Re-arrange inter mode search order in RTC coding flow

This commit makes the ZEROMV mode first in the search order to
ensure that the zero mv is always checked in the RTC coding mode.
It improves the average speed -6 compression performance by 0.3%
in both PSNR and SSIM at no visible speed change.

Change-Id: I465a7e59f4e20cd84fee3f02ced6f98036945949

1 files changed, 8 insertions, 2 deletions

diff --git a/vp9/encoder/vp9_pickmode.c b/vp9/encoder/vp9_pickmode.c
index a34b12258..70e90b6e7 100644
--- a/vp9/encoder/vp9_pickmode.c
+++ b/vp9/encoder/vp9_pickmode.c
@@ -573,6 +573,10 @@ void vp9_pick_intra_mode(VP9_COMP *cpi, MACROBLOCK *x, RD_COST *rd_cost,
   *rd_cost = best_rdc;
 }
 
+static const PREDICTION_MODE inter_mode_set[INTER_MODES] = {
+    ZEROMV, NEARESTMV, NEARMV, NEWMV,
+};
+
 // TODO(jingning) placeholder for inter-frame non-RD mode decision.
 // this needs various further optimizations. to be continued..
 void vp9_pick_inter_mode(VP9_COMP *cpi, MACROBLOCK *x,
@@ -732,10 +736,12 @@ void vp9_pick_inter_mode(VP9_COMP *cpi, MACROBLOCK *x,
     mbmi->ref_frame[0] = ref_frame;
     set_ref_ptrs(cm, xd, ref_frame, NONE);
 
-    for (this_mode = NEARESTMV; this_mode <= NEWMV; ++this_mode) {
+    for (i = 0; i < INTER_MODES; ++i) {
       int rate_mv = 0;
       int mode_rd_thresh;
-      int mode_index = mode_idx[ref_frame][INTER_OFFSET(this_mode)];
+      int mode_index;
+      this_mode = inter_mode_set[i];
+      mode_index = mode_idx[ref_frame][INTER_OFFSET(this_mode)];
 
       if (const_motion[ref_frame] && this_mode == NEARMV)
         continue;