diff --git a/go/gcexportdata/gcexportdata.go b/go/gcexportdata/gcexportdata.go
index f8363d8faa..0d51acad99 100644
--- a/go/gcexportdata/gcexportdata.go
+++ b/go/gcexportdata/gcexportdata.go
@@ -85,15 +85,11 @@ func Read(in io.Reader, fset *token.FileSet, imports map[string]*types.Package,
 		return gcimporter.ImportData(imports, path, path, bytes.NewReader(data))
 	}
 
-	// The indexed export format starts with an 'i'; the older
-	// binary export format starts with a 'c', 'd', or 'v'
-	// (from "version"). Select appropriate importer.
-	if len(data) > 0 && data[0] == 'i' {
-		_, pkg, err := gcimporter.IImportData(fset, imports, data[1:], path)
-		return pkg, err
+	// The indexed export format starts with an 'i'.
+	if len(data) == 0 || data[0] != 'i' {
+		return nil, fmt.Errorf("unknown export data format")
 	}
-
-	_, pkg, err := gcimporter.BImportData(fset, imports, data, path)
+	_, pkg, err := gcimporter.IImportData(fset, imports, data[1:], path)
 	return pkg, err
 }
 
diff --git a/go/internal/gcimporter/bexport.go b/go/internal/gcimporter/bexport.go
deleted file mode 100644
index a807d0aaa2..0000000000
--- a/go/internal/gcimporter/bexport.go
+++ /dev/null
@@ -1,852 +0,0 @@
-// Copyright 2016 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.
-
-// Binary package export.
-// This file was derived from $GOROOT/src/cmd/compile/internal/gc/bexport.go;
-// see that file for specification of the format.
-
-package gcimporter
-
-import (
-	"bytes"
-	"encoding/binary"
-	"fmt"
-	"go/ast"
-	"go/constant"
-	"go/token"
-	"go/types"
-	"math"
-	"math/big"
-	"sort"
-	"strings"
-)
-
-// If debugFormat is set, each integer and string value is preceded by a marker
-// and position information in the encoding. This mechanism permits an importer
-// to recognize immediately when it is out of sync. The importer recognizes this
-// mode automatically (i.e., it can import export data produced with debugging
-// support even if debugFormat is not set at the time of import). This mode will
-// lead to massively larger export data (by a factor of 2 to 3) and should only
-// be enabled during development and debugging.
-//
-// NOTE: This flag is the first flag to enable if importing dies because of
-// (suspected) format errors, and whenever a change is made to the format.
-const debugFormat = false // default: false
-
-// If trace is set, debugging output is printed to std out.
-const trace = false // default: false
-
-// Current export format version. Increase with each format change.
-// Note: The latest binary (non-indexed) export format is at version 6.
-//       This exporter is still at level 4, but it doesn't matter since
-//       the binary importer can handle older versions just fine.
-// 6: package height (CL 105038) -- NOT IMPLEMENTED HERE
-// 5: improved position encoding efficiency (issue 20080, CL 41619) -- NOT IMPLEMEMTED HERE
-// 4: type name objects support type aliases, uses aliasTag
-// 3: Go1.8 encoding (same as version 2, aliasTag defined but never used)
-// 2: removed unused bool in ODCL export (compiler only)
-// 1: header format change (more regular), export package for _ struct fields
-// 0: Go1.7 encoding
-const exportVersion = 4
-
-// trackAllTypes enables cycle tracking for all types, not just named
-// types. The existing compiler invariants assume that unnamed types
-// that are not completely set up are not used, or else there are spurious
-// errors.
-// If disabled, only named types are tracked, possibly leading to slightly
-// less efficient encoding in rare cases. It also prevents the export of
-// some corner-case type declarations (but those are not handled correctly
-// with with the textual export format either).
-// TODO(gri) enable and remove once issues caused by it are fixed
-const trackAllTypes = false
-
-type exporter struct {
-	fset *token.FileSet
-	out  bytes.Buffer
-
-	// object -> index maps, indexed in order of serialization
-	strIndex map[string]int
-	pkgIndex map[*types.Package]int
-	typIndex map[types.Type]int
-
-	// position encoding
-	posInfoFormat bool
-	prevFile      string
-	prevLine      int
-
-	// debugging support
-	written int // bytes written
-	indent  int // for trace
-}
-
-// internalError represents an error generated inside this package.
-type internalError string
-
-func (e internalError) Error() string { return "gcimporter: " + string(e) }
-
-func internalErrorf(format string, args ...interface{}) error {
-	return internalError(fmt.Sprintf(format, args...))
-}
-
-// BExportData returns binary export data for pkg.
-// If no file set is provided, position info will be missing.
-func BExportData(fset *token.FileSet, pkg *types.Package) (b []byte, err error) {
-	defer func() {
-		if e := recover(); e != nil {
-			if ierr, ok := e.(internalError); ok {
-				err = ierr
-				return
-			}
-			// Not an internal error; panic again.
-			panic(e)
-		}
-	}()
-
-	p := exporter{
-		fset:          fset,
-		strIndex:      map[string]int{"": 0}, // empty string is mapped to 0
-		pkgIndex:      make(map[*types.Package]int),
-		typIndex:      make(map[types.Type]int),
-		posInfoFormat: true, // TODO(gri) might become a flag, eventually
-	}
-
-	// write version info
-	// The version string must start with "version %d" where %d is the version
-	// number. Additional debugging information may follow after a blank; that
-	// text is ignored by the importer.
-	p.rawStringln(fmt.Sprintf("version %d", exportVersion))
-	var debug string
-	if debugFormat {
-		debug = "debug"
-	}
-	p.rawStringln(debug) // cannot use p.bool since it's affected by debugFormat; also want to see this clearly
-	p.bool(trackAllTypes)
-	p.bool(p.posInfoFormat)
-
-	// --- generic export data ---
-
-	// populate type map with predeclared "known" types
-	for index, typ := range predeclared() {
-		p.typIndex[typ] = index
-	}
-	if len(p.typIndex) != len(predeclared()) {
-		return nil, internalError("duplicate entries in type map?")
-	}
-
-	// write package data
-	p.pkg(pkg, true)
-	if trace {
-		p.tracef("\n")
-	}
-
-	// write objects
-	objcount := 0
-	scope := pkg.Scope()
-	for _, name := range scope.Names() {
-		if !ast.IsExported(name) {
-			continue
-		}
-		if trace {
-			p.tracef("\n")
-		}
-		p.obj(scope.Lookup(name))
-		objcount++
-	}
-
-	// indicate end of list
-	if trace {
-		p.tracef("\n")
-	}
-	p.tag(endTag)
-
-	// for self-verification only (redundant)
-	p.int(objcount)
-
-	if trace {
-		p.tracef("\n")
-	}
-
-	// --- end of export data ---
-
-	return p.out.Bytes(), nil
-}
-
-func (p *exporter) pkg(pkg *types.Package, emptypath bool) {
-	if pkg == nil {
-		panic(internalError("unexpected nil pkg"))
-	}
-
-	// if we saw the package before, write its index (>= 0)
-	if i, ok := p.pkgIndex[pkg]; ok {
-		p.index('P', i)
-		return
-	}
-
-	// otherwise, remember the package, write the package tag (< 0) and package data
-	if trace {
-		p.tracef("P%d = { ", len(p.pkgIndex))
-		defer p.tracef("} ")
-	}
-	p.pkgIndex[pkg] = len(p.pkgIndex)
-
-	p.tag(packageTag)
-	p.string(pkg.Name())
-	if emptypath {
-		p.string("")
-	} else {
-		p.string(pkg.Path())
-	}
-}
-
-func (p *exporter) obj(obj types.Object) {
-	switch obj := obj.(type) {
-	case *types.Const:
-		p.tag(constTag)
-		p.pos(obj)
-		p.qualifiedName(obj)
-		p.typ(obj.Type())
-		p.value(obj.Val())
-
-	case *types.TypeName:
-		if obj.IsAlias() {
-			p.tag(aliasTag)
-			p.pos(obj)
-			p.qualifiedName(obj)
-		} else {
-			p.tag(typeTag)
-		}
-		p.typ(obj.Type())
-
-	case *types.Var:
-		p.tag(varTag)
-		p.pos(obj)
-		p.qualifiedName(obj)
-		p.typ(obj.Type())
-
-	case *types.Func:
-		p.tag(funcTag)
-		p.pos(obj)
-		p.qualifiedName(obj)
-		sig := obj.Type().(*types.Signature)
-		p.paramList(sig.Params(), sig.Variadic())
-		p.paramList(sig.Results(), false)
-
-	default:
-		panic(internalErrorf("unexpected object %v (%T)", obj, obj))
-	}
-}
-
-func (p *exporter) pos(obj types.Object) {
-	if !p.posInfoFormat {
-		return
-	}
-
-	file, line := p.fileLine(obj)
-	if file == p.prevFile {
-		// common case: write line delta
-		// delta == 0 means different file or no line change
-		delta := line - p.prevLine
-		p.int(delta)
-		if delta == 0 {
-			p.int(-1) // -1 means no file change
-		}
-	} else {
-		// different file
-		p.int(0)
-		// Encode filename as length of common prefix with previous
-		// filename, followed by (possibly empty) suffix. Filenames
-		// frequently share path prefixes, so this can save a lot
-		// of space and make export data size less dependent on file
-		// path length. The suffix is unlikely to be empty because
-		// file names tend to end in ".go".
-		n := commonPrefixLen(p.prevFile, file)
-		p.int(n)           // n >= 0
-		p.string(file[n:]) // write suffix only
-		p.prevFile = file
-		p.int(line)
-	}
-	p.prevLine = line
-}
-
-func (p *exporter) fileLine(obj types.Object) (file string, line int) {
-	if p.fset != nil {
-		pos := p.fset.Position(obj.Pos())
-		file = pos.Filename
-		line = pos.Line
-	}
-	return
-}
-
-func commonPrefixLen(a, b string) int {
-	if len(a) > len(b) {
-		a, b = b, a
-	}
-	// len(a) <= len(b)
-	i := 0
-	for i < len(a) && a[i] == b[i] {
-		i++
-	}
-	return i
-}
-
-func (p *exporter) qualifiedName(obj types.Object) {
-	p.string(obj.Name())
-	p.pkg(obj.Pkg(), false)
-}
-
-func (p *exporter) typ(t types.Type) {
-	if t == nil {
-		panic(internalError("nil type"))
-	}
-
-	// Possible optimization: Anonymous pointer types *T where
-	// T is a named type are common. We could canonicalize all
-	// such types *T to a single type PT = *T. This would lead
-	// to at most one *T entry in typIndex, and all future *T's
-	// would be encoded as the respective index directly. Would
-	// save 1 byte (pointerTag) per *T and reduce the typIndex
-	// size (at the cost of a canonicalization map). We can do
-	// this later, without encoding format change.
