cmd/internal/gc: accept comma-separated list of name=value for -d

This should obviously have no performance impact.
Listing numbers just as a sanity check for the benchmark
comparison program: it should (and does) find nothing
to report.

name                                       old                     new          delta
BenchmarkBinaryTree17              18.0s × (0.99,1.01)     17.9s × (0.99,1.00)  ~
BenchmarkFannkuch11                4.36s × (1.00,1.00)     4.35s × (1.00,1.00)  ~
BenchmarkFmtFprintfEmpty           120ns × (0.99,1.06)     120ns × (0.94,1.05)  ~
BenchmarkFmtFprintfString          480ns × (0.99,1.01)     477ns × (1.00,1.00)  ~
BenchmarkFmtFprintfInt             451ns × (0.99,1.01)     450ns × (0.99,1.01)  ~
BenchmarkFmtFprintfIntInt          766ns × (0.99,1.01)     765ns × (0.99,1.01)  ~
BenchmarkFmtFprintfPrefixedInt     569ns × (0.99,1.01)     569ns × (0.99,1.01)  ~
BenchmarkFmtFprintfFloat           728ns × (1.00,1.01)     728ns × (1.00,1.00)  ~
BenchmarkFmtManyArgs              2.81µs × (1.00,1.01)    2.82µs × (0.99,1.01)  ~
BenchmarkGobDecode                39.4ms × (0.99,1.01)    39.1ms × (0.99,1.01)  ~
BenchmarkGobEncode                39.4ms × (0.99,1.00)    39.4ms × (0.99,1.01)  ~
BenchmarkGzip                      660ms × (1.00,1.01)     661ms × (0.99,1.01)  ~
BenchmarkGunzip                    143ms × (1.00,1.00)     143ms × (1.00,1.00)  ~
BenchmarkHTTPClientServer          132µs × (0.99,1.01)     133µs × (0.99,1.01)  ~
BenchmarkJSONEncode               57.1ms × (0.99,1.01)    57.3ms × (0.99,1.04)  ~
BenchmarkJSONDecode                138ms × (1.00,1.01)     139ms × (0.99,1.00)  ~
BenchmarkMandelbrot200            6.02ms × (1.00,1.00)    6.02ms × (1.00,1.00)  ~
BenchmarkGoParse                  9.79ms × (0.92,1.07)    9.72ms × (0.92,1.11)  ~
BenchmarkRegexpMatchEasy0_32       210ns × (1.00,1.01)     209ns × (1.00,1.01)  ~
BenchmarkRegexpMatchEasy0_1K       593ns × (0.99,1.01)     592ns × (0.99,1.00)  ~
BenchmarkRegexpMatchEasy1_32       182ns × (0.99,1.01)     183ns × (0.98,1.01)  ~
BenchmarkRegexpMatchEasy1_1K      1.01µs × (1.00,1.01)    1.01µs × (1.00,1.01)  ~
BenchmarkRegexpMatchMedium_32      331ns × (1.00,1.00)     330ns × (1.00,1.00)  ~
BenchmarkRegexpMatchMedium_1K     92.6µs × (1.00,1.01)    92.4µs × (1.00,1.00)  ~
BenchmarkRegexpMatchHard_32       4.58µs × (0.99,1.05)    4.77µs × (0.95,1.01)  ~
BenchmarkRegexpMatchHard_1K        136µs × (1.00,1.01)     136µs × (1.00,1.00)  ~
BenchmarkRevcomp                   900ms × (0.99,1.06)     906ms × (0.99,1.05)  ~
BenchmarkTemplate                  171ms × (1.00,1.01)     171ms × (0.99,1.01)  ~
BenchmarkTimeParse                 637ns × (1.00,1.00)     638ns × (1.00,1.00)  ~
BenchmarkTimeFormat                742ns × (1.00,1.00)     745ns × (0.99,1.02)  ~

Change-Id: I59ec875715cb176bbffa709546370a6a7fc5a75d
Reviewed-on: https://go-review.googlesource.com/9309Reviewed-by: Austin Clements <austin@google.com>

src/cmd/internal/gc/lex.go

@@ -258,24 +258,29 @@ func Main() {
 
 	// parse -d argument
 	if debugstr != "" {
-		var j int
-		f := strings.Split(debugstr, ",")
-		for i := range f {
-			if f[i] == "" {
+	Split:
+		for _, name := range strings.Split(debugstr, ",") {
+			if name == "" {
 				continue
 			}
-			for j = 0; j < len(debugtab); j++ {
-				if debugtab[j].name == f[i] {
-					if debugtab[j].val != nil {
-						*debugtab[j].val = 1
-					}
-					break
+			val := 1
+			if i := strings.Index(name, "="); i >= 0 {
+				var err error
+				val, err = strconv.Atoi(name[i+1:])
+				if err != nil {
+					log.Fatalf("invalid debug value %v", name)
 				}
+				name = name[:i]
 			}
-
-			if j >= len(debugtab) {
-				log.Fatalf("unknown debug information -d '%s'\n", f[i])
+			for _, t := range debugtab {
+				if t.name == name {
+					if t.val != nil {
+						*t.val = val
+						continue Split
+					}
+				}
 			}
+			log.Fatalf("unknown debug key -d %s\n", name)
 		}
 	}