Source file src/cmd/compile/internal/noder/writer.go

     1  // Copyright 2021 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  package noder
     6  
     7  import (
     8  	"fmt"
     9  	"go/constant"
    10  	"go/token"
    11  	"go/version"
    12  	"internal/buildcfg"
    13  	"internal/pkgbits"
    14  	"os"
    15  	"slices"
    16  	"strings"
    17  
    18  	"cmd/compile/internal/base"
    19  	"cmd/compile/internal/ir"
    20  	"cmd/compile/internal/syntax"
    21  	"cmd/compile/internal/types"
    22  	"cmd/compile/internal/types2"
    23  )
    24  
    25  // This file implements the Unified IR package writer and defines the
    26  // Unified IR export data format.
    27  //
    28  // Low-level coding details (e.g., byte-encoding of individual
    29  // primitive values, or handling element bitstreams and
    30  // cross-references) are handled by internal/pkgbits, so here we only
    31  // concern ourselves with higher-level worries like mapping Go
    32  // language constructs into elements.
    33  
    34  // There are two central types in the writing process: the "writer"
    35  // type handles writing out individual elements, while the "pkgWriter"
    36  // type keeps track of which elements have already been created.
    37  //
    38  // For each sort of "thing" (e.g., position, package, object, type)
    39  // that can be written into the export data, there are generally
    40  // several methods that work together:
    41  //
    42  // - writer.thing handles writing out a *use* of a thing, which often
    43  //   means writing a relocation to that thing's encoded index.
    44  //
    45  // - pkgWriter.thingIdx handles reserving an index for a thing, and
    46  //   writing out any elements needed for the thing.
    47  //
    48  // - writer.doThing handles writing out the *definition* of a thing,
    49  //   which in general is a mix of low-level coding primitives (e.g.,
    50  //   ints and strings) or uses of other things.
    51  //
    52  // A design goal of Unified IR is to have a single, canonical writer
    53  // implementation, but multiple reader implementations each tailored
    54  // to their respective needs. For example, within cmd/compile's own
    55  // backend, inlining is implemented largely by just re-running the
    56  // function body reading code.
    57  
    58  // TODO(mdempsky): Add an importer for Unified IR to the x/tools repo,
    59  // and better document the file format boundary between public and
    60  // private data.
    61  
    62  type index = pkgbits.Index
    63  
    64  func assert(p bool) { base.Assert(p) }
    65  
    66  // A pkgWriter constructs Unified IR export data from the results of
    67  // running the types2 type checker on a Go compilation unit.
    68  type pkgWriter struct {
    69  	pkgbits.PkgEncoder
    70  
    71  	m                     posMap
    72  	curpkg                *types2.Package
    73  	info                  *types2.Info
    74  	rangeFuncBodyClosures map[*syntax.FuncLit]bool // non-public information, e.g., which functions are closures range function bodies?
    75  
    76  	// Indices for previously written syntax and types2 things.
    77  
    78  	posBasesIdx map[*syntax.PosBase]index
    79  	pkgsIdx     map[*types2.Package]index
    80  	typsIdx     map[types2.Type]index
    81  	objsIdx     map[types2.Object]index
    82  
    83  	// Maps from types2.Objects back to their syntax.Decl.
    84  
    85  	funDecls map[*types2.Func]*syntax.FuncDecl
    86  	typDecls map[*types2.TypeName]typeDeclGen
    87  
    88  	// linknames maps package-scope objects to their linker symbol name,
    89  	// if specified by a //go:linkname or //go:linknamestd directive.
    90  	linknames map[types2.Object]struct {
    91  		remote string
    92  		std    bool
    93  	}
    94  
    95  	// cgoPragmas accumulates any //go:cgo_* pragmas that need to be
    96  	// passed through to cmd/link.
    97  	cgoPragmas [][]string
    98  }
    99  
   100  // newPkgWriter returns an initialized pkgWriter for the specified
   101  // package.
   102  func newPkgWriter(m posMap, pkg *types2.Package, info *types2.Info, otherInfo map[*syntax.FuncLit]bool) *pkgWriter {
   103  	return &pkgWriter{
   104  		PkgEncoder: pkgbits.NewPkgEncoder(uirVersion, base.Debug.SyncFrames),
   105  
   106  		m:                     m,
   107  		curpkg:                pkg,
   108  		info:                  info,
   109  		rangeFuncBodyClosures: otherInfo,
   110  
   111  		pkgsIdx: make(map[*types2.Package]index),
   112  		objsIdx: make(map[types2.Object]index),
   113  		typsIdx: make(map[types2.Type]index),
   114  
   115  		posBasesIdx: make(map[*syntax.PosBase]index),
   116  
   117  		funDecls: make(map[*types2.Func]*syntax.FuncDecl),
   118  		typDecls: make(map[*types2.TypeName]typeDeclGen),
   119  
   120  		linknames: make(map[types2.Object]struct {
   121  			remote string
   122  			std    bool
   123  		}),
   124  	}
   125  }
   126  
   127  // errorf reports a user error about thing p.
   128  func (pw *pkgWriter) errorf(p poser, msg string, args ...any) {
   129  	base.ErrorfAt(pw.m.pos(p), 0, msg, args...)
   130  }
   131  
   132  // fatalf reports an internal compiler error about thing p.
   133  func (pw *pkgWriter) fatalf(p poser, msg string, args ...any) {
   134  	base.FatalfAt(pw.m.pos(p), msg, args...)
   135  }
   136  
   137  // unexpected reports a fatal error about a thing of unexpected
   138  // dynamic type.
   139  func (pw *pkgWriter) unexpected(what string, p poser) {
   140  	pw.fatalf(p, "unexpected %s: %v (%T)", what, p, p)
   141  }
   142  
   143  func (pw *pkgWriter) typeAndValue(x syntax.Expr) syntax.TypeAndValue {
   144  	tv, ok := pw.maybeTypeAndValue(x)
   145  	if !ok {
   146  		pw.fatalf(x, "missing Types entry: %v", syntax.String(x))
   147  	}
   148  	return tv
   149  }
   150  
   151  func (pw *pkgWriter) maybeTypeAndValue(x syntax.Expr) (syntax.TypeAndValue, bool) {
   152  	tv := x.GetTypeInfo()
   153  
   154  	// If x is a generic function whose type arguments are inferred
   155  	// from assignment context, then we need to find its inferred type
   156  	// in Info.Instances instead.
   157  	if name, ok := x.(*syntax.Name); ok {
   158  		if inst, ok := pw.info.Instances[name]; ok {
   159  			tv.Type = inst.Type
   160  		}
   161  	}
   162  
   163  	return tv, tv.Type != nil
   164  }
   165  
   166  // typeOf returns the Type of the given value expression.
   167  func (pw *pkgWriter) typeOf(expr syntax.Expr) types2.Type {
   168  	tv := pw.typeAndValue(expr)
   169  	if !tv.IsValue() {
   170  		pw.fatalf(expr, "expected value: %v", syntax.String(expr))
   171  	}
   172  	return tv.Type
   173  }
   174  
   175  // A writer provides APIs for writing out an individual element.
   176  type writer struct {
   177  	p *pkgWriter
   178  
   179  	*pkgbits.Encoder
   180  
   181  	// sig holds the signature for the current function body, if any.
   182  	sig *types2.Signature
   183  
   184  	// TODO(mdempsky): We should be able to prune localsIdx whenever a
   185  	// scope closes, and then maybe we can just use the same map for
   186  	// storing the TypeParams too (as their TypeName instead).
   187  
   188  	// localsIdx tracks any local variables declared within this
   189  	// function body. It's unused for writing out non-body things.
   190  	localsIdx map[*types2.Var]int
   191  
   192  	// closureVars tracks any free variables that are referenced by this
   193  	// function body. It's unused for writing out non-body things.
   194  	closureVars    []posVar
   195  	closureVarsIdx map[*types2.Var]int // index of previously seen free variables
   196  
   197  	dict *writerDict
   198  
   199  	// derived tracks whether the type being written out references any
   200  	// type parameters. It's unused for writing non-type things.
   201  	derived bool
   202  }
   203  
   204  // A writerDict tracks types and objects that are used by a declaration.
   205  type writerDict struct {
   206  	// implicits contains type parameters from enclosing declarations.
   207  	implicits []*types2.TypeParam
   208  	// receivers contains receiver type parameters of the declaration.
   209  	receivers []*types2.TypeParam
   210  
   211  	// derived is a slice of type indices for computing derived types
   212  	// (i.e., types that depend on the declaration's type parameters).
   213  	derived []derivedInfo
   214  
   215  	// derivedIdx maps a Type to its corresponding index within the
   216  	// derived slice, if present.
   217  	derivedIdx map[types2.Type]index
   218  
   219  	// These slices correspond to entries in the runtime dictionary.
   220  	typeParamMethodExprs []writerMethodExprInfo
   221  	subdicts             []objInfo
   222  	rtypes               []typeInfo
   223  	itabs                []itabInfo
   224  }
   225  
   226  type itabInfo struct {
   227  	typ   typeInfo
   228  	iface typeInfo
   229  }
   230  
   231  // typeParamIndex returns the index of the given type parameter within
   232  // the dictionary. This may differ from typ.Index() when there are
   233  // implicit or receiver type parameters.
   234  func (dict *writerDict) typeParamIndex(typ *types2.TypeParam) int {
   235  	for idx, implicit := range dict.implicits {
   236  		if implicit == typ {
   237  			return idx
   238  		}
   239  	}
   240  
   241  	for idx, receiver := range dict.receivers {
   242  		if receiver == typ {
   243  			return len(dict.implicits) + idx
   244  		}
   245  	}
   246  
   247  	return len(dict.implicits) + len(dict.receivers) + typ.Index()
   248  }
   249  
   250  // A derivedInfo represents a reference to an encoded generic Go type.
   251  type derivedInfo struct {
   252  	idx index
   253  }
   254  
   255  // A typeInfo represents a reference to an encoded Go type.
   256  //
   257  // If derived is true, then the typeInfo represents a generic Go type
   258  // that contains type parameters. In this case, idx is an index into
   259  // the readerDict.derived{,Types} arrays.
   260  //
   261  // Otherwise, the typeInfo represents a non-generic Go type, and idx
   262  // is an index into the reader.typs array instead.
   263  type typeInfo struct {
   264  	idx     index
   265  	derived bool
   266  }
   267  
   268  // An objInfo represents a reference to an encoded, instantiated (if
   269  // applicable) Go object.
   270  type objInfo struct {
   271  	idx       index      // index for the generic function declaration
   272  	explicits []typeInfo // info for the type arguments
   273  }
   274  
   275  // A selectorInfo represents a reference to an encoded field or method
   276  // name (i.e., objects that can only be accessed using selector
   277  // expressions).
   278  type selectorInfo struct {
   279  	pkgIdx  index
   280  	nameIdx index
   281  }
   282  
   283  // anyDerived reports whether any of info's explicit type arguments
   284  // are derived types.
   285  func (info objInfo) anyDerived() bool {
   286  	for _, explicit := range info.explicits {
   287  		if explicit.derived {
   288  			return true
   289  		}
   290  	}
   291  	return false
   292  }
   293  
   294  // equals reports whether info and other represent the same Go object
   295  // (i.e., same base object and identical type arguments, if any).
   296  func (info objInfo) equals(other objInfo) bool {
   297  	if info.idx != other.idx {
   298  		return false
   299  	}
   300  	assert(len(info.explicits) == len(other.explicits))
   301  	for i, targ := range info.explicits {
   302  		if targ != other.explicits[i] {
   303  			return false
   304  		}
   305  	}
   306  	return true
   307  }
   308  
   309  type writerMethodExprInfo struct {
   310  	typeParamIdx int
   311  	methodInfo   selectorInfo
   312  }
   313  
   314  // typeParamMethodExprIdx returns the index where the given encoded
   315  // method expression function pointer appears within this dictionary's
   316  // type parameters method expressions section, adding it if necessary.
   317  func (dict *writerDict) typeParamMethodExprIdx(typeParamIdx int, methodInfo selectorInfo) int {
   318  	newInfo := writerMethodExprInfo{typeParamIdx, methodInfo}
   319  
   320  	for idx, oldInfo := range dict.typeParamMethodExprs {
   321  		if oldInfo == newInfo {
   322  			return idx
   323  		}
   324  	}
   325  
   326  	idx := len(dict.typeParamMethodExprs)
   327  	dict.typeParamMethodExprs = append(dict.typeParamMethodExprs, newInfo)
   328  	return idx
   329  }
   330  
   331  // subdictIdx returns the index where the given encoded object's
   332  // runtime dictionary appears within this dictionary's subdictionary
   333  // section, adding it if necessary.
   334  func (dict *writerDict) subdictIdx(newInfo objInfo) int {
   335  	for idx, oldInfo := range dict.subdicts {
   336  		if oldInfo.equals(newInfo) {
   337  			return idx
   338  		}
   339  	}
   340  
   341  	idx := len(dict.subdicts)
   342  	dict.subdicts = append(dict.subdicts, newInfo)
   343  	return idx
   344  }
   345  
   346  // rtypeIdx returns the index where the given encoded type's
   347  // *runtime._type value appears within this dictionary's rtypes
   348  // section, adding it if necessary.
   349  func (dict *writerDict) rtypeIdx(newInfo typeInfo) int {
   350  	for idx, oldInfo := range dict.rtypes {
   351  		if oldInfo == newInfo {
   352  			return idx
   353  		}
   354  	}
   355  
   356  	idx := len(dict.rtypes)
   357  	dict.rtypes = append(dict.rtypes, newInfo)
   358  	return idx
   359  }
   360  
   361  // itabIdx returns the index where the given encoded type pair's
   362  // *runtime.itab value appears within this dictionary's itabs section,
   363  // adding it if necessary.
   364  func (dict *writerDict) itabIdx(typInfo, ifaceInfo typeInfo) int {
   365  	newInfo := itabInfo{typInfo, ifaceInfo}
   366  
   367  	for idx, oldInfo := range dict.itabs {
   368  		if oldInfo == newInfo {
   369  			return idx
   370  		}
   371  	}
   372  
   373  	idx := len(dict.itabs)
   374  	dict.itabs = append(dict.itabs, newInfo)
   375  	return idx
   376  }
   377  
   378  func (pw *pkgWriter) newWriter(k pkgbits.SectionKind, marker pkgbits.SyncMarker) *writer {
   379  	return &writer{
   380  		Encoder: pw.NewEncoder(k, marker),
   381  		p:       pw,
   382  	}
   383  }
   384  
   385  // @@@ Positions
   386  
   387  // pos writes the position of p into the element bitstream.
   388  func (w *writer) pos(p poser) {
   389  	w.Sync(pkgbits.SyncPos)
   390  	pos := p.Pos()
   391  
   392  	// TODO(mdempsky): Track down the remaining cases here and fix them.
   393  	if !w.Bool(pos.IsKnown()) {
   394  		return
   395  	}
   396  
   397  	// TODO(mdempsky): Delta encoding.
   398  	w.posBase(pos.Base())
   399  	w.Uint(pos.Line())
   400  	w.Uint(pos.Col())
   401  }
   402  
   403  // posBase writes a reference to the given PosBase into the element
   404  // bitstream.
   405  func (w *writer) posBase(b *syntax.PosBase) {
   406  	w.Reloc(pkgbits.SectionPosBase, w.p.posBaseIdx(b))
   407  }
   408  
   409  // posBaseIdx returns the index for the given PosBase.
   410  func (pw *pkgWriter) posBaseIdx(b *syntax.PosBase) index {
   411  	if idx, ok := pw.posBasesIdx[b]; ok {
   412  		return idx
   413  	}
   414  
   415  	w := pw.newWriter(pkgbits.SectionPosBase, pkgbits.SyncPosBase)
   416  	w.p.posBasesIdx[b] = w.Idx
   417  
   418  	w.String(trimFilename(b))
   419  
   420  	if !w.Bool(b.IsFileBase()) {
   421  		w.pos(b)
   422  		w.Uint(b.Line())
   423  		w.Uint(b.Col())
   424  	}
   425  
   426  	return w.Flush()
   427  }
   428  
   429  // @@@ Packages
   430  
   431  // pkg writes a use of the given Package into the element bitstream.
   432  func (w *writer) pkg(pkg *types2.Package) {
   433  	w.pkgRef(w.p.pkgIdx(pkg))
   434  }
   435  
   436  func (w *writer) pkgRef(idx index) {
   437  	w.Sync(pkgbits.SyncPkg)
   438  	w.Reloc(pkgbits.SectionPkg, idx)
   439  }
   440  
   441  // pkgIdx returns the index for the given package, adding it to the
   442  // package export data if needed.
   443  func (pw *pkgWriter) pkgIdx(pkg *types2.Package) index {
   444  	if idx, ok := pw.pkgsIdx[pkg]; ok {
   445  		return idx
   446  	}
   447  
   448  	w := pw.newWriter(pkgbits.SectionPkg, pkgbits.SyncPkgDef)
   449  	pw.pkgsIdx[pkg] = w.Idx
   450  
   451  	// The universe and package unsafe need to be handled specially by
   452  	// importers anyway, so we serialize them using just their package
   453  	// path. This ensures that readers don't confuse them for
   454  	// user-defined packages.
