cmd/compile/internal/ssa: group dump files alphabetically

Change dump file names to group them alphabetically in directory
listings, in pass run order.

Change-Id: I8070578a5b4a3a7983dcc527ea1cfdb10a6d7d24
Reviewed-on: https://go-review.googlesource.com/83958Reviewed-by: Keith Randall <khr@golang.org>
Run-TryBot: Keith Randall <khr@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

src/cmd/compile/fmt_test.go

@@ -673,6 +673,7 @@ var knownFormats = map[string]string{
 	"int %-12d":                                       "",
 	"int %-6d":                                        "",
 	"int %-8o":                                        "",
+	"int %02d":                                        "",
 	"int %6d":                                         "",
 	"int %c":                                          "",
 	"int %d":                                          "",

src/cmd/compile/internal/ssa/compile.go

@@ -123,7 +123,7 @@ var dumpFileSeq int
 // output.
 func (f *Func) dumpFile(phaseName string) {
 	dumpFileSeq++
-	fname := fmt.Sprintf("%s__%s_%d.dump", phaseName, f.Name, dumpFileSeq)
+	fname := fmt.Sprintf("%s_%02d__%s.dump", f.Name, dumpFileSeq, phaseName)
 	fname = strings.Replace(fname, " ", "_", -1)
 	fname = strings.Replace(fname, "/", "_", -1)
 	fname = strings.Replace(fname, ":", "_", -1)