-
-	// if we saw the type before, write its index (>= 0)
-	if i, ok := p.typIndex[t]; ok {
-		p.index('T', i)
-		return
-	}
-
-	// otherwise, remember the type, write the type tag (< 0) and type data
-	if trackAllTypes {
-		if trace {
-			p.tracef("T%d = {>\n", len(p.typIndex))
-			defer p.tracef("<\n} ")
-		}
-		p.typIndex[t] = len(p.typIndex)
-	}
-
-	switch t := t.(type) {
-	case *types.Named:
-		if !trackAllTypes {
-			// if we don't track all types, track named types now
-			p.typIndex[t] = len(p.typIndex)
-		}
-
-		p.tag(namedTag)
-		p.pos(t.Obj())
-		p.qualifiedName(t.Obj())
-		p.typ(t.Underlying())
-		if !types.IsInterface(t) {
-			p.assocMethods(t)
-		}
-
-	case *types.Array:
-		p.tag(arrayTag)
-		p.int64(t.Len())
-		p.typ(t.Elem())
-
-	case *types.Slice:
-		p.tag(sliceTag)
-		p.typ(t.Elem())
-
-	case *dddSlice:
-		p.tag(dddTag)
-		p.typ(t.elem)
-
-	case *types.Struct:
-		p.tag(structTag)
-		p.fieldList(t)
-
-	case *types.Pointer:
-		p.tag(pointerTag)
-		p.typ(t.Elem())
-
-	case *types.Signature:
-		p.tag(signatureTag)
-		p.paramList(t.Params(), t.Variadic())
-		p.paramList(t.Results(), false)
-
-	case *types.Interface:
-		p.tag(interfaceTag)
-		p.iface(t)
-
-	case *types.Map:
-		p.tag(mapTag)
-		p.typ(t.Key())
-		p.typ(t.Elem())
-
-	case *types.Chan:
-		p.tag(chanTag)
-		p.int(int(3 - t.Dir())) // hack
-		p.typ(t.Elem())
-
-	default:
-		panic(internalErrorf("unexpected type %T: %s", t, t))
-	}
-}
-
-func (p *exporter) assocMethods(named *types.Named) {
-	// Sort methods (for determinism).
-	var methods []*types.Func
-	for i := 0; i < named.NumMethods(); i++ {
-		methods = append(methods, named.Method(i))
-	}
-	sort.Sort(methodsByName(methods))
-
-	p.int(len(methods))
-
-	if trace && methods != nil {
-		p.tracef("associated methods {>\n")
-	}
-
-	for i, m := range methods {
-		if trace && i > 0 {
-			p.tracef("\n")
-		}
-
-		p.pos(m)
-		name := m.Name()
-		p.string(name)
-		if !exported(name) {
-			p.pkg(m.Pkg(), false)
-		}
-
-		sig := m.Type().(*types.Signature)
-		p.paramList(types.NewTuple(sig.Recv()), false)
-		p.paramList(sig.Params(), sig.Variadic())
-		p.paramList(sig.Results(), false)
-		p.int(0) // dummy value for go:nointerface pragma - ignored by importer
-	}
-
-	if trace && methods != nil {
-		p.tracef("<\n} ")
-	}
-}
-
-type methodsByName []*types.Func
-
-func (x methodsByName) Len() int           { return len(x) }
-func (x methodsByName) Swap(i, j int)      { x[i], x[j] = x[j], x[i] }
-func (x methodsByName) Less(i, j int) bool { return x[i].Name() < x[j].Name() }
-
-func (p *exporter) fieldList(t *types.Struct) {
-	if trace && t.NumFields() > 0 {
-		p.tracef("fields {>\n")
-		defer p.tracef("<\n} ")
-	}
-
-	p.int(t.NumFields())
-	for i := 0; i < t.NumFields(); i++ {
-		if trace && i > 0 {
-			p.tracef("\n")
-		}
-		p.field(t.Field(i))
-		p.string(t.Tag(i))
-	}
-}
-
-func (p *exporter) field(f *types.Var) {
-	if !f.IsField() {
-		panic(internalError("field expected"))
-	}
-
-	p.pos(f)
-	p.fieldName(f)
-	p.typ(f.Type())
-}
-
-func (p *exporter) iface(t *types.Interface) {
-	// TODO(gri): enable importer to load embedded interfaces,
-	// then emit Embeddeds and ExplicitMethods separately here.
-	p.int(0)
-
-	n := t.NumMethods()
-	if trace && n > 0 {
-		p.tracef("methods {>\n")
-		defer p.tracef("<\n} ")
-	}
-	p.int(n)
-	for i := 0; i < n; i++ {
-		if trace && i > 0 {
-			p.tracef("\n")
-		}
-		p.method(t.Method(i))
-	}
-}
-
-func (p *exporter) method(m *types.Func) {
-	sig := m.Type().(*types.Signature)
-	if sig.Recv() == nil {
-		panic(internalError("method expected"))
-	}
-
-	p.pos(m)
-	p.string(m.Name())
-	if m.Name() != "_" && !ast.IsExported(m.Name()) {
-		p.pkg(m.Pkg(), false)
-	}
-
-	// interface method; no need to encode receiver.
-	p.paramList(sig.Params(), sig.Variadic())
-	p.paramList(sig.Results(), false)
-}
-
-func (p *exporter) fieldName(f *types.Var) {
-	name := f.Name()
-
-	if f.Anonymous() {
-		// anonymous field - we distinguish between 3 cases:
-		// 1) field name matches base type name and is exported
-		// 2) field name matches base type name and is not exported
-		// 3) field name doesn't match base type name (alias name)
-		bname := basetypeName(f.Type())
-		if name == bname {
-			if ast.IsExported(name) {
-				name = "" // 1) we don't need to know the field name or package
-			} else {
-				name = "?" // 2) use unexported name "?" to force package export
-			}
-		} else {
-			// 3) indicate alias and export name as is
-			// (this requires an extra "@" but this is a rare case)
-			p.string("@")
-		}
-	}
-
-	p.string(name)
-	if name != "" && !ast.IsExported(name) {
-		p.pkg(f.Pkg(), false)
-	}
-}
-
-func basetypeName(typ types.Type) string {
-	switch typ := deref(typ).(type) {
-	case *types.Basic:
-		return typ.Name()
-	case *types.Named:
-		return typ.Obj().Name()
-	default:
-		return "" // unnamed type
-	}
-}
-
-func (p *exporter) paramList(params *types.Tuple, variadic bool) {
-	// use negative length to indicate unnamed parameters
-	// (look at the first parameter only since either all
-	// names are present or all are absent)
-	n := params.Len()
-	if n > 0 && params.At(0).Name() == "" {
-		n = -n
-	}
-	p.int(n)
-	for i := 0; i < params.Len(); i++ {
-		q := params.At(i)
-		t := q.Type()
-		if variadic && i == params.Len()-1 {
-			t = &dddSlice{t.(*types.Slice).Elem()}
-		}
-		p.typ(t)
-		if n > 0 {
-			name := q.Name()
-			p.string(name)
-			if name != "_" {
-				p.pkg(q.Pkg(), false)
-			}
-		}
-		p.string("") // no compiler-specific info
-	}
-}
-
-func (p *exporter) value(x constant.Value) {
-	if trace {
-		p.tracef("= ")
-	}
-
-	switch x.Kind() {
-	case constant.Bool:
-		tag := falseTag
-		if constant.BoolVal(x) {
-			tag = trueTag
-		}
-		p.tag(tag)
-
-	case constant.Int:
-		if v, exact := constant.Int64Val(x); exact {
-			// common case: x fits into an int64 - use compact encoding
-			p.tag(int64Tag)
-			p.int64(v)
-			return
-		}
-		// uncommon case: large x - use float encoding
-		// (powers of 2 will be encoded efficiently with exponent)
-		p.tag(floatTag)
-		p.float(constant.ToFloat(x))
-
-	case constant.Float:
-		p.tag(floatTag)
-		p.float(x)
-
-	case constant.Complex:
-		p.tag(complexTag)
-		p.float(constant.Real(x))
-		p.float(constant.Imag(x))
-
-	case constant.String:
-		p.tag(stringTag)
-		p.string(constant.StringVal(x))
-
-	case constant.Unknown:
-		// package contains type errors
-		p.tag(unknownTag)
-
-	default:
-		panic(internalErrorf("unexpected value %v (%T)", x, x))
-	}
-}
-
-func (p *exporter) float(x constant.Value) {
-	if x.Kind() != constant.Float {
-		panic(internalErrorf("unexpected constant %v, want float", x))
-	}
-	// extract sign (there is no -0)
-	sign := constant.Sign(x)
-	if sign == 0 {
-		// x == 0
-		p.int(0)
-		return
-	}
-	// x != 0
-
-	var f big.Float
-	if v, exact := constant.Float64Val(x); exact {
-		// float64
-		f.SetFloat64(v)
-	} else if num, denom := constant.Num(x), constant.Denom(x); num.Kind() == constant.Int {
-		// TODO(gri): add big.Rat accessor to constant.Value.
-		r := valueToRat(num)
-		f.SetRat(r.Quo(r, valueToRat(denom)))
-	} else {
-		// Value too large to represent as a fraction => inaccessible.
-		// TODO(gri): add big.Float accessor to constant.Value.
-		f.SetFloat64(math.MaxFloat64) // FIXME
-	}
-
-	// extract exponent such that 0.5 <= m < 1.0
-	var m big.Float
-	exp := f.MantExp(&m)
-
-	// extract mantissa as *big.Int
-	// - set exponent large enough so mant satisfies mant.IsInt()
-	// - get *big.Int from mant
-	m.SetMantExp(&m, int(m.MinPrec()))
-	mant, acc := m.Int(nil)
-	if acc != big.Exact {
-		panic(internalError("internal error"))
-	}
-
-	p.int(sign)
-	p.int(exp)
-	p.string(string(mant.Bytes()))
-}
-
-func valueToRat(x constant.Value) *big.Rat {
-	// Convert little-endian to big-endian.
-	// I can't believe this is necessary.
-	bytes := constant.Bytes(x)
-	for i := 0; i < len(bytes)/2; i++ {
-		bytes[i], bytes[len(bytes)-1-i] = bytes[len(bytes)-1-i], bytes[i]
-	}
-	return new(big.Rat).SetInt(new(big.Int).SetBytes(bytes))
-}
-
-func (p *exporter) bool(b bool) bool {
-	if trace {
-		p.tracef("[")
-		defer p.tracef("= %v] ", b)
-	}
-
-	x := 0
-	if b {
-		x = 1
-	}
-	p.int(x)
-	return b
-}
-
-// ----------------------------------------------------------------------------
-// Low-level encoders
-
-func (p *exporter) index(marker byte, index int) {
-	if index < 0 {
-		panic(internalError("invalid index < 0"))
-	}
-	if debugFormat {
-		p.marker('t')
-	}
-	if trace {
-		p.tracef("%c%d ", marker, index)
-	}
-	p.rawInt64(int64(index))
-}
-
-func (p *exporter) tag(tag int) {
-	if tag >= 0 {
-		panic(internalError("invalid tag >= 0"))
-	}
-	if debugFormat {
-		p.marker('t')
-	}
-	if trace {
-		p.tracef("%s ", tagString[-tag])
-	}
-	p.rawInt64(int64(tag))
-}
-
-func (p *exporter) int(x int) {
-	p.int64(int64(x))
-}
-
-func (p *exporter) int64(x int64) {
-	if debugFormat {
-		p.marker('i')
-	}
-	if trace {
-		p.tracef("%d ", x)
-	}
-	p.rawInt64(x)
-}
-
-func (p *exporter) string(s string) {
-	if debugFormat {
-		p.marker('s')
-	}
-	if trace {
-		p.tracef("%q ", s)
-	}
-	// if we saw the string before, write its index (>= 0)
-	// (the empty string is mapped to 0)
-	if i, ok := p.strIndex[s]; ok {
-		p.rawInt64(int64(i))
-		return
-	}
-	// otherwise, remember string and write its negative length and bytes
-	p.strIndex[s] = len(p.strIndex)
-	p.rawInt64(-int64(len(s)))
-	for i := 0; i < len(s); i++ {
-		p.rawByte(s[i])
-	}
-}
-
-// marker emits a marker byte and position information which makes
-// it easy for a reader to detect if it is "out of sync". Used for
-// debugFormat format only.