   455  	switch pkg {
   456  	case nil: // universe
   457  		w.String("builtin") // same package path used by godoc
   458  	case types2.Unsafe:
   459  		w.String("unsafe")
   460  	default:
   461  		// TODO(mdempsky): Write out pkg.Path() for curpkg too.
   462  		var path string
   463  		if pkg != w.p.curpkg {
   464  			path = pkg.Path()
   465  		}
   466  		base.Assertf(path != "builtin" && path != "unsafe", "unexpected path for user-defined package: %q", path)
   467  		w.String(path)
   468  		w.String(pkg.Name())
   469  
   470  		w.Len(len(pkg.Imports()))
   471  		for _, imp := range pkg.Imports() {
   472  			w.pkg(imp)
   473  		}
   474  	}
   475  
   476  	return w.Flush()
   477  }
   478  
   479  // @@@ Types
   480  
   481  var (
   482  	anyTypeName        = types2.Universe.Lookup("any").(*types2.TypeName)
   483  	comparableTypeName = types2.Universe.Lookup("comparable").(*types2.TypeName)
   484  	runeTypeName       = types2.Universe.Lookup("rune").(*types2.TypeName)
   485  )
   486  
   487  // typ writes a use of the given type into the bitstream.
   488  func (w *writer) typ(typ types2.Type) {
   489  	w.typInfo(w.p.typIdx(typ, w.dict))
   490  }
   491  
   492  // typInfo writes a use of the given type (specified as a typeInfo
   493  // instead) into the bitstream.
   494  func (w *writer) typInfo(info typeInfo) {
   495  	w.Sync(pkgbits.SyncType)
   496  	if w.Bool(info.derived) {
   497  		w.Len(int(info.idx))
   498  		w.derived = true
   499  	} else {
   500  		w.Reloc(pkgbits.SectionType, info.idx)
   501  	}
   502  }
   503  
   504  // typIdx returns the index where the export data description of type
   505  // can be read back in. If no such index exists yet, it's created.
   506  //
   507  // typIdx also reports whether typ is a derived type; that is, whether
   508  // its identity depends on type parameters.
   509  func (pw *pkgWriter) typIdx(typ types2.Type, dict *writerDict) typeInfo {
   510  	// Strip non-global aliases, because they only appear in inline
   511  	// bodies anyway. Otherwise, they can cause types.Sym collisions
   512  	// (e.g., "main.C" for both of the local type aliases in
   513  	// test/fixedbugs/issue50190.go).
   514  	for {
   515  		if alias, ok := typ.(*types2.Alias); ok && !isGlobal(alias.Obj()) {
   516  			typ = alias.Rhs()
   517  		} else {
   518  			break
   519  		}
   520  	}
   521  
   522  	if idx, ok := pw.typsIdx[typ]; ok {
   523  		return typeInfo{idx: idx, derived: false}
   524  	}
   525  	if dict != nil {
   526  		if idx, ok := dict.derivedIdx[typ]; ok {
   527  			return typeInfo{idx: idx, derived: true}
   528  		}
   529  	}
   530  
   531  	w := pw.newWriter(pkgbits.SectionType, pkgbits.SyncTypeIdx)
   532  	w.dict = dict
   533  
   534  	switch typ := typ.(type) {
   535  	default:
   536  		base.Fatalf("unexpected type: %v (%T)", typ, typ)
   537  
   538  	case *types2.Basic:
   539  		switch kind := typ.Kind(); {
   540  		case kind == types2.Invalid:
   541  			base.Fatalf("unexpected types2.Invalid")
   542  
   543  		case types2.Typ[kind] == typ:
   544  			w.Code(pkgbits.TypeBasic)
   545  			w.Len(int(kind))
   546  
   547  		default:
   548  			// Handle "byte" and "rune" as references to their TypeNames.
   549  			obj := types2.Universe.Lookup(typ.Name()).(*types2.TypeName)
   550  			assert(obj.Type() == typ)
   551  
   552  			w.Code(pkgbits.TypeNamed)
   553  			w.namedType(obj, nil)
   554  		}
   555  
   556  	case *types2.Named:
   557  		w.Code(pkgbits.TypeNamed)
   558  		w.namedType(splitNamed(typ))
   559  
   560  	case *types2.Alias:
   561  		w.Code(pkgbits.TypeNamed)
   562  		w.namedType(splitAlias(typ))
   563  
   564  	case *types2.TypeParam:
   565  		w.derived = true
   566  		w.Code(pkgbits.TypeTypeParam)
   567  		w.Len(w.dict.typeParamIndex(typ))
   568  
   569  	case *types2.Array:
   570  		w.Code(pkgbits.TypeArray)
   571  		w.Uint64(uint64(typ.Len()))
   572  		w.typ(typ.Elem())
   573  
   574  	case *types2.Chan:
   575  		w.Code(pkgbits.TypeChan)
   576  		w.Len(int(typ.Dir()))
   577  		w.typ(typ.Elem())
   578  
   579  	case *types2.Map:
   580  		w.Code(pkgbits.TypeMap)
   581  		w.typ(typ.Key())
   582  		w.typ(typ.Elem())
   583  
   584  	case *types2.Pointer:
   585  		w.Code(pkgbits.TypePointer)
   586  		w.typ(typ.Elem())
   587  
   588  	case *types2.Signature:
   589  		base.Assertf(typ.TypeParams() == nil, "unexpected type params: %v", typ)
   590  		w.Code(pkgbits.TypeSignature)
   591  		w.signature(typ)
   592  
   593  	case *types2.Slice:
   594  		w.Code(pkgbits.TypeSlice)
   595  		w.typ(typ.Elem())
   596  
   597  	case *types2.Struct:
   598  		w.Code(pkgbits.TypeStruct)
   599  		w.structType(typ)
   600  
   601  	case *types2.Interface:
   602  		// Handle "any" as reference to its TypeName.
   603  		// The underlying "any" interface is canonical, so this logic handles both
   604  		// GODEBUG=gotypesalias=1 (when any is represented as a types2.Alias), and
   605  		// gotypesalias=0.
   606  		if types2.Unalias(typ) == types2.Unalias(anyTypeName.Type()) {
   607  			w.Code(pkgbits.TypeNamed)
   608  			w.obj(anyTypeName, nil)
   609  			break
   610  		}
   611  
   612  		w.Code(pkgbits.TypeInterface)
   613  		w.interfaceType(typ)
   614  
   615  	case *types2.Union:
   616  		w.Code(pkgbits.TypeUnion)
   617  		w.unionType(typ)
   618  	}
   619  
   620  	if w.derived {
   621  		idx := index(len(dict.derived))
   622  		dict.derived = append(dict.derived, derivedInfo{idx: w.Flush()})
   623  		dict.derivedIdx[typ] = idx
   624  		return typeInfo{idx: idx, derived: true}
   625  	}
   626  
   627  	pw.typsIdx[typ] = w.Idx
   628  	return typeInfo{idx: w.Flush(), derived: false}
   629  }
   630  
   631  // namedType writes a use of the given named type into the bitstream.
   632  func (w *writer) namedType(obj *types2.TypeName, targs []types2.Type) {
   633  	// Named types that are declared within a generic function (and
   634  	// thus have implicit type parameters) are always derived types.
   635  	if w.p.hasImplicitTypeParams(obj) {
   636  		w.derived = true
   637  	}
   638  
   639  	w.obj(obj, targs)
   640  }
   641  
   642  func (w *writer) structType(typ *types2.Struct) {
   643  	w.Len(typ.NumFields())
   644  	for i := 0; i < typ.NumFields(); i++ {
   645  		f := typ.Field(i)
   646  		w.pos(f)
   647  		w.selector(f)
   648  		w.typ(f.Type())
   649  		w.String(typ.Tag(i))
   650  		w.Bool(f.Embedded())
   651  	}
   652  }
   653  
   654  func (w *writer) unionType(typ *types2.Union) {
   655  	w.Len(typ.Len())
   656  	for i := 0; i < typ.Len(); i++ {
   657  		t := typ.Term(i)
   658  		w.Bool(t.Tilde())
   659  		w.typ(t.Type())
   660  	}
   661  }
   662  
   663  func (w *writer) interfaceType(typ *types2.Interface) {
   664  	// If typ has no embedded types but it's not a basic interface, then
   665  	// the natural description we write out below will fail to
   666  	// reconstruct it.
   667  	if typ.NumEmbeddeds() == 0 && !typ.IsMethodSet() {
   668  		// Currently, this can only happen for the underlying Interface of
   669  		// "comparable", which is needed to handle type declarations like
   670  		// "type C comparable".
   671  		assert(typ == comparableTypeName.Type().(*types2.Named).Underlying())
   672  
   673  		// Export as "interface{ comparable }".
   674  		w.Len(0)                         // NumExplicitMethods
   675  		w.Len(1)                         // NumEmbeddeds
   676  		w.Bool(false)                    // IsImplicit
   677  		w.typ(comparableTypeName.Type()) // EmbeddedType(0)
   678  		return
   679  	}
   680  
   681  	w.Len(typ.NumExplicitMethods())
   682  	w.Len(typ.NumEmbeddeds())
   683  
   684  	if typ.NumExplicitMethods() == 0 && typ.NumEmbeddeds() == 1 {
   685  		w.Bool(typ.IsImplicit())
   686  	} else {
   687  		// Implicit interfaces always have 0 explicit methods and 1
   688  		// embedded type, so we skip writing out the implicit flag
   689  		// otherwise as a space optimization.
   690  		assert(!typ.IsImplicit())
   691  	}
   692  
   693  	for i := 0; i < typ.NumExplicitMethods(); i++ {
   694  		m := typ.ExplicitMethod(i)
   695  		sig := m.Type().(*types2.Signature)
   696  		assert(sig.TypeParams() == nil)
   697  
   698  		w.pos(m)
   699  		w.selector(m)
   700  		w.signature(sig)
   701  	}
   702  
   703  	for i := 0; i < typ.NumEmbeddeds(); i++ {
   704  		w.typ(typ.EmbeddedType(i))
   705  	}
   706  }
   707  
   708  func (w *writer) signature(sig *types2.Signature) {
   709  	w.Sync(pkgbits.SyncSignature)
   710  	w.params(sig.Params())
   711  	w.params(sig.Results())
   712  	w.Bool(sig.Variadic())
   713  }
   714  
   715  func (w *writer) params(typ *types2.Tuple) {
   716  	w.Sync(pkgbits.SyncParams)
   717  	w.Len(typ.Len())
   718  	for i := 0; i < typ.Len(); i++ {
   719  		w.param(typ.At(i))
   720  	}
   721  }
   722  
   723  func (w *writer) param(param *types2.Var) {
   724  	w.Sync(pkgbits.SyncParam)
   725  	w.pos(param)
   726  	w.localIdent(param)
   727  	w.typ(param.Type())
   728  }
   729  
   730  // @@@ Objects
   731  
   732  // obj writes a use of the given object into the bitstream.
   733  //
   734  // If obj is a generic object, then explicits are the explicit type
   735  // arguments used to instantiate it (i.e., used to substitute the
   736  // object's own declared type parameters).
   737  func (w *writer) obj(obj types2.Object, explicits []types2.Type) {
   738  	w.objInfo(w.p.objInstIdx(obj, explicits, w.dict))
   739  }
   740  
   741  // objInfo writes a use of the given encoded object into the
   742  // bitstream.
   743  func (w *writer) objInfo(info objInfo) {
   744  	w.Sync(pkgbits.SyncObject)
   745  	if w.Version().Has(pkgbits.DerivedFuncInstance) {
   746  		w.Bool(false)
   747  	}
   748  	w.Reloc(pkgbits.SectionObj, info.idx)
   749  
   750  	w.Len(len(info.explicits))
   751  	for _, info := range info.explicits {
   752  		w.typInfo(info)
   753  	}
   754  }
   755  
   756  // objInstIdx returns the indices for an object and a corresponding
   757  // list of type arguments used to instantiate it, adding them to the
   758  // export data as needed.
   759  func (pw *pkgWriter) objInstIdx(obj types2.Object, explicits []types2.Type, dict *writerDict) objInfo {
   760  	explicitInfos := make([]typeInfo, len(explicits))
   761  	for i := range explicitInfos {
   762  		explicitInfos[i] = pw.typIdx(explicits[i], dict)
   763  	}
   764  	return objInfo{idx: pw.objIdx(obj), explicits: explicitInfos}
   765  }
   766  
   767  // objIdx returns the index for the given Object, adding it to the
   768  // export data as needed.
   769  func (pw *pkgWriter) objIdx(obj types2.Object) index {
   770  	// TODO(mdempsky): Validate that obj is a global object (or a local
   771  	// defined type, which we hoist to global scope anyway).
   772  
   773  	if idx, ok := pw.objsIdx[obj]; ok {
   774  		return idx
   775  	}
   776  
   777  	dict := &writerDict{
   778  		derivedIdx: make(map[types2.Type]index),
   779  	}
   780  
   781  	if isDefinedType(obj) && obj.Pkg() == pw.curpkg {
   782  		decl, ok := pw.typDecls[obj.(*types2.TypeName)]
   783  		if !ok {
   784  			base.Fatalf("%v not in pw.typDecls", obj.(*types2.TypeName))
   785  		}
   786  		dict.implicits = decl.implicits
   787  	}
   788  
   789  	if isGenericMethod(obj.Type()) {
   790  		dict.receivers = asTypeParamSlice(obj.Type().(*types2.Signature).RecvTypeParams())
   791  	}
   792  
   793  	// We encode objects into 4 elements across different sections, all
   794  	// sharing the same index:
   795  	//
   796  	// - RelocName has just the object's qualified name (i.e.,
   797  	//   Object.Pkg and Object.Name) and the CodeObj indicating what
   798  	//   specific type of Object it is (Var, Func, etc).
   799  	//
   800  	// - RelocObj has the remaining public details about the object,
   801  	//   relevant to go/types importers.
   802  	//
   803  	// - RelocObjExt has additional private details about the object,
   804  	//   which are only relevant to cmd/compile itself. This is
   805  	//   separated from RelocObj so that go/types importers are
   806  	//   unaffected by internal compiler changes.
   807  	//
   808  	// - RelocObjDict has public details about the object's type
   809  	//   parameters and derived type's used by the object. This is
   810  	//   separated to facilitate the eventual introduction of
   811  	//   shape-based stenciling.
   812  	//
   813  	// TODO(mdempsky): Re-evaluate whether RelocName still makes sense
   814  	// to keep separate from RelocObj.
   815  
   816  	w := pw.newWriter(pkgbits.SectionObj, pkgbits.SyncObject1)
   817  	wext := pw.newWriter(pkgbits.SectionObjExt, pkgbits.SyncObject1)
   818  	wname := pw.newWriter(pkgbits.SectionName, pkgbits.SyncObject1)
   819  	wdict := pw.newWriter(pkgbits.SectionObjDict, pkgbits.SyncObject1)
   820  
   821  	pw.objsIdx[obj] = w.Idx // break cycles
   822  	assert(wext.Idx == w.Idx)
   823  	assert(wname.Idx == w.Idx)
   824  	assert(wdict.Idx == w.Idx)
   825  
   826  	w.dict = dict
   827  	wext.dict = dict
   828  
   829  	code := w.doObj(wext, obj)
   830  	w.Flush()
   831  	wext.Flush()
   832  
   833  	wname.qualifiedIdent(obj)
   834  	wname.Code(code)
   835  	wname.Flush()
   836  
   837  	wdict.objDict(obj, w.dict)
   838  	wdict.Flush()
   839  
   840  	return w.Idx
   841  }
   842  
   843  // doObj writes the RelocObj definition for obj to w, and the
   844  // RelocObjExt definition to wext.
   845  func (w *writer) doObj(wext *writer, obj types2.Object) pkgbits.CodeObj {
   846  	if obj.Pkg() != w.p.curpkg {
   847  		return pkgbits.ObjStub
   848  	}
   849  
   850  	switch obj := obj.(type) {
   851  	default:
   852  		w.p.unexpected("object", obj)
   853  		panic("unreachable")
   854  
   855  	case *types2.Const:
   856  		w.pos(obj)
   857  		w.typ(obj.Type())
   858  		w.Value(obj.Val())
   859  		return pkgbits.ObjConst
   860  
   861  	case *types2.Func:
   862  		if base.Flag.LowerH > 0 {
   863  			// Unified IR panics are the worst; this is a huge help in debugging them.
