cmd/compile/internal/noder: handle unsafe.Sizeof, etc in unified IR

[gostls13.git] / src / cmd / compile / internal / noder / reader.go

// Copyright 2021 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

package noder

import (
        "fmt"
        "go/constant"
        "internal/buildcfg"
        "internal/goexperiment"
        "internal/pkgbits"
        "path/filepath"
        "strings"

        "cmd/compile/internal/base"
        "cmd/compile/internal/dwarfgen"
        "cmd/compile/internal/inline"
        "cmd/compile/internal/ir"
        "cmd/compile/internal/objw"
        "cmd/compile/internal/reflectdata"
        "cmd/compile/internal/staticinit"
        "cmd/compile/internal/typecheck"
        "cmd/compile/internal/types"
        "cmd/internal/obj"
        "cmd/internal/objabi"
        "cmd/internal/src"
)

// This file implements cmd/compile backend's reader for the Unified
// IR export data.

// A pkgReader reads Unified IR export data.
type pkgReader struct {
        pkgbits.PkgDecoder

        // Indices for encoded things; lazily populated as needed.
        //
        // Note: Objects (i.e., ir.Names) are lazily instantiated by
        // populating their types.Sym.Def; see objReader below.

        posBases []*src.PosBase
        pkgs     []*types.Pkg
        typs     []*types.Type

        // offset for rewriting the given (absolute!) index into the output,
        // but bitwise inverted so we can detect if we're missing the entry
        // or not.
        newindex []pkgbits.Index
}

func newPkgReader(pr pkgbits.PkgDecoder) *pkgReader {
        return &pkgReader{
                PkgDecoder: pr,

                posBases: make([]*src.PosBase, pr.NumElems(pkgbits.RelocPosBase)),
                pkgs:     make([]*types.Pkg, pr.NumElems(pkgbits.RelocPkg)),
                typs:     make([]*types.Type, pr.NumElems(pkgbits.RelocType)),

                newindex: make([]pkgbits.Index, pr.TotalElems()),
        }
}

// A pkgReaderIndex compactly identifies an index (and its
// corresponding dictionary) within a package's export data.
type pkgReaderIndex struct {
        pr        *pkgReader
        idx       pkgbits.Index
        dict      *readerDict
        methodSym *types.Sym

        synthetic func(pos src.XPos, r *reader)
}

func (pri pkgReaderIndex) asReader(k pkgbits.RelocKind, marker pkgbits.SyncMarker) *reader {
        if pri.synthetic != nil {
                return &reader{synthetic: pri.synthetic}
        }

        r := pri.pr.newReader(k, pri.idx, marker)
        r.dict = pri.dict
        r.methodSym = pri.methodSym
        return r
}

func (pr *pkgReader) newReader(k pkgbits.RelocKind, idx pkgbits.Index, marker pkgbits.SyncMarker) *reader {
        return &reader{
                Decoder: pr.NewDecoder(k, idx, marker),
                p:       pr,
        }
}

// A reader provides APIs for reading an individual element.
type reader struct {
        pkgbits.Decoder

        p *pkgReader

        dict *readerDict

        // TODO(mdempsky): The state below is all specific to reading
        // function bodies. It probably makes sense to split it out
        // separately so that it doesn't take up space in every reader
        // instance.

        curfn       *ir.Func
        locals      []*ir.Name
        closureVars []*ir.Name

        funarghack bool

        // methodSym is the name of method's name, if reading a method.
        // It's nil if reading a normal function or closure body.
        methodSym *types.Sym

        // dictParam is the .dict param, if any.
        dictParam *ir.Name

        // synthetic is a callback function to construct a synthetic
        // function body. It's used for creating the bodies of function
        // literals used to curry arguments to shaped functions.
        synthetic func(pos src.XPos, r *reader)

        // scopeVars is a stack tracking the number of variables declared in
        // the current function at the moment each open scope was opened.
        scopeVars         []int
        marker            dwarfgen.ScopeMarker
        lastCloseScopePos src.XPos

        // === details for handling inline body expansion ===

        // If we're reading in a function body because of inlining, this is
        // the call that we're inlining for.
        inlCaller    *ir.Func
        inlCall      *ir.CallExpr
        inlFunc      *ir.Func
        inlTreeIndex int
        inlPosBases  map[*src.PosBase]*src.PosBase

        // suppressInlPos tracks whether position base rewriting for
        // inlining should be suppressed. See funcLit.
        suppressInlPos int

        delayResults bool

        // Label to return to.
        retlabel *types.Sym

        // inlvars is the list of variables that the inlinee's arguments are
        // assigned to, one for each receiver and normal parameter, in order.
        inlvars ir.Nodes

        // retvars is the list of variables that the inlinee's results are
        // assigned to, one for each result parameter, in order.
        retvars ir.Nodes
}

// A readerDict represents an instantiated "compile-time dictionary,"
// used for resolving any derived types needed for instantiating a
// generic object.
//
// A compile-time dictionary can either be "shaped" or "non-shaped."
// Shaped compile-time dictionaries are only used for instantiating
// shaped type definitions and function bodies, while non-shaped
// compile-time dictionaries are used for instantiating runtime
// dictionaries.
type readerDict struct {
        shaped bool // whether this is a shaped dictionary

        // baseSym is the symbol for the object this dictionary belongs to.
        // If the object is an instantiated function or defined type, then
        // baseSym is the mangled symbol, including any type arguments.
        baseSym *types.Sym

        // For non-shaped dictionaries, shapedObj is a reference to the
        // corresponding shaped object (always a function or defined type).
        shapedObj *ir.Name

        // targs holds the implicit and explicit type arguments in use for
        // reading the current object. For example:
        //
        //      func F[T any]() {
        //              type X[U any] struct { t T; u U }
        //              var _ X[string]
        //      }
        //
        //      var _ = F[int]
        //
        // While instantiating F[int], we need to in turn instantiate
        // X[string]. [int] and [string] are explicit type arguments for F
        // and X, respectively; but [int] is also the implicit type
        // arguments for X.
        //
        // (As an analogy to function literals, explicits are the function
        // literal's formal parameters, while implicits are variables
        // captured by the function literal.)
        targs []*types.Type

        // implicits counts how many of types within targs are implicit type
        // arguments; the rest are explicit.
        implicits int

        derived      []derivedInfo // reloc index of the derived type's descriptor
        derivedTypes []*types.Type // slice of previously computed derived types

        // These slices correspond to entries in the runtime dictionary.
        typeParamMethodExprs []readerMethodExprInfo
        subdicts             []objInfo
        rtypes               []typeInfo
        itabs                []itabInfo
}

type readerMethodExprInfo struct {
        typeParamIdx int
        method       *types.Sym
}

func setType(n ir.Node, typ *types.Type) {
        n.SetType(typ)
        n.SetTypecheck(1)
}

func setValue(name *ir.Name, val constant.Value) {
        name.SetVal(val)
        name.Defn = nil
}

// @@@ Positions

// pos reads a position from the bitstream.
func (r *reader) pos() src.XPos {
        return base.Ctxt.PosTable.XPos(r.pos0())
}

// origPos reads a position from the bitstream, and returns both the
// original raw position and an inlining-adjusted position.
func (r *reader) origPos() (origPos, inlPos src.XPos) {
        r.suppressInlPos++
        origPos = r.pos()
        r.suppressInlPos--
        inlPos = r.inlPos(origPos)
        return
}

func (r *reader) pos0() src.Pos {
        r.Sync(pkgbits.SyncPos)
        if !r.Bool() {
                return src.NoPos
        }

        posBase := r.posBase()
        line := r.Uint()
        col := r.Uint()
        return src.MakePos(posBase, line, col)
}

// posBase reads a position base from the bitstream.
func (r *reader) posBase() *src.PosBase {
        return r.inlPosBase(r.p.posBaseIdx(r.Reloc(pkgbits.RelocPosBase)))
}

// posBaseIdx returns the specified position base, reading it first if
// needed.
func (pr *pkgReader) posBaseIdx(idx pkgbits.Index) *src.PosBase {
        if b := pr.posBases[idx]; b != nil {
                return b
        }

        r := pr.newReader(pkgbits.RelocPosBase, idx, pkgbits.SyncPosBase)
        var b *src.PosBase

        absFilename := r.String()
        filename := absFilename

        // For build artifact stability, the export data format only
        // contains the "absolute" filename as returned by objabi.AbsFile.
        // However, some tests (e.g., test/run.go's asmcheck tests) expect
        // to see the full, original filename printed out. Re-expanding
        // "$GOROOT" to buildcfg.GOROOT is a close-enough approximation to
        // satisfy this.
        //
        // The export data format only ever uses slash paths
        // (for cross-operating-system reproducible builds),
        // but error messages need to use native paths (backslash on Windows)
        // as if they had been specified on the command line.
        // (The go command always passes native paths to the compiler.)
        const dollarGOROOT = "$GOROOT"
        if buildcfg.GOROOT != "" && strings.HasPrefix(filename, dollarGOROOT) {
                filename = filepath.FromSlash(buildcfg.GOROOT + filename[len(dollarGOROOT):])
        }

        if r.Bool() {
                b = src.NewFileBase(filename, absFilename)
        } else {
                pos := r.pos0()
                line := r.Uint()
                col := r.Uint()
                b = src.NewLinePragmaBase(pos, filename, absFilename, line, col)
        }

        pr.posBases[idx] = b
        return b
}

// inlPosBase returns the inlining-adjusted src.PosBase corresponding
// to oldBase, which must be a non-inlined position. When not
// inlining, this is just oldBase.
func (r *reader) inlPosBase(oldBase *src.PosBase) *src.PosBase {
        if index := oldBase.InliningIndex(); index >= 0 {
                base.Fatalf("oldBase %v already has inlining index %v", oldBase, index)
        }

        if r.inlCall == nil || r.suppressInlPos != 0 {
                return oldBase
        }

        if newBase, ok := r.inlPosBases[oldBase]; ok {
                return newBase
        }

        newBase := src.NewInliningBase(oldBase, r.inlTreeIndex)
        r.inlPosBases[oldBase] = newBase
        return newBase
}

