Deprecate Q_ASSUME()

We've known for a long time that this is producing worse code with GCC
because of how we implemented in Q_ASSUME_IMPL(). So bite the bullet and
actually deprecate the macro, replacing all extant Q_ASSUME() with
Q_ASSERT().

The replacement is in C++23. Backporting the support onto Q_ASSUME_IMPL
was previously rejected by reviewers.

[ChangeLog][Deprecation Notice] The Q_ASSUME() macro is deprecated. This
macro has different side-effects depending on the compiler used (GCC
compared to Clang and MSVC), and there are certain conditions under
which GCC is known to produce worse code than if the macro was absent.
To give a hint to the compiler for optimizations, use the C++23
[[assume]] attribute.

Change-Id: I80612a7d275c41f1baf0fffd177a3a4ad819fb2d
Reviewed-by: Volker Hilsheimer <volker.hilsheimer@qt.io>

2 files changed, 3 insertions, 3 deletions

diff --git a/src/gui/painting/qpaintengine_raster.cpp b/src/gui/painting/qpaintengine_raster.cpp
index a50f5aec60..4d730fccc3 100644
--- a/src/gui/painting/qpaintengine_raster.cpp
+++ b/src/gui/painting/qpaintengine_raster.cpp
@@ -2261,7 +2261,7 @@ void QRasterPaintEngine::drawImage(const QRectF &r, const QImage &img, const QRe
             || d->rasterBuffer->compositionMode == QPainter::CompositionMode_Source))
     {
         RotationType rotationType = qRotationType(s->matrix);
-        Q_ASSUME(d->rasterBuffer->format < QImage::NImageFormats);
+        Q_ASSERT(d->rasterBuffer->format < QImage::NImageFormats);
         const QPixelLayout::BPP plBpp = qPixelLayouts[d->rasterBuffer->format].bpp;
 
         if (rotationType != NoRotation && qMemRotateFunctions[plBpp][rotationType] && img.rect().contains(sr.toAlignedRect())) {
diff --git a/src/gui/painting/qpaintengineex.cpp b/src/gui/painting/qpaintengineex.cpp
index 7f1c7e356d..9468876c23 100644
--- a/src/gui/painting/qpaintengineex.cpp
+++ b/src/gui/painting/qpaintengineex.cpp
@@ -902,7 +902,7 @@ void QPaintEngineEx::drawPoints(const QPoint *points, int pointCount)
 
 void QPaintEngineEx::drawPolygon(const QPointF *points, int pointCount, PolygonDrawMode mode)
 {
-    Q_ASSUME(pointCount >= 2);
+    Q_ASSERT(pointCount >= 2);
     QVectorPath path((const qreal *) points, pointCount, nullptr, QVectorPath::polygonFlags(mode));
 
     if (mode == PolylineMode)
@@ -913,7 +913,7 @@ void QPaintEngineEx::drawPolygon(const QPointF *points, int pointCount, PolygonD
 
 void QPaintEngineEx::drawPolygon(const QPoint *points, int pointCount, PolygonDrawMode mode)
 {
-    Q_ASSUME(pointCount >= 2);
+    Q_ASSERT(pointCount >= 2);
     int count = pointCount<<1;
     QVarLengthArray<qreal> pts(count);