QtWidgets: use Q_UNLIKELY for every qWarning() (2)

If, after checking a condition, we issue a qWarning(),
by definition that check is unlikely to be true.

Tell the compiler so it can move the error handling
code out of the normal code path to increase the
effective icache size.

This change contains the changes to the accessible/,
effects/, kernel/, styles/ and itemviews/ subdirs.

Moved conditional code around where possible so that
we could always use Q_UNLIKELY, instead of having to
revert to Q_LIKELY here and there.

In QWidgetPrivate::setWindowModified_helper(), as a
drive-by, I swapped the evaluation order of an
&&-expression (newly wrapped in Q_UNLIKELY) to be
more readable and more efficient (cheaper check
first) at the same time.

In qDraw* (qdrawutil.cpp), simplified boolean
expressions (sometimes by skipping re-checking
conditions already checked in a previous guard clause).

Change-Id: I58be22be0a33522c2629a66c2f6c795771a99f3f
Reviewed-by: Lars Knoll <lars.knoll@theqtcompany.com>

15 files changed, 73 insertions, 73 deletions

diff --git a/src/widgets/kernel/qaction.cpp b/src/widgets/kernel/qaction.cpp
index 1563d020b6..3306754623 100644
--- a/src/widgets/kernel/qaction.cpp
+++ b/src/widgets/kernel/qaction.cpp
@@ -45,7 +45,7 @@
 #include <private/qmenu_p.h>
 
 #define QAPP_CHECK(functionName) \
-    if (!qApp) { \
+    if (Q_UNLIKELY(!qApp)) { \
         qWarning("QAction: Initialize QApplication before calling '" functionName "'."); \
         return; \
     }
diff --git a/src/widgets/kernel/qapplication.cpp b/src/widgets/kernel/qapplication.cpp
index 70c91b9aa4..e5d8960cf8 100644
--- a/src/widgets/kernel/qapplication.cpp
+++ b/src/widgets/kernel/qapplication.cpp
@@ -1368,7 +1368,7 @@ int QApplication::colorSpec()
 
 void QApplication::setColorSpec(int spec)
 {
-    if (qApp)
+    if (Q_UNLIKELY(qApp))
         qWarning("QApplication::setColorSpec: This function must be "
                  "called before the QApplication object is created");
     QApplicationPrivate::app_cspec = spec;
@@ -2485,7 +2485,7 @@ bool QApplicationPrivate::isBlockedByModal(QWidget *widget)
 bool QApplicationPrivate::isWindowBlocked(QWindow *window, QWindow **blockingWindow) const
 {
     QWindow *unused = 0;
-    if (!window) {
+    if (Q_UNLIKELY(!window)) {
         qWarning().nospace() << "window == 0 passed.";
         return false;
     }
@@ -3007,7 +3007,7 @@ bool QApplication::notify(QObject *receiver, QEvent *e)
     if (QApplicationPrivate::is_app_closing)
         return true;
 
-    if (receiver == 0) {                        // serious error
+    if (Q_UNLIKELY(!receiver)) {                        // serious error
         qWarning("QApplication::notify: Unexpected null receiver");
         return true;
     }
@@ -3256,7 +3256,7 @@ bool QApplication::notify(QObject *receiver, QEvent *e)
                         QObject *obj = d->extraData->eventFilters.at(i);
                         if (!obj)
                             continue;
-                        if (obj->d_func()->threadData != w->d_func()->threadData) {
+                        if (Q_UNLIKELY(obj->d_func()->threadData != w->d_func()->threadData)) {
                             qWarning("QApplication: Object event filter cannot be in a different thread.");
                             continue;
                         }
diff --git a/src/widgets/kernel/qdesktopwidget.cpp b/src/widgets/kernel/qdesktopwidget.cpp
index b88b3cc61d..d82d0691be 100644
--- a/src/widgets/kernel/qdesktopwidget.cpp
+++ b/src/widgets/kernel/qdesktopwidget.cpp
@@ -48,7 +48,7 @@ int QDesktopScreenWidget::screenNumber() const
 
