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  		assert(ok)
   784  		dict.implicits = decl.implicits
   785  	}
   786  
   787  	if isGenericMethod(obj.Type()) {
   788  		dict.receivers = asTypeParamSlice(obj.Type().(*types2.Signature).RecvTypeParams())
   789  	}
   790  
   791  	// We encode objects into 4 elements across different sections, all
   792  	// sharing the same index:
   793  	//
   794  	// - RelocName has just the object's qualified name (i.e.,
   795  	//   Object.Pkg and Object.Name) and the CodeObj indicating what
   796  	//   specific type of Object it is (Var, Func, etc).
   797  	//
   798  	// - RelocObj has the remaining public details about the object,
   799  	//   relevant to go/types importers.
   800  	//
   801  	// - RelocObjExt has additional private details about the object,
   802  	//   which are only relevant to cmd/compile itself. This is
   803  	//   separated from RelocObj so that go/types importers are
   804  	//   unaffected by internal compiler changes.
   805  	//
   806  	// - RelocObjDict has public details about the object's type
   807  	//   parameters and derived type's used by the object. This is
   808  	//   separated to facilitate the eventual introduction of
   809  	//   shape-based stenciling.
   810  	//
   811  	// TODO(mdempsky): Re-evaluate whether RelocName still makes sense
   812  	// to keep separate from RelocObj.
   813  
   814  	w := pw.newWriter(pkgbits.SectionObj, pkgbits.SyncObject1)
   815  	wext := pw.newWriter(pkgbits.SectionObjExt, pkgbits.SyncObject1)
   816  	wname := pw.newWriter(pkgbits.SectionName, pkgbits.SyncObject1)
   817  	wdict := pw.newWriter(pkgbits.SectionObjDict, pkgbits.SyncObject1)
   818  
   819  	pw.objsIdx[obj] = w.Idx // break cycles
   820  	assert(wext.Idx == w.Idx)
   821  	assert(wname.Idx == w.Idx)
   822  	assert(wdict.Idx == w.Idx)
   823  
   824  	w.dict = dict
   825  	wext.dict = dict
   826  
   827  	code := w.doObj(wext, obj)
   828  	w.Flush()
   829  	wext.Flush()
   830  
   831  	wname.qualifiedIdent(obj)
   832  	wname.Code(code)
   833  	wname.Flush()
   834  
   835  	wdict.objDict(obj, w.dict)
   836  	wdict.Flush()
   837  
   838  	return w.Idx
   839  }
   840  
   841  // doObj writes the RelocObj definition for obj to w, and the
   842  // RelocObjExt definition to wext.
   843  func (w *writer) doObj(wext *writer, obj types2.Object) pkgbits.CodeObj {
   844  	if obj.Pkg() != w.p.curpkg {
   845  		return pkgbits.ObjStub
   846  	}
   847  
   848  	switch obj := obj.(type) {
   849  	default:
   850  		w.p.unexpected("object", obj)
   851  		panic("unreachable")
   852  
   853  	case *types2.Const:
   854  		w.pos(obj)
   855  		w.typ(obj.Type())
   856  		w.Value(obj.Val())
   857  		return pkgbits.ObjConst
   858  
   859  	case *types2.Func:
   860  		decl, ok := w.p.funDecls[obj]
   861  		assert(ok)
   862  		sig := obj.Type().(*types2.Signature)
   863  
   864  		w.pos(obj)
   865  		if isGenericMethod(sig) {
   866  			// otherwise the reader won't know to expect the flag
   867  			assert(w.Version().Has(pkgbits.GenericMethods))
   868  			w.Bool(true) // generic method
   869  
   870  			w.selector(obj)
   871  			w.typeParamNames(sig.RecvTypeParams())
   872  			w.param(sig.Recv())
   873  		} else {
   874  			if w.Version().Has(pkgbits.GenericMethods) {
   875  				w.Bool(false) // function
   876  			}
   877  		}
   878  		w.typeParamNames(sig.TypeParams())
   879  		w.signature(sig)
   880  		w.pos(decl)
   881  		wext.funcExt(obj)
   882  		return pkgbits.ObjFunc
   883  
   884  	case *types2.TypeName:
   885  		if obj.IsAlias() {
   886  			w.pos(obj)
   887  			rhs := obj.Type()
   888  			var tparams *types2.TypeParamList
   889  			if alias, ok := rhs.(*types2.Alias); ok { // materialized alias
   890  				assert(alias.TypeArgs() == nil)
   891  				tparams = alias.TypeParams()
   892  				rhs = alias.Rhs()
   893  			}
   894  			if w.Version().Has(pkgbits.AliasTypeParamNames) {
   895  				w.typeParamNames(tparams)
   896  			}
   897  			assert(w.Version().Has(pkgbits.AliasTypeParamNames) || tparams.Len() == 0)
   898  			w.typ(rhs)
   899  			return pkgbits.ObjAlias
   900  		}
   901  
   902  		named := obj.Type().(*types2.Named)
   903  		assert(named.TypeArgs() == nil)
   904  
   905  		w.pos(obj)
   906  		w.typeParamNames(named.TypeParams())
   907  		wext.typeExt(obj)
   908  		w.typ(named.Underlying())
   909  
   910  		// separate generic and non-generic methods
   911  		var methods, gmethods []*types2.Func
   912  		for i := range named.NumMethods() {
   913  			m := named.Method(i)
   914  			if isGenericMethod(m.Type()) {
   915  				gmethods = append(gmethods, m)
   916  			} else {
   917  				methods = append(methods, m)
   918  			}
   919  		}
   920  		// encode non-generic methods inline
   921  		w.Len(len(methods))
   922  		for _, m := range methods {
   923  			w.method(wext, m)
   924  		}
   925  		// encode generic methods elsewhere
   926  		for _, m := range gmethods {
   927  			w.p.objIdx(m)
   928  		}
   929  
   930  		return pkgbits.ObjType
   931  
   932  	case *types2.Var:
   933  		w.pos(obj)
   934  		w.typ(obj.Type())
   935  		wext.varExt(obj)
   936  		return pkgbits.ObjVar
   937  	}
   938  }
   939  
   940  // objDict writes the dictionary needed for reading the given object.
   941  func (w *writer) objDict(obj types2.Object, dict *writerDict) {
   942  	// TODO(mdempsky): Split objDict into multiple entries? reader.go
   943  	// doesn't care about the type parameter bounds, and reader2.go
   944  	// doesn't care about referenced functions.
   945  
   946  	w.dict = dict // TODO(mdempsky): This is a bit sketchy.
   947  	w.Len(len(dict.implicits))
   948  
   949  	rtparams := objRecvTypeParams(obj)
   950  	tparams := objTypeParams(obj)
   951  
   952  	if w.Version().Has(pkgbits.GenericMethods) {
   953  		w.Len(len(rtparams))
   954  	} else {
   955  		assert(len(rtparams) == 0)
   956  	}
   957  	w.Len(len(tparams))
   958  
   959  	for _, rtparam := range rtparams {
   960  		w.typ(rtparam.Constraint())
   961  	}
   962  	for _, tparam := range tparams {
   963  		w.typ(tparam.Constraint())
   964  	}
   965  
   966  	nderived := len(dict.derived)
   967  	w.Len(nderived)
   968  	for _, typ := range dict.derived {
   969  		w.Reloc(pkgbits.SectionType, typ.idx)
   970  		if w.Version().Has(pkgbits.DerivedInfoNeeded) {
   971  			w.Bool(false)
   972  		}
   973  	}
   974  
   975  	// Write runtime dictionary information.
   976  	//
   977  	// N.B., the go/types importer reads up to the section, but doesn't
   978  	// read any further, so it's safe to change. (See TODO above.)
   979  
   980  	// For each type parameter, write out whether the constraint is a
   981  	// basic interface. This is used to determine how aggressively we
   982  	// can shape corresponding type arguments.
   983  	//
   984  	// This is somewhat redundant with writing out the full type
   985  	// parameter constraints above, but the compiler currently skips
   986  	// over those. Also, we don't care about the *declared* constraints,
   987  	// but how the type parameters are actually *used*. E.g., if a type
   988  	// parameter is constrained to `int | uint` but then never used in
   989  	// arithmetic/conversions/etc, we could shape those together.
   990  	for _, implicit := range dict.implicits {
   991  		w.Bool(implicit.Underlying().(*types2.Interface).IsMethodSet())
   992  	}
   993  	for _, rtparam := range rtparams {
   994  		w.Bool(rtparam.Underlying().(*types2.Interface).IsMethodSet())
   995  	}
   996  	for _, tparam := range tparams {
   997  		w.Bool(tparam.Underlying().(*types2.Interface).IsMethodSet())
   998  	}
   999  
  1000  	w.Len(len(dict.typeParamMethodExprs))
  1001  	for _, info := range dict.typeParamMethodExprs {
  1002  		w.Len(info.typeParamIdx)
  1003  		w.selectorInfo(info.methodInfo)
  1004  	}
  1005  
  1006  	w.Len(len(dict.subdicts))
  1007  	for _, info := range dict.subdicts {
  1008  		w.objInfo(info)
  1009  	}
  1010  
  1011  	w.Len(len(dict.rtypes))
  1012  	for _, info := range dict.rtypes {
  1013  		w.typInfo(info)
  1014  	}
  1015  
  1016  	w.Len(len(dict.itabs))
  1017  	for _, info := range dict.itabs {
  1018  		w.typInfo(info.typ)
  1019  		w.typInfo(info.iface)
  1020  	}
  1021  
  1022  	assert(len(dict.derived) == nderived)
  1023  }
  1024  
  1025  func (w *writer) typeParamNames(tparams *types2.TypeParamList) {
  1026  	w.Sync(pkgbits.SyncTypeParamNames)
  1027  
  1028  	ntparams := tparams.Len()
  1029  	for i := 0; i < ntparams; i++ {
  1030  		tparam := tparams.At(i).Obj()
  1031  		w.pos(tparam)
  1032  		w.localIdent(tparam)
  1033  	}
  1034  }
  1035  
  1036  func (w *writer) method(wext *writer, meth *types2.Func) {
  1037  	decl, ok := w.p.funDecls[meth]
  1038  	assert(ok)
  1039  	sig := meth.Type().(*types2.Signature)
  1040  
  1041  	w.Sync(pkgbits.SyncMethod)
  1042  	w.pos(meth)
  1043  	w.selector(meth)
  1044  	w.typeParamNames(sig.RecvTypeParams())
  1045  	w.param(sig.Recv())
  1046  	w.signature(sig)
  1047  
  1048  	w.pos(decl) // XXX: Hack to workaround linker limitations.
  1049  	wext.funcExt(meth)
  1050  }
  1051  
  1052  // qualifiedIdent writes out the name of an object typically declared at package
  1053  // scope. It's also used to refer to generic methods and locally defined types.
  1054  func (w *writer) qualifiedIdent(obj types2.Object) {
  1055  	w.Sync(pkgbits.SyncSym)
  1056  
  1057  	name := obj.Name()
  1058  	if isDefinedType(obj) && obj.Pkg() == w.p.curpkg {
  1059  		decl, ok := w.p.typDecls[obj.(*types2.TypeName)]
  1060  		assert(ok)
  1061  		if decl.gen != 0 {
  1062  			// For local defined types, we embed a scope-disambiguation
  1063  			// number directly into their name. types.SplitVargenSuffix then
  1064  			// knows to look for this.
  1065  			//
  1066  			// TODO(mdempsky): Find a better solution; this is terrible.
  1067  			name = fmt.Sprintf("%s·%v", name, decl.gen)
  1068  		}
  1069  	}
  1070  
  1071  	// Generic methods are promoted to objects and thus need qualified identifiers.
  1072  	// They must be contextualized by their defining type.
  1073  	if isGenericMethod(obj.Type()) {
  1074  		recv := types2.Unalias(deref2(obj.Type().(*types2.Signature).Recv().Type()))
  1075  		name = fmt.Sprintf("%s.%s", recv.(*types2.Named).Obj().Name(), name)
  1076  	}
  1077  
  1078  	w.pkg(obj.Pkg())
  1079  	w.String(name)
  1080  }
  1081  
  1082  // TODO(mdempsky): We should be able to omit pkg from both localIdent
  1083  // and selector, because they should always be known from context.
  1084  // However, past frustrations with this optimization in iexport make
  1085  // me a little nervous to try it again.
  1086  
  1087  // localIdent writes the name of a locally declared object (i.e.,
  1088  // objects that can only be accessed by non-qualified name, within the
  1089  // context of a particular function).
  1090  func (w *writer) localIdent(obj types2.Object) {
  1091  	assert(!isGlobal(obj))
  1092  	w.Sync(pkgbits.SyncLocalIdent)
  1093  	w.pkg(obj.Pkg())
  1094  	w.String(obj.Name())
  1095  }
  1096  
  1097  // selector writes the name of a field or method (i.e., objects that
  1098  // can only be accessed using selector expressions).
