[dev.typeparams] cmd/compile: refactor import reading

This CL restructures the gcimports importer to mmap the export data
into memory as a string, and then pass that same string to both the
typecheck and types2 importers.

This is primarily motivated by preparation for unified IR; but it
should also improve performance (fewer string copies) and reduces
divergance between the two importers.

Passes toolstash -cmp.

Change-Id: I397f720693e9e6360bfcb5acb12609ab339d251f
Reviewed-on: https://go-review.googlesource.com/c/go/+/325210
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
Trust: Matthew Dempsky <mdempsky@google.com>
Trust: Robert Griesemer <gri@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Robert Griesemer <gri@golang.org>

7 files changed, 172 insertions, 154 deletions

diff --git a/src/cmd/compile/internal/typecheck/mapfile_mmap.go b/src/cmd/compile/internal/base/mapfile_mmap.go
index 298b385bcb..c1616db8e9 100644
--- a/src/cmd/compile/internal/typecheck/mapfile_mmap.go
+++ b/src/cmd/compile/internal/base/mapfile_mmap.go
@@ -5,7 +5,7 @@
 //go:build darwin || dragonfly || freebsd || linux || netbsd || openbsd
 // +build darwin dragonfly freebsd linux netbsd openbsd
 
-package typecheck
+package base
 
 import (
 	"os"
@@ -19,7 +19,7 @@ import (
 
 // mapFile returns length bytes from the file starting at the
 // specified offset as a string.
-func mapFile(f *os.File, offset, length int64) (string, error) {
+func MapFile(f *os.File, offset, length int64) (string, error) {
 	// POSIX mmap: "The implementation may require that off is a
 	// multiple of the page size."
 	x := offset & int64(os.Getpagesize()-1)
diff --git a/src/cmd/compile/internal/typecheck/mapfile_read.go b/src/cmd/compile/internal/base/mapfile_read.go
index 9637ab97ab..01796a9bab 100644
--- a/src/cmd/compile/internal/typecheck/mapfile_read.go
+++ b/src/cmd/compile/internal/base/mapfile_read.go
@@ -5,14 +5,14 @@
 //go:build !darwin && !dragonfly && !freebsd && !linux && !netbsd && !openbsd
 // +build !darwin,!dragonfly,!freebsd,!linux,!netbsd,!openbsd
 
-package typecheck
+package base
 
 import (
 	"io"
 	"os"
 )
 
-func mapFile(f *os.File, offset, length int64) (string, error) {
+func MapFile(f *os.File, offset, length int64) (string, error) {
 	buf := make([]byte, length)
 	_, err := io.ReadFull(io.NewSectionReader(f, offset, length), buf)
 	if err != nil {
diff --git a/src/cmd/compile/internal/importer/gcimporter.go b/src/cmd/compile/internal/importer/gcimporter.go
index 6c5458fad1..ff40be65bb 100644
--- a/src/cmd/compile/internal/importer/gcimporter.go
+++ b/src/cmd/compile/internal/importer/gcimporter.go
@@ -155,7 +155,7 @@ func Import(packages map[string]*types2.Package, path, srcDir string, lookup fun
 		// 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(packages, data[1:], id)
+			pkg, err = ImportData(packages, string(data[1:]), id)
 		} else {
 			err = fmt.Errorf("import %q: old binary export format no longer supported (recompile library)", path)
 		}
diff --git a/src/cmd/compile/internal/importer/iimport.go b/src/cmd/compile/internal/importer/iimport.go
index fb39e93073..14e64891b8 100644
--- a/src/cmd/compile/internal/importer/iimport.go
+++ b/src/cmd/compile/internal/importer/iimport.go
@@ -8,7 +8,6 @@
 package importer
 
 import (
-	"bytes"
 	"cmd/compile/internal/syntax"
 	"cmd/compile/internal/types2"
 	"encoding/binary"
@@ -18,10 +17,11 @@ import (
 	"io"
 	"math/big"
 	"sort"
+	"strings"
 )
 
 type intReader struct {
-	*bytes.Reader
+	*strings.Reader
 	path string
 }
 
@@ -82,7 +82,7 @@ const io_SeekCurrent = 1 // io.SeekCurrent (not defined in Go 1.4)
 // 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 iImportData(imports map[string]*types2.Package, data []byte, path string) (_ int, pkg *types2.Package, err error) {
+func ImportData(imports map[string]*types2.Package, data, path string) (pkg *types2.Package, err error) {
 	const currentVersion = iexportVersionCurrent
 	version := int64(-1)
 	defer func() {
@@ -95,7 +95,7 @@ func iImportData(imports map[string]*types2.Package, data []byte, path string) (
 		}
 	}()
 
