go/build, cmd/go: update to match recent changes to gc

    
    Several recent changes to the gc version of cmd/go improve the
    gofrontend support. These changes are partially copies of existing
    gofrontend differences, and partially new code. This CL makes the
    gofrontend match the upstream code.
    
    The changes included here come from:
        https://golang.org/cl/111575
        https://golang.org/cl/111595
        https://golang.org/cl/111635
        https://golang.org/cl/111636
    
    For the record, the following recent gc changes are based on code
    already present in the gofrontend repo:
        https://golang.org/cl/110915
        https://golang.org/cl/111615
    
    For the record, a gc change, partially based on earlier gofrontend
    work, also with new gc code, was already copied to gofrontend repo in
    CL 111099:
        https://golang.org/cl/111097
    
    This moves the generated list of standard library packages from
    cmd/go/internal/load to go/build.
    
    Reviewed-on: https://go-review.googlesource.com/112475

gotools/:
	* Makefile.am (check-go-tool): Don't copy zstdpkglist.go.
	* Makefile.in: Rebuild.

From-SVN: r260097

13 files changed, 179 insertions, 60 deletions

diff --git a/gcc/go/gofrontend/MERGE b/gcc/go/gofrontend/MERGE
index 05ecf26..319d2f5 100644
--- a/gcc/go/gofrontend/MERGE
+++ b/gcc/go/gofrontend/MERGE
@@ -1,4 +1,4 @@
-6b0355769edd9543e6c5f2270b26b140bb96e9aa
+290c93f08f4456f0552b0764e28573164e47f259
 
 The first line of this file holds the git revision number of the last
 merge done from the gofrontend repository.
diff --git a/gotools/ChangeLog b/gotools/ChangeLog
index cac11df..0e67186 100644
--- a/gotools/ChangeLog
+++ b/gotools/ChangeLog
@@ -1,3 +1,8 @@
+2018-05-09  Ian Lance Taylor  <iant@golang.org>
+
+	* Makefile.am (check-go-tool): Don't copy zstdpkglist.go.
+	* Makefile.in: Rebuild.
+
 2018-05-04  Ian Lance Taylor  <iant@golang.org>
 
 	PR go/85630
diff --git a/gotools/Makefile.am b/gotools/Makefile.am
index ba5f283..06be89d 100644
--- a/gotools/Makefile.am
+++ b/gotools/Makefile.am
@@ -232,7 +232,6 @@ check-go-tool: go$(EXEEXT) $(noinst_PROGRAMS) check-head check-gccgo check-gcc
 	$(MKDIR_P) check-go-dir/src/cmd/go
 	cp $(cmdsrcdir)/go/*.go check-go-dir/src/cmd/go/
 	cp -r $(cmdsrcdir)/go/internal check-go-dir/src/cmd/go/
-	cp $(libgodir)/zstdpkglist.go check-go-dir/src/cmd/go/internal/load/
 	cp $(libgodir)/zdefaultcc.go check-go-dir/src/cmd/go/internal/cfg/
 	cp -r $(cmdsrcdir)/go/testdata check-go-dir/src/cmd/go/
 	cp -r $(cmdsrcdir)/internal check-go-dir/src/cmd/
diff --git a/gotools/Makefile.in b/gotools/Makefile.in
index 8e60e9f..503ec4e 100644
--- a/gotools/Makefile.in
+++ b/gotools/Makefile.in
@@ -637,8 +637,8 @@ distclean-generic:
 maintainer-clean-generic:
 	@echo "This command is intended for maintainers to use"
 	@echo "it deletes files that may require special tools to rebuild."
-@NATIVE_FALSE@install-exec-local:
 @NATIVE_FALSE@uninstall-local:
+@NATIVE_FALSE@install-exec-local:
 clean: clean-am
 
 clean-am: clean-binPROGRAMS clean-generic clean-noinstPROGRAMS \
@@ -811,7 +811,6 @@ mostlyclean-local:
 @NATIVE_TRUE@	$(MKDIR_P) check-go-dir/src/cmd/go
 @NATIVE_TRUE@	cp $(cmdsrcdir)/go/*.go check-go-dir/src/cmd/go/
 @NATIVE_TRUE@	cp -r $(cmdsrcdir)/go/internal check-go-dir/src/cmd/go/
-@NATIVE_TRUE@	cp $(libgodir)/zstdpkglist.go check-go-dir/src/cmd/go/internal/load/
 @NATIVE_TRUE@	cp $(libgodir)/zdefaultcc.go check-go-dir/src/cmd/go/internal/cfg/
 @NATIVE_TRUE@	cp -r $(cmdsrcdir)/go/testdata check-go-dir/src/cmd/go/
 @NATIVE_TRUE@	cp -r $(cmdsrcdir)/internal check-go-dir/src/cmd/
diff --git a/libgo/Makefile.am b/libgo/Makefile.am
index 119d241..d847413 100644
--- a/libgo/Makefile.am
+++ b/libgo/Makefile.am
@@ -602,13 +602,13 @@ s-runtime-inc: runtime.lo Makefile
 	$(SHELL) $(srcdir)/mvifdiff.sh tmp-runtime.inc runtime.inc
 	$(STAMP) $@
 
-noinst_DATA += zstdpkglist.go zdefaultcc.go
+noinst_DATA += zdefaultcc.go
 
 # Generate the list of go std packages that were included in libgo
 zstdpkglist.go: s-zstdpkglist; @true
 s-zstdpkglist: Makefile
 	rm -f zstdpkglist.go.tmp
-	echo 'package load' > zstdpkglist.go.tmp
+	echo 'package build' > zstdpkglist.go.tmp
 	echo "" >> zstdpkglist.go.tmp
 	echo 'var stdpkg = map[string]bool{' >> zstdpkglist.go.tmp
 	echo $(libgo_go_objs) 'unsafe.lo' 'runtime/cgo.lo' | sed 's|[a-z0-9_/]*_c\.lo||g' | sed 's|\([a-z0-9_/]*\)\.lo|"\1": true,|g' >> zstdpkglist.go.tmp
@@ -960,6 +960,9 @@ runtime_pprof_check_GOCFLAGS = -static-libgo -fno-inline
 extra_go_files_runtime_internal_sys = version.go
 runtime/internal/sys.lo.dep: $(extra_go_files_runtime_internal_sys)
 
+extra_go_files_go_build = zstdpkglist.go
+go/build.lo.dep: $(extra_go_files_go_build)
+
 extra_go_files_go_types = gccgosizes.go
 go/types.lo.dep: $(extra_go_files_go_types)
 
@@ -969,9 +972,6 @@ cmd/internal/objabi.lo.dep: $(extra_go_files_cmd_internal_objabi)
 extra_go_files_cmd_go_internal_cfg = zdefaultcc.go
 cmd/go/internal/cfg.lo.dep: $(extra_go_files_cmd_go_internal_cfg)
 
-extra_go_files_cmd_go_internal_load = zstdpkglist.go
-cmd/go/internal/load.lo.dep: $(extra_go_files_cmd_go_internal_load)
-
 extra_check_libs_cmd_go_internal_cache = $(abs_builddir)/libgotool.a
 extra_check_libs_cmd_go_internal_generate = $(abs_builddir)/libgotool.a
 extra_check_libs_cmd_go_internal_get = $(abs_builddir)/libgotool.a
diff --git a/libgo/Makefile.in b/libgo/Makefile.in
index a30e427..6b3c597 100644
--- a/libgo/Makefile.in
+++ b/libgo/Makefile.in
@@ -759,7 +759,7 @@ noinst_DATA = golang_org/x/net/internal/nettest.gox \
 	golang_org/x/net/nettest.gox internal/testenv.gox \
 	internal/trace.gox net/internal/socktest.gox \
 	os/signal/internal/pty.gox runtime/pprof/internal/profile.gox \
-	zstdpkglist.go zdefaultcc.go
+	zdefaultcc.go
 @LIBGO_IS_RTEMS_FALSE@rtems_task_variable_add_file = 
 @LIBGO_IS_RTEMS_TRUE@rtems_task_variable_add_file = runtime/rtems-task-variable-add.c
 @LIBGO_IS_AIX_FALSE@@LIBGO_IS_DARWIN_FALSE@@LIBGO_IS_FREEBSD_FALSE@@LIBGO_IS_IRIX_FALSE@@LIBGO_IS_LINUX_FALSE@@LIBGO_IS_NETBSD_FALSE@@LIBGO_IS_SOLARIS_FALSE@runtime_getncpu_file = runtime/getncpu-none.c
@@ -999,10 +999,10 @@ runtime_internal_sys_lo_check_GOCFLAGS = -fgo-compiling-runtime
 # Also use -fno-inline to get better results from the memory profiler.
 runtime_pprof_check_GOCFLAGS = -static-libgo -fno-inline
 extra_go_files_runtime_internal_sys = version.go
+extra_go_files_go_build = zstdpkglist.go
 extra_go_files_go_types = gccgosizes.go
 extra_go_files_cmd_internal_objabi = objabi.go
 extra_go_files_cmd_go_internal_cfg = zdefaultcc.go
-extra_go_files_cmd_go_internal_load = zstdpkglist.go
 extra_check_libs_cmd_go_internal_cache = $(abs_builddir)/libgotool.a
 extra_check_libs_cmd_go_internal_generate = $(abs_builddir)/libgotool.a
 extra_check_libs_cmd_go_internal_get = $(abs_builddir)/libgotool.a
@@ -2816,7 +2816,7 @@ s-runtime-inc: runtime.lo Makefile
 zstdpkglist.go: s-zstdpkglist; @true
 s-zstdpkglist: Makefile
 	rm -f zstdpkglist.go.tmp
-	echo 'package load' > zstdpkglist.go.tmp
+	echo 'package build' > zstdpkglist.go.tmp
 	echo "" >> zstdpkglist.go.tmp
 	echo 'var stdpkg = map[string]bool{' >> zstdpkglist.go.tmp
 	echo $(libgo_go_objs) 'unsafe.lo' 'runtime/cgo.lo' | sed 's|[a-z0-9_/]*_c\.lo||g' | sed 's|\([a-z0-9_/]*\)\.lo|"\1": true,|g' >> zstdpkglist.go.tmp
@@ -2943,10 +2943,10 @@ $(foreach package,$(GOTOOL_PACKAGES),$(eval $(call PACKAGE_template,$(package)))
 runtime.lo.dep: $(extra_go_files_runtime)
 syscall.lo.dep: $(extra_go_files_syscall)
 runtime/internal/sys.lo.dep: $(extra_go_files_runtime_internal_sys)
+go/build.lo.dep: $(extra_go_files_go_build)
 go/types.lo.dep: $(extra_go_files_go_types)
 cmd/internal/objabi.lo.dep: $(extra_go_files_cmd_internal_objabi)
 cmd/go/internal/cfg.lo.dep: $(extra_go_files_cmd_go_internal_cfg)
-cmd/go/internal/load.lo.dep: $(extra_go_files_cmd_go_internal_load)
 
 # FIXME: The following C files may as well move to the runtime
 # directory and be treated like other C files.
diff --git a/libgo/go/cmd/go/internal/load/pkg.go b/libgo/go/cmd/go/internal/load/pkg.go
index d302607..b2a757a 100644
--- a/libgo/go/cmd/go/internal/load/pkg.go
+++ b/libgo/go/cmd/go/internal/load/pkg.go
@@ -223,9 +223,6 @@ func (p *Package) copyBuild(pp *build.Package) {
 	// TODO? Target
 	p.Goroot = pp.Goroot
 	p.Standard = p.Goroot && p.ImportPath != "" && isStandardImportPath(p.ImportPath)
-	if cfg.BuildToolchainName == "gccgo" {
-		p.Standard = stdpkg[p.ImportPath]
-	}
 	p.GoFiles = pp.GoFiles
 	p.CgoFiles = pp.CgoFiles
 	p.IgnoredGoFiles = pp.IgnoredGoFiles
@@ -894,13 +891,6 @@ var foldPath = make(map[string]string)
 func (p *Package) load(stk *ImportStack, bp *build.Package, err error) {
 	p.copyBuild(bp)
 
-	// When using gccgo the go/build package will not be able to
-	// find a standard package. It would be nicer to not get that
-	// error, but go/build doesn't know stdpkg.
-	if cfg.BuildToolchainName == "gccgo" && err != nil && p.Standard {
-		err = nil
-	}
-
 	// Decide whether p was listed on the command line.
 	// Given that load is called while processing the command line,
 	// you might think we could simply pass a flag down into load
@@ -1096,9 +1086,6 @@ func (p *Package) load(stk *ImportStack, bp *build.Package, err error) {
 			continue
 		}
 		p1 := LoadImport(path, p.Dir, p, stk, p.Internal.Build.ImportPos[path], UseVendor)
-		if cfg.BuildToolchainName == "gccgo" && p1.Standard {
-			continue
-		}
 		if p.Standard && p.Error == nil && !p1.Standard && p1.Error == nil {
 			p.Error = &PackageError{
 				ImportStack: stk.Copy(),
@@ -1610,9 +1597,6 @@ func GetTestPackagesFor(p *Package, forceTest bool) (ptest, pxtest *Package, err
 	rawTestImports := str.StringList(p.TestImports)
 	for i, path := range p.TestImports {
 		p1 := LoadImport(path, p.Dir, p, &stk, p.Internal.Build.TestImportPos[path], UseVendor)
-		if cfg.BuildToolchainName == "gccgo" && p1.Standard {
-			continue
-		}
 		if p1.Error != nil {
 			return nil, nil, p1.Error
 		}
@@ -1641,9 +1625,6 @@ func GetTestPackagesFor(p *Package, forceTest bool) (ptest, pxtest *Package, err
 	rawXTestImports := str.StringList(p.XTestImports)
 	for i, path := range p.XTestImports {
 		p1 := LoadImport(path, p.Dir, p, &stk, p.Internal.Build.XTestImportPos[path], UseVendor)
-		if cfg.BuildToolchainName == "gccgo" && p1.Standard {
-			continue
-		}
 		if p1.Error != nil {
 			return nil, nil, p1.Error
 		}
diff --git a/libgo/go/cmd/go/internal/test/test.go b/libgo/go/cmd/go/internal/test/test.go
index 9785470..dbf6eea 100644
--- a/libgo/go/cmd/go/internal/test/test.go
+++ b/libgo/go/cmd/go/internal/test/test.go
@@ -633,6 +633,8 @@ func runTest(cmd *base.Command, args []string) {
 		a := &work.Action{Mode: "go test -i"}
 		for _, p := range load.PackagesForBuild(all) {
 			if cfg.BuildToolchainName == "gccgo" && p.Standard {
+				// gccgo's standard library packages
+				// can not be reinstalled.
 				continue
