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vp10: don't reset contextual skip flag if block has no coefficients.

The implicitly changed value would be used for contextualizing future
skip flags of neighbour blocks (bottom/right), which is certainly not
what was intended. The original code stems from vp8, and was useful
in cases where coding of the skip flag was disabled. In vp9, the skip
flag is always coded. The result of this change is that for bitstream
parsing purposes, decoding of the skip flag becomes independent of
decoding of block coefficients.

See issue 1014.

Change-Id: I8629e6abe76f7c1d649f28cd6fe22a675ce4a15d

--- a/vp10/common/blockd.h

+++ b/vp10/common/blockd.h

@@ -70,6 +70,9 @@

   PREDICTION_MODE mode;

   TX_SIZE tx_size;

   int8_t skip;

+#if CONFIG_MISC_FIXES

+  int8_t has_no_coeffs;

+#endif

   int8_t segment_id;

   int8_t seg_id_predicted;  // valid only when temporal_update is enabled

--- a/vp10/common/loopfilter.c

+++ b/vp10/common/loopfilter.c

@@ -754,8 +754,13 @@

   // If the block has no coefficients and is not intra we skip applying

   // the loop filter on block edges.

+#if CONFIG_MISC_FIXES

+  if ((mbmi->skip || mbmi->has_no_coeffs) && is_inter_block(mbmi))

+    return;

+#else

   if (mbmi->skip && is_inter_block(mbmi))

     return;

+#endif

   // Here we are adding a mask for the transform size. The transform

   // size mask is set to be correct for a 64x64 prediction block size. We

@@ -812,8 +817,13 @@

   *above_y |= above_prediction_mask[block_size] << shift_y;

   *left_y |= left_prediction_mask[block_size] << shift_y;

+#if CONFIG_MISC_FIXES

+  if ((mbmi->skip || mbmi->has_no_coeffs) && is_inter_block(mbmi))

+    return;

+#else

   if (mbmi->skip && is_inter_block(mbmi))

     return;

+#endif

   *above_y |= (size_mask[block_size] &

                above_64x64_txform_mask[tx_size_y]) << shift_y;

--- a/vp10/decoder/decodeframe.c

+++ b/vp10/decoder/decodeframe.c

@@ -858,7 +858,11 @@

       }

       if (!less8x8 && eobtotal == 0)

+#if CONFIG_MISC_FIXES

+        mbmi->has_no_coeffs = 1;  // skip loopfilter

+#else

         mbmi->skip = 1;  // skip loopfilter

+#endif

     }

   }