 const QRect QDesktopWidget::screenGeometry(const QWidget *widget) const
 {
-    if (!widget) {
+    if (Q_UNLIKELY(!widget)) {
         qWarning("QDesktopWidget::screenGeometry(): Attempt "
                  "to get the screen geometry of a null widget");
         return QRect();
@@ -61,7 +61,7 @@ const QRect QDesktopWidget::screenGeometry(const QWidget *widget) const
 
 const QRect QDesktopWidget::availableGeometry(const QWidget *widget) const
 {
-    if (!widget) {
+    if (Q_UNLIKELY(!widget)) {
         qWarning("QDesktopWidget::availableGeometry(): Attempt "
                  "to get the available geometry of a null widget");
         return QRect();
diff --git a/src/widgets/kernel/qformlayout.cpp b/src/widgets/kernel/qformlayout.cpp
index a7f9021c42..464d09cde1 100644
--- a/src/widgets/kernel/qformlayout.cpp
+++ b/src/widgets/kernel/qformlayout.cpp
@@ -945,7 +945,7 @@ void QFormLayoutPrivate::setItem(int row, QFormLayout::ItemRole role, QLayoutIte
 {
     const bool fullRow = role == QFormLayout::SpanningRole;
     const int column =  role == QFormLayout::SpanningRole ? 1 : static_cast<int>(role);
-    if (uint(row) >= uint(m_matrix.rowCount()) || uint(column) > 1U) {
+    if (Q_UNLIKELY(uint(row) >= uint(m_matrix.rowCount()) || uint(column) > 1U)) {
         qWarning("QFormLayoutPrivate::setItem: Invalid cell (%d, %d)", row, column);
         return;
     }
@@ -953,7 +953,7 @@ void QFormLayoutPrivate::setItem(int row, QFormLayout::ItemRole role, QLayoutIte
     if (!item)
         return;
 
-    if (m_matrix(row, column)) {
+    if (Q_UNLIKELY(m_matrix(row, column))) {
         qWarning("QFormLayoutPrivate::setItem: Cell (%d, %d) already occupied", row, column);
         return;
     }
@@ -1000,7 +1000,7 @@ QLayoutItem* QFormLayoutPrivate::replaceAt(int index, QLayoutItem *newitem)
     if (!newitem)
         return 0;
     const int storageIndex = storageIndexFromLayoutItem(m_matrix, m_things.value(index));
-    if (storageIndex == -1) {
+    if (Q_UNLIKELY(storageIndex == -1)) {
         // ### Qt6 - fix warning too when this class becomes public
         qWarning("QFormLayoutPrivate::replaceAt: Invalid index %d", index);
         return 0;
@@ -1414,7 +1414,7 @@ QLayoutItem *QFormLayout::takeAt(int index)
     Q_D(QFormLayout);
 
     const int storageIndex = storageIndexFromLayoutItem(d->m_matrix, d->m_things.value(index));
-    if (storageIndex == -1) {
+    if (Q_UNLIKELY(storageIndex == -1)) {
         qWarning("QFormLayout::takeAt: Invalid index %d", index);
         return 0;
     }
diff --git a/src/widgets/kernel/qgesturemanager.cpp b/src/widgets/kernel/qgesturemanager.cpp
index 51cffc6321..2bf5eece64 100644
--- a/src/widgets/kernel/qgesturemanager.cpp
+++ b/src/widgets/kernel/qgesturemanager.cpp
@@ -117,7 +117,7 @@ QGestureManager::~QGestureManager()
 Qt::GestureType QGestureManager::registerGestureRecognizer(QGestureRecognizer *recognizer)
 {
     QGesture *dummy = recognizer->create(0);
-    if (!dummy) {
+    if (Q_UNLIKELY(!dummy)) {
         qWarning("QGestureManager::registerGestureRecognizer: "
                  "the recognizer fails to create a gesture object, skipping registration.");
         return Qt::GestureType(0);
@@ -640,17 +640,17 @@ void QGestureManager::deliverEvents(const QSet<QGesture *> &gestures,
         Q_ASSERT(gestureType != Qt::CustomGesture);
         Q_UNUSED(gestureType);
 