-	r := &intReader{bytes.NewReader(data), path}
+	r := &intReader{strings.NewReader(data), path}
 
 	version = int64(r.uint64())
 	switch version {
@@ -122,7 +122,6 @@ func iImportData(imports map[string]*types2.Package, data []byte, path string) (
 		version:       int(version),
 
 		stringData:   stringData,
-		stringCache:  make(map[uint64]string),
 		pkgCache:     make(map[uint64]*types2.Package),
 		posBaseCache: make(map[uint64]*syntax.PosBase),
 
@@ -196,8 +195,7 @@ func iImportData(imports map[string]*types2.Package, data []byte, path string) (
 	// package was imported completely and without errors
 	localpkg.MarkComplete()
 
-	consumed, _ := r.Seek(0, io_SeekCurrent)
-	return int(consumed), localpkg, nil
+	return localpkg, nil
 }
 
 type iimporter struct {
@@ -205,12 +203,11 @@ type iimporter struct {
 	ipath         string
 	version       int
 
-	stringData   []byte
-	stringCache  map[uint64]string
+	stringData   string
 	pkgCache     map[uint64]*types2.Package
 	posBaseCache map[uint64]*syntax.PosBase
 
-	declData    []byte
+	declData    string
 	pkgIndex    map[*types2.Package]map[string]uint64
 	typCache    map[uint64]types2.Type
 	tparamIndex map[ident]types2.Type
@@ -233,24 +230,21 @@ func (p *iimporter) doDecl(pkg *types2.Package, name string) {
 	// Reader.Reset is not available in Go 1.4.
 	// Use bytes.NewReader for now.
 	// r.declReader.Reset(p.declData[off:])
-	r.declReader = *bytes.NewReader(p.declData[off:])
+	r.declReader = *strings.NewReader(p.declData[off:])
 
 	r.obj(name)
 }
 
 func (p *iimporter) stringAt(off uint64) string {
-	if s, ok := p.stringCache[off]; ok {
-		return s
-	}
+	var x [binary.MaxVarintLen64]byte
+	n := copy(x[:], p.stringData[off:])
 
-	slen, n := binary.Uvarint(p.stringData[off:])
+	slen, n := binary.Uvarint(x[:n])
 	if n <= 0 {
 		errorf("varint failed")
 	}
 	spos := off + uint64(n)
-	s := string(p.stringData[spos : spos+slen])
-	p.stringCache[off] = s
-	return s
+	return p.stringData[spos : spos+slen]
 }
 
 func (p *iimporter) pkgAt(off uint64) *types2.Package {
@@ -285,7 +279,7 @@ func (p *iimporter) typAt(off uint64, base *types2.Named) types2.Type {
 	// Reader.Reset is not available in Go 1.4.
 	// Use bytes.NewReader for now.
 	// r.declReader.Reset(p.declData[off-predeclReserved:])
-	r.declReader = *bytes.NewReader(p.declData[off-predeclReserved:])
+	r.declReader = *strings.NewReader(p.declData[off-predeclReserved:])
 	t := r.doType(base)
 
 	if base == nil || !isInterface(t) {
@@ -296,7 +290,7 @@ func (p *iimporter) typAt(off uint64, base *types2.Named) types2.Type {
 
 type importReader struct {
 	p           *iimporter
-	declReader  bytes.Reader
+	declReader  strings.Reader
 	currPkg     *types2.Package
 	prevPosBase *syntax.PosBase
 	prevLine    int64
diff --git a/src/cmd/compile/internal/noder/decl.go b/src/cmd/compile/internal/noder/decl.go
index 5c80b20671..96abbe66ae 100644
--- a/src/cmd/compile/internal/noder/decl.go
+++ b/src/cmd/compile/internal/noder/decl.go
@@ -41,21 +41,15 @@ func (g *irgen) decls(decls []syntax.Decl) []ir.Node {
 }
 
 func (g *irgen) importDecl(p *noder, decl *syntax.ImportDecl) {
-	// TODO(mdempsky): Merge with gcimports so we don't have to import
-	// packages twice.
-
 	g.pragmaFlags(decl.Pragma, 0)
 
