reader.go

						for len(rtypes) < i {
							rtypes = append(rtypes, nil)
						}
						rtypes = append(rtypes, reflectdata.TypePtrAt(cas.Pos(), types.Types[types.TBOOL]))
					}
				}
			}
		}

		clause := ir.NewCaseStmt(pos, cases, nil)
		clause.RTypes = rtypes

		if ident != nil {
			pos := r.pos()
			typ := r.typ()

			name := ir.NewNameAt(pos, ident.Sym())
			setType(name, typ)
			r.addLocal(name, ir.PAUTO)
			clause.Var = name
			name.Defn = tag
		}

		clause.Body = r.stmts()
		clauses[i] = clause
	}
	if len(clauses) > 0 {
		r.closeScope()
	}
	r.closeScope()

	n := ir.NewSwitchStmt(pos, tag, clauses)
	n.Label = label
	if init != nil {
		n.SetInit([]ir.Node{init})
	}
	return n
}

func (r *reader) label() *types.Sym {
	r.Sync(pkgbits.SyncLabel)
	name := r.String()
	if r.inlCall != nil {
		name = fmt.Sprintf("~%s·%d", name, inlgen)
	}
	return typecheck.Lookup(name)
}

func (r *reader) optLabel() *types.Sym {
	r.Sync(pkgbits.SyncOptLabel)
	if r.Bool() {
		return r.label()
	}
	return nil
}

// initDefn marks the given names as declared by defn and populates
// its Init field with ODCL nodes. It then reports whether any names
// were so declared, which can be used to initialize defn.Def.
func (r *reader) initDefn(defn ir.InitNode, names []*ir.Name) bool {
	if len(names) == 0 {
		return false
	}

	init := make([]ir.Node, len(names))
	for i, name := range names {
		name.Defn = defn
		init[i] = ir.NewDecl(name.Pos(), ir.ODCL, name)
	}
	defn.SetInit(init)
	return true
}

// @@@ Expressions

// expr reads and returns a typechecked expression.
func (r *reader) expr() (res ir.Node) {
	defer func() {
		if res != nil && res.Typecheck() == 0 {
			base.FatalfAt(res.Pos(), "%v missed typecheck", res)
		}
	}()

	switch tag := codeExpr(r.Code(pkgbits.SyncExpr)); tag {
	default:
		panic("unhandled expression")

	case exprLocal:
		return typecheck.Expr(r.useLocal())

	case exprGlobal:
		// Callee instead of Expr allows builtins
		// TODO(mdempsky): Handle builtins directly in exprCall, like method calls?
		return typecheck.Callee(r.obj())

	case exprFuncInst:
		pos := r.pos()
		wrapperFn, baseFn, dictPtr := r.funcInst(pos)
		if wrapperFn != nil {
			return wrapperFn
		}
		return r.curry(pos, false, baseFn, dictPtr, nil)

	case exprConst:
		pos := r.pos()
		typ := r.typ()
		val := FixValue(typ, r.Value())
		op := r.op()
		orig := r.String()
		return typecheck.Expr(OrigConst(pos, typ, val, op, orig))

	case exprNil:
		pos := r.pos()
		typ := r.typ()
		return Nil(pos, typ)

	case exprCompLit:
		return r.compLit()

	case exprFuncLit:
		return r.funcLit()

	case exprFieldVal:
		x := r.expr()
		pos := r.pos()
		_, sym := r.selector()

		return typecheck.Expr(ir.NewSelectorExpr(pos, ir.OXDOT, x, sym)).(*ir.SelectorExpr)

	case exprMethodVal:
		recv := r.expr()
		pos := r.pos()
		wrapperFn, baseFn, dictPtr := r.methodExpr()

		// For simple wrapperFn values, the existing machinery for creating
		// and deduplicating wrapperFn value wrappers still works fine.
		if wrapperFn, ok := wrapperFn.(*ir.SelectorExpr); ok && wrapperFn.Op() == ir.OMETHEXPR {
			// The receiver expression we constructed may have a shape type.
			// For example, in fixedbugs/issue54343.go, `New[int]()` is
			// constructed as `New[go.shape.int](&.dict.New[int])`, which
			// has type `*T[go.shape.int]`, not `*T[int]`.
			//
			// However, the method we want to select here is `(*T[int]).M`,
			// not `(*T[go.shape.int]).M`, so we need to manually convert
			// the type back so that the OXDOT resolves correctly.
			//
			// TODO(mdempsky): Logically it might make more sense for
			// exprCall to take responsibility for setting a non-shaped
			// result type, but this is the only place where we care
			// currently. And only because existing ir.OMETHVALUE backend
			// code relies on n.X.Type() instead of n.Selection.Recv().Type
			// (because the latter is types.FakeRecvType() in the case of
			// interface method values).
			//
			if recv.Type().HasShape() {
				typ := wrapperFn.Type().Params().Field(0).Type
				if !types.Identical(typ, recv.Type()) {
					base.FatalfAt(wrapperFn.Pos(), "receiver %L does not match %L", recv, wrapperFn)
				}
				recv = typecheck.Expr(ir.NewConvExpr(recv.Pos(), ir.OCONVNOP, typ, recv))
			}