// inlPos returns the inlining-adjusted src.XPos corresponding to
// xpos, which must be a non-inlined position. When not inlining, this
// is just xpos.
func (r *reader) inlPos(xpos src.XPos) src.XPos {
        pos := base.Ctxt.PosTable.Pos(xpos)
        pos.SetBase(r.inlPosBase(pos.Base()))
        return base.Ctxt.PosTable.XPos(pos)
}

// @@@ Packages

// pkg reads a package reference from the bitstream.
func (r *reader) pkg() *types.Pkg {
        r.Sync(pkgbits.SyncPkg)
        return r.p.pkgIdx(r.Reloc(pkgbits.RelocPkg))
}

// pkgIdx returns the specified package from the export data, reading
// it first if needed.
func (pr *pkgReader) pkgIdx(idx pkgbits.Index) *types.Pkg {
        if pkg := pr.pkgs[idx]; pkg != nil {
                return pkg
        }

        pkg := pr.newReader(pkgbits.RelocPkg, idx, pkgbits.SyncPkgDef).doPkg()
        pr.pkgs[idx] = pkg
        return pkg
}

// doPkg reads a package definition from the bitstream.
func (r *reader) doPkg() *types.Pkg {
        path := r.String()
        switch path {
        case "":
                path = r.p.PkgPath()
        case "builtin":
                return types.BuiltinPkg
        case "unsafe":
                return types.UnsafePkg
        }

        name := r.String()

        pkg := types.NewPkg(path, "")

        if pkg.Name == "" {
                pkg.Name = name
        } else {
                base.Assertf(pkg.Name == name, "package %q has name %q, but want %q", pkg.Path, pkg.Name, name)
        }

        return pkg
}

// @@@ Types

func (r *reader) typ() *types.Type {
        return r.typWrapped(true)
}

// typWrapped is like typ, but allows suppressing generation of
// unnecessary wrappers as a compile-time optimization.
func (r *reader) typWrapped(wrapped bool) *types.Type {
        return r.p.typIdx(r.typInfo(), r.dict, wrapped)
}

func (r *reader) typInfo() typeInfo {
        r.Sync(pkgbits.SyncType)
        if r.Bool() {
                return typeInfo{idx: pkgbits.Index(r.Len()), derived: true}
        }
        return typeInfo{idx: r.Reloc(pkgbits.RelocType), derived: false}
}

// typListIdx returns a list of the specified types, resolving derived
// types within the given dictionary.
func (pr *pkgReader) typListIdx(infos []typeInfo, dict *readerDict) []*types.Type {
        typs := make([]*types.Type, len(infos))
        for i, info := range infos {
                typs[i] = pr.typIdx(info, dict, true)
        }
        return typs
}

// typIdx returns the specified type. If info specifies a derived
// type, it's resolved within the given dictionary. If wrapped is
// true, then method wrappers will be generated, if appropriate.
func (pr *pkgReader) typIdx(info typeInfo, dict *readerDict, wrapped bool) *types.Type {
        idx := info.idx
        var where **types.Type
        if info.derived {
                where = &dict.derivedTypes[idx]
                idx = dict.derived[idx].idx
        } else {
                where = &pr.typs[idx]
        }

        if typ := *where; typ != nil {
                return typ
        }

        r := pr.newReader(pkgbits.RelocType, idx, pkgbits.SyncTypeIdx)
        r.dict = dict

        typ := r.doTyp()
        assert(typ != nil)

        // For recursive type declarations involving interfaces and aliases,
        // above r.doTyp() call may have already set pr.typs[idx], so just
        // double check and return the type.
        //
        // Example:
        //
        //     type F = func(I)
        //
        //     type I interface {
        //         m(F)
        //     }
        //
        // The writer writes data types in following index order:
        //
        //     0: func(I)
        //     1: I
        //     2: interface{m(func(I))}
        //
        // The reader resolves it in following index order:
        //
        //     0 -> 1 -> 2 -> 0 -> 1
        //
        // and can divide in logically 2 steps:
        //
        //  - 0 -> 1     : first time the reader reach type I,
        //                 it creates new named type with symbol I.
        //
        //  - 2 -> 0 -> 1: the reader ends up reaching symbol I again,
        //                 now the symbol I was setup in above step, so
        //                 the reader just return the named type.
        //
        // Now, the functions called return, the pr.typs looks like below:
        //
        //  - 0 -> 1 -> 2 -> 0 : [<T> I <T>]
        //  - 0 -> 1 -> 2      : [func(I) I <T>]
        //  - 0 -> 1           : [func(I) I interface { "".m(func("".I)) }]
        //
        // The idx 1, corresponding with type I was resolved successfully
        // after r.doTyp() call.

        if prev := *where; prev != nil {
                return prev
        }

        if wrapped {
                // Only cache if we're adding wrappers, so that other callers that
                // find a cached type know it was wrapped.
                *where = typ

                r.needWrapper(typ)
        }

        if !typ.IsUntyped() {
                types.CheckSize(typ)
        }

        return typ
}

func (r *reader) doTyp() *types.Type {
        switch tag := pkgbits.CodeType(r.Code(pkgbits.SyncType)); tag {
        default:
                panic(fmt.Sprintf("unexpected type: %v", tag))

        case pkgbits.TypeBasic:
                return *basics[r.Len()]

        case pkgbits.TypeNamed:
                obj := r.obj()
                assert(obj.Op() == ir.OTYPE)
                return obj.Type()

        case pkgbits.TypeTypeParam:
                return r.dict.targs[r.Len()]

        case pkgbits.TypeArray:
                len := int64(r.Uint64())
                return types.NewArray(r.typ(), len)
        case pkgbits.TypeChan:
                dir := dirs[r.Len()]
                return types.NewChan(r.typ(), dir)
        case pkgbits.TypeMap:
                return types.NewMap(r.typ(), r.typ())
        case pkgbits.TypePointer:
                return types.NewPtr(r.typ())
        case pkgbits.TypeSignature:
                return r.signature(nil)
        case pkgbits.TypeSlice:
                return types.NewSlice(r.typ())
        case pkgbits.TypeStruct:
                return r.structType()
        case pkgbits.TypeInterface:
                return r.interfaceType()
        case pkgbits.TypeUnion:
                return r.unionType()
        }
}

func (r *reader) unionType() *types.Type {
        // In the types1 universe, we only need to handle value types.
        // Impure interfaces (i.e., interfaces with non-trivial type sets
        // like "int | string") can only appear as type parameter bounds,
        // and this is enforced by the types2 type checker.
        //
        // However, type unions can still appear in pure interfaces if the
        // type union is equivalent to "any". E.g., typeparam/issue52124.go
        // declares variables with the type "interface { any | int }".
        //
        // To avoid needing to represent type unions in types1 (since we
        // don't have any uses for that today anyway), we simply fold them
        // to "any".