-        if (target) {
+        if (Q_UNLIKELY(!target)) {
+            qCDebug(lcGestureManager) << "QGestureManager::deliverEvent: could not find the target for gesture"
+                    << gesture->gestureType();
+            qWarning("QGestureManager::deliverEvent: could not find the target for gesture");
+            undeliveredGestures->insert(gesture);
+        } else {
             if (gesture->state() == Qt::GestureStarted) {
                 startedGestures.insert(gesture);
             } else {
                 normalStartedGestures[target].append(gesture);
             }
-        } else {
-            qCDebug(lcGestureManager) << "QGestureManager::deliverEvent: could not find the target for gesture"
-                    << gesture->gestureType();
-            qWarning("QGestureManager::deliverEvent: could not find the target for gesture");
-            undeliveredGestures->insert(gesture);
         }
     }
 
diff --git a/src/widgets/kernel/qgridlayout.cpp b/src/widgets/kernel/qgridlayout.cpp
index 85898ae86c..f3272731d9 100644
--- a/src/widgets/kernel/qgridlayout.cpp
+++ b/src/widgets/kernel/qgridlayout.cpp
@@ -557,9 +557,9 @@ void QGridLayoutPrivate::add(QGridBox *box, int row, int col)
 
 void QGridLayoutPrivate::add(QGridBox *box, int row1, int row2, int col1, int col2)
 {
-    if (row2 >= 0 && row2 < row1)
+    if (Q_UNLIKELY(row2 >= 0 && row2 < row1))
         qWarning("QGridLayout: Multi-cell fromRow greater than toRow");
-    if (col2 >= 0 && col2 < col1)
+    if (Q_UNLIKELY(col2 >= 0 && col2 < col1))
         qWarning("QGridLayout: Multi-cell fromCol greater than toCol");
     if (row1 == row2 && col1 == col2) {
         add(box, row1, col1);
@@ -1435,7 +1435,7 @@ void QGridLayout::addWidget(QWidget *widget, int row, int column, Qt::Alignment
     Q_D(QGridLayout);
     if (!d->checkWidget(widget))
         return;
-    if (row < 0 || column < 0) {
+    if (Q_UNLIKELY(row < 0 || column < 0)) {
         qWarning("QGridLayout: Cannot add %s/%s to %s/%s at row %d column %d",
                  widget->metaObject()->className(), widget->objectName().toLocal8Bit().data(),
                  metaObject()->className(), objectName().toLocal8Bit().data(), row, column);
diff --git a/src/widgets/kernel/qlayout.cpp b/src/widgets/kernel/qlayout.cpp
index b6d87dc17e..eec60b14d0 100644
--- a/src/widgets/kernel/qlayout.cpp
+++ b/src/widgets/kernel/qlayout.cpp
@@ -129,7 +129,7 @@ QLayout::QLayout(QLayoutPrivate &dd, QLayout *lay, QWidget *w)
     if (lay) {
         lay->addItem(this);
     } else if (w) {
-        if (w->layout()) {
+        if (Q_UNLIKELY(w->layout())) {
             qWarning("QLayout: Attempting to add QLayout \"%ls\" to %s \"%ls\", which"
                      " already has a layout",
                      qUtf16Printable(QObject::objectName()), w->metaObject()->className(),
@@ -469,7 +469,7 @@ QWidget *QLayout::parentWidget() const
     if (!d->topLevel) {
         if (parent()) {
             QLayout *parentLayout = qobject_cast<QLayout*>(parent());
-            if (!parentLayout) {
+            if (Q_UNLIKELY(!parentLayout)) {
                 qWarning("QLayout::parentWidget: A layout can only have another layout as a parent.");
                 return 0;
             }
@@ -776,7 +776,7 @@ QLayout::~QLayout()
 */
 void QLayout::addChildLayout(QLayout *l)
 {
-    if (l->parent()) {
+    if (Q_UNLIKELY(l->parent())) {
         qWarning("QLayout::addChildLayout: layout \"%ls\" already has a parent",
                  qUtf16Printable(l->objectName()));
         return;
@@ -826,7 +826,7 @@ void QLayoutPrivate::reparentChildWidgets(QWidget *mw)
         if (QWidget *w = item->widget()) {
             QWidget *pw = w->parentWidget();
 #ifdef QT_DEBUG
-            if (pw && pw != mw && layoutDebug()) {
+            if (Q_UNLIKELY(pw && pw != mw && layoutDebug())) {