			n := typecheck.Expr(ir.NewSelectorExpr(pos, ir.OXDOT, recv, wrapperFn.Sel)).(*ir.SelectorExpr)
			assert(n.Selection == wrapperFn.Selection)

			wrapper := methodValueWrapper{
				rcvr:   n.X.Type(),
				method: n.Selection,
			}

			if r.importedDef() {
				haveMethodValueWrappers = append(haveMethodValueWrappers, wrapper)
			} else {
				needMethodValueWrappers = append(needMethodValueWrappers, wrapper)
			}
			return n
		}

		// For more complicated method expressions, we construct a
		// function literal wrapper.
		return r.curry(pos, true, baseFn, recv, dictPtr)

	case exprMethodExpr:
		recv := r.typ()

		implicits := make([]int, r.Len())
		for i := range implicits {
			implicits[i] = r.Len()
		}
		var deref, addr bool
		if r.Bool() {
			deref = true
		} else if r.Bool() {
			addr = true
		}

		pos := r.pos()
		wrapperFn, baseFn, dictPtr := r.methodExpr()

		// If we already have a wrapper and don't need to do anything with
		// it, we can just return the wrapper directly.
		//
		// N.B., we use implicits/deref/addr here as the source of truth
		// rather than types.Identical, because the latter can be confused
		// by tricky promoted methods (e.g., typeparam/mdempsky/21.go).
		if wrapperFn != nil && len(implicits) == 0 && !deref && !addr {
			if !types.Identical(recv, wrapperFn.Type().Params().Field(0).Type) {
				base.FatalfAt(pos, "want receiver type %v, but have method %L", recv, wrapperFn)
			}
			return wrapperFn
		}

		// Otherwise, if the wrapper function is a static method
		// expression (OMETHEXPR) and the receiver type is unshaped, then
		// we can rely on a statically generated wrapper being available.
		if method, ok := wrapperFn.(*ir.SelectorExpr); ok && method.Op() == ir.OMETHEXPR && !recv.HasShape() {
			return typecheck.Expr(ir.NewSelectorExpr(pos, ir.OXDOT, ir.TypeNode(recv), method.Sel)).(*ir.SelectorExpr)
		}

		return r.methodExprWrap(pos, recv, implicits, deref, addr, baseFn, dictPtr)

	case exprIndex:
		x := r.expr()
		pos := r.pos()
		index := r.expr()
		n := typecheck.Expr(ir.NewIndexExpr(pos, x, index))
		switch n.Op() {
		case ir.OINDEXMAP:
			n := n.(*ir.IndexExpr)
			n.RType = r.rtype(pos)
		}
		return n

	case exprSlice:
		x := r.expr()
		pos := r.pos()
		var index [3]ir.Node
		for i := range index {
			index[i] = r.optExpr()
		}
		op := ir.OSLICE
		if index[2] != nil {
			op = ir.OSLICE3
		}
		return typecheck.Expr(ir.NewSliceExpr(pos, op, x, index[0], index[1], index[2]))

	case exprAssert:
		x := r.expr()
		pos := r.pos()
		typ := r.exprType()
		srcRType := r.rtype(pos)

		// TODO(mdempsky): Always emit ODYNAMICDOTTYPE for uniformity?
		if typ, ok := typ.(*ir.DynamicType); ok && typ.Op() == ir.ODYNAMICTYPE {
			assert := ir.NewDynamicTypeAssertExpr(pos, ir.ODYNAMICDOTTYPE, x, typ.RType)
			assert.SrcRType = srcRType
			assert.ITab = typ.ITab
			return typed(typ.Type(), assert)
		}
		return typecheck.Expr(ir.NewTypeAssertExpr(pos, x, typ.Type()))

	case exprUnaryOp:
		op := r.op()
		pos := r.pos()
		x := r.expr()

