Implement the composition mode Plus with Neon.

On the benchmark tst_QPainter::compositionModes(), this patches gives
the following improvements:
-300x300:opaque: 390%
-300x300:!opaque: 1085%

Reviewed-by: Samuel Rødal

5 files changed, 83 insertions, 22 deletions

diff --git a/src/gui/painting/qdrawhelper.cpp b/src/gui/painting/qdrawhelper.cpp
index 276da9362e..0b74fc0e3a 100644
--- a/src/gui/painting/qdrawhelper.cpp
+++ b/src/gui/painting/qdrawhelper.cpp
@@ -1757,9 +1757,7 @@ Q_STATIC_TEMPLATE_FUNCTION inline void comp_func_solid_Plus_impl(uint *dest, int
     for (int i = 0; i < length; ++i) {
         PRELOAD_COND(dest)
         uint d = dest[i];
-#define MIX(mask) (qMin(((qint64(s)&mask) + (qint64(d)&mask)), qint64(mask)))
-        d = (MIX(AMASK) | MIX(RMASK) | MIX(GMASK) | MIX(BMASK));
-#undef MIX
+        d = comp_func_Plus_one_pixel(d, s);
         coverage.store(&dest[i], d);
     }
 }
@@ -1781,9 +1779,7 @@ Q_STATIC_TEMPLATE_FUNCTION inline void comp_func_Plus_impl(uint *dest, const uin
         uint d = dest[i];
         uint s = src[i];
 
-#define MIX(mask) (qMin(((qint64(s)&mask) + (qint64(d)&mask)), qint64(mask)))
-        d = (MIX(AMASK) | MIX(RMASK) | MIX(GMASK) | MIX(BMASK));
-#undef MIX
+        d = comp_func_Plus_one_pixel(d, s);
 
         coverage.store(&dest[i], d);
     }
@@ -7911,6 +7907,7 @@ void qInitDrawhelperAsm()
 
             functionForMode_C[QPainter::CompositionMode_SourceOver] = qt_blend_argb32_on_argb32_scanline_neon;
             functionForModeSolid_C[QPainter::CompositionMode_SourceOver] = comp_func_solid_SourceOver_neon;
+            functionForMode_C[QPainter::CompositionMode_Plus] = comp_func_Plus_neon;
             destFetchProc[QImage::Format_RGB16] = qt_destFetchRGB16_neon;
             destStoreProc[QImage::Format_RGB16] = qt_destStoreRGB16_neon;
 
diff --git a/src/gui/painting/qdrawhelper_neon.cpp b/src/gui/painting/qdrawhelper_neon.cpp
index 03fe0755f9..c1f815d636 100644
--- a/src/gui/painting/qdrawhelper_neon.cpp
+++ b/src/gui/painting/qdrawhelper_neon.cpp
@@ -622,6 +622,61 @@ void QT_FASTCALL comp_func_solid_SourceOver_neon(uint *destPixels, int length, u
     }
 }
 
+void QT_FASTCALL comp_func_Plus_neon(uint *dst, const uint *src, int length, uint const_alpha)
+{
+    if (const_alpha == 255) {
+        uint *const end = dst + length;
+        uint *const neonEnd = end - 3;
+
+        while (dst < neonEnd) {
+            asm volatile (
+                "vld2.8     { d0, d1 }, [%[SRC]] !\n\t"
+                "vld2.8     { d2, d3 }, [%[DST]]\n\t"
+                "vqadd.u8 q0, q0, q1\n\t"
+                "vst2.8     { d0, d1 }, [%[DST]] !\n\t"
+                : [DST]"+r" (dst), [SRC]"+r" (src)
+                :
+                : "memory", "d0", "d1", "d2", "d3", "q0", "q1"
+            );
+        }
+
+        while (dst != end) {
+            *dst = comp_func_Plus_one_pixel(*dst, *src);
+            ++dst;
+            ++src;
+        }
+    } else {
+        int x = 0;
+        const int one_minus_const_alpha = 255 - const_alpha;
+        const uint16x8_t constAlphaVector = vdupq_n_u16(const_alpha);
+        const uint16x8_t oneMinusconstAlphaVector = vdupq_n_u16(one_minus_const_alpha);
+
+        const uint16x8_t half = vdupq_n_u16(0x80);
+        for (; x < length - 3; x += 4) {
+            const uint32x4_t src32 = vld1q_u32((uint32_t *)&src[x]);
+            const uint8x16_t src8 = vreinterpretq_u8_u32(src32);
+            uint8x16_t dst8 = vld1q_u8((uint8_t *)&dst[x]);
+            uint8x16_t result = vqaddq_u8(dst8, src8);
+
+            uint16x8_t result_low = vmovl_u8(vget_low_u8(result));
+            uint16x8_t result_high = vmovl_u8(vget_high_u8(result));
+
+            uint16x8_t dst_low = vmovl_u8(vget_low_u8(dst8));
+            uint16x8_t dst_high = vmovl_u8(vget_high_u8(dst8));
+
+            result_low = qvinterpolate_pixel_255(result_low, constAlphaVector, dst_low, oneMinusconstAlphaVector, half);
+            result_high = qvinterpolate_pixel_255(result_high, constAlphaVector, dst_high, oneMinusconstAlphaVector, half);
+
+            const uint32x2_t result32_low = vreinterpret_u32_u8(vmovn_u16(result_low));
+            const uint32x2_t result32_high = vreinterpret_u32_u8(vmovn_u16(result_high));
+            vst1q_u32((uint32_t *)&dst[x], vcombine_u32(result32_low, result32_high));
+        }
+
+        for (; x < length; ++x)
+            dst[x] = comp_func_Plus_one_pixel_const_alpha(dst[x], src[x], const_alpha, one_minus_const_alpha);
+    }
+}
+
 static const int tileSize = 32;
 