        // TODO(mdempsky): Restore consistency check to make sure folding to
        // "any" is safe. This is unfortunately tricky, because a pure
        // interface can reference impure interfaces too, including
        // cyclically (#60117).
        if false {
                pure := false
                for i, n := 0, r.Len(); i < n; i++ {
                        _ = r.Bool() // tilde
                        term := r.typ()
                        if term.IsEmptyInterface() {
                                pure = true
                        }
                }
                if !pure {
                        base.Fatalf("impure type set used in value type")
                }
        }

        return types.Types[types.TINTER]
}

func (r *reader) interfaceType() *types.Type {
        nmethods, nembeddeds := r.Len(), r.Len()
        implicit := nmethods == 0 && nembeddeds == 1 && r.Bool()
        assert(!implicit) // implicit interfaces only appear in constraints

        fields := make([]*types.Field, nmethods+nembeddeds)
        methods, embeddeds := fields[:nmethods], fields[nmethods:]

        for i := range methods {
                pos := r.pos()
                _, sym := r.selector()
                mtyp := r.signature(types.FakeRecv())
                methods[i] = types.NewField(pos, sym, mtyp)
        }
        for i := range embeddeds {
                embeddeds[i] = types.NewField(src.NoXPos, nil, r.typ())
        }

        if len(fields) == 0 {
                return types.Types[types.TINTER] // empty interface
        }
        return types.NewInterface(fields)
}

func (r *reader) structType() *types.Type {
        fields := make([]*types.Field, r.Len())
        for i := range fields {
                pos := r.pos()
                _, sym := r.selector()
                ftyp := r.typ()
                tag := r.String()
                embedded := r.Bool()

                f := types.NewField(pos, sym, ftyp)
                f.Note = tag
                if embedded {
                        f.Embedded = 1
                }
                fields[i] = f
        }
        return types.NewStruct(fields)
}

func (r *reader) signature(recv *types.Field) *types.Type {
        r.Sync(pkgbits.SyncSignature)

        params := r.params()
        results := r.params()
        if r.Bool() { // variadic
                params[len(params)-1].SetIsDDD(true)
        }

        return types.NewSignature(recv, params, results)
}

func (r *reader) params() []*types.Field {
        r.Sync(pkgbits.SyncParams)
        fields := make([]*types.Field, r.Len())
        for i := range fields {
                _, fields[i] = r.param()
        }
        return fields
}

func (r *reader) param() (*types.Pkg, *types.Field) {
        r.Sync(pkgbits.SyncParam)

        pos := r.pos()
        pkg, sym := r.localIdent()
        typ := r.typ()

        return pkg, types.NewField(pos, sym, typ)
}

// @@@ Objects

// objReader maps qualified identifiers (represented as *types.Sym) to
// a pkgReader and corresponding index that can be used for reading
// that object's definition.
var objReader = map[*types.Sym]pkgReaderIndex{}

// obj reads an instantiated object reference from the bitstream.
func (r *reader) obj() ir.Node {
        return r.p.objInstIdx(r.objInfo(), r.dict, false)
}

// objInfo reads an instantiated object reference from the bitstream
// and returns the encoded reference to it, without instantiating it.
func (r *reader) objInfo() objInfo {
        r.Sync(pkgbits.SyncObject)
        assert(!r.Bool()) // TODO(mdempsky): Remove; was derived func inst.
        idx := r.Reloc(pkgbits.RelocObj)

        explicits := make([]typeInfo, r.Len())
        for i := range explicits {
                explicits[i] = r.typInfo()
        }

        return objInfo{idx, explicits}
}

// objInstIdx returns the encoded, instantiated object. If shaped is
// true, then the shaped variant of the object is returned instead.
func (pr *pkgReader) objInstIdx(info objInfo, dict *readerDict, shaped bool) ir.Node {
        explicits := pr.typListIdx(info.explicits, dict)

        var implicits []*types.Type
        if dict != nil {
                implicits = dict.targs
        }

        return pr.objIdx(info.idx, implicits, explicits, shaped)
}

// objIdx returns the specified object, instantiated with the given
// type arguments, if any. If shaped is true, then the shaped variant
// of the object is returned instead.
func (pr *pkgReader) objIdx(idx pkgbits.Index, implicits, explicits []*types.Type, shaped bool) ir.Node {
        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())
                switch sym.Pkg {
                case types.BuiltinPkg, types.UnsafePkg:
                        return sym.Def.(ir.Node)
                }
                if pri, ok := objReader[sym]; ok {
                        return pri.pr.objIdx(pri.idx, nil, explicits, shaped)
                }
                base.Fatalf("unresolved stub: %v", sym)
        }

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

        sym = dict.baseSym
        if !sym.IsBlank() && sym.Def != nil {
                return sym.Def.(*ir.Name)
        }

        r := pr.newReader(pkgbits.RelocObj, idx, pkgbits.SyncObject1)
        rext := pr.newReader(pkgbits.RelocObjExt, idx, pkgbits.SyncObject1)

        r.dict = dict
        rext.dict = dict

        do := func(op ir.Op, hasTParams bool) *ir.Name {
                pos := r.pos()
                setBasePos(pos)
                if hasTParams {
                        r.typeParamNames()
                }

                name := ir.NewDeclNameAt(pos, op, sym)
                name.Class = ir.PEXTERN // may be overridden later
                if !sym.IsBlank() {
                        if sym.Def != nil {
                                base.FatalfAt(name.Pos(), "already have a definition for %v", name)
                        }
                        assert(sym.Def == nil)
                        sym.Def = name
                }
                return name
        }

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

        case pkgbits.ObjAlias:
                name := do(ir.OTYPE, false)
                setType(name, r.typ())
                name.SetAlias(true)
                return name

        case pkgbits.ObjConst:
                name := do(ir.OLITERAL, false)
                typ := r.typ()
                val := FixValue(typ, r.Value())
                setType(name, typ)
                setValue(name, val)
                return name

        case pkgbits.ObjFunc:
                if sym.Name == "init" {
                        sym = Renameinit()
                }

                npos := r.pos()
                setBasePos(npos)
                r.typeParamNames()
                typ := r.signature(nil)
                fpos := r.pos()

                fn := ir.NewFunc(fpos, npos, sym, typ)
                name := fn.Nname
                if !sym.IsBlank() {
                        if sym.Def != nil {
                                base.FatalfAt(name.Pos(), "already have a definition for %v", name)
                        }
                        assert(sym.Def == nil)
                        sym.Def = name
                }

                if r.hasTypeParams() {
                        name.Func.SetDupok(true)
                        if r.dict.shaped {
                                setType(name, shapeSig(name.Func, r.dict))
                        } else {
                                todoDicts = append(todoDicts, func() {
                                        r.dict.shapedObj = pr.objIdx(idx, implicits, explicits, true).(*ir.Name)
                                })
                        }
                }

                rext.funcExt(name, nil)
                return name

        case pkgbits.ObjType:
                name := do(ir.OTYPE, true)
                typ := types.NewNamed(name)
                setType(name, typ)
                if r.hasTypeParams() && r.dict.shaped {
                        typ.SetHasShape(true)
                }

                // Important: We need to do this before SetUnderlying.
                rext.typeExt(name)

                // We need to defer CheckSize until we've called SetUnderlying to
                // handle recursive types.
                types.DeferCheckSize()
                typ.SetUnderlying(r.typWrapped(false))
                types.ResumeCheckSize()

                if r.hasTypeParams() && !r.dict.shaped {
                        todoDicts = append(todoDicts, func() {
                                r.dict.shapedObj = pr.objIdx(idx, implicits, explicits, true).(*ir.Name)
                        })
                }

                methods := make([]*types.Field, r.Len())
                for i := range methods {
                        methods[i] = r.method(rext)
                }
                if len(methods) != 0 {
                        typ.SetMethods(methods)
                }

                if !r.dict.shaped {
                        r.needWrapper(typ)
                }

                return name

        case pkgbits.ObjVar:
                name := do(ir.ONAME, false)
                setType(name, r.typ())
                rext.varExt(name)
                return name
        }
}

func (dict *readerDict) mangle(sym *types.Sym) *types.Sym {
        if !dict.hasTypeParams() {
                return sym
        }

        // If sym is a locally defined generic type, we need the suffix to
        // stay at the end after mangling so that types/fmt.go can strip it
        // out again when writing the type's runtime descriptor (#54456).
        base, suffix := types.SplitVargenSuffix(sym.Name)

        var buf strings.Builder
        buf.WriteString(base)
        buf.WriteByte('[')
        for i, targ := range dict.targs {
                if i > 0 {
                        if i == dict.implicits {
                                buf.WriteByte(';')
                        } else {
                                buf.WriteByte(',')
                        }
                }
                buf.WriteString(targ.LinkString())
        }
        buf.WriteByte(']')
        buf.WriteString(suffix)
        return sym.Pkg.Lookup(buf.String())
}

// shapify returns the shape type for targ.
//
// If basic is true, then the type argument is used to instantiate a
// type parameter whose constraint is a basic interface.
func shapify(targ *types.Type, basic bool) *types.Type {
        if targ.Kind() == types.TFORW {
                if targ.IsFullyInstantiated() {
                        // For recursive instantiated type argument, it may  still be a TFORW
                        // when shapifying happens. If we don't have targ's underlying type,
                        // shapify won't work. The worst case is we end up not reusing code
                        // optimally in some tricky cases.
                        if base.Debug.Shapify != 0 {
                                base.Warn("skipping shaping of recursive type %v", targ)
                        }
                        if targ.HasShape() {
                                return targ
                        }
                } else {
                        base.Fatalf("%v is missing its underlying type", targ)
                }
        }

