cmd/compile: add ability to indicate 'concurrentOk' for debug flags

Also removes no-longer-needed "Any" field from compiler's DebugFlags.
Test/use case for this is the fmahash CL.

Change-Id: I214f02c91f30fc2ce53caf75fa5e2b905dd33429
Reviewed-on: https://go-review.googlesource.com/c/go/+/445495
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@google.com>
Reviewed-by: Keith Randall <khr@golang.org>
Run-TryBot: David Chase <drchase@google.com>

src/cmd/compile/internal/base/debug.go

@@ -50,7 +50,7 @@ type DebugFlags struct {
 	InlineHotBudget            int    `help:"inline budget for hot functions"`
 	PGOInline                  int    `help:"debug profile-guided inlining"`
 
-	Any bool // set when any of the debug flags have been set
+	ConcurrentOk bool // true if only concurrentOk flags seen
 }
 
 // DebugSSA is called to set a -d ssa/... option.

src/cmd/compile/internal/base/flag.go

@@ -165,6 +165,7 @@ func ParseFlags() {
 	Flag.Shared = &Ctxt.Flag_shared
 	Flag.WB = true
 
+	Debug.ConcurrentOk = true
 	Debug.InlFuncsWithClosures = 1
 	if buildcfg.Experiment.Unified {
 		Debug.Unified = 1
@@ -373,7 +374,7 @@ func concurrentBackendAllowed() bool {
 	// while writing the object file, and that is non-concurrent.
 	// Adding Debug_vlog, however, causes Debug.S to also print
 	// while flushing the plist, which happens concurrently.
-	if Ctxt.Debugvlog || Debug.Any || Flag.Live > 0 {
+	if Ctxt.Debugvlog || !Debug.ConcurrentOk || Flag.Live > 0 {
 		return false
 	}
 	// TODO: Test and delete this condition.

src/cmd/internal/objabi/flag.go

@@ -203,16 +203,16 @@ func DecodeArg(arg string) string {
 }
 
 type debugField struct {
-	name string
+	name         string
-	help string
+	help         string
-	val  interface{} // *int or *string
+	concurrentOk bool        // true if this field/flag is compatible with concurrent compilation
+	val          interface{} // *int or *string
 }
 
 type DebugFlag struct {
-	tab map[string]debugField
+	tab          map[string]debugField
-	any *bool
+	concurrentOk *bool    // this is non-nil only for compiler's DebugFlags, but only compiler has concurrent:ok fields
-
+	debugSSA     DebugSSA // this is non-nil only for compiler's DebugFlags.
-	debugSSA DebugSSA
 }
 
 // A DebugSSA function is called to set a -d ssa/... option.
@@ -244,12 +244,12 @@ func NewDebugFlag(debug interface{}, debugSSA DebugSSA) *DebugFlag {
 	for i := 0; i < t.NumField(); i++ {
 		f := t.Field(i)
 		ptr := v.Field(i).Addr().Interface()
-		if f.Name == "Any" {
+		if f.Name == "ConcurrentOk" {
 			switch ptr := ptr.(type) {
 			default:
-				panic("debug.Any must have type bool")
+				panic("debug.ConcurrentOk must have type bool")
 			case *bool:
-				flag.any = ptr
+				flag.concurrentOk = ptr
 			}
 			continue
 		}
@@ -258,13 +258,15 @@ func NewDebugFlag(debug interface{}, debugSSA DebugSSA) *DebugFlag {
 		if help == "" {
 			panic(fmt.Sprintf("debug.%s is missing help text", f.Name))
 		}
+		concurrent := f.Tag.Get("concurrent")
+
 		switch ptr.(type) {
 		default:
 			panic(fmt.Sprintf("debug.%s has invalid type %v (must be int or string)", f.Name, f.Type))
 		case *int, *string:
 			// ok
 		}
-		flag.tab[name] = debugField{name, help, ptr}
+		flag.tab[name] = debugField{name, help, concurrent == "ok", ptr}
 	}
 
 	return flag
@@ -274,9 +276,6 @@ func (f *DebugFlag) Set(debugstr string) error {
 	if debugstr == "" {
 		return nil
 	}
-	if f.any != nil {
-		*f.any = true
-	}
 	for _, name := range strings.Split(debugstr, ",") {
 		if name == "" {
 			continue
@@ -332,6 +331,10 @@ func (f *DebugFlag) Set(debugstr string) error {
 			default:
 				panic("bad debugtab type")
 			}
+			// assembler DebugFlags don't have a ConcurrentOk field to reset, so check against that.
+			if !t.concurrentOk && f.concurrentOk != nil {
+				*f.concurrentOk = false
+			}
 		} else if f.debugSSA != nil && strings.HasPrefix(name, "ssa/") {
 			// expect form ssa/phase/flag
 			// e.g. -d=ssa/generic_cse/time
@@ -346,6 +349,11 @@ func (f *DebugFlag) Set(debugstr string) error {
 			if err != "" {
 				log.Fatalf(err)
 			}
+			// Setting this false for -d=ssa/... preserves old behavior
+			// of turning off concurrency for any debug flags.
+			// It's not known for sure if this is necessary, but it is safe.
+			*f.concurrentOk = false
+
 		} else {
 			return fmt.Errorf("unknown debug key %s\n", name)
 		}