go/ssa: make *BuilderMode satisfy flag.Value

The BuilderModeFlag function does not work with flag packages (such as
Google's) that define their own FlagSet.  This change exposes a type
that satisifies flag.Value insted of a function.  That type
is *BuilderMode; there's no need for a separate wrapper type.

Change-Id: I8095b80de499e3c52a29a5c1996d1b1fe3799358
Reviewed-on: https://go-review.googlesource.com/20330
Reviewed-by: Michael Matloob <matloob@golang.org>

cmd/ssadump/main.go

@@ -23,8 +23,9 @@ import (
 	"golang.org/x/tools/go/ssa/ssautil"
 )
 
+// flags
 var (
-	modeFlag = ssa.BuilderModeFlag(flag.CommandLine, "build", 0)
+	mode = ssa.BuilderMode(0)
 
 	testFlag = flag.Bool("test", false, "Loads test code (*_test.go) for imported packages.")
 
@@ -35,8 +36,15 @@ The value is a sequence of zero or more more of these letters:
 R	disable [R]ecover() from panic; show interpreter crash instead.
 T	[T]race execution of the program.  Best for single-threaded programs!
 `)
+
+	cpuprofile = flag.String("cpuprofile", "", "write cpu profile to file")
 )
 
+func init() {
+	flag.Var(&mode, "build", ssa.BuilderModeDoc)
+	flag.Var((*buildutil.TagsFlag)(&build.Default.BuildTags), "tags", buildutil.TagsFlagDoc)
+}
+
 const usage = `SSA builder and interpreter.
 Usage: ssadump [<flag> ...] <args> ...
 Use -help flag to display options.
@@ -53,22 +61,6 @@ if clear, it runs the first package named main.
 if set, it runs the tests of each package.
 `
 
-var cpuprofile = flag.String("cpuprofile", "", "write cpu profile to file")
-
-func init() {
-	flag.Var((*buildutil.TagsFlag)(&build.Default.BuildTags), "tags", buildutil.TagsFlagDoc)
-
-	// If $GOMAXPROCS isn't set, use the full capacity of the machine.
-	// For small machines, use at least 4 threads.
-	if os.Getenv("GOMAXPROCS") == "" {
-		n := runtime.NumCPU()
-		if n < 4 {
-			n = 4
-		}
-		runtime.GOMAXPROCS(n)
-	}
-}
-
 func main() {
 	if err := doMain(); err != nil {
 		fmt.Fprintf(os.Stderr, "ssadump: %s\n", err)
@@ -139,7 +131,7 @@ func doMain() error {
 	}
 
 	// Create and build SSA-form program representation.
-	prog := ssautil.CreateProgram(iprog, *modeFlag)
+	prog := ssautil.CreateProgram(iprog, mode)
 
 	// Build and display only the initial packages
 	// (and synthetic wrappers), unless -run is specified.

go/ssa/mode.go

@@ -8,11 +8,16 @@ package ssa
 
 import (
 	"bytes"
-	"flag"
 	"fmt"
 )
 
 // BuilderMode is a bitmask of options for diagnostics and checking.
+//
+// *BuilderMode satisfies the flag.Value interface.  Example:
+//
+// 	var mode = ssa.BuilderMode(0)
+// 	func init() { flag.Var(&mode, "build", ssa.BuilderModeDoc) }
+//
 type BuilderMode uint
 
 const (
@@ -26,7 +31,7 @@ const (
 	BareInits                                    // Build init functions without guards or calls to dependent inits
 )
 
-const modeFlagUsage = `Options controlling the SSA builder.
+const BuilderModeDoc = `Options controlling the SSA builder.
 The value is a sequence of zero or more of these letters:
 C	perform sanity [C]hecking of the SSA form.
 D	include [D]ebug info for every function.
@@ -38,20 +43,34 @@ N	build [N]aive SSA form: don't replace local loads/stores with registers.
 I	build bare [I]nit functions: no init guards or calls to dependent inits.
 `
 
-// BuilderModeFlag creates a new command line flag of type BuilderMode,
+func (m BuilderMode) String() string {
-// adds it to the specified flag set, and returns it.
+	var buf bytes.Buffer
-//
+	if m&GlobalDebug != 0 {
-// Example:
+		buf.WriteByte('D')
-// 	var ssabuild = BuilderModeFlag(flag.CommandLine, "ssabuild", 0)
+	}
-//
+	if m&PrintPackages != 0 {
-func BuilderModeFlag(set *flag.FlagSet, name string, value BuilderMode) *BuilderMode {
+		buf.WriteByte('P')
-	set.Var((*builderModeValue)(&value), name, modeFlagUsage)
+	}
-	return &value
+	if m&PrintFunctions != 0 {
+		buf.WriteByte('F')
+	}
+	if m&LogSource != 0 {
+		buf.WriteByte('S')
+	}
+	if m&SanityCheckFunctions != 0 {
+		buf.WriteByte('C')
+	}
+	if m&NaiveForm != 0 {
+		buf.WriteByte('N')
+	}
+	if m&BuildSerially != 0 {
+		buf.WriteByte('L')
+	}
+	return buf.String()
 }
 
-type builderModeValue BuilderMode // satisfies flag.Value and flag.Getter.
+// Set parses the flag characters in s and updates *m.
-
+func (m *BuilderMode) Set(s string) error {
-func (v *builderModeValue) Set(s string) error {
 	var mode BuilderMode
 	for _, c := range s {
 		switch c {
@@ -73,35 +92,9 @@ func (v *builderModeValue) Set(s string) error {
 			return fmt.Errorf("unknown BuilderMode option: %q", c)
 		}
 	}
-	*v = builderModeValue(mode)
+	*m = mode
 	return nil
 }
 
-func (v *builderModeValue) Get() interface{} { return BuilderMode(*v) }
+// Get returns m.
-
+func (m BuilderMode) Get() interface{} { return m }
-func (v *builderModeValue) String() string {
-	mode := BuilderMode(*v)
-	var buf bytes.Buffer
-	if mode&GlobalDebug != 0 {
-		buf.WriteByte('D')
-	}
-	if mode&PrintPackages != 0 {
-		buf.WriteByte('P')
-	}
-	if mode&PrintFunctions != 0 {
-		buf.WriteByte('F')
-	}
-	if mode&LogSource != 0 {
-		buf.WriteByte('S')
-	}
-	if mode&SanityCheckFunctions != 0 {
-		buf.WriteByte('C')
-	}
-	if mode&NaiveForm != 0 {
-		buf.WriteByte('N')
-	}
-	if mode&BuildSerially != 0 {
-		buf.WriteByte('L')
-	}
-	return buf.String()
-}