Rework sb_compute_dering_list()

Use a unified is_8x8_block_skip() to find if an 8x8 block is coded
in skip mode. This covers cases w/o cb4x4 mode turned on.

Change-Id: I94b72ca7cf0fadbb61bfaa8b97f482feb94fd0f2

av1/common/cdef.c

@@ -44,6 +44,16 @@ int sb_all_skip(const AV1_COMMON *const cm, int mi_row, int mi_col) {
   return skip;
 }
 
+static int is_8x8_block_skip(MODE_INFO **grid, int mi_row, int mi_col,
+                             int mi_stride) {
+  int is_skip = 1;
+  for (int r = 0; r < mi_size_high[BLOCK_8X8]; ++r)
+    for (int c = 0; c < mi_size_wide[BLOCK_8X8]; ++c)
+      is_skip &= grid[(mi_row + r) * mi_stride + (mi_col + c)]->mbmi.skip;
+
+  return is_skip;
+}
+
 int sb_compute_dering_list(const AV1_COMMON *const cm, int mi_row, int mi_col,
                            dering_list *dlist) {
   int r, c;
@@ -63,14 +73,17 @@ int sb_compute_dering_list(const AV1_COMMON *const cm, int mi_row, int mi_col,
 
   const int r_step = mi_size_high[BLOCK_8X8];
   const int c_step = mi_size_wide[BLOCK_8X8];
+  const int r_shift = (r_step == 2);
+  const int c_shift = (c_step == 2);
+
+  assert(r_step == 1 || r_step == 2);
+  assert(c_step == 1 || c_step == 2);
 
   for (r = 0; r < maxr; r += r_step) {
-    MODE_INFO **grid_row;
-    grid_row = &grid[(mi_row + r) * cm->mi_stride + mi_col];
     for (c = 0; c < maxc; c += c_step) {
-      if (!grid_row[c]->mbmi.skip) {
-        dlist[count].by = r;
-        dlist[count].bx = c;
+      if (!is_8x8_block_skip(grid, mi_row + r, mi_col + c, cm->mi_stride)) {
+        dlist[count].by = r >> r_shift;
+        dlist[count].bx = c >> c_shift;
         count++;
       }
     }