Skip NEW_MV when new_mv is same as ref

The BDRate is moreorless neutral, but the encoding gets about 0.5%
faster.

STATS_CHANGED

Change-Id: I66c1c6f01d79c5cebfe9c1a2707e414f94885bba

av1/encoder/encodemv.c

diff --git a/av1/encoder/encodemv.c b/av1/encoder/encodemv.c
index 43b7237..a101c9c 100644
--- a/av1/encoder/encodemv.c
+++ b/av1/encoder/encodemv.c
@@ -195,6 +195,8 @@
                    nmv_context *mvctx, int usehp) {
   const MV diff = { mv->row - ref->row, mv->col - ref->col };
   const MV_JOINT_TYPE j = av1_get_mv_joint(&diff);
+  // If the mv_diff is zero, then we should have used near or nearest instead.
+  assert(j != MV_JOINT_ZERO);
   if (cpi->common.cur_frame_force_integer_mv) {
     usehp = MV_SUBPEL_NONE;
   }

av1/encoder/rdopt.c

diff --git a/av1/encoder/rdopt.c b/av1/encoder/rdopt.c
index e203037..5118fc0 100644
--- a/av1/encoder/rdopt.c
+++ b/av1/encoder/rdopt.c
@@ -10258,6 +10258,32 @@
       if (ret < 0) continue;
     }
 
+    // If we are searching newmv and the mv is the same as refmv, skip the
+    // current mode
+    if (this_mode == NEW_NEWMV) {
+      const int_mv ref_mv_0 = av1_get_ref_mv(x, 0);
+      const int_mv ref_mv_1 = av1_get_ref_mv(x, 1);
+      if (mbmi->mv[0].as_int == ref_mv_0.as_int ||
+          mbmi->mv[1].as_int == ref_mv_1.as_int) {
+        continue;
+      }
+    } else if (this_mode == NEAREST_NEWMV || this_mode == NEAR_NEWMV) {
+      const int_mv ref_mv_1 = av1_get_ref_mv(x, 1);
+      if (mbmi->mv[1].as_int == ref_mv_1.as_int) {
+        continue;
+      }
+    } else if (this_mode == NEW_NEARESTMV || this_mode == NEW_NEARMV) {
+      const int_mv ref_mv_0 = av1_get_ref_mv(x, 0);
+      if (mbmi->mv[0].as_int == ref_mv_0.as_int) {
+        continue;
+      }
+    } else if (this_mode == NEWMV) {
+      const int_mv ref_mv_0 = av1_get_ref_mv(x, 0);
+      if (mbmi->mv[0].as_int == ref_mv_0.as_int) {
+        continue;
+      }
+    }
+
     x->skip = 0;
     rd_stats->dist = 0;
     rd_stats->sse = 0;
@@ -11286,8 +11312,11 @@
                   break;
                 } else {
                   // If the cost is less than current best result, make this
-                  // the best and update corresponding variables
-                  if (best_mbmi.ref_mv_idx == i) {
+                  // the best and update corresponding variables unless the
+                  // best_mv is the same as ref_mv. In this case we skip and
+                  // rely on NEAR(EST)MV instead
+                  if (best_mbmi.ref_mv_idx == i &&
+                      mode_info[i].mv.as_int != ref_mv.as_int) {
                     assert(best_rd != INT64_MAX);
                     best_mbmi.ref_mv_idx = ref_mv_idx;
                     motion_mode_cand->rate_mv = this_rate_mv;