                 qWarning("QLayout::addChildLayout: widget %s \"%ls\" in wrong parent; moved to correct parent",
                          w->metaObject()->className(), qUtf16Printable(w->objectName()));
             }
@@ -849,12 +849,12 @@ void QLayoutPrivate::reparentChildWidgets(QWidget *mw)
 bool QLayoutPrivate::checkWidget(QWidget *widget) const
 {
     Q_Q(const QLayout);
-    if (!widget) {
+    if (Q_UNLIKELY(!widget)) {
         qWarning("QLayout: Cannot add a null widget to %s/%ls", q->metaObject()->className(),
                   qUtf16Printable(q->objectName()));
         return false;
     }
-    if (widget == q->parentWidget()) {
+    if (Q_UNLIKELY(widget == q->parentWidget())) {
         qWarning("QLayout: Cannot add parent widget %s/%ls to its child layout %s/%ls",
                   widget->metaObject()->className(), qUtf16Printable(widget->objectName()),
                   q->metaObject()->className(), qUtf16Printable(q->objectName()));
@@ -870,12 +870,12 @@ bool QLayoutPrivate::checkWidget(QWidget *widget) const
 bool QLayoutPrivate::checkLayout(QLayout *otherLayout) const
 {
     Q_Q(const QLayout);
-    if (!otherLayout) {
+    if (Q_UNLIKELY(!otherLayout)) {
         qWarning("QLayout: Cannot add a null layout to %s/%ls",
                  q->metaObject()->className(), qUtf16Printable(q->objectName()));
         return false;
     }
-    if (otherLayout == q) {
+    if (Q_UNLIKELY(otherLayout == q)) {
         qWarning("QLayout: Cannot add layout %s/%ls to itself",
                  q->metaObject()->className(), qUtf16Printable(q->objectName()));
         return false;
@@ -902,7 +902,7 @@ void QLayout::addChildWidget(QWidget *w)
         QLayout *l = pw->layout();
         if (l && removeWidgetRecursively(l, w)) {
 #ifdef QT_DEBUG
-            if (layoutDebug())
+            if (Q_UNLIKELY(layoutDebug()))
                 qWarning("QLayout::addChildWidget: %s \"%ls\" is already in a layout; moved to new layout",
                          w->metaObject()->className(), qUtf16Printable(w->objectName()));
 #endif
@@ -910,7 +910,7 @@ void QLayout::addChildWidget(QWidget *w)
     }
     if (pw && mw && pw != mw) {
 #ifdef QT_DEBUG
-            if (layoutDebug())
+            if (Q_UNLIKELY(layoutDebug()))
                 qWarning("QLayout::addChildWidget: %s \"%ls\" in wrong parent; moved to correct parent",
                          w->metaObject()->className(), qUtf16Printable(w->objectName()));
 #endif
@@ -1064,7 +1064,7 @@ bool QLayout::activate()
     if (d->activated)
         return false;
     QWidget *mw = static_cast<QWidget*>(parent());
-    if (mw == 0) {
+    if (Q_UNLIKELY(!mw)) {
         qWarning("QLayout::activate: %s \"%ls\" does not have a main widget",
                  metaObject()->className(), qUtf16Printable(objectName()));
         return false;
diff --git a/src/widgets/kernel/qopenglwidget.cpp b/src/widgets/kernel/qopenglwidget.cpp
index 3a4a3a0d63..1522b065a7 100644
--- a/src/widgets/kernel/qopenglwidget.cpp
+++ b/src/widgets/kernel/qopenglwidget.cpp
@@ -740,7 +740,7 @@ void QOpenGLWidgetPrivate::initialize()
     // texture usable by the underlying window's backingstore.
     QWidget *tlw = q->window();
     QOpenGLContext *shareContext = get(tlw)->shareContext();
-    if (!shareContext) {
+    if (Q_UNLIKELY(!shareContext)) {
         qWarning("QOpenGLWidget: Cannot be used without a context shared with the toplevel.");
         return;
     }
@@ -756,7 +756,7 @@ void QOpenGLWidgetPrivate::initialize()
     ctx->setShareContext(shareContext);
     ctx->setFormat(requestedFormat);
     ctx->setScreen(shareContext->screen());
-    if (!ctx->create()) {
+    if (Q_UNLIKELY(!ctx->create())) {
         qWarning("QOpenGLWidget: Failed to create context");
         return;
     }
@@ -782,7 +782,7 @@ void QOpenGLWidgetPrivate::initialize()
     surface->setScreen(ctx->screen());
     surface->create();
 
