elemtype := s.Type().Elem()

	// Decompose slice.
	oldPtr := ir.NewUnaryExpr(base.Pos, ir.OSPTR, s)
	oldLen := ir.NewUnaryExpr(base.Pos, ir.OLEN, s)
	oldCap := ir.NewUnaryExpr(base.Pos, ir.OCAP, s)

	// Number of elements we are adding
	num := ir.NewUnaryExpr(base.Pos, ir.OLEN, l2)

	// newLen := oldLen + num

		n.X = walkExpr(n.X, nil)

		tab := ir.NewUnaryExpr(base.Pos, ir.OITAB, n.X)
		check := ir.NewUnaryExpr(base.Pos, ir.OCHECKNIL, tab)
		init.Append(typecheck.Stmt(check))
	}

	typ := typecheck.MethodValueType(n)

	clos := ir.NewCompLitExpr(base.Pos, ir.OCOMPLIT, typ, nil)
	clos.SetEsc(n.Esc())
	clos.List = []ir.Node{ir.NewUnaryExpr(base.Pos, ir.OCFUNC, methodValueWrapper(n)), n.X}

		hn := typecheck.TempAt(base.Pos, ir.CurFunc, types.Types[types.TINT])

		init = append(init, ir.NewAssignStmt(base.Pos, hv1, nil))
		init = append(init, ir.NewAssignStmt(base.Pos, hn, ir.NewUnaryExpr(base.Pos, ir.OLEN, ha)))

		nfor.Cond = ir.NewBinaryExpr(base.Pos, ir.OLT, hv1, hn)
		nfor.Post = ir.NewAssignStmt(base.Pos, hv1, ir.NewBinaryExpr(base.Pos, ir.OADD, hv1, ir.NewInt(base.Pos, 1)))

	l = append(l, ir.NewAssignStmt(base.Pos, nr, n.Y))

	nfrm := ir.NewUnaryExpr(base.Pos, ir.OSPTR, nr)
	nto := ir.NewUnaryExpr(base.Pos, ir.OSPTR, nl)

	nlen := typecheck.TempAt(base.Pos, ir.CurFunc, types.Types[types.TINT])

	// n = len(to)
	l = append(l, ir.NewAssignStmt(base.Pos, nlen, ir.NewUnaryExpr(base.Pos, ir.OLEN, nl)))

	// if n > len(frm) { n = len(frm) }

		//   l.tab != nil && l.tab._type == type(r)
		//
		// TODO(mdempsky): For non-empty interface comparisons, just
		// compare against the itab address directly?
		var eqtype ir.Node
		tab := ir.NewUnaryExpr(base.Pos, ir.OITAB, l)
		rtyp := reflectdata.CompareRType(base.Pos, n)
		if l.Type().IsEmptyInterface() {
			tab.SetType(types.NewPtr(types.Types[types.TUINT8]))
			tab.SetTypecheck(1)

	if c != n || len(init) != 0 {
		base.Fatalf("backingArrayPtrLen not cheap: %v", n)
	}
	ptr = ir.NewUnaryExpr(base.Pos, ir.OSPTR, n)
	if n.Type().IsString() {
		ptr.SetType(types.Types[types.TUINT8].PtrTo())
	} else {
		ptr.SetType(n.Type().Elem().PtrTo())
	}
	ptr.SetTypecheck(1)
	length = ir.NewUnaryExpr(base.Pos, ir.OLEN, n)
	length.SetType(types.Types[types.TINT])
	length.SetTypecheck(1)
	return ptr, length

		// var res *uint8
		// res = (*uint8)(unsafe.Pointer(itab))
		// if res != nil {
		//    res = res.type
		// }

		// Grab its parts.
		itab := ir.NewUnaryExpr(base.Pos, ir.OITAB, c)
		itab.SetType(types.Types[types.TUINTPTR].PtrTo())
		itab.SetTypecheck(1)
		data := ir.NewUnaryExpr(n.Pos(), ir.OIDATA, c)
		data.SetType(types.Types[types.TUINT8].PtrTo()) // Type is generic pointer - we're just passing it through.
		data.SetTypecheck(1)

	// Get interface descriptor word.
	// For empty interfaces this will be the type.
	// For non-empty interfaces this will be the itab.
	srcItab := ir.NewUnaryExpr(base.Pos, ir.OITAB, s.srcName)
	srcData := ir.NewUnaryExpr(base.Pos, ir.OIDATA, s.srcName)
	srcData.SetType(types.Types[types.TUINT8].PtrTo())
	srcData.SetTypecheck(1)

	// For empty interfaces, do:
	//     if e._type == nil {

		}
		a = initStackTemp(init, x, vstat)
	} else if n.Esc() == ir.EscNone {
		a = initStackTemp(init, typecheck.TempAt(base.Pos, ir.CurFunc, t), vstat)
	} else {
		a = ir.NewUnaryExpr(base.Pos, ir.ONEW, ir.TypeNode(t))
	}
	appendWalkStmt(init, ir.NewAssignStmt(base.Pos, vauto, a))

	if vstat != nil && n.Prealloc == nil && n.Esc() != ir.EscNone {

		// For "go/defer iface.M()", if iface is nil, we need to panic at
		// the point of the go/defer statement.
		if call.Op() == ir.OCALLINTER {
			iface := as.Lhs[0]
			init.Append(Stmt(ir.NewUnaryExpr(stmtPos, ir.OCHECKNIL, ir.NewUnaryExpr(iface.Pos(), ir.OITAB, iface))))
		}
	}

	// Move call into the wrapper function, now that it's safe to
	// evaluate there.
	wrapperFn.Body = []ir.Node{call}