-func (p *exporter) marker(m byte) {
-	p.rawByte(m)
-	// Enable this for help tracking down the location
-	// of an incorrect marker when running in debugFormat.
-	if false && trace {
-		p.tracef("#%d ", p.written)
-	}
-	p.rawInt64(int64(p.written))
-}
-
-// rawInt64 should only be used by low-level encoders.
-func (p *exporter) rawInt64(x int64) {
-	var tmp [binary.MaxVarintLen64]byte
-	n := binary.PutVarint(tmp[:], x)
-	for i := 0; i < n; i++ {
-		p.rawByte(tmp[i])
-	}
-}
-
-// rawStringln should only be used to emit the initial version string.
-func (p *exporter) rawStringln(s string) {
-	for i := 0; i < len(s); i++ {
-		p.rawByte(s[i])
-	}
-	p.rawByte('\n')
-}
-
-// rawByte is the bottleneck interface to write to p.out.
-// rawByte escapes b as follows (any encoding does that
-// hides '$'):
-//
-//	'$'  => '|' 'S'
-//	'|'  => '|' '|'
-//
-// Necessary so other tools can find the end of the
-// export data by searching for "$$".
-// rawByte should only be used by low-level encoders.
-func (p *exporter) rawByte(b byte) {
-	switch b {
-	case '$':
-		// write '$' as '|' 'S'
-		b = 'S'
-		fallthrough
-	case '|':
-		// write '|' as '|' '|'
-		p.out.WriteByte('|')
-		p.written++
-	}
-	p.out.WriteByte(b)
-	p.written++
-}
-
-// tracef is like fmt.Printf but it rewrites the format string
-// to take care of indentation.
-func (p *exporter) tracef(format string, args ...interface{}) {
-	if strings.ContainsAny(format, "<>\n") {
-		var buf bytes.Buffer
-		for i := 0; i < len(format); i++ {
-			// no need to deal with runes
-			ch := format[i]
-			switch ch {
-			case '>':
-				p.indent++
-				continue
-			case '<':
-				p.indent--
-				continue
-			}
-			buf.WriteByte(ch)
-			if ch == '\n' {
-				for j := p.indent; j > 0; j-- {
-					buf.WriteString(".  ")
-				}
-			}
-		}
-		format = buf.String()
-	}
-	fmt.Printf(format, args...)
-}
-
-// Debugging support.
-// (tagString is only used when tracing is enabled)
-var tagString = [...]string{
-	// Packages
-	-packageTag: "package",
-
-	// Types
-	-namedTag:     "named type",
-	-arrayTag:     "array",
-	-sliceTag:     "slice",
-	-dddTag:       "ddd",
-	-structTag:    "struct",
-	-pointerTag:   "pointer",
-	-signatureTag: "signature",
-	-interfaceTag: "interface",
-	-mapTag:       "map",
-	-chanTag:      "chan",
-
-	// Values
-	-falseTag:    "false",
-	-trueTag:     "true",
-	-int64Tag:    "int64",
-	-floatTag:    "float",
-	-fractionTag: "fraction",
-	-complexTag:  "complex",
-	-stringTag:   "string",
-	-unknownTag:  "unknown",
-
-	// Type aliases
-	-aliasTag: "alias",
-}
diff --git a/go/internal/gcimporter/bexport_test.go b/go/internal/gcimporter/bexport_test.go
deleted file mode 100644
index de7b921af0..0000000000
--- a/go/internal/gcimporter/bexport_test.go
+++ /dev/null
@@ -1,419 +0,0 @@
-// Copyright 2016 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 gcimporter_test
-
-import (
-	"fmt"
-	"go/ast"
-	"go/build"
-	"go/constant"
-	"go/parser"
-	"go/token"
-	"go/types"
-	"reflect"
-	"runtime"
-	"strings"
-	"testing"
-
-	"golang.org/x/tools/go/buildutil"
-	"golang.org/x/tools/go/internal/gcimporter"
-	"golang.org/x/tools/go/loader"
-)
-
-var isRace = false
-
-func TestBExportData_stdlib(t *testing.T) {
-	if runtime.Compiler == "gccgo" {
-		t.Skip("gccgo standard library is inaccessible")
-	}
-	if runtime.GOOS == "android" {
-		t.Skipf("incomplete std lib on %s", runtime.GOOS)
-	}
-	if isRace {
-		t.Skipf("stdlib tests take too long in race mode and flake on builders")
-	}
-
-	// Load, parse and type-check the program.
-	ctxt := build.Default // copy
-	ctxt.GOPATH = ""      // disable GOPATH
-	conf := loader.Config{
-		Build:       &ctxt,
-		AllowErrors: true,
-	}
-	for _, path := range buildutil.AllPackages(conf.Build) {
-		conf.Import(path)
-	}
-
-	// Create a package containing type and value errors to ensure
-	// they are properly encoded/decoded.
-	f, err := conf.ParseFile("haserrors/haserrors.go", `package haserrors
-const UnknownValue = "" + 0
-type UnknownType undefined
-`)
-	if err != nil {
-		t.Fatal(err)
-	}
-	conf.CreateFromFiles("haserrors", f)
-
-	prog, err := conf.Load()
-	if err != nil {
-		t.Fatalf("Load failed: %v", err)
-	}
-
-	numPkgs := len(prog.AllPackages)
-	if want := 248; numPkgs < want {
-		t.Errorf("Loaded only %d packages, want at least %d", numPkgs, want)
-	}
-
-	for pkg, info := range prog.AllPackages {
-		if info.Files == nil {
-			continue // empty directory
-		}
-		exportdata, err := gcimporter.BExportData(conf.Fset, pkg)
-		if err != nil {
-			t.Fatal(err)
-		}
-
-		imports := make(map[string]*types.Package)
-		fset2 := token.NewFileSet()
-		n, pkg2, err := gcimporter.BImportData(fset2, imports, exportdata, pkg.Path())
-		if err != nil {
-			t.Errorf("BImportData(%s): %v", pkg.Path(), err)
-			continue
-		}
-		if n != len(exportdata) {
-			t.Errorf("BImportData(%s) decoded %d bytes, want %d",
-				pkg.Path(), n, len(exportdata))
-		}
-
-		// Compare the packages' corresponding members.
-		for _, name := range pkg.Scope().Names() {
-			if !ast.IsExported(name) {
-				continue
-			}
-			obj1 := pkg.Scope().Lookup(name)
-			obj2 := pkg2.Scope().Lookup(name)
-			if obj2 == nil {
-				t.Errorf("%s.%s not found, want %s", pkg.Path(), name, obj1)
-				continue
-			}
-
-			fl1 := fileLine(conf.Fset, obj1)
-			fl2 := fileLine(fset2, obj2)
-			if fl1 != fl2 {
-				t.Errorf("%s.%s: got posn %s, want %s",
-					pkg.Path(), name, fl2, fl1)
-			}
-
-			if err := equalObj(obj1, obj2); err != nil {
-				t.Errorf("%s.%s: %s\ngot:  %s\nwant: %s",
-					pkg.Path(), name, err, obj2, obj1)
-			}
-		}
-	}
-}
-
-func fileLine(fset *token.FileSet, obj types.Object) string {
-	posn := fset.Position(obj.Pos())
-	return fmt.Sprintf("%s:%d", posn.Filename, posn.Line)
-}
-
-// equalObj reports how x and y differ.  They are assumed to belong to
-// different universes so cannot be compared directly.
-func equalObj(x, y types.Object) error {
-	if reflect.TypeOf(x) != reflect.TypeOf(y) {
-		return fmt.Errorf("%T vs %T", x, y)
-	}
-	xt := x.Type()
-	yt := y.Type()
-	switch x.(type) {
-	case *types.Var, *types.Func:
-		// ok
-	case *types.Const:
-		xval := x.(*types.Const).Val()
-		yval := y.(*types.Const).Val()
-		// Use string comparison for floating-point values since rounding is permitted.
-		if constant.Compare(xval, token.NEQ, yval) &&
-			!(xval.Kind() == constant.Float && xval.String() == yval.String()) {
-			return fmt.Errorf("unequal constants %s vs %s", xval, yval)
-		}
-	case *types.TypeName:
-		xt = xt.Underlying()
-		yt = yt.Underlying()
-	default:
-		return fmt.Errorf("unexpected %T", x)
-	}
-	return equalType(xt, yt)
-}
-
-func equalType(x, y types.Type) error {
-	if reflect.TypeOf(x) != reflect.TypeOf(y) {
-		return fmt.Errorf("unequal kinds: %T vs %T", x, y)
-	}
-	switch x := x.(type) {
-	case *types.Interface:
-		y := y.(*types.Interface)
-		// TODO(gri): enable separate emission of Embedded interfaces
-		// and ExplicitMethods then use this logic.
-		// if x.NumEmbeddeds() != y.NumEmbeddeds() {
-		// 	return fmt.Errorf("unequal number of embedded interfaces: %d vs %d",
-		// 		x.NumEmbeddeds(), y.NumEmbeddeds())
-		// }
-		// for i := 0; i < x.NumEmbeddeds(); i++ {
-		// 	xi := x.Embedded(i)
-		// 	yi := y.Embedded(i)
-		// 	if xi.String() != yi.String() {
-		// 		return fmt.Errorf("mismatched %th embedded interface: %s vs %s",
-		// 			i, xi, yi)
-		// 	}
-		// }
-		// if x.NumExplicitMethods() != y.NumExplicitMethods() {
-		// 	return fmt.Errorf("unequal methods: %d vs %d",
-		// 		x.NumExplicitMethods(), y.NumExplicitMethods())
-		// }
-		// for i := 0; i < x.NumExplicitMethods(); i++ {
-		// 	xm := x.ExplicitMethod(i)
-		// 	ym := y.ExplicitMethod(i)
-		// 	if xm.Name() != ym.Name() {
-		// 		return fmt.Errorf("mismatched %th method: %s vs %s", i, xm, ym)
-		// 	}
-		// 	if err := equalType(xm.Type(), ym.Type()); err != nil {
-		// 		return fmt.Errorf("mismatched %s method: %s", xm.Name(), err)
-		// 	}
-		// }
-		if x.NumMethods() != y.NumMethods() {
-			return fmt.Errorf("unequal methods: %d vs %d",
-				x.NumMethods(), y.NumMethods())
-		}
-		for i := 0; i < x.NumMethods(); i++ {
-			xm := x.Method(i)
-			ym := y.Method(i)
-			if xm.Name() != ym.Name() {
-				return fmt.Errorf("mismatched %dth method: %s vs %s", i, xm, ym)
-			}
-			if err := equalType(xm.Type(), ym.Type()); err != nil {
-				return fmt.Errorf("mismatched %s method: %s", xm.Name(), err)
-			}
-		}
-	case *types.Array:
-		y := y.(*types.Array)
-		if x.Len() != y.Len() {
-			return fmt.Errorf("unequal array lengths: %d vs %d", x.Len(), y.Len())
-		}
-		if err := equalType(x.Elem(), y.Elem()); err != nil {
-			return fmt.Errorf("array elements: %s", err)
-		}
-	case *types.Basic:
-		y := y.(*types.Basic)
-		if x.Kind() != y.Kind() {
-			return fmt.Errorf("unequal basic types: %s vs %s", x, y)
-		}
-	case *types.Chan:
-		y := y.(*types.Chan)
-		if x.Dir() != y.Dir() {
-			return fmt.Errorf("unequal channel directions: %d vs %d", x.Dir(), y.Dir())
-		}
-		if err := equalType(x.Elem(), y.Elem()); err != nil {
-			return fmt.Errorf("channel elements: %s", err)
-		}
-	case *types.Map:
-		y := y.(*types.Map)
-		if err := equalType(x.Key(), y.Key()); err != nil {
-			return fmt.Errorf("map keys: %s", err)
-		}
-		if err := equalType(x.Elem(), y.Elem()); err != nil {
-			return fmt.Errorf("map values: %s", err)
-		}
-	case *types.Named:
-		y := y.(*types.Named)
-		if x.String() != y.String() {
-			return fmt.Errorf("unequal named types: %s vs %s", x, y)
-		}
-	case *types.Pointer:
-		y := y.(*types.Pointer)
-		if err := equalType(x.Elem(), y.Elem()); err != nil {
-			return fmt.Errorf("pointer elements: %s", err)
-		}
-	case *types.Signature:
-		y := y.(*types.Signature)
-		if err := equalType(x.Params(), y.Params()); err != nil {
-			return fmt.Errorf("parameters: %s", err)
-		}
-		if err := equalType(x.Results(), y.Results()); err != nil {
-			return fmt.Errorf("results: %s", err)
-		}
-		if x.Variadic() != y.Variadic() {
-			return fmt.Errorf("unequal variadicity: %t vs %t",
-				x.Variadic(), y.Variadic())
-		}
-		if (x.Recv() != nil) != (y.Recv() != nil) {
-			return fmt.Errorf("unequal receivers: %s vs %s", x.Recv(), y.Recv())
-		}
-		if x.Recv() != nil {
-			// TODO(adonovan): fix: this assertion fires for interface methods.
