Cherry pick buffer re-allocation fix

source/libvpx/vp9/common/vp9_alloccommon.c

Index: source/libvpx/vp9/common/vp9_alloccommon.c
diff --git a/source/libvpx/vp9/common/vp9_alloccommon.c b/source/libvpx/vp9/common/vp9_alloccommon.c
index 7db210c3ae018df2b1cf25804d13f17e60627e9f..222b88eff5d09a310f7d638ac6e14ea71fd72bab 100644
--- a/source/libvpx/vp9/common/vp9_alloccommon.c
+++ b/source/libvpx/vp9/common/vp9_alloccommon.c
@@ -56,6 +56,7 @@ static int alloc_seg_map(VP9_COMMON *cm, int seg_map_size) {
     if (cm->seg_map_array[i] == NULL)
       return 1;
   }
+  cm->seg_map_alloc_size = seg_map_size;
 
   // Init the index.
   cm->seg_map_idx = 0;
@@ -117,25 +118,36 @@ void vp9_free_context_buffers(VP9_COMMON *cm) {
 }
 
 int vp9_alloc_context_buffers(VP9_COMMON *cm, int width, int height) {
-  vp9_free_context_buffers(cm);
+  int new_mi_size;
 
   vp9_set_mb_mi(cm, width, height);
-  if (cm->alloc_mi(cm, cm->mi_stride * calc_mi_size(cm->mi_rows)))
-    goto fail;
-
-  // Create the segmentation map structure and set to 0.
-  free_seg_map(cm);
-  if (alloc_seg_map(cm, cm->mi_rows * cm->mi_cols))
-    goto fail;
+  new_mi_size = cm->mi_stride * calc_mi_size(cm->mi_rows);
+  if (cm->mi_alloc_size < new_mi_size) {
+    cm->free_mi(cm);
+    if (cm->alloc_mi(cm, new_mi_size))
+      goto fail;
+  }
 
-  cm->above_context = (ENTROPY_CONTEXT *)vpx_calloc(
-      2 * mi_cols_aligned_to_sb(cm->mi_cols) * MAX_MB_PLANE,
-      sizeof(*cm->above_context));
-  if (!cm->above_context) goto fail;
+  if (cm->seg_map_alloc_size < cm->mi_rows * cm->mi_cols) {
+    // Create the segmentation map structure and set to 0.
+    free_seg_map(cm);
+    if (alloc_seg_map(cm, cm->mi_rows * cm->mi_cols))
+      goto fail;
+  }
 
-  cm->above_seg_context = (PARTITION_CONTEXT *)vpx_calloc(
-      mi_cols_aligned_to_sb(cm->mi_cols), sizeof(*cm->above_seg_context));
-  if (!cm->above_seg_context) goto fail;
+  if (cm->above_context_alloc_cols < cm->mi_cols) {
+    vpx_free(cm->above_context);
+    cm->above_context = (ENTROPY_CONTEXT *)vpx_calloc(
+        2 * mi_cols_aligned_to_sb(cm->mi_cols) * MAX_MB_PLANE,
+        sizeof(*cm->above_context));
+    if (!cm->above_context) goto fail;
+
+    vpx_free(cm->above_seg_context);
+    cm->above_seg_context = (PARTITION_CONTEXT *)vpx_calloc(
+        mi_cols_aligned_to_sb(cm->mi_cols), sizeof(*cm->above_seg_context));
+    if (!cm->above_seg_context) goto fail;
+    cm->above_context_alloc_cols = cm->mi_cols;
+  }
 
   return 0;