MIPS: Fast path for rgb888 to rgb32 conversion

Add a hand-coded MIPS assembler function to convert a stream of rgb888
bytes to an array of 32-bit ARGB values. This is used in QImage for
image conversion, and also in QJpegHandler for decoding JPEG image
scanlines.

Change-Id: Ia74a5ff799b29fad3d4acbfcafe790cd60586d72
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

src/gui/image/qimage_conversions.cpp

@@ -2176,7 +2176,11 @@ void qInitImageConversions()
 #ifdef QT_COMPILER_SUPPORTS_MIPS_DSPR2
     extern bool convert_ARGB_to_ARGB_PM_inplace_mips_dspr2(QImageData *data, Qt::ImageConversionFlags);
     inplace_converter_map[QImage::Format_ARGB32][QImage::Format_ARGB32_Premultiplied] = convert_ARGB_to_ARGB_PM_inplace_mips_dspr2;
-    return;
+
+    extern void convert_RGB888_to_RGB32_mips_dspr2(QImageData *dest, const QImageData *src, Qt::ImageConversionFlags);
+    qimage_converter_map[QImage::Format::RGB888][QImage::Format_RGB32] = convert_RGB888_to_RGB32_mips_dspr2;
+    qimage_converter_map[QImage::Format::RGB888][QImage::Format_ARGB32] = convert_RGB888_to_RGB32_mips_dspr2;
+    qimage_converter_map[QImage::Format::RGB888][QImage::Format_ARGB32_Premultiplied] = convert_RGB888_to_RGB32_mips_dspr2;
 #endif
 }
 

src/gui/image/qimage_mips_dspr2.cpp

@@ -66,4 +66,24 @@ bool convert_ARGB_to_ARGB_PM_inplace_mips_dspr2(QImageData *data, Qt::ImageConve
     return true;
 }
 
+extern "C" void qt_convert_rgb888_to_rgb32_mips_dspr2_asm(uint *dst, const uchar *src, int len);
+
+void convert_RGB888_to_RGB32_mips_dspr2(QImageData *dest, const QImageData *src, Qt::ImageConversionFlags)
+{
+    Q_ASSERT(src->format == QImage::Format_RGB888);
+    Q_ASSERT(dest->format == QImage::Format_RGB32 || dest->format == QImage::Format_ARGB32 || dest->format == QImage::Format_ARGB32_Premultiplied);
+    Q_ASSERT(src->width == dest->width);
+    Q_ASSERT(src->height == dest->height);
+
+    const uchar *src_data = (const uchar*) src->data;
+    quint32 *dest_data = (quint32*) dest->data;
+
+    for (int i = 0; i < src->height; ++i) {
+        qt_convert_rgb888_to_rgb32_mips_dspr2_asm(dest_data, src_data, src->width);
+        src_data += src->bytes_per_line;
+        dest_data = (quint32*) ((uchar*) dest_data + dest->bytes_per_line);
+    }
+}
+
 QT_END_NAMESPACE
+

src/gui/image/qimage_mips_dspr2_asm.S

@@ -205,3 +205,95 @@ LEAF_MIPS_DSPR2(premultiply_argb_inplace_mips_asm)
 
 END(premultiply_argb_inplace_mips_asm)
 