		switch op {
		case ir.OADDR:
			return typecheck.Expr(typecheck.NodAddrAt(pos, x))
		case ir.ODEREF:
			return typecheck.Expr(ir.NewStarExpr(pos, x))
		}
		return typecheck.Expr(ir.NewUnaryExpr(pos, op, x))

	case exprBinaryOp:
		op := r.op()
		x := r.expr()
		pos := r.pos()
		y := r.expr()

		switch op {
		case ir.OANDAND, ir.OOROR:
			return typecheck.Expr(ir.NewLogicalExpr(pos, op, x, y))
		}
		return typecheck.Expr(ir.NewBinaryExpr(pos, op, x, y))

	case exprRecv:
		x := r.expr()
		pos := r.pos()
		for i, n := 0, r.Len(); i < n; i++ {
			x = Implicit(DotField(pos, x, r.Len()))
		}
		if r.Bool() { // needs deref
			x = Implicit(Deref(pos, x.Type().Elem(), x))
		} else if r.Bool() { // needs addr
			x = Implicit(Addr(pos, x))
		}
		return x

	case exprCall:
		var fun ir.Node
		var args ir.Nodes
		if r.Bool() { // method call
			recv := r.expr()
			_, method, dictPtr := r.methodExpr()

			if recv.Type().IsInterface() && method.Op() == ir.OMETHEXPR {
				method := method.(*ir.SelectorExpr)

				// The compiler backend (e.g., devirtualization) handle
				// OCALLINTER/ODOTINTER better than OCALLFUNC/OMETHEXPR for
				// interface calls, so we prefer to continue constructing
				// calls that way where possible.
				//
				// There are also corner cases where semantically it's perhaps
				// significant; e.g., fixedbugs/issue15975.go, #38634, #52025.

				fun = typecheck.Callee(ir.NewSelectorExpr(method.Pos(), ir.OXDOT, recv, method.Sel))
			} else {
				if recv.Type().IsInterface() {
					// N.B., this happens currently for typeparam/issue51521.go
					// and typeparam/typeswitch3.go.
					if base.Flag.LowerM > 0 {
						base.WarnfAt(method.Pos(), "imprecise interface call")
					}
				}

				fun = method
				args.Append(recv)
			}
			if dictPtr != nil {
				args.Append(dictPtr)
			}
		} else if r.Bool() { // call to instanced function
			pos := r.pos()
			_, shapedFn, dictPtr := r.funcInst(pos)
			fun = shapedFn
			args.Append(dictPtr)
		} else {
			fun = r.expr()
		}
		pos := r.pos()
		args.Append(r.multiExpr()...)
		dots := r.Bool()
		n := typecheck.Call(pos, fun, args, dots)
		switch n.Op() {
		case ir.OAPPEND:
			n := n.(*ir.CallExpr)
			n.RType = r.rtype(pos)
			// For append(a, b...), we don't need the implicit conversion. The typechecker already
			// ensured that a and b are both slices with the same base type, or []byte and string.
			if n.IsDDD {
				if conv, ok := n.Args[1].(*ir.ConvExpr); ok && conv.Op() == ir.OCONVNOP && conv.Implicit() {
					n.Args[1] = conv.X
				}
			}
		case ir.OCOPY:
			n := n.(*ir.BinaryExpr)
			n.RType = r.rtype(pos)
		case ir.ODELETE:
			n := n.(*ir.CallExpr)
			n.RType = r.rtype(pos)
		case ir.OUNSAFESLICE:
			n := n.(*ir.BinaryExpr)
			n.RType = r.rtype(pos)
		}
		return n

	case exprMake:
		pos := r.pos()
		typ := r.exprType()
		extra := r.exprs()
		n := typecheck.Expr(ir.NewCallExpr(pos, ir.OMAKE, nil, append([]ir.Node{typ}, extra...))).(*ir.MakeExpr)
		n.RType = r.rtype(pos)
		return n

	case exprNew:
		pos := r.pos()
		typ := r.exprType()
		return typecheck.Expr(ir.NewUnaryExpr(pos, ir.ONEW, typ))

	case exprReshape:
		typ := r.typ()
		x := r.expr()

		if types.IdenticalStrict(x.Type(), typ) {
			return x
		}

		// Comparison expressions are constructed as "untyped bool" still.
		//
		// TODO(mdempsky): It should be safe to reshape them here too, but
		// maybe it's better to construct them with the proper type
		// instead.
		if x.Type() == types.UntypedBool && typ.IsBoolean() {
			return x
		}

		base.AssertfAt(x.Type().HasShape() || typ.HasShape(), x.Pos(), "%L and %v are not shape types", x, typ)
		base.AssertfAt(types.Identical(x.Type(), typ), x.Pos(), "%L is not shape-identical to %v", x, typ)

