vp9_find_mv_refs_idx change for last frame.

Restrict get_matching_candidate() to considering
mvs at 8x8 and larger sizes for last frame case.

This is to reduce the HW load of using vectors down
to the 4x4 level from the previous frame.

Change-Id: I6505e610fd63a4e22d67f136aec7905a01b893ba

vp9/common/vp9_mvref_common.c

@@ -101,39 +101,12 @@ static void get_non_matching_candidates(const MODE_INFO *candidate_mi,
 static void scale_mv(MACROBLOCKD *xd, MV_REFERENCE_FRAME this_ref_frame,
                      MV_REFERENCE_FRAME candidate_ref_frame,
                      int_mv *candidate_mv, int *ref_sign_bias) {
-  // int frame_distances[MAX_REF_FRAMES];
-  // int last_distance = 1;
-  // int gf_distance = xd->frames_since_golden;
-  // int arf_distance = xd->frames_till_alt_ref_frame;
 
   // Sign inversion where appropriate.
   if (ref_sign_bias[candidate_ref_frame] != ref_sign_bias[this_ref_frame]) {
     candidate_mv->as_mv.row = -candidate_mv->as_mv.row;
     candidate_mv->as_mv.col = -candidate_mv->as_mv.col;
   }
-
-  /*
-  // Scale based on frame distance if the reference frames not the same.
-  frame_distances[INTRA_FRAME] = 1;   // should never be used
-  frame_distances[LAST_FRAME] = 1;
-  frame_distances[GOLDEN_FRAME] =
-    (xd->frames_since_golden) ? xd->frames_si nce_golden : 1;
-  frame_distances[ALTREF_FRAME] =
-    (xd->frames_till_alt_ref_frame) ? xd->frames_till_alt_ref_frame : 1;
-
-  if (frame_distances[this_ref_frame] &&
-      frame_distances[candidate_ref_frame]) {
-    candidate_mv->as_mv.row =
-      (short)(((int)(candidate_mv->as_mv.row) *
-               frame_distances[this_ref_frame]) /
-              frame_distances[candidate_ref_frame]);
-
-    candidate_mv->as_mv.col =
-      (short)(((int)(candidate_mv->as_mv.col) *
-               frame_distances[this_ref_frame]) /
-              frame_distances[candidate_ref_frame]);
-  }
-  */
 }
 
 // Add a candidate mv.
@@ -230,16 +203,6 @@ void vp9_find_mv_refs_idx(VP9_COMMON *cm, MACROBLOCKD *xd, MODE_INFO *here,
     }
   }
 
-  // If at this stage wwe have a 0 vector and a non zero vector from the
-  // correct reference frame then make sure that the non zero one is given
-  // precedence as we have other options for coding 0,0
-  /* if (refmv_count == MAX_MV_REF_CANDIDATES) {
-    if (mv_ref_list[1].as_int && !mv_ref_list[0].as_int) {
-      mv_ref_list[0].as_int = mv_ref_list[1].as_int;
-      mv_ref_list[1].as_int = 0;
-    }
-  } */
-
   // More distant neigbours
   for (i = 2; (i < MVREF_NEIGHBOURS) &&
               (refmv_count < MAX_MV_REF_CANDIDATES); ++i) {
@@ -261,7 +224,7 @@ void vp9_find_mv_refs_idx(VP9_COMMON *cm, MACROBLOCKD *xd, MODE_INFO *here,
   // Look in the last frame if it exists
   if (lf_here && (refmv_count < MAX_MV_REF_CANDIDATES)) {
     candidate_mi = lf_here;
-    if (get_matching_candidate(candidate_mi, ref_frame, &c_refmv, block_idx)) {
+    if (get_matching_candidate(candidate_mi, ref_frame, &c_refmv, -1)) {
       add_candidate_mv(mv_ref_list, candidate_scores,
                        &refmv_count, c_refmv, 16);
     }