  1099  func (w *writer) selector(obj types2.Object) {
  1100  	w.selectorInfo(w.p.selectorIdx(obj))
  1101  }
  1102  
  1103  func (w *writer) selectorInfo(info selectorInfo) {
  1104  	w.Sync(pkgbits.SyncSelector)
  1105  	w.pkgRef(info.pkgIdx)
  1106  	w.StringRef(info.nameIdx)
  1107  }
  1108  
  1109  func (pw *pkgWriter) selectorIdx(obj types2.Object) selectorInfo {
  1110  	pkgIdx := pw.pkgIdx(obj.Pkg())
  1111  	nameIdx := pw.StringIdx(obj.Name())
  1112  	return selectorInfo{pkgIdx: pkgIdx, nameIdx: nameIdx}
  1113  }
  1114  
  1115  // @@@ Compiler extensions
  1116  
  1117  func (w *writer) funcExt(obj *types2.Func) {
  1118  	decl, ok := w.p.funDecls[obj]
  1119  	assert(ok)
  1120  
  1121  	// TODO(mdempsky): Extend these pragma validation flags to account
  1122  	// for generics. E.g., linkname probably doesn't make sense at
  1123  	// least.
  1124  
  1125  	pragma := asPragmaFlag(decl.Pragma)
  1126  	if pragma&ir.Systemstack != 0 && pragma&ir.Nosplit != 0 {
  1127  		w.p.errorf(decl, "go:nosplit and go:systemstack cannot be combined")
  1128  	}
  1129  	wi := asWasmImport(decl.Pragma)
  1130  	we := asWasmExport(decl.Pragma)
  1131  
  1132  	if decl.Body != nil {
  1133  		if pragma&ir.Noescape != 0 {
  1134  			w.p.errorf(decl, "can only use //go:noescape with external func implementations")
  1135  		}
  1136  		if wi != nil {
  1137  			w.p.errorf(decl, "can only use //go:wasmimport with external func implementations")
  1138  		}
  1139  		if (pragma&ir.UintptrKeepAlive != 0 && pragma&ir.UintptrEscapes == 0) && pragma&ir.Nosplit == 0 {
  1140  			// Stack growth can't handle uintptr arguments that may
  1141  			// be pointers (as we don't know which are pointers
  1142  			// when creating the stack map). Thus uintptrkeepalive
  1143  			// functions (and all transitive callees) must be
  1144  			// nosplit.
  1145  			//
  1146  			// N.B. uintptrescapes implies uintptrkeepalive but it
  1147  			// is OK since the arguments must escape to the heap.
  1148  			//
  1149  			// TODO(prattmic): Add recursive nosplit check of callees.
  1150  			// TODO(prattmic): Functions with no body (i.e.,
  1151  			// assembly) must also be nosplit, but we can't check
  1152  			// that here.
  1153  			w.p.errorf(decl, "go:uintptrkeepalive requires go:nosplit")
  1154  		}
  1155  	} else {
  1156  		if base.Flag.Complete || decl.Name.Value == "init" {
  1157  			// Linknamed functions are allowed to have no body. Hopefully
  1158  			// the linkname target has a body. See issue 23311.
  1159  			// Wasmimport functions are also allowed to have no body.
  1160  			if _, ok := w.p.linknames[obj]; !ok && wi == nil {
  1161  				w.p.errorf(decl, "missing function body")
  1162  			}
  1163  		}
  1164  	}
  1165  
  1166  	sig, block := obj.Type().(*types2.Signature), decl.Body
  1167  	body, closureVars := w.p.bodyIdx(sig, block, w.dict)
  1168  	if len(closureVars) > 0 {
  1169  		fmt.Fprintln(os.Stderr, "CLOSURE", closureVars)
  1170  	}
  1171  	assert(len(closureVars) == 0)
  1172  
  1173  	w.Sync(pkgbits.SyncFuncExt)
  1174  	w.pragmaFlag(pragma)
  1175  	w.linkname(obj)
  1176  
  1177  	if buildcfg.GOARCH == "wasm" {
  1178  		if wi != nil {
  1179  			w.String(wi.Module)
  1180  			w.String(wi.Name)
  1181  		} else {
  1182  			w.String("")
  1183  			w.String("")
  1184  		}
  1185  		if we != nil {
  1186  			w.String(we.Name)
  1187  		} else {
  1188  			w.String("")
  1189  		}
  1190  	}
  1191  
  1192  	w.Bool(false) // stub extension
  1193  	w.Reloc(pkgbits.SectionBody, body)
  1194  	w.Sync(pkgbits.SyncEOF)
  1195  }
  1196  
  1197  func (w *writer) typeExt(obj *types2.TypeName) {
  1198  	decl, ok := w.p.typDecls[obj]
  1199  	assert(ok)
  1200  
  1201  	w.Sync(pkgbits.SyncTypeExt)
  1202  
  1203  	w.pragmaFlag(asPragmaFlag(decl.Pragma))
  1204  
  1205  	// No LSym.SymIdx info yet.
  1206  	w.Int64(-1)
  1207  	w.Int64(-1)
  1208  }
  1209  
  1210  func (w *writer) varExt(obj *types2.Var) {
  1211  	w.Sync(pkgbits.SyncVarExt)
  1212  	w.linkname(obj)
  1213  }
  1214  
  1215  func (w *writer) linkname(obj types2.Object) {
  1216  	w.Sync(pkgbits.SyncLinkname)
  1217  	w.Int64(-1)
  1218  	info := w.p.linknames[obj]
  1219  	w.String(info.remote)
  1220  	w.Bool(info.std)
  1221  }
  1222  
  1223  func (w *writer) pragmaFlag(p ir.PragmaFlag) {
  1224  	w.Sync(pkgbits.SyncPragma)
  1225  	w.Int(int(p))
  1226  }
  1227  
  1228  // @@@ Function bodies
  1229  
  1230  // bodyIdx returns the index for the given function body (specified by
  1231  // block), adding it to the export data
  1232  func (pw *pkgWriter) bodyIdx(sig *types2.Signature, block *syntax.BlockStmt, dict *writerDict) (idx index, closureVars []posVar) {
  1233  	w := pw.newWriter(pkgbits.SectionBody, pkgbits.SyncFuncBody)
  1234  	w.sig = sig
  1235  	w.dict = dict
  1236  
  1237  	w.declareParams(sig)
  1238  	if w.Bool(block != nil) {
  1239  		w.stmts(block.List)
  1240  		w.pos(block.Rbrace)
  1241  	}
  1242  
  1243  	return w.Flush(), w.closureVars
  1244  }
  1245  
  1246  func (w *writer) declareParams(sig *types2.Signature) {
  1247  	addLocals := func(params *types2.Tuple) {
  1248  		for i := 0; i < params.Len(); i++ {
  1249  			w.addLocal(params.At(i))
  1250  		}
  1251  	}
  1252  
  1253  	if recv := sig.Recv(); recv != nil {
  1254  		w.addLocal(recv)
  1255  	}
  1256  	addLocals(sig.Params())
  1257  	addLocals(sig.Results())
  1258  }
  1259  
  1260  // addLocal records the declaration of a new local variable.
  1261  func (w *writer) addLocal(obj *types2.Var) {
  1262  	idx := len(w.localsIdx)
  1263  
  1264  	w.Sync(pkgbits.SyncAddLocal)
  1265  	if w.p.SyncMarkers() {
  1266  		w.Int(idx)
  1267  	}
  1268  	w.varDictIndex(obj)
  1269  
  1270  	if w.localsIdx == nil {
  1271  		w.localsIdx = make(map[*types2.Var]int)
  1272  	}
  1273  	w.localsIdx[obj] = idx
  1274  }
  1275  
  1276  // useLocal writes a reference to the given local or free variable
  1277  // into the bitstream.
  1278  func (w *writer) useLocal(pos syntax.Pos, obj *types2.Var) {
  1279  	w.Sync(pkgbits.SyncUseObjLocal)
  1280  
  1281  	if idx, ok := w.localsIdx[obj]; w.Bool(ok) {
  1282  		w.Len(idx)
  1283  		return
  1284  	}
  1285  
  1286  	idx, ok := w.closureVarsIdx[obj]
  1287  	if !ok {
  1288  		if w.closureVarsIdx == nil {
  1289  			w.closureVarsIdx = make(map[*types2.Var]int)
  1290  		}
  1291  		idx = len(w.closureVars)
  1292  		w.closureVars = append(w.closureVars, posVar{pos, obj})
  1293  		w.closureVarsIdx[obj] = idx
  1294  	}
  1295  	w.Len(idx)
  1296  }
  1297  
  1298  func (w *writer) openScope(pos syntax.Pos) {
  1299  	w.Sync(pkgbits.SyncOpenScope)
  1300  	w.pos(pos)
  1301  }
  1302  
  1303  func (w *writer) closeScope(pos syntax.Pos) {
  1304  	w.Sync(pkgbits.SyncCloseScope)
  1305  	w.pos(pos)
  1306  	w.closeAnotherScope()
  1307  }
  1308  
  1309  func (w *writer) closeAnotherScope() {
  1310  	w.Sync(pkgbits.SyncCloseAnotherScope)
  1311  }
  1312  
  1313  // @@@ Statements
  1314  
  1315  // stmt writes the given statement into the function body bitstream.
  1316  func (w *writer) stmt(stmt syntax.Stmt) {
  1317  	var stmts []syntax.Stmt
  1318  	if stmt != nil {
  1319  		stmts = []syntax.Stmt{stmt}
  1320  	}
  1321  	w.stmts(stmts)
  1322  }
  1323  
  1324  func (w *writer) stmts(stmts []syntax.Stmt) {
  1325  	dead := false
  1326  	w.Sync(pkgbits.SyncStmts)
  1327  	var lastLabel = -1
  1328  	for i, stmt := range stmts {
  1329  		if _, ok := stmt.(*syntax.LabeledStmt); ok {
  1330  			lastLabel = i
  1331  		}
  1332  	}
  1333  	for i, stmt := range stmts {
  1334  		if dead && i > lastLabel {
  1335  			// Any statements after a terminating and last label statement are safe to omit.
  1336  			// Otherwise, code after label statement may refer to dead stmts between terminating
  1337  			// and label statement, see issue #65593.
  1338  			if _, ok := stmt.(*syntax.LabeledStmt); !ok {
  1339  				continue
  1340  			}
  1341  		}
  1342  		w.stmt1(stmt)
  1343  		dead = w.p.terminates(stmt)
  1344  	}
  1345  	w.Code(stmtEnd)
  1346  	w.Sync(pkgbits.SyncStmtsEnd)
  1347  }
  1348  
  1349  func (w *writer) stmt1(stmt syntax.Stmt) {
  1350  	switch stmt := stmt.(type) {
  1351  	default:
  1352  		w.p.unexpected("statement", stmt)
  1353  
  1354  	case nil, *syntax.EmptyStmt:
  1355  		return
  1356  
  1357  	case *syntax.AssignStmt:
  1358  		switch {
  1359  		case stmt.Rhs == nil:
  1360  			w.Code(stmtIncDec)
  1361  			w.op(binOps[stmt.Op])
  1362  			w.expr(stmt.Lhs)
  1363  			w.pos(stmt)
  1364  
  1365  		case stmt.Op != 0 && stmt.Op != syntax.Def:
  1366  			w.Code(stmtAssignOp)
  1367  			w.op(binOps[stmt.Op])
  1368  			w.expr(stmt.Lhs)
  1369  			w.pos(stmt)
  1370  
  1371  			var typ types2.Type
  1372  			if stmt.Op != syntax.Shl && stmt.Op != syntax.Shr {
  1373  				typ = w.p.typeOf(stmt.Lhs)
  1374  			}
  1375  			w.implicitConvExpr(typ, stmt.Rhs)
  1376  
  1377  		default:
  1378  			w.assignStmt(stmt, stmt.Lhs, stmt.Rhs)
  1379  		}
  1380  
  1381  	case *syntax.BlockStmt:
  1382  		w.Code(stmtBlock)
  1383  		w.blockStmt(stmt)
  1384  
  1385  	case *syntax.BranchStmt:
  1386  		w.Code(stmtBranch)
  1387  		w.pos(stmt)
  1388  		var op ir.Op
  1389  		switch stmt.Tok {
  1390  		case syntax.Break:
  1391  			op = ir.OBREAK
  1392  		case syntax.Continue:
  1393  			op = ir.OCONTINUE
  1394  		case syntax.Fallthrough:
  1395  			op = ir.OFALL
  1396  		case syntax.Goto:
  1397  			op = ir.OGOTO
  1398  		}
  1399  		w.op(op)
  1400  		w.optLabel(stmt.Label)
  1401  
  1402  	case *syntax.CallStmt:
  1403  		w.Code(stmtCall)
  1404  		w.pos(stmt)
  1405  		var op ir.Op
  1406  		switch stmt.Tok {
  1407  		case syntax.Defer:
  1408  			op = ir.ODEFER
  1409  		case syntax.Go:
  1410  			op = ir.OGO
  1411  		}
  1412  		w.op(op)
  1413  		w.expr(stmt.Call)
  1414  		if stmt.Tok == syntax.Defer {
  1415  			w.optExpr(stmt.DeferAt)
  1416  		}
  1417  
  1418  	case *syntax.DeclStmt:
  1419  		for _, decl := range stmt.DeclList {
  1420  			w.declStmt(decl)
  1421  		}
  1422  
  1423  	case *syntax.ExprStmt:
  1424  		w.Code(stmtExpr)
  1425  		w.expr(stmt.X)
  1426  
  1427  	case *syntax.ForStmt:
  1428  		w.Code(stmtFor)
  1429  		w.forStmt(stmt)
  1430  
  1431  	case *syntax.IfStmt:
  1432  		w.Code(stmtIf)
  1433  		w.ifStmt(stmt)
  1434  
  1435  	case *syntax.LabeledStmt:
  1436  		w.Code(stmtLabel)
  1437  		w.pos(stmt)
  1438  		w.label(stmt.Label)
  1439  		w.stmt1(stmt.Stmt)
  1440  
  1441  	case *syntax.ReturnStmt:
  1442  		w.Code(stmtReturn)
  1443  		w.pos(stmt)
  1444  
  1445  		resultTypes := w.sig.Results()
  1446  		dstType := func(i int) types2.Type {
  1447  			return resultTypes.At(i).Type()
  1448  		}
  1449  		w.multiExpr(stmt, dstType, syntax.UnpackListExpr(stmt.Results))
  1450  
  1451  	case *syntax.SelectStmt:
  1452  		w.Code(stmtSelect)
  1453  		w.selectStmt(stmt)
  1454  
  1455  	case *syntax.SendStmt:
  1456  		chanType := types2.CoreType(w.p.typeOf(stmt.Chan)).(*types2.Chan)
  1457  
  1458  		w.Code(stmtSend)
  1459  		w.pos(stmt)
  1460  		w.expr(stmt.Chan)
  1461  		w.implicitConvExpr(chanType.Elem(), stmt.Value)
  1462  
  1463  	case *syntax.SwitchStmt:
  1464  		w.Code(stmtSwitch)
  1465  		w.switchStmt(stmt)
  1466  	}
  1467  }
  1468  
  1469  func (w *writer) assignList(expr syntax.Expr) {
  1470  	exprs := syntax.UnpackListExpr(expr)
  1471  	w.Len(len(exprs))
  1472  
  1473  	for _, expr := range exprs {
  1474  		w.assign(expr)
  1475  	}
  1476  }
  1477  
  1478  func (w *writer) assign(expr syntax.Expr) {
  1479  	expr = syntax.Unparen(expr)
  1480  
  1481  	if name, ok := expr.(*syntax.Name); ok {
  1482  		if name.Value == "_" {
  1483  			w.Code(assignBlank)
  1484  			return
  1485  		}
  1486  
  1487  		if obj, ok := w.p.info.Defs[name]; ok {
  1488  			obj := obj.(*types2.Var)
  1489  
  1490  			w.Code(assignDef)
  1491  			w.pos(obj)
  1492  			w.localIdent(obj)
  1493  			w.typ(obj.Type())
  1494  
  1495  			// TODO(mdempsky): Minimize locals index size by deferring
  1496  			// this until the variables actually come into scope.