-			// The type of the receiver of an interface method is a named type
-			// if the Package was loaded from export data, or an unnamed (interface)
-			// type if the Package was produced by type-checking ASTs.
-			// if err := equalType(x.Recv().Type(), y.Recv().Type()); err != nil {
-			// 	return fmt.Errorf("receiver: %s", err)
-			// }
-		}
-	case *types.Slice:
-		y := y.(*types.Slice)
-		if err := equalType(x.Elem(), y.Elem()); err != nil {
-			return fmt.Errorf("slice elements: %s", err)
-		}
-	case *types.Struct:
-		y := y.(*types.Struct)
-		if x.NumFields() != y.NumFields() {
-			return fmt.Errorf("unequal struct fields: %d vs %d",
-				x.NumFields(), y.NumFields())
-		}
-		for i := 0; i < x.NumFields(); i++ {
-			xf := x.Field(i)
-			yf := y.Field(i)
-			if xf.Name() != yf.Name() {
-				return fmt.Errorf("mismatched fields: %s vs %s", xf, yf)
-			}
-			if err := equalType(xf.Type(), yf.Type()); err != nil {
-				return fmt.Errorf("struct field %s: %s", xf.Name(), err)
-			}
-			if x.Tag(i) != y.Tag(i) {
-				return fmt.Errorf("struct field %s has unequal tags: %q vs %q",
-					xf.Name(), x.Tag(i), y.Tag(i))
-			}
-		}
-	case *types.Tuple:
-		y := y.(*types.Tuple)
-		if x.Len() != y.Len() {
-			return fmt.Errorf("unequal tuple lengths: %d vs %d", x.Len(), y.Len())
-		}
-		for i := 0; i < x.Len(); i++ {
-			if err := equalType(x.At(i).Type(), y.At(i).Type()); err != nil {
-				return fmt.Errorf("tuple element %d: %s", i, err)
-			}
-		}
-	}
-	return nil
-}
-
-// TestVeryLongFile tests the position of an import object declared in
-// a very long input file.  Line numbers greater than maxlines are
-// reported as line 1, not garbage or token.NoPos.
-func TestVeryLongFile(t *testing.T) {
-	// parse and typecheck
-	longFile := "package foo" + strings.Repeat("\n", 123456) + "var X int"
-	fset1 := token.NewFileSet()
-	f, err := parser.ParseFile(fset1, "foo.go", longFile, 0)
-	if err != nil {
-		t.Fatal(err)
-	}
-	var conf types.Config
-	pkg, err := conf.Check("foo", fset1, []*ast.File{f}, nil)
-	if err != nil {
-		t.Fatal(err)
-	}
-
-	// export
-	exportdata, err := gcimporter.BExportData(fset1, pkg)
-	if err != nil {
-		t.Fatal(err)
-	}
-
-	// import
-	imports := make(map[string]*types.Package)
-	fset2 := token.NewFileSet()
-	_, pkg2, err := gcimporter.BImportData(fset2, imports, exportdata, pkg.Path())
-	if err != nil {
-		t.Fatalf("BImportData(%s): %v", pkg.Path(), err)
-	}
-
-	// compare
-	posn1 := fset1.Position(pkg.Scope().Lookup("X").Pos())
-	posn2 := fset2.Position(pkg2.Scope().Lookup("X").Pos())
-	if want := "foo.go:1:1"; posn2.String() != want {
-		t.Errorf("X position = %s, want %s (orig was %s)",
-			posn2, want, posn1)
-	}
-}
-
-const src = `
-package p
-
-type (
-	T0 = int32
-	T1 = struct{}
-	T2 = struct{ T1 }
-	Invalid = foo // foo is undeclared
-)
-`
-
-func checkPkg(t *testing.T, pkg *types.Package, label string) {
-	T1 := types.NewStruct(nil, nil)
-	T2 := types.NewStruct([]*types.Var{types.NewField(0, pkg, "T1", T1, true)}, nil)
-
-	for _, test := range []struct {
-		name string
-		typ  types.Type
-	}{
-		{"T0", types.Typ[types.Int32]},
-		{"T1", T1},
-		{"T2", T2},
-		{"Invalid", types.Typ[types.Invalid]},
-	} {
-		obj := pkg.Scope().Lookup(test.name)
-		if obj == nil {
-			t.Errorf("%s: %s not found", label, test.name)
-			continue
-		}
-		tname, _ := obj.(*types.TypeName)
-		if tname == nil {
-			t.Errorf("%s: %v not a type name", label, obj)
-			continue
-		}
-		if !tname.IsAlias() {
-			t.Errorf("%s: %v: not marked as alias", label, tname)
-			continue
-		}
-		if got := tname.Type(); !types.Identical(got, test.typ) {
-			t.Errorf("%s: %v: got %v; want %v", label, tname, got, test.typ)
-		}
-	}
-}
-
-func TestTypeAliases(t *testing.T) {
-	// parse and typecheck
-	fset1 := token.NewFileSet()
-	f, err := parser.ParseFile(fset1, "p.go", src, 0)
-	if err != nil {
-		t.Fatal(err)
-	}
-	var conf types.Config
-	pkg1, err := conf.Check("p", fset1, []*ast.File{f}, nil)
-	if err == nil {
-		// foo in undeclared in src; we should see an error
-		t.Fatal("invalid source type-checked without error")
-	}
-	if pkg1 == nil {
-		// despite incorrect src we should see a (partially) type-checked package
-		t.Fatal("nil package returned")
-	}
-	checkPkg(t, pkg1, "export")
-
-	// export
-	exportdata, err := gcimporter.BExportData(fset1, pkg1)
-	if err != nil {
-		t.Fatal(err)
-	}
-
-	// import
-	imports := make(map[string]*types.Package)
-	fset2 := token.NewFileSet()
-	_, pkg2, err := gcimporter.BImportData(fset2, imports, exportdata, pkg1.Path())
-	if err != nil {
-		t.Fatalf("BImportData(%s): %v", pkg1.Path(), err)
-	}
-	checkPkg(t, pkg2, "import")
-}
diff --git a/go/internal/gcimporter/bimport.go b/go/internal/gcimporter/bimport.go
deleted file mode 100644
index e9f73d14a1..0000000000
--- a/go/internal/gcimporter/bimport.go
+++ /dev/null
@@ -1,1039 +0,0 @@
-// Copyright 2015 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.
-
-// This file is a copy of $GOROOT/src/go/internal/gcimporter/bimport.go.
-
-package gcimporter
-
-import (
-	"encoding/binary"
-	"fmt"
-	"go/constant"
-	"go/token"
-	"go/types"
-	"sort"
-	"strconv"
-	"strings"
-	"sync"
-	"unicode"
-	"unicode/utf8"
-)
-
-type importer struct {
-	imports    map[string]*types.Package
-	data       []byte
-	importpath string
-	buf        []byte // for reading strings
-	version    int    // export format version
-
-	// object lists
-	strList       []string           // in order of appearance
-	pathList      []string           // in order of appearance
-	pkgList       []*types.Package   // in order of appearance
-	typList       []types.Type       // in order of appearance
-	interfaceList []*types.Interface // for delayed completion only
-	trackAllTypes bool
-
-	// position encoding
-	posInfoFormat bool
-	prevFile      string
-	prevLine      int
-	fake          fakeFileSet
-
-	// debugging support
-	debugFormat bool
-	read        int // bytes read
-}
-
-// BImportData imports a package from the serialized package data
-// and returns the number of bytes consumed and a reference to the package.
-// If the export data version is not recognized or the format is otherwise
-// compromised, an error is returned.
-func BImportData(fset *token.FileSet, imports map[string]*types.Package, data []byte, path string) (_ int, pkg *types.Package, err error) {
-	// catch panics and return them as errors
-	const currentVersion = 6
-	version := -1 // unknown version
-	defer func() {
-		if e := recover(); e != nil {
-			// Return a (possibly nil or incomplete) package unchanged (see #16088).
-			if version > currentVersion {
-				err = fmt.Errorf("cannot import %q (%v), export data is newer version - update tool", path, e)
-			} else {
-				err = fmt.Errorf("cannot import %q (%v), possibly version skew - reinstall package", path, e)
-			}
-		}
-	}()
-
-	p := importer{
-		imports:    imports,
-		data:       data,
-		importpath: path,
-		version:    version,
-		strList:    []string{""}, // empty string is mapped to 0
-		pathList:   []string{""}, // empty string is mapped to 0
-		fake: fakeFileSet{
-			fset:  fset,
-			files: make(map[string]*token.File),
-		},
-	}
-
-	// read version info
-	var versionstr string
-	if b := p.rawByte(); b == 'c' || b == 'd' {
-		// Go1.7 encoding; first byte encodes low-level
-		// encoding format (compact vs debug).
-		// For backward-compatibility only (avoid problems with
-		// old installed packages). Newly compiled packages use
-		// the extensible format string.
-		// TODO(gri) Remove this support eventually; after Go1.8.
