src/cmd/compile/internal/noder/unified.go - go - Git at Google

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

 package noder

 import (
 	"fmt"
 	"internal/goversion"
 	"internal/pkgbits"
 	"io"
 	"runtime"
 	"sort"
 	"strings"

 	"cmd/compile/internal/base"
 	"cmd/compile/internal/inline"
 	"cmd/compile/internal/ir"
 	"cmd/compile/internal/typecheck"
 	"cmd/compile/internal/types"
 	"cmd/compile/internal/types2"
 	"cmd/internal/src"
 )

 // localPkgReader holds the package reader used for reading the local
 // package. It exists so the unified IR linker can refer back to it
 // later.
 var localPkgReader *pkgReader

 // unified constructs the local package's Internal Representation (IR)
 // from its syntax tree (AST).
 //
 // The pipeline contains 2 steps:
 //
 //  1. Generate the export data "stub".
 //
 //  2. Generate the IR from the export data above.
 //
 // The package data "stub" at step (1) contains everything from the local package,
 // but nothing that has been imported. When we're actually writing out export data
 // to the output files (see writeNewExport), we run the "linker", which:
 //
 //   - Updates compiler extensions data (e.g. inlining cost, escape analysis results).
 //
 //   - Handles re-exporting any transitive dependencies.
 //
 //   - Prunes out any unnecessary details (e.g. non-inlineable functions, because any
 //     downstream importers only care about inlinable functions).
 //
 // The source files are typechecked twice: once before writing the export data
 // using types2, and again after reading the export data using gc/typecheck.
 // The duplication of work will go away once we only use the types2 type checker,
 // removing the gc/typecheck step. For now, it is kept because:
 //
 //   - It reduces the engineering costs in maintaining a fork of typecheck
 //     (e.g. no need to backport fixes like CL 327651).
 //
 //   - It makes it easier to pass toolstash -cmp.
 //
 //   - Historically, we would always re-run the typechecker after importing a package,
 //     even though we know the imported data is valid. It's not ideal, but it's
 //     not causing any problems either.
 //
 //   - gc/typecheck is still in charge of some transformations, such as rewriting
 //     multi-valued function calls or transforming ir.OINDEX to ir.OINDEXMAP.
 //
 // Using the syntax tree with types2, which has a complete representation of generics,
 // the unified IR has the full typed AST needed for introspection during step (1).
 // In other words, we have all the necessary information to build the generic IR form
 // (see writer.captureVars for an example).
 func unified(m posMap, noders []*noder) {
 	inline.InlineCall = unifiedInlineCall
 	typecheck.HaveInlineBody = unifiedHaveInlineBody

 	data := writePkgStub(m, noders)

 	// We already passed base.Flag.Lang to types2 to handle validating
 	// the user's source code. Bump it up now to the current version and
 	// re-parse, so typecheck doesn't complain if we construct IR that
 	// utilizes newer Go features.
 	base.Flag.Lang = fmt.Sprintf("go1.%d", goversion.Version)
 	types.ParseLangFlag()

 	target := typecheck.Target

 	typecheck.TypecheckAllowed = true

 	localPkgReader = newPkgReader(pkgbits.NewPkgDecoder(types.LocalPkg.Path, data))
 	readPackage(localPkgReader, types.LocalPkg, true)

 	r := localPkgReader.newReader(pkgbits.RelocMeta, pkgbits.PrivateRootIdx, pkgbits.SyncPrivate)
 	r.pkgInit(types.LocalPkg, target)

 	// Type-check any top-level assignments. We ignore non-assignments
 	// here because other declarations are typechecked as they're
 	// constructed.
 	for i, ndecls := 0, len(target.Decls); i < ndecls; i++ {
 		switch n := target.Decls[i]; n.Op() {
 		case ir.OAS, ir.OAS2:
 			target.Decls[i] = typecheck.Stmt(n)
 		}
 	}

 	readBodies(target, false)