  1497  			w.addLocal(obj)
  1498  			return
  1499  		}
  1500  	}
  1501  
  1502  	w.Code(assignExpr)
  1503  	w.expr(expr)
  1504  }
  1505  
  1506  func (w *writer) declStmt(decl syntax.Decl) {
  1507  	switch decl := decl.(type) {
  1508  	default:
  1509  		w.p.unexpected("declaration", decl)
  1510  
  1511  	case *syntax.ConstDecl, *syntax.TypeDecl:
  1512  
  1513  	case *syntax.VarDecl:
  1514  		w.assignStmt(decl, namesAsExpr(decl.NameList), decl.Values)
  1515  	}
  1516  }
  1517  
  1518  // assignStmt writes out an assignment for "lhs = rhs".
  1519  func (w *writer) assignStmt(pos poser, lhs0, rhs0 syntax.Expr) {
  1520  	lhs := syntax.UnpackListExpr(lhs0)
  1521  	rhs := syntax.UnpackListExpr(rhs0)
  1522  
  1523  	w.Code(stmtAssign)
  1524  	w.pos(pos)
  1525  
  1526  	// As if w.assignList(lhs0).
  1527  	w.Len(len(lhs))
  1528  	for _, expr := range lhs {
  1529  		w.assign(expr)
  1530  	}
  1531  
  1532  	dstType := func(i int) types2.Type {
  1533  		dst := lhs[i]
  1534  
  1535  		// Finding dstType is somewhat involved, because for VarDecl
  1536  		// statements, the Names are only added to the info.{Defs,Uses}
  1537  		// maps, not to info.Types.
  1538  		if name, ok := syntax.Unparen(dst).(*syntax.Name); ok {
  1539  			if name.Value == "_" {
  1540  				return nil // ok: no implicit conversion
  1541  			} else if def, ok := w.p.info.Defs[name].(*types2.Var); ok {
  1542  				return def.Type()
  1543  			} else if use, ok := w.p.info.Uses[name].(*types2.Var); ok {
  1544  				return use.Type()
  1545  			} else {
  1546  				w.p.fatalf(dst, "cannot find type of destination object: %v", dst)
  1547  			}
  1548  		}
  1549  
  1550  		return w.p.typeOf(dst)
  1551  	}
  1552  
  1553  	w.multiExpr(pos, dstType, rhs)
  1554  }
  1555  
  1556  func (w *writer) blockStmt(stmt *syntax.BlockStmt) {
  1557  	w.Sync(pkgbits.SyncBlockStmt)
  1558  	w.openScope(stmt.Pos())
  1559  	w.stmts(stmt.List)
  1560  	w.closeScope(stmt.Rbrace)
  1561  }
  1562  
  1563  func (w *writer) forStmt(stmt *syntax.ForStmt) {
  1564  	w.Sync(pkgbits.SyncForStmt)
  1565  	w.openScope(stmt.Pos())
  1566  
  1567  	if rang, ok := stmt.Init.(*syntax.RangeClause); w.Bool(ok) {
  1568  		w.pos(rang)
  1569  		w.assignList(rang.Lhs)
  1570  		w.expr(rang.X)
  1571  
  1572  		xtyp := w.p.typeOf(rang.X)
  1573  		if _, isMap := types2.CoreType(xtyp).(*types2.Map); isMap {
  1574  			w.rtype(xtyp)
  1575  		}
  1576  		{
  1577  			lhs := syntax.UnpackListExpr(rang.Lhs)
  1578  			assign := func(i int, src types2.Type) {
  1579  				if i >= len(lhs) {
  1580  					return
  1581  				}
  1582  				dst := syntax.Unparen(lhs[i])
  1583  				if name, ok := dst.(*syntax.Name); ok && name.Value == "_" {
  1584  					return
  1585  				}
  1586  
  1587  				var dstType types2.Type
  1588  				if rang.Def {
  1589  					// For `:=` assignments, the LHS names only appear in Defs,
  1590  					// not Types (as used by typeOf).
  1591  					dstType = w.p.info.Defs[dst.(*syntax.Name)].(*types2.Var).Type()
  1592  				} else {
  1593  					dstType = w.p.typeOf(dst)
  1594  				}
  1595  
  1596  				w.convRTTI(src, dstType)
  1597  			}
  1598  
  1599  			keyType, valueType := types2.RangeKeyVal(w.p.typeOf(rang.X))
  1600  			assign(0, keyType)
  1601  			assign(1, valueType)
  1602  		}
  1603  
  1604  	} else {
  1605  		if stmt.Cond != nil && w.p.staticBool(&stmt.Cond) < 0 { // always false
  1606  			stmt.Post = nil
  1607  			stmt.Body.List = nil
  1608  		}
  1609  
  1610  		w.pos(stmt)
  1611  		w.stmt(stmt.Init)
  1612  		w.optExpr(stmt.Cond)
  1613  		w.stmt(stmt.Post)
  1614  	}
  1615  
  1616  	w.blockStmt(stmt.Body)
  1617  	w.Bool(w.distinctVars(stmt))
  1618  	w.closeAnotherScope()
  1619  }
  1620  
  1621  func (w *writer) distinctVars(stmt *syntax.ForStmt) bool {
  1622  	lv := base.Debug.LoopVar
  1623  	fileVersion := w.p.info.FileVersions[stmt.Pos().FileBase()]
  1624  	is122 := fileVersion == "" || version.Compare(fileVersion, "go1.22") >= 0
  1625  
  1626  	// Turning off loopvar for 1.22 is only possible with loopvarhash=qn
  1627  	//
  1628  	// Debug.LoopVar values to be preserved for 1.21 compatibility are 1 and 2,
  1629  	// which are also set (=1) by GOEXPERIMENT=loopvar.  The knobs for turning on
  1630  	// the new, unshared, loopvar behavior apply to versions less than 1.21 because
  1631  	// (1) 1.21 also did that and (2) this is believed to be the likely use case;
  1632  	// anyone checking to see if it affects their code will just run the GOEXPERIMENT
  1633  	// but will not also update all their go.mod files to 1.21.
  1634  	//
  1635  	// -gcflags=-d=loopvar=3 enables logging for 1.22 but does not turn loopvar on for <= 1.21.
  1636  
  1637  	return is122 || lv > 0 && lv != 3
  1638  }
  1639  
  1640  func (w *writer) ifStmt(stmt *syntax.IfStmt) {
  1641  	cond := w.p.staticBool(&stmt.Cond)
  1642  
  1643  	w.Sync(pkgbits.SyncIfStmt)
  1644  	w.openScope(stmt.Pos())
  1645  	w.pos(stmt)
  1646  	w.stmt(stmt.Init)
  1647  	w.expr(stmt.Cond)
  1648  	w.Int(cond)
  1649  	if cond >= 0 {
  1650  		w.blockStmt(stmt.Then)
  1651  	} else {
  1652  		w.pos(stmt.Then.Rbrace)
  1653  	}
  1654  	if cond <= 0 {
  1655  		w.stmt(stmt.Else)
  1656  	}
  1657  	w.closeAnotherScope()
  1658  }
  1659  
  1660  func (w *writer) selectStmt(stmt *syntax.SelectStmt) {
  1661  	w.Sync(pkgbits.SyncSelectStmt)
  1662  
  1663  	w.pos(stmt)
  1664  	w.Len(len(stmt.Body))
  1665  	for i, clause := range stmt.Body {
  1666  		if i > 0 {
  1667  			w.closeScope(clause.Pos())
  1668  		}
  1669  		w.openScope(clause.Pos())
  1670  
  1671  		w.pos(clause)
  1672  		w.stmt(clause.Comm)
  1673  		w.stmts(clause.Body)
  1674  	}
  1675  	if len(stmt.Body) > 0 {
  1676  		w.closeScope(stmt.Rbrace)
  1677  	}
  1678  }
  1679  
  1680  func (w *writer) switchStmt(stmt *syntax.SwitchStmt) {
  1681  	w.Sync(pkgbits.SyncSwitchStmt)
  1682  
  1683  	w.openScope(stmt.Pos())
  1684  	w.pos(stmt)
  1685  	w.stmt(stmt.Init)
  1686  
  1687  	var iface, tagType types2.Type
  1688  	var tagTypeIsChan bool
  1689  	if guard, ok := stmt.Tag.(*syntax.TypeSwitchGuard); w.Bool(ok) {
  1690  		iface = w.p.typeOf(guard.X)
  1691  
  1692  		w.pos(guard)
  1693  		if tag := guard.Lhs; w.Bool(tag != nil) {
  1694  			w.pos(tag)
  1695  
  1696  			// Like w.localIdent, but we don't have a types2.Object.
  1697  			w.Sync(pkgbits.SyncLocalIdent)
  1698  			w.pkg(w.p.curpkg)
  1699  			w.String(tag.Value)
  1700  		}
  1701  		w.expr(guard.X)
  1702  	} else {
  1703  		tag := stmt.Tag
  1704  
  1705  		var tagValue constant.Value
  1706  		if tag != nil {
  1707  			tv := w.p.typeAndValue(tag)
  1708  			tagType = tv.Type
  1709  			tagValue = tv.Value
  1710  			_, tagTypeIsChan = tagType.Underlying().(*types2.Chan)
  1711  		} else {
  1712  			tagType = types2.Typ[types2.Bool]
  1713  			tagValue = constant.MakeBool(true)
  1714  		}
  1715  
  1716  		if tagValue != nil {
  1717  			// If the switch tag has a constant value, look for a case
  1718  			// clause that we always branch to.
  1719  			func() {
  1720  				var target *syntax.CaseClause
  1721  			Outer:
  1722  				for _, clause := range stmt.Body {
  1723  					if clause.Cases == nil {
  1724  						target = clause
  1725  					}
  1726  					for _, cas := range syntax.UnpackListExpr(clause.Cases) {
  1727  						tv := w.p.typeAndValue(cas)
  1728  						if tv.Value == nil {
  1729  							return // non-constant case; give up
  1730  						}
  1731  						if constant.Compare(tagValue, token.EQL, tv.Value) {
  1732  							target = clause
  1733  							break Outer
  1734  						}
  1735  					}
  1736  				}
  1737  				// We've found the target clause, if any.
  1738  
  1739  				if target != nil {
  1740  					if hasFallthrough(target.Body) {
  1741  						return // fallthrough is tricky; give up
  1742  					}
  1743  
  1744  					// Rewrite as single "default" case.
  1745  					target.Cases = nil
  1746  					stmt.Body = []*syntax.CaseClause{target}
  1747  				} else {
  1748  					stmt.Body = nil
  1749  				}
  1750  
  1751  				// Clear switch tag (i.e., replace with implicit "true").
