pack-objects: move tree_depth into 'struct packing_data'

This reduces the size of 'struct object_entry' and therefore
makes packing objects more efficient.

This also renames cmp_tree_depth() into tree_depth_compare(),
as it is more modern to have the name of the compare functions
end with "compare".

Helped-by: Jeff King <peff@peff.net>
Helped-by: Duy Nguyen <pclouds@gmail.com>
Signed-off-by: Christian Couder <chriscool@tuxfamily.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/pack-objects.c

@@ -2716,8 +2716,8 @@ static void show_object(struct object *obj, const char *name, void *data)
 			depth++;
 
 		ent = packlist_find(&to_pack, obj->oid.hash, NULL);
-		if (ent && depth > ent->tree_depth)
-			ent->tree_depth = depth;
+		if (ent && depth > oe_tree_depth(&to_pack, ent))
+			oe_set_tree_depth(&to_pack, ent, depth);
 	}
 }
 

delta-islands.c

@@ -224,17 +224,23 @@ static void mark_remote_island_1(struct remote_island *rl, int is_core_island)
 	island_counter++;
 }
 
-static int cmp_tree_depth(const void *va, const void *vb)
+struct tree_islands_todo {
+	struct object_entry *entry;
+	unsigned int depth;
+};
+
+static int tree_depth_compare(const void *a, const void *b)
 {
-	struct object_entry *a = *(struct object_entry **)va;
-	struct object_entry *b = *(struct object_entry **)vb;
-	return a->tree_depth - b->tree_depth;
+	const struct tree_islands_todo *todo_a = a;
+	const struct tree_islands_todo *todo_b = b;
+
+	return todo_a->depth - todo_b->depth;
 }
 
 void resolve_tree_islands(int progress, struct packing_data *to_pack)
 {
 	struct progress *progress_state = NULL;
-	struct object_entry **todo;
+	struct tree_islands_todo *todo;
 	int nr = 0;
 	int i;
 
@@ -250,16 +256,19 @@ void resolve_tree_islands(int progress, struct packing_data *to_pack)
 	 */
 	ALLOC_ARRAY(todo, to_pack->nr_objects);
 	for (i = 0; i < to_pack->nr_objects; i++) {
-		if (oe_type(&to_pack->objects[i]) == OBJ_TREE)
-			todo[nr++] = &to_pack->objects[i];
+		if (oe_type(&to_pack->objects[i]) == OBJ_TREE) {
+			todo[nr].entry = &to_pack->objects[i];
+			todo[nr].depth = oe_tree_depth(to_pack, &to_pack->objects[i]);
+			nr++;
+		}
 	}
-	QSORT(todo, nr, cmp_tree_depth);
+	QSORT(todo, nr, tree_depth_compare);
 
 	if (progress)
 		progress_state = start_progress(_("Propagating island marks"), nr);
 
 	for (i = 0; i < nr; i++) {
-		struct object_entry *ent = todo[i];
+		struct object_entry *ent = todo[i].entry;
 		struct island_bitmap *root_marks;
 		struct tree *tree;
 		struct tree_desc desc;

pack-objects.c

@@ -160,6 +160,9 @@ struct object_entry *packlist_alloc(struct packing_data *pdata,
 
 		if (!pdata->in_pack_by_idx)
 			REALLOC_ARRAY(pdata->in_pack, pdata->nr_alloc);
+
+		if (pdata->tree_depth)
+			REALLOC_ARRAY(pdata->tree_depth, pdata->nr_alloc);
 	}
 
 	new_entry = pdata->objects + pdata->nr_objects++;
@@ -175,5 +178,8 @@ struct object_entry *packlist_alloc(struct packing_data *pdata,
 	if (pdata->in_pack)
 		pdata->in_pack[pdata->nr_objects - 1] = NULL;
 
+	if (pdata->tree_depth)
+		pdata->tree_depth[pdata->nr_objects - 1] = 0;
+
 	return new_entry;
 }

pack-objects.h

@@ -101,7 +101,6 @@ struct object_entry {
 	unsigned no_try_delta:1;
 	unsigned in_pack_type:TYPE_BITS; /* could be delta */
 
-	unsigned int tree_depth; /* should be repositioned for packing? */
 	unsigned char layer;
 
 	unsigned preferred_base:1; /*
@@ -145,6 +144,9 @@ struct packing_data {
 	struct packed_git **in_pack;
 
 	uintmax_t oe_size_limit;
+
+	/* delta islands */
+	unsigned int *tree_depth;
 };
 
 void prepare_packing_data(struct packing_data *pdata);
@@ -350,4 +352,21 @@ static inline void oe_set_delta_size(struct packing_data *pack,
 		    "where delta size is the same as entry size");
 }
 
+static inline unsigned int oe_tree_depth(struct packing_data *pack,
+					 struct object_entry *e)
+{
+	if (!pack->tree_depth)
+		return 0;
+	return pack->tree_depth[e - pack->objects];
+}
+
+static inline void oe_set_tree_depth(struct packing_data *pack,
+				     struct object_entry *e,
+				     unsigned int tree_depth)
+{
+	if (!pack->tree_depth)
+		ALLOC_ARRAY(pack->tree_depth, pack->nr_objects);
+	pack->tree_depth[e - pack->objects] = tree_depth;
+}
+
 #endif