2:
		n := n.(*ir.AssignListStmt)
		t := o.markTemp()
		o.exprList(n.Lhs)
		o.exprList(n.Rhs)
		o.out = append(o.out, n)
		o.popTemp(t)

	// Special: avoid copy of func call n.Right
	case ir.OAS2FUNC:

	}
}

// appendWalkStmt typechecks and walks stmt and then appends it to init.
func appendWalkStmt(init *ir.Nodes, stmt ir.Node) {
	op := stmt.Op()
	n := typecheck.Stmt(stmt)
	if op == ir.OAS || op == ir.OAS2 {
		// If the assignment has side effects, walkExpr will append them
		// directly to init for us, while walkStmt will wrap it in an OBLOCK.
		// We need to append them directly.
		// TODO(rsc): Clean this up.

		// The concrete cases can all be handled without a runtime call.
		if len(concreteCases) > 0 {
			var clauses []typeClause
			for _, c := range concreteCases {
				as := ir.NewAssignListStmt(c.pos, ir.OAS2,
					[]ir.Node{ir.BlankNode, s.okName},                               // _, ok =
					[]ir.Node{ir.NewTypeAssertExpr(c.pos, s.srcName, c.typ.Type())}) // iface.(type)
				nif := ir.NewIfStmt(c.pos, s.okName, []ir.Node{c.jmp}, nil)

		n.Rhs = []ir.Node{r}
		return n
	}
	init.Append(r)

	ll := ascompatet(n.Lhs, r.Type())
	return ir.NewBlockStmt(src.NoXPos, ll)
}

// walkAssignList walks an OAS2 node.
func walkAssignList(init *ir.Nodes, n *ir.AssignListStmt) ir.Node {
	init.Append(ir.TakeInit(n)...)
	return ir.NewBlockStmt(src.NoXPos, ascompatee(ir.OAS, n.Lhs, n.Rhs))
}