-    if (!ctx->makeCurrent(surface)) {
+    if (Q_UNLIKELY(!ctx->makeCurrent(surface))) {
         qWarning("QOpenGLWidget: Failed to make context current");
         return;
     }
@@ -915,10 +915,10 @@ QOpenGLWidget::QOpenGLWidget(QWidget *parent, Qt::WindowFlags f)
     : QWidget(*(new QOpenGLWidgetPrivate), parent, f)
 {
     Q_D(QOpenGLWidget);
-    if (QGuiApplicationPrivate::platformIntegration()->hasCapability(QPlatformIntegration::RasterGLSurface))
-        d->setRenderToTexture();
-    else
+    if (Q_UNLIKELY(!QGuiApplicationPrivate::platformIntegration()->hasCapability(QPlatformIntegration::RasterGLSurface)))
         qWarning("QOpenGLWidget is not supported on this platform.");
+    else
+        d->setRenderToTexture();
 }
 
 /*!
@@ -984,7 +984,7 @@ void QOpenGLWidget::setFormat(const QSurfaceFormat &format)
 {
     Q_UNUSED(format);
     Q_D(QOpenGLWidget);
-    if (d->initialized) {
+    if (Q_UNLIKELY(d->initialized)) {
         qWarning("QOpenGLWidget: Already initialized, setting the format has no effect");
         return;
     }
diff --git a/src/widgets/kernel/qshortcut.cpp b/src/widgets/kernel/qshortcut.cpp
index c08c4eeb32..55b57c5c57 100644
--- a/src/widgets/kernel/qshortcut.cpp
+++ b/src/widgets/kernel/qshortcut.cpp
@@ -49,7 +49,7 @@
 QT_BEGIN_NAMESPACE
 
 #define QAPP_CHECK(functionName) \
-    if (!qApp) { \
+    if (Q_UNLIKELY(!qApp)) {                                            \
         qWarning("QShortcut: Initialize QApplication before calling '" functionName "'."); \
         return; \
     }
@@ -410,7 +410,7 @@ public:
 void QShortcutPrivate::redoGrab(QShortcutMap &map)
 {
     Q_Q(QShortcut);
-    if (!parent) {
+    if (Q_UNLIKELY(!parent)) {
         qWarning("QShortcut: No widget parent defined");
         return;
     }
diff --git a/src/widgets/kernel/qstackedlayout.cpp b/src/widgets/kernel/qstackedlayout.cpp
index 957b6f09b5..b76e92bc35 100644
--- a/src/widgets/kernel/qstackedlayout.cpp
+++ b/src/widgets/kernel/qstackedlayout.cpp
@@ -57,7 +57,7 @@ QLayoutItem* QStackedLayoutPrivate::replaceAt(int idx, QLayoutItem *newitem)
     if (idx < 0 || idx >= list.size() || !newitem)
         return 0;
     QWidget *wdg = newitem->widget();
-    if (!wdg) {
+    if (Q_UNLIKELY(!wdg)) {
         qWarning("QStackedLayout::replaceAt: Only widgets can be added");
         return 0;
     }
@@ -367,7 +367,7 @@ int QStackedLayout::currentIndex() const
 void QStackedLayout::setCurrentWidget(QWidget *widget)
 {
     int index = indexOf(widget);
-    if (index == -1) {
+    if (Q_UNLIKELY(index == -1)) {
         qWarning("QStackedLayout::setCurrentWidget: Widget %p not contained in stack", widget);
         return;
     }
@@ -420,12 +420,12 @@ int QStackedLayout::count() const
 void QStackedLayout::addItem(QLayoutItem *item)
 {
     QWidget *widget = item->widget();
-    if (widget) {
-        addWidget(widget);
-        delete item;
-    } else {
+    if (Q_UNLIKELY(!widget)) {
         qWarning("QStackedLayout::addItem: Only widgets can be added");
+        return;
     }
+    addWidget(widget);
+    delete item;
 }
 
