x/tools/cmd/callgraph: add -ptalog flag

Since this tool is a handy way to run the pointer analysis during debugging.

Change-Id: If9a62f71dd8651ad6c782ead85bb84f09c703cba
Reviewed-on: https://go-review.googlesource.com/17382
Reviewed-by: Robert Griesemer <gri@golang.org>

cmd/callgraph/main.go

@@ -20,12 +20,14 @@ package main // import "golang.org/x/tools/cmd/callgraph"
 //     callee file/line/col
 
 import (
+	"bufio"
 	"bytes"
 	"flag"
 	"fmt"
 	"go/build"
 	"go/token"
 	"io"
+	"log"
 	"os"
 	"runtime"
 	"text/template"
@@ -41,15 +43,21 @@ import (
 	"golang.org/x/tools/go/ssa/ssautil"
 )
 
-var algoFlag = flag.String("algo", "rta",
+// flags
-	`Call graph construction algorithm (static, cha, rta, pta)`)
+var (
+	algoFlag = flag.String("algo", "rta",
+		`Call graph construction algorithm (static, cha, rta, pta)`)
 
-var testFlag = flag.Bool("test", false,
+	testFlag = flag.Bool("test", false,
-	"Loads test code (*_test.go) for imported packages")
+		"Loads test code (*_test.go) for imported packages")
 
-var formatFlag = flag.String("format",
+	formatFlag = flag.String("format",
-	"{{.Caller}}\t--{{.Dynamic}}-{{.Line}}:{{.Column}}-->\t{{.Callee}}",
+		"{{.Caller}}\t--{{.Dynamic}}-{{.Line}}:{{.Column}}-->\t{{.Callee}}",
-	"A template expression specifying how to format an edge")
+		"A template expression specifying how to format an edge")
+
+	ptalogFlag = flag.String("ptalog", "",
+		"Location of the points-to analysis log file, or empty to disable logging.")
+)
 
 func init() {
 	flag.Var((*buildutil.TagsFlag)(&build.Default.BuildTags), "tags", buildutil.TagsFlagDoc)
@@ -194,6 +202,25 @@ func doCallgraph(ctxt *build.Context, algo, format string, tests bool, args []st
 		cg = cha.CallGraph(prog)
 
 	case "pta":
+		// Set up points-to analysis log file.
+		var ptalog io.Writer
+		if *ptalogFlag != "" {
+			if f, err := os.Create(*ptalogFlag); err != nil {
+				log.Fatalf("Failed to create PTA log file: %s", err)
+			} else {
+				buf := bufio.NewWriter(f)
+				ptalog = buf
+				defer func() {
+					if err := buf.Flush(); err != nil {
+						log.Printf("flush: %s", err)
+					}
+					if err := f.Close(); err != nil {
+						log.Printf("close: %s", err)
+					}
+				}()
+			}
+		}
+
 		main, err := mainPackage(prog, tests)
 		if err != nil {
 			return err
@@ -201,6 +228,7 @@ func doCallgraph(ctxt *build.Context, algo, format string, tests bool, args []st
 		config := &pointer.Config{
 			Mains:          []*ssa.Package{main},
 			BuildCallGraph: true,
+			Log:            ptalog,
 		}
 		ptares, err := pointer.Analyze(config)
 		if err != nil {