-		if b == 'd' {
-			p.debugFormat = true
-		}
-		p.trackAllTypes = p.rawByte() == 'a'
-		p.posInfoFormat = p.int() != 0
-		versionstr = p.string()
-		if versionstr == "v1" {
-			version = 0
-		}
-	} else {
-		// Go1.8 extensible encoding
-		// read version string and extract version number (ignore anything after the version number)
-		versionstr = p.rawStringln(b)
-		if s := strings.SplitN(versionstr, " ", 3); len(s) >= 2 && s[0] == "version" {
-			if v, err := strconv.Atoi(s[1]); err == nil && v > 0 {
-				version = v
-			}
-		}
-	}
-	p.version = version
-
-	// read version specific flags - extend as necessary
-	switch p.version {
-	// case currentVersion:
-	// 	...
-	//	fallthrough
-	case currentVersion, 5, 4, 3, 2, 1:
-		p.debugFormat = p.rawStringln(p.rawByte()) == "debug"
-		p.trackAllTypes = p.int() != 0
-		p.posInfoFormat = p.int() != 0
-	case 0:
-		// Go1.7 encoding format - nothing to do here
-	default:
-		errorf("unknown bexport format version %d (%q)", p.version, versionstr)
-	}
-
-	// --- generic export data ---
-
-	// populate typList with predeclared "known" types
-	p.typList = append(p.typList, predeclared()...)
-
-	// read package data
-	pkg = p.pkg()
-
-	// read objects of phase 1 only (see cmd/compile/internal/gc/bexport.go)
-	objcount := 0
-	for {
-		tag := p.tagOrIndex()
-		if tag == endTag {
-			break
-		}
-		p.obj(tag)
-		objcount++
-	}
-
-	// self-verification
-	if count := p.int(); count != objcount {
-		errorf("got %d objects; want %d", objcount, count)
-	}
-
-	// ignore compiler-specific import data
-
-	// complete interfaces
-	// TODO(gri) re-investigate if we still need to do this in a delayed fashion
-	for _, typ := range p.interfaceList {
-		typ.Complete()
-	}
-
-	// record all referenced packages as imports
-	list := append(([]*types.Package)(nil), p.pkgList[1:]...)
-	sort.Sort(byPath(list))
-	pkg.SetImports(list)
-
-	// package was imported completely and without errors
-	pkg.MarkComplete()
-
-	return p.read, pkg, nil
-}
-
-func errorf(format string, args ...interface{}) {
-	panic(fmt.Sprintf(format, args...))
-}
-
-func (p *importer) pkg() *types.Package {
-	// if the package was seen before, i is its index (>= 0)
-	i := p.tagOrIndex()
-	if i >= 0 {
-		return p.pkgList[i]
-	}
-
-	// otherwise, i is the package tag (< 0)
-	if i != packageTag {
-		errorf("unexpected package tag %d version %d", i, p.version)
-	}
-
-	// read package data
-	name := p.string()
-	var path string
-	if p.version >= 5 {
-		path = p.path()
-	} else {
-		path = p.string()
-	}
-	if p.version >= 6 {
-		p.int() // package height; unused by go/types
-	}
-
-	// we should never see an empty package name
-	if name == "" {
-		errorf("empty package name in import")
-	}
-
-	// an empty path denotes the package we are currently importing;
-	// it must be the first package we see
-	if (path == "") != (len(p.pkgList) == 0) {
-		errorf("package path %q for pkg index %d", path, len(p.pkgList))
-	}
-
-	// if the package was imported before, use that one; otherwise create a new one
-	if path == "" {
-		path = p.importpath
-	}
-	pkg := p.imports[path]
-	if pkg == nil {
-		pkg = types.NewPackage(path, name)
-		p.imports[path] = pkg
-	} else if pkg.Name() != name {
-		errorf("conflicting names %s and %s for package %q", pkg.Name(), name, path)
-	}
-	p.pkgList = append(p.pkgList, pkg)
-
-	return pkg
-}
-
-// objTag returns the tag value for each object kind.
-func objTag(obj types.Object) int {
-	switch obj.(type) {
-	case *types.Const:
-		return constTag
-	case *types.TypeName:
-		return typeTag
-	case *types.Var:
-		return varTag
-	case *types.Func:
-		return funcTag
-	default:
-		errorf("unexpected object: %v (%T)", obj, obj) // panics
-		panic("unreachable")
-	}
-}
-
-func sameObj(a, b types.Object) bool {
-	// Because unnamed types are not canonicalized, we cannot simply compare types for
-	// (pointer) identity.
-	// Ideally we'd check equality of constant values as well, but this is good enough.
-	return objTag(a) == objTag(b) && types.Identical(a.Type(), b.Type())
-}
-
-func (p *importer) declare(obj types.Object) {
-	pkg := obj.Pkg()
-	if alt := pkg.Scope().Insert(obj); alt != nil {
-		// This can only trigger if we import a (non-type) object a second time.
-		// Excluding type aliases, this cannot happen because 1) we only import a package
-		// once; and b) we ignore compiler-specific export data which may contain
-		// functions whose inlined function bodies refer to other functions that
-		// were already imported.
-		// However, type aliases require reexporting the original type, so we need
-		// to allow it (see also the comment in cmd/compile/internal/gc/bimport.go,
-		// method importer.obj, switch case importing functions).
-		// TODO(gri) review/update this comment once the gc compiler handles type aliases.
-		if !sameObj(obj, alt) {
-			errorf("inconsistent import:\n\t%v\npreviously imported as:\n\t%v\n", obj, alt)
-		}
-	}
-}
-
-func (p *importer) obj(tag int) {
-	switch tag {
-	case constTag:
-		pos := p.pos()
-		pkg, name := p.qualifiedName()
-		typ := p.typ(nil, nil)
-		val := p.value()
-		p.declare(types.NewConst(pos, pkg, name, typ, val))
-
-	case aliasTag:
-		// TODO(gri) verify type alias hookup is correct
-		pos := p.pos()
-		pkg, name := p.qualifiedName()
-		typ := p.typ(nil, nil)
-		p.declare(types.NewTypeName(pos, pkg, name, typ))
-
-	case typeTag:
-		p.typ(nil, nil)
-
-	case varTag:
-		pos := p.pos()
-		pkg, name := p.qualifiedName()
-		typ := p.typ(nil, nil)
-		p.declare(types.NewVar(pos, pkg, name, typ))
-
-	case funcTag:
-		pos := p.pos()
-		pkg, name := p.qualifiedName()
-		params, isddd := p.paramList()
-		result, _ := p.paramList()
-		sig := types.NewSignature(nil, params, result, isddd)
-		p.declare(types.NewFunc(pos, pkg, name, sig))
-
-	default:
-		errorf("unexpected object tag %d", tag)
-	}
-}
-
-const deltaNewFile = -64 // see cmd/compile/internal/gc/bexport.go
-
-func (p *importer) pos() token.Pos {
-	if !p.posInfoFormat {
-		return token.NoPos
-	}
-
-	file := p.prevFile
-	line := p.prevLine
-	delta := p.int()
-	line += delta
-	if p.version >= 5 {
-		if delta == deltaNewFile {
-			if n := p.int(); n >= 0 {
-				// file changed
-				file = p.path()
-				line = n
-			}
-		}
-	} else {
-		if delta == 0 {
-			if n := p.int(); n >= 0 {
-				// file changed
-				file = p.prevFile[:n] + p.string()
-				line = p.int()
-			}
-		}
-	}
-	p.prevFile = file
-	p.prevLine = line
-
-	return p.fake.pos(file, line, 0)
-}
-
-// Synthesize a token.Pos
-type fakeFileSet struct {
-	fset  *token.FileSet
-	files map[string]*token.File
-}
-
-func (s *fakeFileSet) pos(file string, line, column int) token.Pos {
-	// TODO(mdempsky): Make use of column.
-
-	// Since we don't know the set of needed file positions, we
-	// reserve maxlines positions per file.
-	const maxlines = 64 * 1024
-	f := s.files[file]
-	if f == nil {
-		f = s.fset.AddFile(file, -1, maxlines)
-		s.files[file] = f
-		// Allocate the fake linebreak indices on first use.
-		// TODO(adonovan): opt: save ~512KB using a more complex scheme?
-		fakeLinesOnce.Do(func() {
-			fakeLines = make([]int, maxlines)
-			for i := range fakeLines {
-				fakeLines[i] = i
-			}
-		})
-		f.SetLines(fakeLines)
-	}
-
-	if line > maxlines {
-		line = 1
-	}
-
-	// Treat the file as if it contained only newlines
-	// and column=1: use the line number as the offset.
-	return f.Pos(line - 1)
-}
-
-var (
-	fakeLines     []int
-	fakeLinesOnce sync.Once
-)
-
-func (p *importer) qualifiedName() (pkg *types.Package, name string) {
-	name = p.string()
-	pkg = p.pkg()
-	return
-}
-
-func (p *importer) record(t types.Type) {
-	p.typList = append(p.typList, t)
-}
-
-// A dddSlice is a types.Type representing ...T parameters.
-// It only appears for parameter types and does not escape
-// the importer.
-type dddSlice struct {
-	elem types.Type
-}
-
-func (t *dddSlice) Underlying() types.Type { return t }
-func (t *dddSlice) String() string         { return "..." + t.elem.String() }
-
-// parent is the package which declared the type; parent == nil means
-// the package currently imported. The parent package is needed for
-// exported struct fields and interface methods which don't contain
-// explicit package information in the export data.
-//
-// A non-nil tname is used as the "owner" of the result type; i.e.,
-// the result type is the underlying type of tname. tname is used
-// to give interface methods a named receiver type where possible.
-func (p *importer) typ(parent *types.Package, tname *types.Named) types.Type {
-	// if the type was seen before, i is its index (>= 0)
-	i := p.tagOrIndex()
-	if i >= 0 {
-		return p.typList[i]
-	}
-
-	// otherwise, i is the type tag (< 0)
-	switch i {
-	case namedTag:
-		// read type object
-		pos := p.pos()
-		parent, name := p.qualifiedName()
-		scope := parent.Scope()
-		obj := scope.Lookup(name)
-
-		// if the object doesn't exist yet, create and insert it
-		if obj == nil {
-			obj = types.NewTypeName(pos, parent, name, nil)
-			scope.Insert(obj)
-		}
-
-		if _, ok := obj.(*types.TypeName); !ok {
-			errorf("pkg = %s, name = %s => %s", parent, name, obj)
-		}
-
-		// associate new named type with obj if it doesn't exist yet
-		t0 := types.NewNamed(obj.(*types.TypeName), nil, nil)
-
-		// but record the existing type, if any
-		tname := obj.Type().(*types.Named) // tname is either t0 or the existing type
-		p.record(tname)
-
-		// read underlying type
-		t0.SetUnderlying(p.typ(parent, t0))
-
-		// interfaces don't have associated methods
-		if types.IsInterface(t0) {
-			return tname
-		}
-
-		// read associated methods
-		for i := p.int(); i > 0; i-- {
-			// TODO(gri) replace this with something closer to fieldName
-			pos := p.pos()
-			name := p.string()
-			if !exported(name) {
-				p.pkg()
-			}
-
-			recv, _ := p.paramList() // TODO(gri) do we need a full param list for the receiver?
