reader.go

	meth.Nname = name
	meth.SetNointerface(name.Func.Pragma&ir.Nointerface != 0)

	return meth
}

func (r *reader) qualifiedIdent() (pkg *types.Pkg, sym *types.Sym) {
	r.Sync(pkgbits.SyncSym)
	pkg = r.pkg()
	if name := r.String(); name != "" {
		sym = pkg.Lookup(name)
	}
	return
}

func (r *reader) localIdent() (pkg *types.Pkg, sym *types.Sym) {
	r.Sync(pkgbits.SyncLocalIdent)
	pkg = r.pkg()
	if name := r.String(); name != "" {
		sym = pkg.Lookup(name)
	}
	return
}

func (r *reader) selector() (origPkg *types.Pkg, sym *types.Sym) {
	r.Sync(pkgbits.SyncSelector)
	origPkg = r.pkg()
	name := r.String()
	pkg := origPkg
	if types.IsExported(name) {
		pkg = types.LocalPkg
	}
	sym = pkg.Lookup(name)
	return
}

func (r *reader) hasTypeParams() bool {
	return r.dict.hasTypeParams()
}

func (dict *readerDict) hasTypeParams() bool {
	return dict != nil && len(dict.targs) != 0
}

// @@@ Compiler extensions

func (r *reader) funcExt(name *ir.Name, method *types.Sym) {
	r.Sync(pkgbits.SyncFuncExt)

	name.Class = 0 // so MarkFunc doesn't complain
	ir.MarkFunc(name)

	fn := name.Func

	// XXX: Workaround because linker doesn't know how to copy Pos.
	if !fn.Pos().IsKnown() {
		fn.SetPos(name.Pos())
	}

	// Normally, we only compile local functions, which saves redundant compilation work.
	// n.Defn is not nil for local functions, and is nil for imported function. But for
	// generic functions, we might have an instantiation that no other package has seen before.
	// So we need to be conservative and compile it again.
	//
	// That's why name.Defn is set here, so ir.VisitFuncsBottomUp can analyze function.
	// TODO(mdempsky,cuonglm): find a cleaner way to handle this.
	if name.Sym().Pkg == types.LocalPkg || r.hasTypeParams() {
		name.Defn = fn
	}

	fn.Pragma = r.pragmaFlag()
	r.linkname(name)

	typecheck.Func(fn)

	if r.Bool() {
		assert(name.Defn == nil)

		fn.ABI = obj.ABI(r.Uint64())

		// Escape analysis.
		for _, fs := range &types.RecvsParams {
			for _, f := range fs(name.Type()).FieldSlice() {
				f.Note = r.String()
			}
		}

		if r.Bool() {
			fn.Inl = &ir.Inline{
				Cost:            int32(r.Len()),
				CanDelayResults: r.Bool(),
			}
		}
	} else {
		r.addBody(name.Func, method)
	}
	r.Sync(pkgbits.SyncEOF)
}

func (r *reader) typeExt(name *ir.Name) {
	r.Sync(pkgbits.SyncTypeExt)

	typ := name.Type()

	if r.hasTypeParams() {
		// Set "RParams" (really type arguments here, not parameters) so
		// this type is treated as "fully instantiated". This ensures the
		// type descriptor is written out as DUPOK and method wrappers are
		// generated even for imported types.
		var targs []*types.Type
		targs = append(targs, r.dict.targs...)
		typ.SetRParams(targs)
	}

	name.SetPragma(r.pragmaFlag())

	typecheck.SetBaseTypeIndex(typ, r.Int64(), r.Int64())
}

func (r *reader) varExt(name *ir.Name) {
	r.Sync(pkgbits.SyncVarExt)
	r.linkname(name)
}

func (r *reader) linkname(name *ir.Name) {
	assert(name.Op() == ir.ONAME)
	r.Sync(pkgbits.SyncLinkname)

	if idx := r.Int64(); idx >= 0 {
		lsym := name.Linksym()
		lsym.SymIdx = int32(idx)
		lsym.Set(obj.AttrIndexed, true)
	} else {
		name.Sym().Linkname = r.String()
	}
}

func (r *reader) pragmaFlag() ir.PragmaFlag {
	r.Sync(pkgbits.SyncPragma)
	return ir.PragmaFlag(r.Int())
}