   864  			defer func() {
   865  				if p := recover(); p != nil {
   866  					fmt.Printf("Intercepted unified IR writer panic for function %s, repanicking", obj.FullName())
   867  					panic(p)
   868  				}
   869  			}()
   870  		}
   871  		decl, ok := w.p.funDecls[obj]
   872  		assert(ok)
   873  		sig := obj.Type().(*types2.Signature)
   874  
   875  		w.pos(obj)
   876  		if isGenericMethod(sig) {
   877  			w.Bool(true) // generic method
   878  
   879  			w.selector(obj)
   880  			w.typeParamNames(sig.RecvTypeParams())
   881  			w.param(sig.Recv())
   882  		} else {
   883  			if w.Version().Has(pkgbits.GenericMethods) {
   884  				w.Bool(false) // function
   885  			}
   886  		}
   887  		w.typeParamNames(sig.TypeParams())
   888  		w.signature(sig)
   889  		w.pos(decl)
   890  		wext.funcExt(obj)
   891  		return pkgbits.ObjFunc
   892  
   893  	case *types2.TypeName:
   894  		if obj.IsAlias() {
   895  			w.pos(obj)
   896  			rhs := obj.Type()
   897  			var tparams *types2.TypeParamList
   898  			if alias, ok := rhs.(*types2.Alias); ok { // materialized alias
   899  				assert(alias.TypeArgs() == nil)
   900  				tparams = alias.TypeParams()
   901  				rhs = alias.Rhs()
   902  			}
   903  			if w.Version().Has(pkgbits.AliasTypeParamNames) {
   904  				w.typeParamNames(tparams)
   905  			}
   906  			assert(w.Version().Has(pkgbits.AliasTypeParamNames) || tparams.Len() == 0)
   907  			w.typ(rhs)
   908  			return pkgbits.ObjAlias
   909  		}
   910  
   911  		named := obj.Type().(*types2.Named)
   912  		assert(named.TypeArgs() == nil)
   913  
   914  		w.pos(obj)
   915  		w.typeParamNames(named.TypeParams())
   916  		wext.typeExt(obj)
   917  		w.typ(named.Underlying())
   918  
   919  		// separate generic and non-generic methods
   920  		var methods, gmethods []*types2.Func
   921  		for i := range named.NumMethods() {
   922  			m := named.Method(i)
   923  			if isGenericMethod(m.Type()) {
   924  				gmethods = append(gmethods, m)
   925  			} else {
   926  				methods = append(methods, m)
   927  			}
   928  		}
   929  		// encode non-generic methods inline
   930  		w.Len(len(methods))
   931  		for _, m := range methods {
   932  			w.method(wext, m)
   933  		}
   934  		if len(gmethods) > 0 {
   935  			assert(w.Version().Has(pkgbits.GenericMethods))
   936  		}
   937  		// encode a pointer to each generic method
   938  		if w.Version().Has(pkgbits.GenericMethods) {
   939  			w.Len(len(gmethods))
   940  			for _, m := range gmethods {
   941  				w.Reloc(pkgbits.SectionObj, w.p.objIdx(m))
   942  			}
   943  		}
   944  
   945  		return pkgbits.ObjType
   946  
   947  	case *types2.Var:
   948  		w.pos(obj)
   949  		w.typ(obj.Type())
   950  		wext.varExt(obj)
   951  		return pkgbits.ObjVar
   952  	}
   953  }
   954  
   955  // objDict writes the dictionary needed for reading the given object.
   956  func (w *writer) objDict(obj types2.Object, dict *writerDict) {
   957  	// TODO(mdempsky): Split objDict into multiple entries? reader.go
   958  	// doesn't care about the type parameter bounds, and reader2.go
   959  	// doesn't care about referenced functions.
   960  
   961  	w.dict = dict // TODO(mdempsky): This is a bit sketchy.
   962  	w.Len(len(dict.implicits))
   963  
   964  	rtparams := objRecvTypeParams(obj)
   965  	tparams := objTypeParams(obj)
   966  
   967  	if w.Version().Has(pkgbits.GenericMethods) {
   968  		w.Len(len(rtparams))
   969  	} else {
   970  		assert(len(rtparams) == 0)
   971  	}
   972  	w.Len(len(tparams))
   973  
   974  	for _, rtparam := range rtparams {
   975  		w.typ(rtparam.Constraint())
   976  	}
   977  	for _, tparam := range tparams {
   978  		w.typ(tparam.Constraint())
   979  	}
   980  
   981  	nderived := len(dict.derived)
   982  	w.Len(nderived)
   983  	for _, typ := range dict.derived {
   984  		w.Reloc(pkgbits.SectionType, typ.idx)
   985  		if w.Version().Has(pkgbits.DerivedInfoNeeded) {
   986  			w.Bool(false)
   987  		}
   988  	}
   989  
   990  	// Write runtime dictionary information.
   991  	//
   992  	// N.B., the go/types importer reads up to the section, but doesn't
   993  	// read any further, so it's safe to change. (See TODO above.)
   994  
   995  	// For each type parameter, write out whether the constraint is a
   996  	// basic interface. This is used to determine how aggressively we
   997  	// can shape corresponding type arguments.
   998  	//
   999  	// This is somewhat redundant with writing out the full type
  1000  	// parameter constraints above, but the compiler currently skips
  1001  	// over those. Also, we don't care about the *declared* constraints,
  1002  	// but how the type parameters are actually *used*. E.g., if a type
  1003  	// parameter is constrained to `int | uint` but then never used in
  1004  	// arithmetic/conversions/etc, we could shape those together.
  1005  	for _, implicit := range dict.implicits {
  1006  		w.Bool(implicit.Underlying().(*types2.Interface).IsMethodSet())
  1007  	}
  1008  	for _, rtparam := range rtparams {
  1009  		w.Bool(rtparam.Underlying().(*types2.Interface).IsMethodSet())
  1010  	}
  1011  	for _, tparam := range tparams {
  1012  		w.Bool(tparam.Underlying().(*types2.Interface).IsMethodSet())
  1013  	}
  1014  
  1015  	w.Len(len(dict.typeParamMethodExprs))
  1016  	for _, info := range dict.typeParamMethodExprs {
  1017  		w.Len(info.typeParamIdx)
  1018  		w.selectorInfo(info.methodInfo)
  1019  	}
  1020  
  1021  	w.Len(len(dict.subdicts))
  1022  	for _, info := range dict.subdicts {
  1023  		w.objInfo(info)
  1024  	}
  1025  
  1026  	w.Len(len(dict.rtypes))
  1027  	for _, info := range dict.rtypes {
  1028  		w.typInfo(info)
  1029  	}
  1030  
  1031  	w.Len(len(dict.itabs))
  1032  	for _, info := range dict.itabs {
  1033  		w.typInfo(info.typ)
  1034  		w.typInfo(info.iface)
  1035  	}
  1036  
  1037  	assert(len(dict.derived) == nderived)
  1038  }
  1039  
  1040  func (w *writer) typeParamNames(tparams *types2.TypeParamList) {
  1041  	w.Sync(pkgbits.SyncTypeParamNames)
  1042  
  1043  	ntparams := tparams.Len()
  1044  	for i := 0; i < ntparams; i++ {
  1045  		tparam := tparams.At(i).Obj()
  1046  		w.pos(tparam)
  1047  		w.localIdent(tparam)
  1048  	}
  1049  }
  1050  
  1051  func (w *writer) method(wext *writer, meth *types2.Func) {
  1052  	decl, ok := w.p.funDecls[meth]
  1053  	assert(ok)
  1054  	sig := meth.Type().(*types2.Signature)
  1055  
  1056  	w.Sync(pkgbits.SyncMethod)
  1057  	w.pos(meth)
  1058  	w.selector(meth)
  1059  	w.typeParamNames(sig.RecvTypeParams())
  1060  	w.param(sig.Recv())
  1061  	w.signature(sig)
  1062  
  1063  	w.pos(decl) // XXX: Hack to workaround linker limitations.
  1064  	wext.funcExt(meth)
  1065  }
  1066  
  1067  // qualifiedIdent writes out the name of an object typically declared at package
  1068  // scope. It's also used to refer to generic methods and locally defined types.
  1069  func (w *writer) qualifiedIdent(obj types2.Object) {
  1070  	w.Sync(pkgbits.SyncSym)
  1071  
  1072  	name := obj.Name()
  1073  	if isDefinedType(obj) && obj.Pkg() == w.p.curpkg {
  1074  		decl, ok := w.p.typDecls[obj.(*types2.TypeName)]
  1075  		assert(ok)
  1076  		if decl.gen != 0 {
  1077  			// For local defined types, we embed a scope-disambiguation
  1078  			// number directly into their name. types.SplitVargenSuffix then
  1079  			// knows to look for this.
  1080  			//
  1081  			// TODO(mdempsky): Find a better solution; this is terrible.
  1082  			name = fmt.Sprintf("%s·%v", name, decl.gen)
  1083  		}
  1084  	}
  1085  
  1086  	// Generic methods are promoted to objects and thus need qualified identifiers.
  1087  	// They must be contextualized by their defining type.
  1088  	if isGenericMethod(obj.Type()) {
  1089  		recv := obj.Type().(*types2.Signature).Recv().Type()
  1090  		fstr := "%s.%s"
  1091  		if _, ok := types2.Unalias(recv).(*types2.Pointer); ok {
  1092  			fstr = "(*%s).%s"
  1093  		}
  1094  		name = fmt.Sprintf(fstr, types2.Unalias(deref2(recv)).(*types2.Named).Obj().Name(), name)
  1095  	}
  1096  
  1097  	w.pkg(obj.Pkg())
  1098  	w.String(name)
  1099  }
  1100  
  1101  // TODO(mdempsky): We should be able to omit pkg from both localIdent
  1102  // and selector, because they should always be known from context.
  1103  // However, past frustrations with this optimization in iexport make
  1104  // me a little nervous to try it again.
  1105  
  1106  // localIdent writes the name of a locally declared object (i.e.,
  1107  // objects that can only be accessed by non-qualified name, within the
  1108  // context of a particular function).
  1109  func (w *writer) localIdent(obj types2.Object) {
  1110  	assert(!isGlobal(obj))
  1111  	w.Sync(pkgbits.SyncLocalIdent)
  1112  	w.pkg(obj.Pkg())
  1113  	w.String(obj.Name())
  1114  }
  1115  
  1116  // selector writes the name of a field or method (i.e., objects that
  1117  // can only be accessed using selector expressions).
  1118  func (w *writer) selector(obj types2.Object) {
  1119  	w.selectorInfo(w.p.selectorIdx(obj))
  1120  }
  1121  
  1122  func (w *writer) selectorInfo(info selectorInfo) {
  1123  	w.Sync(pkgbits.SyncSelector)
  1124  	w.pkgRef(info.pkgIdx)
  1125  	w.StringRef(info.nameIdx)
  1126  }
  1127  
  1128  func (pw *pkgWriter) selectorIdx(obj types2.Object) selectorInfo {
  1129  	pkgIdx := pw.pkgIdx(obj.Pkg())
  1130  	nameIdx := pw.StringIdx(obj.Name())
  1131  	return selectorInfo{pkgIdx: pkgIdx, nameIdx: nameIdx}
  1132  }
  1133  
  1134  // @@@ Compiler extensions
  1135  
  1136  func (w *writer) funcExt(obj *types2.Func) {
  1137  	decl, ok := w.p.funDecls[obj]
  1138  	assert(ok)
  1139  
  1140  	// TODO(mdempsky): Extend these pragma validation flags to account
  1141  	// for generics. E.g., linkname probably doesn't make sense at
  1142  	// least.
  1143  
  1144  	pragma := asPragmaFlag(decl.Pragma)
  1145  	if pragma&ir.Systemstack != 0 && pragma&ir.Nosplit != 0 {
  1146  		w.p.errorf(decl, "go:nosplit and go:systemstack cannot be combined")
  1147  	}
  1148  	wi := asWasmImport(decl.Pragma)
  1149  	we := asWasmExport(decl.Pragma)
  1150  
  1151  	if decl.Body != nil {
  1152  		if pragma&ir.Noescape != 0 {
  1153  			w.p.errorf(decl, "can only use //go:noescape with external func implementations")
  1154  		}
  1155  		if wi != nil {
  1156  			w.p.errorf(decl, "can only use //go:wasmimport with external func implementations")
  1157  		}
  1158  		if (pragma&ir.UintptrKeepAlive != 0 && pragma&ir.UintptrEscapes == 0) && pragma&ir.Nosplit == 0 {
  1159  			// Stack growth can't handle uintptr arguments that may
  1160  			// be pointers (as we don't know which are pointers
  1161  			// when creating the stack map). Thus uintptrkeepalive
  1162  			// functions (and all transitive callees) must be
  1163  			// nosplit.
  1164  			//
  1165  			// N.B. uintptrescapes implies uintptrkeepalive but it
  1166  			// is OK since the arguments must escape to the heap.
  1167  			//
  1168  			// TODO(prattmic): Add recursive nosplit check of callees.
  1169  			// TODO(prattmic): Functions with no body (i.e.,
  1170  			// assembly) must also be nosplit, but we can't check
  1171  			// that here.
  1172  			w.p.errorf(decl, "go:uintptrkeepalive requires go:nosplit")
  1173  		}
  1174  	} else {
  1175  		if base.Flag.Complete || decl.Name.Value == "init" {
  1176  			// Linknamed functions are allowed to have no body. Hopefully
  1177  			// the linkname target has a body. See issue 23311.
  1178  			// Wasmimport functions are also allowed to have no body.
  1179  			if _, ok := w.p.linknames[obj]; !ok && wi == nil {
  1180  				w.p.errorf(decl, "missing function body")
  1181  			}
  1182  		}
  1183  	}
  1184  
  1185  	sig, block := obj.Type().(*types2.Signature), decl.Body
  1186  	body, closureVars := w.p.bodyIdx(sig, block, w.dict)
  1187  	if len(closureVars) > 0 {
  1188  		fmt.Fprintln(os.Stderr, "CLOSURE", closureVars)
  1189  	}
  1190  	assert(len(closureVars) == 0)
  1191  
  1192  	w.Sync(pkgbits.SyncFuncExt)
  1193  	w.pragmaFlag(pragma)
  1194  	w.linkname(obj)
  1195  
  1196  	if buildcfg.GOARCH == "wasm" {
  1197  		if wi != nil {
  1198  			w.String(wi.Module)
  1199  			w.String(wi.Name)
  1200  		} else {
  1201  			w.String("")
  1202  			w.String("")
  1203  		}
  1204  		if we != nil {
  1205  			w.String(we.Name)
  1206  		} else {
  1207  			w.String("")
  1208  		}
  1209  	}
  1210  
  1211  	w.Bool(false) // stub extension
  1212  	w.Reloc(pkgbits.SectionBody, body)
  1213  	w.Sync(pkgbits.SyncEOF)
  1214  }
  1215  
  1216  func (w *writer) typeExt(obj *types2.TypeName) {
  1217  	decl, ok := w.p.typDecls[obj]
  1218  	assert(ok)
  1219  
  1220  	w.Sync(pkgbits.SyncTypeExt)
  1221  
  1222  	w.pragmaFlag(asPragmaFlag(decl.Pragma))
  1223  
  1224  	// No LSym.SymIdx info yet.
  1225  	w.Int64(-1)
  1226  	w.Int64(-1)
  1227  }
  1228  
  1229  func (w *writer) varExt(obj *types2.Var) {
  1230  	w.Sync(pkgbits.SyncVarExt)
  1231  	w.linkname(obj)
  1232  }
  1233  
  1234  func (w *writer) linkname(obj types2.Object) {
  1235  	w.Sync(pkgbits.SyncLinkname)
  1236  	w.Int64(-1)
  1237  	info := w.p.linknames[obj]
  1238  	w.String(info.remote)
  1239  	w.Bool(info.std)
  1240  }
  1241  
  1242  func (w *writer) pragmaFlag(p ir.PragmaFlag) {
  1243  	w.Sync(pkgbits.SyncPragma)
  1244  	w.Int(int(p))
  1245  }
  1246  
  1247  // @@@ Function bodies
  1248  
  1249  // bodyIdx returns the index for the given function body (specified by
  1250  // block), adding it to the export data
  1251  func (pw *pkgWriter) bodyIdx(sig *types2.Signature, block *syntax.BlockStmt, dict *writerDict) (idx index, closureVars []posVar) {
  1252  	w := pw.newWriter(pkgbits.SectionBody, pkgbits.SyncFuncBody)
  1253  	w.sig = sig
  1254  	w.dict = dict
  1255  
  1256  	w.declareParams(sig)
  1257  	if w.Bool(block != nil) {
  1258  		w.stmts(block.List)
  1259  		w.pos(block.Rbrace)
  1260  	}
  1261  
  1262  	return w.Flush(), w.closureVars
  1263  }
  1264  
  1265  func (w *writer) declareParams(sig *types2.Signature) {
  1266  	addLocals := func(params *types2.Tuple) {
  1267  		for i := 0; i < params.Len(); i++ {
  1268  			w.addLocal(params.At(i))
  1269  		}
  1270  	}
  1271  
  1272  	if recv := sig.Recv(); recv != nil {
  1273  		w.addLocal(recv)
  1274  	}
  1275  	addLocals(sig.Params())
  1276  	addLocals(sig.Results())
  1277  }
  1278  
  1279  // addLocal records the declaration of a new local variable.