 	// Check that nothing snuck past typechecking.
 	for _, n := range target.Decls {
 		if n.Typecheck() == 0 {
 			base.FatalfAt(n.Pos(), "missed typecheck: %v", n)
 		}

 		// For functions, check that at least their first statement (if
 		// any) was typechecked too.
 		if fn, ok := n.(*ir.Func); ok && len(fn.Body) != 0 {
 			if stmt := fn.Body[0]; stmt.Typecheck() == 0 {
 				base.FatalfAt(stmt.Pos(), "missed typecheck: %v", stmt)
 			}
 		}
 	}

 	base.ExitIfErrors() // just in case
 }

 // readBodies iteratively expands all pending dictionaries and
 // function bodies.
 //
 // If duringInlining is true, then the inline.InlineDecls is called as
 // necessary on instantiations of imported generic functions, so their
 // inlining costs can be computed.
 func readBodies(target *ir.Package, duringInlining bool) {
 	var inlDecls []ir.Node

 	// Don't use range--bodyIdx can add closures to todoBodies.
 	for {
 		// The order we expand dictionaries and bodies doesn't matter, so
 		// pop from the end to reduce todoBodies reallocations if it grows
 		// further.
 		//
 		// However, we do at least need to flush any pending dictionaries
 		// before reading bodies, because bodies might reference the
 		// dictionaries.

 		if len(todoDicts) > 0 {
 			fn := todoDicts[len(todoDicts)-1]
 			todoDicts = todoDicts[:len(todoDicts)-1]
 			fn()
 			continue
 		}

 		if len(todoBodies) > 0 {
 			fn := todoBodies[len(todoBodies)-1]
 			todoBodies = todoBodies[:len(todoBodies)-1]

 			pri, ok := bodyReader[fn]
 			assert(ok)
 			pri.funcBody(fn)

 			// Instantiated generic function: add to Decls for typechecking
 			// and compilation.
 			if fn.OClosure == nil && len(pri.dict.targs) != 0 {
 				// cmd/link does not support a type symbol referencing a method symbol
 				// across DSO boundary, so force re-compiling methods on a generic type
 				// even it was seen from imported package in linkshared mode, see #58966.
 				canSkipNonGenericMethod := !(base.Ctxt.Flag_linkshared && ir.IsMethod(fn))
 				if duringInlining && canSkipNonGenericMethod {
 					inlDecls = append(inlDecls, fn)
 				} else {
 					target.Decls = append(target.Decls, fn)
 				}
 			}

 			continue
 		}

 		break
 	}

 	todoDicts = nil
 	todoBodies = nil

 	if len(inlDecls) != 0 {
 		// If we instantiated any generic functions during inlining, we need
 		// to call CanInline on them so they'll be transitively inlined
 		// correctly (#56280).
 		//
 		// We know these functions were already compiled in an imported
 		// package though, so we don't need to actually apply InlineCalls or
 		// save the function bodies any further than this.
 		//
 		// We can also lower the -m flag to 0, to suppress duplicate "can
 		// inline" diagnostics reported against the imported package. Again,
 		// we already reported those diagnostics in the original package, so
 		// it's pointless repeating them here.

 		oldLowerM := base.Flag.LowerM
 		base.Flag.LowerM = 0
 		inline.InlineDecls(nil, inlDecls, false)
 		base.Flag.LowerM = oldLowerM

 		for _, fn := range inlDecls {
 			fn.(*ir.Func).Body = nil // free memory
 		}
 	}
 }

 // writePkgStub type checks the given parsed source files,
 // writes an export data package stub representing them,
 // and returns the result.
 func writePkgStub(m posMap, noders []*noder) string {
 	pkg, info := checkFiles(m, noders)

 	pw := newPkgWriter(m, pkg, info)

 	pw.collectDecls(noders)

 	publicRootWriter := pw.newWriter(pkgbits.RelocMeta, pkgbits.SyncPublic)
 	privateRootWriter := pw.newWriter(pkgbits.RelocMeta, pkgbits.SyncPrivate)

 	assert(publicRootWriter.Idx == pkgbits.PublicRootIdx)
 	assert(privateRootWriter.Idx == pkgbits.PrivateRootIdx)