		// We use ir.HasUniquePos here as a check that x only appears once
		// in the AST, so it's okay for us to call SetType without
		// breaking any other uses of it.
		//
		// Notably, any ONAMEs should already have the exactly right shape
		// type and been caught by types.IdenticalStrict above.
		base.AssertfAt(ir.HasUniquePos(x), x.Pos(), "cannot call SetType(%v) on %L", typ, x)

		if base.Debug.Reshape != 0 {
			base.WarnfAt(x.Pos(), "reshaping %L to %v", x, typ)
		}

		x.SetType(typ)
		return x

	case exprConvert:
		implicit := r.Bool()
		typ := r.typ()
		pos := r.pos()
		typeWord, srcRType := r.convRTTI(pos)
		dstTypeParam := r.Bool()
		x := r.expr()

		// TODO(mdempsky): Stop constructing expressions of untyped type.
		x = typecheck.DefaultLit(x, typ)

		if op, why := typecheck.Convertop(x.Op() == ir.OLITERAL, x.Type(), typ); op == ir.OXXX {
			// types2 ensured that x is convertable to typ under standard Go
			// semantics, but cmd/compile also disallows some conversions
			// involving //go:notinheap.
			//
			// TODO(mdempsky): This can be removed after #46731 is implemented.
			base.ErrorfAt(pos, "cannot convert %L to type %v%v", x, typ, why)
			base.ErrorExit() // harsh, but prevents constructing invalid IR
		}

		ce := ir.NewConvExpr(pos, ir.OCONV, typ, x)
		ce.TypeWord, ce.SrcRType = typeWord, srcRType
		if implicit {
			ce.SetImplicit(true)
		}
		n := typecheck.Expr(ce)

		// Conversions between non-identical, non-empty interfaces always
		// requires a runtime call, even if they have identical underlying
		// interfaces. This is because we create separate itab instances
		// for each unique interface type, not merely each unique
		// interface shape.
		//
		// However, due to shape types, typecheck.Expr might mistakenly
		// think a conversion between two non-empty interfaces are
		// identical and set ir.OCONVNOP, instead of ir.OCONVIFACE. To
		// ensure we update the itab field appropriately, we force it to
		// ir.OCONVIFACE instead when shape types are involved.
		//
		// TODO(mdempsky): Are there other places we might get this wrong?
		// Should this be moved down into typecheck.{Assign,Convert}op?
		// This would be a non-issue if itabs were unique for each
		// *underlying* interface type instead.
		if n, ok := n.(*ir.ConvExpr); ok && n.Op() == ir.OCONVNOP && n.Type().IsInterface() && !n.Type().IsEmptyInterface() && (n.Type().HasShape() || n.X.Type().HasShape()) {
			n.SetOp(ir.OCONVIFACE)
		}

		// spec: "If the type is a type parameter, the constant is converted
		// into a non-constant value of the type parameter."
		if dstTypeParam && ir.IsConstNode(n) {
			// Wrap in an OCONVNOP node to ensure result is non-constant.
			n = Implicit(ir.NewConvExpr(pos, ir.OCONVNOP, n.Type(), n))
			n.SetTypecheck(1)
		}
		return n
	}
}

// funcInst reads an instantiated function reference, and returns
// three (possibly nil) expressions related to it:
//
// baseFn is always non-nil: it's either a function of the appropriate
// type already, or it has an extra dictionary parameter as the first
// parameter.
//
// If dictPtr is non-nil, then it's a dictionary argument that must be
// passed as the first argument to baseFn.
//
// If wrapperFn is non-nil, then it's either the same as baseFn (if
// dictPtr is nil), or it's semantically equivalent to currying baseFn
// to pass dictPtr. (wrapperFn is nil when dictPtr is an expression
// that needs to be computed dynamically.)
//
// For callers that are creating a call to the returned function, it's
// best to emit a call to baseFn, and include dictPtr in the arguments
// list as appropriate.
//
// For callers that want to return the function without invoking it,
// they may return wrapperFn if it's non-nil; but otherwise, they need
// to create their own wrapper.
func (r *reader) funcInst(pos src.XPos) (wrapperFn, baseFn, dictPtr ir.Node) {
	// Like in methodExpr, I'm pretty sure this isn't needed.
	var implicits []*types.Type
	if r.dict != nil {
		implicits = r.dict.targs
	}

	if r.Bool() { // dynamic subdictionary
		idx := r.Len()
		info := r.dict.subdicts[idx]
		explicits := r.p.typListIdx(info.explicits, r.dict)

		baseFn = r.p.objIdx(info.idx, implicits, explicits, true).(*ir.Name)