  1280  func (w *writer) addLocal(obj *types2.Var) {
  1281  	idx := len(w.localsIdx)
  1282  
  1283  	w.Sync(pkgbits.SyncAddLocal)
  1284  	if w.p.SyncMarkers() {
  1285  		w.Int(idx)
  1286  	}
  1287  	w.varDictIndex(obj)
  1288  
  1289  	if w.localsIdx == nil {
  1290  		w.localsIdx = make(map[*types2.Var]int)
  1291  	}
  1292  	w.localsIdx[obj] = idx
  1293  }
  1294  
  1295  // useLocal writes a reference to the given local or free variable
  1296  // into the bitstream.
  1297  func (w *writer) useLocal(pos syntax.Pos, obj *types2.Var) {
  1298  	w.Sync(pkgbits.SyncUseObjLocal)
  1299  
  1300  	if idx, ok := w.localsIdx[obj]; w.Bool(ok) {
  1301  		w.Len(idx)
  1302  		return
  1303  	}
  1304  
  1305  	idx, ok := w.closureVarsIdx[obj]
  1306  	if !ok {
  1307  		if w.closureVarsIdx == nil {
  1308  			w.closureVarsIdx = make(map[*types2.Var]int)
  1309  		}
  1310  		idx = len(w.closureVars)
  1311  		w.closureVars = append(w.closureVars, posVar{pos, obj})
  1312  		w.closureVarsIdx[obj] = idx
  1313  	}
  1314  	w.Len(idx)
  1315  }
  1316  
  1317  func (w *writer) openScope(pos syntax.Pos) {
  1318  	w.Sync(pkgbits.SyncOpenScope)
  1319  	w.pos(pos)
  1320  }
  1321  
  1322  func (w *writer) closeScope(pos syntax.Pos) {
  1323  	w.Sync(pkgbits.SyncCloseScope)
  1324  	w.pos(pos)
  1325  	w.closeAnotherScope()
  1326  }
  1327  
  1328  func (w *writer) closeAnotherScope() {
  1329  	w.Sync(pkgbits.SyncCloseAnotherScope)
  1330  }
  1331  
  1332  // @@@ Statements
  1333  
  1334  // stmt writes the given statement into the function body bitstream.
  1335  func (w *writer) stmt(stmt syntax.Stmt) {
  1336  	var stmts []syntax.Stmt
  1337  	if stmt != nil {
  1338  		stmts = []syntax.Stmt{stmt}
  1339  	}
  1340  	w.stmts(stmts)
  1341  }
  1342  
  1343  func (w *writer) stmts(stmts []syntax.Stmt) {
  1344  	dead := false
  1345  	w.Sync(pkgbits.SyncStmts)
  1346  	var lastLabel = -1
  1347  	for i, stmt := range stmts {
  1348  		if _, ok := stmt.(*syntax.LabeledStmt); ok {
  1349  			lastLabel = i
  1350  		}
  1351  	}
  1352  	for i, stmt := range stmts {
  1353  		if dead && i > lastLabel {
  1354  			// Any statements after a terminating and last label statement are safe to omit.
  1355  			// Otherwise, code after label statement may refer to dead stmts between terminating
  1356  			// and label statement, see issue #65593.
  1357  			if _, ok := stmt.(*syntax.LabeledStmt); !ok {
  1358  				continue
  1359  			}
  1360  		}
  1361  		w.stmt1(stmt)
  1362  		dead = w.p.terminates(stmt)
  1363  	}
  1364  	w.Code(stmtEnd)
  1365  	w.Sync(pkgbits.SyncStmtsEnd)
  1366  }
  1367  
  1368  func (w *writer) stmt1(stmt syntax.Stmt) {
  1369  	switch stmt := stmt.(type) {
  1370  	default:
  1371  		w.p.unexpected("statement", stmt)
  1372  
  1373  	case nil, *syntax.EmptyStmt:
  1374  		return
  1375  
  1376  	case *syntax.AssignStmt:
  1377  		switch {
  1378  		case stmt.Rhs == nil:
  1379  			w.Code(stmtIncDec)
  1380  			w.op(binOps[stmt.Op])
  1381  			w.expr(stmt.Lhs)
  1382  			w.pos(stmt)
  1383  
  1384  		case stmt.Op != 0 && stmt.Op != syntax.Def:
  1385  			w.Code(stmtAssignOp)
  1386  			w.op(binOps[stmt.Op])
  1387  			w.expr(stmt.Lhs)
  1388  			w.pos(stmt)
  1389  
  1390  			var typ types2.Type
  1391  			if stmt.Op != syntax.Shl && stmt.Op != syntax.Shr {
  1392  				typ = w.p.typeOf(stmt.Lhs)
  1393  			}
  1394  			w.implicitConvExpr(typ, stmt.Rhs)
  1395  
  1396  		default:
  1397  			w.assignStmt(stmt, stmt.Lhs, stmt.Rhs)
  1398  		}
  1399  
  1400  	case *syntax.BlockStmt:
  1401  		w.Code(stmtBlock)
  1402  		w.blockStmt(stmt)
  1403  
  1404  	case *syntax.BranchStmt:
  1405  		w.Code(stmtBranch)
  1406  		w.pos(stmt)
  1407  		var op ir.Op
  1408  		switch stmt.Tok {
  1409  		case syntax.Break:
  1410  			op = ir.OBREAK
  1411  		case syntax.Continue:
  1412  			op = ir.OCONTINUE
  1413  		case syntax.Fallthrough:
  1414  			op = ir.OFALL
  1415  		case syntax.Goto:
  1416  			op = ir.OGOTO
  1417  		}
  1418  		w.op(op)
  1419  		w.optLabel(stmt.Label)
  1420  
  1421  	case *syntax.CallStmt:
  1422  		w.Code(stmtCall)
  1423  		w.pos(stmt)
  1424  		var op ir.Op
  1425  		switch stmt.Tok {
  1426  		case syntax.Defer:
  1427  			op = ir.ODEFER
  1428  		case syntax.Go:
  1429  			op = ir.OGO
  1430  		}
  1431  		w.op(op)
  1432  		w.expr(stmt.Call)
  1433  		if stmt.Tok == syntax.Defer {
  1434  			w.optExpr(stmt.DeferAt)
  1435  		}
  1436  
  1437  	case *syntax.DeclStmt:
  1438  		for _, decl := range stmt.DeclList {
  1439  			w.declStmt(decl)
  1440  		}
  1441  
  1442  	case *syntax.ExprStmt:
  1443  		w.Code(stmtExpr)
  1444  		w.expr(stmt.X)
  1445  
  1446  	case *syntax.ForStmt:
  1447  		w.Code(stmtFor)
  1448  		w.forStmt(stmt)
  1449  
  1450  	case *syntax.IfStmt:
  1451  		w.Code(stmtIf)
  1452  		w.ifStmt(stmt)
  1453  
  1454  	case *syntax.LabeledStmt:
  1455  		w.Code(stmtLabel)
  1456  		w.pos(stmt)
  1457  		w.label(stmt.Label)
  1458  		w.stmt1(stmt.Stmt)
  1459  
  1460  	case *syntax.ReturnStmt:
  1461  		w.Code(stmtReturn)
  1462  		w.pos(stmt)
  1463  
  1464  		resultTypes := w.sig.Results()
  1465  		dstType := func(i int) types2.Type {
  1466  			return resultTypes.At(i).Type()
  1467  		}
  1468  		w.multiExpr(stmt, dstType, syntax.UnpackListExpr(stmt.Results))
  1469  
  1470  	case *syntax.SelectStmt:
  1471  		w.Code(stmtSelect)
  1472  		w.selectStmt(stmt)
  1473  
  1474  	case *syntax.SendStmt:
  1475  		chanType := types2.CoreType(w.p.typeOf(stmt.Chan)).(*types2.Chan)
  1476  
  1477  		w.Code(stmtSend)
  1478  		w.pos(stmt)
  1479  		w.expr(stmt.Chan)
  1480  		w.implicitConvExpr(chanType.Elem(), stmt.Value)
  1481  
  1482  	case *syntax.SwitchStmt:
  1483  		w.Code(stmtSwitch)
  1484  		w.switchStmt(stmt)
  1485  	}
  1486  }
  1487  
  1488  func (w *writer) assignList(expr syntax.Expr) {
  1489  	exprs := syntax.UnpackListExpr(expr)
  1490  	w.Len(len(exprs))
  1491  
  1492  	for _, expr := range exprs {
  1493  		w.assign(expr)
  1494  	}
  1495  }
  1496  
  1497  func (w *writer) assign(expr syntax.Expr) {
  1498  	expr = syntax.Unparen(expr)
  1499  
  1500  	if name, ok := expr.(*syntax.Name); ok {
  1501  		if name.Value == "_" {
  1502  			w.Code(assignBlank)
  1503  			return
  1504  		}
  1505  
  1506  		if obj, ok := w.p.info.Defs[name]; ok {
  1507  			obj := obj.(*types2.Var)
  1508  
  1509  			w.Code(assignDef)
  1510  			w.pos(obj)
  1511  			w.localIdent(obj)
  1512  			w.typ(obj.Type())
  1513  
  1514  			// TODO(mdempsky): Minimize locals index size by deferring
  1515  			// this until the variables actually come into scope.
  1516  			w.addLocal(obj)
  1517  			return
  1518  		}
  1519  	}
  1520  
  1521  	w.Code(assignExpr)
  1522  	w.expr(expr)
  1523  }
  1524  
  1525  func (w *writer) declStmt(decl syntax.Decl) {
  1526  	switch decl := decl.(type) {
  1527  	default:
  1528  		w.p.unexpected("declaration", decl)
  1529  
  1530  	case *syntax.ConstDecl, *syntax.TypeDecl:
  1531  
  1532  	case *syntax.VarDecl:
  1533  		w.assignStmt(decl, namesAsExpr(decl.NameList), decl.Values)
  1534  	}
  1535  }
  1536  
  1537  // assignStmt writes out an assignment for "lhs = rhs".
  1538  func (w *writer) assignStmt(pos poser, lhs0, rhs0 syntax.Expr) {
  1539  	lhs := syntax.UnpackListExpr(lhs0)
  1540  	rhs := syntax.UnpackListExpr(rhs0)
  1541  
  1542  	w.Code(stmtAssign)
  1543  	w.pos(pos)
  1544  
  1545  	// As if w.assignList(lhs0).
  1546  	w.Len(len(lhs))
  1547  	for _, expr := range lhs {
  1548  		w.assign(expr)
  1549  	}
  1550  
  1551  	dstType := func(i int) types2.Type {
  1552  		dst := lhs[i]
  1553  
  1554  		// Finding dstType is somewhat involved, because for VarDecl
  1555  		// statements, the Names are only added to the info.{Defs,Uses}
  1556  		// maps, not to info.Types.
  1557  		if name, ok := syntax.Unparen(dst).(*syntax.Name); ok {
  1558  			if name.Value == "_" {
  1559  				return nil // ok: no implicit conversion
  1560  			} else if def, ok := w.p.info.Defs[name].(*types2.Var); ok {
  1561  				return def.Type()
  1562  			} else if use, ok := w.p.info.Uses[name].(*types2.Var); ok {
  1563  				return use.Type()
  1564  			} else {
  1565  				w.p.fatalf(dst, "cannot find type of destination object: %v", dst)
  1566  			}
  1567  		}
  1568  
  1569  		return w.p.typeOf(dst)
  1570  	}
  1571  
  1572  	w.multiExpr(pos, dstType, rhs)
  1573  }
  1574  
  1575  func (w *writer) blockStmt(stmt *syntax.BlockStmt) {
  1576  	w.Sync(pkgbits.SyncBlockStmt)
  1577  	w.openScope(stmt.Pos())
  1578  	w.stmts(stmt.List)
  1579  	w.closeScope(stmt.Rbrace)
  1580  }
  1581  
  1582  func (w *writer) forStmt(stmt *syntax.ForStmt) {
  1583  	w.Sync(pkgbits.SyncForStmt)
  1584  	w.openScope(stmt.Pos())
  1585  
  1586  	if rang, ok := stmt.Init.(*syntax.RangeClause); w.Bool(ok) {
  1587  		w.pos(rang)
  1588  		w.assignList(rang.Lhs)
  1589  		w.expr(rang.X)
  1590  
  1591  		xtyp := w.p.typeOf(rang.X)
  1592  		if _, isMap := types2.CoreType(xtyp).(*types2.Map); isMap {
  1593  			w.rtype(xtyp)
  1594  		}
  1595  		{
  1596  			lhs := syntax.UnpackListExpr(rang.Lhs)
  1597  			assign := func(i int, src types2.Type) {
  1598  				if i >= len(lhs) {
  1599  					return
  1600  				}
  1601  				dst := syntax.Unparen(lhs[i])
  1602  				if name, ok := dst.(*syntax.Name); ok && name.Value == "_" {
  1603  					return
  1604  				}
  1605  
  1606  				var dstType types2.Type
  1607  				if rang.Def {
  1608  					// For `:=` assignments, the LHS names only appear in Defs,
  1609  					// not Types (as used by typeOf).
  1610  					dstType = w.p.info.Defs[dst.(*syntax.Name)].(*types2.Var).Type()
  1611  				} else {
  1612  					dstType = w.p.typeOf(dst)
  1613  				}
  1614  
  1615  				w.convRTTI(src, dstType)
  1616  			}
  1617  
  1618  			keyType, valueType := types2.RangeKeyVal(w.p.typeOf(rang.X))
  1619  			assign(0, keyType)
  1620  			assign(1, valueType)
  1621  		}
  1622  
  1623  	} else {
  1624  		if stmt.Cond != nil && w.p.staticBool(&stmt.Cond) < 0 { // always false
  1625  			stmt.Post = nil
  1626  			stmt.Body.List = nil
  1627  		}
  1628  
  1629  		w.pos(stmt)
  1630  		w.stmt(stmt.Init)
  1631  		w.optExpr(stmt.Cond)
  1632  		w.stmt(stmt.Post)
  1633  	}
  1634  
  1635  	w.blockStmt(stmt.Body)
  1636  	w.Bool(w.distinctVars(stmt))
  1637  	w.closeAnotherScope()
  1638  }
  1639  
  1640  func (w *writer) distinctVars(stmt *syntax.ForStmt) bool {
  1641  	lv := base.Debug.LoopVar
  1642  	fileVersion := w.p.info.FileVersions[stmt.Pos().FileBase()]
  1643  	is122 := fileVersion == "" || version.Compare(fileVersion, "go1.22") >= 0
  1644  
  1645  	// Turning off loopvar for 1.22 is only possible with loopvarhash=qn
  1646  	//
  1647  	// Debug.LoopVar values to be preserved for 1.21 compatibility are 1 and 2,
  1648  	// which are also set (=1) by GOEXPERIMENT=loopvar.  The knobs for turning on
  1649  	// the new, unshared, loopvar behavior apply to versions less than 1.21 because
  1650  	// (1) 1.21 also did that and (2) this is believed to be the likely use case;
  1651  	// anyone checking to see if it affects their code will just run the GOEXPERIMENT
  1652  	// but will not also update all their go.mod files to 1.21.
  1653  	//
  1654  	// -gcflags=-d=loopvar=3 enables logging for 1.22 but does not turn loopvar on for <= 1.21.
  1655  
  1656  	return is122 || lv > 0 && lv != 3
  1657  }
  1658  
  1659  func (w *writer) ifStmt(stmt *syntax.IfStmt) {
  1660  	cond := w.p.staticBool(&stmt.Cond)
  1661  
  1662  	w.Sync(pkgbits.SyncIfStmt)
  1663  	w.openScope(stmt.Pos())
  1664  	w.pos(stmt)
  1665  	w.stmt(stmt.Init)
  1666  	w.expr(stmt.Cond)
  1667  	w.Int(cond)
  1668  	if cond >= 0 {
  1669  		w.blockStmt(stmt.Then)
  1670  	} else {
  1671  		w.pos(stmt.Then.Rbrace)
  1672  	}
  1673  	if cond <= 0 {
  1674  		w.stmt(stmt.Else)
  1675  	}
  1676  	w.closeAnotherScope()
  1677  }
  1678  
  1679  func (w *writer) selectStmt(stmt *syntax.SelectStmt) {
  1680  	w.Sync(pkgbits.SyncSelectStmt)
  1681  
  1682  	w.pos(stmt)
  1683  	w.Len(len(stmt.Body))
  1684  	for i, clause := range stmt.Body {
  1685  		if i > 0 {
  1686  			w.closeScope(clause.Pos())
  1687  		}
  1688  		w.openScope(clause.Pos())
  1689  
  1690  		w.pos(clause)
  1691  		w.stmt(clause.Comm)
  1692  		w.stmts(clause.Body)
  1693  	}
  1694  	if len(stmt.Body) > 0 {
  1695  		w.closeScope(stmt.Rbrace)
  1696  	}
  1697  }
  1698  
  1699  func (w *writer) switchStmt(stmt *syntax.SwitchStmt) {
  1700  	w.Sync(pkgbits.SyncSwitchStmt)
  1701  
  1702  	w.openScope(stmt.Pos())
  1703  	w.pos(stmt)
  1704  	w.stmt(stmt.Init)
  1705  
  1706  	var iface, tagType types2.Type
  1707  	var tagTypeIsChan bool
  1708  	if guard, ok := stmt.Tag.(*syntax.TypeSwitchGuard); w.Bool(ok) {
  1709  		iface = w.p.typeOf(guard.X)
  1710  
  1711  		w.pos(guard)
  1712  		if tag := guard.Lhs; w.Bool(tag != nil) {
  1713  			w.pos(tag)
  1714  
  1715  			// Like w.localIdent, but we don't have a types2.Object.
