From 459905b93f6bd3cdd4f4bb4820475f90ec5f49fe Mon Sep 17 00:00:00 2001
From: Jingning Han <jingning@google.com>
Date: Fri, 21 Sep 2018 08:24:24 -0700
Subject: [PATCH] Rework is_compound_allowed logic at encoder

Allow the encoder to fully utilize the decoder's capability to
handle both 1 fwd + 2 bwd case and 2 fwd + 1 bw case.

Change-Id: I3f984d52552ddb701b80b042d979f8fe09dd3a80
---
 vp9/common/vp9_pred_common.c  |  8 ++++++++
 vp9/common/vp9_pred_common.h  |  2 ++
 vp9/decoder/vp9_decodeframe.c | 10 +---------
 vp9/encoder/vp9_encodeframe.c |  9 +++------
 4 files changed, 14 insertions(+), 15 deletions(-)

diff --git a/vp9/common/vp9_pred_common.c b/vp9/common/vp9_pred_common.c
index 51d1207..375cb4d 100644
--- a/vp9/common/vp9_pred_common.c
+++ b/vp9/common/vp9_pred_common.c
@@ -13,6 +13,14 @@
 #include "vp9/common/vp9_pred_common.h"
 #include "vp9/common/vp9_seg_common.h"
 
+int vp9_compound_reference_allowed(const VP9_COMMON *cm) {
+  int i;
+  for (i = 1; i < REFS_PER_FRAME; ++i)
+    if (cm->ref_frame_sign_bias[i + 1] != cm->ref_frame_sign_bias[1]) return 1;
+
+  return 0;
+}
+
 void vp9_setup_compound_reference_mode(VP9_COMMON *cm) {
   if (cm->ref_frame_sign_bias[LAST_FRAME] ==
       cm->ref_frame_sign_bias[GOLDEN_FRAME]) {
diff --git a/vp9/common/vp9_pred_common.h b/vp9/common/vp9_pred_common.h
index 7806da8..ee59669 100644
--- a/vp9/common/vp9_pred_common.h
+++ b/vp9/common/vp9_pred_common.h
@@ -145,6 +145,8 @@ static INLINE vpx_prob vp9_get_pred_prob_single_ref_p2(const VP9_COMMON *cm,
   return cm->fc->single_ref_prob[vp9_get_pred_context_single_ref_p2(xd)][1];
 }
 
+int vp9_compound_reference_allowed(const VP9_COMMON *cm);
+
 void vp9_setup_compound_reference_mode(VP9_COMMON *cm);
 
 // Returns a context number for the given MB prediction signal
diff --git a/vp9/decoder/vp9_decodeframe.c b/vp9/decoder/vp9_decodeframe.c
index cd7c16a..de61a05 100644
--- a/vp9/decoder/vp9_decodeframe.c
+++ b/vp9/decoder/vp9_decodeframe.c
@@ -45,14 +45,6 @@
 
 #define MAX_VP9_HEADER_SIZE 80
 
-static int is_compound_reference_allowed(const VP9_COMMON *cm) {
-  int i;
-  for (i = 1; i < REFS_PER_FRAME; ++i)
-    if (cm->ref_frame_sign_bias[i + 1] != cm->ref_frame_sign_bias[1]) return 1;
-
-  return 0;
-}
-
 static int read_is_valid(const uint8_t *start, size_t len, const uint8_t *end) {
   return len != 0 && len <= (size_t)(end - start);
 }
@@ -100,7 +92,7 @@ static void read_inter_mode_probs(FRAME_CONTEXT *fc, vpx_reader *r) {
 
 static REFERENCE_MODE read_frame_reference_mode(const VP9_COMMON *cm,
                                                 vpx_reader *r) {
-  if (is_compound_reference_allowed(cm)) {
+  if (vp9_compound_reference_allowed(cm)) {
     return vpx_read_bit(r)
                ? (vpx_read_bit(r) ? REFERENCE_MODE_SELECT : COMPOUND_REFERENCE)
                : SINGLE_REFERENCE;
diff --git a/vp9/encoder/vp9_encodeframe.c b/vp9/encoder/vp9_encodeframe.c
index 4c131bb..f1527f9 100644
--- a/vp9/encoder/vp9_encodeframe.c
+++ b/vp9/encoder/vp9_encodeframe.c
@@ -5480,14 +5480,11 @@ void vp9_encode_frame(VP9_COMP *cpi) {
   // side behavior is where the ALT ref buffer has opposite sign bias to
   // the other two.
   if (!frame_is_intra_only(cm)) {
-    if ((cm->ref_frame_sign_bias[ALTREF_FRAME] ==
-         cm->ref_frame_sign_bias[GOLDEN_FRAME]) ||
-        (cm->ref_frame_sign_bias[ALTREF_FRAME] ==
-         cm->ref_frame_sign_bias[LAST_FRAME])) {
-      cpi->allow_comp_inter_inter = 0;
-    } else {
+    if (vp9_compound_reference_allowed(cm)) {
       cpi->allow_comp_inter_inter = 1;
       vp9_setup_compound_reference_mode(cm);
+    } else {
+      cpi->allow_comp_inter_inter = 0;
     }
   }
 
-- 
2.7.4