 	// Get the imported package's path, as resolved already by types2
 	// and gcimporter. This is the same path as would be computed by
 	// parseImportPath.
-	path := pkgNameOf(g.info, decl).Imported().Path()
-
-	ipkg := readImportFile(g.target, path)
-	if ipkg == ir.Pkgs.Unsafe {
+	switch pkgNameOf(g.info, decl).Imported().Path() {
+	case "unsafe":
 		p.importedUnsafe = true
-	}
-	if ipkg.Path == "embed" {
+	case "embed":
 		p.importedEmbed = true
 	}
 }
diff --git a/src/cmd/compile/internal/noder/import.go b/src/cmd/compile/internal/noder/import.go
index 24d911ba38..8076b74650 100644
--- a/src/cmd/compile/internal/noder/import.go
+++ b/src/cmd/compile/internal/noder/import.go
@@ -8,7 +8,6 @@ import (
 	"errors"
 	"fmt"
 	"internal/buildcfg"
-	"io"
 	"os"
 	pathpkg "path"
 	"runtime"
@@ -46,13 +45,8 @@ func (m *gcimports) ImportFrom(path, srcDir string, mode types2.ImportMode) (*ty
 		panic("mode must be 0")
 	}
 
-	path, err := resolveImportPath(path)
-	if err != nil {
-		return nil, err
-	}
-
-	lookup := func(path string) (io.ReadCloser, error) { return openPackage(path) }
-	return importer.Import(m.packages, path, srcDir, lookup)
+	_, pkg, err := readImportFile(path, typecheck.Target, m.packages)
+	return pkg, err
 }
 
 func isDriveLetter(b byte) bool {
@@ -182,7 +176,12 @@ func importfile(decl *syntax.ImportDecl) *types.Pkg {
 		return nil
 	}
 
-	pkg := readImportFile(typecheck.Target, path)
+	pkg, _, err := readImportFile(path, typecheck.Target, nil)
+	if err != nil {
+		base.Errorf("%s", err)
+		return nil
+	}
+
 	if pkg != ir.Pkgs.Unsafe && pkg.Height >= myheight {
 		myheight = pkg.Height + 1
 	}
@@ -203,136 +202,184 @@ func parseImportPath(pathLit *syntax.BasicLit) (string, error) {
 		return "", err
 	}
 
-	return resolveImportPath(path)
+	return path, err
 }
 
-func readImportFile(target *ir.Package, path string) *types.Pkg {
-	importpkg := types.NewPkg(path, "")
-	if importpkg.Direct {
-		return importpkg // already fully loaded
+// readImportFile reads the import file for the given package path and
+// returns its types.Pkg representation. If packages is non-nil, the
+// types2.Package representation is also returned.
+func readImportFile(path string, target *ir.Package, packages map[string]*types2.Package) (pkg1 *types.Pkg, pkg2 *types2.Package, err error) {
+	path, err = resolveImportPath(path)
+	if err != nil {
+		return
 	}
-	importpkg.Direct = true
-	target.Imports = append(target.Imports, importpkg)
 
 	if path == "unsafe" {
-		return importpkg // initialized with universe
+		pkg1, pkg2 = ir.Pkgs.Unsafe, types2.Unsafe
+
+		// TODO(mdempsky): Investigate if this actually matters. Why would
+		// the linker or runtime care whether a package imported unsafe?
+		if !pkg1.Direct {
+			pkg1.Direct = true
+			target.Imports = append(target.Imports, pkg1)
+		}
+
+		return
+	}
+
+	pkg1 = types.NewPkg(path, "")
+	if packages != nil {
+		pkg2 = packages[path]
+		assert(pkg1.Direct == (pkg2 != nil && pkg2.Complete()))
+	}
+
+	if pkg1.Direct {
+		return
 	}
+	pkg1.Direct = true
+	target.Imports = append(target.Imports, pkg1)
 
 	f, err := openPackage(path)
 	if err != nil {
-		base.Errorf("could not import %q: %v", path, err)
-		base.ErrorExit()
+		return
 	}
-	imp := bio.NewReader(f)
-	defer imp.Close()
-	file := f.Name()
+	defer f.Close()
+
+	r, end, err := findExportData(f)
+	if err != nil {
+		return
+	}
+
+	if base.Debug.Export != 0 {
+		fmt.Printf("importing %s (%s)\n", path, f.Name())
+	}
+
+	var c byte
+	switch c, err = r.ReadByte(); {
+	case err != nil:
+		return
+
+	case c != 'i':
+		// Indexed format is distinguished by an 'i' byte,
+		// whereas previous export formats started with 'c', 'd', or 'v'.
+		err = fmt.Errorf("unexpected package format byte: %v", c)
+		return
+	}
+
+	// Map string (and data) section into memory as a single large
+	// string. This reduces heap fragmentation and allows
+	// returning individual substrings very efficiently.
+	pos := r.Offset()
+	data, err := base.MapFile(r.File(), pos, end-pos)
+	if err != nil {
+		return
+	}
+
+	typecheck.ReadImports(pkg1, data)
+
+	if packages != nil {
+		pkg2, err = importer.ImportData(packages, data, path)
+		if err != nil {
+			return
+		}
+	}
+
+	err = addFingerprint(path, f, end)
+	return
+}
+
+// findExportData returns a *bio.Reader positioned at the start of the
+// binary export data section, and a file offset for where to stop
+// reading.
+func findExportData(f *os.File) (r *bio.Reader, end int64, err error) {
+	r = bio.NewReader(f)
 