  1752  				tag = nil
  1753  				stmt.Tag = nil
  1754  				tagType = types2.Typ[types2.Bool]
  1755  			}()
  1756  		}
  1757  
  1758  		// Walk is going to emit comparisons between the tag value and
  1759  		// each case expression, and we want these comparisons to always
  1760  		// have the same type. If there are any case values that can't be
  1761  		// converted to the tag value's type, then convert everything to
  1762  		// `any` instead.
  1763  		//
  1764  		// Except that we need to keep comparisons of channel values from
  1765  		// being wrapped in any(). See issue #67190.
  1766  
  1767  		if !tagTypeIsChan {
  1768  		Outer:
  1769  			for _, clause := range stmt.Body {
  1770  				for _, cas := range syntax.UnpackListExpr(clause.Cases) {
  1771  					if casType := w.p.typeOf(cas); !types2.AssignableTo(casType, tagType) && (types2.IsInterface(casType) || types2.IsInterface(tagType)) {
  1772  						tagType = types2.NewInterfaceType(nil, nil)
  1773  						break Outer
  1774  					}
  1775  				}
  1776  			}
  1777  		}
  1778  
  1779  		if w.Bool(tag != nil) {
  1780  			w.implicitConvExpr(tagType, tag)
  1781  		}
  1782  	}
  1783  
  1784  	w.Len(len(stmt.Body))
  1785  	for i, clause := range stmt.Body {
  1786  		if i > 0 {
  1787  			w.closeScope(clause.Pos())
  1788  		}
  1789  		w.openScope(clause.Pos())
  1790  
  1791  		w.pos(clause)
  1792  
  1793  		cases := syntax.UnpackListExpr(clause.Cases)
  1794  		if iface != nil {
  1795  			w.Len(len(cases))
  1796  			for _, cas := range cases {
  1797  				if w.Bool(isNil(w.p, cas)) {
  1798  					continue
  1799  				}
  1800  				w.exprType(iface, cas)
  1801  			}
  1802  		} else {
  1803  			// As if w.exprList(clause.Cases),
  1804  			// but with implicit conversions to tagType.
  1805  
  1806  			w.Sync(pkgbits.SyncExprList)
  1807  			w.Sync(pkgbits.SyncExprs)
  1808  			w.Len(len(cases))
  1809  			for _, cas := range cases {
  1810  				typ := tagType
  1811  				if tagTypeIsChan {
  1812  					typ = nil
  1813  				}
  1814  				w.implicitConvExpr(typ, cas)
  1815  			}
  1816  		}
  1817  
  1818  		if obj, ok := w.p.info.Implicits[clause]; ok {
  1819  			// TODO(mdempsky): These pos details are quirkish, but also
  1820  			// necessary so the variable's position is correct for DWARF
  1821  			// scope assignment later. It would probably be better for us to
  1822  			// instead just set the variable's DWARF scoping info earlier so
  1823  			// we can give it the correct position information.
  1824  			pos := clause.Pos()
  1825  			if typs := syntax.UnpackListExpr(clause.Cases); len(typs) != 0 {
  1826  				pos = typeExprEndPos(typs[len(typs)-1])
  1827  			}
  1828  			w.pos(pos)
  1829  
  1830  			obj := obj.(*types2.Var)
  1831  			w.typ(obj.Type())
  1832  			w.addLocal(obj)
  1833  		}
  1834  
  1835  		w.stmts(clause.Body)
  1836  	}
  1837  	if len(stmt.Body) > 0 {
  1838  		w.closeScope(stmt.Rbrace)
  1839  	}
  1840  
  1841  	w.closeScope(stmt.Rbrace)
  1842  }
  1843  
  1844  func (w *writer) label(label *syntax.Name) {
  1845  	w.Sync(pkgbits.SyncLabel)
  1846  
  1847  	// TODO(mdempsky): Replace label strings with dense indices.
  1848  	w.String(label.Value)
  1849  }
  1850  
  1851  func (w *writer) optLabel(label *syntax.Name) {
  1852  	w.Sync(pkgbits.SyncOptLabel)
  1853  	if w.Bool(label != nil) {
  1854  		w.label(label)
  1855  	}
  1856  }
  1857  
  1858  // @@@ Expressions
  1859  
  1860  // expr writes the given expression into the function body bitstream.
  1861  func (w *writer) expr(expr syntax.Expr) {
  1862  	base.Assertf(expr != nil, "missing expression")
  1863  
  1864  	expr = syntax.Unparen(expr) // skip parens; unneeded after typecheck
  1865  
  1866  	obj, inst := lookupObj(w.p, expr)
  1867  	targs := asTypeSlice(inst.TypeArgs)
  1868  
  1869  	if tv, ok := w.p.maybeTypeAndValue(expr); ok {
  1870  		if tv.IsRuntimeHelper() {
  1871  			if pkg := obj.Pkg(); pkg != nil && pkg.Name() == "runtime" {
  1872  				objName := obj.Name()
  1873  				w.Code(exprRuntimeBuiltin)
  1874  				w.String(objName)
  1875  				return
  1876  			}
  1877  		}
  1878  
  1879  		if tv.IsType() {
  1880  			w.p.fatalf(expr, "unexpected type expression %v", syntax.String(expr))
  1881  		}
  1882  
  1883  		if tv.Value != nil {
  1884  			w.Code(exprConst)
  1885  			w.pos(expr)
  1886  			typ := idealType(tv)
  1887  			assert(typ != nil)
  1888  			w.typ(typ)
  1889  			w.Value(tv.Value)
  1890  			return
  1891  		}
  1892  
  1893  		if _, isNil := obj.(*types2.Nil); isNil {
  1894  			w.Code(exprZero)
  1895  			w.pos(expr)
  1896  			w.typ(tv.Type)
  1897  			return
  1898  		}
  1899  
  1900  		// With shape types (and particular pointer shaping), we may have
  1901  		// an expression of type "go.shape.*uint8", but need to reshape it
  1902  		// to another shape-identical type to allow use in field
  1903  		// selection, indexing, etc.
  1904  		if typ := tv.Type; !tv.IsBuiltin() && !isTuple(typ) && !isUntyped(typ) {
  1905  			w.Code(exprReshape)
  1906  			w.typ(typ)
  1907  			// fallthrough
  1908  		}
  1909  	}
  1910  
  1911  	if obj != nil {
  1912  		if len(targs) != 0 {
  1913  			obj := obj.(*types2.Func)
  1914  
  1915  			w.Code(exprFuncInst)
  1916  			w.pos(expr)
  1917  			w.funcInst(obj, targs)
  1918  			return
  1919  		}
  1920  
  1921  		if isGlobal(obj) {
  1922  			w.Code(exprGlobal)
  1923  			w.obj(obj, nil)
  1924  			return
  1925  		}
  1926  
  1927  		obj := obj.(*types2.Var)
  1928  		assert(!obj.IsField())
  1929  
  1930  		w.Code(exprLocal)
  1931  		w.useLocal(expr.Pos(), obj)
  1932  		return
  1933  	}
  1934  
  1935  	switch expr := expr.(type) {
  1936  	default:
  1937  		w.p.unexpected("expression", expr)
  1938  
  1939  	case *syntax.CompositeLit:
  1940  		w.Code(exprCompLit)
  1941  		w.compLit(expr)
  1942  
  1943  	case *syntax.FuncLit:
  1944  		w.Code(exprFuncLit)
  1945  		w.funcLit(expr)
  1946  
  1947  	case *syntax.SelectorExpr:
  1948  		sel, ok := w.p.info.Selections[expr]
  1949  		assert(ok)
  1950  
  1951  		switch sel.Kind() {
  1952  		default:
  1953  			w.p.fatalf(expr, "unexpected selection kind: %v", sel.Kind())
  1954  
  1955  		case types2.FieldVal:
  1956  			w.Code(exprFieldVal)
  1957  			w.expr(expr.X)
  1958  			w.pos(expr)
  1959  			w.selector(sel.Obj())
  1960  
  1961  		case types2.MethodVal:
  1962  			w.methVal(expr, sel)
  1963  
  1964  		case types2.MethodExpr:
  1965  			w.methExpr(expr, sel)
  1966  		}
  1967  
  1968  	case *syntax.IndexExpr:
  1969  		// might be explicit instantiation of a generic method
  1970  		if selector, ok := expr.X.(*syntax.SelectorExpr); ok {
  1971  			if sel, ok := w.p.info.Selections[selector]; ok {
  1972  				switch sel.Kind() {
  1973  				default:
  1974  					w.p.fatalf(selector, "unexpected selection kind: %v", sel.Kind())
  1975  				case types2.FieldVal:
  1976  					// not a method
  1977  				case types2.MethodVal:
  1978  					w.methVal(selector, sel)
  1979  					return
  1980  				case types2.MethodExpr:
  1981  					w.methExpr(selector, sel)
  1982  					return
  1983  				}
  1984  			}
  1985  		}
  1986  		_ = w.p.typeOf(expr.Index) // ensure this is an index expression, not an instantiation
  1987  
  1988  		xtyp := w.p.typeOf(expr.X)
  1989  
  1990  		var keyType types2.Type
  1991  		if mapType, ok := types2.CoreType(xtyp).(*types2.Map); ok {
  1992  			keyType = mapType.Key()
  1993  		}
  1994  
  1995  		w.Code(exprIndex)
  1996  		w.expr(expr.X)
  1997  		w.pos(expr)
  1998  		w.implicitConvExpr(keyType, expr.Index)
  1999  		if keyType != nil {
  2000  			w.rtype(xtyp)
  2001  		}
  2002  
  2003  	case *syntax.SliceExpr:
  2004  		w.Code(exprSlice)
  2005  		w.expr(expr.X)
  2006  		w.pos(expr)
  2007  		for _, n := range &expr.Index {
  2008  			w.optExpr(n)
  2009  		}
  2010  
  2011  	case *syntax.AssertExpr:
  2012  		iface := w.p.typeOf(expr.X)
  2013  
  2014  		w.Code(exprAssert)
  2015  		w.expr(expr.X)
  2016  		w.pos(expr)
  2017  		w.exprType(iface, expr.Type)
  2018  		w.rtype(iface)
  2019  
  2020  	case *syntax.Operation:
  2021  		if expr.Y == nil {
  2022  			w.Code(exprUnaryOp)
  2023  			w.op(unOps[expr.Op])
  2024  			w.pos(expr)
  2025  			w.expr(expr.X)
  2026  			break
  2027  		}
  2028  
  2029  		var commonType types2.Type
  2030  		switch expr.Op {
  2031  		case syntax.Shl, syntax.Shr:
  2032  			// ok: operands are allowed to have different types
  2033  		default:
  2034  			xtyp := w.p.typeOf(expr.X)
  2035  			ytyp := w.p.typeOf(expr.Y)
  2036  			switch {
  2037  			case types2.AssignableTo(xtyp, ytyp):
  2038  				commonType = ytyp
  2039  			case types2.AssignableTo(ytyp, xtyp):
  2040  				commonType = xtyp
  2041  			default:
  2042  				w.p.fatalf(expr, "failed to find common type between %v and %v", xtyp, ytyp)
  2043  			}
  2044  		}
  2045  
  2046  		w.Code(exprBinaryOp)
  2047  		w.op(binOps[expr.Op])
  2048  		w.implicitConvExpr(commonType, expr.X)
  2049  		w.pos(expr)
  2050  		w.implicitConvExpr(commonType, expr.Y)
  2051  
  2052  	case *syntax.CallExpr:
  2053  		tv := w.p.typeAndValue(expr.Fun)
  2054  		if tv.IsType() {
  2055  			assert(len(expr.ArgList) == 1)
  2056  			assert(!expr.HasDots)
  2057  			w.convertExpr(tv.Type, expr.ArgList[0], false)
  2058  			break
  2059  		}
  2060  
  2061  		var rtype types2.Type
  2062  		if tv.IsBuiltin() {
  2063  			switch obj, _ := lookupObj(w.p, syntax.Unparen(expr.Fun)); obj.Name() {
  2064  			case "make":
  2065  				assert(len(expr.ArgList) >= 1)
  2066  				assert(!expr.HasDots)
  2067  
  2068  				w.Code(exprMake)
  2069  				w.pos(expr)
  2070  				w.exprType(nil, expr.ArgList[0])
  2071  				w.exprs(expr.ArgList[1:])
  2072  
  2073  				typ := w.p.typeOf(expr)
  2074  				switch coreType := types2.CoreType(typ).(type) {
  2075  				default:
  2076  					w.p.fatalf(expr, "unexpected core type: %v", coreType)
  2077  				case *types2.Chan:
  2078  					w.rtype(typ)
  2079  				case *types2.Map:
  2080  					w.rtype(typ)
  2081  				case *types2.Slice:
  2082  					w.rtype(sliceElem(typ))
  2083  				}
  2084  
  2085  				return
  2086  
  2087  			case "new":
  2088  				assert(len(expr.ArgList) == 1)
  2089  				assert(!expr.HasDots)
  2090  				arg := expr.ArgList[0]
  2091  
  2092  				w.Code(exprNew)
  2093  				w.pos(expr)
  2094  				tv := w.p.typeAndValue(arg)
  2095  				if w.Bool(!tv.IsType()) {
  2096  					w.expr(arg) // new(expr), go1.26
  2097  				} else {
  2098  					w.exprType(nil, arg) // new(T)
  2099  				}
  2100  				return