-			params, isddd := p.paramList()
-			result, _ := p.paramList()
-			p.int() // go:nointerface pragma - discarded
-
-			sig := types.NewSignature(recv.At(0), params, result, isddd)
-			t0.AddMethod(types.NewFunc(pos, parent, name, sig))
-		}
-
-		return tname
-
-	case arrayTag:
-		t := new(types.Array)
-		if p.trackAllTypes {
-			p.record(t)
-		}
-
-		n := p.int64()
-		*t = *types.NewArray(p.typ(parent, nil), n)
-		return t
-
-	case sliceTag:
-		t := new(types.Slice)
-		if p.trackAllTypes {
-			p.record(t)
-		}
-
-		*t = *types.NewSlice(p.typ(parent, nil))
-		return t
-
-	case dddTag:
-		t := new(dddSlice)
-		if p.trackAllTypes {
-			p.record(t)
-		}
-
-		t.elem = p.typ(parent, nil)
-		return t
-
-	case structTag:
-		t := new(types.Struct)
-		if p.trackAllTypes {
-			p.record(t)
-		}
-
-		*t = *types.NewStruct(p.fieldList(parent))
-		return t
-
-	case pointerTag:
-		t := new(types.Pointer)
-		if p.trackAllTypes {
-			p.record(t)
-		}
-
-		*t = *types.NewPointer(p.typ(parent, nil))
-		return t
-
-	case signatureTag:
-		t := new(types.Signature)
-		if p.trackAllTypes {
-			p.record(t)
-		}
-
-		params, isddd := p.paramList()
-		result, _ := p.paramList()
-		*t = *types.NewSignature(nil, params, result, isddd)
-		return t
-
-	case interfaceTag:
-		// Create a dummy entry in the type list. This is safe because we
-		// cannot expect the interface type to appear in a cycle, as any
-		// such cycle must contain a named type which would have been
-		// first defined earlier.
-		// TODO(gri) Is this still true now that we have type aliases?
-		// See issue #23225.
-		n := len(p.typList)
-		if p.trackAllTypes {
-			p.record(nil)
-		}
-
-		var embeddeds []types.Type
-		for n := p.int(); n > 0; n-- {
-			p.pos()
-			embeddeds = append(embeddeds, p.typ(parent, nil))
-		}
-
-		t := newInterface(p.methodList(parent, tname), embeddeds)
-		p.interfaceList = append(p.interfaceList, t)
-		if p.trackAllTypes {
-			p.typList[n] = t
-		}
-		return t
-
-	case mapTag:
-		t := new(types.Map)
-		if p.trackAllTypes {
-			p.record(t)
-		}
-
-		key := p.typ(parent, nil)
-		val := p.typ(parent, nil)
-		*t = *types.NewMap(key, val)
-		return t
-
-	case chanTag:
-		t := new(types.Chan)
-		if p.trackAllTypes {
-			p.record(t)
-		}
-
-		dir := chanDir(p.int())
-		val := p.typ(parent, nil)
-		*t = *types.NewChan(dir, val)
-		return t
-
-	default:
-		errorf("unexpected type tag %d", i) // panics
-		panic("unreachable")
-	}
-}
-
-func chanDir(d int) types.ChanDir {
-	// tag values must match the constants in cmd/compile/internal/gc/go.go
-	switch d {
-	case 1 /* Crecv */ :
-		return types.RecvOnly
-	case 2 /* Csend */ :
-		return types.SendOnly
-	case 3 /* Cboth */ :
-		return types.SendRecv
-	default:
-		errorf("unexpected channel dir %d", d)
-		return 0
-	}
-}
-
-func (p *importer) fieldList(parent *types.Package) (fields []*types.Var, tags []string) {
-	if n := p.int(); n > 0 {
-		fields = make([]*types.Var, n)
-		tags = make([]string, n)
-		for i := range fields {
-			fields[i], tags[i] = p.field(parent)
-		}
-	}
-	return
-}
-
-func (p *importer) field(parent *types.Package) (*types.Var, string) {
-	pos := p.pos()
-	pkg, name, alias := p.fieldName(parent)
-	typ := p.typ(parent, nil)
-	tag := p.string()
-
-	anonymous := false
-	if name == "" {
-		// anonymous field - typ must be T or *T and T must be a type name
-		switch typ := deref(typ).(type) {
-		case *types.Basic: // basic types are named types
-			pkg = nil // // objects defined in Universe scope have no package
-			name = typ.Name()
-		case *types.Named:
-			name = typ.Obj().Name()
-		default:
-			errorf("named base type expected")
-		}
-		anonymous = true
-	} else if alias {
-		// anonymous field: we have an explicit name because it's an alias
-		anonymous = true
-	}
-
-	return types.NewField(pos, pkg, name, typ, anonymous), tag
-}
-
-func (p *importer) methodList(parent *types.Package, baseType *types.Named) (methods []*types.Func) {
-	if n := p.int(); n > 0 {
-		methods = make([]*types.Func, n)
-		for i := range methods {
-			methods[i] = p.method(parent, baseType)
-		}
-	}
-	return
-}
-
-func (p *importer) method(parent *types.Package, baseType *types.Named) *types.Func {
-	pos := p.pos()
-	pkg, name, _ := p.fieldName(parent)
-	// If we don't have a baseType, use a nil receiver.
-	// A receiver using the actual interface type (which
-	// we don't know yet) will be filled in when we call
-	// types.Interface.Complete.
-	var recv *types.Var
-	if baseType != nil {
-		recv = types.NewVar(token.NoPos, parent, "", baseType)
-	}
-	params, isddd := p.paramList()
-	result, _ := p.paramList()
-	sig := types.NewSignature(recv, params, result, isddd)
-	return types.NewFunc(pos, pkg, name, sig)
-}
-
-func (p *importer) fieldName(parent *types.Package) (pkg *types.Package, name string, alias bool) {
-	name = p.string()
-	pkg = parent
-	if pkg == nil {
-		// use the imported package instead
-		pkg = p.pkgList[0]
-	}
-	if p.version == 0 && name == "_" {
-		// version 0 didn't export a package for _ fields
-		return
-	}
-	switch name {
-	case "":
-		// 1) field name matches base type name and is exported: nothing to do
-	case "?":
-		// 2) field name matches base type name and is not exported: need package
-		name = ""
-		pkg = p.pkg()
-	case "@":
-		// 3) field name doesn't match type name (alias)
-		name = p.string()
-		alias = true
-		fallthrough
-	default:
-		if !exported(name) {
-			pkg = p.pkg()
-		}
-	}
-	return
-}
-
-func (p *importer) paramList() (*types.Tuple, bool) {
-	n := p.int()
-	if n == 0 {
-		return nil, false
-	}
-	// negative length indicates unnamed parameters
-	named := true
-	if n < 0 {
-		n = -n
-		named = false
-	}
-	// n > 0
-	params := make([]*types.Var, n)
-	isddd := false
-	for i := range params {
-		params[i], isddd = p.param(named)
-	}
-	return types.NewTuple(params...), isddd
-}
-
-func (p *importer) param(named bool) (*types.Var, bool) {
-	t := p.typ(nil, nil)
-	td, isddd := t.(*dddSlice)
-	if isddd {
-		t = types.NewSlice(td.elem)
-	}
-
-	var pkg *types.Package
-	var name string
-	if named {
-		name = p.string()
-		if name == "" {
-			errorf("expected named parameter")
-		}
-		if name != "_" {
-			pkg = p.pkg()
-		}
-		if i := strings.Index(name, "·"); i > 0 {
-			name = name[:i] // cut off gc-specific parameter numbering
-		}
-	}
-
-	// read and discard compiler-specific info
-	p.string()
-
-	return types.NewVar(token.NoPos, pkg, name, t), isddd
-}
-
-func exported(name string) bool {
-	ch, _ := utf8.DecodeRuneInString(name)
-	return unicode.IsUpper(ch)
-}
-
-func (p *importer) value() constant.Value {
-	switch tag := p.tagOrIndex(); tag {
-	case falseTag:
-		return constant.MakeBool(false)
-	case trueTag:
-		return constant.MakeBool(true)
-	case int64Tag:
-		return constant.MakeInt64(p.int64())
-	case floatTag:
-		return p.float()
-	case complexTag:
-		re := p.float()
-		im := p.float()
-		return constant.BinaryOp(re, token.ADD, constant.MakeImag(im))
-	case stringTag:
-		return constant.MakeString(p.string())
-	case unknownTag:
-		return constant.MakeUnknown()
-	default:
-		errorf("unexpected value tag %d", tag) // panics
-		panic("unreachable")
-	}
-}
-
-func (p *importer) float() constant.Value {
-	sign := p.int()
-	if sign == 0 {
-		return constant.MakeInt64(0)
-	}
-
-	exp := p.int()
-	mant := []byte(p.string()) // big endian
-
-	// remove leading 0's if any
-	for len(mant) > 0 && mant[0] == 0 {
-		mant = mant[1:]
-	}
-
-	// convert to little endian
-	// TODO(gri) go/constant should have a more direct conversion function
-	//           (e.g., once it supports a big.Float based implementation)
-	for i, j := 0, len(mant)-1; i < j; i, j = i+1, j-1 {
-		mant[i], mant[j] = mant[j], mant[i]
-	}
-
-	// adjust exponent (constant.MakeFromBytes creates an integer value,
-	// but mant represents the mantissa bits such that 0.5 <= mant < 1.0)
-	exp -= len(mant) << 3
-	if len(mant) > 0 {
-		for msd := mant[len(mant)-1]; msd&0x80 == 0; msd <<= 1 {
-			exp++
-		}
-	}
-
-	x := constant.MakeFromBytes(mant)
-	switch {
-	case exp < 0:
-		d := constant.Shift(constant.MakeInt64(1), token.SHL, uint(-exp))
-		x = constant.BinaryOp(x, token.QUO, d)
-	case exp > 0:
-		x = constant.Shift(x, token.SHL, uint(exp))
-	}
-
-	if sign < 0 {
-		x = constant.UnaryOp(token.SUB, x, 0)
-	}
-	return x
-}
-
-// ----------------------------------------------------------------------------
-// Low-level decoders
-
-func (p *importer) tagOrIndex() int {
-	if p.debugFormat {
-		p.marker('t')
-	}
-
-	return int(p.rawInt64())
-}
-
-func (p *importer) int() int {
-	x := p.int64()
-	if int64(int(x)) != x {
-		errorf("exported integer too large")
-	}
-	return int(x)
-}
-
-func (p *importer) int64() int64 {
-	if p.debugFormat {
-		p.marker('i')
-	}
-
-	return p.rawInt64()
-}
-
-func (p *importer) path() string {
-	if p.debugFormat {
-		p.marker('p')
-	}
-	// if the path was seen before, i is its index (>= 0)
-	// (the empty string is at index 0)
-	i := p.rawInt64()
-	if i >= 0 {
-		return p.pathList[i]
-	}
-	// otherwise, i is the negative path length (< 0)
-	a := make([]string, -i)
-	for n := range a {
-		a[n] = p.string()
-	}
-	s := strings.Join(a, "/")
-	p.pathList = append(p.pathList, s)
-	return s
-}
-
-func (p *importer) string() string {
-	if p.debugFormat {
-		p.marker('s')
-	}
-	// if the string was seen before, i is its index (>= 0)
-	// (the empty string is at index 0)
-	i := p.rawInt64()
-	if i >= 0 {
-		return p.strList[i]
-	}
-	// otherwise, i is the negative string length (< 0)
-	if n := int(-i); n <= cap(p.buf) {
-		p.buf = p.buf[:n]
-	} else {
-		p.buf = make([]byte, n)
-	}
-	for i := range p.buf {
-		p.buf[i] = p.rawByte()
-	}
-	s := string(p.buf)
-	p.strList = append(p.strList, s)
-	return s
-}
-
-func (p *importer) marker(want byte) {
-	if got := p.rawByte(); got != want {
-		errorf("incorrect marker: got %c; want %c (pos = %d)", got, want, p.read)
-	}
-
-	pos := p.read
-	if n := int(p.rawInt64()); n != pos {
-		errorf("incorrect position: got %d; want %d", n, pos)
-	}
-}
-
-// rawInt64 should only be used by low-level decoders.