		// TODO(mdempsky): Is there a more robust way to get the
		// dictionary pointer type here?
		dictPtrType := baseFn.Type().Params().Field(0).Type
		dictPtr = typecheck.Expr(ir.NewConvExpr(pos, ir.OCONVNOP, dictPtrType, r.dictWord(pos, r.dict.subdictsOffset()+idx)))

		return
	}

	info := r.objInfo()
	explicits := r.p.typListIdx(info.explicits, r.dict)

	wrapperFn = r.p.objIdx(info.idx, implicits, explicits, false).(*ir.Name)
	baseFn = r.p.objIdx(info.idx, implicits, explicits, true).(*ir.Name)

	dictName := r.p.objDictName(info.idx, implicits, explicits)
	dictPtr = typecheck.Expr(ir.NewAddrExpr(pos, dictName))

	return
}

func (pr *pkgReader) objDictName(idx pkgbits.Index, implicits, explicits []*types.Type) *ir.Name {
	rname := pr.newReader(pkgbits.RelocName, idx, pkgbits.SyncObject1)
	_, sym := rname.qualifiedIdent()
	tag := pkgbits.CodeObj(rname.Code(pkgbits.SyncCodeObj))

	if tag == pkgbits.ObjStub {
		assert(!sym.IsBlank())
		if pri, ok := objReader[sym]; ok {
			return pri.pr.objDictName(pri.idx, nil, explicits)
		}
		base.Fatalf("unresolved stub: %v", sym)
	}

	dict := pr.objDictIdx(sym, idx, implicits, explicits, false)

	return pr.dictNameOf(dict)
}

// curry returns a function literal that calls fun with arg0 and
// (optionally) arg1, accepting additional arguments to the function
// literal as necessary to satisfy fun's signature.
//
// If nilCheck is true and arg0 is an interface value, then it's
// checked to be non-nil as an initial step at the point of evaluating
// the function literal itself.
func (r *reader) curry(pos src.XPos, ifaceHack bool, fun ir.Node, arg0, arg1 ir.Node) ir.Node {
	var captured ir.Nodes
	captured.Append(fun, arg0)
	if arg1 != nil {
		captured.Append(arg1)
	}

	params, results := syntheticSig(fun.Type())
	params = params[len(captured)-1:] // skip curried parameters
	typ := types.NewSignature(types.NoPkg, nil, nil, params, results)

	addBody := func(pos src.XPos, r *reader, captured []ir.Node) {
		recvs, params := r.syntheticArgs(pos)
		assert(len(recvs) == 0)

		fun := captured[0]

		var args ir.Nodes
		args.Append(captured[1:]...)
		args.Append(params...)

		r.syntheticTailCall(pos, fun, args)
	}

	return r.syntheticClosure(pos, typ, ifaceHack, captured, addBody)
}

// methodExprWrap returns a function literal that changes method's
// first parameter's type to recv, and uses implicits/deref/addr to
// select the appropriate receiver parameter to pass to method.
func (r *reader) methodExprWrap(pos src.XPos, recv *types.Type, implicits []int, deref, addr bool, method, dictPtr ir.Node) ir.Node {
	var captured ir.Nodes
	captured.Append(method)

	params, results := syntheticSig(method.Type())

	// Change first parameter to recv.
	params[0].Type = recv

	// If we have a dictionary pointer argument to pass, then omit the
	// underlying method expression's dictionary parameter from the
	// returned signature too.
	if dictPtr != nil {
		captured.Append(dictPtr)
		params = append(params[:1], params[2:]...)
	}

	typ := types.NewSignature(types.NoPkg, nil, nil, params, results)

	addBody := func(pos src.XPos, r *reader, captured []ir.Node) {
		recvs, args := r.syntheticArgs(pos)
		assert(len(recvs) == 0)

		fn := captured[0]

		// Rewrite first argument based on implicits/deref/addr.
		{
			arg := args[0]
			for _, ix := range implicits {
				arg = Implicit(DotField(pos, arg, ix))
			}
			if deref {
				arg = Implicit(Deref(pos, arg.Type().Elem(), arg))
			} else if addr {
				arg = Implicit(Addr(pos, arg))
			}
			args[0] = arg
		}

