Fix potential invalid partition size use

For blocks at frame boundary, the selected block size sometimes needs
to be smaller than that was first given. This commit forces such block
size change only between square blocks, so as to avoid the potential
use case containing 32x16 + 16x8 + 16x8, for 1080p sequences.

Local test suggested no visible coding speed difference. Borg test
reveals no difference in terms of compression performance.

Change-Id: Ie8de87f3c6febc3acf11b4cbfdf2077f9f6def52

vp9/encoder/vp9_encodeframe.c

@@ -995,7 +995,7 @@ static BLOCK_SIZE find_partition_size(BLOCK_SIZE bsize,
   if (rows_left <= 0 || cols_left <= 0) {
     return MIN(bsize, BLOCK_8X8);
   } else {
-    for (; bsize > 0; --bsize) {
+    for (; bsize > 0; bsize -= 3) {
       *bh = num_8x8_blocks_high_lookup[bsize];
       *bw = num_8x8_blocks_wide_lookup[bsize];
       if ((*bh <= rows_left) && (*bw <= cols_left)) {
@@ -2332,8 +2332,6 @@ static void nonrd_use_partition(VP9_COMP *cpi, const TileInfo *const tile,
   int mis = cm->mode_info_stride;
   int br, bc;
   int i, j;
-  int chosen_rate = INT_MAX;
-  int64_t chosen_dist = INT64_MAX;
   MB_PREDICTION_MODE mode = DC_PRED;
   int rows = MIN(MI_BLOCK_SIZE, tile->mi_row_end - mi_row);
   int cols = MIN(MI_BLOCK_SIZE, tile->mi_col_end - mi_col);
@@ -2354,6 +2352,7 @@ static void nonrd_use_partition(VP9_COMP *cpi, const TileInfo *const tile,
 
       BLOCK_SIZE bs = find_partition_size(bsize, rows - br, cols - bc,
                                           &bh, &bw);
+
       set_offsets(cpi, tile, row, col, bs);
 
       if (cm->frame_type != KEY_FRAME)
@@ -2365,16 +2364,10 @@ static void nonrd_use_partition(VP9_COMP *cpi, const TileInfo *const tile,
       *dist += bdist;
 
       for (j = 0; j < bh; ++j)
-        for (i = 0; i < bw; ++i) {
+        for (i = 0; i < bw; ++i)
           xd->mi_8x8[j * mis + i] = xd->mi_8x8[0];
-        }
     }
   }
-
-  *rate = chosen_rate;
-  *dist = chosen_dist;
-
-  encode_sb_rt(cpi, tile, tp, mi_row, mi_col, 1, BLOCK_64X64);
 }
 
 static void encode_nonrd_sb_row(VP9_COMP *cpi, const TileInfo *const tile,
@@ -2397,6 +2390,7 @@ static void encode_nonrd_sb_row(VP9_COMP *cpi, const TileInfo *const tile,
       nonrd_use_partition(cpi, tile, tp, mi_row, mi_col,
                           cpi->sf.always_this_block_size,
                           &dummy_rate, &dummy_dist);
+      encode_sb_rt(cpi, tile, tp, mi_row, mi_col, 1, BLOCK_64X64);
     } else if (cpi->sf.partition_search_type == VAR_BASED_FIXED_PARTITION ||
                cpi->sf.partition_search_type == VAR_BASED_PARTITION) {
       // TODO(debargha): Implement VAR_BASED_PARTITION as a separate case.
@@ -2407,6 +2401,7 @@ static void encode_nonrd_sb_row(VP9_COMP *cpi, const TileInfo *const tile,
                                                              mi_col);
       nonrd_use_partition(cpi, tile, tp, mi_row, mi_col,
                           bsize, &dummy_rate, &dummy_dist);
+      encode_sb_rt(cpi, tile, tp, mi_row, mi_col, 1, BLOCK_64X64);
     } else {
       assert(0);
     }