 	// check object header
-	p, err := imp.ReadString('\n')
+	line, err := r.ReadString('\n')
 	if err != nil {
-		base.Errorf("import %s: reading input: %v", file, err)
-		base.ErrorExit()
+		return
 	}
 
-	if p == "!<arch>\n" { // package archive
+	if line == "!<arch>\n" { // package archive
 		// package export block should be first
-		sz := archive.ReadHeader(imp.Reader, "__.PKGDEF")
+		sz := int64(archive.ReadHeader(r.Reader, "__.PKGDEF"))
 		if sz <= 0 {
-			base.Errorf("import %s: not a package file", file)
-			base.ErrorExit()
+			err = errors.New("not a package file")
+			return
+		}
+		end = r.Offset() + sz
+		line, err = r.ReadString('\n')
+		if err != nil {
+			return
 		}
-		p, err = imp.ReadString('\n')
+	} else {
+		// Not an archive; provide end of file instead.
+		// TODO(mdempsky): I don't think this happens anymore.
+		var fi os.FileInfo
+		fi, err = f.Stat()
 		if err != nil {
-			base.Errorf("import %s: reading input: %v", file, err)
-			base.ErrorExit()
+			return
 		}
+		end = fi.Size()
 	}
 
-	if !strings.HasPrefix(p, "go object ") {
-		base.Errorf("import %s: not a go object file: %s", file, p)
-		base.ErrorExit()
+	if !strings.HasPrefix(line, "go object ") {
+		err = fmt.Errorf("not a go object file: %s", line)
+		return
 	}
-	q := objabi.HeaderString()
-	if p != q {
-		base.Errorf("import %s: object is [%s] expected [%s]", file, p, q)
-		base.ErrorExit()
+	if expect := objabi.HeaderString(); line != expect {
+		err = fmt.Errorf("object is [%s] expected [%s]", line, expect)
+		return
 	}
 
 	// process header lines
-	for {
-		p, err = imp.ReadString('\n')
+	for !strings.HasPrefix(line, "$$") {
+		line, err = r.ReadString('\n')
 		if err != nil {
-			base.Errorf("import %s: reading input: %v", file, err)
-			base.ErrorExit()
-		}
-		if p == "\n" {
-			break // header ends with blank line
+			return
 		}
 	}
 
 	// Expect $$B\n to signal binary import format.
-
-	// look for $$
-	var c byte
-	for {
-		c, err = imp.ReadByte()
-		if err != nil {
-			break
-		}
-		if c == '$' {
-			c, err = imp.ReadByte()
-			if c == '$' || err != nil {
-				break
-			}
-		}
+	if line != "$$B\n" {
+		err = errors.New("old export format no longer supported (recompile library)")
+		return
 	}
 
-	// get character after $$
-	if err == nil {
-		c, _ = imp.ReadByte()
-	}
+	return
+}
 
+// addFingerprint reads the linker fingerprint included at the end of
+// the exportdata.
+func addFingerprint(path string, f *os.File, end int64) error {
+	const eom = "\n$$\n"
 	var fingerprint goobj.FingerprintType
-	switch c {
-	case '\n':
-		base.Errorf("cannot import %s: old export format no longer supported (recompile library)", path)
-		return nil
-
-	case 'B':
-		if base.Debug.Export != 0 {
-			fmt.Printf("importing %s (%s)\n", path, file)
-		}
-		imp.ReadByte() // skip \n after $$B
-
-		c, err = imp.ReadByte()
-		if err != nil {
-			base.Errorf("import %s: reading input: %v", file, err)
-			base.ErrorExit()
-		}
 
-		// Indexed format is distinguished by an 'i' byte,
-		// whereas previous export formats started with 'c', 'd', or 'v'.
-		if c != 'i' {
-			base.Errorf("import %s: unexpected package format byte: %v", file, c)
-			base.ErrorExit()
-		}
-		fingerprint = typecheck.ReadImports(importpkg, imp)
+	var buf [len(fingerprint) + len(eom)]byte
+	if _, err := f.ReadAt(buf[:], end-int64(len(buf))); err != nil {
+		return err
+	}
 
