Avoid qMin in format conversions when possible

Calling qMin often prevents effective vectorization, and it is only
necessary when converting from formats with mixed color-channel widths.

Change-Id: I2a0f3f3fb528d45be1fd025758f9d915ee1736c0
Reviewed-by: Gunnar Sletta <gunnar@sletta.org>

2 files changed, 71 insertions, 22 deletions

diff --git a/src/gui/painting/qdrawhelper.cpp b/src/gui/painting/qdrawhelper.cpp
index 933ff407e2..85c023f1ff 100644
--- a/src/gui/painting/qdrawhelper.cpp
+++ b/src/gui/painting/qdrawhelper.cpp
@@ -245,17 +245,36 @@ static const uint *QT_FASTCALL convertARGBPMToARGB32PM(uint *buffer, const uint
     Q_CONSTEXPR uchar greenRightShift = 2 * greenWidth<Format>() - 8;
     Q_CONSTEXPR uchar blueRightShift = 2 * blueWidth<Format>() - 8;
 
-    for (int i = 0; i < count; ++i) {
-        uint alpha = (src[i] >> alphaShift<Format>()) & alphaMask;
-        uint red = (src[i] >> redShift<Format>()) & redMask;
-        uint green = (src[i] >> greenShift<Format>()) & greenMask;
-        uint blue = (src[i] >> blueShift<Format>()) & blueMask;
-
-        alpha = (alpha << alphaLeftShift) | (alpha >> alphaRightShift);
-        red = qMin(alpha, (red << redLeftShift) | (red >> redRightShift));
-        green = qMin(alpha, (green << greenLeftShift) | (green >> greenRightShift));
-        blue = qMin(alpha, (blue << blueLeftShift) | (blue >> blueRightShift));
-        buffer[i] = (alpha << 24) | (red << 16) | (green << 8) | blue;
+    Q_CONSTEXPR bool mustMin = (alphaWidth<Format>() != redWidth<Format>()) ||
+                               (alphaWidth<Format>() != greenWidth<Format>()) ||
+                               (alphaWidth<Format>() != blueWidth<Format>());
+
+    if (mustMin) {
+        for (int i = 0; i < count; ++i) {
+            uint alpha = (src[i] >> alphaShift<Format>()) & alphaMask;
+            uint red = (src[i] >> redShift<Format>()) & redMask;
+            uint green = (src[i] >> greenShift<Format>()) & greenMask;
+            uint blue = (src[i] >> blueShift<Format>()) & blueMask;
+
+            alpha = (alpha << alphaLeftShift) | (alpha >> alphaRightShift);
+            red = qMin(alpha, (red << redLeftShift) | (red >> redRightShift));
+            green = qMin(alpha, (green << greenLeftShift) | (green >> greenRightShift));
+            blue = qMin(alpha, (blue << blueLeftShift) | (blue >> blueRightShift));
+            buffer[i] = (alpha << 24) | (red << 16) | (green << 8) | blue;
+        }
+    } else {
+        for (int i = 0; i < count; ++i) {
+            uint alpha = (src[i] >> alphaShift<Format>()) & alphaMask;
+            uint red   = (src[i] >> redShift<Format>())   & redMask;
+            uint green = (src[i] >> greenShift<Format>()) & greenMask;
+            uint blue  = (src[i] >> blueShift<Format>())  & blueMask;
+
+            alpha = ((alpha << alphaLeftShift) | (alpha >> alphaRightShift)) << 24;
+            red   = ((red << redLeftShift) | (red >> redRightShift)) << 16;
+            green = ((green << greenLeftShift) | (green >> greenRightShift)) << 8;
+            blue  = (blue << blueLeftShift)  | (blue >> blueRightShift);
+            buffer[i] = alpha | red | green | blue;
+        }
     }
 
     return buffer;
@@ -280,17 +299,36 @@ static const QRgba64 *QT_FASTCALL convertARGBPMToARGB64PM(QRgba64 *buffer, const
     Q_CONSTEXPR uchar greenRightShift = 2 * greenWidth<Format>() - 8;
     Q_CONSTEXPR uchar blueRightShift = 2 * blueWidth<Format>() - 8;
 