        // When a pointer type is used to instantiate a type parameter
        // constrained by a basic interface, we know the pointer's element
        // type can't matter to the generated code. In this case, we can use
        // an arbitrary pointer type as the shape type. (To match the
        // non-unified frontend, we use `*byte`.)
        //
        // Otherwise, we simply use the type's underlying type as its shape.
        //
        // TODO(mdempsky): It should be possible to do much more aggressive
        // shaping still; e.g., collapsing all pointer-shaped types into a
        // common type, collapsing scalars of the same size/alignment into a
        // common type, recursively shaping the element types of composite
        // types, and discarding struct field names and tags. However, we'll
        // need to start tracking how type parameters are actually used to
        // implement some of these optimizations.
        under := targ.Underlying()
        if basic && targ.IsPtr() && !targ.Elem().NotInHeap() {
                under = types.NewPtr(types.Types[types.TUINT8])
        }

        sym := types.ShapePkg.Lookup(under.LinkString())
        if sym.Def == nil {
                name := ir.NewDeclNameAt(under.Pos(), ir.OTYPE, sym)
                typ := types.NewNamed(name)
                typ.SetUnderlying(under)
                sym.Def = typed(typ, name)
        }
        res := sym.Def.Type()
        assert(res.IsShape())
        assert(res.HasShape())
        return res
}

// objDictIdx reads and returns the specified object dictionary.
func (pr *pkgReader) objDictIdx(sym *types.Sym, idx pkgbits.Index, implicits, explicits []*types.Type, shaped bool) *readerDict {
        r := pr.newReader(pkgbits.RelocObjDict, idx, pkgbits.SyncObject1)

        dict := readerDict{
                shaped: shaped,
        }

        nimplicits := r.Len()
        nexplicits := r.Len()

        if nimplicits > len(implicits) || nexplicits != len(explicits) {
                base.Fatalf("%v has %v+%v params, but instantiated with %v+%v args", sym, nimplicits, nexplicits, len(implicits), len(explicits))
        }

        dict.targs = append(implicits[:nimplicits:nimplicits], explicits...)
        dict.implicits = nimplicits

        // Within the compiler, we can just skip over the type parameters.
        for range dict.targs[dict.implicits:] {
                // Skip past bounds without actually evaluating them.
                r.typInfo()
        }

        dict.derived = make([]derivedInfo, r.Len())
        dict.derivedTypes = make([]*types.Type, len(dict.derived))
        for i := range dict.derived {
                dict.derived[i] = derivedInfo{r.Reloc(pkgbits.RelocType), r.Bool()}
        }

        // Runtime dictionary information; private to the compiler.

        // If any type argument is already shaped, then we're constructing a
        // shaped object, even if not explicitly requested (i.e., calling
        // objIdx with shaped==true). This can happen with instantiating
        // types that are referenced within a function body.
        for _, targ := range dict.targs {
                if targ.HasShape() {
                        dict.shaped = true
                        break
                }
        }

        // And if we're constructing a shaped object, then shapify all type
        // arguments.
        for i, targ := range dict.targs {
                basic := r.Bool()
                if dict.shaped {
                        dict.targs[i] = shapify(targ, basic)
                }
        }

        dict.baseSym = dict.mangle(sym)

        dict.typeParamMethodExprs = make([]readerMethodExprInfo, r.Len())
        for i := range dict.typeParamMethodExprs {
                typeParamIdx := r.Len()
                _, method := r.selector()

                dict.typeParamMethodExprs[i] = readerMethodExprInfo{typeParamIdx, method}
        }

        dict.subdicts = make([]objInfo, r.Len())
        for i := range dict.subdicts {
                dict.subdicts[i] = r.objInfo()
        }

        dict.rtypes = make([]typeInfo, r.Len())
        for i := range dict.rtypes {
                dict.rtypes[i] = r.typInfo()
        }

        dict.itabs = make([]itabInfo, r.Len())
        for i := range dict.itabs {
                dict.itabs[i] = itabInfo{typ: r.typInfo(), iface: r.typInfo()}
        }

        return &dict
}

func (r *reader) typeParamNames() {
        r.Sync(pkgbits.SyncTypeParamNames)

        for range r.dict.targs[r.dict.implicits:] {
                r.pos()
                r.localIdent()
        }
}

func (r *reader) method(rext *reader) *types.Field {
        r.Sync(pkgbits.SyncMethod)
        npos := r.pos()
        _, sym := r.selector()
        r.typeParamNames()
        _, recv := r.param()
        typ := r.signature(recv)

        fpos := r.pos()
        fn := ir.NewFunc(fpos, npos, ir.MethodSym(recv.Type, sym), typ)
        name := fn.Nname

        if r.hasTypeParams() {
                name.Func.SetDupok(true)
                if r.dict.shaped {
                        typ = shapeSig(name.Func, r.dict)
                        setType(name, typ)
                }
        }

        rext.funcExt(name, sym)

        meth := types.NewField(name.Func.Pos(), sym, typ)
        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)

        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)

        if buildcfg.GOARCH == "wasm" {
                xmod := r.String()
                xname := r.String()

                if xmod != "" && xname != "" {
                        fn.WasmImport = &ir.WasmImport{
                                Module: xmod,
                                Name:   xname,
                        }
                }
        }

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

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

                // Escape analysis.
                for _, f := range name.Type().RecvParams() {
                        f.Note = r.String()
                }

                if r.Bool() {
                        fn.Inl = &ir.Inline{
                                Cost:            int32(r.Len()),
                                CanDelayResults: r.Bool(),
                        }
                        if goexperiment.NewInliner {
                                fn.Inl.Properties = r.String()
                        }
                }
        } 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())
        addParams(&params, sig.Params())
        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, dict.varType())
        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.NewMethodExpr(pos, typeParam, info.method)

                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)

        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() {
                r.funcarg(param, param.Sym, ir.PPARAM)
        }

        for i, param := range sig.Results() {
                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 := r.addLocal(r.inlPos(param.Pos), sym, ctxt, param.Type)

        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(pos src.XPos, sym *types.Sym, ctxt ir.Class, typ *types.Type) *ir.Name {
        assert(ctxt == ir.PAUTO || ctxt == ir.PPARAM || ctxt == ir.PPARAMOUT)

        name := ir.NewNameAt(pos, sym, typ)

        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 name
        }

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

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

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

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

        return name
}

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 {
        return block(r.stmts())
}

func block(stmts []ir.Node) ir.Node {
        switch len(stmts) {
        case 0:
                return nil
        case 1:
                return stmts[0]
        default:
                return ir.NewBlockStmt(stmts[0].Pos(), stmts)
        }
}

func (r *reader) stmts() ir.Nodes {
        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.NewOne(pos, lhs.Type()))
                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 := r.addLocal(pos, sym, ir.PAUTO, typ)
                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, false)
                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()
                rang.DistinctVars = r.Bool()
                r.closeAnotherScope()

                return rang
        }

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

        if ir.IsConst(cond, constant.Bool) && !ir.BoolVal(cond) {
                return init // simplify "for init; false; post { ... }" into "init"
        }

        stmt := ir.NewForStmt(pos, init, cond, post, body, perLoopVars)
        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()
        staticCond := r.Int()
        var then, els []ir.Node
        if staticCond >= 0 {
                then = r.blockStmt()
        } else {
                r.lastCloseScopePos = r.pos()
        }
        if staticCond <= 0 {
                els = r.stmts()
        }
        r.closeAnotherScope()

        if staticCond != 0 {
                // We may have removed a dead return statement, which can trip up
                // later passes (#62211). To avoid confusion, we instead flatten
                // the if statement into a block.

                if cond.Op() != ir.OLITERAL {
                        init.Append(typecheck.Stmt(ir.NewAssignStmt(pos, ir.BlankNode, cond))) // for side effects
                }
                init.Append(then...)
                init.Append(els...)
                return block(init)
        }

        n := ir.NewIfStmt(pos, cond, then, els)
        n.SetInit(init)
        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.
                        }
                        for i := range cases {
                                if r.Bool() { // case nil
                                        cases[i] = typecheck.Expr(types.BuiltinPkg.Lookup("nil").Def.(*ir.NilExpr))
                                } else {
                                        cases[i] = r.exprType()
                                }
                        }
                } else {
                        cases = r.exprList()

                        // For `switch { case any(true): }` (e.g., issue 3980 in
                        // test/switch.go), the backend still creates a mixed bool/any
                        // comparison, and we need to explicitly supply the RTTI for the
                        // comparison.
                        //
                        // TODO(mdempsky): Change writer.go to desugar "switch {" into
                        // "switch true {", which we already handle correctly.
                        if tag == nil {
                                for i, cas := range cases {
                                        if cas.Type().IsEmptyInterface() {
                                                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 := r.addLocal(pos, ident.Sym(), ir.PAUTO, typ)
                        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:
                origPos, pos := r.origPos()
                wrapperFn, baseFn, dictPtr := r.funcInst(pos)
                if wrapperFn != nil {
                        return wrapperFn
                }
                return r.curry(origPos, false, baseFn, dictPtr, nil)

        case exprConst:
                pos := r.pos()
                typ := r.typ()
                val := FixValue(typ, r.Value())
                return ir.NewBasicLit(pos, typ, val)

        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.XDotField(pos, x, sym)

        case exprMethodVal:
                recv := r.expr()
                origPos, pos := r.origPos()
                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().Param(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.XDotMethod(pos, recv, wrapperFn.Sel, false)