// @@@ Function bodies

// bodyReader tracks where the serialized IR for a local or imported,
// generic function's body can be found.
var bodyReader = map[*ir.Func]pkgReaderIndex{}

// importBodyReader tracks where the serialized IR for an imported,
// static (i.e., non-generic) function body can be read.
var importBodyReader = map[*types.Sym]pkgReaderIndex{}

// bodyReaderFor returns the pkgReaderIndex for reading fn's
// serialized IR, and whether one was found.
func bodyReaderFor(fn *ir.Func) (pri pkgReaderIndex, ok bool) {
	if fn.Nname.Defn != nil {
		pri, ok = bodyReader[fn]
		base.AssertfAt(ok, base.Pos, "must have bodyReader for %v", fn) // must always be available
	} else {
		pri, ok = importBodyReader[fn.Sym()]
	}
	return
}

// todoDicts holds the list of dictionaries that still need their
// runtime dictionary objects constructed.
var todoDicts []func()

// todoBodies holds the list of function bodies that still need to be
// constructed.
var todoBodies []*ir.Func

// addBody reads a function body reference from the element bitstream,
// and associates it with fn.
func (r *reader) addBody(fn *ir.Func, method *types.Sym) {
	// addBody should only be called for local functions or imported
	// generic functions; see comment in funcExt.
	assert(fn.Nname.Defn != nil)

	idx := r.Reloc(pkgbits.RelocBody)

	pri := pkgReaderIndex{r.p, idx, r.dict, method, nil}
	bodyReader[fn] = pri

	if r.curfn == nil {
		todoBodies = append(todoBodies, fn)
		return
	}

	pri.funcBody(fn)
}

func (pri pkgReaderIndex) funcBody(fn *ir.Func) {
	r := pri.asReader(pkgbits.RelocBody, pkgbits.SyncFuncBody)
	r.funcBody(fn)
}

// funcBody reads a function body definition from the element
// bitstream, and populates fn with it.
func (r *reader) funcBody(fn *ir.Func) {
	r.curfn = fn
	r.closureVars = fn.ClosureVars
	if len(r.closureVars) != 0 && r.hasTypeParams() {
		r.dictParam = r.closureVars[len(r.closureVars)-1] // dictParam is last; see reader.funcLit
	}

	ir.WithFunc(fn, func() {
		r.funcargs(fn)

		if r.syntheticBody(fn.Pos()) {
			return
		}

		if !r.Bool() {
			return
		}

		body := r.stmts()
		if body == nil {
			body = []ir.Node{typecheck.Stmt(ir.NewBlockStmt(src.NoXPos, nil))}
		}
		fn.Body = body
		fn.Endlineno = r.pos()
	})

	r.marker.WriteTo(fn)
}

// syntheticBody adds a synthetic body to r.curfn if appropriate, and
// reports whether it did.
func (r *reader) syntheticBody(pos src.XPos) bool {
	if r.synthetic != nil {
		r.synthetic(pos, r)
		return true
	}

	// If this function has type parameters and isn't shaped, then we
	// just tail call its corresponding shaped variant.
	if r.hasTypeParams() && !r.dict.shaped {
		r.callShaped(pos)
		return true
	}

	return false
}

// callShaped emits a tail call to r.shapedFn, passing along the
// arguments to the current function.
func (r *reader) callShaped(pos src.XPos) {
	shapedObj := r.dict.shapedObj
	assert(shapedObj != nil)

	var shapedFn ir.Node
	if r.methodSym == nil {
		// Instantiating a generic function; shapedObj is the shaped
		// function itself.
		assert(shapedObj.Op() == ir.ONAME && shapedObj.Class == ir.PFUNC)
		shapedFn = shapedObj
	} else {
		// Instantiating a generic type's method; shapedObj is the shaped
		// type, so we need to select it's corresponding method.
		shapedFn = shapedMethodExpr(pos, shapedObj, r.methodSym)
	}

	recvs, params := r.syntheticArgs(pos)

