Change MV_REFERENCE_FRAME type back to int8_t.

It can take values outside the range of any single enum, so we define
its type to be int8_t as before.

This fixes some build issues.

BUG=aomedia:2236
BUG=aomedia:2230

Change-Id: If9c50d6917b20770b556287732ed128613e4cb6f

av1/common/enums.h

diff --git a/av1/common/enums.h b/av1/common/enums.h
index be6d7a6..e06d7cf 100644
--- a/av1/common/enums.h
+++ b/av1/common/enums.h
@@ -539,8 +539,8 @@
 #define TXFM_PARTITION_CONTEXTS ((TX_SIZES - TX_8X8) * 6 - 3)
 typedef uint8_t TXFM_CONTEXT;
 
-// An enum for various types of reference frame types (and some derived values).
-typedef enum ATTRIBUTE_PACKED {
+// An enum for single reference types (and some derived values).
+enum ATTRIBUTE_PACKED {
   NONE_FRAME = -1,
   INTRA_FRAME,
   LAST_FRAME,
@@ -567,7 +567,7 @@
   BWD_REFS = ALTREF_FRAME - BWDREF_FRAME + 1,
 
   SINGLE_REFS = FWD_REFS + BWD_REFS,
-} MV_REFERENCE_FRAME;
+};
 
 #define REF_FRAMES_LOG2 3
 
@@ -604,6 +604,10 @@
 //       possible to have a reference pair not listed for explicit signaling.
 #define MODE_CTX_REF_FRAMES (REF_FRAMES + TOTAL_COMP_REFS)
 
+// Note: It includes single and compound references. So, it can take values from
+// NONE_FRAME to (MODE_CTX_REF_FRAMES - 1). Hence, it is not defined as an enum.
+typedef int8_t MV_REFERENCE_FRAME;
+
 typedef enum ATTRIBUTE_PACKED {
   RESTORE_NONE,
   RESTORE_WIENER,

av1/common/mvref_common.h

diff --git a/av1/common/mvref_common.h b/av1/common/mvref_common.h
index bb37357..1ef50e7 100644
--- a/av1/common/mvref_common.h
+++ b/av1/common/mvref_common.h
@@ -169,13 +169,13 @@
 // clang-format on
 
 static INLINE void av1_set_ref_frame(MV_REFERENCE_FRAME *rf,
-                                     int8_t ref_frame_type) {
+                                     MV_REFERENCE_FRAME ref_frame_type) {
   if (ref_frame_type >= REF_FRAMES) {
     rf[0] = ref_frame_map[ref_frame_type - REF_FRAMES][0];
     rf[1] = ref_frame_map[ref_frame_type - REF_FRAMES][1];
   } else {
     assert(ref_frame_type > NONE_FRAME);
-    rf[0] = (MV_REFERENCE_FRAME)ref_frame_type;
+    rf[0] = ref_frame_type;
     rf[1] = NONE_FRAME;
   }
 }

av1/encoder/encoder.h

diff --git a/av1/encoder/encoder.h b/av1/encoder/encoder.h
index ea7d03a..8b35cae 100644
--- a/av1/encoder/encoder.h
+++ b/av1/encoder/encoder.h
@@ -961,14 +961,13 @@
 
 static INLINE int enc_is_ref_frame_buf(AV1_COMP *cpi, RefCntBuffer *frame_buf) {
   AV1_COMMON *const cm = &cpi->common;
-  int ref_num;
-  for (ref_num = LAST_FRAME; ref_num <= ALTREF_FRAME; ++ref_num) {
-    const MV_REFERENCE_FRAME ref_frame = (MV_REFERENCE_FRAME)ref_num;
+  MV_REFERENCE_FRAME ref_frame;
+  for (ref_frame = LAST_FRAME; ref_frame <= ALTREF_FRAME; ++ref_frame) {
     const int buf_idx = get_ref_frame_buf_idx(cpi, ref_frame);
     if (buf_idx == INVALID_IDX) continue;
     if (frame_buf == &cm->buffer_pool->frame_bufs[buf_idx]) break;
   }
-  return (ref_num <= ALTREF_FRAME);
+  return (ref_frame <= ALTREF_FRAME);
 }
 
 // Token buffer is only used for palette tokens.