Tune fast-exit for signal activation for QML.

When using QML, it quite often happens that only the QML engine is
connected to a signal, and no C++ handlers. By splitting up the
fast-exit case and handling QML separately, we can prevent a call to
QThread::currentThreadId, and locking+unlocking the mutex.

On x86 this saves ~130 instructions according to valgrind.

Change-Id: I947fe42afe351922339ac982a6d498bc2f7b5192
Reviewed-by: Simon Hausmann <simon.hausmann@theqtcompany.com>
Reviewed-by: Olivier Goffart (Woboq GmbH) <ogoffart@woboq.com>

2 files changed, 20 insertions, 11 deletions

diff --git a/src/corelib/kernel/qobject.cpp b/src/corelib/kernel/qobject.cpp
index 2b0eff3708..04ec713522 100644
--- a/src/corelib/kernel/qobject.cpp
+++ b/src/corelib/kernel/qobject.cpp
@@ -3609,18 +3609,21 @@ void QMetaObject::activate(QObject *sender, int signalOffset, int local_signal_i
 {
     int signal_index = signalOffset + local_signal_index;
 
-    if (!sender->d_func()->isSignalConnected(signal_index)
-        && !qt_signal_spy_callback_set.signal_begin_callback
-        && !qt_signal_spy_callback_set.signal_end_callback) {
-        return; // nothing connected to these signals, and no spy
-    }
-
     if (sender->d_func()->blockSig)
         return;
 
-    if (sender->d_func()->declarativeData && QAbstractDeclarativeData::signalEmitted)
+    if (sender->d_func()->isDeclarativeSignalConnected(signal_index)
+            && QAbstractDeclarativeData::signalEmitted) {
         QAbstractDeclarativeData::signalEmitted(sender->d_func()->declarativeData, sender,
                                                 signal_index, argv);
+    }
+
+    if (!sender->d_func()->isSignalConnected(signal_index, /*checkDeclarative =*/ false)
+        && !qt_signal_spy_callback_set.signal_begin_callback
+        && !qt_signal_spy_callback_set.signal_end_callback) {
+        // The possible declarative connection is done, and nothing else is connected, so:
+        return;
+    }
 
     void *empty_argv[] = { 0 };
     if (qt_signal_spy_callback_set.signal_begin_callback != 0) {
diff --git a/src/corelib/kernel/qobject_p.h b/src/corelib/kernel/qobject_p.h
index e6ab75f104..4383ece245 100644
--- a/src/corelib/kernel/qobject_p.h
+++ b/src/corelib/kernel/qobject_p.h
@@ -199,7 +199,8 @@ public:
     }
 
     int signalIndex(const char *signalName, const QMetaObject **meta = 0) const;
-    inline bool isSignalConnected(uint signalIdx) const;
+    inline bool isSignalConnected(uint signalIdx, bool checkDeclarative = true) const;
+    inline bool isDeclarativeSignalConnected(uint signalIdx) const;
 
     // To allow abitrary objects to call connectNotify()/disconnectNotify() without making
     // the API public in QObject. This is used by QQmlNotifierEndpoint.
@@ -250,12 +251,17 @@ public:
 
   \a signal_index must be the index returned by QObjectPrivate::signalIndex;
 */
-inline bool QObjectPrivate::isSignalConnected(uint signal_index) const
+inline bool QObjectPrivate::isSignalConnected(uint signal_index, bool checkDeclarative) const
 {
     return signal_index >= sizeof(connectedSignals) * 8
         || (connectedSignals[signal_index >> 5] & (1 << (signal_index & 0x1f))
-        || (declarativeData && QAbstractDeclarativeData::isSignalConnected
-            && QAbstractDeclarativeData::isSignalConnected(declarativeData, q_func(), signal_index)));
+        || (checkDeclarative && isDeclarativeSignalConnected(signal_index)));
+}
+
+inline bool QObjectPrivate::isDeclarativeSignalConnected(uint signal_index) const
+{
+    return declarativeData && QAbstractDeclarativeData::isSignalConnected
+            && QAbstractDeclarativeData::isSignalConnected(declarativeData, q_func(), signal_index);
 }
 
 inline QObjectPrivate::Sender *QObjectPrivate::setCurrentSender(QObject *receiver,