tal: optimize case where no (non-destructor) notifiers are used.

$ for i in `seq 10`; do ./samba-allocs talloc.dump --tal; done | stats.c --trim-outliers
Before:
Read 25998 nodes
Tal time:                2857988-2981158(2904324)ns
Tal_free time:           2417170-2582088(2470931)ns
Single tal_free time:    1551654-1609583(1575984)ns

After:
Read 25998 nodes
Tal time:                2780974-2901323(2839352)ns
Tal_free time:           2241725-2355309(2285165)ns
Single tal_free time:    1549908-1612485(1566609)ns
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

ccan/tal/tal.c

@@ -70,6 +70,9 @@ static void *(*allocfn)(size_t size) = malloc;
 static void *(*resizefn)(void *, size_t size) = realloc;
 static void (*freefn)(void *) = free;
 static void (*errorfn)(const char *msg) = (void *)abort;
+static bool initialized = false;
+/* Count on non-destrutor notifiers; often stays zero. */
+static size_t notifiers = 0;
 
 static inline void COLD call_error(const char *msg)
 {
@@ -91,8 +94,6 @@ static struct children *ignore_destroying_bit(struct children *parent_child)
 	return (void *)((size_t)parent_child & ~(size_t)1);
 }
 
-static bool initialized = false;
-
 /* This means valgrind can see leaks. */
 static void tal_cleanup(void)
 {
@@ -291,9 +292,10 @@ static struct notifier *add_notifier_property(struct tal_hdr *t,
 	return prop;
 }
 
-static bool del_notifier_property(struct tal_hdr *t,
+static enum tal_notify_type del_notifier_property(struct tal_hdr *t,
 						  void (*fn)(tal_t *,
-					     enum tal_notify_type, void *))
+							     enum tal_notify_type,
+							     void *))
 {
         struct prop_hdr **p;
 
@@ -306,12 +308,13 @@ static bool del_notifier_property(struct tal_hdr *t,
 			continue;
 		n = (struct notifier *)*p;
 		if (n->u.notifyfn == fn) {
+			enum tal_notify_type types = n->types;
 			*p = (*p)->next;
 			freefn(n);
-			return true;
+			return types & ~NOTIFY_IS_DESTRUCTOR;
 		}
         }
-        return false;
+        return 0;
 }
 
 static struct name *add_name_property(struct tal_hdr *t, const char *name)
@@ -405,7 +408,8 @@ void *tal_alloc_(const tal_t *ctx, size_t size, bool clear, const char *label)
 		return NULL;
 	}
 	debug_tal(parent);
-	notify(parent, TAL_NOTIFY_ADD_CHILD, from_tal_hdr(debug_tal(child)));
+	if (notifiers)
+		notify(parent, TAL_NOTIFY_ADD_CHILD, from_tal_hdr(child));
 	return from_tal_hdr(debug_tal(child));
 }
 
@@ -415,6 +419,7 @@ void *tal_free(const tal_t *ctx)
 		struct tal_hdr *t;
 		int saved_errno = errno;
 		t = debug_tal(to_tal_hdr(ctx));
+		if (notifiers)
 			notify(ignore_destroying_bit(t->parent_child)->parent,
 			       TAL_NOTIFY_DEL_CHILD, ctx);
 		list_del(&t->list);
@@ -444,6 +449,7 @@ void *tal_steal_(const tal_t *new_parent, const tal_t *ctx)
 			return NULL;
 		}
 		debug_tal(newpar);
+		if (notifiers)
 			notify(t, TAL_NOTIFY_STEAL, new_parent);
         }
         return (void *)ctx;
@@ -474,8 +480,12 @@ bool tal_add_notifier_(tal_t *ctx, enum tal_notify_type types,
 	if (unlikely(!n))
 		return false;
 
+	if (notifiers)
 		notify(t, TAL_NOTIFY_ADD_NOTIFIER, callback);
+
 	n->types = types;
+	if (types != TAL_NOTIFY_FREE)
+		notifiers++;
 	return true;
 }
 
@@ -483,12 +493,16 @@ bool tal_del_notifier_(tal_t *ctx,
 		       void (*callback)(tal_t *, enum tal_notify_type, void *))
 {
 	struct tal_hdr *t = debug_tal(to_tal_hdr(ctx));
-	bool ret;
+	enum tal_notify_type types;
 
-        ret = del_notifier_property(t, callback);
-	if (ret)
+        types = del_notifier_property(t, callback);
+	if (types) {
 		notify(t, TAL_NOTIFY_DEL_NOTIFIER, callback);
-	return ret;
+		if (types != TAL_NOTIFY_FREE)
+			notifiers--;
+		return true;
+	}
+	return false;
 }
 
 bool tal_del_destructor_(tal_t *ctx, void (*destroy)(void *me))
@@ -522,6 +536,7 @@ bool tal_set_name_(tal_t *ctx, const char *name, bool literal)
 		return false;
 
 	debug_tal(t);
+	if (notifiers)
 		notify(t, TAL_NOTIFY_RENAME, name);
 	return true;
 }
@@ -635,8 +650,10 @@ bool tal_resize_(tal_t **ctxp, size_t size)
 			child->parent = t;
 		}
 		*ctxp = from_tal_hdr(debug_tal(t));
+		if (notifiers)
 			notify(t, TAL_NOTIFY_MOVE, from_tal_hdr(old_t));
 	}
+	if (notifiers)
 		notify(t, TAL_NOTIFY_RESIZE, (void *)size);
 
 	return true;