	// Construct the arguments list: receiver (if any), then runtime
	// dictionary, and finally normal parameters.
	//
	// Note: For simplicity, shaped methods are added as normal methods
	// on their shaped types. So existing code (e.g., packages ir and
	// typecheck) expects the shaped type to appear as the receiver
	// parameter (or first parameter, as a method expression). Hence
	// putting the dictionary parameter after that is the least invasive
	// solution at the moment.
	var args ir.Nodes
	args.Append(recvs...)
	args.Append(typecheck.Expr(ir.NewAddrExpr(pos, r.p.dictNameOf(r.dict))))
	args.Append(params...)

	r.syntheticTailCall(pos, shapedFn, args)
}

// syntheticArgs returns the recvs and params arguments passed to the
// current function.
func (r *reader) syntheticArgs(pos src.XPos) (recvs, params ir.Nodes) {
	sig := r.curfn.Nname.Type()

	inlVarIdx := 0
	addParams := func(out *ir.Nodes, params []*types.Field) {
		for _, param := range params {
			var arg ir.Node
			if param.Nname != nil {
				name := param.Nname.(*ir.Name)
				if !ir.IsBlank(name) {
					if r.inlCall != nil {
						// During inlining, we want the respective inlvar where we
						// assigned the callee's arguments.
						arg = r.inlvars[inlVarIdx]
					} else {
						// Otherwise, we can use the parameter itself directly.
						base.AssertfAt(name.Curfn == r.curfn, name.Pos(), "%v has curfn %v, but want %v", name, name.Curfn, r.curfn)
						arg = name
					}
				}
			}

			// For anonymous and blank parameters, we don't have an *ir.Name
			// to use as the argument. However, since we know the shaped
			// function won't use the value either, we can just pass the
			// zero value. (Also unfortunately, we don't have an easy
			// zero-value IR node; so we use a default-initialized temporary
			// variable.)
			if arg == nil {
				tmp := typecheck.TempAt(pos, r.curfn, param.Type)
				r.curfn.Body.Append(
					typecheck.Stmt(ir.NewDecl(pos, ir.ODCL, tmp)),
					typecheck.Stmt(ir.NewAssignStmt(pos, tmp, nil)),
				)
				arg = tmp
			}

			out.Append(arg)
			inlVarIdx++
		}
	}

	addParams(&recvs, sig.Recvs().FieldSlice())
	addParams(&params, sig.Params().FieldSlice())
	return
}

// syntheticTailCall emits a tail call to fn, passing the given
// arguments list.
func (r *reader) syntheticTailCall(pos src.XPos, fn ir.Node, args ir.Nodes) {
	// Mark the function as a wrapper so it doesn't show up in stack
	// traces.
	r.curfn.SetWrapper(true)

	call := typecheck.Call(pos, fn, args, fn.Type().IsVariadic()).(*ir.CallExpr)

	var stmt ir.Node
	if fn.Type().NumResults() != 0 {
		stmt = typecheck.Stmt(ir.NewReturnStmt(pos, []ir.Node{call}))
	} else {
		stmt = call
	}
	r.curfn.Body.Append(stmt)
}

// dictNameOf returns the runtime dictionary corresponding to dict.
func (pr *pkgReader) dictNameOf(dict *readerDict) *ir.Name {
	pos := base.AutogeneratedPos