 /*!
diff --git a/src/widgets/kernel/qtooltip.cpp b/src/widgets/kernel/qtooltip.cpp
index 51bf6e4684..39a58d60dc 100644
--- a/src/widgets/kernel/qtooltip.cpp
+++ b/src/widgets/kernel/qtooltip.cpp
@@ -264,12 +264,12 @@ void QTipLabel::hideTipImmediately()
 
 void QTipLabel::setTipRect(QWidget *w, const QRect &r)
 {
-    if (!r.isNull() && !w)
+    if (Q_UNLIKELY(!r.isNull() && !w)) {
         qWarning("QToolTip::setTipRect: Cannot pass null widget if rect is set");
-    else{
-        widget = w;
-        rect = r;
+        return;
     }
+    widget = w;
+    rect = r;
 }
 
 void QTipLabel::timerEvent(QTimerEvent *e)
diff --git a/src/widgets/kernel/qwidget.cpp b/src/widgets/kernel/qwidget.cpp
index 0f580f7369..e8169d0bd1 100644
--- a/src/widgets/kernel/qwidget.cpp
+++ b/src/widgets/kernel/qwidget.cpp
@@ -1528,7 +1528,7 @@ QWidget::~QWidget()
     d->data.in_destructor = true;
 
 #if defined (QT_CHECK_STATE)
-    if (paintingActive())
+    if (Q_UNLIKELY(paintingActive()))
         qWarning("QWidget: %s (%s) deleted while being painted", className(), name());
 #endif
 
@@ -3267,7 +3267,7 @@ void QWidget::addActions(QList<QAction*> actions)
 */
 void QWidget::insertAction(QAction *before, QAction *action)
 {
-    if(!action) {
+    if (Q_UNLIKELY(!action)) {
         qWarning("QWidget::insertAction: Attempt to insert null action");
         return;
     }
@@ -3913,7 +3913,7 @@ bool QWidgetPrivate::setMinimumSize_helper(int &minw, int &minh)
         mw = 0;
     if (mh == QWIDGETSIZE_MAX)
         mh = 0;
-    if (minw > QWIDGETSIZE_MAX || minh > QWIDGETSIZE_MAX) {
+    if (Q_UNLIKELY(minw > QWIDGETSIZE_MAX || minh > QWIDGETSIZE_MAX)) {
         qWarning("QWidget::setMinimumSize: (%s/%s) "
                 "The largest allowed size is (%d,%d)",
                  q->objectName().toLocal8Bit().data(), q->metaObject()->className(), QWIDGETSIZE_MAX,
@@ -3921,7 +3921,7 @@ bool QWidgetPrivate::setMinimumSize_helper(int &minw, int &minh)
         minw = mw = qMin<int>(minw, QWIDGETSIZE_MAX);
         minh = mh = qMin<int>(minh, QWIDGETSIZE_MAX);
     }
-    if (minw < 0 || minh < 0) {
+    if (Q_UNLIKELY(minw < 0 || minh < 0)) {
         qWarning("QWidget::setMinimumSize: (%s/%s) Negative sizes (%d,%d) "
                 "are not possible",
                 q->objectName().toLocal8Bit().data(), q->metaObject()->className(), minw, minh);
@@ -3995,7 +3995,7 @@ void QWidget::setMinimumSize(int minw, int minh)
 bool QWidgetPrivate::setMaximumSize_helper(int &maxw, int &maxh)
 {
     Q_Q(QWidget);
-    if (maxw > QWIDGETSIZE_MAX || maxh > QWIDGETSIZE_MAX) {
+    if (Q_UNLIKELY(maxw > QWIDGETSIZE_MAX || maxh > QWIDGETSIZE_MAX)) {
         qWarning("QWidget::setMaximumSize: (%s/%s) "
                 "The largest allowed size is (%d,%d)",
                  q->objectName().toLocal8Bit().data(), q->metaObject()->className(), QWIDGETSIZE_MAX,
@@ -4003,7 +4003,7 @@ bool QWidgetPrivate::setMaximumSize_helper(int &maxw, int &maxh)
         maxw = qMin<int>(maxw, QWIDGETSIZE_MAX);
         maxh = qMin<int>(maxh, QWIDGETSIZE_MAX);
     }
-    if (maxw < 0 || maxh < 0) {
+    if (Q_UNLIKELY(maxw < 0 || maxh < 0)) {
         qWarning("QWidget::setMaximumSize: (%s/%s) Negative sizes (%d,%d) "
                 "are not possible",
                 q->objectName().toLocal8Bit().data(), q->metaObject()->className(), maxw, maxh);
@@ -5104,12 +5104,12 @@ void QWidget::render(QPaintDevice *target, const QPoint &targetOffset,
 void QWidget::render(QPainter *painter, const QPoint &targetOffset,
                      const QRegion &sourceRegion, RenderFlags renderFlags)
 {
-    if (!painter) {
+    if (Q_UNLIKELY(!painter)) {
         qWarning("QWidget::render: Null pointer to painter");
         return;
     }
 