                        // As a consistency check here, we make sure "n" selected the
                        // same method (represented by a types.Field) that wrapperFn
                        // selected. However, for anonymous receiver types, there can be
                        // multiple such types.Field instances (#58563). So we may need
                        // to fallback to making sure Sym and Type (including the
                        // receiver parameter's type) match.
                        if n.Selection != wrapperFn.Selection {
                                assert(n.Selection.Sym == wrapperFn.Selection.Sym)
                                assert(types.Identical(n.Selection.Type, wrapperFn.Selection.Type))
                                assert(types.Identical(n.Selection.Type.Recv().Type, wrapperFn.Selection.Type.Recv().Type))
                        }

                        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(origPos, 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
                }

                origPos, pos := r.origPos()
                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().Param(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.NewMethodExpr(pos, recv, method.Sel)
                }

                return r.methodExprWrap(origPos, 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(typecheck.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.XDotMethod(method.Pos(), recv, method.Sel, true)
                        } 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 exprSizeof:
                return ir.NewUintptr(r.pos(), r.typ().Size())

        case exprAlignof:
                return ir.NewUintptr(r.pos(), r.typ().Alignment())

        case exprOffsetof:
                pos := r.pos()
                typ := r.typ()
                types.CalcSize(typ)

                var offset int64
                for i := r.Len(); i >= 0; i-- {
                        field := typ.Field(r.Len())
                        offset += field.Offset
                        typ = field.Type
                }

                return ir.NewUintptr(pos, offset)

        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()
                identical := r.Bool()
                x := r.expr()

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

                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 !identical {
                        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().Param(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(origPos 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(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(origPos, 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(origPos 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(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(typecheck.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(origPos, typ, false, captured, addBody)
}

// syntheticClosure constructs a synthetic function literal for
// currying dictionary arguments. origPos is the position used for the
// closure, which must be a non-inlined position. 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(origPos 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 := r.inlClosureFunc(origPos, typ)
        fn.SetWrapper(true)

        clo := fn.OClosure
        inlPos := clo.Pos()

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

                tmp := r.tempCopy(inlPos, n, &init)
                ir.NewClosureVar(origPos, 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(inlPos, ir.OCHECKNIL, ir.NewUnaryExpr(inlPos, 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(origPos, r, captured)
        }}
        bodyReader[fn] = pri
        pri.funcBody(fn)

        return ir.InitExpr(init, clo)
}

// 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()), clone(sig.Results())
}

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().Param(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().Param(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.NewMethodExpr(pos, recv, sym)
                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.NewMethodExpr(pos, recv, sym)
        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() {
                        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.NewMethodExpr(pos, recv, sym)
}

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 {
        return typecheck.TempAt(pos, r.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 {
        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() {
                        kv := ir.NewKeyExpr(r.pos(), r.expr(), nil)
                        *elemp, elemp = kv, &kv.Value
                }

                *elemp = wrapName(r.pos(), r.expr())
        }

        lit := typecheck.Expr(ir.NewCompLitExpr(pos, ir.OCOMPLIT, typ, elems))
        if rtype != nil {
                lit := lit.(*ir.CompLitExpr)
                lit.RType = rtype
        }
        if typ0.IsPtr() {
                lit = typecheck.Expr(typecheck.NodAddrAt(pos, lit))
                lit.SetType(typ0)
        }
        return lit
}

func wrapName(pos src.XPos, x ir.Node) ir.Node {
        // These nodes do not carry line numbers.
        // Introduce a wrapper node to give them the correct line.
        switch x.Op() {
        case ir.OTYPE, ir.OLITERAL:
                if x.Sym() == nil {
                        break
                }
                fallthrough
        case ir.ONAME, ir.ONONAME, ir.ONIL:
                p := ir.NewParenExpr(pos, x)
                p.SetImplicit(true)
                return p
        }
        return x
}

func (r *reader) funcLit() ir.Node {
        r.Sync(pkgbits.SyncFuncLit)

        // The underlying function declaration (including its parameters'
        // positions, if any) need to remain the original, uninlined
        // positions. This is because we track inlining-context on nodes so
        // we can synthesize the extra implied stack frames dynamically when
        // generating tracebacks, whereas those stack frames don't make
        // sense *within* the function literal. (Any necessary inlining
        // adjustments will have been applied to the call expression
        // instead.)
        //
        // This is subtle, and getting it wrong leads to cycles in the
        // inlining tree, which lead to infinite loops during stack
        // unwinding (#46234, #54625).
        //
        // Note that we *do* want the inline-adjusted position for the
        // OCLOSURE node, because that position represents where any heap
        // allocation of the closure is credited (#49171).
        r.suppressInlPos++
        origPos := r.pos()
        sig := r.signature(nil)
        r.suppressInlPos--

        fn := r.inlClosureFunc(origPos, sig)

        fn.ClosureVars = make([]*ir.Name, 0, r.Len())
        for len(fn.ClosureVars) < cap(fn.ClosureVars) {
                // TODO(mdempsky): I think these should be original positions too
                // (i.e., not inline-adjusted).
                ir.NewClosureVar(r.pos(), fn, r.useLocal())
        }
        if param := r.dictParam; param != nil {
                // If we have a dictionary parameter, capture it too. For
                // simplicity, we capture it last and unconditionally.
                ir.NewClosureVar(param.Pos(), fn, param)
        }

        r.addBody(fn, nil)

        // un-hide closures belong to init function.
        if (r.curfn.IsPackageInit() || strings.HasPrefix(r.curfn.Sym().Name, "init.")) && ir.IsTrivialClosure(fn.OClosure) {
                fn.SetIsHiddenClosure(false)
        }

        return fn.OClosure
}

// inlClosureFunc constructs a new closure function, but correctly
// handles inlining.
func (r *reader) inlClosureFunc(origPos src.XPos, sig *types.Type) *ir.Func {
        curfn := r.inlCaller
        if curfn == nil {
                curfn = r.curfn
        }

        // TODO(mdempsky): Remove hard-coding of typecheck.Target.
        return ir.NewClosureFunc(origPos, r.inlPos(origPos), ir.OCLOSURE, sig, curfn, typecheck.Target)
}

func (r *reader) exprList() []ir.Node {
        r.Sync(pkgbits.SyncExprList)
        return r.exprs()
}

func (r *reader) exprs() []ir.Node {
        r.Sync(pkgbits.SyncExprs)
        nodes := make([]ir.Node, r.Len())
        if len(nodes) == 0 {
                return nil // TODO(mdempsky): Unclear if this matters.
        }
        for i := range nodes {
                nodes[i] = r.expr()
        }
        return nodes
}

// dictWord returns an expression to return the specified
// uintptr-typed word from the dictionary parameter.
func (r *reader) dictWord(pos src.XPos, idx int) ir.Node {
        base.AssertfAt(r.dictParam != nil, pos, "expected dictParam in %v", r.curfn)
        return typecheck.Expr(ir.NewIndexExpr(pos, r.dictParam, ir.NewInt(pos, int64(idx))))
}

// rttiWord is like dictWord, but converts it to *byte (the type used
// internally to represent *runtime._type and *runtime.itab).
func (r *reader) rttiWord(pos src.XPos, idx int) ir.Node {
        return typecheck.Expr(ir.NewConvExpr(pos, ir.OCONVNOP, types.NewPtr(types.Types[types.TUINT8]), r.dictWord(pos, idx)))
}

// rtype reads a type reference from the element bitstream, and
// returns an expression of type *runtime._type representing that
// type.
func (r *reader) rtype(pos src.XPos) ir.Node {
        _, rtype := r.rtype0(pos)
        return rtype
}

func (r *reader) rtype0(pos src.XPos) (typ *types.Type, rtype ir.Node) {
        r.Sync(pkgbits.SyncRType)
        if r.Bool() { // derived type
                idx := r.Len()
                info := r.dict.rtypes[idx]
                typ = r.p.typIdx(info, r.dict, true)
                rtype = r.rttiWord(pos, r.dict.rtypesOffset()+idx)
                return
        }

        typ = r.typ()
        rtype = reflectdata.TypePtrAt(pos, typ)
        return
}

// varDictIndex populates name.DictIndex if name is a derived type.
func (r *reader) varDictIndex(name *ir.Name) {
        if r.Bool() {
                idx := 1 + r.dict.rtypesOffset() + r.Len()
                if int(uint16(idx)) != idx {
                        base.FatalfAt(name.Pos(), "DictIndex overflow for %v: %v", name, idx)
                }
                name.DictIndex = uint16(idx)
        }
}

// itab returns a (typ, iface) pair of types.
//
// typRType and ifaceRType are expressions that evaluate to the
// *runtime._type for typ and iface, respectively.
//
// If typ is a concrete type and iface is a non-empty interface type,
// then itab is an expression that evaluates to the *runtime.itab for
// the pair. Otherwise, itab is nil.
func (r *reader) itab(pos src.XPos) (typ *types.Type, typRType ir.Node, iface *types.Type, ifaceRType ir.Node, itab ir.Node) {
        typ, typRType = r.rtype0(pos)
        iface, ifaceRType = r.rtype0(pos)

        idx := -1
        if r.Bool() {
                idx = r.Len()
        }

        if !typ.IsInterface() && iface.IsInterface() && !iface.IsEmptyInterface() {
                if idx >= 0 {
                        itab = r.rttiWord(pos, r.dict.itabsOffset()+idx)
                } else {
                        base.AssertfAt(!typ.HasShape(), pos, "%v is a shape type", typ)
                        base.AssertfAt(!iface.HasShape(), pos, "%v is a shape type", iface)