  1716  			w.Sync(pkgbits.SyncLocalIdent)
  1717  			w.pkg(w.p.curpkg)
  1718  			w.String(tag.Value)
  1719  		}
  1720  		w.expr(guard.X)
  1721  	} else {
  1722  		tag := stmt.Tag
  1723  
  1724  		var tagValue constant.Value
  1725  		if tag != nil {
  1726  			tv := w.p.typeAndValue(tag)
  1727  			tagType = tv.Type
  1728  			tagValue = tv.Value
  1729  			_, tagTypeIsChan = tagType.Underlying().(*types2.Chan)
  1730  		} else {
  1731  			tagType = types2.Typ[types2.Bool]
  1732  			tagValue = constant.MakeBool(true)
  1733  		}
  1734  
  1735  		if tagValue != nil {
  1736  			// If the switch tag has a constant value, look for a case
  1737  			// clause that we always branch to.
  1738  			func() {
  1739  				var target *syntax.CaseClause
  1740  			Outer:
  1741  				for _, clause := range stmt.Body {
  1742  					if clause.Cases == nil {
  1743  						target = clause
  1744  					}
  1745  					for _, cas := range syntax.UnpackListExpr(clause.Cases) {
  1746  						tv := w.p.typeAndValue(cas)
  1747  						if tv.Value == nil {
  1748  							return // non-constant case; give up
  1749  						}
  1750  						if constant.Compare(tagValue, token.EQL, tv.Value) {
  1751  							target = clause
  1752  							break Outer
  1753  						}
  1754  					}
  1755  				}
  1756  				// We've found the target clause, if any.
  1757  
  1758  				if target != nil {
  1759  					if hasFallthrough(target.Body) {
  1760  						return // fallthrough is tricky; give up
  1761  					}
  1762  
  1763  					// Rewrite as single "default" case.
  1764  					target.Cases = nil
  1765  					stmt.Body = []*syntax.CaseClause{target}
  1766  				} else {
  1767  					stmt.Body = nil
  1768  				}
  1769  
  1770  				// Clear switch tag (i.e., replace with implicit "true").
  1771  				tag = nil
  1772  				stmt.Tag = nil
  1773  				tagType = types2.Typ[types2.Bool]
  1774  			}()
  1775  		}
  1776  
  1777  		// Walk is going to emit comparisons between the tag value and
  1778  		// each case expression, and we want these comparisons to always
  1779  		// have the same type. If there are any case values that can't be
  1780  		// converted to the tag value's type, then convert everything to
  1781  		// `any` instead.
  1782  		//
  1783  		// Except that we need to keep comparisons of channel values from
  1784  		// being wrapped in any(). See issue #67190.
  1785  
  1786  		if !tagTypeIsChan {
  1787  		Outer:
  1788  			for _, clause := range stmt.Body {
  1789  				for _, cas := range syntax.UnpackListExpr(clause.Cases) {
  1790  					if casType := w.p.typeOf(cas); !types2.AssignableTo(casType, tagType) && (types2.IsInterface(casType) || types2.IsInterface(tagType)) {
  1791  						tagType = types2.NewInterfaceType(nil, nil)
  1792  						break Outer
  1793  					}
  1794  				}
  1795  			}
  1796  		}
  1797  
  1798  		if w.Bool(tag != nil) {
  1799  			w.implicitConvExpr(tagType, tag)
  1800  		}
  1801  	}
  1802  
  1803  	w.Len(len(stmt.Body))
  1804  	for i, clause := range stmt.Body {
  1805  		if i > 0 {
  1806  			w.closeScope(clause.Pos())
  1807  		}
  1808  		w.openScope(clause.Pos())
  1809  
  1810  		w.pos(clause)
  1811  
  1812  		cases := syntax.UnpackListExpr(clause.Cases)
  1813  		if iface != nil {
  1814  			w.Len(len(cases))
  1815  			for _, cas := range cases {
  1816  				if w.Bool(isNil(w.p, cas)) {
  1817  					continue
  1818  				}
  1819  				w.exprType(iface, cas)
  1820  			}
  1821  		} else {
  1822  			// As if w.exprList(clause.Cases),
  1823  			// but with implicit conversions to tagType.
  1824  
  1825  			w.Sync(pkgbits.SyncExprList)
  1826  			w.Sync(pkgbits.SyncExprs)
  1827  			w.Len(len(cases))
  1828  			for _, cas := range cases {
  1829  				typ := tagType
  1830  				if tagTypeIsChan {
  1831  					typ = nil
  1832  				}
  1833  				w.implicitConvExpr(typ, cas)
  1834  			}
  1835  		}
  1836  
  1837  		if obj, ok := w.p.info.Implicits[clause]; ok {
  1838  			// TODO(mdempsky): These pos details are quirkish, but also
  1839  			// necessary so the variable's position is correct for DWARF
  1840  			// scope assignment later. It would probably be better for us to
  1841  			// instead just set the variable's DWARF scoping info earlier so
  1842  			// we can give it the correct position information.
  1843  			pos := clause.Pos()
  1844  			if typs := syntax.UnpackListExpr(clause.Cases); len(typs) != 0 {
  1845  				pos = typeExprEndPos(typs[len(typs)-1])
  1846  			}
  1847  			w.pos(pos)
  1848  
  1849  			obj := obj.(*types2.Var)
  1850  			w.typ(obj.Type())
  1851  			w.addLocal(obj)
  1852  		}
  1853  
  1854  		w.stmts(clause.Body)
  1855  	}
  1856  	if len(stmt.Body) > 0 {
  1857  		w.closeScope(stmt.Rbrace)
  1858  	}
  1859  
  1860  	w.closeScope(stmt.Rbrace)
  1861  }
  1862  
  1863  func (w *writer) label(label *syntax.Name) {
  1864  	w.Sync(pkgbits.SyncLabel)
  1865  
  1866  	// TODO(mdempsky): Replace label strings with dense indices.
  1867  	w.String(label.Value)
  1868  }
  1869  
  1870  func (w *writer) optLabel(label *syntax.Name) {
  1871  	w.Sync(pkgbits.SyncOptLabel)
  1872  	if w.Bool(label != nil) {
  1873  		w.label(label)
  1874  	}
  1875  }
  1876  
  1877  // @@@ Expressions
  1878  
  1879  // expr writes the given expression into the function body bitstream.
  1880  func (w *writer) expr(expr syntax.Expr) {
  1881  	base.Assertf(expr != nil, "missing expression")
  1882  
  1883  	expr = syntax.Unparen(expr) // skip parens; unneeded after typecheck
  1884  
  1885  	obj, inst := lookupObj(w.p, expr)
  1886  	targs := asTypeSlice(inst.TypeArgs)
  1887  
  1888  	if tv, ok := w.p.maybeTypeAndValue(expr); ok {
  1889  		if tv.IsRuntimeHelper() {
  1890  			if pkg := obj.Pkg(); pkg != nil && pkg.Name() == "runtime" {
  1891  				objName := obj.Name()
  1892  				w.Code(exprRuntimeBuiltin)
  1893  				w.String(objName)
  1894  				return
  1895  			}
  1896  		}
  1897  
  1898  		if tv.IsType() {
  1899  			w.p.fatalf(expr, "unexpected type expression %v", syntax.String(expr))
  1900  		}
  1901  
  1902  		if tv.Value != nil {
  1903  			w.Code(exprConst)
  1904  			w.pos(expr)
  1905  			typ := idealType(tv)
  1906  			assert(typ != nil)
  1907  			w.typ(typ)
  1908  			w.Value(tv.Value)
  1909  			return
  1910  		}
  1911  
  1912  		if _, isNil := obj.(*types2.Nil); isNil {
  1913  			w.Code(exprZero)
  1914  			w.pos(expr)
  1915  			w.typ(tv.Type)
  1916  			return
  1917  		}
  1918  
  1919  		// With shape types (and particular pointer shaping), we may have
  1920  		// an expression of type "go.shape.*uint8", but need to reshape it
  1921  		// to another shape-identical type to allow use in field
  1922  		// selection, indexing, etc.
  1923  		if typ := tv.Type; !tv.IsBuiltin() && !isTuple(typ) && !isUntyped(typ) {
  1924  			w.Code(exprReshape)
  1925  			w.typ(typ)
  1926  			// fallthrough
  1927  		}
  1928  	}
  1929  
  1930  	if obj != nil {
  1931  		if len(targs) != 0 {
  1932  			obj := obj.(*types2.Func)
  1933  
  1934  			w.Code(exprFuncInst)
  1935  			w.pos(expr)
  1936  			w.funcInst(obj, targs)
  1937  			return
  1938  		}
  1939  
  1940  		if isGlobal(obj) {
  1941  			w.Code(exprGlobal)
  1942  			w.obj(obj, nil)
  1943  			return
  1944  		}
  1945  
  1946  		obj := obj.(*types2.Var)
  1947  		assert(!obj.IsField())
  1948  
  1949  		w.Code(exprLocal)
  1950  		w.useLocal(expr.Pos(), obj)
  1951  		return
  1952  	}
  1953  
  1954  	switch expr := expr.(type) {
  1955  	default:
  1956  		w.p.unexpected("expression", expr)
  1957  
  1958  	case *syntax.CompositeLit:
  1959  		w.Code(exprCompLit)
  1960  		w.compLit(expr)
  1961  
  1962  	case *syntax.FuncLit:
  1963  		w.Code(exprFuncLit)
  1964  		w.funcLit(expr)
  1965  
  1966  	case *syntax.SelectorExpr:
  1967  		sel, ok := w.p.info.Selections[expr]
  1968  		assert(ok)
  1969  
  1970  		switch sel.Kind() {
  1971  		default:
  1972  			w.p.fatalf(expr, "unexpected selection kind: %v", sel.Kind())
  1973  
  1974  		case types2.FieldVal:
  1975  			w.Code(exprFieldVal)
  1976  			w.expr(expr.X)
  1977  			w.pos(expr)
  1978  			w.selector(sel.Obj())
  1979  
  1980  		case types2.MethodVal:
  1981  			w.methVal(expr, sel)
  1982  
  1983  		case types2.MethodExpr:
  1984  			w.methExpr(expr, sel)
  1985  		}
  1986  
  1987  	case *syntax.IndexExpr:
  1988  		// might be explicit instantiation of a generic method
  1989  		if selector, ok := expr.X.(*syntax.SelectorExpr); ok {
  1990  			if sel, ok := w.p.info.Selections[selector]; ok {
  1991  				switch sel.Kind() {
  1992  				default:
  1993  					w.p.fatalf(selector, "unexpected selection kind: %v", sel.Kind())
  1994  				case types2.FieldVal:
  1995  					// not a method
  1996  				case types2.MethodVal:
  1997  					w.methVal(selector, sel)
  1998  					return
  1999  				case types2.MethodExpr:
  2000  					w.methExpr(selector, sel)
  2001  					return
  2002  				}
  2003  			}
  2004  		}
  2005  		_ = w.p.typeOf(expr.Index) // ensure this is an index expression, not an instantiation
  2006  
  2007  		xtyp := w.p.typeOf(expr.X)
  2008  
  2009  		var keyType types2.Type
  2010  		if mapType, ok := types2.CoreType(xtyp).(*types2.Map); ok {
  2011  			keyType = mapType.Key()
  2012  		}
  2013  
  2014  		w.Code(exprIndex)
  2015  		w.expr(expr.X)
  2016  		w.pos(expr)
  2017  		w.implicitConvExpr(keyType, expr.Index)
  2018  		if keyType != nil {
  2019  			w.rtype(xtyp)
  2020  		}
  2021  
  2022  	case *syntax.SliceExpr:
  2023  		w.Code(exprSlice)
  2024  		w.expr(expr.X)
  2025  		w.pos(expr)
  2026  		for _, n := range &expr.Index {
  2027  			w.optExpr(n)
  2028  		}
  2029  
  2030  	case *syntax.AssertExpr:
  2031  		iface := w.p.typeOf(expr.X)
  2032  
  2033  		w.Code(exprAssert)
  2034  		w.expr(expr.X)
  2035  		w.pos(expr)
  2036  		w.exprType(iface, expr.Type)
  2037  		w.rtype(iface)
  2038  
  2039  	case *syntax.Operation:
  2040  		if expr.Y == nil {
  2041  			w.Code(exprUnaryOp)
  2042  			w.op(unOps[expr.Op])
  2043  			w.pos(expr)
  2044  			w.expr(expr.X)
  2045  			break
  2046  		}
  2047  
  2048  		var commonType types2.Type
  2049  		switch expr.Op {
  2050  		case syntax.Shl, syntax.Shr:
  2051  			// ok: operands are allowed to have different types
  2052  		default:
  2053  			xtyp := w.p.typeOf(expr.X)
  2054  			ytyp := w.p.typeOf(expr.Y)
  2055  			switch {
  2056  			case types2.AssignableTo(xtyp, ytyp):
  2057  				commonType = ytyp
  2058  			case types2.AssignableTo(ytyp, xtyp):
  2059  				commonType = xtyp
  2060  			default:
  2061  				w.p.fatalf(expr, "failed to find common type between %v and %v", xtyp, ytyp)
  2062  			}
  2063  		}
  2064  
  2065  		w.Code(exprBinaryOp)
  2066  		w.op(binOps[expr.Op])
  2067  		w.implicitConvExpr(commonType, expr.X)
  2068  		w.pos(expr)
  2069  		w.implicitConvExpr(commonType, expr.Y)
  2070  
  2071  	case *syntax.CallExpr:
  2072  		tv := w.p.typeAndValue(expr.Fun)
  2073  		if tv.IsType() {
  2074  			assert(len(expr.ArgList) == 1)
  2075  			assert(!expr.HasDots)
  2076  			w.convertExpr(tv.Type, expr.ArgList[0], false)
  2077  			break
  2078  		}
  2079  
  2080  		var rtype types2.Type
  2081  		if tv.IsBuiltin() {
  2082  			switch obj, _ := lookupObj(w.p, syntax.Unparen(expr.Fun)); obj.Name() {
  2083  			case "make":
  2084  				assert(len(expr.ArgList) >= 1)
  2085  				assert(!expr.HasDots)
  2086  
  2087  				w.Code(exprMake)
  2088  				w.pos(expr)
  2089  				w.exprType(nil, expr.ArgList[0])
  2090  				w.exprs(expr.ArgList[1:])
  2091  
  2092  				typ := w.p.typeOf(expr)
  2093  				switch coreType := types2.CoreType(typ).(type) {
  2094  				default:
  2095  					w.p.fatalf(expr, "unexpected core type: %v", coreType)
  2096  				case *types2.Chan:
  2097  					w.rtype(typ)
  2098  				case *types2.Map:
  2099  					w.rtype(typ)
  2100  				case *types2.Slice:
  2101  					w.rtype(sliceElem(typ))
  2102  				}
  2103  
  2104  				return
  2105  
  2106  			case "new":
  2107  				assert(len(expr.ArgList) == 1)
  2108  				assert(!expr.HasDots)
  2109  				arg := expr.ArgList[0]
  2110  
  2111  				w.Code(exprNew)
  2112  				w.pos(expr)
  2113  				tv := w.p.typeAndValue(arg)
  2114  				if w.Bool(!tv.IsType()) {
  2115  					w.expr(arg) // new(expr), go1.26
  2116  				} else {
  2117  					w.exprType(nil, arg) // new(T)
  2118  				}
  2119  				return
  2120  
  2121  			case "Sizeof":
  2122  				assert(len(expr.ArgList) == 1)
  2123  				assert(!expr.HasDots)
  2124  
  2125  				w.Code(exprSizeof)
  2126  				w.pos(expr)
  2127  				w.typ(w.p.typeOf(expr.ArgList[0]))
  2128  				return
  2129  
  2130  			case "Alignof":
  2131  				assert(len(expr.ArgList) == 1)
  2132  				assert(!expr.HasDots)
  2133  
  2134  				w.Code(exprAlignof)
  2135  				w.pos(expr)
  2136  				w.typ(w.p.typeOf(expr.ArgList[0]))
  2137  				return
  2138  
  2139  			case "Offsetof":
  2140  				assert(len(expr.ArgList) == 1)
  2141  				assert(!expr.HasDots)
  2142  				selector := syntax.Unparen(expr.ArgList[0]).(*syntax.SelectorExpr)
  2143  				index := w.p.info.Selections[selector].Index()
  2144  
  2145  				w.Code(exprOffsetof)
  2146  				w.pos(expr)
  2147  				w.typ(deref2(w.p.typeOf(selector.X)))
  2148  				w.Len(len(index) - 1)
  2149  				for _, idx := range index {
  2150  					w.Len(idx)
  2151  				}
  2152  				return
  2153  
  2154  			case "append":
  2155  				rtype = sliceElem(w.p.typeOf(expr))
  2156  			case "copy":
  2157  				typ := w.p.typeOf(expr.ArgList[0])
  2158  				if tuple, ok := typ.(*types2.Tuple); ok { // "copy(g())"
  2159  					typ = tuple.At(0).Type()
  2160  				}
  2161  				rtype = sliceElem(typ)
  2162  			case "delete":
  2163  				typ := w.p.typeOf(expr.ArgList[0])
  2164  				if tuple, ok := typ.(*types2.Tuple); ok { // "delete(g())"
  2165  					typ = tuple.At(0).Type()
  2166  				}
  2167  				rtype = typ
  2168  			case "Slice":
  2169  				rtype = sliceElem(w.p.typeOf(expr))
  2170  			}
  2171  		}
  2172  
  2173  		writeFunExpr := func() {
  2174  			fun := syntax.Unparen(expr.Fun)
  2175  
  2176  			expr := fun
  2177  			if idx, ok := expr.(*syntax.IndexExpr); ok {
  2178  				expr = idx.X
  2179  			}
  2180  			if selector, ok := expr.(*syntax.SelectorExpr); ok {
  2181  				if sel, ok := w.p.info.Selections[selector]; ok && sel.Kind() == types2.MethodVal {
  2182  					w.Bool(true) // method call
  2183  					typ := w.recvExpr(selector, sel)
  2184  					w.methodExpr(selector, typ, sel)
  2185  					return
  2186  				}
  2187  			}
  2188  
  2189  			w.Bool(false) // not a method call (i.e., normal function call)
  2190  
  2191  			if obj, inst := lookupObj(w.p, fun); w.Bool(obj != nil && inst.TypeArgs.Len() != 0) {
  2192  				obj := obj.(*types2.Func)
  2193  
  2194  				w.pos(fun)
  2195  				w.funcInst(obj, asTypeSlice(inst.TypeArgs))
  2196  				return
  2197  			}
  2198  
  2199  			w.expr(fun)
  2200  		}
  2201  
  2202  		sigType := types2.CoreType(tv.Type).(*types2.Signature)
  2203  		paramTypes := sigType.Params()
  2204  
  2205  		w.Code(exprCall)
  2206  		writeFunExpr()
  2207  		w.pos(expr)
  2208  
  2209  		paramType := func(i int) types2.Type {
  2210  			if sigType.Variadic() && !expr.HasDots && i >= paramTypes.Len()-1 {
  2211  				return paramTypes.At(paramTypes.Len() - 1).Type().(*types2.Slice).Elem()
  2212  			}
  2213  			return paramTypes.At(i).Type()
  2214  		}
  2215  
  2216  		w.multiExpr(expr, paramType, expr.ArgList)
  2217  		w.Bool(expr.HasDots)
  2218  		if rtype != nil {
  2219  			w.rtype(rtype)
  2220  		}
  2221  	}
  2222  }
  2223  
  2224  func sliceElem(typ types2.Type) types2.Type {
  2225  	return types2.CoreType(typ).(*types2.Slice).Elem()
  2226  }
  2227  
  2228  func (w *writer) optExpr(expr syntax.Expr) {
  2229  	if w.Bool(expr != nil) {
  2230  		w.expr(expr)
  2231  	}
  2232  }
  2233  
  2234  func (w *writer) methVal(expr *syntax.SelectorExpr, sel *types2.Selection) {
  2235  	w.Code(exprMethodVal)
  2236  	typ := w.recvExpr(expr, sel)
  2237  	w.pos(expr)
  2238  	w.methodExpr(expr, typ, sel)
  2239  }
  2240  
  2241  func (w *writer) methExpr(expr *syntax.SelectorExpr, sel *types2.Selection) {
  2242  	w.Code(exprMethodExpr)
  2243  
  2244  	tv := w.p.typeAndValue(expr.X)
  2245  	assert(tv.IsType())
  2246  
  2247  	index := sel.Index()
  2248  	implicits := index[:len(index)-1]
  2249  
  2250  	typ := tv.Type
  2251  	w.typ(typ)
  2252  
  2253  	w.Len(len(implicits))
  2254  	for _, ix := range implicits {
  2255  		w.Len(ix)
  2256  		typ = deref2(typ).Underlying().(*types2.Struct).Field(ix).Type()
  2257  	}
  2258  
  2259  	recv := sel.Obj().(*types2.Func).Type().(*types2.Signature).Recv().Type()
  2260  	if w.Bool(isPtrTo(typ, recv)) { // need deref
  2261  		typ = recv
  2262  	} else if w.Bool(isPtrTo(recv, typ)) { // need addr
  2263  		typ = recv
  2264  	}
  2265  
  2266  	w.pos(expr)
  2267  	w.methodExpr(expr, typ, sel)
  2268  }
  2269  
  2270  // recvExpr writes out expr.X, but handles any implicit addressing,
  2271  // dereferencing, and field selections appropriate for the method
  2272  // selection.