  2101  
  2102  			case "Sizeof":
  2103  				assert(len(expr.ArgList) == 1)
  2104  				assert(!expr.HasDots)
  2105  
  2106  				w.Code(exprSizeof)
  2107  				w.pos(expr)
  2108  				w.typ(w.p.typeOf(expr.ArgList[0]))
  2109  				return
  2110  
  2111  			case "Alignof":
  2112  				assert(len(expr.ArgList) == 1)
  2113  				assert(!expr.HasDots)
  2114  
  2115  				w.Code(exprAlignof)
  2116  				w.pos(expr)
  2117  				w.typ(w.p.typeOf(expr.ArgList[0]))
  2118  				return
  2119  
  2120  			case "Offsetof":
  2121  				assert(len(expr.ArgList) == 1)
  2122  				assert(!expr.HasDots)
  2123  				selector := syntax.Unparen(expr.ArgList[0]).(*syntax.SelectorExpr)
  2124  				index := w.p.info.Selections[selector].Index()
  2125  
  2126  				w.Code(exprOffsetof)
  2127  				w.pos(expr)
  2128  				w.typ(deref2(w.p.typeOf(selector.X)))
  2129  				w.Len(len(index) - 1)
  2130  				for _, idx := range index {
  2131  					w.Len(idx)
  2132  				}
  2133  				return
  2134  
  2135  			case "append":
  2136  				rtype = sliceElem(w.p.typeOf(expr))
  2137  			case "copy":
  2138  				typ := w.p.typeOf(expr.ArgList[0])
  2139  				if tuple, ok := typ.(*types2.Tuple); ok { // "copy(g())"
  2140  					typ = tuple.At(0).Type()
  2141  				}
  2142  				rtype = sliceElem(typ)
  2143  			case "delete":
  2144  				typ := w.p.typeOf(expr.ArgList[0])
  2145  				if tuple, ok := typ.(*types2.Tuple); ok { // "delete(g())"
  2146  					typ = tuple.At(0).Type()
  2147  				}
  2148  				rtype = typ
  2149  			case "Slice":
  2150  				rtype = sliceElem(w.p.typeOf(expr))
  2151  			}
  2152  		}
  2153  
  2154  		writeFunExpr := func() {
  2155  			fun := syntax.Unparen(expr.Fun)
  2156  
  2157  			expr := fun
  2158  			if idx, ok := expr.(*syntax.IndexExpr); ok {
  2159  				expr = idx.X
  2160  			}
  2161  			if selector, ok := expr.(*syntax.SelectorExpr); ok {
  2162  				if sel, ok := w.p.info.Selections[selector]; ok && sel.Kind() == types2.MethodVal {
  2163  					w.Bool(true) // method call
  2164  					typ := w.recvExpr(selector, sel)
  2165  					w.methodExpr(selector, typ, sel)
  2166  					return
  2167  				}
  2168  			}
  2169  
  2170  			w.Bool(false) // not a method call (i.e., normal function call)
  2171  
  2172  			if obj, inst := lookupObj(w.p, fun); w.Bool(obj != nil && inst.TypeArgs.Len() != 0) {
  2173  				obj := obj.(*types2.Func)
  2174  
  2175  				w.pos(fun)
  2176  				w.funcInst(obj, asTypeSlice(inst.TypeArgs))
  2177  				return
  2178  			}
  2179  
  2180  			w.expr(fun)
  2181  		}
  2182  
  2183  		sigType := types2.CoreType(tv.Type).(*types2.Signature)
  2184  		paramTypes := sigType.Params()
  2185  
  2186  		w.Code(exprCall)
  2187  		writeFunExpr()
  2188  		w.pos(expr)
  2189  
  2190  		paramType := func(i int) types2.Type {
  2191  			if sigType.Variadic() && !expr.HasDots && i >= paramTypes.Len()-1 {
  2192  				return paramTypes.At(paramTypes.Len() - 1).Type().(*types2.Slice).Elem()
  2193  			}
  2194  			return paramTypes.At(i).Type()
  2195  		}
  2196  
  2197  		w.multiExpr(expr, paramType, expr.ArgList)
  2198  		w.Bool(expr.HasDots)
  2199  		if rtype != nil {
  2200  			w.rtype(rtype)
  2201  		}
  2202  	}
  2203  }
  2204  
  2205  func sliceElem(typ types2.Type) types2.Type {
  2206  	return types2.CoreType(typ).(*types2.Slice).Elem()
  2207  }
  2208  
  2209  func (w *writer) optExpr(expr syntax.Expr) {
  2210  	if w.Bool(expr != nil) {
  2211  		w.expr(expr)
  2212  	}
  2213  }
  2214  
  2215  func (w *writer) methVal(expr *syntax.SelectorExpr, sel *types2.Selection) {
  2216  	w.Code(exprMethodVal)
  2217  	typ := w.recvExpr(expr, sel)
  2218  	w.pos(expr)
  2219  	w.methodExpr(expr, typ, sel)
  2220  }
  2221  
  2222  func (w *writer) methExpr(expr *syntax.SelectorExpr, sel *types2.Selection) {
  2223  	w.Code(exprMethodExpr)
  2224  
  2225  	tv := w.p.typeAndValue(expr.X)
  2226  	assert(tv.IsType())
  2227  
  2228  	index := sel.Index()
  2229  	implicits := index[:len(index)-1]
  2230  
  2231  	typ := tv.Type
  2232  	w.typ(typ)
  2233  
  2234  	w.Len(len(implicits))
  2235  	for _, ix := range implicits {
  2236  		w.Len(ix)
  2237  		typ = deref2(typ).Underlying().(*types2.Struct).Field(ix).Type()
  2238  	}
  2239  
  2240  	recv := sel.Obj().(*types2.Func).Type().(*types2.Signature).Recv().Type()
  2241  	if w.Bool(isPtrTo(typ, recv)) { // need deref
  2242  		typ = recv
  2243  	} else if w.Bool(isPtrTo(recv, typ)) { // need addr
  2244  		typ = recv
  2245  	}
  2246  
  2247  	w.pos(expr)
  2248  	w.methodExpr(expr, typ, sel)
  2249  }
  2250  
  2251  // recvExpr writes out expr.X, but handles any implicit addressing,
  2252  // dereferencing, and field selections appropriate for the method
  2253  // selection.
  2254  func (w *writer) recvExpr(expr *syntax.SelectorExpr, sel *types2.Selection) types2.Type {
  2255  	index := sel.Index()
  2256  	implicits := index[:len(index)-1]
  2257  
  2258  	w.Code(exprRecv)
  2259  	w.expr(expr.X)
  2260  	w.pos(expr)
  2261  	w.Len(len(implicits))
  2262  
  2263  	typ := w.p.typeOf(expr.X)
  2264  	for _, ix := range implicits {
  2265  		typ = deref2(typ).Underlying().(*types2.Struct).Field(ix).Type()
  2266  		w.Len(ix)
  2267  	}
  2268  
  2269  	recv := sel.Obj().(*types2.Func).Type().(*types2.Signature).Recv().Type()
  2270  	if w.Bool(isPtrTo(typ, recv)) { // needs deref
  2271  		typ = recv
  2272  	} else if w.Bool(isPtrTo(recv, typ)) { // needs addr
  2273  		typ = recv
  2274  	}
  2275  
  2276  	return typ
  2277  }
  2278  
  2279  // funcInst writes a reference to an instantiated function.
  2280  func (w *writer) funcInst(obj *types2.Func, targs []types2.Type) {
  2281  	info := w.p.objInstIdx(obj, targs, w.dict)
  2282  
  2283  	// Type arguments list contains derived types; we can emit a static
  2284  	// call to the shaped function, but need to dynamically compute the
  2285  	// runtime dictionary pointer.
  2286  	if w.Bool(info.anyDerived()) {
  2287  		w.Len(w.dict.subdictIdx(info))
  2288  		return
  2289  	}
  2290  
  2291  	// Type arguments list is statically known; we can emit a static
  2292  	// call with a statically reference to the respective runtime
  2293  	// dictionary.
  2294  	w.objInfo(info)
  2295  }
  2296  
  2297  // methodExpr writes out a reference to the method selected by
  2298  // expr. sel should be the corresponding types2.Selection, and recv
  2299  // the type produced after any implicit addressing, dereferencing, and
  2300  // field selection. (Note: recv might differ from sel.Obj()'s receiver
  2301  // parameter in the case of interface types, and is needed for
  2302  // handling type parameter methods.)
  2303  func (w *writer) methodExpr(expr *syntax.SelectorExpr, recv types2.Type, sel *types2.Selection) {
  2304  	fun := sel.Obj().(*types2.Func)
  2305  	sig := fun.Type().(*types2.Signature)
  2306  
  2307  	w.typ(recv)
  2308  
  2309  	// only pass the signature if it's not a generic method
  2310  	if isGenericMethod(sig) {
  2311  		assert(w.Version().Has(pkgbits.GenericMethods))
  2312  		w.Bool(true)
  2313  	} else {
  2314  		if w.Version().Has(pkgbits.GenericMethods) {
  2315  			w.Bool(false)
  2316  		}
  2317  		w.typ(sig)
  2318  	}
  2319  
  2320  	w.pos(expr)
  2321  	w.selector(fun)
  2322  
  2323  	// Method on a type parameter. These require an indirect call
  2324  	// through the current function's runtime dictionary.
  2325  	if typeParam, ok := types2.Unalias(recv).(*types2.TypeParam); w.Bool(ok) {
  2326  		typeParamIdx := w.dict.typeParamIndex(typeParam)
  2327  		methodInfo := w.p.selectorIdx(fun)
  2328  
  2329  		w.Len(w.dict.typeParamMethodExprIdx(typeParamIdx, methodInfo))
  2330  		return
  2331  	}
  2332  
  2333  	if isInterface(recv) != isInterface(sig.Recv().Type()) {
  2334  		w.p.fatalf(expr, "isInterface inconsistency: %v and %v", recv, sig.Recv().Type())
  2335  	}
  2336  
  2337  	if isConcreteMethod(sig) {
  2338  		tname, tExplicits := splitNamed(types2.Unalias(deref2(recv)).(*types2.Named))
  2339  		var info objInfo
  2340  		if isGenericMethod(sig) {
  2341  			// For generic methods, the shaped object is the method itself.
  2342  			mExplicits := asTypeSlice(w.p.info.Instances[expr.Sel].TypeArgs)
  2343  			info = w.p.objInstIdx(fun.Origin(), slices.Concat(tExplicits, mExplicits), w.dict)
  2344  		} else {
  2345  			// For non-generic concrete methods on generic types, the shaped object
  2346  			// is the type. The method must be looked up on the type by name.
  2347  			info = w.p.objInstIdx(tname, tExplicits, w.dict)
  2348  		}
  2349  		// We don't know all of the type arguments statically. These can be
  2350  		// handled by a static call to the shaped method, but require
  2351  		// dynamically looking up the appropriate dictionary argument
  2352  		// in the current function's runtime dictionary.
  2353  		if info.anyDerived() {
  2354  			w.Bool(true) // dynamic subdictionary
  2355  			w.Len(w.dict.subdictIdx(info))
  2356  			return
  2357  		}
  2358  		// We know all of the type arguments statically. These can be handled
  2359  		// by a static call to the shaped method, and with a static reference
  2360  		// to either the receiver type's or method's dictionary (see above).
  2361  		if len(info.explicits) > 0 {
  2362  			w.Bool(false) // no dynamic subdictionary
  2363  			w.Bool(true)  // static dictionary
  2364  			w.objInfo(info)
  2365  			return
  2366  		}
  2367  		// no type arguments
  2368  	}
  2369  
  2370  	w.Bool(false) // no dynamic subdictionary
  2371  	w.Bool(false) // no static dictionary
  2372  }
  2373  
  2374  // multiExpr writes a sequence of expressions, where the i'th value is
  2375  // implicitly converted to dstType(i). It also handles when exprs is a
  2376  // single, multi-valued expression (e.g., the multi-valued argument in
  2377  // an f(g()) call, or the RHS operand in a comma-ok assignment).
  2378  func (w *writer) multiExpr(pos poser, dstType func(int) types2.Type, exprs []syntax.Expr) {
  2379  	w.Sync(pkgbits.SyncMultiExpr)
  2380  
  2381  	if len(exprs) == 1 {
  2382  		expr := exprs[0]
  2383  		if tuple, ok := w.p.typeOf(expr).(*types2.Tuple); ok {
  2384  			assert(tuple.Len() > 1)
  2385  			w.Bool(true) // N:1 assignment
  2386  			w.pos(pos)
  2387  			w.expr(expr)
  2388  
  2389  			w.Len(tuple.Len())
  2390  			for i := 0; i < tuple.Len(); i++ {
  2391  				src := tuple.At(i).Type()
  2392  				// TODO(mdempsky): Investigate not writing src here. I think
  2393  				// the reader should be able to infer it from expr anyway.