	// Check that we only instantiate runtime dictionaries with real types.
	base.AssertfAt(!dict.shaped, pos, "runtime dictionary of shaped object %v", dict.baseSym)

	sym := dict.baseSym.Pkg.Lookup(objabi.GlobalDictPrefix + "." + dict.baseSym.Name)
	if sym.Def != nil {
		return sym.Def.(*ir.Name)
	}

	name := ir.NewNameAt(pos, sym)
	name.Class = ir.PEXTERN
	sym.Def = name // break cycles with mutual subdictionaries

	lsym := name.Linksym()
	ot := 0

	assertOffset := func(section string, offset int) {
		base.AssertfAt(ot == offset*types.PtrSize, pos, "writing section %v at offset %v, but it should be at %v*%v", section, ot, offset, types.PtrSize)
	}

	assertOffset("type param method exprs", dict.typeParamMethodExprsOffset())
	for _, info := range dict.typeParamMethodExprs {
		typeParam := dict.targs[info.typeParamIdx]
		method := typecheck.Expr(ir.NewSelectorExpr(pos, ir.OXDOT, ir.TypeNode(typeParam), info.method)).(*ir.SelectorExpr)
		assert(method.Op() == ir.OMETHEXPR)

		rsym := method.FuncName().Linksym()
		assert(rsym.ABI() == obj.ABIInternal) // must be ABIInternal; see ir.OCFUNC in ssagen/ssa.go

		ot = objw.SymPtr(lsym, ot, rsym, 0)
	}

	assertOffset("subdictionaries", dict.subdictsOffset())
	for _, info := range dict.subdicts {
		explicits := pr.typListIdx(info.explicits, dict)

		// Careful: Due to subdictionary cycles, name may not be fully
		// initialized yet.
		name := pr.objDictName(info.idx, dict.targs, explicits)

		ot = objw.SymPtr(lsym, ot, name.Linksym(), 0)
	}

	assertOffset("rtypes", dict.rtypesOffset())
	for _, info := range dict.rtypes {
		typ := pr.typIdx(info, dict, true)
		ot = objw.SymPtr(lsym, ot, reflectdata.TypeLinksym(typ), 0)

		// TODO(mdempsky): Double check this.
		reflectdata.MarkTypeUsedInInterface(typ, lsym)
	}

	// For each (typ, iface) pair, we write the *runtime.itab pointer
	// for the pair. For pairs that don't actually require an itab
	// (i.e., typ is an interface, or iface is an empty interface), we
	// write a nil pointer instead. This is wasteful, but rare in
	// practice (e.g., instantiating a type parameter with an interface
	// type).
	assertOffset("itabs", dict.itabsOffset())
	for _, info := range dict.itabs {
		typ := pr.typIdx(info.typ, dict, true)
		iface := pr.typIdx(info.iface, dict, true)

		if !typ.IsInterface() && iface.IsInterface() && !iface.IsEmptyInterface() {
			ot = objw.SymPtr(lsym, ot, reflectdata.ITabLsym(typ, iface), 0)
		} else {
			ot += types.PtrSize
		}

		// TODO(mdempsky): Double check this.
		reflectdata.MarkTypeUsedInInterface(typ, lsym)
		reflectdata.MarkTypeUsedInInterface(iface, lsym)
	}

	objw.Global(lsym, int32(ot), obj.DUPOK|obj.RODATA)

	name.SetType(dict.varType())
	name.SetTypecheck(1)

	return name
}

// typeParamMethodExprsOffset returns the offset of the runtime
// dictionary's type parameter method expressions section, in words.
func (dict *readerDict) typeParamMethodExprsOffset() int {
	return 0
}

// subdictsOffset returns the offset of the runtime dictionary's
// subdictionary section, in words.
func (dict *readerDict) subdictsOffset() int {
	return dict.typeParamMethodExprsOffset() + len(dict.typeParamMethodExprs)
}

// rtypesOffset returns the offset of the runtime dictionary's rtypes
// section, in words.
func (dict *readerDict) rtypesOffset() int {
	return dict.subdictsOffset() + len(dict.subdicts)
}

// itabsOffset returns the offset of the runtime dictionary's itabs
// section, in words.
func (dict *readerDict) itabsOffset() int {
	return dict.rtypesOffset() + len(dict.rtypes)
}