		// Insert dictionary argument, if provided.
		if dictPtr != nil {
			newArgs := make([]ir.Node, len(args)+1)
			newArgs[0] = args[0]
			newArgs[1] = captured[1]
			copy(newArgs[2:], args[1:])
			args = newArgs
		}

		r.syntheticTailCall(pos, fn, args)
	}

	return r.syntheticClosure(pos, typ, false, captured, addBody)
}

// syntheticClosure constructs a synthetic function literal for
// currying dictionary arguments. pos is the position used for the
// closure. typ is the function literal's signature type.
//
// captures is a list of expressions that need to be evaluated at the
// point of function literal evaluation and captured by the function
// literal. If ifaceHack is true and captures[1] is an interface type,
// it's checked to be non-nil after evaluation.
//
// addBody is a callback function to populate the function body. The
// list of captured values passed back has the captured variables for
// use within the function literal, corresponding to the expressions
// in captures.
func (r *reader) syntheticClosure(pos src.XPos, typ *types.Type, ifaceHack bool, captures ir.Nodes, addBody func(pos src.XPos, r *reader, captured []ir.Node)) ir.Node {
	// isSafe reports whether n is an expression that we can safely
	// defer to evaluating inside the closure instead, to avoid storing
	// them into the closure.
	//
	// In practice this is always (and only) the wrappee function.
	isSafe := func(n ir.Node) bool {
		if n.Op() == ir.ONAME && n.(*ir.Name).Class == ir.PFUNC {
			return true
		}
		if n.Op() == ir.OMETHEXPR {
			return true
		}

		return false
	}

	fn := ir.NewClosureFunc(pos, r.curfn != nil)
	fn.SetWrapper(true)
	clo := fn.OClosure
	ir.NameClosure(clo, r.curfn)

	setType(fn.Nname, typ)
	typecheck.Func(fn)
	setType(clo, fn.Type())

	var init ir.Nodes
	for i, n := range captures {
		if isSafe(n) {
			continue // skip capture; can reference directly
		}

		tmp := r.tempCopy(pos, n, &init)
		ir.NewClosureVar(pos, fn, tmp)

		// We need to nil check interface receivers at the point of method
		// value evaluation, ugh.
		if ifaceHack && i == 1 && n.Type().IsInterface() {
			check := ir.NewUnaryExpr(pos, ir.OCHECKNIL, ir.NewUnaryExpr(pos, ir.OITAB, tmp))
			init.Append(typecheck.Stmt(check))
		}
	}

	pri := pkgReaderIndex{synthetic: func(pos src.XPos, r *reader) {
		captured := make([]ir.Node, len(captures))
		next := 0
		for i, n := range captures {
			if isSafe(n) {
				captured[i] = n
			} else {
				captured[i] = r.closureVars[next]
				next++
			}
		}
		assert(next == len(r.closureVars))

		addBody(pos, r, captured)
	}}
	bodyReader[fn] = pri
	pri.funcBody(fn)

	// TODO(mdempsky): Remove hard-coding of typecheck.Target.
	return ir.InitExpr(init, ir.UseClosure(clo, typecheck.Target))
}

// syntheticSig duplicates and returns the params and results lists
// for sig, but renaming anonymous parameters so they can be assigned
// ir.Names.
func syntheticSig(sig *types.Type) (params, results []*types.Field) {
	clone := func(params []*types.Field) []*types.Field {
		res := make([]*types.Field, len(params))
		for i, param := range params {
			sym := param.Sym
			if sym == nil || sym.Name == "_" {
				sym = typecheck.LookupNum(".anon", i)
			}
			// TODO(mdempsky): It would be nice to preserve the original
			// parameter positions here instead, but at least
			// typecheck.NewMethodType replaces them with base.Pos, making
			// them useless. Worse, the positions copied from base.Pos may
			// have inlining contexts, which we definitely don't want here
			// (e.g., #54625).
			res[i] = types.NewField(base.AutogeneratedPos, sym, param.Type)
			res[i].SetIsDDD(param.IsDDD())
		}
		return res
	}

	return clone(sig.Params().FieldSlice()), clone(sig.Results().FieldSlice())
}

func (r *reader) optExpr() ir.Node {
	if r.Bool() {
		return r.expr()
	}
	return nil
}