  2394  				w.typ(src)
  2395  				if dst := dstType(i); w.Bool(dst != nil && !types2.Identical(src, dst)) {
  2396  					if src == nil || dst == nil {
  2397  						w.p.fatalf(pos, "src is %v, dst is %v", src, dst)
  2398  					}
  2399  					if !types2.AssignableTo(src, dst) {
  2400  						w.p.fatalf(pos, "%v is not assignable to %v", src, dst)
  2401  					}
  2402  					w.typ(dst)
  2403  					w.convRTTI(src, dst)
  2404  				}
  2405  			}
  2406  			return
  2407  		}
  2408  	}
  2409  
  2410  	w.Bool(false) // N:N assignment
  2411  	w.Len(len(exprs))
  2412  	for i, expr := range exprs {
  2413  		w.implicitConvExpr(dstType(i), expr)
  2414  	}
  2415  }
  2416  
  2417  // implicitConvExpr is like expr, but if dst is non-nil and different
  2418  // from expr's type, then an implicit conversion operation is inserted
  2419  // at expr's position.
  2420  func (w *writer) implicitConvExpr(dst types2.Type, expr syntax.Expr) {
  2421  	w.convertExpr(dst, expr, true)
  2422  }
  2423  
  2424  func (w *writer) convertExpr(dst types2.Type, expr syntax.Expr, implicit bool) {
  2425  	src := w.p.typeOf(expr)
  2426  
  2427  	// Omit implicit no-op conversions.
  2428  	identical := dst == nil || types2.Identical(src, dst)
  2429  	if implicit && identical {
  2430  		w.expr(expr)
  2431  		return
  2432  	}
  2433  
  2434  	if implicit && !types2.AssignableTo(src, dst) {
  2435  		w.p.fatalf(expr, "%v is not assignable to %v", src, dst)
  2436  	}
  2437  
  2438  	w.Code(exprConvert)
  2439  	w.Bool(implicit)
  2440  	w.typ(dst)
  2441  	w.pos(expr)
  2442  	w.convRTTI(src, dst)
  2443  	w.Bool(isTypeParam(dst))
  2444  	w.Bool(identical)
  2445  	w.expr(expr)
  2446  }
  2447  
  2448  func (w *writer) compLit(lit *syntax.CompositeLit) {
  2449  	typ := w.p.typeOf(lit)
  2450  
  2451  	w.Sync(pkgbits.SyncCompLit)
  2452  	w.pos(lit)
  2453  	w.typ(typ)
  2454  
  2455  	if ptr, ok := types2.CoreType(typ).(*types2.Pointer); ok {
  2456  		typ = ptr.Elem()
  2457  	}
  2458  
  2459  	if w.Version().Has(pkgbits.CompactCompLiterals) {
  2460  		switch typ0 := typ; typ := types2.CoreType(typ).(type) {
  2461  		default:
  2462  			w.p.fatalf(lit, "unexpected composite literal type: %v", typ)
  2463  		case *types2.Array:
  2464  			w.arrayElems(typ.Elem(), lit.ElemList)
  2465  		case *types2.Map:
  2466  			w.rtype(typ0)
  2467  			w.mapElems(typ.Key(), typ.Elem(), lit.ElemList)
  2468  		case *types2.Slice:
  2469  			w.arrayElems(typ.Elem(), lit.ElemList)
  2470  		case *types2.Struct:
  2471  			w.structElems(typ, lit.NKeys == 0, lit.ElemList)
  2472  		}
  2473  		return
  2474  	}
  2475  
  2476  	// old format
  2477  	var keyType, elemType types2.Type
  2478  	var structType *types2.Struct
  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  		elemType = typ.Elem()
  2484  	case *types2.Map:
  2485  		w.rtype(typ0)
  2486  		keyType, elemType = typ.Key(), typ.Elem()
  2487  	case *types2.Slice:
  2488  		elemType = typ.Elem()
  2489  	case *types2.Struct:
  2490  		structType = typ
  2491  	}
  2492  
  2493  	w.Len(len(lit.ElemList))
  2494  	for i, elem := range lit.ElemList {
  2495  		elemType := elemType
  2496  		if structType != nil {
  2497  			if kv, ok := elem.(*syntax.KeyValueExpr); ok {
  2498  				// use position of expr.Key rather than of elem (which has position of ':')
  2499  				w.pos(kv.Key)
  2500  				i = fieldIndex(w.p.info, structType, kv.Key.(*syntax.Name))
  2501  				elem = kv.Value
  2502  			} else {
  2503  				w.pos(elem)
  2504  			}
  2505  			elemType = structType.Field(i).Type()
  2506  			w.Len(i)
  2507  		} else {
  2508  			if kv, ok := elem.(*syntax.KeyValueExpr); w.Bool(ok) {
  2509  				// use position of expr.Key rather than of elem (which has position of ':')
  2510  				w.pos(kv.Key)
  2511  				w.implicitConvExpr(keyType, kv.Key)
  2512  				elem = kv.Value
  2513  			}
  2514  		}
  2515  		w.implicitConvExpr(elemType, elem)
  2516  	}
  2517  }
  2518  
  2519  func (w *writer) arrayElems(elemType types2.Type, elems []syntax.Expr) {
  2520  	valuesOnly := true
  2521  	for _, elem := range elems {
  2522  		if _, ok := elem.(*syntax.KeyValueExpr); ok {
  2523  			valuesOnly = false
  2524  			break
  2525  		}
  2526  	}
  2527  
  2528  	if valuesOnly {
  2529  		w.Int(len(elems))
  2530  		for _, elem := range elems {
  2531  			w.implicitConvExpr(elemType, elem)
  2532  		}
  2533  		return
  2534  	}
  2535  	// some elements may have a key
  2536  	w.Int(-len(elems))
  2537  	for _, elem := range elems {
  2538  		if kv, ok := elem.(*syntax.KeyValueExpr); w.Bool(ok) {
  2539  			w.pos(kv.Key) // use position of Key rather than of elem (which has position of ':')
  2540  			w.implicitConvExpr(nil, kv.Key)
  2541  			elem = kv.Value
  2542  		}
  2543  		w.implicitConvExpr(elemType, elem)
  2544  	}
  2545  }
  2546  
  2547  func (w *writer) mapElems(keyType, valueType types2.Type, elems []syntax.Expr) {
  2548  	// all elements have a key
  2549  	w.Int(-len(elems))
  2550  	for _, elem := range elems {
  2551  		kv := elem.(*syntax.KeyValueExpr)
  2552  		w.pos(kv.Key) // use position of Key rather than of elem (which has position of ':')
  2553  		w.implicitConvExpr(keyType, kv.Key)
  2554  		w.implicitConvExpr(valueType, kv.Value)
  2555  	}
  2556  }
  2557  
  2558  func (w *writer) structElems(typ *types2.Struct, valuesOnly bool, elems []syntax.Expr) {
  2559  	n := len(elems)
  2560  	if valuesOnly {
  2561  		// no element has a key
  2562  		w.Int(n)
  2563  		for i, elem := range elems {
  2564  			w.pos(elem)
  2565  			w.implicitConvExpr(typ.Field(i).Type(), elem)
  2566  		}
  2567  		return
  2568  	}
  2569  	// all elements have a key
  2570  	w.Int(-n)
  2571  	for _, elem := range elems {
  2572  		kv := elem.(*syntax.KeyValueExpr)
  2573  		w.pos(kv.Key) // use position of Key rather than of elem (which has position of ':')
  2574  		// TODO(gri): rather than doing this lookup again, perhaps the index should be recorded by types2
  2575  		fld, index, _ := types2.LookupFieldOrMethod(typ, false, w.p.curpkg, kv.Key.(*syntax.Name).Value)
  2576  		if n := len(index); n > 1 {
  2577  			// embedded field
  2578  			w.Int(-n)
  2579  			for _, i := range index {
  2580  				w.Int(i)
  2581  			}
  2582  		} else { // n == 1
  2583  			w.Int(index[0])
  2584  		}
  2585  		w.implicitConvExpr(fld.Type(), kv.Value)
  2586  	}
  2587  }
  2588  
  2589  func (w *writer) funcLit(expr *syntax.FuncLit) {
  2590  	sig := w.p.typeOf(expr).(*types2.Signature)
  2591  
  2592  	body, closureVars := w.p.bodyIdx(sig, expr.Body, w.dict)
  2593  
  2594  	w.Sync(pkgbits.SyncFuncLit)
  2595  	w.pos(expr)
  2596  	w.signature(sig)
  2597  	w.Bool(w.p.rangeFuncBodyClosures[expr])
  2598  
  2599  	w.Len(len(closureVars))
  2600  	for _, cv := range closureVars {
  2601  		w.pos(cv.pos)
  2602  		w.useLocal(cv.pos, cv.var_)
  2603  	}
  2604  
  2605  	w.Reloc(pkgbits.SectionBody, body)
  2606  }
  2607  
  2608  type posVar struct {
  2609  	pos  syntax.Pos
  2610  	var_ *types2.Var
  2611  }
  2612  
  2613  func (p posVar) String() string {
  2614  	return p.pos.String() + ":" + p.var_.String()
  2615  }
  2616  
  2617  func (w *writer) exprs(exprs []syntax.Expr) {
  2618  	w.Sync(pkgbits.SyncExprs)
  2619  	w.Len(len(exprs))
  2620  	for _, expr := range exprs {
  2621  		w.expr(expr)
  2622  	}
  2623  }
  2624  
  2625  // rtype writes information so that the reader can construct an
  2626  // expression of type *runtime._type representing typ.
  2627  func (w *writer) rtype(typ types2.Type) {
  2628  	typ = types2.Default(typ)
  2629  
  2630  	info := w.p.typIdx(typ, w.dict)
  2631  	w.rtypeInfo(info)
  2632  }
  2633  
  2634  func (w *writer) rtypeInfo(info typeInfo) {
  2635  	w.Sync(pkgbits.SyncRType)
  2636  
  2637  	if w.Bool(info.derived) {
  2638  		w.Len(w.dict.rtypeIdx(info))
  2639  	} else {
  2640  		w.typInfo(info)
  2641  	}
  2642  }
  2643  
  2644  // varDictIndex writes out information for populating DictIndex for
  2645  // the ir.Name that will represent obj.
  2646  func (w *writer) varDictIndex(obj *types2.Var) {
  2647  	info := w.p.typIdx(obj.Type(), w.dict)
  2648  	if w.Bool(info.derived) {
  2649  		w.Len(w.dict.rtypeIdx(info))
  2650  	}
  2651  }
  2652  
  2653  // isUntyped reports whether typ is an untyped type.
  2654  func isUntyped(typ types2.Type) bool {
  2655  	// Note: types2.Unalias is unnecessary here, since untyped types can't be aliased.
  2656  	basic, ok := typ.(*types2.Basic)
  2657  	return ok && basic.Info()&types2.IsUntyped != 0
  2658  }
  2659  
  2660  // isTuple reports whether typ is a tuple type.
  2661  func isTuple(typ types2.Type) bool {
  2662  	// Note: types2.Unalias is unnecessary here, since tuple types can't be aliased.
  2663  	_, ok := typ.(*types2.Tuple)
  2664  	return ok
  2665  }
  2666  
  2667  func (w *writer) itab(typ, iface types2.Type) {
  2668  	typ = types2.Default(typ)
  2669  	iface = types2.Default(iface)
  2670  
  2671  	typInfo := w.p.typIdx(typ, w.dict)
  2672  	ifaceInfo := w.p.typIdx(iface, w.dict)
  2673  
  2674  	w.rtypeInfo(typInfo)
  2675  	w.rtypeInfo(ifaceInfo)
  2676  	if w.Bool(typInfo.derived || ifaceInfo.derived) {
  2677  		w.Len(w.dict.itabIdx(typInfo, ifaceInfo))
  2678  	}
  2679  }
  2680  
  2681  // convRTTI writes information so that the reader can construct
  2682  // expressions for converting from src to dst.
  2683  func (w *writer) convRTTI(src, dst types2.Type) {
  2684  	w.Sync(pkgbits.SyncConvRTTI)
  2685  	w.itab(src, dst)
  2686  }
  2687  
  2688  func (w *writer) exprType(iface types2.Type, typ syntax.Expr) {
  2689  	base.Assertf(iface == nil || isInterface(iface), "%v must be nil or an interface type", iface)
  2690  
  2691  	tv := w.p.typeAndValue(typ)
  2692  	assert(tv.IsType())
  2693  
  2694  	w.Sync(pkgbits.SyncExprType)
  2695  	w.pos(typ)
  2696  
  2697  	if w.Bool(iface != nil && !iface.Underlying().(*types2.Interface).Empty()) {
  2698  		w.itab(tv.Type, iface)
  2699  	} else {
  2700  		w.rtype(tv.Type)
  2701  
  2702  		info := w.p.typIdx(tv.Type, w.dict)
  2703  		w.Bool(info.derived)
  2704  	}
  2705  }
  2706  
  2707  // isInterface reports whether typ is known to be an interface type.
  2708  // If typ is a type parameter, then isInterface reports an internal
  2709  // compiler error instead.
  2710  func isInterface(typ types2.Type) bool {
  2711  	if _, ok := types2.Unalias(typ).(*types2.TypeParam); ok {
  2712  		// typ is a type parameter and may be instantiated as either a
  2713  		// concrete or interface type, so the writer can't depend on
  2714  		// knowing this.