  2273  func (w *writer) recvExpr(expr *syntax.SelectorExpr, sel *types2.Selection) types2.Type {
  2274  	index := sel.Index()
  2275  	implicits := index[:len(index)-1]
  2276  
  2277  	w.Code(exprRecv)
  2278  	w.expr(expr.X)
  2279  	w.pos(expr)
  2280  	w.Len(len(implicits))
  2281  
  2282  	typ := w.p.typeOf(expr.X)
  2283  	for _, ix := range implicits {
  2284  		typ = deref2(typ).Underlying().(*types2.Struct).Field(ix).Type()
  2285  		w.Len(ix)
  2286  	}
  2287  
  2288  	recv := sel.Obj().(*types2.Func).Type().(*types2.Signature).Recv().Type()
  2289  	if w.Bool(isPtrTo(typ, recv)) { // needs deref
  2290  		typ = recv
  2291  	} else if w.Bool(isPtrTo(recv, typ)) { // needs addr
  2292  		typ = recv
  2293  	}
  2294  
  2295  	return typ
  2296  }
  2297  
  2298  // funcInst writes a reference to an instantiated function.
  2299  func (w *writer) funcInst(obj *types2.Func, targs []types2.Type) {
  2300  	info := w.p.objInstIdx(obj, targs, w.dict)
  2301  
  2302  	// Type arguments list contains derived types; we can emit a static
  2303  	// call to the shaped function, but need to dynamically compute the
  2304  	// runtime dictionary pointer.
  2305  	if w.Bool(info.anyDerived()) {
  2306  		w.Len(w.dict.subdictIdx(info))
  2307  		return
  2308  	}
  2309  
  2310  	// Type arguments list is statically known; we can emit a static
  2311  	// call with a statically reference to the respective runtime
  2312  	// dictionary.
  2313  	w.objInfo(info)
  2314  }
  2315  
  2316  // methodExpr writes out a reference to the method selected by
  2317  // expr. sel should be the corresponding types2.Selection, and recv
  2318  // the type produced after any implicit addressing, dereferencing, and
  2319  // field selection. (Note: recv might differ from sel.Obj()'s receiver
  2320  // parameter in the case of interface types, and is needed for
  2321  // handling type parameter methods.)
  2322  func (w *writer) methodExpr(expr *syntax.SelectorExpr, recv types2.Type, sel *types2.Selection) {
  2323  	fun := sel.Obj().(*types2.Func)
  2324  	sig := fun.Type().(*types2.Signature)
  2325  
  2326  	w.typ(recv)
  2327  
  2328  	// only pass the signature if it's not a generic method
  2329  	if isGenericMethod(sig) {
  2330  		assert(w.Version().Has(pkgbits.GenericMethods))
  2331  		w.Bool(true)
  2332  	} else {
  2333  		if w.Version().Has(pkgbits.GenericMethods) {
  2334  			w.Bool(false)
  2335  		}
  2336  		w.typ(sig)
  2337  	}
  2338  
  2339  	w.pos(expr)
  2340  	w.selector(fun)
  2341  
  2342  	// Method on a type parameter. These require an indirect call
  2343  	// through the current function's runtime dictionary.
  2344  	if typeParam, ok := types2.Unalias(recv).(*types2.TypeParam); w.Bool(ok) {
  2345  		typeParamIdx := w.dict.typeParamIndex(typeParam)
  2346  		methodInfo := w.p.selectorIdx(fun)
  2347  
  2348  		w.Len(w.dict.typeParamMethodExprIdx(typeParamIdx, methodInfo))
  2349  		return
  2350  	}
  2351  
  2352  	if isInterface(recv) != isInterface(sig.Recv().Type()) {
  2353  		w.p.fatalf(expr, "isInterface inconsistency: %v and %v", recv, sig.Recv().Type())
  2354  	}
  2355  
  2356  	if isConcreteMethod(sig) {
  2357  		tname, tExplicits := splitNamed(types2.Unalias(deref2(recv)).(*types2.Named))
  2358  		var info objInfo
  2359  		if isGenericMethod(sig) {
  2360  			// For generic methods, the shaped object is the method itself.
  2361  			mExplicits := asTypeSlice(w.p.info.Instances[expr.Sel].TypeArgs)
  2362  			info = w.p.objInstIdx(fun.Origin(), slices.Concat(tExplicits, mExplicits), w.dict)
  2363  		} else {
  2364  			// For non-generic concrete methods on generic types, the shaped object
  2365  			// is the type. The method must be looked up on the type by name.
  2366  			info = w.p.objInstIdx(tname, tExplicits, w.dict)
  2367  		}
  2368  		// We don't know all of the type arguments statically. These can be
  2369  		// handled by a static call to the shaped method, but require
  2370  		// dynamically looking up the appropriate dictionary argument
  2371  		// in the current function's runtime dictionary.
  2372  		if info.anyDerived() {
  2373  			w.Bool(true) // dynamic subdictionary
  2374  			w.Len(w.dict.subdictIdx(info))
  2375  			return
  2376  		}
  2377  		// We know all of the type arguments statically. These can be handled
  2378  		// by a static call to the shaped method, and with a static reference
  2379  		// to either the receiver type's or method's dictionary (see above).
  2380  		if len(info.explicits) > 0 {
  2381  			w.Bool(false) // no dynamic subdictionary
  2382  			w.Bool(true)  // static dictionary
  2383  			w.objInfo(info)
  2384  			return
  2385  		}
  2386  		// no type arguments
  2387  	}
  2388  
  2389  	w.Bool(false) // no dynamic subdictionary
  2390  	w.Bool(false) // no static dictionary
  2391  }
  2392  
  2393  // multiExpr writes a sequence of expressions, where the i'th value is
  2394  // implicitly converted to dstType(i). It also handles when exprs is a
  2395  // single, multi-valued expression (e.g., the multi-valued argument in
  2396  // an f(g()) call, or the RHS operand in a comma-ok assignment).
  2397  func (w *writer) multiExpr(pos poser, dstType func(int) types2.Type, exprs []syntax.Expr) {
  2398  	w.Sync(pkgbits.SyncMultiExpr)
  2399  
  2400  	if len(exprs) == 1 {
  2401  		expr := exprs[0]
  2402  		if tuple, ok := w.p.typeOf(expr).(*types2.Tuple); ok {
  2403  			assert(tuple.Len() > 1)
  2404  			w.Bool(true) // N:1 assignment
  2405  			w.pos(pos)
  2406  			w.expr(expr)
  2407  
  2408  			w.Len(tuple.Len())
  2409  			for i := 0; i < tuple.Len(); i++ {
  2410  				src := tuple.At(i).Type()
  2411  				// TODO(mdempsky): Investigate not writing src here. I think
  2412  				// the reader should be able to infer it from expr anyway.
  2413  				w.typ(src)
  2414  				if dst := dstType(i); w.Bool(dst != nil && !types2.Identical(src, dst)) {
  2415  					if src == nil || dst == nil {
  2416  						w.p.fatalf(pos, "src is %v, dst is %v", src, dst)
  2417  					}
  2418  					if !types2.AssignableTo(src, dst) {
  2419  						w.p.fatalf(pos, "%v is not assignable to %v", src, dst)
  2420  					}
  2421  					w.typ(dst)
  2422  					w.convRTTI(src, dst)
  2423  				}
  2424  			}
  2425  			return
  2426  		}
  2427  	}
  2428  
  2429  	w.Bool(false) // N:N assignment
  2430  	w.Len(len(exprs))
  2431  	for i, expr := range exprs {
  2432  		w.implicitConvExpr(dstType(i), expr)
  2433  	}
  2434  }
  2435  
  2436  // implicitConvExpr is like expr, but if dst is non-nil and different
  2437  // from expr's type, then an implicit conversion operation is inserted
  2438  // at expr's position.
  2439  func (w *writer) implicitConvExpr(dst types2.Type, expr syntax.Expr) {
  2440  	w.convertExpr(dst, expr, true)
  2441  }
  2442  
  2443  func (w *writer) convertExpr(dst types2.Type, expr syntax.Expr, implicit bool) {
  2444  	src := w.p.typeOf(expr)
  2445  
  2446  	// Omit implicit no-op conversions.
  2447  	identical := dst == nil || types2.Identical(src, dst)
  2448  	if implicit && identical {
  2449  		w.expr(expr)
  2450  		return
  2451  	}
  2452  
  2453  	if implicit && !types2.AssignableTo(src, dst) {
  2454  		w.p.fatalf(expr, "%v is not assignable to %v", src, dst)
  2455  	}
  2456  
  2457  	w.Code(exprConvert)
  2458  	w.Bool(implicit)
  2459  	w.typ(dst)
  2460  	w.pos(expr)
  2461  	w.convRTTI(src, dst)
  2462  	w.Bool(isTypeParam(dst))
  2463  	w.Bool(identical)
  2464  	w.expr(expr)
  2465  }
  2466  
  2467  func (w *writer) compLit(lit *syntax.CompositeLit) {
  2468  	typ := w.p.typeOf(lit)
  2469  
  2470  	w.Sync(pkgbits.SyncCompLit)
  2471  	w.pos(lit)
  2472  	w.typ(typ)
  2473  
  2474  	if ptr, ok := types2.CoreType(typ).(*types2.Pointer); ok {
  2475  		typ = ptr.Elem()
  2476  	}
  2477  
  2478  	if w.Version().Has(pkgbits.CompactCompLiterals) {
  2479  		switch typ0 := typ; typ := types2.CoreType(typ).(type) {
  2480  		default:
  2481  			w.p.fatalf(lit, "unexpected composite literal type: %v", typ)
  2482  		case *types2.Array:
  2483  			w.arrayElems(typ.Elem(), lit.ElemList)
  2484  		case *types2.Map:
  2485  			w.rtype(typ0)
  2486  			w.mapElems(typ.Key(), typ.Elem(), lit.ElemList)
  2487  		case *types2.Slice:
  2488  			w.arrayElems(typ.Elem(), lit.ElemList)
  2489  		case *types2.Struct:
  2490  			w.structElems(typ, lit.NKeys == 0, lit.ElemList)
  2491  		}
  2492  		return
  2493  	}
  2494  
  2495  	// old format
  2496  	var keyType, elemType types2.Type
  2497  	var structType *types2.Struct
  2498  	switch typ0 := typ; typ := types2.CoreType(typ).(type) {
  2499  	default:
  2500  		w.p.fatalf(lit, "unexpected composite literal type: %v", typ)
  2501  	case *types2.Array:
  2502  		elemType = typ.Elem()
  2503  	case *types2.Map:
  2504  		w.rtype(typ0)
  2505  		keyType, elemType = typ.Key(), typ.Elem()
  2506  	case *types2.Slice:
  2507  		elemType = typ.Elem()
  2508  	case *types2.Struct:
  2509  		structType = typ
  2510  	}
  2511  
  2512  	w.Len(len(lit.ElemList))
  2513  	for i, elem := range lit.ElemList {
  2514  		elemType := elemType
  2515  		if structType != nil {
  2516  			if kv, ok := elem.(*syntax.KeyValueExpr); ok {
  2517  				// use position of expr.Key rather than of elem (which has position of ':')
  2518  				w.pos(kv.Key)
  2519  				i = fieldIndex(w.p.info, structType, kv.Key.(*syntax.Name))
  2520  				elem = kv.Value
  2521  			} else {
  2522  				w.pos(elem)
  2523  			}
  2524  			elemType = structType.Field(i).Type()
  2525  			w.Len(i)
  2526  		} else {
  2527  			if kv, ok := elem.(*syntax.KeyValueExpr); w.Bool(ok) {
  2528  				// use position of expr.Key rather than of elem (which has position of ':')
  2529  				w.pos(kv.Key)
  2530  				w.implicitConvExpr(keyType, kv.Key)
  2531  				elem = kv.Value
  2532  			}
  2533  		}
  2534  		w.implicitConvExpr(elemType, elem)
  2535  	}
  2536  }
  2537  
  2538  func (w *writer) arrayElems(elemType types2.Type, elems []syntax.Expr) {
  2539  	valuesOnly := true
  2540  	for _, elem := range elems {
  2541  		if _, ok := elem.(*syntax.KeyValueExpr); ok {
  2542  			valuesOnly = false
  2543  			break
  2544  		}
  2545  	}
  2546  
  2547  	if valuesOnly {
  2548  		w.Int(len(elems))
  2549  		for _, elem := range elems {
  2550  			w.implicitConvExpr(elemType, elem)
  2551  		}
  2552  		return
  2553  	}
  2554  	// some elements may have a key
  2555  	w.Int(-len(elems))
  2556  	for _, elem := range elems {
  2557  		if kv, ok := elem.(*syntax.KeyValueExpr); w.Bool(ok) {
  2558  			w.pos(kv.Key) // use position of Key rather than of elem (which has position of ':')
  2559  			w.implicitConvExpr(nil, kv.Key)
  2560  			elem = kv.Value
  2561  		}
  2562  		w.implicitConvExpr(elemType, elem)
  2563  	}
  2564  }
  2565  
  2566  func (w *writer) mapElems(keyType, valueType types2.Type, elems []syntax.Expr) {
  2567  	// all elements have a key
  2568  	w.Int(-len(elems))
  2569  	for _, elem := range elems {
  2570  		kv := elem.(*syntax.KeyValueExpr)
  2571  		w.pos(kv.Key) // use position of Key rather than of elem (which has position of ':')
  2572  		w.implicitConvExpr(keyType, kv.Key)
  2573  		w.implicitConvExpr(valueType, kv.Value)
  2574  	}
  2575  }
  2576  
  2577  func (w *writer) structElems(typ *types2.Struct, valuesOnly bool, elems []syntax.Expr) {
  2578  	n := len(elems)
  2579  	if valuesOnly {
  2580  		// no element has a key
  2581  		w.Int(n)
  2582  		for i, elem := range elems {
  2583  			w.pos(elem)
  2584  			w.implicitConvExpr(typ.Field(i).Type(), elem)
  2585  		}
  2586  		return
  2587  	}
  2588  	// all elements have a key
  2589  	w.Int(-n)
  2590  	for _, elem := range elems {
  2591  		kv := elem.(*syntax.KeyValueExpr)
  2592  		w.pos(kv.Key) // use position of Key rather than of elem (which has position of ':')
  2593  		// TODO(gri): rather than doing this lookup again, perhaps the index should be recorded by types2
  2594  		fld, index, _ := types2.LookupFieldOrMethod(typ, false, w.p.curpkg, kv.Key.(*syntax.Name).Value)
  2595  		if n := len(index); n > 1 {
  2596  			// embedded field
  2597  			w.Int(-n)
  2598  			for _, i := range index {
  2599  				w.Int(i)
  2600  			}
  2601  		} else { // n == 1
  2602  			w.Int(index[0])
  2603  		}
  2604  		w.implicitConvExpr(fld.Type(), kv.Value)
  2605  	}
  2606  }
  2607  
  2608  func (w *writer) funcLit(expr *syntax.FuncLit) {
  2609  	sig := w.p.typeOf(expr).(*types2.Signature)
  2610  
  2611  	body, closureVars := w.p.bodyIdx(sig, expr.Body, w.dict)
  2612  
  2613  	w.Sync(pkgbits.SyncFuncLit)
  2614  	w.pos(expr)
  2615  	w.signature(sig)
  2616  	w.Bool(w.p.rangeFuncBodyClosures[expr])
  2617  
  2618  	w.Len(len(closureVars))
  2619  	for _, cv := range closureVars {
  2620  		w.pos(cv.pos)
  2621  		w.useLocal(cv.pos, cv.var_)
  2622  	}
  2623  
  2624  	w.Reloc(pkgbits.SectionBody, body)
  2625  }
  2626  
  2627  type posVar struct {
  2628  	pos  syntax.Pos
  2629  	var_ *types2.Var
  2630  }
  2631  
  2632  func (p posVar) String() string {
  2633  	return p.pos.String() + ":" + p.var_.String()
  2634  }
  2635  
  2636  func (w *writer) exprs(exprs []syntax.Expr) {
  2637  	w.Sync(pkgbits.SyncExprs)
  2638  	w.Len(len(exprs))
  2639  	for _, expr := range exprs {
  2640  		w.expr(expr)
  2641  	}
  2642  }
  2643  
  2644  // rtype writes information so that the reader can construct an
  2645  // expression of type *runtime._type representing typ.