// methodExpr reads a method expression reference, and returns three
// (possibly nil) expressions related to it:
//
// baseFn is always non-nil: it's either a function of the appropriate
// type already, or it has an extra dictionary parameter as the second
// parameter (i.e., immediately after the promoted receiver
// parameter).
//
// If dictPtr is non-nil, then it's a dictionary argument that must be
// passed as the second argument to baseFn.
//
// If wrapperFn is non-nil, then it's either the same as baseFn (if
// dictPtr is nil), or it's semantically equivalent to currying baseFn
// to pass dictPtr. (wrapperFn is nil when dictPtr is an expression
// that needs to be computed dynamically.)
//
// For callers that are creating a call to the returned method, it's
// best to emit a call to baseFn, and include dictPtr in the arguments
// list as appropriate.
//
// For callers that want to return a method expression without
// invoking it, they may return wrapperFn if it's non-nil; but
// otherwise, they need to create their own wrapper.
func (r *reader) methodExpr() (wrapperFn, baseFn, dictPtr ir.Node) {
	recv := r.typ()
	sig0 := r.typ()
	pos := r.pos()
	_, sym := r.selector()

	// Signature type to return (i.e., recv prepended to the method's
	// normal parameters list).
	sig := typecheck.NewMethodType(sig0, recv)

	if r.Bool() { // type parameter method expression
		idx := r.Len()
		word := r.dictWord(pos, r.dict.typeParamMethodExprsOffset()+idx)

		// TODO(mdempsky): If the type parameter was instantiated with an
		// interface type (i.e., embed.IsInterface()), then we could
		// return the OMETHEXPR instead and save an indirection.

		// We wrote the method expression's entry point PC into the
		// dictionary, but for Go `func` values we need to return a
		// closure (i.e., pointer to a structure with the PC as the first
		// field). Because method expressions don't have any closure
		// variables, we pun the dictionary entry as the closure struct.
		fn := typecheck.Expr(ir.NewConvExpr(pos, ir.OCONVNOP, sig, ir.NewAddrExpr(pos, word)))
		return fn, fn, nil
	}

	// TODO(mdempsky): I'm pretty sure this isn't needed: implicits is
	// only relevant to locally defined types, but they can't have
	// (non-promoted) methods.
	var implicits []*types.Type
	if r.dict != nil {
		implicits = r.dict.targs
	}

	if r.Bool() { // dynamic subdictionary
		idx := r.Len()
		info := r.dict.subdicts[idx]
		explicits := r.p.typListIdx(info.explicits, r.dict)

		shapedObj := r.p.objIdx(info.idx, implicits, explicits, true).(*ir.Name)
		shapedFn := shapedMethodExpr(pos, shapedObj, sym)

		// TODO(mdempsky): Is there a more robust way to get the
		// dictionary pointer type here?
		dictPtrType := shapedFn.Type().Params().Field(1).Type
		dictPtr := typecheck.Expr(ir.NewConvExpr(pos, ir.OCONVNOP, dictPtrType, r.dictWord(pos, r.dict.subdictsOffset()+idx)))

		return nil, shapedFn, dictPtr
	}

	if r.Bool() { // static dictionary
		info := r.objInfo()
		explicits := r.p.typListIdx(info.explicits, r.dict)

		shapedObj := r.p.objIdx(info.idx, implicits, explicits, true).(*ir.Name)
		shapedFn := shapedMethodExpr(pos, shapedObj, sym)

		dict := r.p.objDictName(info.idx, implicits, explicits)
		dictPtr := typecheck.Expr(ir.NewAddrExpr(pos, dict))

		// Check that dictPtr matches shapedFn's dictionary parameter.
		if !types.Identical(dictPtr.Type(), shapedFn.Type().Params().Field(1).Type) {
			base.FatalfAt(pos, "dict %L, but shaped method %L", dict, shapedFn)
		}

		// For statically known instantiations, we can take advantage of
		// the stenciled wrapper.
		base.AssertfAt(!recv.HasShape(), pos, "shaped receiver %v", recv)
		wrapperFn := typecheck.Expr(ir.NewSelectorExpr(pos, ir.OXDOT, ir.TypeNode(recv), sym)).(*ir.SelectorExpr)
		base.AssertfAt(types.Identical(sig, wrapperFn.Type()), pos, "wrapper %L does not have type %v", wrapperFn, sig)

		return wrapperFn, shapedFn, dictPtr
	}

	// Simple method expression; no dictionary needed.
	base.AssertfAt(!recv.HasShape() || recv.IsInterface(), pos, "shaped receiver %v", recv)
	fn := typecheck.Expr(ir.NewSelectorExpr(pos, ir.OXDOT, ir.TypeNode(recv), sym)).(*ir.SelectorExpr)
	return fn, fn, nil
}

// shapedMethodExpr returns the specified method on the given shaped
// type.
func shapedMethodExpr(pos src.XPos, obj *ir.Name, sym *types.Sym) *ir.SelectorExpr {
	assert(obj.Op() == ir.OTYPE)

	typ := obj.Type()
	assert(typ.HasShape())

	method := func() *types.Field {
		for _, method := range typ.Methods().Slice() {
			if method.Sym == sym {
				return method
			}
		}

		base.FatalfAt(pos, "failed to find method %v in shaped type %v", sym, typ)
		panic("unreachable")
	}()