                        lsym := reflectdata.ITabLsym(typ, iface)
                        itab = typecheck.LinksymAddr(pos, lsym, types.Types[types.TUINT8])
                }
        }

        return
}

// convRTTI returns expressions appropriate for populating an
// ir.ConvExpr's TypeWord and SrcRType fields, respectively.
func (r *reader) convRTTI(pos src.XPos) (typeWord, srcRType ir.Node) {
        r.Sync(pkgbits.SyncConvRTTI)
        src, srcRType0, dst, dstRType, itab := r.itab(pos)
        if !dst.IsInterface() {
                return
        }

        // See reflectdata.ConvIfaceTypeWord.
        switch {
        case dst.IsEmptyInterface():
                if !src.IsInterface() {
                        typeWord = srcRType0 // direct eface construction
                }
        case !src.IsInterface():
                typeWord = itab // direct iface construction
        default:
                typeWord = dstRType // convI2I
        }

        // See reflectdata.ConvIfaceSrcRType.
        if !src.IsInterface() {
                srcRType = srcRType0
        }

        return
}

func (r *reader) exprType() ir.Node {
        r.Sync(pkgbits.SyncExprType)
        pos := r.pos()

        var typ *types.Type
        var rtype, itab ir.Node

        if r.Bool() {
                typ, rtype, _, _, itab = r.itab(pos)
                if !typ.IsInterface() {
                        rtype = nil // TODO(mdempsky): Leave set?
                }
        } else {
                typ, rtype = r.rtype0(pos)

                if !r.Bool() { // not derived
                        return ir.TypeNode(typ)
                }
        }

        dt := ir.NewDynamicType(pos, rtype)
        dt.ITab = itab
        return typed(typ, dt)
}

func (r *reader) op() ir.Op {
        r.Sync(pkgbits.SyncOp)
        return ir.Op(r.Len())
}

// @@@ Package initialization

func (r *reader) pkgInit(self *types.Pkg, target *ir.Package) {
        cgoPragmas := make([][]string, r.Len())
        for i := range cgoPragmas {
                cgoPragmas[i] = r.Strings()
        }
        target.CgoPragmas = cgoPragmas

        r.pkgInitOrder(target)

        r.pkgDecls(target)

        r.Sync(pkgbits.SyncEOF)
}

// pkgInitOrder creates a synthetic init function to handle any
// package-scope initialization statements.
func (r *reader) pkgInitOrder(target *ir.Package) {
        initOrder := make([]ir.Node, r.Len())
        if len(initOrder) == 0 {
                return
        }

        // Make a function that contains all the initialization statements.
        pos := base.AutogeneratedPos
        base.Pos = pos

        fn := ir.NewFunc(pos, pos, typecheck.Lookup("init"), types.NewSignature(nil, nil, nil))
        fn.SetIsPackageInit(true)
        fn.SetInlinabilityChecked(true) // suppress useless "can inline" diagnostics

        typecheck.DeclFunc(fn)
        r.curfn = fn

        for i := range initOrder {
                lhs := make([]ir.Node, r.Len())
                for j := range lhs {
                        lhs[j] = r.obj()
                }
                rhs := r.expr()
                pos := lhs[0].Pos()

                var as ir.Node
                if len(lhs) == 1 {
                        as = typecheck.Stmt(ir.NewAssignStmt(pos, lhs[0], rhs))
                } else {
                        as = typecheck.Stmt(ir.NewAssignListStmt(pos, ir.OAS2, lhs, []ir.Node{rhs}))
                }

                for _, v := range lhs {
                        v.(*ir.Name).Defn = as
                }

                initOrder[i] = as
        }

        fn.Body = initOrder

        typecheck.FinishFuncBody()
        r.curfn = nil
        r.locals = nil

        // Outline (if legal/profitable) global map inits.
        staticinit.OutlineMapInits(fn)

        target.Inits = append(target.Inits, fn)
}

func (r *reader) pkgDecls(target *ir.Package) {
        r.Sync(pkgbits.SyncDecls)
        for {
                switch code := codeDecl(r.Code(pkgbits.SyncDecl)); code {
                default:
                        panic(fmt.Sprintf("unhandled decl: %v", code))

                case declEnd:
                        return

                case declFunc:
                        names := r.pkgObjs(target)
                        assert(len(names) == 1)
                        target.Funcs = append(target.Funcs, names[0].Func)

                case declMethod:
                        typ := r.typ()
                        _, sym := r.selector()

                        method := typecheck.Lookdot1(nil, sym, typ, typ.Methods(), 0)
                        target.Funcs = append(target.Funcs, method.Nname.(*ir.Name).Func)

                case declVar:
                        names := r.pkgObjs(target)

                        if n := r.Len(); n > 0 {
                                assert(len(names) == 1)
                                embeds := make([]ir.Embed, n)
                                for i := range embeds {
                                        embeds[i] = ir.Embed{Pos: r.pos(), Patterns: r.Strings()}
                                }
                                names[0].Embed = &embeds
                                target.Embeds = append(target.Embeds, names[0])
                        }

                case declOther:
                        r.pkgObjs(target)
                }
        }
}

func (r *reader) pkgObjs(target *ir.Package) []*ir.Name {
        r.Sync(pkgbits.SyncDeclNames)
        nodes := make([]*ir.Name, r.Len())
        for i := range nodes {
                r.Sync(pkgbits.SyncDeclName)

                name := r.obj().(*ir.Name)
                nodes[i] = name

                sym := name.Sym()
                if sym.IsBlank() {
                        continue
                }

                switch name.Class {
                default:
                        base.FatalfAt(name.Pos(), "unexpected class: %v", name.Class)

                case ir.PEXTERN:
                        target.Externs = append(target.Externs, name)

                case ir.PFUNC:
                        assert(name.Type().Recv() == nil)

                        // TODO(mdempsky): Cleaner way to recognize init?
                        if strings.HasPrefix(sym.Name, "init.") {
                                target.Inits = append(target.Inits, name.Func)
                        }
                }

                if base.Ctxt.Flag_dynlink && types.LocalPkg.Name == "main" && types.IsExported(sym.Name) && name.Op() == ir.ONAME {
                        assert(!sym.OnExportList())
                        target.PluginExports = append(target.PluginExports, name)
                        sym.SetOnExportList(true)
                }

                if base.Flag.AsmHdr != "" && (name.Op() == ir.OLITERAL || name.Op() == ir.OTYPE) {
                        assert(!sym.Asm())
                        target.AsmHdrDecls = append(target.AsmHdrDecls, name)
                        sym.SetAsm(true)
                }
        }

        return nodes
}

// @@@ Inlining

// unifiedHaveInlineBody reports whether we have the function body for
// fn, so we can inline it.
func unifiedHaveInlineBody(fn *ir.Func) bool {
        if fn.Inl == nil {
                return false
        }

        _, ok := bodyReaderFor(fn)
        return ok
}

var inlgen = 0

// unifiedInlineCall implements inline.NewInline by re-reading the function
// body from its Unified IR export data.
func unifiedInlineCall(callerfn *ir.Func, call *ir.CallExpr, fn *ir.Func, inlIndex int) *ir.InlinedCallExpr {
        pri, ok := bodyReaderFor(fn)
        if !ok {
                base.FatalfAt(call.Pos(), "cannot inline call to %v: missing inline body", fn)
        }

        if !fn.Inl.HaveDcl {
                expandInline(fn, pri)
        }

        r := pri.asReader(pkgbits.RelocBody, pkgbits.SyncFuncBody)

        tmpfn := ir.NewFunc(fn.Pos(), fn.Nname.Pos(), callerfn.Sym(), fn.Type())

        r.curfn = tmpfn

        r.inlCaller = callerfn
        r.inlCall = call
        r.inlFunc = fn
        r.inlTreeIndex = inlIndex
        r.inlPosBases = make(map[*src.PosBase]*src.PosBase)

        r.closureVars = make([]*ir.Name, len(r.inlFunc.ClosureVars))
        for i, cv := range r.inlFunc.ClosureVars {
                // TODO(mdempsky): It should be possible to support this case, but
                // for now we rely on the inliner avoiding it.
                if cv.Outer.Curfn != callerfn {
                        base.FatalfAt(call.Pos(), "inlining closure call across frames")
                }
                r.closureVars[i] = cv.Outer
        }
        if len(r.closureVars) != 0 && r.hasTypeParams() {
                r.dictParam = r.closureVars[len(r.closureVars)-1] // dictParam is last; see reader.funcLit
        }

        r.funcargs(fn)

        r.delayResults = fn.Inl.CanDelayResults

        r.retlabel = typecheck.AutoLabel(".i")
        inlgen++

        init := ir.TakeInit(call)

        // For normal function calls, the function callee expression
        // may contain side effects. Make sure to preserve these,
        // if necessary (#42703).
        if call.Op() == ir.OCALLFUNC {
                inline.CalleeEffects(&init, call.X)
        }

        var args ir.Nodes
        if call.Op() == ir.OCALLMETH {
                base.FatalfAt(call.Pos(), "OCALLMETH missed by typecheck")
        }
        args.Append(call.Args...)

