sse2: Skip src pixels that are zero in sse2_composite_over_8888_n_8888()

This is a big speed-up in the SVG helicopter game:

   http://ie.microsoft.com/testdrive/Performance/Helicopter/Default.xhtml

when rendered by Firefox 4 since it is compositing big images
consisting almost entirely of zeros.

diff --git a/pixman/pixman-sse2.c b/pixman/pixman-sse2.c
index 5907de0..032f13b 100644 (file)
--- a/pixman/pixman-sse2.c
+++ b/pixman/pixman-sse2.c
@@ -3051,37 +3051,45 @@ sse2_composite_over_8888_n_8888 (pixman_implementation_t *imp,
        while (w && (unsigned long)dst & 15)
        {
            uint32_t s = *src++;
-           uint32_t d = *dst;
-
-           __m64 ms = unpack_32_1x64 (s);
-           __m64 alpha    = expand_alpha_1x64 (ms);
-           __m64 dest     = _mm_movepi64_pi64 (xmm_mask);
-           __m64 alpha_dst = unpack_32_1x64 (d);
-
-           *dst++ = pack_1x64_32 (
-               in_over_1x64 (&ms, &alpha, &dest, &alpha_dst));
 
+           if (s)
+           {
+               uint32_t d = *dst;
+               
+               __m64 ms = unpack_32_1x64 (s);
+               __m64 alpha    = expand_alpha_1x64 (ms);
+               __m64 dest     = _mm_movepi64_pi64 (xmm_mask);
+               __m64 alpha_dst = unpack_32_1x64 (d);
+               
+               *dst = pack_1x64_32 (
+                   in_over_1x64 (&ms, &alpha, &dest, &alpha_dst));
+           }
+           dst++;
            w--;
        }
 
        while (w >= 4)
        {
            xmm_src = load_128_unaligned ((__m128i*)src);
-           xmm_dst = load_128_aligned ((__m128i*)dst);
-
-           unpack_128_2x128 (xmm_src, &xmm_src_lo, &xmm_src_hi);
-           unpack_128_2x128 (xmm_dst, &xmm_dst_lo, &xmm_dst_hi);
-           expand_alpha_2x128 (xmm_src_lo, xmm_src_hi,
-                               &xmm_alpha_lo, &xmm_alpha_hi);
-
-           in_over_2x128 (&xmm_src_lo, &xmm_src_hi,
-                          &xmm_alpha_lo, &xmm_alpha_hi,
-                          &xmm_mask, &xmm_mask,
-                          &xmm_dst_lo, &xmm_dst_hi);
-
-           save_128_aligned (
-               (__m128i*)dst, pack_2x128_128 (xmm_dst_lo, xmm_dst_hi));
 
+           if (!is_zero (xmm_src))
+           {
+               xmm_dst = load_128_aligned ((__m128i*)dst);
+               
+               unpack_128_2x128 (xmm_src, &xmm_src_lo, &xmm_src_hi);
+               unpack_128_2x128 (xmm_dst, &xmm_dst_lo, &xmm_dst_hi);
+               expand_alpha_2x128 (xmm_src_lo, xmm_src_hi,
+                                   &xmm_alpha_lo, &xmm_alpha_hi);
+               
+               in_over_2x128 (&xmm_src_lo, &xmm_src_hi,
+                              &xmm_alpha_lo, &xmm_alpha_hi,
+                              &xmm_mask, &xmm_mask,
+                              &xmm_dst_lo, &xmm_dst_hi);
+               
+               save_128_aligned (
+                   (__m128i*)dst, pack_2x128_128 (xmm_dst_lo, xmm_dst_hi));
+           }
+               
            dst += 4;
            src += 4;
            w -= 4;
@@ -3090,16 +3098,21 @@ sse2_composite_over_8888_n_8888 (pixman_implementation_t *imp,
        while (w)
        {
            uint32_t s = *src++;
-           uint32_t d = *dst;
 
-           __m64 ms = unpack_32_1x64 (s);
-           __m64 alpha = expand_alpha_1x64 (ms);
-           __m64 mask  = _mm_movepi64_pi64 (xmm_mask);
-           __m64 dest  = unpack_32_1x64 (d);
-
-           *dst++ = pack_1x64_32 (
-               in_over_1x64 (&ms, &alpha, &mask, &dest));
+           if (s)
+           {
+               uint32_t d = *dst;
+               
+               __m64 ms = unpack_32_1x64 (s);
+               __m64 alpha = expand_alpha_1x64 (ms);
+               __m64 mask  = _mm_movepi64_pi64 (xmm_mask);
+               __m64 dest  = unpack_32_1x64 (d);
+               
+               *dst = pack_1x64_32 (
+                   in_over_1x64 (&ms, &alpha, &mask, &dest));
+           }
 
+           dst++;
            w--;
        }
     }