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>

1 files changed, 4 insertions, 4 deletions

diff --git a/src/widgets/styles/qwindowsxpstyle.cpp b/src/widgets/styles/qwindowsxpstyle.cpp
index 0b33213378..8bd4f69d20 100644
--- a/src/widgets/styles/qwindowsxpstyle.cpp
+++ b/src/widgets/styles/qwindowsxpstyle.cpp
@@ -337,14 +337,14 @@ void QWindowsXPStylePrivate::cleanupHandleMap()
 
 HTHEME QWindowsXPStylePrivate::createTheme(int theme, HWND hwnd)
 {
-    if (theme < 0 || theme >= NThemes || !hwnd) {
+    if (Q_UNLIKELY(theme < 0 || theme >= NThemes || !hwnd)) {
         qWarning("%s: Invalid parameters #%d, %p", Q_FUNC_INFO, theme, hwnd);
         return 0;
     }
     if (!m_themes[theme]) {
         const wchar_t *name = themeNames[theme];
         m_themes[theme] = pOpenThemeData(hwnd, name);
-        if (!m_themes[theme])
+        if (Q_UNLIKELY(!m_themes[theme]))
             qErrnoWarning("%s: OpenThemeData() failed for theme %d (%s).",
                           Q_FUNC_INFO, theme, qPrintable(themeName(theme)));
     }
@@ -504,13 +504,13 @@ HBITMAP QWindowsXPStylePrivate::buffer(int w, int h)
     GdiFlush();
     nullBitmap = (HBITMAP)SelectObject(bufferDC, bufferBitmap);
 
-    if (!bufferBitmap) {
+    if (Q_UNLIKELY(!bufferBitmap)) {
         qErrnoWarning("QWindowsXPStylePrivate::buffer(%dx%d), CreateDIBSection() failed.", w, h);
         bufferW = 0;
         bufferH = 0;
         return 0;
     }
-    if (!bufferPixels) {
+    if (Q_UNLIKELY(!bufferPixels)) {
         qErrnoWarning("QWindowsXPStylePrivate::buffer(%dx%d), CreateDIBSection() did not allocate pixel data.", w, h);
         bufferW = 0;
         bufferH = 0;