  2715  		base.Fatalf("%v is a type parameter", typ)
  2716  	}
  2717  
  2718  	_, ok := typ.Underlying().(*types2.Interface)
  2719  	return ok
  2720  }
  2721  
  2722  // isConcreteMethod reports whether typ is a concrete method. That is,
  2723  // it's a method with a receiver that isn't an interface type.
  2724  func isConcreteMethod(typ types2.Type) bool {
  2725  	sig, ok := typ.(*types2.Signature)
  2726  	return ok && sig.Recv() != nil && !isInterface(sig.Recv().Type())
  2727  }
  2728  
  2729  // TODO(mark): Use isGenericMethod. It is included now to help justify
  2730  // the existence of isConcreteMethod.
  2731  
  2732  // isGenericMethod reports whether typ is a generic method. That is,
  2733  // it's a method with type parameters apart from those which may or
  2734  // may not appear on the receiver type.
  2735  //
  2736  // Note that generic methods are always concrete methods.
  2737  func isGenericMethod(typ types2.Type) bool {
  2738  	sig, ok := typ.(*types2.Signature)
  2739  	return ok && sig.Recv() != nil && sig.TypeParams().Len() > 0
  2740  }
  2741  
  2742  // op writes an Op into the bitstream.
  2743  func (w *writer) op(op ir.Op) {
  2744  	// TODO(mdempsky): Remove in favor of explicit codes? Would make
  2745  	// export data more stable against internal refactorings, but low
  2746  	// priority at the moment.
  2747  	assert(op != 0)
  2748  	w.Sync(pkgbits.SyncOp)
  2749  	w.Len(int(op))
  2750  }
  2751  
  2752  // @@@ Package initialization
  2753  
  2754  // Caution: This code is still clumsy, because toolstash -cmp is
  2755  // particularly sensitive to it.
  2756  
  2757  type typeDeclGen struct {
  2758  	*syntax.TypeDecl
  2759  	gen int
  2760  
  2761  	// Implicit type parameters in scope at this type declaration.
  2762  	implicits []*types2.TypeParam
  2763  }
  2764  
  2765  type fileImports struct {
  2766  	importedEmbed, importedUnsafe bool
  2767  }
  2768  
  2769  // declCollector is a visitor type that collects compiler-needed
  2770  // information about declarations that types2 doesn't track.
  2771  //
  2772  // Notably, it maps declared types and functions back to their
  2773  // declaration statement, keeps track of implicit type parameters, and
  2774  // assigns unique type "generation" numbers to local defined types.
  2775  type declCollector struct {
  2776  	pw         *pkgWriter
  2777  	typegen    *int
  2778  	file       *fileImports
  2779  	withinFunc bool
  2780  	implicits  []*types2.TypeParam
  2781  }
  2782  
  2783  func (c *declCollector) withTParams(obj types2.Object) *declCollector {
  2784  	tparams := slices.Concat(objRecvTypeParams(obj), objTypeParams(obj))
  2785  	if len(tparams) == 0 {
  2786  		return c
  2787  	}
  2788  
  2789  	copy := *c
  2790  	copy.implicits = copy.implicits[:len(copy.implicits):len(copy.implicits)]
  2791  	for _, tparam := range tparams {
  2792  		copy.implicits = append(copy.implicits, tparam)
  2793  	}
  2794  	return &copy
  2795  }
  2796  
  2797  func (c *declCollector) Visit(n syntax.Node) syntax.Visitor {
  2798  	pw := c.pw
  2799  
  2800  	switch n := n.(type) {
  2801  	case *syntax.File:
  2802  		pw.checkPragmas(n.Pragma, ir.GoBuildPragma, false)
  2803  
  2804  	case *syntax.ImportDecl:
  2805  		pw.checkPragmas(n.Pragma, 0, false)
  2806  
  2807  		switch pw.info.PkgNameOf(n).Imported().Path() {
  2808  		case "embed":
  2809  			c.file.importedEmbed = true
  2810  		case "unsafe":
  2811  			c.file.importedUnsafe = true
  2812  		}
  2813  
  2814  	case *syntax.ConstDecl:
  2815  		pw.checkPragmas(n.Pragma, 0, false)
  2816  
  2817  	case *syntax.FuncDecl:
  2818  		pw.checkPragmas(n.Pragma, funcPragmas, false)
  2819  
  2820  		obj := pw.info.Defs[n.Name].(*types2.Func)
  2821  		pw.funDecls[obj] = n
  2822  
  2823  		return c.withTParams(obj)
  2824  
  2825  	case *syntax.TypeDecl:
  2826  		obj := pw.info.Defs[n.Name].(*types2.TypeName)
  2827  		d := typeDeclGen{TypeDecl: n, implicits: c.implicits}
  2828  
  2829  		if n.Alias {
  2830  			pw.checkPragmas(n.Pragma, 0, false)
  2831  		} else {
  2832  			pw.checkPragmas(n.Pragma, 0, false)
  2833  
  2834  			// Assign a unique ID to function-scoped defined types.
  2835  			if c.withinFunc {
  2836  				*c.typegen++
  2837  				d.gen = *c.typegen
  2838  			}
  2839  		}
  2840  
  2841  		pw.typDecls[obj] = d
  2842  
  2843  		// TODO(mdempsky): Omit? Not strictly necessary; only matters for
  2844  		// type declarations within function literals within parameterized
  2845  		// type declarations, but types2 the function literals will be
  2846  		// constant folded away.
  2847  		return c.withTParams(obj)
  2848  
  2849  	case *syntax.VarDecl:
  2850  		pw.checkPragmas(n.Pragma, 0, true)
  2851  
  2852  		if p, ok := n.Pragma.(*pragmas); ok && len(p.Embeds) > 0 {
  2853  			if err := checkEmbed(n, c.file.importedEmbed, c.withinFunc); err != nil {
  2854  				pw.errorf(p.Embeds[0].Pos, "%s", err)
  2855  			}
  2856  		}
  2857  
  2858  	case *syntax.BlockStmt:
  2859  		if !c.withinFunc {
  2860  			copy := *c
  2861  			copy.withinFunc = true
  2862  			return &copy
  2863  		}
  2864  	}
  2865  
  2866  	return c
  2867  }
  2868  
  2869  func (pw *pkgWriter) collectDecls(noders []*noder) {
  2870  	var typegen int
  2871  	for _, p := range noders {
  2872  		var file fileImports
  2873  
  2874  		syntax.Walk(p.file, &declCollector{
  2875  			pw:      pw,
  2876  			typegen: &typegen,
  2877  			file:    &file,
  2878  		})
  2879  
  2880  		pw.cgoPragmas = append(pw.cgoPragmas, p.pragcgobuf...)
  2881  
  2882  		for _, l := range p.linknames {
  2883  			directive := "go:linkname"
  2884  			if l.std {
  2885  				directive = "go:linknamestd"
  2886  			}
  2887  			if !file.importedUnsafe {
  2888  				pw.errorf(l.pos, "//%s only allowed in Go files that import \"unsafe\"", directive)
  2889  				continue
  2890  			}
  2891  			if strings.Contains(l.remote, "[") && strings.Contains(l.remote, "]") {
  2892  				pw.errorf(l.pos, "//%s reference of an instantiation is not allowed", directive)
  2893  				continue
  2894  			}
  2895  
  2896  			switch obj := pw.curpkg.Scope().Lookup(l.local).(type) {
  2897  			case *types2.Func, *types2.Var:
  2898  				if _, ok := pw.linknames[obj]; !ok {
  2899  					pw.linknames[obj] = struct {
  2900  						remote string
  2901  						std    bool
  2902  					}{l.remote, l.std}
  2903  				} else {
  2904  					pw.errorf(l.pos, "duplicate //%s for %s", directive, l.local)
  2905  				}
  2906  
  2907  			default:
  2908  				if types.AllowsGoVersion(1, 18) {
  2909  					pw.errorf(l.pos, "//%s must refer to declared function or variable", directive)
  2910  				}
  2911  			}
  2912  		}
  2913  	}
  2914  }
  2915  
  2916  func (pw *pkgWriter) checkPragmas(p syntax.Pragma, allowed ir.PragmaFlag, embedOK bool) {
  2917  	if p == nil {
  2918  		return
  2919  	}
  2920  	pragma := p.(*pragmas)
  2921  
  2922  	for _, pos := range pragma.Pos {
  2923  		if pos.Flag&^allowed != 0 {
  2924  			pw.errorf(pos.Pos, "misplaced compiler directive")
  2925  		}
  2926  	}
  2927  
  2928  	if !embedOK {
  2929  		for _, e := range pragma.Embeds {
  2930  			pw.errorf(e.Pos, "misplaced go:embed directive")
  2931  		}
  2932  	}
  2933  }
  2934  
  2935  func (w *writer) pkgInit(noders []*noder) {
  2936  	w.Len(len(w.p.cgoPragmas))
  2937  	for _, cgoPragma := range w.p.cgoPragmas {
  2938  		w.Strings(cgoPragma)
  2939  	}
  2940  
  2941  	w.pkgInitOrder()
  2942  
  2943  	w.Sync(pkgbits.SyncDecls)
  2944  	for _, p := range noders {
  2945  		for _, decl := range p.file.DeclList {
  2946  			w.pkgDecl(decl)
  2947  		}
  2948  	}
  2949  	w.Code(declEnd)
  2950  
  2951  	w.Sync(pkgbits.SyncEOF)
  2952  }
  2953  
  2954  func (w *writer) pkgInitOrder() {
  2955  	// TODO(mdempsky): Write as a function body instead?
  2956  	w.Len(len(w.p.info.InitOrder))
  2957  	for _, init := range w.p.info.InitOrder {
  2958  		w.Len(len(init.Lhs))
  2959  		for _, v := range init.Lhs {
  2960  			w.obj(v, nil)
  2961  		}
  2962  		w.expr(init.Rhs)
  2963  	}
  2964  }
  2965  
  2966  func (w *writer) pkgDecl(decl syntax.Decl) {
  2967  	switch decl := decl.(type) {
  2968  	default:
  2969  		w.p.unexpected("declaration", decl)
  2970  
  2971  	case *syntax.ImportDecl:
  2972  
  2973  	case *syntax.ConstDecl:
  2974  		w.Code(declOther)
  2975  		w.pkgObjs(decl.NameList...)
  2976  
  2977  	case *syntax.FuncDecl:
  2978  		if decl.Name.Value == "_" {
  2979  			break // skip blank functions
  2980  		}
  2981  
  2982  		obj := w.p.info.Defs[decl.Name].(*types2.Func)
  2983  		sig := obj.Type().(*types2.Signature)
  2984  
  2985  		if sig.RecvTypeParams() != nil || sig.TypeParams() != nil {
  2986  			break // skip generic functions
  2987  		}
  2988  
  2989  		if recv := sig.Recv(); recv != nil {
  2990  			w.Code(declMethod)
  2991  			w.typ(recvBase(recv))
  2992  			w.selector(obj)
  2993  			break
  2994  		}
  2995  
  2996  		w.Code(declFunc)
  2997  		w.pkgObjs(decl.Name)
  2998  
  2999  	case *syntax.TypeDecl:
  3000  		if len(decl.TParamList) != 0 {
  3001  			break // skip generic type decls
  3002  		}
  3003  
  3004  		if decl.Name.Value == "_" {
  3005  			break // skip blank type decls
  3006  		}
  3007  
  3008  		name := w.p.info.Defs[decl.Name].(*types2.TypeName)
  3009  		// Skip type declarations for interfaces that are only usable as
  3010  		// type parameter bounds.
  3011  		if iface, ok := name.Type().Underlying().(*types2.Interface); ok && !iface.IsMethodSet() {
  3012  			break
  3013  		}
  3014  
  3015  		w.Code(declOther)
  3016  		w.pkgObjs(decl.Name)
  3017  
  3018  	case *syntax.VarDecl:
  3019  		w.Code(declVar)
  3020  		w.pkgObjs(decl.NameList...)
  3021  
  3022  		var embeds []pragmaEmbed
  3023  		if p, ok := decl.Pragma.(*pragmas); ok {
  3024  			embeds = p.Embeds
  3025  		}
  3026  		w.Len(len(embeds))
  3027  		for _, embed := range embeds {
  3028  			w.pos(embed.Pos)
  3029  			w.Strings(embed.Patterns)
  3030  		}
  3031  	}
  3032  }
  3033  
  3034  func (w *writer) pkgObjs(names ...*syntax.Name) {
  3035  	w.Sync(pkgbits.SyncDeclNames)
  3036  	w.Len(len(names))
  3037  
  3038  	for _, name := range names {
  3039  		obj, ok := w.p.info.Defs[name]
  3040  		assert(ok)
  3041  
  3042  		w.Sync(pkgbits.SyncDeclName)
  3043  		w.obj(obj, nil)
  3044  	}
  3045  }
  3046  
  3047  // @@@ Helpers
  3048  
  3049  // staticBool analyzes a boolean expression and reports whether it's
  3050  // always true (positive result), always false (negative result), or
  3051  // unknown (zero).
  3052  //
  3053  // It also simplifies the expression while preserving semantics, if
  3054  // possible.