-    for (int i = 0; i < count; ++i) {
-        uint alpha = (src[i] >> alphaShift<Format>()) & alphaMask;
-        uint red = (src[i] >> redShift<Format>()) & redMask;
-        uint green = (src[i] >> greenShift<Format>()) & greenMask;
-        uint blue = (src[i] >> blueShift<Format>()) & blueMask;
-
-        alpha = (alpha << alphaLeftShift) | (alpha >> alphaRightShift);
-        red = qMin(alpha, (red << redLeftShift) | (red >> redRightShift));
-        green = qMin(alpha, (green << greenLeftShift) | (green >> greenRightShift));
-        blue = qMin(alpha, (blue << blueLeftShift) | (blue >> blueRightShift));
-        buffer[i] = QRgba64::fromRgba(red, green, blue, alpha);
+    Q_CONSTEXPR bool mustMin = (alphaWidth<Format>() != redWidth<Format>()) ||
+                               (alphaWidth<Format>() != greenWidth<Format>()) ||
+                               (alphaWidth<Format>() != blueWidth<Format>());
+
+    if (mustMin) {
+        for (int i = 0; i < count; ++i) {
+            uint alpha = (src[i] >> alphaShift<Format>()) & alphaMask;
+            uint red = (src[i] >> redShift<Format>()) & redMask;
+            uint green = (src[i] >> greenShift<Format>()) & greenMask;
+            uint blue = (src[i] >> blueShift<Format>()) & blueMask;
+
+            alpha = (alpha << alphaLeftShift) | (alpha >> alphaRightShift);
+            red = qMin(alpha, (red << redLeftShift) | (red >> redRightShift));
+            green = qMin(alpha, (green << greenLeftShift) | (green >> greenRightShift));
+            blue = qMin(alpha, (blue << blueLeftShift) | (blue >> blueRightShift));
+            buffer[i] = QRgba64::fromRgba(red, green, blue, alpha);
+        }
+    } else {
+        for (int i = 0; i < count; ++i) {
+            uint alpha = (src[i] >> alphaShift<Format>()) & alphaMask;
+            uint red = (src[i] >> redShift<Format>()) & redMask;
+            uint green = (src[i] >> greenShift<Format>()) & greenMask;
+            uint blue = (src[i] >> blueShift<Format>()) & blueMask;
+
+            alpha = (alpha << alphaLeftShift) | (alpha >> alphaRightShift);
+            red = (red << redLeftShift) | (red >> redRightShift);
+            green = (green << greenLeftShift) | (green >> greenRightShift);
+            blue = (blue << blueLeftShift) | (blue >> blueRightShift);
+            buffer[i] = QRgba64::fromRgba(red, green, blue, alpha);
+        }
     }
 
     return buffer;
diff --git a/tests/benchmarks/gui/image/qimageconversion/tst_qimageconversion.cpp b/tests/benchmarks/gui/image/qimageconversion/tst_qimageconversion.cpp
index 31c5520b55..7b49b89709 100644
--- a/tests/benchmarks/gui/image/qimageconversion/tst_qimageconversion.cpp
+++ b/tests/benchmarks/gui/image/qimageconversion/tst_qimageconversion.cpp
@@ -199,6 +199,7 @@ void tst_QImageConversion::convertRgb32_data()
     QTest::newRow("argb32 -> rgb666") << argb32 << QImage::Format_RGB666;
     QTest::newRow("argb32 -> argb8565pm") << argb32 << QImage::Format_ARGB8565_Premultiplied;
     QTest::newRow("argb32 -> argb4444pm") << argb32 << QImage::Format_ARGB4444_Premultiplied;
+    QTest::newRow("argb32 -> argb6666pm") << argb32 << QImage::Format_ARGB6666_Premultiplied;
 
     QTest::newRow("argb32pm -> rgb16") << argb32pm << QImage::Format_RGB16;
     QTest::newRow("argb32pm -> rgb32") << argb32pm << QImage::Format_RGB32;
@@ -212,6 +213,7 @@ void tst_QImageConversion::convertRgb32_data()
     QTest::newRow("argb32pm -> rgb666") << argb32pm << QImage::Format_RGB666;
     QTest::newRow("argb32pm -> argb8565pm") << argb32pm << QImage::Format_ARGB8565_Premultiplied;
     QTest::newRow("argb32pm -> argb4444pm") << argb32pm << QImage::Format_ARGB4444_Premultiplied;
+    QTest::newRow("argb32pm -> argb6666pm") << argb32pm << QImage::Format_ARGB6666_Premultiplied;
 }
 
 void tst_QImageConversion::convertRgb32()
@@ -235,6 +237,7 @@ void tst_QImageConversion::convertGeneric_data()
     QImage bgr30 = rgb32.convertToFormat(QImage::Format_BGR30);
     QImage a2rgb30 = argb32.convertToFormat(QImage::Format_A2RGB30_Premultiplied);
     QImage rgb666 = rgb32.convertToFormat(QImage::Format_RGB666);
+    QImage argb4444 = argb32.convertToFormat(QImage::Format_ARGB4444_Premultiplied);
 
     QTest::newRow("rgba8888 -> rgb32") << rgba32 << QImage::Format_RGB32;
     QTest::newRow("rgba8888 -> argb32") << rgba32 << QImage::Format_ARGB32;
@@ -271,6 +274,14 @@ void tst_QImageConversion::convertGeneric_data()
     QTest::newRow("rgb666 -> rgb16") << rgb666 << QImage::Format_RGB16;
     QTest::newRow("rgb666 -> rgb555") << rgb666 << QImage::Format_RGB555;
     QTest::newRow("rgb666 -> rgb30") << rgb666 << QImage::Format_RGB30;
+
+    QTest::newRow("argb4444pm -> rgb32") << argb4444 << QImage::Format_RGB32;
+    QTest::newRow("argb4444pm -> argb32") << argb4444 << QImage::Format_ARGB32;
+    QTest::newRow("argb4444pm -> argb32pm") << argb4444 << QImage::Format_ARGB32_Premultiplied;
+    QTest::newRow("argb4444pm -> rgbx8888") << argb4444 << QImage::Format_RGBX8888;
+    QTest::newRow("argb4444pm -> rgba8888pm") << argb4444 << QImage::Format_RGBA8888_Premultiplied;
+    QTest::newRow("argb4444pm -> rgb30") << argb4444 << QImage::Format_RGB30;
+    QTest::newRow("argb4444pm -> a2bgr30") << argb4444 << QImage::Format_A2BGR30_Premultiplied;
 }
 
 void tst_QImageConversion::convertGeneric()