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

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