// numWords returns the total number of words that comprise dict's
// runtime dictionary variable.
func (dict *readerDict) numWords() int64 {
	return int64(dict.itabsOffset() + len(dict.itabs))
}

// varType returns the type of dict's runtime dictionary variable.
func (dict *readerDict) varType() *types.Type {
	return types.NewArray(types.Types[types.TUINTPTR], dict.numWords())
}

func (r *reader) funcargs(fn *ir.Func) {
	sig := fn.Nname.Type()

	if recv := sig.Recv(); recv != nil {
		r.funcarg(recv, recv.Sym, ir.PPARAM)
	}
	for _, param := range sig.Params().FieldSlice() {
		r.funcarg(param, param.Sym, ir.PPARAM)
	}

	for i, param := range sig.Results().FieldSlice() {
		sym := types.OrigSym(param.Sym)

		if sym == nil || sym.IsBlank() {
			prefix := "~r"
			if r.inlCall != nil {
				prefix = "~R"
			} else if sym != nil {
				prefix = "~b"
			}
			sym = typecheck.LookupNum(prefix, i)
		}

		r.funcarg(param, sym, ir.PPARAMOUT)
	}
}

func (r *reader) funcarg(param *types.Field, sym *types.Sym, ctxt ir.Class) {
	if sym == nil {
		assert(ctxt == ir.PPARAM)
		if r.inlCall != nil {
			r.inlvars.Append(ir.BlankNode)
		}
		return
	}

	name := ir.NewNameAt(r.inlPos(param.Pos), sym)
	setType(name, param.Type)
	r.addLocal(name, ctxt)

	if r.inlCall == nil {
		if !r.funarghack {
			param.Sym = sym
			param.Nname = name
		}
	} else {
		if ctxt == ir.PPARAMOUT {
			r.retvars.Append(name)
		} else {
			r.inlvars.Append(name)
		}
	}
}

func (r *reader) addLocal(name *ir.Name, ctxt ir.Class) {
	assert(ctxt == ir.PAUTO || ctxt == ir.PPARAM || ctxt == ir.PPARAMOUT)

	if name.Sym().Name == dictParamName {
		r.dictParam = name
	} else {
		if r.synthetic == nil {
			r.Sync(pkgbits.SyncAddLocal)
			if r.p.SyncMarkers() {
				want := r.Int()
				if have := len(r.locals); have != want {
					base.FatalfAt(name.Pos(), "locals table has desynced")
				}
			}
			r.varDictIndex(name)
		}

		r.locals = append(r.locals, name)
	}

	name.SetUsed(true)

	// TODO(mdempsky): Move earlier.
	if ir.IsBlank(name) {
		return
	}

	if r.inlCall != nil {
		if ctxt == ir.PAUTO {
			name.SetInlLocal(true)
		} else {
			name.SetInlFormal(true)
			ctxt = ir.PAUTO
		}

		// TODO(mdempsky): Rethink this hack.
		if strings.HasPrefix(name.Sym().Name, "~") || base.Flag.GenDwarfInl == 0 {
			name.SetPos(r.inlCall.Pos())
			name.SetInlFormal(false)
			name.SetInlLocal(false)
		}
	}

	name.Class = ctxt
	name.Curfn = r.curfn

	r.curfn.Dcl = append(r.curfn.Dcl, name)

	if ctxt == ir.PAUTO {
		name.SetFrameOffset(0)
	}
}

func (r *reader) useLocal() *ir.Name {
	r.Sync(pkgbits.SyncUseObjLocal)
	if r.Bool() {
		return r.locals[r.Len()]
	}
	return r.closureVars[r.Len()]
}

func (r *reader) openScope() {
	r.Sync(pkgbits.SyncOpenScope)
	pos := r.pos()

	if base.Flag.Dwarf {
		r.scopeVars = append(r.scopeVars, len(r.curfn.Dcl))
		r.marker.Push(pos)
	}
}

func (r *reader) closeScope() {
	r.Sync(pkgbits.SyncCloseScope)
	r.lastCloseScopePos = r.pos()

	r.closeAnotherScope()
}

// closeAnotherScope is like closeScope, but it reuses the same mark
// position as the last closeScope call. This is useful for "for" and
// "if" statements, as their implicit blocks always end at the same
// position as an explicit block.
func (r *reader) closeAnotherScope() {
	r.Sync(pkgbits.SyncCloseAnotherScope)

	if base.Flag.Dwarf {
		scopeVars := r.scopeVars[len(r.scopeVars)-1]
		r.scopeVars = r.scopeVars[:len(r.scopeVars)-1]

