n.SetType(nil)
			return n
		}
	}
	return n
}

// tcITab typechecks an OITAB node.
func tcITab(n *ir.UnaryExpr) ir.Node {
	n.X = Expr(n.X)
	t := n.X.Type()
	if t == nil {
		n.SetType(nil)
		return n
	}
	if !t.IsInterface() {
		base.Fatalf("OITAB of %v", t)
	}
	n.SetType(types.NewPtr(types.Types[types.TUINTPTR]))
	return n
}

			ir.OAND, ir.OANDNOT, ir.OLSH, ir.OOR, ir.ORSH, ir.OXOR, ir.OCOMPLEX, ir.OMAKEFACE,
			ir.OADDR, ir.OBITNOT, ir.ONOT, ir.OPLUS,
			ir.OCAP, ir.OIMAG, ir.OLEN, ir.OREAL,
			ir.OCONVNOP, ir.ODOT,
			ir.OCFUNC, ir.OIDATA, ir.OITAB, ir.OSPTR,
			ir.OBYTES2STRTMP, ir.OGETG, ir.OGETCALLERPC, ir.OGETCALLERSP, ir.OSLICEHEADER, ir.OSTRINGHEADER:
			// ok: operations that don't require function calls.
			// Expand as needed.
		}

		return false

	ptrType := v.Block.Func.Config.Types.BytePtr

	itab := v.Block.NewValue0(v.Pos, OpPhi, uintptrType)
	data := v.Block.NewValue0(v.Pos, OpPhi, ptrType)
	for _, a := range v.Args {
		itab.AddArg(a.Block.NewValue1(v.Pos, OpITab, uintptrType, a))
		data.AddArg(a.Block.NewValue1(v.Pos, OpIData, ptrType, a))
	}
	v.reset(OpIMake)
	v.AddArg(itab)
	v.AddArg(data)
}

func decomposeUser(f *Func) {
	for _, b := range f.Blocks {

	case ir.OUNSAFESTRINGDATA:
		n := n.(*ir.UnaryExpr)
		return tcUnsafeData(n)

	case ir.OITAB:
		n := n.(*ir.UnaryExpr)
		return tcITab(n)

	case ir.OIDATA:
		// Whoever creates the OIDATA node must know a priori the concrete type at that moment,
		// usually by just having checked the OITAB.
		n := n.(*ir.UnaryExpr)
		base.Fatalf("cannot typecheck interface data %v", n)
		panic("unreachable")

		//   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)
			eqtype = ir.NewBinaryExpr(base.Pos, eq, tab, rtyp)

		//
		// 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)

		// 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}

	// Finally, construct a call to the wrapper.

		v = v.Args[0]
	}
	switch v.Op {
	case OpSP, OpLocalAddr, OpSelectNAddr:
		// Stack addresses are always safe.
		return true
	case OpITab, OpStringPtr, OpGetClosurePtr:
		// Itabs, string data, and closure fields are
		// read-only once initialized.
		return true
	case OpAddr:
		vt := v.Aux.(*obj.LSym).Type

		return rewriteValuedec_OpComplexImag(v)
	case OpComplexReal:
		return rewriteValuedec_OpComplexReal(v)
	case OpIData:
		return rewriteValuedec_OpIData(v)
	case OpIMake:
		return rewriteValuedec_OpIMake(v)
	case OpITab:
		return rewriteValuedec_OpITab(v)
	case OpLoad:
		return rewriteValuedec_OpLoad(v)
	case OpSliceCap:
		return rewriteValuedec_OpSliceCap(v)
	case OpSliceLen:
		return rewriteValuedec_OpSliceLen(v)

		n := n.(*ir.SelectorExpr)
		return n.FuncName()

	case ir.OMIN, ir.OMAX:
		n := n.(*ir.CallExpr)
		return walkMinMax(n, init)

	case ir.ONOT, ir.ONEG, ir.OPLUS, ir.OBITNOT, ir.OREAL, ir.OIMAG, ir.OSPTR, ir.OITAB, ir.OIDATA:
		n := n.(*ir.UnaryExpr)
		n.X = walkExpr(n.X, init)
		return n

	case ir.ODOTMETH, ir.ODOTINTER:
		n := n.(*ir.SelectorExpr)
		n.X = walkExpr(n.X, init)
		return n

	case ir.OADDR: