dashboard/builder: add -gccopts flag; use shallow clones for gccgo

Change-Id: I3a48e2f664996bf99bb8a7f850d876731dd80808
Reviewed-on: https://go-review.googlesource.com/1253
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

builder/env.go

@@ -153,7 +153,32 @@ func (env *gccgoEnv) setup(repo *Repo, workpath, hash string, envv []string) (st
 	if _, err := os.Stat(gccpath); err != nil {
 		if err := timeout(*cmdTimeout, func() error {
 			// pull down a working copy of GCC.
-			return git.Create(gccpath, *gccPath)
+
+			cloneCmd := []string{
+				"clone",
+				// This is just a guess since there are ~6000 commits to
+				// GCC per year. It's likely there will be enough history
+				// to cross-reference the Gofrontend commit against GCC.
+				// The disadvantage would be if the commit being built is more than
+				// a year old; in this case, the user should make a clone that has
+				// the full history.
+				"--depth", "6000",
+				// We only care about the master branch.
+				"--branch", "master", "--single-branch",
+				*gccPath,
+			}
+
+			// Clone Kind			Clone Time(Dry run)	Clone Size
+			// ---------------------------------------------------------------
+			// Full Clone			10 - 15 min		2.2 GiB
+			// Master Branch		2 - 3 min		1.5 GiB
+			// Full Clone(shallow)		1 min			900 MiB
+			// Master Branch(shallow)	40 sec			900 MiB
+			//
+			// The shallow clones have the same size, which is expected,
+			// but the full shallow clone will only have 6000 commits
+			// spread across all branches.  There are ~50 branches.
+			return run(exec.Command("git", cloneCmd...), runEnv(envv), allOutput(os.Stdout), runDir(repo.Path))
 		}); err != nil {
 			return "", err
 		}
@@ -240,7 +265,7 @@ func (env *gccgoEnv) setup(repo *Repo, workpath, hash string, envv []string) (st
 	}
 
 	// build gcc
-	if err := run(exec.Command("make"), runTimeout(*buildTimeout), runEnv(envv), runDir(gccobjdir)); err != nil {
+	if err := run(exec.Command("make", *gccOpts), runTimeout(*buildTimeout), runEnv(envv), runDir(gccobjdir)); err != nil {
 		return "", fmt.Errorf("Failed to build GCC: %s", err)
 	}
 

builder/main.go

@@ -55,6 +55,7 @@ var (
 	buildTool     = flag.String("tool", "go", "Tool to build.")
 	gcPath        = flag.String("gcpath", "code.google.com/p/go", "Path to download gc from")
 	gccPath       = flag.String("gccpath", "https://github.com/mirrors/gcc.git", "Path to download gcc from")
+	gccOpts       = flag.String("gccopts", "", "Command-line options to pass to `make` when building gccgo")
 	benchPath     = flag.String("benchpath", "golang.org/x/benchmarks/bench", "Path to download benchmarks from")
 	failAll       = flag.Bool("fail", false, "fail all builds")
 	parallel      = flag.Bool("parallel", false, "Build multiple targets in parallel")
@@ -429,10 +430,12 @@ func (b *Builder) buildHash(hash string) error {
 		return fmt.Errorf("recordResult: %s", err)
 	}
 
-	// build sub-repositories
-	goRoot := filepath.Join(workpath, *buildTool)
-	goPath := workpath
-	b.buildSubrepos(goRoot, goPath, hash)
+	if *buildTool == "go" {
+		// build sub-repositories
+		goRoot := filepath.Join(workpath, *buildTool)
+		goPath := workpath
+		b.buildSubrepos(goRoot, goPath, hash)
+	}
 
 	return nil
 }