 			}
 			a.Deps = append(a.Deps, b.CompileAction(work.ModeInstall, work.ModeInstall, p))
@@ -862,9 +864,6 @@ func builderTest(b *work.Builder, p *load.Package) (buildAction, runAction, prin
 			pmain.Internal.Imports = append(pmain.Internal.Imports, ptest)
 		} else {
 			p1 := load.LoadImport(dep, "", nil, &stk, nil, 0)
-			if cfg.BuildToolchainName == "gccgo" && p1.Standard {
-				continue
-			}
 			if p1.Error != nil {
 				return nil, nil, nil, p1.Error
 			}
diff --git a/libgo/go/cmd/go/internal/work/buildid.go b/libgo/go/cmd/go/internal/work/buildid.go
index 2636128..6150bbb 100644
--- a/libgo/go/cmd/go/internal/work/buildid.go
+++ b/libgo/go/cmd/go/internal/work/buildid.go
@@ -234,18 +234,9 @@ func (b *Builder) gccgoToolID(name, language string) (string, error) {
 	// compile an empty file on standard input.
 	cmdline := str.StringList(cfg.BuildToolexec, name, "-###", "-x", language, "-c", "-")
 	cmd := exec.Command(cmdline[0], cmdline[1:]...)
-
-	// Strip any LANG or LC_ environment variables, and force
-	// LANG=C, so that we get the untranslated output.
-	var env []string
-	for _, e := range os.Environ() {
-		if !strings.HasPrefix(e, "LANG=") && !strings.HasPrefix(e, "LC_") {
-			env = append(env, e)
-		}
-	}
-	env = append(env, "LANG=C")
-
-	cmd.Env = base.EnvForDir(cmd.Dir, env)
+	cmd.Env = base.EnvForDir(cmd.Dir, os.Environ())
+	// Force untranslated output so that we see the string "version".
+	cmd.Env = append(cmd.Env, "LC_ALL=C")
 	out, err := cmd.CombinedOutput()
 	if err != nil {
 		return "", fmt.Errorf("%s: %v; output: %q", name, err, out)
diff --git a/libgo/go/cmd/go/internal/work/exec.go b/libgo/go/cmd/go/internal/work/exec.go
index 40d4602..85bdff8 100644
--- a/libgo/go/cmd/go/internal/work/exec.go
+++ b/libgo/go/cmd/go/internal/work/exec.go
@@ -1545,6 +1545,8 @@ func joinUnambiguously(a []string) string {
 			buf.WriteByte(' ')
 		}
 		q := strconv.Quote(s)
+		// A gccgo command line can contain -( and -).
+		// Make sure we quote them since they are special to the shell.
 		if s == "" || strings.ContainsAny(s, " ()") || len(q) > len(s)+2 {
 			buf.WriteString(q)
 		} else {
@@ -1585,13 +1587,17 @@ func (b *Builder) Mkdir(dir string) error {
 