	// Construct an OMETHEXPR node.
	recv := method.Type.Recv().Type
	return typecheck.Expr(ir.NewSelectorExpr(pos, ir.OXDOT, ir.TypeNode(recv), sym)).(*ir.SelectorExpr)
}

func (r *reader) multiExpr() []ir.Node {
	r.Sync(pkgbits.SyncMultiExpr)

	if r.Bool() { // N:1
		pos := r.pos()
		expr := r.expr()

		results := make([]ir.Node, r.Len())
		as := ir.NewAssignListStmt(pos, ir.OAS2, nil, []ir.Node{expr})
		as.Def = true
		for i := range results {
			tmp := r.temp(pos, r.typ())
			as.PtrInit().Append(ir.NewDecl(pos, ir.ODCL, tmp))
			as.Lhs.Append(tmp)

			res := ir.Node(tmp)
			if r.Bool() {
				n := ir.NewConvExpr(pos, ir.OCONV, r.typ(), res)
				n.TypeWord, n.SrcRType = r.convRTTI(pos)
				n.SetImplicit(true)
				res = typecheck.Expr(n)
			}
			results[i] = res
		}

		// TODO(mdempsky): Could use ir.InlinedCallExpr instead?
		results[0] = ir.InitExpr([]ir.Node{typecheck.Stmt(as)}, results[0])
		return results
	}

	// N:N
	exprs := make([]ir.Node, r.Len())
	if len(exprs) == 0 {
		return nil
	}
	for i := range exprs {
		exprs[i] = r.expr()
	}
	return exprs
}

// temp returns a new autotemp of the specified type.
func (r *reader) temp(pos src.XPos, typ *types.Type) *ir.Name {
	// See typecheck.typecheckargs.
	curfn := r.curfn
	if curfn == nil {
		curfn = typecheck.InitTodoFunc
	}

	return typecheck.TempAt(pos, curfn, typ)
}

// tempCopy declares and returns a new autotemp initialized to the
// value of expr.
func (r *reader) tempCopy(pos src.XPos, expr ir.Node, init *ir.Nodes) *ir.Name {
	if r.curfn == nil {
		// Escape analysis doesn't know how to handle package-scope
		// function literals with free variables (i.e., that capture
		// temporary variables added to typecheck.InitTodoFunc).
		//
		// stencil.go works around this limitation by spilling values to
		// global variables instead, but that causes the value to stay
		// alive indefinitely; see go.dev/issue/54343.
		//
		// This code path (which implements the same workaround) isn't
		// actually needed by unified IR, because it creates uses normal
		// OMETHEXPR/OMETHVALUE nodes when statically-known instantiated
		// types are used. But it's kept around for now because it's handy
		// for testing that the generic fallback paths work correctly.
		base.Fatalf("tempCopy called at package scope")

		tmp := staticinit.StaticName(expr.Type())

		assign := ir.NewAssignStmt(pos, tmp, expr)
		assign.Def = true
		tmp.Defn = assign

		typecheck.Target.Decls = append(typecheck.Target.Decls, typecheck.Stmt(assign))

		return tmp
	}

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

	init.Append(typecheck.Stmt(ir.NewDecl(pos, ir.ODCL, tmp)))

	assign := ir.NewAssignStmt(pos, tmp, expr)
	assign.Def = true
	init.Append(typecheck.Stmt(ir.NewAssignStmt(pos, tmp, expr)))

	tmp.Defn = assign

	return tmp
}

func (r *reader) compLit() ir.Node {
	r.Sync(pkgbits.SyncCompLit)
	pos := r.pos()
	typ0 := r.typ()

	typ := typ0
	if typ.IsPtr() {
		typ = typ.Elem()
	}
	if typ.Kind() == types.TFORW {
		base.FatalfAt(pos, "unresolved composite literal type: %v", typ)
	}
	var rtype ir.Node
	if typ.IsMap() {
		rtype = r.rtype(pos)
	}
	isStruct := typ.Kind() == types.TSTRUCT

	elems := make([]ir.Node, r.Len())
	for i := range elems {
		elemp := &elems[i]

		if isStruct {
			sk := ir.NewStructKeyExpr(r.pos(), typ.Field(r.Len()), nil)
			*elemp, elemp = sk, &sk.Value
		} else if r.Bool() {