 	{
 		w := publicRootWriter
 		w.pkg(pkg)
 		w.Bool(false) // TODO(mdempsky): Remove; was "has init"

 		scope := pkg.Scope()
 		names := scope.Names()
 		w.Len(len(names))
 		for _, name := range names {
 			w.obj(scope.Lookup(name), nil)
 		}

 		w.Sync(pkgbits.SyncEOF)
 		w.Flush()
 	}

 	{
 		w := privateRootWriter
 		w.pkgInit(noders)
 		w.Flush()
 	}

 	var sb strings.Builder
 	pw.DumpTo(&sb)

 	// At this point, we're done with types2. Make sure the package is
 	// garbage collected.
 	freePackage(pkg)

 	return sb.String()
 }

 // freePackage ensures the given package is garbage collected.
 func freePackage(pkg *types2.Package) {
 	// The GC test below relies on a precise GC that runs finalizers as
 	// soon as objects are unreachable. Our implementation provides
 	// this, but other/older implementations may not (e.g., Go 1.4 does
 	// not because of #22350). To avoid imposing unnecessary
 	// restrictions on the GOROOT_BOOTSTRAP toolchain, we skip the test
 	// during bootstrapping.
 	if base.CompilerBootstrap || base.Debug.GCCheck == 0 {
 		*pkg = types2.Package{}
 		return
 	}

 	// Set a finalizer on pkg so we can detect if/when it's collected.
 	done := make(chan struct{})
 	runtime.SetFinalizer(pkg, func(*types2.Package) { close(done) })

 	// Important: objects involved in cycles are not finalized, so zero
 	// out pkg to break its cycles and allow the finalizer to run.
 	*pkg = types2.Package{}

 	// It typically takes just 1 or 2 cycles to release pkg, but it
 	// doesn't hurt to try a few more times.
 	for i := 0; i < 10; i++ {
 		select {
 		case <-done:
 			return
 		default:
 			runtime.GC()
 		}
 	}

 	base.Fatalf("package never finalized")
 }

 // readPackage reads package export data from pr to populate
 // importpkg.
 //
 // localStub indicates whether pr is reading the stub export data for
 // the local package, as opposed to relocated export data for an
 // import.
 func readPackage(pr *pkgReader, importpkg *types.Pkg, localStub bool) {
 	{
 		r := pr.newReader(pkgbits.RelocMeta, pkgbits.PublicRootIdx, pkgbits.SyncPublic)

 		pkg := r.pkg()
 		base.Assertf(pkg == importpkg, "have package %q (%p), want package %q (%p)", pkg.Path, pkg, importpkg.Path, importpkg)

 		r.Bool() // TODO(mdempsky): Remove; was "has init"

 		for i, n := 0, r.Len(); i < n; i++ {
 			r.Sync(pkgbits.SyncObject)
 			assert(!r.Bool())
 			idx := r.Reloc(pkgbits.RelocObj)
 			assert(r.Len() == 0)

 			path, name, code := r.p.PeekObj(idx)
 			if code != pkgbits.ObjStub {
 				objReader[types.NewPkg(path, "").Lookup(name)] = pkgReaderIndex{pr, idx, nil, nil, nil}
 			}
 		}

 		r.Sync(pkgbits.SyncEOF)
 	}

 	if !localStub {
 		r := pr.newReader(pkgbits.RelocMeta, pkgbits.PrivateRootIdx, pkgbits.SyncPrivate)

 		if r.Bool() {
 			sym := importpkg.Lookup(".inittask")
 			task := ir.NewNameAt(src.NoXPos, sym)
 			task.Class = ir.PEXTERN
 			sym.Def = task
 		}