        // Create assignment to declare and initialize inlvars.
        as2 := ir.NewAssignListStmt(call.Pos(), ir.OAS2, r.inlvars, args)
        as2.Def = true
        var as2init ir.Nodes
        for _, name := range r.inlvars {
                if ir.IsBlank(name) {
                        continue
                }
                // TODO(mdempsky): Use inlined position of name.Pos() instead?
                name := name.(*ir.Name)
                as2init.Append(ir.NewDecl(call.Pos(), ir.ODCL, name))
                name.Defn = as2
        }
        as2.SetInit(as2init)
        init.Append(typecheck.Stmt(as2))

        if !r.delayResults {
                // If not delaying retvars, declare and zero initialize the
                // result variables now.
                for _, name := range r.retvars {
                        // TODO(mdempsky): Use inlined position of name.Pos() instead?
                        name := name.(*ir.Name)
                        init.Append(ir.NewDecl(call.Pos(), ir.ODCL, name))
                        ras := ir.NewAssignStmt(call.Pos(), name, nil)
                        init.Append(typecheck.Stmt(ras))
                }
        }

        // Add an inline mark just before the inlined body.
        // This mark is inline in the code so that it's a reasonable spot
        // to put a breakpoint. Not sure if that's really necessary or not
        // (in which case it could go at the end of the function instead).
        // Note issue 28603.
        init.Append(ir.NewInlineMarkStmt(call.Pos().WithIsStmt(), int64(r.inlTreeIndex)))

        ir.WithFunc(r.curfn, func() {
                if !r.syntheticBody(call.Pos()) {
                        assert(r.Bool()) // have body

                        r.curfn.Body = r.stmts()
                        r.curfn.Endlineno = r.pos()
                }

                // TODO(mdempsky): This shouldn't be necessary. Inlining might
                // read in new function/method declarations, which could
                // potentially be recursively inlined themselves; but we shouldn't
                // need to read in the non-inlined bodies for the declarations
                // themselves. But currently it's an easy fix to #50552.
                readBodies(typecheck.Target, true)

                // Replace any "return" statements within the function body.
                var edit func(ir.Node) ir.Node
                edit = func(n ir.Node) ir.Node {
                        if ret, ok := n.(*ir.ReturnStmt); ok {
                                n = typecheck.Stmt(r.inlReturn(ret))
                        }
                        ir.EditChildren(n, edit)
                        return n
                }
                edit(r.curfn)
        })

        body := ir.Nodes(r.curfn.Body)

        // Reparent any declarations into the caller function.
        for _, name := range r.curfn.Dcl {
                name.Curfn = callerfn
                callerfn.Dcl = append(callerfn.Dcl, name)

                if name.AutoTemp() {
                        name.SetEsc(ir.EscUnknown)
                        name.SetInlLocal(true)
                }
        }

        body.Append(ir.NewLabelStmt(call.Pos(), r.retlabel))

        res := ir.NewInlinedCallExpr(call.Pos(), body, append([]ir.Node(nil), r.retvars...))
        res.SetInit(init)
        res.SetType(call.Type())
        res.SetTypecheck(1)

        // Inlining shouldn't add any functions to todoBodies.
        assert(len(todoBodies) == 0)

        return res
}

// inlReturn returns a statement that can substitute for the given
// return statement when inlining.
func (r *reader) inlReturn(ret *ir.ReturnStmt) *ir.BlockStmt {
        pos := r.inlCall.Pos()

        block := ir.TakeInit(ret)

        if results := ret.Results; len(results) != 0 {
                assert(len(r.retvars) == len(results))

                as2 := ir.NewAssignListStmt(pos, ir.OAS2, append([]ir.Node(nil), r.retvars...), ret.Results)

                if r.delayResults {
                        for _, name := range r.retvars {
                                // TODO(mdempsky): Use inlined position of name.Pos() instead?
                                name := name.(*ir.Name)
                                block.Append(ir.NewDecl(pos, ir.ODCL, name))
                                name.Defn = as2
                        }
                }

                block.Append(as2)
        }

        block.Append(ir.NewBranchStmt(pos, ir.OGOTO, r.retlabel))
        return ir.NewBlockStmt(pos, block)
}

// expandInline reads in an extra copy of IR to populate
// fn.Inl.Dcl.
func expandInline(fn *ir.Func, pri pkgReaderIndex) {
        // TODO(mdempsky): Remove this function. It's currently needed by
        // dwarfgen/dwarf.go:preInliningDcls, which requires fn.Inl.Dcl to
        // create abstract function DIEs. But we should be able to provide it
        // with the same information some other way.

        fndcls := len(fn.Dcl)
        topdcls := len(typecheck.Target.Funcs)

        tmpfn := ir.NewFunc(fn.Pos(), fn.Nname.Pos(), fn.Sym(), fn.Type())
        tmpfn.ClosureVars = fn.ClosureVars

        {
                r := pri.asReader(pkgbits.RelocBody, pkgbits.SyncFuncBody)

                // Don't change parameter's Sym/Nname fields.
                r.funarghack = true

                r.funcBody(tmpfn)
        }

        used := usedLocals(tmpfn.Body)

        for _, name := range tmpfn.Dcl {
                if name.Class != ir.PAUTO || used.Has(name) {
                        name.Curfn = fn
                        fn.Inl.Dcl = append(fn.Inl.Dcl, name)
                } else {
                        // TODO(mdempsky): Simplify code after confident that this never
                        // happens anymore.
                        base.FatalfAt(name.Pos(), "unused auto: %v", name)
                }
        }
        fn.Inl.HaveDcl = true

        // Double check that we didn't change fn.Dcl by accident.
        assert(fndcls == len(fn.Dcl))

        // typecheck.Stmts may have added function literals to
        // typecheck.Target.Decls. Remove them again so we don't risk trying
        // to compile them multiple times.
        typecheck.Target.Funcs = typecheck.Target.Funcs[:topdcls]
}

// usedLocals returns a set of local variables that are used within body.
func usedLocals(body []ir.Node) ir.NameSet {
        var used ir.NameSet
        ir.VisitList(body, func(n ir.Node) {
                if n, ok := n.(*ir.Name); ok && n.Op() == ir.ONAME && n.Class == ir.PAUTO {
                        used.Add(n)
                }
        })
        return used
}

// @@@ Method wrappers

// needWrapperTypes lists types for which we may need to generate
// method wrappers.
var needWrapperTypes []*types.Type

// haveWrapperTypes lists types for which we know we already have
// method wrappers, because we found the type in an imported package.
var haveWrapperTypes []*types.Type

// needMethodValueWrappers lists methods for which we may need to
// generate method value wrappers.
var needMethodValueWrappers []methodValueWrapper

// haveMethodValueWrappers lists methods for which we know we already
// have method value wrappers, because we found it in an imported
// package.
var haveMethodValueWrappers []methodValueWrapper

type methodValueWrapper struct {
        rcvr   *types.Type
        method *types.Field
}

func (r *reader) needWrapper(typ *types.Type) {
        if typ.IsPtr() {
                return
        }

        // If a type was found in an imported package, then we can assume
        // that package (or one of its transitive dependencies) already
        // generated method wrappers for it.
        if r.importedDef() {
                haveWrapperTypes = append(haveWrapperTypes, typ)
        } else {
                needWrapperTypes = append(needWrapperTypes, typ)
        }
}

// importedDef reports whether r is reading from an imported and
// non-generic element.
//
// If a type was found in an imported package, then we can assume that
// package (or one of its transitive dependencies) already generated
// method wrappers for it.
//
// Exception: If we're instantiating an imported generic type or
// function, we might be instantiating it with type arguments not
// previously seen before.
//
// TODO(mdempsky): Distinguish when a generic function or type was
// instantiated in an imported package so that we can add types to
// haveWrapperTypes instead.
func (r *reader) importedDef() bool {
        return r.p != localPkgReader && !r.hasTypeParams()
}

func MakeWrappers(target *ir.Package) {
        // always generate a wrapper for error.Error (#29304)
        needWrapperTypes = append(needWrapperTypes, types.ErrorType)

        seen := make(map[string]*types.Type)

        for _, typ := range haveWrapperTypes {
                wrapType(typ, target, seen, false)
        }
        haveWrapperTypes = nil

        for _, typ := range needWrapperTypes {
                wrapType(typ, target, seen, true)
        }
        needWrapperTypes = nil

        for _, wrapper := range haveMethodValueWrappers {
                wrapMethodValue(wrapper.rcvr, wrapper.method, target, false)
        }
        haveMethodValueWrappers = nil

        for _, wrapper := range needMethodValueWrappers {
                wrapMethodValue(wrapper.rcvr, wrapper.method, target, true)
        }
        needMethodValueWrappers = nil
}

func wrapType(typ *types.Type, target *ir.Package, seen map[string]*types.Type, needed bool) {
        key := typ.LinkString()
        if prev := seen[key]; prev != nil {
                if !types.Identical(typ, prev) {
                        base.Fatalf("collision: types %v and %v have link string %q", typ, prev, key)
                }
                return
        }
        seen[key] = typ

        if !needed {
                // Only called to add to 'seen'.
                return
        }

        if !typ.IsInterface() {
                typecheck.CalcMethods(typ)
        }
        for _, meth := range typ.AllMethods() {
                if meth.Sym.IsBlank() || !meth.IsMethod() {
                        base.FatalfAt(meth.Pos, "invalid method: %v", meth)
                }

                methodWrapper(0, typ, meth, target)