  2646  func (w *writer) rtype(typ types2.Type) {
  2647  	typ = types2.Default(typ)
  2648  
  2649  	info := w.p.typIdx(typ, w.dict)
  2650  	w.rtypeInfo(info)
  2651  }
  2652  
  2653  func (w *writer) rtypeInfo(info typeInfo) {
  2654  	w.Sync(pkgbits.SyncRType)
  2655  
  2656  	if w.Bool(info.derived) {
  2657  		w.Len(w.dict.rtypeIdx(info))
  2658  	} else {
  2659  		w.typInfo(info)
  2660  	}
  2661  }
  2662  
  2663  // varDictIndex writes out information for populating DictIndex for
  2664  // the ir.Name that will represent obj.
  2665  func (w *writer) varDictIndex(obj *types2.Var) {
  2666  	info := w.p.typIdx(obj.Type(), w.dict)
  2667  	if w.Bool(info.derived) {
  2668  		w.Len(w.dict.rtypeIdx(info))
  2669  	}
  2670  }
  2671  
  2672  // isUntyped reports whether typ is an untyped type.
  2673  func isUntyped(typ types2.Type) bool {
  2674  	// Note: types2.Unalias is unnecessary here, since untyped types can't be aliased.
  2675  	basic, ok := typ.(*types2.Basic)
  2676  	return ok && basic.Info()&types2.IsUntyped != 0
  2677  }
  2678  
  2679  // isTuple reports whether typ is a tuple type.
  2680  func isTuple(typ types2.Type) bool {
  2681  	// Note: types2.Unalias is unnecessary here, since tuple types can't be aliased.
  2682  	_, ok := typ.(*types2.Tuple)
  2683  	return ok
  2684  }
  2685  
  2686  func (w *writer) itab(typ, iface types2.Type) {
  2687  	typ = types2.Default(typ)
  2688  	iface = types2.Default(iface)
  2689  
  2690  	typInfo := w.p.typIdx(typ, w.dict)
  2691  	ifaceInfo := w.p.typIdx(iface, w.dict)
  2692  
  2693  	w.rtypeInfo(typInfo)
  2694  	w.rtypeInfo(ifaceInfo)
  2695  	if w.Bool(typInfo.derived || ifaceInfo.derived) {
  2696  		w.Len(w.dict.itabIdx(typInfo, ifaceInfo))
  2697  	}
  2698  }
  2699  
  2700  // convRTTI writes information so that the reader can construct
  2701  // expressions for converting from src to dst.
  2702  func (w *writer) convRTTI(src, dst types2.Type) {
  2703  	w.Sync(pkgbits.SyncConvRTTI)
  2704  	w.itab(src, dst)
  2705  }
  2706  
  2707  func (w *writer) exprType(iface types2.Type, typ syntax.Expr) {
  2708  	base.Assertf(iface == nil || isInterface(iface), "%v must be nil or an interface type", iface)
  2709  
  2710  	tv := w.p.typeAndValue(typ)
  2711  	assert(tv.IsType())
  2712  
  2713  	w.Sync(pkgbits.SyncExprType)
  2714  	w.pos(typ)
  2715  
  2716  	if w.Bool(iface != nil && !iface.Underlying().(*types2.Interface).Empty()) {
  2717  		w.itab(tv.Type, iface)
  2718  	} else {
  2719  		w.rtype(tv.Type)
  2720  
  2721  		info := w.p.typIdx(tv.Type, w.dict)
  2722  		w.Bool(info.derived)
  2723  	}
  2724  }
  2725  
  2726  // isInterface reports whether typ is known to be an interface type.
  2727  // If typ is a type parameter, then isInterface reports an internal
  2728  // compiler error instead.
  2729  func isInterface(typ types2.Type) bool {
  2730  	if _, ok := types2.Unalias(typ).(*types2.TypeParam); ok {
  2731  		// typ is a type parameter and may be instantiated as either a
  2732  		// concrete or interface type, so the writer can't depend on
  2733  		// knowing this.
  2734  		base.Fatalf("%v is a type parameter", typ)
  2735  	}
  2736  
  2737  	_, ok := typ.Underlying().(*types2.Interface)
  2738  	return ok
  2739  }
  2740  
  2741  // isConcreteMethod reports whether typ is a concrete method. That is,
  2742  // it's a method with a receiver that isn't an interface type.
  2743  func isConcreteMethod(typ types2.Type) bool {
  2744  	sig, ok := typ.(*types2.Signature)
  2745  	return ok && sig.Recv() != nil && !isInterface(sig.Recv().Type())
  2746  }
  2747  
  2748  // TODO(mark): Use isGenericMethod. It is included now to help justify
  2749  // the existence of isConcreteMethod.
  2750  
  2751  // isGenericMethod reports whether typ is a generic method. That is,
  2752  // it's a method with type parameters apart from those which may or
  2753  // may not appear on the receiver type.
  2754  //
  2755  // Note that generic methods are always concrete methods.
  2756  func isGenericMethod(typ types2.Type) bool {
  2757  	sig, ok := typ.(*types2.Signature)
  2758  	return ok && sig.Recv() != nil && sig.TypeParams().Len() > 0
  2759  }
  2760  
  2761  // op writes an Op into the bitstream.
  2762  func (w *writer) op(op ir.Op) {
  2763  	// TODO(mdempsky): Remove in favor of explicit codes? Would make
  2764  	// export data more stable against internal refactorings, but low
  2765  	// priority at the moment.
  2766  	assert(op != 0)
  2767  	w.Sync(pkgbits.SyncOp)
  2768  	w.Len(int(op))
  2769  }
  2770  
  2771  // @@@ Package initialization
  2772  
  2773  // Caution: This code is still clumsy, because toolstash -cmp is
  2774  // particularly sensitive to it.
  2775  
  2776  type typeDeclGen struct {
  2777  	*syntax.TypeDecl
  2778  	gen int
  2779  
  2780  	// Implicit type parameters in scope at this type declaration.
  2781  	implicits []*types2.TypeParam
  2782  }
  2783  
  2784  type fileImports struct {
  2785  	importedEmbed, importedUnsafe bool
  2786  }
  2787  
  2788  // declCollector is a visitor type that collects compiler-needed
  2789  // information about declarations that types2 doesn't track.
  2790  //
  2791  // Notably, it maps declared types and functions back to their
  2792  // declaration statement, keeps track of implicit type parameters, and
  2793  // assigns unique type "generation" numbers to local defined types.
  2794  type declCollector struct {
  2795  	pw         *pkgWriter
  2796  	typegen    *int
  2797  	file       *fileImports
  2798  	withinFunc bool
  2799  	implicits  []*types2.TypeParam
  2800  }
  2801  
  2802  func (c *declCollector) withTParams(obj types2.Object) *declCollector {
  2803  	tparams := slices.Concat(objRecvTypeParams(obj), objTypeParams(obj))
  2804  	if len(tparams) == 0 {
  2805  		return c
  2806  	}
  2807  
  2808  	copy := *c
  2809  	copy.implicits = copy.implicits[:len(copy.implicits):len(copy.implicits)]
  2810  	for _, tparam := range tparams {
  2811  		copy.implicits = append(copy.implicits, tparam)
  2812  	}
  2813  	return &copy
  2814  }
  2815  
  2816  func (c *declCollector) Visit(n syntax.Node) syntax.Visitor {
  2817  	pw := c.pw
  2818  
  2819  	switch n := n.(type) {
  2820  	case *syntax.File:
  2821  		pw.checkPragmas(n.Pragma, ir.GoBuildPragma, false)
  2822  
  2823  	case *syntax.ImportDecl:
  2824  		pw.checkPragmas(n.Pragma, 0, false)
  2825  
  2826  		switch pw.info.PkgNameOf(n).Imported().Path() {
  2827  		case "embed":
  2828  			c.file.importedEmbed = true
  2829  		case "unsafe":
  2830  			c.file.importedUnsafe = true
  2831  		}
  2832  
  2833  	case *syntax.ConstDecl:
  2834  		pw.checkPragmas(n.Pragma, 0, false)
  2835  
  2836  	case *syntax.FuncDecl:
  2837  		pw.checkPragmas(n.Pragma, funcPragmas, false)
  2838  
  2839  		obj := pw.info.Defs[n.Name].(*types2.Func)
  2840  		pw.funDecls[obj] = n
  2841  
  2842  		return c.withTParams(obj)
  2843  
  2844  	case *syntax.TypeDecl:
  2845  		obj := pw.info.Defs[n.Name].(*types2.TypeName)
  2846  		d := typeDeclGen{TypeDecl: n, implicits: c.implicits}
  2847  
  2848  		if n.Alias {
  2849  			pw.checkPragmas(n.Pragma, 0, false)
  2850  		} else {
  2851  			pw.checkPragmas(n.Pragma, 0, false)
  2852  
  2853  			// Assign a unique ID to function-scoped defined types.
  2854  			if c.withinFunc {
  2855  				*c.typegen++
  2856  				d.gen = *c.typegen
  2857  			}
  2858  		}
  2859  
  2860  		pw.typDecls[obj] = d
  2861  
  2862  		// TODO(mdempsky): Omit? Not strictly necessary; only matters for
  2863  		// type declarations within function literals within parameterized
  2864  		// type declarations, but types2 the function literals will be
  2865  		// constant folded away.
  2866  		return c.withTParams(obj)
  2867  
  2868  	case *syntax.VarDecl:
  2869  		pw.checkPragmas(n.Pragma, 0, true)
  2870  
  2871  		if p, ok := n.Pragma.(*pragmas); ok && len(p.Embeds) > 0 {
  2872  			if err := checkEmbed(n, c.file.importedEmbed, c.withinFunc); err != nil {
  2873  				pw.errorf(p.Embeds[0].Pos, "%s", err)
  2874  			}
  2875  		}
  2876  
  2877  	case *syntax.BlockStmt:
  2878  		if !c.withinFunc {
  2879  			copy := *c
  2880  			copy.withinFunc = true
  2881  			return &copy
  2882  		}
  2883  	}
  2884  
  2885  	return c
  2886  }
  2887  
  2888  func (pw *pkgWriter) collectDecls(noders []*noder) {
  2889  	var typegen int
  2890  	for _, p := range noders {
  2891  		var file fileImports
  2892  
  2893  		syntax.Walk(p.file, &declCollector{
  2894  			pw:      pw,
  2895  			typegen: &typegen,
  2896  			file:    &file,
  2897  		})
  2898  
  2899  		pw.cgoPragmas = append(pw.cgoPragmas, p.pragcgobuf...)
  2900  
  2901  		for _, l := range p.linknames {
  2902  			directive := "go:linkname"
  2903  			if l.std {
  2904  				directive = "go:linknamestd"
  2905  			}
  2906  			if !file.importedUnsafe {
  2907  				pw.errorf(l.pos, "//%s only allowed in Go files that import \"unsafe\"", directive)
  2908  				continue
  2909  			}
  2910  			if strings.Contains(l.remote, "[") && strings.Contains(l.remote, "]") {
  2911  				pw.errorf(l.pos, "//%s reference of an instantiation is not allowed", directive)
  2912  				continue
  2913  			}
  2914  
  2915  			switch obj := pw.curpkg.Scope().Lookup(l.local).(type) {
  2916  			case *types2.Func, *types2.Var:
  2917  				if _, ok := pw.linknames[obj]; !ok {
  2918  					pw.linknames[obj] = struct {
  2919  						remote string
  2920  						std    bool
  2921  					}{l.remote, l.std}
  2922  				} else {
  2923  					pw.errorf(l.pos, "duplicate //%s for %s", directive, l.local)
  2924  				}
  2925  
  2926  			default:
  2927  				if types.AllowsGoVersion(1, 18) {
  2928  					pw.errorf(l.pos, "//%s must refer to declared function or variable", directive)
  2929  				}
  2930  			}
  2931  		}
  2932  	}
  2933  }
  2934  
  2935  func (pw *pkgWriter) checkPragmas(p syntax.Pragma, allowed ir.PragmaFlag, embedOK bool) {
  2936  	if p == nil {
  2937  		return
  2938  	}
  2939  	pragma := p.(*pragmas)
  2940  
  2941  	for _, pos := range pragma.Pos {
  2942  		if pos.Flag&^allowed != 0 {
  2943  			pw.errorf(pos.Pos, "misplaced compiler directive")
  2944  		}
  2945  	}
  2946  
  2947  	if !embedOK {
  2948  		for _, e := range pragma.Embeds {
  2949  			pw.errorf(e.Pos, "misplaced go:embed directive")
  2950  		}
  2951  	}
  2952  }
  2953  
  2954  func (w *writer) pkgInit(noders []*noder) {
  2955  	w.Len(len(w.p.cgoPragmas))
  2956  	for _, cgoPragma := range w.p.cgoPragmas {
  2957  		w.Strings(cgoPragma)
  2958  	}
  2959  
  2960  	w.pkgInitOrder()
  2961  
  2962  	w.Sync(pkgbits.SyncDecls)
  2963  	for _, p := range noders {
  2964  		for _, decl := range p.file.DeclList {
  2965  			w.pkgDecl(decl)
  2966  		}
  2967  	}
  2968  	w.Code(declEnd)
  2969  
  2970  	w.Sync(pkgbits.SyncEOF)
  2971  }
  2972  
  2973  func (w *writer) pkgInitOrder() {
  2974  	// TODO(mdempsky): Write as a function body instead?