-func (p *importer) rawInt64() int64 {
-	i, err := binary.ReadVarint(p)
-	if err != nil {
-		errorf("read error: %v", err)
-	}
-	return i
-}
-
-// rawStringln should only be used to read the initial version string.
-func (p *importer) rawStringln(b byte) string {
-	p.buf = p.buf[:0]
-	for b != '\n' {
-		p.buf = append(p.buf, b)
-		b = p.rawByte()
-	}
-	return string(p.buf)
-}
-
-// needed for binary.ReadVarint in rawInt64
-func (p *importer) ReadByte() (byte, error) {
-	return p.rawByte(), nil
-}
-
-// byte is the bottleneck interface for reading p.data.
-// It unescapes '|' 'S' to '$' and '|' '|' to '|'.
-// rawByte should only be used by low-level decoders.
-func (p *importer) rawByte() byte {
-	b := p.data[0]
-	r := 1
-	if b == '|' {
-		b = p.data[1]
-		r = 2
-		switch b {
-		case 'S':
-			b = '$'
-		case '|':
-			// nothing to do
-		default:
-			errorf("unexpected escape sequence in export data")
-		}
-	}
-	p.data = p.data[r:]
-	p.read += r
-	return b
-
-}
-
-// ----------------------------------------------------------------------------
-// Export format
-
-// Tags. Must be < 0.
-const (
-	// Objects
-	packageTag = -(iota + 1)
-	constTag
-	typeTag
-	varTag
-	funcTag
-	endTag
-
-	// Types
-	namedTag
-	arrayTag
-	sliceTag
-	dddTag
-	structTag
-	pointerTag
-	signatureTag
-	interfaceTag
-	mapTag
-	chanTag
-
-	// Values
-	falseTag
-	trueTag
-	int64Tag
-	floatTag
-	fractionTag // not used by gc
-	complexTag
-	stringTag
-	nilTag     // only used by gc (appears in exported inlined function bodies)
-	unknownTag // not used by gc (only appears in packages with errors)
-
-	// Type aliases
-	aliasTag
-)
-
-var predeclOnce sync.Once
-var predecl []types.Type // initialized lazily
-
-func predeclared() []types.Type {
-	predeclOnce.Do(func() {
-		// initialize lazily to be sure that all
-		// elements have been initialized before
-		predecl = []types.Type{ // basic types
-			types.Typ[types.Bool],
-			types.Typ[types.Int],
-			types.Typ[types.Int8],
-			types.Typ[types.Int16],
-			types.Typ[types.Int32],
-			types.Typ[types.Int64],
-			types.Typ[types.Uint],
-			types.Typ[types.Uint8],
-			types.Typ[types.Uint16],
-			types.Typ[types.Uint32],
-			types.Typ[types.Uint64],
-			types.Typ[types.Uintptr],
-			types.Typ[types.Float32],
-			types.Typ[types.Float64],
-			types.Typ[types.Complex64],
-			types.Typ[types.Complex128],
-			types.Typ[types.String],
-
-			// basic type aliases
-			types.Universe.Lookup("byte").Type(),
-			types.Universe.Lookup("rune").Type(),
-
-			// error
-			types.Universe.Lookup("error").Type(),
-
-			// untyped types
-			types.Typ[types.UntypedBool],
-			types.Typ[types.UntypedInt],
-			types.Typ[types.UntypedRune],
-			types.Typ[types.UntypedFloat],
-			types.Typ[types.UntypedComplex],
-			types.Typ[types.UntypedString],
-			types.Typ[types.UntypedNil],
-
-			// package unsafe
-			types.Typ[types.UnsafePointer],
-
-			// invalid type
-			types.Typ[types.Invalid], // only appears in packages with errors
-
-			// used internally by gc; never used by this package or in .a files
-			anyType{},
-		}
-	})
-	return predecl
-}
-
-type anyType struct{}
-
-func (t anyType) Underlying() types.Type { return t }
-func (t anyType) String() string         { return "any" }
diff --git a/go/internal/gcimporter/gcimporter.go b/go/internal/gcimporter/gcimporter.go
index 8dcd8bbb71..6a9265ea94 100644
--- a/go/internal/gcimporter/gcimporter.go
+++ b/go/internal/gcimporter/gcimporter.go
@@ -204,14 +204,11 @@ func Import(packages map[string]*types.Package, path, srcDir string, lookup func
 		// Or, define a new standard go/types/gcexportdata package.
 		fset := token.NewFileSet()
 
-		// The indexed export format starts with an 'i'; the older
-		// binary export format starts with a 'c', 'd', or 'v'
-		// (from "version"). Select appropriate importer.
-		if len(data) > 0 && data[0] == 'i' {
-			_, pkg, err = IImportData(fset, packages, data[1:], id)
-		} else {
-			_, pkg, err = BImportData(fset, packages, data, id)
+		// The indexed export format starts with an 'i'.
+		if len(data) == 0 || data[0] != 'i' {
+			return nil, fmt.Errorf("unknown export data format")
 		}
+		_, pkg, err = IImportData(fset, packages, data[1:], id)
 
 	default:
 		err = fmt.Errorf("unknown export data header: %q", hdr)
diff --git a/go/internal/gcimporter/iexport.go b/go/internal/gcimporter/iexport.go
index 4be32a2e55..858eb9f456 100644
--- a/go/internal/gcimporter/iexport.go
+++ b/go/internal/gcimporter/iexport.go
@@ -11,6 +11,7 @@ package gcimporter
 import (
 	"bytes"
 	"encoding/binary"
+	"fmt"
 	"go/ast"
 	"go/constant"
 	"go/token"
@@ -25,6 +26,15 @@ import (
 // 0: Go1.11 encoding
 const iexportVersion = 0
 
+// internalError represents an error generated inside this package.
+type internalError string
+
+func (e internalError) Error() string { return "gcimporter: " + string(e) }
+
+func internalErrorf(format string, args ...interface{}) error {
+	return internalError(fmt.Sprintf(format, args...))
+}
+
 // IExportData returns the binary export data for pkg.
 //
 // If no file set is provided, position info will be missing.
@@ -528,6 +538,16 @@ func constantToFloat(x constant.Value) *big.Float {
 	return &f
 }
 
+func valueToRat(x constant.Value) *big.Rat {
+	// Convert little-endian to big-endian.
+	// I can't believe this is necessary.
+	bytes := constant.Bytes(x)
+	for i := 0; i < len(bytes)/2; i++ {
+		bytes[i], bytes[len(bytes)-1-i] = bytes[len(bytes)-1-i], bytes[i]
+	}
+	return new(big.Rat).SetInt(new(big.Int).SetBytes(bytes))
+}
+
 // mpint exports a multi-precision integer.
 //
 // For unsigned types, small values are written out as a single
diff --git a/go/internal/gcimporter/iexport_test.go b/go/internal/gcimporter/iexport_test.go
index 502457081f..f66135d541 100644
--- a/go/internal/gcimporter/iexport_test.go
+++ b/go/internal/gcimporter/iexport_test.go
@@ -28,6 +28,8 @@ import (
 	"golang.org/x/tools/go/loader"
 )
 
+var isRace = false
+
 func TestIExportData_stdlib(t *testing.T) {
 	if runtime.Compiler == "gccgo" {
 		t.Skip("gccgo standard library is inaccessible")
@@ -178,6 +180,16 @@ func TestIExportData_long(t *testing.T) {
 	}
 }
 
+const src = `
+package p
+type (
+	T0 = int32
+	T1 = struct{}
+	T2 = struct{ T1 }
+	Invalid = foo // foo is undeclared
+)
+`
+
 func TestIExportData_typealiases(t *testing.T) {
 	// parse and typecheck
 	fset1 := token.NewFileSet()
@@ -307,3 +319,220 @@ func valueToRat(x constant.Value) *big.Rat {
 	}
 	return new(big.Rat).SetInt(new(big.Int).SetBytes(bytes))
 }
+
+func fileLine(fset *token.FileSet, obj types.Object) string {
+	posn := fset.Position(obj.Pos())
+	return fmt.Sprintf("%s:%d", posn.Filename, posn.Line)
+}
+
+// equalObj reports how x and y differ.  They are assumed to belong to
+// different universes so cannot be compared directly.
+func equalObj(x, y types.Object) error {
+	if reflect.TypeOf(x) != reflect.TypeOf(y) {
+		return fmt.Errorf("%T vs %T", x, y)
+	}
+	xt := x.Type()
+	yt := y.Type()
+	switch x.(type) {
+	case *types.Var, *types.Func:
+		// ok
+	case *types.Const:
+		xval := x.(*types.Const).Val()
+		yval := y.(*types.Const).Val()
+		// Use string comparison for floating-point values since rounding is permitted.
+		if constant.Compare(xval, token.NEQ, yval) &&
+			!(xval.Kind() == constant.Float && xval.String() == yval.String()) {
+			return fmt.Errorf("unequal constants %s vs %s", xval, yval)
+		}
+	case *types.TypeName:
+		xt = xt.Underlying()
+		yt = yt.Underlying()
+	default:
+		return fmt.Errorf("unexpected %T", x)
+	}
+	return equalType(xt, yt)
+}
+
+func equalType(x, y types.Type) error {
+	if reflect.TypeOf(x) != reflect.TypeOf(y) {
+		return fmt.Errorf("unequal kinds: %T vs %T", x, y)
+	}
+	switch x := x.(type) {
+	case *types.Interface:
+		y := y.(*types.Interface)
+		// TODO(gri): enable separate emission of Embedded interfaces
+		// and ExplicitMethods then use this logic.