 		for i, n := 0, r.Len(); i < n; i++ {
 			path := r.String()
 			name := r.String()
 			idx := r.Reloc(pkgbits.RelocBody)

 			sym := types.NewPkg(path, "").Lookup(name)
 			if _, ok := importBodyReader[sym]; !ok {
 				importBodyReader[sym] = pkgReaderIndex{pr, idx, nil, nil, nil}
 			}
 		}

 		r.Sync(pkgbits.SyncEOF)
 	}
 }

 // writeUnifiedExport writes to `out` the finalized, self-contained
 // Unified IR export data file for the current compilation unit.
 func writeUnifiedExport(out io.Writer) {
 	l := linker{
 		pw: pkgbits.NewPkgEncoder(base.Debug.SyncFrames),

 		pkgs:   make(map[string]pkgbits.Index),
 		decls:  make(map[*types.Sym]pkgbits.Index),
 		bodies: make(map[*types.Sym]pkgbits.Index),
 	}

 	publicRootWriter := l.pw.NewEncoder(pkgbits.RelocMeta, pkgbits.SyncPublic)
 	privateRootWriter := l.pw.NewEncoder(pkgbits.RelocMeta, pkgbits.SyncPrivate)
 	assert(publicRootWriter.Idx == pkgbits.PublicRootIdx)
 	assert(privateRootWriter.Idx == pkgbits.PrivateRootIdx)

 	var selfPkgIdx pkgbits.Index

 	{
 		pr := localPkgReader
 		r := pr.NewDecoder(pkgbits.RelocMeta, pkgbits.PublicRootIdx, pkgbits.SyncPublic)

 		r.Sync(pkgbits.SyncPkg)
 		selfPkgIdx = l.relocIdx(pr, pkgbits.RelocPkg, r.Reloc(pkgbits.RelocPkg))

 		r.Bool() // TODO(mdempsky): Remove; was "has init"

 		for i, n := 0, r.Len(); i < n; i++ {
 			r.Sync(pkgbits.SyncObject)
 			assert(!r.Bool())
 			idx := r.Reloc(pkgbits.RelocObj)
 			assert(r.Len() == 0)

 			xpath, xname, xtag := pr.PeekObj(idx)
 			assert(xpath == pr.PkgPath())
 			assert(xtag != pkgbits.ObjStub)

 			if types.IsExported(xname) {
 				l.relocIdx(pr, pkgbits.RelocObj, idx)
 			}
 		}

 		r.Sync(pkgbits.SyncEOF)
 	}

 	{
 		var idxs []pkgbits.Index
 		for _, idx := range l.decls {
 			idxs = append(idxs, idx)
 		}
 		sort.Slice(idxs, func(i, j int) bool { return idxs[i] < idxs[j] })

 		w := publicRootWriter

 		w.Sync(pkgbits.SyncPkg)
 		w.Reloc(pkgbits.RelocPkg, selfPkgIdx)
 		w.Bool(false) // TODO(mdempsky): Remove; was "has init"

 		w.Len(len(idxs))
 		for _, idx := range idxs {
 			w.Sync(pkgbits.SyncObject)
 			w.Bool(false)
 			w.Reloc(pkgbits.RelocObj, idx)
 			w.Len(0)
 		}

 		w.Sync(pkgbits.SyncEOF)
 		w.Flush()
 	}

 	{
 		type symIdx struct {
 			sym *types.Sym
 			idx pkgbits.Index
 		}
 		var bodies []symIdx
 		for sym, idx := range l.bodies {
 			bodies = append(bodies, symIdx{sym, idx})
 		}
 		sort.Slice(bodies, func(i, j int) bool { return bodies[i].idx < bodies[j].idx })

 		w := privateRootWriter

 		w.Bool(typecheck.Lookup(".inittask").Def != nil)

 		w.Len(len(bodies))
 		for _, body := range bodies {
 			w.String(body.sym.Pkg.Path)
 			w.String(body.sym.Name)
 			w.Reloc(pkgbits.RelocBody, body.idx)
 		}

 		w.Sync(pkgbits.SyncEOF)
 		w.Flush()
 	}

 	base.Ctxt.Fingerprint = l.pw.DumpTo(out)
 }
	// Copyright 2021 The Go Authors. All rights reserved.
	// Use of this source code is governed by a BSD-style
	// license that can be found in the LICENSE file.