 extern "C" void qt_rotate90_16_neon(quint16 *dst, const quint16 *src, int sstride, int dstride, int count);
diff --git a/src/gui/painting/qdrawhelper_neon_p.h b/src/gui/painting/qdrawhelper_neon_p.h
index cd2dbfcb0d..182c936627 100644
--- a/src/gui/painting/qdrawhelper_neon_p.h
+++ b/src/gui/painting/qdrawhelper_neon_p.h
@@ -131,6 +131,7 @@ void QT_FASTCALL qt_destStoreRGB16_neon(QRasterBuffer *rasterBuffer,
                                         int x, int y, const uint *buffer, int length);
 
 void QT_FASTCALL comp_func_solid_SourceOver_neon(uint *destPixels, int length, uint color, uint const_alpha);
+void QT_FASTCALL comp_func_Plus_neon(uint *dst, const uint *src, int length, uint const_alpha);
 
 #endif // QT_HAVE_NEON
 
diff --git a/src/gui/painting/qdrawhelper_p.h b/src/gui/painting/qdrawhelper_p.h
index d04c70d451..75f42a0556 100644
--- a/src/gui/painting/qdrawhelper_p.h
+++ b/src/gui/painting/qdrawhelper_p.h
@@ -1944,6 +1944,30 @@ const uint qt_bayer_matrix[16][16] = {
     ((((argb >> 24) * alpha) >> 8) << 24) | (argb & 0x00ffffff)
 
 
+#if QT_POINTER_SIZE == 8 // 64-bit versions
+#define AMIX(mask) (qMin(((qint64(s)&mask) + (qint64(d)&mask)), qint64(mask)))
+#define MIX(mask) (qMin(((qint64(s)&mask) + (qint64(d)&mask)), qint64(mask)))
+#else // 32 bits
+// The mask for alpha can overflow over 32 bits
+#define AMIX(mask) quint32(qMin(((qint64(s)&mask) + (qint64(d)&mask)), qint64(mask)))
+#define MIX(mask) (qMin(((quint32(s)&mask) + (quint32(d)&mask)), quint32(mask)))
+#endif
+
+inline int comp_func_Plus_one_pixel_const_alpha(uint d, const uint s, const uint const_alpha, const uint one_minus_const_alpha)
+{
+    const int result = (AMIX(AMASK) | MIX(RMASK) | MIX(GMASK) | MIX(BMASK));
+    return INTERPOLATE_PIXEL_255(result, const_alpha, d, one_minus_const_alpha);
+}
+
+inline int comp_func_Plus_one_pixel(uint d, const uint s)
+{
+    const int result = (AMIX(AMASK) | MIX(RMASK) | MIX(GMASK) | MIX(BMASK));
+    return result;
+}
+
+#undef MIX
+#undef AMIX
+
 // prototypes of all the composition functions
 void QT_FASTCALL comp_func_SourceOver(uint *dest, const uint *src, int length, uint const_alpha);
 void QT_FASTCALL comp_func_DestinationOver(uint *dest, const uint *src, int length, uint const_alpha);
diff --git a/src/gui/painting/qdrawhelper_sse2.cpp b/src/gui/painting/qdrawhelper_sse2.cpp
index 22c0384c08..30454af9e4 100644
--- a/src/gui/painting/qdrawhelper_sse2.cpp
+++ b/src/gui/painting/qdrawhelper_sse2.cpp
@@ -161,22 +161,6 @@ void QT_FASTCALL comp_func_SourceOver_sse2(uint *destPixels, const uint *srcPixe
     }
 }
 
-inline int comp_func_Plus_one_pixel_const_alpha(uint d, const uint s, const uint const_alpha, const uint one_minus_const_alpha)
-{
-#define MIX(mask) (qMin(((qint64(s)&mask) + (qint64(d)&mask)), qint64(mask)))
-    const int result = (MIX(AMASK) | MIX(RMASK) | MIX(GMASK) | MIX(BMASK));
-#undef MIX
-    return INTERPOLATE_PIXEL_255(result, const_alpha, d, one_minus_const_alpha);
-}
-
-inline int comp_func_Plus_one_pixel(uint d, const uint s)
-{
-#define MIX(mask) (qMin(((qint64(s)&mask) + (qint64(d)&mask)), qint64(mask)))
-    const int result = (MIX(AMASK) | MIX(RMASK) | MIX(GMASK) | MIX(BMASK));
-#undef MIX
-    return result;
-}
-
 void QT_FASTCALL comp_func_Plus_sse2(uint *dst, const uint *src, int length, uint const_alpha)
 {
     int x = 0;