+		// if x.NumEmbeddeds() != y.NumEmbeddeds() {
+		// 	return fmt.Errorf("unequal number of embedded interfaces: %d vs %d",
+		// 		x.NumEmbeddeds(), y.NumEmbeddeds())
+		// }
+		// for i := 0; i < x.NumEmbeddeds(); i++ {
+		// 	xi := x.Embedded(i)
+		// 	yi := y.Embedded(i)
+		// 	if xi.String() != yi.String() {
+		// 		return fmt.Errorf("mismatched %th embedded interface: %s vs %s",
+		// 			i, xi, yi)
+		// 	}
+		// }
+		// if x.NumExplicitMethods() != y.NumExplicitMethods() {
+		// 	return fmt.Errorf("unequal methods: %d vs %d",
+		// 		x.NumExplicitMethods(), y.NumExplicitMethods())
+		// }
+		// for i := 0; i < x.NumExplicitMethods(); i++ {
+		// 	xm := x.ExplicitMethod(i)
+		// 	ym := y.ExplicitMethod(i)
+		// 	if xm.Name() != ym.Name() {
+		// 		return fmt.Errorf("mismatched %th method: %s vs %s", i, xm, ym)
+		// 	}
+		// 	if err := equalType(xm.Type(), ym.Type()); err != nil {
+		// 		return fmt.Errorf("mismatched %s method: %s", xm.Name(), err)
+		// 	}
+		// }
+		if x.NumMethods() != y.NumMethods() {
+			return fmt.Errorf("unequal methods: %d vs %d",
+				x.NumMethods(), y.NumMethods())
+		}
+		for i := 0; i < x.NumMethods(); i++ {
+			xm := x.Method(i)
+			ym := y.Method(i)
+			if xm.Name() != ym.Name() {
+				return fmt.Errorf("mismatched %dth method: %s vs %s", i, xm, ym)
+			}
+			if err := equalType(xm.Type(), ym.Type()); err != nil {
+				return fmt.Errorf("mismatched %s method: %s", xm.Name(), err)
+			}
+		}
+	case *types.Array:
+		y := y.(*types.Array)
+		if x.Len() != y.Len() {
+			return fmt.Errorf("unequal array lengths: %d vs %d", x.Len(), y.Len())
+		}
+		if err := equalType(x.Elem(), y.Elem()); err != nil {
+			return fmt.Errorf("array elements: %s", err)
+		}
+	case *types.Basic:
+		y := y.(*types.Basic)
+		if x.Kind() != y.Kind() {
+			return fmt.Errorf("unequal basic types: %s vs %s", x, y)
+		}
+	case *types.Chan:
+		y := y.(*types.Chan)
+		if x.Dir() != y.Dir() {
+			return fmt.Errorf("unequal channel directions: %d vs %d", x.Dir(), y.Dir())
+		}
+		if err := equalType(x.Elem(), y.Elem()); err != nil {
+			return fmt.Errorf("channel elements: %s", err)
+		}
+	case *types.Map:
+		y := y.(*types.Map)
+		if err := equalType(x.Key(), y.Key()); err != nil {
+			return fmt.Errorf("map keys: %s", err)
+		}
+		if err := equalType(x.Elem(), y.Elem()); err != nil {
+			return fmt.Errorf("map values: %s", err)
+		}
+	case *types.Named:
+		y := y.(*types.Named)
+		if x.String() != y.String() {
+			return fmt.Errorf("unequal named types: %s vs %s", x, y)
+		}
+	case *types.Pointer:
+		y := y.(*types.Pointer)
+		if err := equalType(x.Elem(), y.Elem()); err != nil {
+			return fmt.Errorf("pointer elements: %s", err)
+		}
+	case *types.Signature:
+		y := y.(*types.Signature)
+		if err := equalType(x.Params(), y.Params()); err != nil {
+			return fmt.Errorf("parameters: %s", err)
+		}
+		if err := equalType(x.Results(), y.Results()); err != nil {
+			return fmt.Errorf("results: %s", err)
+		}
+		if x.Variadic() != y.Variadic() {
+			return fmt.Errorf("unequal variadicity: %t vs %t",
+				x.Variadic(), y.Variadic())
+		}
+		if (x.Recv() != nil) != (y.Recv() != nil) {
+			return fmt.Errorf("unequal receivers: %s vs %s", x.Recv(), y.Recv())
+		}
+		if x.Recv() != nil {
+			// TODO(adonovan): fix: this assertion fires for interface methods.
+			// The type of the receiver of an interface method is a named type
+			// if the Package was loaded from export data, or an unnamed (interface)
+			// type if the Package was produced by type-checking ASTs.
+			// if err := equalType(x.Recv().Type(), y.Recv().Type()); err != nil {
+			// 	return fmt.Errorf("receiver: %s", err)
+			// }
+		}
+	case *types.Slice:
+		y := y.(*types.Slice)
+		if err := equalType(x.Elem(), y.Elem()); err != nil {
+			return fmt.Errorf("slice elements: %s", err)
+		}
+	case *types.Struct:
+		y := y.(*types.Struct)
+		if x.NumFields() != y.NumFields() {
+			return fmt.Errorf("unequal struct fields: %d vs %d",
+				x.NumFields(), y.NumFields())
+		}
+		for i := 0; i < x.NumFields(); i++ {
+			xf := x.Field(i)
+			yf := y.Field(i)
+			if xf.Name() != yf.Name() {
+				return fmt.Errorf("mismatched fields: %s vs %s", xf, yf)
+			}
+			if err := equalType(xf.Type(), yf.Type()); err != nil {
+				return fmt.Errorf("struct field %s: %s", xf.Name(), err)
+			}
+			if x.Tag(i) != y.Tag(i) {
+				return fmt.Errorf("struct field %s has unequal tags: %q vs %q",
+					xf.Name(), x.Tag(i), y.Tag(i))
+			}
+		}
+	case *types.Tuple:
+		y := y.(*types.Tuple)
+		if x.Len() != y.Len() {
+			return fmt.Errorf("unequal tuple lengths: %d vs %d", x.Len(), y.Len())
+		}
+		for i := 0; i < x.Len(); i++ {
+			if err := equalType(x.At(i).Type(), y.At(i).Type()); err != nil {
+				return fmt.Errorf("tuple element %d: %s", i, err)
+			}
+		}
+	}
+	return nil
+}
+
+func checkPkg(t *testing.T, pkg *types.Package, label string) {
+	T1 := types.NewStruct(nil, nil)
+	T2 := types.NewStruct([]*types.Var{types.NewField(0, pkg, "T1", T1, true)}, nil)
+
+	for _, test := range []struct {
+		name string
+		typ  types.Type
+	}{
+		{"T0", types.Typ[types.Int32]},
+		{"T1", T1},
+		{"T2", T2},
+		{"Invalid", types.Typ[types.Invalid]},
+	} {
+		obj := pkg.Scope().Lookup(test.name)
+		if obj == nil {
+			t.Errorf("%s: %s not found", label, test.name)
+			continue
+		}
+		tname, _ := obj.(*types.TypeName)
+		if tname == nil {
+			t.Errorf("%s: %v not a type name", label, obj)
+			continue
+		}
+		if !tname.IsAlias() {
+			t.Errorf("%s: %v: not marked as alias", label, tname)
+			continue
+		}
+		if got := tname.Type(); !types.Identical(got, test.typ) {
+			t.Errorf("%s: %v: got %v; want %v", label, tname, got, test.typ)
+		}
+	}
+}
diff --git a/go/internal/gcimporter/iimport.go b/go/internal/gcimporter/iimport.go
index a31a880263..fef8b30080 100644
--- a/go/internal/gcimporter/iimport.go
+++ b/go/internal/gcimporter/iimport.go
@@ -18,6 +18,9 @@ import (
 	"go/types"
 	"io"
 	"sort"
+	"sync"
+	"unicode"
+	"unicode/utf8"
 )
 
 type intReader struct {
@@ -25,6 +28,10 @@ type intReader struct {
 	path string
 }
 
+func errorf(format string, args ...interface{}) {
+	panic(fmt.Sprintf(format, args...))
+}
+
 func (r *intReader) int64() int64 {
 	i, err := binary.ReadVarint(r.Reader)
 	if err != nil {
@@ -628,3 +635,166 @@ func (r *importReader) byte() byte {
 	}
 	return x
 }
+
+const deltaNewFile = -64 // see cmd/compile/internal/gc/bexport.go
+
+// Synthesize a token.Pos
+type fakeFileSet struct {
+	fset  *token.FileSet
+	files map[string]*token.File
+}
+
+func (s *fakeFileSet) pos(file string, line, column int) token.Pos {
+	// TODO(mdempsky): Make use of column.
+
+	// Since we don't know the set of needed file positions, we
+	// reserve maxlines positions per file.
+	const maxlines = 64 * 1024
+	f := s.files[file]
+	if f == nil {
+		f = s.fset.AddFile(file, -1, maxlines)
+		s.files[file] = f
+		// Allocate the fake linebreak indices on first use.
+		// TODO(adonovan): opt: save ~512KB using a more complex scheme?
+		fakeLinesOnce.Do(func() {
+			fakeLines = make([]int, maxlines)
+			for i := range fakeLines {
+				fakeLines[i] = i
+			}
+		})
+		f.SetLines(fakeLines)
+	}
+
+	if line > maxlines {
+		line = 1
+	}
+
+	// Treat the file as if it contained only newlines
+	// and column=1: use the line number as the offset.
+	return f.Pos(line - 1)
+}
+
+var (
+	fakeLines     []int
+	fakeLinesOnce sync.Once
+)
+
+func chanDir(d int) types.ChanDir {
+	// tag values must match the constants in cmd/compile/internal/gc/go.go
+	switch d {
+	case 1 /* Crecv */ :
+		return types.RecvOnly
+	case 2 /* Csend */ :
+		return types.SendOnly
+	case 3 /* Cboth */ :
+		return types.SendRecv
+	default:
+		errorf("unexpected channel dir %d", d)
+		return 0
+	}
+}
+
+func exported(name string) bool {
+	ch, _ := utf8.DecodeRuneInString(name)
+	return unicode.IsUpper(ch)
+}
+
+// ----------------------------------------------------------------------------
+// Export format
+
+// Tags. Must be < 0.
+const (
+	// Objects
+	packageTag = -(iota + 1)
+	constTag
+	typeTag
+	varTag
+	funcTag
+	endTag
+
+	// Types
+	namedTag
+	arrayTag
+	sliceTag
+	dddTag
+	structTag
+	pointerTag
+	signatureTag
+	interfaceTag
+	mapTag
+	chanTag
+
+	// Values
+	falseTag
+	trueTag
+	int64Tag
+	floatTag
+	fractionTag // not used by gc
+	complexTag
+	stringTag
+	nilTag     // only used by gc (appears in exported inlined function bodies)
+	unknownTag // not used by gc (only appears in packages with errors)
+
+	// Type aliases
+	aliasTag
+)
+
+var predeclOnce sync.Once
+var predecl []types.Type // initialized lazily
+
+func predeclared() []types.Type {
+	predeclOnce.Do(func() {
+		// initialize lazily to be sure that all
+		// elements have been initialized before
+		predecl = []types.Type{ // basic types
+			types.Typ[types.Bool],
+			types.Typ[types.Int],
+			types.Typ[types.Int8],
+			types.Typ[types.Int16],
+			types.Typ[types.Int32],
+			types.Typ[types.Int64],
+			types.Typ[types.Uint],
+			types.Typ[types.Uint8],
+			types.Typ[types.Uint16],
+			types.Typ[types.Uint32],
+			types.Typ[types.Uint64],
+			types.Typ[types.Uintptr],
+			types.Typ[types.Float32],
+			types.Typ[types.Float64],
+			types.Typ[types.Complex64],
+			types.Typ[types.Complex128],
+			types.Typ[types.String],
+
+			// basic type aliases
+			types.Universe.Lookup("byte").Type(),
+			types.Universe.Lookup("rune").Type(),
+
+			// error
+			types.Universe.Lookup("error").Type(),
+
+			// untyped types
+			types.Typ[types.UntypedBool],
+			types.Typ[types.UntypedInt],
+			types.Typ[types.UntypedRune],
+			types.Typ[types.UntypedFloat],
+			types.Typ[types.UntypedComplex],
+			types.Typ[types.UntypedString],
+			types.Typ[types.UntypedNil],
+
+			// package unsafe
+			types.Typ[types.UnsafePointer],
+
+			// invalid type
+			types.Typ[types.Invalid], // only appears in packages with errors
+
+			// used internally by gc; never used by this package or in .a files
+			anyType{},
+		}
+	})
+	return predecl
+}
+
+type anyType struct{}
+
+func (t anyType) Underlying() types.Type { return t }
+func (t anyType) String() string         { return "any" }
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