	package noder

	import (
	"fmt"
	"internal/goversion"
	"internal/pkgbits"
	"io"
	"runtime"
	"sort"
	"strings"

	"cmd/compile/internal/base"
	"cmd/compile/internal/inline"
	"cmd/compile/internal/ir"
	"cmd/compile/internal/typecheck"
	"cmd/compile/internal/types"
	"cmd/compile/internal/types2"
	"cmd/internal/src"
	)

	// localPkgReader holds the package reader used for reading the local
	// package. It exists so the unified IR linker can refer back to it
	// later.
	var localPkgReader *pkgReader

	// unified constructs the local package's Internal Representation (IR)
	// from its syntax tree (AST).
	//
	// The pipeline contains 2 steps:
	//
	// 1. Generate the export data "stub".
	//
	// 2. Generate the IR from the export data above.
	//
	// The package data "stub" at step (1) contains everything from the local package,
	// but nothing that has been imported. When we're actually writing out export data
	// to the output files (see writeNewExport), we run the "linker", which:
	//
	// - Updates compiler extensions data (e.g. inlining cost, escape analysis results).
	//
	// - Handles re-exporting any transitive dependencies.
	//
	// - Prunes out any unnecessary details (e.g. non-inlineable functions, because any
	// downstream importers only care about inlinable functions).
	//
	// The source files are typechecked twice: once before writing the export data
	// using types2, and again after reading the export data using gc/typecheck.
	// The duplication of work will go away once we only use the types2 type checker,
	// removing the gc/typecheck step. For now, it is kept because:
	//
	// - It reduces the engineering costs in maintaining a fork of typecheck
	// (e.g. no need to backport fixes like CL 327651).
	//
	// - It makes it easier to pass toolstash -cmp.
	//
	// - Historically, we would always re-run the typechecker after importing a package,
	// even though we know the imported data is valid. It's not ideal, but it's
	// not causing any problems either.
	//
	// - gc/typecheck is still in charge of some transformations, such as rewriting
	// multi-valued function calls or transforming ir.OINDEX to ir.OINDEXMAP.
	//
	// Using the syntax tree with types2, which has a complete representation of generics,
	// the unified IR has the full typed AST needed for introspection during step (1).
	// In other words, we have all the necessary information to build the generic IR form
	// (see writer.captureVars for an example).
	func unified(m posMap, noders []*noder) {
	inline.InlineCall = unifiedInlineCall
	typecheck.HaveInlineBody = unifiedHaveInlineBody

	data := writePkgStub(m, noders)

	// We already passed base.Flag.Lang to types2 to handle validating
	// the user's source code. Bump it up now to the current version and
	// re-parse, so typecheck doesn't complain if we construct IR that
	// utilizes newer Go features.
	base.Flag.Lang = fmt.Sprintf("go1.%d", goversion.Version)
	types.ParseLangFlag()

	target := typecheck.Target

	typecheck.TypecheckAllowed = true

	localPkgReader = newPkgReader(pkgbits.NewPkgDecoder(types.LocalPkg.Path, data))
	readPackage(localPkgReader, types.LocalPkg, true)

	r := localPkgReader.newReader(pkgbits.RelocMeta, pkgbits.PrivateRootIdx, pkgbits.SyncPrivate)
	r.pkgInit(types.LocalPkg, target)