-	default:
-		base.Errorf("no import in %q", path)
-		base.ErrorExit()
+	// Caller should have given us the end position of the export data,
+	// which should end with the "\n$$\n" marker. As a consistency check
+	// to make sure we're reading at the right offset, make sure we
+	// found the marker.
+	if s := string(buf[len(fingerprint):]); s != eom {
+		return fmt.Errorf("expected $$ marker, but found %q", s)
 	}
 
+	copy(fingerprint[:], buf[:])
+
 	// assume files move (get installed) so don't record the full path
 	if base.Flag.Cfg.PackageFile != nil {
 		// If using a packageFile map, assume path_ can be recorded directly.
 		base.Ctxt.AddImport(path, fingerprint)
 	} else {
 		// For file "/Users/foo/go/pkg/darwin_amd64/math.a" record "math.a".
+		file := f.Name()
 		base.Ctxt.AddImport(file[len(file)-len(path)-len(".a"):], fingerprint)
 	}
-
-	return importpkg
+	return nil
 }
 
 // The linker uses the magic symbol prefixes "go." and "type."
diff --git a/src/cmd/compile/internal/typecheck/iimport.go b/src/cmd/compile/internal/typecheck/iimport.go
index 45a177951e..cafb18d7a8 100644
--- a/src/cmd/compile/internal/typecheck/iimport.go
+++ b/src/cmd/compile/internal/typecheck/iimport.go
@@ -12,7 +12,6 @@ import (
 	"encoding/binary"
 	"fmt"
 	"go/constant"
-	"io"
 	"math/big"
 	"os"
 	"strings"
@@ -20,8 +19,6 @@ import (
 	"cmd/compile/internal/base"
 	"cmd/compile/internal/ir"
 	"cmd/compile/internal/types"
-	"cmd/internal/bio"
-	"cmd/internal/goobj"
 	"cmd/internal/obj"
 	"cmd/internal/src"
 )
@@ -95,7 +92,7 @@ func importReaderFor(sym *types.Sym, importers map[*types.Sym]iimporterAndOffset
 }
 
 type intReader struct {
-	*bio.Reader
+	*strings.Reader
 	pkg *types.Pkg
 }
 
@@ -117,8 +114,8 @@ func (r *intReader) uint64() uint64 {
 	return i
 }
 
-func ReadImports(pkg *types.Pkg, in *bio.Reader) (fingerprint goobj.FingerprintType) {
-	ird := &intReader{in, pkg}
+func ReadImports(pkg *types.Pkg, data string) {
+	ird := &intReader{strings.NewReader(data), pkg}
 
 	version := ird.uint64()
 	switch version {
@@ -132,21 +129,15 @@ func ReadImports(pkg *types.Pkg, in *bio.Reader) (fingerprint goobj.FingerprintT
 		base.ErrorExit()
 	}
 
-	sLen := ird.uint64()
-	dLen := ird.uint64()
+	sLen := int64(ird.uint64())
+	dLen := int64(ird.uint64())
 
-	// Map string (and data) section into memory as a single large
-	// string. This reduces heap fragmentation and allows
-	// returning individual substrings very efficiently.
-	data, err := mapFile(in.File(), in.Offset(), int64(sLen+dLen))
-	if err != nil {
-		base.Errorf("import %q: mapping input: %v", pkg.Path, err)
-		base.ErrorExit()
-	}
-	stringData := data[:sLen]
-	declData := data[sLen:]
-
-	in.MustSeek(int64(sLen+dLen), os.SEEK_CUR)
+	// TODO(mdempsky): Replace os.SEEK_CUR with io.SeekCurrent after
+	// #44505 is fixed.
+	whence, _ := ird.Seek(0, os.SEEK_CUR)
+	stringData := data[whence : whence+sLen]
+	declData := data[whence+sLen : whence+sLen+dLen]
+	ird.Seek(sLen+dLen, os.SEEK_CUR)
 
 	p := &iimporter{
 		exportVersion: version,
@@ -208,14 +199,6 @@ func ReadImports(pkg *types.Pkg, in *bio.Reader) (fingerprint goobj.FingerprintT
 			}
 		}
 	}
-
-	// Fingerprint.
-	_, err = io.ReadFull(in, fingerprint[:])
-	if err != nil {
-		base.Errorf("import %s: error reading fingerprint", pkg.Path)
-		base.ErrorExit()
-	}
-	return fingerprint
 }
 
 type iimporter struct {