 // symlink creates a symlink newname -> oldname.
 func (b *Builder) Symlink(oldname, newname string) error {
+	// It's not an error to try to recreate an existing symlink.
+	if link, err := os.Readlink(newname); err == nil && link == oldname {
+		return nil
+	}
+
 	if cfg.BuildN || cfg.BuildX {
-		b.Showcmd("", "ln -sf %s %s", oldname, newname)
+		b.Showcmd("", "ln -s %s %s", oldname, newname)
 		if cfg.BuildN {
 			return nil
 		}
 	}
-	os.Remove(newname)
 	return os.Symlink(oldname, newname)
 }
 
diff --git a/libgo/go/go/build/build.go b/libgo/go/go/build/build.go
index 4e77955..9df4930 100644
--- a/libgo/go/go/build/build.go
+++ b/libgo/go/go/build/build.go
@@ -238,7 +238,7 @@ func (ctxt *Context) gopath() []string {
 // that do not exist.
 func (ctxt *Context) SrcDirs() []string {
 	var all []string
-	if ctxt.GOROOT != "" {
+	if ctxt.GOROOT != "" && ctxt.Compiler != "gccgo" {
 		dir := ctxt.joinPath(ctxt.GOROOT, "src")
 		if ctxt.isDir(dir) {
 			all = append(all, dir)
@@ -540,7 +540,7 @@ func (ctxt *Context) Import(path string, srcDir string, mode ImportMode) (*Packa
 		inTestdata := func(sub string) bool {
 			return strings.Contains(sub, "/testdata/") || strings.HasSuffix(sub, "/testdata") || strings.HasPrefix(sub, "testdata/") || sub == "testdata"
 		}
-		if ctxt.GOROOT != "" {
+		if ctxt.GOROOT != "" && ctxt.Compiler != "gccgo" {
 			root := ctxt.joinPath(ctxt.GOROOT, "src")
 			if sub, ok := ctxt.hasSubdir(root, p.Dir); ok && !inTestdata(sub) {
 				p.Goroot = true
@@ -557,7 +557,7 @@ func (ctxt *Context) Import(path string, srcDir string, mode ImportMode) (*Packa
 				// We found a potential import path for dir,
 				// but check that using it wouldn't find something
 				// else first.
-				if ctxt.GOROOT != "" {
+				if ctxt.GOROOT != "" && ctxt.Compiler != "gccgo" {
 					if dir := ctxt.joinPath(ctxt.GOROOT, "src", sub); ctxt.isDir(dir) {
 						p.ConflictDir = dir
 						goto Found
@@ -622,7 +622,7 @@ func (ctxt *Context) Import(path string, srcDir string, mode ImportMode) (*Packa
 				}
 				return false
 			}
-			if searchVendor(ctxt.GOROOT, true) {
+			if ctxt.Compiler != "gccgo" && searchVendor(ctxt.GOROOT, true) {
 				goto Found
 			}
 			for _, root := range gopath {
@@ -635,16 +635,24 @@ func (ctxt *Context) Import(path string, srcDir string, mode ImportMode) (*Packa
 		// Determine directory from import path.
 		if ctxt.GOROOT != "" {
 			dir := ctxt.joinPath(ctxt.GOROOT, "src", path)
-			isDir := ctxt.isDir(dir)
-			binaryOnly = !isDir && mode&AllowBinary != 0 && pkga != "" && ctxt.isFile(ctxt.joinPath(ctxt.GOROOT, pkga))
-			if isDir || binaryOnly {
-				p.Dir = dir
-				p.Goroot = true
-				p.Root = ctxt.GOROOT
-				goto Found
+			if ctxt.Compiler != "gccgo" {
+				isDir := ctxt.isDir(dir)
+				binaryOnly = !isDir && mode&AllowBinary != 0 && pkga != "" && ctxt.isFile(ctxt.joinPath(ctxt.GOROOT, pkga))
+				if isDir || binaryOnly {
+					p.Dir = dir
+					p.Goroot = true
+					p.Root = ctxt.GOROOT
+					goto Found
+				}
 			}
 			tried.goroot = dir
 		}
+		if ctxt.Compiler == "gccgo" && isStandardPackage(path) {
+			p.Dir = ctxt.joinPath(ctxt.GOROOT, "src", path)
+			p.Goroot = true
+			p.Root = ctxt.GOROOT
+			goto Found
+		}
 		for _, root := range gopath {
 			dir := ctxt.joinPath(root, "src", path)
 			isDir := ctxt.isDir(dir)
@@ -708,6 +716,11 @@ Found:
 		return p, pkgerr
 	}
 
+	if ctxt.Compiler == "gccgo" && p.Goroot {
+		// gccgo has no sources for GOROOT packages.
+		return p, nil
+	}
+
 	dirs, err := ctxt.readDir(p.Dir)
 	if err != nil {
 		return p, err
diff --git a/libgo/go/go/build/gc.go b/libgo/go/go/build/gc.go
index 3025cd5..e2be2cb 100644
--- a/libgo/go/go/build/gc.go
+++ b/libgo/go/go/build/gc.go
@@ -7,11 +7,131 @@
 package build
 
 import (
+	"os"
+	"os/exec"
 	"path/filepath"
 	"runtime"
+	"strings"
+	"sync"
 )
 