		// Quirkish: noder decides which scopes to keep before
		// typechecking, whereas incremental typechecking during IR
		// construction can result in new autotemps being allocated. To
		// produce identical output, we ignore autotemps here for the
		// purpose of deciding whether to retract the scope.
		//
		// This is important for net/http/fcgi, because it contains:
		//
		//	var body io.ReadCloser
		//	if len(content) > 0 {
		//		body, req.pw = io.Pipe()
		//	} else { … }
		//
		// Notably, io.Pipe is inlinable, and inlining it introduces a ~R0
		// variable at the call site.
		//
		// Noder does not preserve the scope where the io.Pipe() call
		// resides, because it doesn't contain any declared variables in
		// source. So the ~R0 variable ends up being assigned to the
		// enclosing scope instead.
		//
		// However, typechecking this assignment also introduces
		// autotemps, because io.Pipe's results need conversion before
		// they can be assigned to their respective destination variables.
		//
		// TODO(mdempsky): We should probably just keep all scopes, and
		// let dwarfgen take care of pruning them instead.
		retract := true
		for _, n := range r.curfn.Dcl[scopeVars:] {
			if !n.AutoTemp() {
				retract = false
				break
			}
		}

		if retract {
			// no variables were declared in this scope, so we can retract it.
			r.marker.Unpush()
		} else {
			r.marker.Pop(r.lastCloseScopePos)
		}
	}
}

// @@@ Statements

func (r *reader) stmt() ir.Node {
	switch stmts := r.stmts(); len(stmts) {
	case 0:
		return nil
	case 1:
		return stmts[0]
	default:
		return ir.NewBlockStmt(stmts[0].Pos(), stmts)
	}
}

func (r *reader) stmts() []ir.Node {
	assert(ir.CurFunc == r.curfn)
	var res ir.Nodes

	r.Sync(pkgbits.SyncStmts)
	for {
		tag := codeStmt(r.Code(pkgbits.SyncStmt1))
		if tag == stmtEnd {
			r.Sync(pkgbits.SyncStmtsEnd)
			return res
		}

		if n := r.stmt1(tag, &res); n != nil {
			res.Append(typecheck.Stmt(n))
		}
	}
}

func (r *reader) stmt1(tag codeStmt, out *ir.Nodes) ir.Node {
	var label *types.Sym
	if n := len(*out); n > 0 {
		if ls, ok := (*out)[n-1].(*ir.LabelStmt); ok {
			label = ls.Label
		}
	}

	switch tag {
	default:
		panic("unexpected statement")

	case stmtAssign:
		pos := r.pos()
		names, lhs := r.assignList()
		rhs := r.multiExpr()

		if len(rhs) == 0 {
			for _, name := range names {
				as := ir.NewAssignStmt(pos, name, nil)
				as.PtrInit().Append(ir.NewDecl(pos, ir.ODCL, name))
				out.Append(typecheck.Stmt(as))
			}
			return nil
		}

		if len(lhs) == 1 && len(rhs) == 1 {
			n := ir.NewAssignStmt(pos, lhs[0], rhs[0])
			n.Def = r.initDefn(n, names)
			return n
		}

		n := ir.NewAssignListStmt(pos, ir.OAS2, lhs, rhs)
		n.Def = r.initDefn(n, names)
		return n

	case stmtAssignOp:
		op := r.op()
		lhs := r.expr()
		pos := r.pos()
		rhs := r.expr()
		return ir.NewAssignOpStmt(pos, op, lhs, rhs)