-    if (!painter->isActive()) {
+    if (Q_UNLIKELY(!painter->isActive())) {
         qWarning("QWidget::render: Cannot render with an inactive painter");
         return;
     }
@@ -5498,7 +5498,7 @@ void QWidgetPrivate::drawWidget(QPaintDevice *pdev, const QRegion &rgn, const QP
     if (!toBePainted.isEmpty()) {
         if (!onScreen || alsoOnScreen) {
             //update the "in paint event" flag
-            if (q->testAttribute(Qt::WA_WState_InPaintEvent))
+            if (Q_UNLIKELY(q->testAttribute(Qt::WA_WState_InPaintEvent)))
                 qWarning("QWidget::repaint: Recursive repaint detected");
             q->setAttribute(Qt::WA_WState_InPaintEvent);
 
@@ -5605,7 +5605,7 @@ void QWidgetPrivate::drawWidget(QPaintDevice *pdev, const QRegion &rgn, const QP
                 setSystemClip(pdev, QRegion());
             }
             q->setAttribute(Qt::WA_WState_InPaintEvent, false);
-            if (q->paintingActive())
+            if (Q_UNLIKELY(q->paintingActive()))
                 qWarning("QWidget::repaint: It is dangerous to leave painters active on a widget outside of the PaintEvent");
 
             if (paintEngine && paintEngine->autoDestruct()) {
@@ -5654,7 +5654,7 @@ void QWidgetPrivate::sendPaintEvent(const QRegion &toBePainted)
 void QWidgetPrivate::render(QPaintDevice *target, const QPoint &targetOffset,
                             const QRegion &sourceRegion, QWidget::RenderFlags renderFlags)
 {
-    if (!target) {
+    if (Q_UNLIKELY(!target)) {
         qWarning("QWidget::render: null pointer to paint device");
         return;
     }
@@ -5788,7 +5788,7 @@ QRectF QWidgetEffectSourcePrivate::boundingRect(Qt::CoordinateSystem system) con
     if (system != Qt::DeviceCoordinates)
         return m_widget->rect();
 
-    if (!context) {
+    if (Q_UNLIKELY(!context)) {
         // Device coordinates without context not yet supported.
         qWarning("QGraphicsEffectSource::boundingRect: Not yet implemented, lacking device context");
         return QRectF();
@@ -5820,7 +5820,7 @@ QPixmap QWidgetEffectSourcePrivate::pixmap(Qt::CoordinateSystem system, QPoint *
                                            QGraphicsEffect::PixmapPadMode mode) const
 {
     const bool deviceCoordinates = (system == Qt::DeviceCoordinates);
-    if (!context && deviceCoordinates) {
+    if (Q_UNLIKELY(!context && deviceCoordinates)) {
         // Device coordinates without context not yet supported.
         qWarning("QGraphicsEffectSource::pixmap: Not yet implemented, lacking device context");
         return QPixmap();
@@ -6353,7 +6353,7 @@ void QWidget::setFocusProxy(QWidget * w)
         return;
 
     for (QWidget* fp  = w; fp; fp = fp->focusProxy()) {
-        if (fp == this) {
+        if (Q_UNLIKELY(fp == this)) {
             qWarning("QWidget: %s (%s) already in focus proxy chain", metaObject()->className(), objectName().toLocal8Bit().constData());
             return;
         }
@@ -6867,7 +6867,7 @@ void QWidget::setTabOrder(QWidget* first, QWidget *second)
     if (!first || !second || first->focusPolicy() == Qt::NoFocus || second->focusPolicy() == Qt::NoFocus)
         return;
 