  2975  	w.Len(len(w.p.info.InitOrder))
  2976  	for _, init := range w.p.info.InitOrder {
  2977  		w.Len(len(init.Lhs))
  2978  		for _, v := range init.Lhs {
  2979  			w.obj(v, nil)
  2980  		}
  2981  		w.expr(init.Rhs)
  2982  	}
  2983  }
  2984  
  2985  func (w *writer) pkgDecl(decl syntax.Decl) {
  2986  	switch decl := decl.(type) {
  2987  	default:
  2988  		w.p.unexpected("declaration", decl)
  2989  
  2990  	case *syntax.ImportDecl:
  2991  
  2992  	case *syntax.ConstDecl:
  2993  		w.Code(declOther)
  2994  		w.pkgObjs(decl.NameList...)
  2995  
  2996  	case *syntax.FuncDecl:
  2997  		if decl.Name.Value == "_" {
  2998  			break // skip blank functions
  2999  		}
  3000  
  3001  		obj := w.p.info.Defs[decl.Name].(*types2.Func)
  3002  		sig := obj.Type().(*types2.Signature)
  3003  
  3004  		if sig.RecvTypeParams() != nil || sig.TypeParams() != nil {
  3005  			break // skip generic functions
  3006  		}
  3007  
  3008  		if recv := sig.Recv(); recv != nil {
  3009  			w.Code(declMethod)
  3010  			w.typ(recvBase(recv))
  3011  			w.selector(obj)
  3012  			break
  3013  		}
  3014  
  3015  		w.Code(declFunc)
  3016  		w.pkgObjs(decl.Name)
  3017  
  3018  	case *syntax.TypeDecl:
  3019  		if len(decl.TParamList) != 0 {
  3020  			break // skip generic type decls
  3021  		}
  3022  
  3023  		if decl.Name.Value == "_" {
  3024  			break // skip blank type decls
  3025  		}
  3026  
  3027  		name := w.p.info.Defs[decl.Name].(*types2.TypeName)
  3028  		// Skip type declarations for interfaces that are only usable as
  3029  		// type parameter bounds.
  3030  		if iface, ok := name.Type().Underlying().(*types2.Interface); ok && !iface.IsMethodSet() {
  3031  			break
  3032  		}
  3033  
  3034  		w.Code(declOther)
  3035  		w.pkgObjs(decl.Name)
  3036  
  3037  	case *syntax.VarDecl:
  3038  		w.Code(declVar)
  3039  		w.pkgObjs(decl.NameList...)
  3040  
  3041  		var embeds []pragmaEmbed
  3042  		if p, ok := decl.Pragma.(*pragmas); ok {
  3043  			embeds = p.Embeds
  3044  		}
  3045  		w.Len(len(embeds))
  3046  		for _, embed := range embeds {
  3047  			w.pos(embed.Pos)
  3048  			w.Strings(embed.Patterns)
  3049  		}
  3050  	}
  3051  }
  3052  
  3053  func (w *writer) pkgObjs(names ...*syntax.Name) {
  3054  	w.Sync(pkgbits.SyncDeclNames)
  3055  	w.Len(len(names))
  3056  
  3057  	for _, name := range names {
  3058  		obj, ok := w.p.info.Defs[name]
  3059  		assert(ok)
  3060  
  3061  		w.Sync(pkgbits.SyncDeclName)
  3062  		w.obj(obj, nil)
  3063  	}
  3064  }
  3065  
  3066  // @@@ Helpers
  3067  
  3068  // staticBool analyzes a boolean expression and reports whether it's
  3069  // always true (positive result), always false (negative result), or
  3070  // unknown (zero).
  3071  //
  3072  // It also simplifies the expression while preserving semantics, if
  3073  // possible.
  3074  func (pw *pkgWriter) staticBool(ep *syntax.Expr) int {
  3075  	if val := pw.typeAndValue(*ep).Value; val != nil {
  3076  		if constant.BoolVal(val) {
  3077  			return +1
  3078  		} else {
  3079  			return -1
  3080  		}
  3081  	}
  3082  
  3083  	if e, ok := (*ep).(*syntax.Operation); ok {
  3084  		switch e.Op {
  3085  		case syntax.Not:
  3086  			return pw.staticBool(&e.X)
  3087  
  3088  		case syntax.AndAnd:
  3089  			x := pw.staticBool(&e.X)
  3090  			if x < 0 {
  3091  				*ep = e.X
  3092  				return x
  3093  			}
  3094  
  3095  			y := pw.staticBool(&e.Y)
  3096  			if x > 0 || y < 0 {
  3097  				if pw.typeAndValue(e.X).Value != nil {
  3098  					*ep = e.Y
  3099  				}
  3100  				return y
  3101  			}
  3102  
  3103  		case syntax.OrOr:
  3104  			x := pw.staticBool(&e.X)
  3105  			if x > 0 {
  3106  				*ep = e.X
  3107  				return x
  3108  			}
  3109  
  3110  			y := pw.staticBool(&e.Y)
  3111  			if x < 0 || y > 0 {
  3112  				if pw.typeAndValue(e.X).Value != nil {
  3113  					*ep = e.Y
  3114  				}
  3115  				return y
  3116  			}
  3117  		}
  3118  	}
  3119  
  3120  	return 0
  3121  }
  3122  
  3123  // hasImplicitTypeParams reports whether obj is a defined type with
  3124  // implicit type parameters (e.g., declared within a generic function
  3125  // or method).
  3126  func (pw *pkgWriter) hasImplicitTypeParams(obj *types2.TypeName) bool {
  3127  	if obj.Pkg() == pw.curpkg {
  3128  		decl, ok := pw.typDecls[obj]
  3129  		assert(ok)
  3130  		if len(decl.implicits) != 0 {
  3131  			return true
  3132  		}
  3133  	}
  3134  	return false
  3135  }
  3136  
  3137  // isDefinedType reports whether obj is a defined type.
  3138  func isDefinedType(obj types2.Object) bool {
  3139  	if obj, ok := obj.(*types2.TypeName); ok {
  3140  		return !obj.IsAlias()
  3141  	}
  3142  	return false
  3143  }
  3144  
  3145  // isGlobal reports whether obj was declared at package scope.
  3146  //
  3147  // Caveat: blank objects are not declared.
  3148  func isGlobal(obj types2.Object) bool {
  3149  	return obj.Parent() == obj.Pkg().Scope()
  3150  }
  3151  
  3152  // lookupObj returns the object that expr refers to, if any. If expr
  3153  // is an explicit instantiation of a generic object, then the instance
  3154  // object is returned as well.
  3155  func lookupObj(p *pkgWriter, expr syntax.Expr) (obj types2.Object, inst types2.Instance) {
  3156  	if index, ok := expr.(*syntax.IndexExpr); ok {
  3157  		args := syntax.UnpackListExpr(index.Index)
  3158  		if len(args) == 1 {
  3159  			tv := p.typeAndValue(args[0])
  3160  			if tv.IsValue() {
  3161  				return // normal index expression
  3162  			}
  3163  		}
  3164  
  3165  		expr = index.X
  3166  	}
  3167  
  3168  	// Strip package qualifier, if present.
  3169  	if sel, ok := expr.(*syntax.SelectorExpr); ok {
  3170  		if !isPkgQual(p.info, sel) {
  3171  			return // normal selector expression
  3172  		}
  3173  		expr = sel.Sel
  3174  	}
  3175  
  3176  	if name, ok := expr.(*syntax.Name); ok {
  3177  		obj = p.info.Uses[name]
  3178  		inst = p.info.Instances[name]
  3179  	}
  3180  	return
  3181  }
  3182  
  3183  // isPkgQual reports whether the given selector expression is a
  3184  // package-qualified identifier.
  3185  func isPkgQual(info *types2.Info, sel *syntax.SelectorExpr) bool {
  3186  	if name, ok := sel.X.(*syntax.Name); ok {
  3187  		_, isPkgName := info.Uses[name].(*types2.PkgName)
  3188  		return isPkgName
  3189  	}
  3190  	return false
  3191  }
  3192  
  3193  // isNil reports whether expr is a (possibly parenthesized) reference
  3194  // to the predeclared nil value.
  3195  func isNil(p *pkgWriter, expr syntax.Expr) bool {
  3196  	tv := p.typeAndValue(expr)
  3197  	return tv.IsNil()
  3198  }
  3199  
  3200  // isBuiltin reports whether expr is a (possibly parenthesized)
  3201  // referenced to the specified built-in function.
  3202  func (pw *pkgWriter) isBuiltin(expr syntax.Expr, builtin string) bool {
  3203  	if name, ok := syntax.Unparen(expr).(*syntax.Name); ok && name.Value == builtin {
  3204  		return pw.typeAndValue(name).IsBuiltin()
  3205  	}
  3206  	return false
  3207  }
  3208  
  3209  // recvBase returns the base type for the given receiver parameter.
  3210  func recvBase(recv *types2.Var) *types2.Named {
  3211  	typ := types2.Unalias(recv.Type())
  3212  	if ptr, ok := typ.(*types2.Pointer); ok {
  3213  		typ = types2.Unalias(ptr.Elem())
  3214  	}
  3215  	return typ.(*types2.Named)
  3216  }
  3217  
  3218  // namesAsExpr returns a list of names as a syntax.Expr.
  3219  func namesAsExpr(names []*syntax.Name) syntax.Expr {
  3220  	if len(names) == 1 {
  3221  		return names[0]
  3222  	}
  3223  
  3224  	exprs := make([]syntax.Expr, len(names))
  3225  	for i, name := range names {
  3226  		exprs[i] = name
  3227  	}
  3228  	return &syntax.ListExpr{ElemList: exprs}
  3229  }
  3230  
  3231  // fieldIndex returns the index of the struct field named by key.
  3232  func fieldIndex(info *types2.Info, str *types2.Struct, key *syntax.Name) int {
  3233  	field := info.Uses[key].(*types2.Var)
  3234  
  3235  	for i := 0; i < str.NumFields(); i++ {
  3236  		if str.Field(i) == field {
  3237  			return i
  3238  		}
  3239  	}
  3240  
  3241  	panic(fmt.Sprintf("%s: %v is not a field of %v", key.Pos(), field, str))
  3242  }
  3243  
  3244  // objRecvTypeParams returns the receiver type parameters on the given object.
  3245  func objRecvTypeParams(obj types2.Object) []*types2.TypeParam {
  3246  	if f, ok := obj.(*types2.Func); ok {
  3247  		return asTypeParamSlice(f.Signature().RecvTypeParams())
  3248  	}
  3249  	return nil
  3250  }
  3251  
  3252  // objTypeParams returns the type parameters on the given object.
  3253  func objTypeParams(obj types2.Object) []*types2.TypeParam {
  3254  	switch t := obj.(type) {
  3255  	case *types2.Func:
  3256  		return asTypeParamSlice(t.Signature().TypeParams())
  3257  	case *types2.TypeName:
  3258  		switch t := obj.Type().(type) {
  3259  		case *types2.Named:
  3260  			return asTypeParamSlice(t.TypeParams())
  3261  		case *types2.Alias:
  3262  			return asTypeParamSlice(t.TypeParams())
  3263  		}
  3264  	}
  3265  	return nil
  3266  }
  3267  
  3268  // asTypeParamSlice unpacks a types2.TypeParamList to a []types2.TypeParam
  3269  func asTypeParamSlice(l *types2.TypeParamList) []*types2.TypeParam {
  3270  	if l.Len() == 0 {
  3271  		return nil
  3272  	}
  3273  	s := make([]*types2.TypeParam, l.Len())
  3274  	for i := range l.Len() {
  3275  		s[i] = l.At(i)
  3276  	}
  3277  	return s
  3278  }
  3279  
  3280  // splitNamed decomposes a use of a defined type into its original
  3281  // type definition and the type arguments used to instantiate it.
  3282  func splitNamed(typ *types2.Named) (*types2.TypeName, []types2.Type) {
  3283  	base.Assertf(typ.TypeParams().Len() == typ.TypeArgs().Len(), "use of uninstantiated type: %v", typ)
  3284  
  3285  	orig := typ.Origin()
  3286  	base.Assertf(orig.TypeArgs() == nil, "origin %v of %v has type arguments", orig, typ)
  3287  	base.Assertf(typ.Obj() == orig.Obj(), "%v has object %v, but %v has object %v", typ, typ.Obj(), orig, orig.Obj())
  3288  
  3289  	return typ.Obj(), asTypeSlice(typ.TypeArgs())
  3290  }
  3291  
  3292  // splitAlias is like splitNamed, but for an alias type.
  3293  func splitAlias(typ *types2.Alias) (*types2.TypeName, []types2.Type) {
  3294  	orig := typ.Origin()
  3295  	base.Assertf(typ.Obj() == orig.Obj(), "alias type %v has object %v, but %v has object %v", typ, typ.Obj(), orig, orig.Obj())
  3296  
  3297  	return typ.Obj(), asTypeSlice(typ.TypeArgs())
  3298  }
  3299  
  3300  // asTypeSlice unpacks a types2.TypeList to a []types2.Type
  3301  func asTypeSlice(l *types2.TypeList) []types2.Type {
  3302  	if l.Len() == 0 {
  3303  		return nil
  3304  	}
  3305  	s := make([]types2.Type, l.Len())
  3306  	for i := range l.Len() {
  3307  		s[i] = l.At(i)
  3308  	}
  3309  	return s
  3310  }
  3311  
  3312  func asPragmaFlag(p syntax.Pragma) ir.PragmaFlag {
  3313  	if p == nil {
  3314  		return 0
  3315  	}
  3316  	return p.(*pragmas).Flag
  3317  }
  3318  
  3319  func asWasmImport(p syntax.Pragma) *WasmImport {
  3320  	if p == nil {
  3321  		return nil
  3322  	}
  3323  	return p.(*pragmas).WasmImport
  3324  }
  3325  
  3326  func asWasmExport(p syntax.Pragma) *WasmExport {
  3327  	if p == nil {
  3328  		return nil
  3329  	}
  3330  	return p.(*pragmas).WasmExport
  3331  }
  3332  
  3333  // isPtrTo reports whether from is the type *to.
  3334  func isPtrTo(from, to types2.Type) bool {
  3335  	ptr, ok := types2.Unalias(from).(*types2.Pointer)
  3336  	return ok && types2.Identical(ptr.Elem(), to)
  3337  }
  3338  
  3339  // hasFallthrough reports whether stmts ends in a fallthrough
  3340  // statement.
  3341  func hasFallthrough(stmts []syntax.Stmt) bool {
  3342  	// From spec: the last non-empty statement may be a (possibly labeled) "fallthrough" statement
  3343  	// Stripping (possible nested) labeled statement if any.
  3344  	stmt := lastNonEmptyStmt(stmts)
  3345  	for {
  3346  		ls, ok := stmt.(*syntax.LabeledStmt)
  3347  		if !ok {
  3348  			break
  3349  		}
  3350  		stmt = ls.Stmt
  3351  	}
  3352  	last, ok := stmt.(*syntax.BranchStmt)
  3353  	return ok && last.Tok == syntax.Fallthrough
  3354  }
  3355  
  3356  // lastNonEmptyStmt returns the last non-empty statement in list, if
  3357  // any.
  3358  func lastNonEmptyStmt(stmts []syntax.Stmt) syntax.Stmt {
  3359  	for i := len(stmts) - 1; i >= 0; i-- {
  3360  		stmt := stmts[i]
  3361  		if _, ok := stmt.(*syntax.EmptyStmt); !ok {
  3362  			return stmt
  3363  		}
  3364  	}
  3365  	return nil
  3366  }
  3367  
  3368  // terminates reports whether stmt terminates normal control flow
  3369  // (i.e., does not merely advance to the following statement).
  3370  func (pw *pkgWriter) terminates(stmt syntax.Stmt) bool {
  3371  	switch stmt := stmt.(type) {
  3372  	case *syntax.BranchStmt:
  3373  		if stmt.Tok == syntax.Goto {
  3374  			return true
  3375  		}
  3376  	case *syntax.ReturnStmt:
  3377  		return true
  3378  	case *syntax.ExprStmt:
  3379  		if call, ok := syntax.Unparen(stmt.X).(*syntax.CallExpr); ok {
  3380  			if pw.isBuiltin(call.Fun, "panic") {
  3381  				return true
  3382  			}
  3383  		}
  3384  
  3385  		// The handling of BlockStmt here is approximate, but it serves to
  3386  		// allow dead-code elimination for:
  3387  		//
  3388  		//	if true {
  3389  		//		return x
  3390  		//	}
  3391  		//	unreachable
  3392  	case *syntax.IfStmt:
  3393  		cond := pw.staticBool(&stmt.Cond)
  3394  		return (cond < 0 || pw.terminates(stmt.Then)) && (cond > 0 || pw.terminates(stmt.Else))
  3395  	case *syntax.BlockStmt:
  3396  		return pw.terminates(lastNonEmptyStmt(stmt.List))
  3397  	}
  3398  
  3399  	return false
  3400  }
  3401  

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