  3055  func (pw *pkgWriter) staticBool(ep *syntax.Expr) int {
  3056  	if val := pw.typeAndValue(*ep).Value; val != nil {
  3057  		if constant.BoolVal(val) {
  3058  			return +1
  3059  		} else {
  3060  			return -1
  3061  		}
  3062  	}
  3063  
  3064  	if e, ok := (*ep).(*syntax.Operation); ok {
  3065  		switch e.Op {
  3066  		case syntax.Not:
  3067  			return pw.staticBool(&e.X)
  3068  
  3069  		case syntax.AndAnd:
  3070  			x := pw.staticBool(&e.X)
  3071  			if x < 0 {
  3072  				*ep = e.X
  3073  				return x
  3074  			}
  3075  
  3076  			y := pw.staticBool(&e.Y)
  3077  			if x > 0 || y < 0 {
  3078  				if pw.typeAndValue(e.X).Value != nil {
  3079  					*ep = e.Y
  3080  				}
  3081  				return y
  3082  			}
  3083  
  3084  		case syntax.OrOr:
  3085  			x := pw.staticBool(&e.X)
  3086  			if x > 0 {
  3087  				*ep = e.X
  3088  				return x
  3089  			}
  3090  
  3091  			y := pw.staticBool(&e.Y)
  3092  			if x < 0 || y > 0 {
  3093  				if pw.typeAndValue(e.X).Value != nil {
  3094  					*ep = e.Y
  3095  				}
  3096  				return y
  3097  			}
  3098  		}
  3099  	}
  3100  
  3101  	return 0
  3102  }
  3103  
  3104  // hasImplicitTypeParams reports whether obj is a defined type with
  3105  // implicit type parameters (e.g., declared within a generic function
  3106  // or method).
  3107  func (pw *pkgWriter) hasImplicitTypeParams(obj *types2.TypeName) bool {
  3108  	if obj.Pkg() == pw.curpkg {
  3109  		decl, ok := pw.typDecls[obj]
  3110  		assert(ok)
  3111  		if len(decl.implicits) != 0 {
  3112  			return true
  3113  		}
  3114  	}
  3115  	return false
  3116  }
  3117  
  3118  // isDefinedType reports whether obj is a defined type.
  3119  func isDefinedType(obj types2.Object) bool {
  3120  	if obj, ok := obj.(*types2.TypeName); ok {
  3121  		return !obj.IsAlias()
  3122  	}
  3123  	return false
  3124  }
  3125  
  3126  // isGlobal reports whether obj was declared at package scope.
  3127  //
  3128  // Caveat: blank objects are not declared.
  3129  func isGlobal(obj types2.Object) bool {
  3130  	return obj.Parent() == obj.Pkg().Scope()
  3131  }
  3132  
  3133  // lookupObj returns the object that expr refers to, if any. If expr
  3134  // is an explicit instantiation of a generic object, then the instance
  3135  // object is returned as well.
  3136  func lookupObj(p *pkgWriter, expr syntax.Expr) (obj types2.Object, inst types2.Instance) {
  3137  	if index, ok := expr.(*syntax.IndexExpr); ok {
  3138  		args := syntax.UnpackListExpr(index.Index)
  3139  		if len(args) == 1 {
  3140  			tv := p.typeAndValue(args[0])
  3141  			if tv.IsValue() {
  3142  				return // normal index expression
  3143  			}
  3144  		}
  3145  
  3146  		expr = index.X
  3147  	}
  3148  
  3149  	// Strip package qualifier, if present.
  3150  	if sel, ok := expr.(*syntax.SelectorExpr); ok {
  3151  		if !isPkgQual(p.info, sel) {
  3152  			return // normal selector expression
  3153  		}
  3154  		expr = sel.Sel
  3155  	}
  3156  
  3157  	if name, ok := expr.(*syntax.Name); ok {
  3158  		obj = p.info.Uses[name]
  3159  		inst = p.info.Instances[name]
  3160  	}
  3161  	return
  3162  }
  3163  
  3164  // isPkgQual reports whether the given selector expression is a
  3165  // package-qualified identifier.
  3166  func isPkgQual(info *types2.Info, sel *syntax.SelectorExpr) bool {
  3167  	if name, ok := sel.X.(*syntax.Name); ok {
  3168  		_, isPkgName := info.Uses[name].(*types2.PkgName)
  3169  		return isPkgName
  3170  	}
  3171  	return false
  3172  }
  3173  
  3174  // isNil reports whether expr is a (possibly parenthesized) reference
  3175  // to the predeclared nil value.
  3176  func isNil(p *pkgWriter, expr syntax.Expr) bool {
  3177  	tv := p.typeAndValue(expr)
  3178  	return tv.IsNil()
  3179  }
  3180  
  3181  // isBuiltin reports whether expr is a (possibly parenthesized)
  3182  // referenced to the specified built-in function.
  3183  func (pw *pkgWriter) isBuiltin(expr syntax.Expr, builtin string) bool {
  3184  	if name, ok := syntax.Unparen(expr).(*syntax.Name); ok && name.Value == builtin {
  3185  		return pw.typeAndValue(name).IsBuiltin()
  3186  	}
  3187  	return false
  3188  }
  3189  
  3190  // recvBase returns the base type for the given receiver parameter.
  3191  func recvBase(recv *types2.Var) *types2.Named {
  3192  	typ := types2.Unalias(recv.Type())
  3193  	if ptr, ok := typ.(*types2.Pointer); ok {
  3194  		typ = types2.Unalias(ptr.Elem())
  3195  	}
  3196  	return typ.(*types2.Named)
  3197  }
  3198  
  3199  // namesAsExpr returns a list of names as a syntax.Expr.
  3200  func namesAsExpr(names []*syntax.Name) syntax.Expr {
  3201  	if len(names) == 1 {
  3202  		return names[0]
  3203  	}
  3204  
  3205  	exprs := make([]syntax.Expr, len(names))
  3206  	for i, name := range names {
  3207  		exprs[i] = name
  3208  	}
  3209  	return &syntax.ListExpr{ElemList: exprs}
  3210  }
  3211  
  3212  // fieldIndex returns the index of the struct field named by key.
  3213  func fieldIndex(info *types2.Info, str *types2.Struct, key *syntax.Name) int {
  3214  	field := info.Uses[key].(*types2.Var)
  3215  
  3216  	for i := 0; i < str.NumFields(); i++ {
  3217  		if str.Field(i) == field {
  3218  			return i
  3219  		}
  3220  	}
  3221  
  3222  	panic(fmt.Sprintf("%s: %v is not a field of %v", key.Pos(), field, str))
  3223  }
  3224  
  3225  // objRecvTypeParams returns the receiver type parameters on the given object.
  3226  func objRecvTypeParams(obj types2.Object) []*types2.TypeParam {
  3227  	if f, ok := obj.(*types2.Func); ok {
  3228  		return asTypeParamSlice(f.Signature().RecvTypeParams())
  3229  	}
  3230  	return nil
  3231  }
  3232  
  3233  // objTypeParams returns the type parameters on the given object.
  3234  func objTypeParams(obj types2.Object) []*types2.TypeParam {
  3235  	switch t := obj.(type) {
  3236  	case *types2.Func:
  3237  		return asTypeParamSlice(t.Signature().TypeParams())
  3238  	case *types2.TypeName:
  3239  		switch t := obj.Type().(type) {
  3240  		case *types2.Named:
  3241  			return asTypeParamSlice(t.TypeParams())
  3242  		case *types2.Alias:
  3243  			return asTypeParamSlice(t.TypeParams())
  3244  		}
  3245  	}
  3246  	return nil
  3247  }
  3248  
  3249  // asTypeParamSlice unpacks a types2.TypeParamList to a []types2.TypeParam
  3250  func asTypeParamSlice(l *types2.TypeParamList) []*types2.TypeParam {
  3251  	if l.Len() == 0 {
  3252  		return nil
  3253  	}
  3254  	s := make([]*types2.TypeParam, l.Len())
  3255  	for i := range l.Len() {
  3256  		s[i] = l.At(i)
  3257  	}
  3258  	return s
  3259  }
  3260  
  3261  // splitNamed decomposes a use of a defined type into its original
  3262  // type definition and the type arguments used to instantiate it.
  3263  func splitNamed(typ *types2.Named) (*types2.TypeName, []types2.Type) {
  3264  	base.Assertf(typ.TypeParams().Len() == typ.TypeArgs().Len(), "use of uninstantiated type: %v", typ)
  3265  
  3266  	orig := typ.Origin()
  3267  	base.Assertf(orig.TypeArgs() == nil, "origin %v of %v has type arguments", orig, typ)
  3268  	base.Assertf(typ.Obj() == orig.Obj(), "%v has object %v, but %v has object %v", typ, typ.Obj(), orig, orig.Obj())
  3269  
  3270  	return typ.Obj(), asTypeSlice(typ.TypeArgs())
  3271  }
  3272  
  3273  // splitAlias is like splitNamed, but for an alias type.
  3274  func splitAlias(typ *types2.Alias) (*types2.TypeName, []types2.Type) {
  3275  	orig := typ.Origin()
  3276  	base.Assertf(typ.Obj() == orig.Obj(), "alias type %v has object %v, but %v has object %v", typ, typ.Obj(), orig, orig.Obj())
  3277  
  3278  	return typ.Obj(), asTypeSlice(typ.TypeArgs())
  3279  }
  3280  
  3281  // asTypeSlice unpacks a types2.TypeList to a []types2.Type
  3282  func asTypeSlice(l *types2.TypeList) []types2.Type {
  3283  	if l.Len() == 0 {
  3284  		return nil
  3285  	}
  3286  	s := make([]types2.Type, l.Len())
  3287  	for i := range l.Len() {
  3288  		s[i] = l.At(i)
  3289  	}
  3290  	return s
  3291  }
  3292  
  3293  func asPragmaFlag(p syntax.Pragma) ir.PragmaFlag {
  3294  	if p == nil {
  3295  		return 0
  3296  	}
  3297  	return p.(*pragmas).Flag
  3298  }
  3299  
  3300  func asWasmImport(p syntax.Pragma) *WasmImport {
  3301  	if p == nil {
  3302  		return nil
  3303  	}
  3304  	return p.(*pragmas).WasmImport
  3305  }
  3306  
  3307  func asWasmExport(p syntax.Pragma) *WasmExport {
  3308  	if p == nil {
  3309  		return nil
  3310  	}
  3311  	return p.(*pragmas).WasmExport
  3312  }
  3313  
  3314  // isPtrTo reports whether from is the type *to.
  3315  func isPtrTo(from, to types2.Type) bool {
  3316  	ptr, ok := types2.Unalias(from).(*types2.Pointer)
  3317  	return ok && types2.Identical(ptr.Elem(), to)
  3318  }
  3319  
  3320  // hasFallthrough reports whether stmts ends in a fallthrough
  3321  // statement.
  3322  func hasFallthrough(stmts []syntax.Stmt) bool {
  3323  	// From spec: the last non-empty statement may be a (possibly labeled) "fallthrough" statement
  3324  	// Stripping (possible nested) labeled statement if any.
  3325  	stmt := lastNonEmptyStmt(stmts)
  3326  	for {
  3327  		ls, ok := stmt.(*syntax.LabeledStmt)
  3328  		if !ok {
  3329  			break
  3330  		}
  3331  		stmt = ls.Stmt
  3332  	}
  3333  	last, ok := stmt.(*syntax.BranchStmt)
  3334  	return ok && last.Tok == syntax.Fallthrough
  3335  }
  3336  
  3337  // lastNonEmptyStmt returns the last non-empty statement in list, if
  3338  // any.
  3339  func lastNonEmptyStmt(stmts []syntax.Stmt) syntax.Stmt {
  3340  	for i := len(stmts) - 1; i >= 0; i-- {
  3341  		stmt := stmts[i]
  3342  		if _, ok := stmt.(*syntax.EmptyStmt); !ok {
  3343  			return stmt
  3344  		}
  3345  	}
  3346  	return nil
  3347  }
  3348  
  3349  // terminates reports whether stmt terminates normal control flow
  3350  // (i.e., does not merely advance to the following statement).
  3351  func (pw *pkgWriter) terminates(stmt syntax.Stmt) bool {
  3352  	switch stmt := stmt.(type) {
  3353  	case *syntax.BranchStmt:
  3354  		if stmt.Tok == syntax.Goto {
  3355  			return true
  3356  		}
  3357  	case *syntax.ReturnStmt:
  3358  		return true
  3359  	case *syntax.ExprStmt:
  3360  		if call, ok := syntax.Unparen(stmt.X).(*syntax.CallExpr); ok {
  3361  			if pw.isBuiltin(call.Fun, "panic") {
  3362  				return true
  3363  			}
  3364  		}
  3365  
  3366  		// The handling of BlockStmt here is approximate, but it serves to
  3367  		// allow dead-code elimination for:
  3368  		//
  3369  		//	if true {
  3370  		//		return x
  3371  		//	}
  3372  		//	unreachable
  3373  	case *syntax.IfStmt:
  3374  		cond := pw.staticBool(&stmt.Cond)
  3375  		return (cond < 0 || pw.terminates(stmt.Then)) && (cond > 0 || pw.terminates(stmt.Else))
  3376  	case *syntax.BlockStmt:
  3377  		return pw.terminates(lastNonEmptyStmt(stmt.List))
  3378  	}
  3379  
  3380  	return false
  3381  }
  3382  

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