                // For non-interface types, we also want *T wrappers.
                if !typ.IsInterface() {
                        methodWrapper(1, typ, meth, target)

                        // For not-in-heap types, *T is a scalar, not pointer shaped,
                        // so the interface wrappers use **T.
                        if typ.NotInHeap() {
                                methodWrapper(2, typ, meth, target)
                        }
                }
        }
}

func methodWrapper(derefs int, tbase *types.Type, method *types.Field, target *ir.Package) {
        wrapper := tbase
        for i := 0; i < derefs; i++ {
                wrapper = types.NewPtr(wrapper)
        }

        sym := ir.MethodSym(wrapper, method.Sym)
        base.Assertf(!sym.Siggen(), "already generated wrapper %v", sym)
        sym.SetSiggen(true)

        wrappee := method.Type.Recv().Type
        if types.Identical(wrapper, wrappee) ||
                !types.IsMethodApplicable(wrapper, method) ||
                !reflectdata.NeedEmit(tbase) {
                return
        }

        // TODO(mdempsky): Use method.Pos instead?
        pos := base.AutogeneratedPos

        fn := newWrapperFunc(pos, sym, wrapper, method)

        var recv ir.Node = fn.Nname.Type().Recv().Nname.(*ir.Name)

        // For simple *T wrappers around T methods, panicwrap produces a
        // nicer panic message.
        if wrapper.IsPtr() && types.Identical(wrapper.Elem(), wrappee) {
                cond := ir.NewBinaryExpr(pos, ir.OEQ, recv, types.BuiltinPkg.Lookup("nil").Def.(ir.Node))
                then := []ir.Node{ir.NewCallExpr(pos, ir.OCALL, typecheck.LookupRuntime("panicwrap"), nil)}
                fn.Body.Append(ir.NewIfStmt(pos, cond, then, nil))
        }

        // typecheck will add one implicit deref, if necessary,
        // but not-in-heap types require more for their **T wrappers.
        for i := 1; i < derefs; i++ {
                recv = Implicit(ir.NewStarExpr(pos, recv))
        }

        addTailCall(pos, fn, recv, method)

        finishWrapperFunc(fn, target)
}

func wrapMethodValue(recvType *types.Type, method *types.Field, target *ir.Package, needed bool) {
        sym := ir.MethodSymSuffix(recvType, method.Sym, "-fm")
        if sym.Uniq() {
                return
        }
        sym.SetUniq(true)

        // TODO(mdempsky): Use method.Pos instead?
        pos := base.AutogeneratedPos

        fn := newWrapperFunc(pos, sym, nil, method)
        sym.Def = fn.Nname

        // Declare and initialize variable holding receiver.
        recv := ir.NewHiddenParam(pos, fn, typecheck.Lookup(".this"), recvType)

        if !needed {
                return
        }

        addTailCall(pos, fn, recv, method)

        finishWrapperFunc(fn, target)
}

func newWrapperFunc(pos src.XPos, sym *types.Sym, wrapper *types.Type, method *types.Field) *ir.Func {
        sig := newWrapperType(wrapper, method)

        fn := ir.NewFunc(pos, pos, sym, sig)
        fn.SetDupok(true) // TODO(mdempsky): Leave unset for local, non-generic wrappers?

        // TODO(mdempsky): De-duplicate with similar logic in funcargs.
        defParams := func(class ir.Class, params []*types.Field) {
                for _, param := range params {
                        param.Nname = fn.NewLocal(param.Pos, param.Sym, class, param.Type)
                }
        }

        defParams(ir.PPARAM, sig.Recvs())
        defParams(ir.PPARAM, sig.Params())
        defParams(ir.PPARAMOUT, sig.Results())

        return fn
}

func finishWrapperFunc(fn *ir.Func, target *ir.Package) {
        ir.WithFunc(fn, func() {
                typecheck.Stmts(fn.Body)
        })

        // We generate wrappers after the global inlining pass,
        // so we're responsible for applying inlining ourselves here.
        // TODO(prattmic): plumb PGO.
        inline.InlineCalls(fn, nil)

        // The body of wrapper function after inlining may reveal new ir.OMETHVALUE node,
        // we don't know whether wrapper function has been generated for it or not, so
        // generate one immediately here.
        //
        // Further, after CL 492017, function that construct closures is allowed to be inlined,
        // even though the closure itself can't be inline. So we also need to visit body of any
        // closure that we see when visiting body of the wrapper function.
        ir.VisitFuncAndClosures(fn, func(n ir.Node) {
                if n, ok := n.(*ir.SelectorExpr); ok && n.Op() == ir.OMETHVALUE {
                        wrapMethodValue(n.X.Type(), n.Selection, target, true)
                }
        })

        fn.Nname.Defn = fn
        target.Funcs = append(target.Funcs, fn)
}

// newWrapperType returns a copy of the given signature type, but with
// the receiver parameter type substituted with recvType.
// If recvType is nil, newWrapperType returns a signature
// without a receiver parameter.
func newWrapperType(recvType *types.Type, method *types.Field) *types.Type {
        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)
                        }
                        res[i] = types.NewField(param.Pos, sym, param.Type)
                        res[i].SetIsDDD(param.IsDDD())
                }
                return res
        }

        sig := method.Type

        var recv *types.Field
        if recvType != nil {
                recv = types.NewField(sig.Recv().Pos, typecheck.Lookup(".this"), recvType)
        }
        params := clone(sig.Params())
        results := clone(sig.Results())

        return types.NewSignature(recv, params, results)
}

func addTailCall(pos src.XPos, fn *ir.Func, recv ir.Node, method *types.Field) {
        sig := fn.Nname.Type()
        args := make([]ir.Node, sig.NumParams())
        for i, param := range sig.Params() {
                args[i] = param.Nname.(*ir.Name)
        }

        // TODO(mdempsky): Support creating OTAILCALL, when possible. See reflectdata.methodWrapper.
        // Not urgent though, because tail calls are currently incompatible with regabi anyway.

        fn.SetWrapper(true) // TODO(mdempsky): Leave unset for tail calls?

        dot := typecheck.XDotMethod(pos, recv, method.Sym, true)
        call := typecheck.Call(pos, dot, args, method.Type.IsVariadic()).(*ir.CallExpr)

        if method.Type.NumResults() == 0 {
                fn.Body.Append(call)
                return
        }

        ret := ir.NewReturnStmt(pos, nil)
        ret.Results = []ir.Node{call}
        fn.Body.Append(ret)
}

func setBasePos(pos src.XPos) {
        // Set the position for any error messages we might print (e.g. too large types).
        base.Pos = pos
}

// dictParamName is the name of the synthetic dictionary parameter
// added to shaped functions.
//
// N.B., this variable name is known to Delve:
// https://github.com/go-delve/delve/blob/cb91509630529e6055be845688fd21eb89ae8714/pkg/proc/eval.go#L28
const dictParamName = typecheck.LocalDictName

// shapeSig returns a copy of fn's signature, except adding a
// dictionary parameter and promoting the receiver parameter (if any)
// to a normal parameter.
//
// The parameter types.Fields are all copied too, so their Nname
// fields can be initialized for use by the shape function.
func shapeSig(fn *ir.Func, dict *readerDict) *types.Type {
        sig := fn.Nname.Type()
        oldRecv := sig.Recv()

        var recv *types.Field
        if oldRecv != nil {
                recv = types.NewField(oldRecv.Pos, oldRecv.Sym, oldRecv.Type)
        }

        params := make([]*types.Field, 1+sig.NumParams())
        params[0] = types.NewField(fn.Pos(), fn.Sym().Pkg.Lookup(dictParamName), types.NewPtr(dict.varType()))
        for i, param := range sig.Params() {
                d := types.NewField(param.Pos, param.Sym, param.Type)
                d.SetIsDDD(param.IsDDD())
                params[1+i] = d
        }

        results := make([]*types.Field, sig.NumResults())
        for i, result := range sig.Results() {
                results[i] = types.NewField(result.Pos, result.Sym, result.Type)
        }

        return types.NewSignature(recv, params, results)
}