	// Type-check any top-level assignments. We ignore non-assignments
	// here because other declarations are typechecked as they're
	// constructed.
	for i, ndecls := 0, len(target.Decls); i < ndecls; i++ {
	switch n := target.Decls[i]; n.Op() {
	case ir.OAS, ir.OAS2:
	target.Decls[i] = typecheck.Stmt(n)
	}
	}

	readBodies(target, false)

	// Check that nothing snuck past typechecking.
	for _, n := range target.Decls {
	if n.Typecheck() == 0 {
	base.FatalfAt(n.Pos(), "missed typecheck: %v", n)
	}

	// For functions, check that at least their first statement (if
	// any) was typechecked too.
	if fn, ok := n.(*ir.Func); ok && len(fn.Body) != 0 {
	if stmt := fn.Body[0]; stmt.Typecheck() == 0 {
	base.FatalfAt(stmt.Pos(), "missed typecheck: %v", stmt)
	}
	}
	}

	base.ExitIfErrors() // just in case
	}

	// readBodies iteratively expands all pending dictionaries and
	// function bodies.
	//
	// If duringInlining is true, then the inline.InlineDecls is called as
	// necessary on instantiations of imported generic functions, so their
	// inlining costs can be computed.
	func readBodies(target *ir.Package, duringInlining bool) {
	var inlDecls []ir.Node

	// Don't use range--bodyIdx can add closures to todoBodies.
	for {
	// The order we expand dictionaries and bodies doesn't matter, so
	// pop from the end to reduce todoBodies reallocations if it grows
	// further.
	//
	// However, we do at least need to flush any pending dictionaries
	// before reading bodies, because bodies might reference the
	// dictionaries.

	if len(todoDicts) > 0 {
	fn := todoDicts[len(todoDicts)-1]
	todoDicts = todoDicts[:len(todoDicts)-1]
	fn()
	continue
	}

	if len(todoBodies) > 0 {
	fn := todoBodies[len(todoBodies)-1]
	todoBodies = todoBodies[:len(todoBodies)-1]

	pri, ok := bodyReader[fn]
	assert(ok)
	pri.funcBody(fn)

	// Instantiated generic function: add to Decls for typechecking
	// and compilation.
	if fn.OClosure == nil && len(pri.dict.targs) != 0 {
	// cmd/link does not support a type symbol referencing a method symbol
	// across DSO boundary, so force re-compiling methods on a generic type
	// even it was seen from imported package in linkshared mode, see #58966.
	canSkipNonGenericMethod := !(base.Ctxt.Flag_linkshared && ir.IsMethod(fn))
	if duringInlining && canSkipNonGenericMethod {
	inlDecls = append(inlDecls, fn)
	} else {
	target.Decls = append(target.Decls, fn)
	}
	}

	continue
	}

	break
	}

	todoDicts = nil
	todoBodies = nil

	if len(inlDecls) != 0 {
	// If we instantiated any generic functions during inlining, we need
	// to call CanInline on them so they'll be transitively inlined
	// correctly (#56280).
	//
	// We know these functions were already compiled in an imported
	// package though, so we don't need to actually apply InlineCalls or
	// save the function bodies any further than this.
	//
	// We can also lower the -m flag to 0, to suppress duplicate "can
	// inline" diagnostics reported against the imported package. Again,
	// we already reported those diagnostics in the original package, so
	// it's pointless repeating them here.

	oldLowerM := base.Flag.LowerM
	base.Flag.LowerM = 0
	inline.InlineDecls(nil, inlDecls, false)
	base.Flag.LowerM = oldLowerM

	for _, fn := range inlDecls {
	fn.(*ir.Func).Body = nil // free memory
	}
	}
	}

	// writePkgStub type checks the given parsed source files,
	// writes an export data package stub representing them,
	// and returns the result.
	func writePkgStub(m posMap, noders []*noder) string {
	pkg, info := checkFiles(m, noders)

	pw := newPkgWriter(m, pkg, info)

	pw.collectDecls(noders)

	publicRootWriter := pw.newWriter(pkgbits.RelocMeta, pkgbits.SyncPublic)
	privateRootWriter := pw.newWriter(pkgbits.RelocMeta, pkgbits.SyncPrivate)

	assert(publicRootWriter.Idx == pkgbits.PublicRootIdx)
	assert(privateRootWriter.Idx == pkgbits.PrivateRootIdx)