 // getToolDir returns the default value of ToolDir.
 func getToolDir() string {
 	return filepath.Join(runtime.GOROOT(), "pkg/tool/"+runtime.GOOS+"_"+runtime.GOARCH)
 }
+
+// isStandardPackage is not used for the gc toolchain.
+// However, this function may be called when using `go build -compiler=gccgo`.
+func isStandardPackage(path string) bool {
+	return gccgoSearch.isStandard(path)
+}
+
+// gccgoSearch holds the gccgo search directories.
+type gccgoDirs struct {
+	once sync.Once
+	dirs []string
+}
+
+// gccgoSearch is used to check whether a gccgo package exists in the
+// standard library.
+var gccgoSearch gccgoDirs
+
+// init finds the gccgo search directories. If this fails it leaves dirs == nil.
+func (gd *gccgoDirs) init() {
+	gccgo := os.Getenv("GCCGO")
+	if gccgo == "" {
+		gccgo = "gccgo"
+	}
+	bin, err := exec.LookPath(gccgo)
+	if err != nil {
+		return
+	}
+
+	allDirs, err := exec.Command(bin, "-print-search-dirs").Output()
+	if err != nil {
+		return
+	}
+	versionB, err := exec.Command(bin, "-dumpversion").Output()
+	if err != nil {
+		return
+	}
+	version := strings.TrimSpace(string(versionB))
+	machineB, err := exec.Command(bin, "-dumpmachine").Output()
+	if err != nil {
+		return
+	}
+	machine := strings.TrimSpace(string(machineB))
+
+	dirsEntries := strings.Split(string(allDirs), "\n")
+	const prefix = "libraries: ="
+	var dirs []string
+	for _, dirEntry := range dirsEntries {
+		if strings.HasPrefix(dirEntry, prefix) {
+			dirs = filepath.SplitList(strings.TrimPrefix(dirEntry, prefix))
+			break
+		}
+	}
+	if len(dirs) == 0 {
+		return
+	}
+
+	var lastDirs []string
+	for _, dir := range dirs {
+		goDir := filepath.Join(dir, "go", version)
+		if fi, err := os.Stat(goDir); err == nil && fi.IsDir() {
+			gd.dirs = append(gd.dirs, goDir)
+			goDir = filepath.Join(goDir, machine)
+			if fi, err = os.Stat(goDir); err == nil && fi.IsDir() {
+				gd.dirs = append(gd.dirs, goDir)
+			}
+		}
+		if fi, err := os.Stat(dir); err == nil && fi.IsDir() {
+			lastDirs = append(lastDirs, dir)
+		}
+	}
+	gd.dirs = append(gd.dirs, lastDirs...)
+}
+
+// isStandard returns whether path is a standard library for gccgo.
+func (gd *gccgoDirs) isStandard(path string) bool {
+	// Quick check: if the first path component has a '.', it's not
+	// in the standard library. This skips most GOPATH directories.
+	i := strings.Index(path, "/")
+	if i < 0 {
+		i = len(path)
+	}
+	if strings.Contains(path[:i], ".") {
+		return false
+	}
+
+	if path == "unsafe" {
+		// Special case.
+		return true
+	}
+
+	gd.once.Do(gd.init)
+	if gd.dirs == nil {
+		// We couldn't find the gccgo search directories.
+		// Best guess, since the first component did not contain
+		// '.', is that this is a standard library package.
+		return true
+	}
+
+	for _, dir := range gd.dirs {
+		full := filepath.Join(dir, path)
+		pkgdir, pkg := filepath.Split(full)
+		for _, p := range [...]string{
+			full,
+			full + ".gox",
+			pkgdir + "lib" + pkg + ".so",
+			pkgdir + "lib" + pkg + ".a",
+			full + ".o",
+		} {
+			if fi, err := os.Stat(p); err == nil && !fi.IsDir() {
+				return true
+			}
+		}
+	}
+
+	return false
+}
diff --git a/libgo/go/go/build/gccgo.go b/libgo/go/go/build/gccgo.go
index c6aac9a..59e089d 100644
--- a/libgo/go/go/build/gccgo.go
+++ b/libgo/go/go/build/gccgo.go
@@ -12,3 +12,9 @@ import "runtime"
 func getToolDir() string {
 	return envOr("GCCGOTOOLDIR", runtime.GCCGOTOOLDIR)
 }
+
+// isStandardPackage returns whether path names a standard library package.
+// This uses a list generated at build time.
+func isStandardPackage(path string) bool {
+	return stdpkg[path]
+}