+
+LEAF_MIPS_DSPR2(qt_convert_rgb888_to_rgb32_mips_dspr2_asm)
+/*
+ * Parameters:
+ *   a0 - dst *a8r8g8b8
+ *   a1 - src *r8g8b8
+ *   a2 - len
+ *
+ * R G B r  g b R G  B r g b  R G B r  g b . . .  -- input
+ * -------  -------  -------  -------  -------
+ * _ R G B  _ r g b  _ R G B  _ r g b  _ R G . .  -- output
+ *
+ * Register usage:
+ *   a2 - tail (len % 4) == (len & 0x3)
+ *   t0 - batches (len / 4) == (len >> 2)
+ *   t1-t7, s1-s3 - temporary
+ */
+
+    srl   t0, a2, 2     /* batches = len / 4 */
+    andi  a2, a2, 0x3   /* tail = len % 4 */
+
+    beqz  t0, 5f        /* if !batches: tail */
+     lui  t7, 0xff00    /* [FF 00 00 00] */
+    SAVE_REGS_ON_STACK 8, s1, s2, s3, s0, v0, v1
+
+1:  pref    4, 0 (a1)   /* hint: read-streamed */
+    pref    5, 0 (a0)   /* hint: prepare-write */
+    addiu  t0, t0, -1   /* batches-- */
+
+    lbu    t1,  0 (a1)  /* [__ __ __ R1] */
+    lbu    t2,  1 (a1)  /* [__ __ __ G1] */
+    lbu    t3,  2 (a1)  /* [__ __ __ B1] */
+
+    lbu    t4,  3 (a1)  /* [__ __ __ r2] */
+    lbu    t5,  4 (a1)  /* [__ __ __ g2] */
+    lbu    t6,  5 (a1)  /* [__ __ __ b2] */
+
+    lbu    s1,  6 (a1)  /* [__ __ __ R3] */
+    lbu    s2,  7 (a1)  /* [__ __ __ G3] */
+    lbu    s3,  8 (a1)  /* [__ __ __ B3] */
+
+    lbu    s0,  9 (a1)  /* [__ __ __ r4] */
+    lbu    v0, 10 (a1)  /* [__ __ __ g4] */
+    lbu    v1, 11 (a1)  /* [__ __ __ b4] */
+
+    append t1, t2, 8    /* [__ __ R1 G1] */
+    append t4, t5, 8    /* [__ __ r2 g2] */
+    append s1, s2, 8    /* [__ __ R3 G3] */
+    append s0, v0, 8    /* [__ __ r4 g4] */
+    append t1, t3, 8    /* [__ R1 G1 B1] */
+    append t4, t6, 8    /* [__ r2 g2 b2] */
+    append s1, s3, 8    /* [__ R3 G4 B3] */
+    append s0, v1, 8    /* [__ r4 g4 b4] */
+    or     t1, t1, t7   /* [FF R1 G1 B1] */
+    or     t4, t4, t7   /* [FF r2 g2 b2] */
+    or     s1, s1, t7   /* [FF R3 G3 B3] */
+    or     s0, s0, t7   /* [FF r4 g4 b4] */
+
+    sw     t1,  0 (a0)
+    sw     t4,  4 (a0)
+    sw     s1,  8 (a0)
+    sw     s0, 12 (a0)
+
+    addiu  a1, a1, 12   /* src += 4*3 */
+    bnez   t0, 1b       /* if batches: loop */
+     addiu a0, a0, 16   /* dst += 4 */
+
+    RESTORE_REGS_FROM_STACK 8, s1, s2, s3, s0, v0, v1
+
+    /* handle remaining "tail" (a2) items */
+5:  beqz   a2, 0f
+     lui   t0, 0xff00   /* [FF __ __ __] */
+
+1:  lbu    t1, 0 (a1)   /* [__ __ __ RR] */
+    lbu    t2, 1 (a1)   /* [__ __ __ GG] */
+    lbu    t3, 2 (a1)   /* [__ __ __ BB] */
+    sll    t1, t1, 16   /* [__ RR __ __] */
+    sll    t2, t2,  8   /* [__ __ GG __] */
+    or     t0, t0, t1   /* [FF RR __ __] */
+    or     t2, t2, t3   /* [__ __ GG BB] */
+    addi   a2, a2, -1   /* len--         */
+    or     t0, t0, t2   /* [FF RR GG BB] */
+    addiu  a1, a1,  3   /* src += 3      */
+    sw     t0, 0 (a0)
+    addiu  a0, a0,  4   /* dst++         */
+    bnez   a2, 1b       /* if tail: loop */
+     lui   t0, 0xff00   /* [FF __ __ __] */
+
+0:  jr ra
+     nop
+
+END(qt_convert_rgb888_to_rgb32_mips_dspr2_asm)

src/gui/image/qjpeghandler.cpp

@@ -857,6 +857,7 @@ bool QJpegHandlerPrivate::read(QImage *image)
 Q_GUI_EXPORT void QT_FASTCALL qt_convert_rgb888_to_rgb32_neon(quint32 *dst, const uchar *src, int len);
 Q_GUI_EXPORT void QT_FASTCALL qt_convert_rgb888_to_rgb32_ssse3(quint32 *dst, const uchar *src, int len);
 Q_GUI_EXPORT void QT_FASTCALL qt_convert_rgb888_to_rgb32_avx(quint32 *dst, const uchar *src, int len);
+extern "C" void qt_convert_rgb888_to_rgb32_mips_dspr2_asm(quint32 *dst, const uchar *src, int len);
 
 QJpegHandler::QJpegHandler()
     : d(new QJpegHandlerPrivate(this))
@@ -875,6 +876,9 @@ QJpegHandler::QJpegHandler()
         rgb888ToRgb32ConverterPtr = qt_convert_rgb888_to_rgb32_ssse3;
     }
 #endif // QT_COMPILER_SUPPORTS_SSSE3
+#if defined(QT_COMPILER_SUPPORTS_MIPS_DSPR2)
+    rgb888ToRgb32ConverterPtr = qt_convert_rgb888_to_rgb32_mips_dspr2_asm;
+#endif // QT_COMPILER_SUPPORTS_DSPR2
 }
 
 QJpegHandler::~QJpegHandler()