	{
	w := publicRootWriter
	w.pkg(pkg)
	w.Bool(false) // TODO(mdempsky): Remove; was "has init"

	scope := pkg.Scope()
	names := scope.Names()
	w.Len(len(names))
	for _, name := range names {
	w.obj(scope.Lookup(name), nil)
	}

	w.Sync(pkgbits.SyncEOF)
	w.Flush()
	}

	{
	w := privateRootWriter
	w.pkgInit(noders)
	w.Flush()
	}

	var sb strings.Builder
	pw.DumpTo(&sb)

	// At this point, we're done with types2. Make sure the package is
	// garbage collected.
	freePackage(pkg)

	return sb.String()
	}

	// freePackage ensures the given package is garbage collected.
	func freePackage(pkg *types2.Package) {
	// The GC test below relies on a precise GC that runs finalizers as
	// soon as objects are unreachable. Our implementation provides
	// this, but other/older implementations may not (e.g., Go 1.4 does
	// not because of #22350). To avoid imposing unnecessary
	// restrictions on the GOROOT_BOOTSTRAP toolchain, we skip the test
	// during bootstrapping.
	if base.CompilerBootstrap \|\| base.Debug.GCCheck == 0 {
	*pkg = types2.Package{}
	return
	}

	// Set a finalizer on pkg so we can detect if/when it's collected.
	done := make(chan struct{})
	runtime.SetFinalizer(pkg, func(*types2.Package) { close(done) })

	// Important: objects involved in cycles are not finalized, so zero
	// out pkg to break its cycles and allow the finalizer to run.
	*pkg = types2.Package{}

	// It typically takes just 1 or 2 cycles to release pkg, but it
	// doesn't hurt to try a few more times.
	for i := 0; i < 10; i++ {
	select {
	case <-done:
	return
	default:
	runtime.GC()
	}
	}

	base.Fatalf("package never finalized")
	}

	// readPackage reads package export data from pr to populate
	// importpkg.
	//
	// localStub indicates whether pr is reading the stub export data for
	// the local package, as opposed to relocated export data for an
	// import.
	func readPackage(pr pkgReader, importpkg types.Pkg, localStub bool) {
	{
	r := pr.newReader(pkgbits.RelocMeta, pkgbits.PublicRootIdx, pkgbits.SyncPublic)

	pkg := r.pkg()
	base.Assertf(pkg == importpkg, "have package %q (%p), want package %q (%p)", pkg.Path, pkg, importpkg.Path, importpkg)

	r.Bool() // TODO(mdempsky): Remove; was "has init"

	for i, n := 0, r.Len(); i < n; i++ {
	r.Sync(pkgbits.SyncObject)
	assert(!r.Bool())
	idx := r.Reloc(pkgbits.RelocObj)
	assert(r.Len() == 0)

	path, name, code := r.p.PeekObj(idx)
	if code != pkgbits.ObjStub {
	objReader[types.NewPkg(path, "").Lookup(name)] = pkgReaderIndex{pr, idx, nil, nil, nil}
	}
	}

	r.Sync(pkgbits.SyncEOF)
	}

	if !localStub {
	r := pr.newReader(pkgbits.RelocMeta, pkgbits.PrivateRootIdx, pkgbits.SyncPrivate)

	if r.Bool() {
	sym := importpkg.Lookup(".inittask")
	task := ir.NewNameAt(src.NoXPos, sym)
	task.Class = ir.PEXTERN
	sym.Def = task
	}