	case stmtIncDec:
		op := r.op()
		lhs := r.expr()
		pos := r.pos()
		n := ir.NewAssignOpStmt(pos, op, lhs, ir.NewBasicLit(pos, one))
		n.IncDec = true
		return n

	case stmtBlock:
		out.Append(r.blockStmt()...)
		return nil

	case stmtBranch:
		pos := r.pos()
		op := r.op()
		sym := r.optLabel()
		return ir.NewBranchStmt(pos, op, sym)

	case stmtCall:
		pos := r.pos()
		op := r.op()
		call := r.expr()
		return ir.NewGoDeferStmt(pos, op, call)

	case stmtExpr:
		return r.expr()

	case stmtFor:
		return r.forStmt(label)

	case stmtIf:
		return r.ifStmt()

	case stmtLabel:
		pos := r.pos()
		sym := r.label()
		return ir.NewLabelStmt(pos, sym)

	case stmtReturn:
		pos := r.pos()
		results := r.multiExpr()
		return ir.NewReturnStmt(pos, results)

	case stmtSelect:
		return r.selectStmt(label)

	case stmtSend:
		pos := r.pos()
		ch := r.expr()
		value := r.expr()
		return ir.NewSendStmt(pos, ch, value)

	case stmtSwitch:
		return r.switchStmt(label)
	}
}

func (r *reader) assignList() ([]*ir.Name, []ir.Node) {
	lhs := make([]ir.Node, r.Len())
	var names []*ir.Name

	for i := range lhs {
		expr, def := r.assign()
		lhs[i] = expr
		if def {
			names = append(names, expr.(*ir.Name))
		}
	}

	return names, lhs
}

// assign returns an assignee expression. It also reports whether the
// returned expression is a newly declared variable.
func (r *reader) assign() (ir.Node, bool) {
	switch tag := codeAssign(r.Code(pkgbits.SyncAssign)); tag {
	default:
		panic("unhandled assignee expression")

	case assignBlank:
		return typecheck.AssignExpr(ir.BlankNode), false

	case assignDef:
		pos := r.pos()
		setBasePos(pos)
		_, sym := r.localIdent()
		typ := r.typ()

		name := ir.NewNameAt(pos, sym)
		setType(name, typ)
		r.addLocal(name, ir.PAUTO)
		return name, true

	case assignExpr:
		return r.expr(), false
	}
}

func (r *reader) blockStmt() []ir.Node {
	r.Sync(pkgbits.SyncBlockStmt)
	r.openScope()
	stmts := r.stmts()
	r.closeScope()
	return stmts
}

func (r *reader) forStmt(label *types.Sym) ir.Node {
	r.Sync(pkgbits.SyncForStmt)

	r.openScope()

	if r.Bool() {
		pos := r.pos()
		rang := ir.NewRangeStmt(pos, nil, nil, nil, nil)
		rang.Label = label

		names, lhs := r.assignList()
		if len(lhs) >= 1 {
			rang.Key = lhs[0]
			if len(lhs) >= 2 {
				rang.Value = lhs[1]
			}
		}
		rang.Def = r.initDefn(rang, names)

		rang.X = r.expr()
		if rang.X.Type().IsMap() {
			rang.RType = r.rtype(pos)
		}
		if rang.Key != nil && !ir.IsBlank(rang.Key) {
			rang.KeyTypeWord, rang.KeySrcRType = r.convRTTI(pos)
		}
		if rang.Value != nil && !ir.IsBlank(rang.Value) {
			rang.ValueTypeWord, rang.ValueSrcRType = r.convRTTI(pos)
		}

		rang.Body = r.blockStmt()
		r.closeAnotherScope()

		return rang
	}

	pos := r.pos()
	init := r.stmt()
	cond := r.optExpr()
	post := r.stmt()
	body := r.blockStmt()
	r.closeAnotherScope()

	stmt := ir.NewForStmt(pos, init, cond, post, body)
	stmt.Label = label
	return stmt
}