-    if (first->window() != second->window()) {
+    if (Q_UNLIKELY(first->window() != second->window())) {
         qWarning("QWidget::setTabOrder: 'first' and 'second' must be in the same window");
         return;
     }
@@ -10024,12 +10024,12 @@ QLayout *QWidget::layout() const
 
 void QWidget::setLayout(QLayout *l)
 {
-    if (!l) {
+    if (Q_UNLIKELY(!l)) {
         qWarning("QWidget::setLayout: Cannot set layout to 0");
         return;
     }
     if (layout()) {
-        if (layout() != l)
+        if (Q_UNLIKELY(layout() != l))
             qWarning("QWidget::setLayout: Attempting to set QLayout \"%s\" on %s \"%s\", which already has a"
                      " layout", l->objectName().toLocal8Bit().data(), metaObject()->className(),
                      objectName().toLocal8Bit().data());
@@ -11374,7 +11374,7 @@ void QWidgetPrivate::setWindowModified_helper()
         return;
     bool on = q->testAttribute(Qt::WA_WindowModified);
     if (!platformWindow->setWindowModified(on)) {
-        if (!q->windowTitle().contains(QLatin1String("[*]")) && on)
+        if (Q_UNLIKELY(on && !q->windowTitle().contains(QLatin1String("[*]"))))
             qWarning("QWidget::setWindowModified: The window title does not contain a '[*]' placeholder");
         setWindowTitle_helper(q->windowTitle());
         setWindowIconText_helper(q->windowIconText());
@@ -12124,7 +12124,7 @@ QOpenGLContext *QWidgetPrivate::shareContext() const
 #ifdef QT_NO_OPENGL
     return 0;
 #else
-    if (!extra || !extra->topextra || !extra->topextra->window) {
+    if (Q_UNLIKELY(!extra || !extra->topextra || !extra->topextra->window)) {
         qWarning("Asking for share context for widget that does not have a window handle");
         return 0;
     }
diff --git a/src/widgets/kernel/qwidgetbackingstore.cpp b/src/widgets/kernel/qwidgetbackingstore.cpp
index 55b8513072..90311b0f0a 100644
--- a/src/widgets/kernel/qwidgetbackingstore.cpp
+++ b/src/widgets/kernel/qwidgetbackingstore.cpp
@@ -1554,7 +1554,7 @@ void QWidgetPrivate::repaint_sys(const QRegion &rgn)
         QWidgetBackingStore::unflushPaint(q, toBePainted);
 #endif
 
-    if (q->paintingActive())
+    if (Q_UNLIKELY(q->paintingActive()))
         qWarning("QWidget::repaint: It is dangerous to leave painters active on a widget outside of the PaintEvent");
 }
 
diff --git a/src/widgets/kernel/qwidgetwindow.cpp b/src/widgets/kernel/qwidgetwindow.cpp
index e3c40ef95e..cce667ffbf 100644
--- a/src/widgets/kernel/qwidgetwindow.cpp
+++ b/src/widgets/kernel/qwidgetwindow.cpp
@@ -798,7 +798,7 @@ void QWidgetWindow::handleDragLeaveEvent(QDragLeaveEvent *event)
 
 void QWidgetWindow::handleDropEvent(QDropEvent *event)
 {
-    if (m_dragTarget.isNull()) {
+    if (Q_UNLIKELY(m_dragTarget.isNull())) {
         qWarning() << Q_FUNC_INFO << m_widget << ": No drag target set.";
         event->ignore();
         return;
diff --git a/src/widgets/kernel/qwindowcontainer.cpp b/src/widgets/kernel/qwindowcontainer.cpp
index 3885431b05..98a3330822 100644
--- a/src/widgets/kernel/qwindowcontainer.cpp
+++ b/src/widgets/kernel/qwindowcontainer.cpp
@@ -193,7 +193,7 @@ QWindowContainer::QWindowContainer(QWindow *embeddedWindow, QWidget *parent, Qt:
     : QWidget(*new QWindowContainerPrivate, parent, flags)
 {
     Q_D(QWindowContainer);
-    if (!embeddedWindow) {
+    if (Q_UNLIKELY(!embeddedWindow)) {
         qWarning("QWindowContainer: embedded window cannot be null");
         return;
     }