	for i, n := 0, r.Len(); i < n; i++ {
	path := r.String()
	name := r.String()
	idx := r.Reloc(pkgbits.RelocBody)

	sym := types.NewPkg(path, "").Lookup(name)
	if _, ok := importBodyReader[sym]; !ok {
	importBodyReader[sym] = pkgReaderIndex{pr, idx, nil, nil, nil}
	}
	}

	r.Sync(pkgbits.SyncEOF)
	}
	}

	// writeUnifiedExport writes to `out` the finalized, self-contained
	// Unified IR export data file for the current compilation unit.
	func writeUnifiedExport(out io.Writer) {
	l := linker{
	pw: pkgbits.NewPkgEncoder(base.Debug.SyncFrames),

	pkgs: make(map[string]pkgbits.Index),
	decls: make(map[*types.Sym]pkgbits.Index),
	bodies: make(map[*types.Sym]pkgbits.Index),
	}

	publicRootWriter := l.pw.NewEncoder(pkgbits.RelocMeta, pkgbits.SyncPublic)
	privateRootWriter := l.pw.NewEncoder(pkgbits.RelocMeta, pkgbits.SyncPrivate)
	assert(publicRootWriter.Idx == pkgbits.PublicRootIdx)
	assert(privateRootWriter.Idx == pkgbits.PrivateRootIdx)

	var selfPkgIdx pkgbits.Index

	{
	pr := localPkgReader
	r := pr.NewDecoder(pkgbits.RelocMeta, pkgbits.PublicRootIdx, pkgbits.SyncPublic)

	r.Sync(pkgbits.SyncPkg)
	selfPkgIdx = l.relocIdx(pr, pkgbits.RelocPkg, r.Reloc(pkgbits.RelocPkg))

	r.Bool() // TODO(mdempsky): Remove; was "has init"

	for i, n := 0, r.Len(); i < n; i++ {
	r.Sync(pkgbits.SyncObject)
	assert(!r.Bool())
	idx := r.Reloc(pkgbits.RelocObj)
	assert(r.Len() == 0)

	xpath, xname, xtag := pr.PeekObj(idx)
	assert(xpath == pr.PkgPath())
	assert(xtag != pkgbits.ObjStub)

	if types.IsExported(xname) {
	l.relocIdx(pr, pkgbits.RelocObj, idx)
	}
	}

	r.Sync(pkgbits.SyncEOF)
	}

	{
	var idxs []pkgbits.Index
	for _, idx := range l.decls {
	idxs = append(idxs, idx)
	}
	sort.Slice(idxs, func(i, j int) bool { return idxs[i] < idxs[j] })

	w := publicRootWriter

	w.Sync(pkgbits.SyncPkg)
	w.Reloc(pkgbits.RelocPkg, selfPkgIdx)
	w.Bool(false) // TODO(mdempsky): Remove; was "has init"

	w.Len(len(idxs))
	for _, idx := range idxs {
	w.Sync(pkgbits.SyncObject)
	w.Bool(false)
	w.Reloc(pkgbits.RelocObj, idx)
	w.Len(0)
	}

	w.Sync(pkgbits.SyncEOF)
	w.Flush()
	}

	{
	type symIdx struct {
	sym *types.Sym
	idx pkgbits.Index
	}
	var bodies []symIdx
	for sym, idx := range l.bodies {
	bodies = append(bodies, symIdx{sym, idx})
	}
	sort.Slice(bodies, func(i, j int) bool { return bodies[i].idx < bodies[j].idx })

	w := privateRootWriter

	w.Bool(typecheck.Lookup(".inittask").Def != nil)

	w.Len(len(bodies))
	for _, body := range bodies {
	w.String(body.sym.Pkg.Path)
	w.String(body.sym.Name)
	w.Reloc(pkgbits.RelocBody, body.idx)
	}

	w.Sync(pkgbits.SyncEOF)
	w.Flush()
	}

	base.Ctxt.Fingerprint = l.pw.DumpTo(out)
	}