func (r *reader) ifStmt() ir.Node {
	r.Sync(pkgbits.SyncIfStmt)
	r.openScope()
	pos := r.pos()
	init := r.stmts()
	cond := r.expr()
	then := r.blockStmt()
	els := r.stmts()
	n := ir.NewIfStmt(pos, cond, then, els)
	n.SetInit(init)
	r.closeAnotherScope()
	return n
}

func (r *reader) selectStmt(label *types.Sym) ir.Node {
	r.Sync(pkgbits.SyncSelectStmt)

	pos := r.pos()
	clauses := make([]*ir.CommClause, r.Len())
	for i := range clauses {
		if i > 0 {
			r.closeScope()
		}
		r.openScope()

		pos := r.pos()
		comm := r.stmt()
		body := r.stmts()

		// "case i = <-c: ..." may require an implicit conversion (e.g.,
		// see fixedbugs/bug312.go). Currently, typecheck throws away the
		// implicit conversion and relies on it being reinserted later,
		// but that would lose any explicit RTTI operands too. To preserve
		// RTTI, we rewrite this as "case tmp := <-c: i = tmp; ...".
		if as, ok := comm.(*ir.AssignStmt); ok && as.Op() == ir.OAS && !as.Def {
			if conv, ok := as.Y.(*ir.ConvExpr); ok && conv.Op() == ir.OCONVIFACE {
				base.AssertfAt(conv.Implicit(), conv.Pos(), "expected implicit conversion: %v", conv)

				recv := conv.X
				base.AssertfAt(recv.Op() == ir.ORECV, recv.Pos(), "expected receive expression: %v", recv)

				tmp := r.temp(pos, recv.Type())

				// Replace comm with `tmp := <-c`.
				tmpAs := ir.NewAssignStmt(pos, tmp, recv)
				tmpAs.Def = true
				tmpAs.PtrInit().Append(ir.NewDecl(pos, ir.ODCL, tmp))
				comm = tmpAs

				// Change original assignment to `i = tmp`, and prepend to body.
				conv.X = tmp
				body = append([]ir.Node{as}, body...)
			}
		}

		// multiExpr will have desugared a comma-ok receive expression
		// into a separate statement. However, the rest of the compiler
		// expects comm to be the OAS2RECV statement itself, so we need to
		// shuffle things around to fit that pattern.
		if as2, ok := comm.(*ir.AssignListStmt); ok && as2.Op() == ir.OAS2 {
			init := ir.TakeInit(as2.Rhs[0])
			base.AssertfAt(len(init) == 1 && init[0].Op() == ir.OAS2RECV, as2.Pos(), "unexpected assignment: %+v", as2)

			comm = init[0]
			body = append([]ir.Node{as2}, body...)
		}

		clauses[i] = ir.NewCommStmt(pos, comm, body)
	}
	if len(clauses) > 0 {
		r.closeScope()
	}
	n := ir.NewSelectStmt(pos, clauses)
	n.Label = label
	return n
}

func (r *reader) switchStmt(label *types.Sym) ir.Node {
	r.Sync(pkgbits.SyncSwitchStmt)

	r.openScope()
	pos := r.pos()
	init := r.stmt()

	var tag ir.Node
	var ident *ir.Ident
	var iface *types.Type
	if r.Bool() {
		pos := r.pos()
		if r.Bool() {
			pos := r.pos()
			_, sym := r.localIdent()
			ident = ir.NewIdent(pos, sym)
		}
		x := r.expr()
		iface = x.Type()
		tag = ir.NewTypeSwitchGuard(pos, ident, x)
	} else {
		tag = r.optExpr()
	}

	clauses := make([]*ir.CaseClause, r.Len())
	for i := range clauses {
		if i > 0 {
			r.closeScope()
		}
		r.openScope()

		pos := r.pos()
		var cases, rtypes []ir.Node
		if iface != nil {
			cases = make([]ir.Node, r.Len())
			if len(cases) == 0 {
				cases = nil // TODO(mdempsky): Unclear if this matters.
			}