libvpx: Pull from upstream

source/libvpx/vp9/common/vp9_entropymode.c

 /*
  *  Copyright (c) 2010 The WebM project authors. All Rights Reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
@@ skipping 447 matching lines @@
   if (cm->frame_type == KEY_FRAME ||
       cm->error_resilient_mode || cm->reset_frame_context == 3) {
     // Reset all frame contexts.
     for (i = 0; i < FRAME_CONTEXTS; ++i)
       cm->frame_contexts[i] = cm->fc;
   } else if (cm->reset_frame_context == 2) {
     // Reset only the frame context specified in the frame header.
     cm->frame_contexts[cm->frame_context_idx] = cm->fc;
   }
 
-  vpx_memset(cm->prev_mip, 0,
-             cm->mode_info_stride * (cm->mi_rows + 1) * sizeof(MODE_INFO));
+  if (frame_is_intra_only(cm))
+    vpx_memset(cm->prev_mip, 0,
+               cm->mode_info_stride * (cm->mi_rows + 1) * sizeof(MODE_INFO));
+
   vpx_memset(cm->mip, 0,
              cm->mode_info_stride * (cm->mi_rows + 1) * sizeof(MODE_INFO));
 
   vp9_zero(cm->ref_frame_sign_bias);
 
   cm->frame_context_idx = 0;
 }