index-pack: smarter memory usage during delta resolution

There is no need to keep the base object data around after its last delta
has been resolved.  This also means that long delta chains with only one
delta per base won't grow the cache size unnecessarily as the base will
be freed before recursing down.

To make it easy, find_delta_children() is modified so the first and last
indices are initialized in all cases.

Signed-off-by: Nicolas Pitre <nico@cam.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

index-pack.c

@@ -221,17 +221,23 @@ static void bad_object(unsigned long offset, const char *format, ...)
 	die("pack has bad object at offset %lu: %s", offset, buf);
 }
 
+static void free_base_data(struct base_data *c)
+{
+	if (c->data) {
+		free(c->data);
+		c->data = NULL;
+		base_cache_used -= c->size;
+	}
+}
+
 static void prune_base_data(struct base_data *retain)
 {
 	struct base_data *b = base_cache;
 	for (b = base_cache;
 	     base_cache_used > delta_base_cache_limit && b;
 	     b = b->child) {
-		if (b->data && b != retain) {
-			free(b->data);
-			b->data = NULL;
-			base_cache_used -= b->size;
-		}
+		if (b->data && b != retain)
+			free_base_data(b);
 	}
 }
 
@@ -256,10 +262,7 @@ static void unlink_base_data(struct base_data *c)
 		base->child = NULL;
 	else
 		base_cache = NULL;
-	if (c->data) {
-		free(c->data);
-		base_cache_used -= c->size;
-	}
+	free_base_data(c);
 }
 
 static void *unpack_entry_data(unsigned long offset, unsigned long size)
@@ -409,22 +412,24 @@ static int find_delta(const union delta_base *base)
         return -first-1;
 }
 
-static int find_delta_children(const union delta_base *base,
-			       int *first_index, int *last_index)
+static void find_delta_children(const union delta_base *base,
+				int *first_index, int *last_index)
 {
 	int first = find_delta(base);
 	int last = first;
 	int end = nr_deltas - 1;
 
-	if (first < 0)
-		return -1;
+	if (first < 0) {
+		*first_index = 0;
+		*last_index = -1;
+		return;
+	}
 	while (first > 0 && !memcmp(&deltas[first - 1].base, base, UNION_BASE_SZ))
 		--first;
 	while (last < end && !memcmp(&deltas[last + 1].base, base, UNION_BASE_SZ))
 		++last;
 	*first_index = first;
 	*last_index = last;
-	return 0;
 }
 
 static void sha1_object(const void *data, unsigned long size,
@@ -529,7 +534,7 @@ static void resolve_delta(struct object_entry *delta_obj,
 static void find_unresolved_deltas(struct base_data *base,
 				   struct base_data *prev_base)
 {
-	int i, ref, ref_first, ref_last, ofs, ofs_first, ofs_last;
+	int i, ref_first, ref_last, ofs_first, ofs_last;
 
 	/*
 	 * This is a recursive function. Those brackets should help reducing
@@ -539,37 +544,37 @@ static void find_unresolved_deltas(struct base_data *base,
 		union delta_base base_spec;
 
 		hashcpy(base_spec.sha1, base->obj->idx.sha1);
-		ref = !find_delta_children(&base_spec, &ref_first, &ref_last);
+		find_delta_children(&base_spec, &ref_first, &ref_last);
 
 		memset(&base_spec, 0, sizeof(base_spec));
 		base_spec.offset = base->obj->idx.offset;
-		ofs = !find_delta_children(&base_spec, &ofs_first, &ofs_last);
+		find_delta_children(&base_spec, &ofs_first, &ofs_last);
 	}
 
-	if (!ref && !ofs)
+	if (ref_last == -1 && ofs_last == -1)
 		return;
 
 	link_base_data(prev_base, base);
 
-	if (ref) {
-		for (i = ref_first; i <= ref_last; i++) {
-			struct object_entry *child = objects + deltas[i].obj_no;
-			if (child->real_type == OBJ_REF_DELTA) {
-				struct base_data result;
-				resolve_delta(child, base, &result);
-				find_unresolved_deltas(&result, base);
-			}
+	for (i = ref_first; i <= ref_last; i++) {
+		struct object_entry *child = objects + deltas[i].obj_no;
+		if (child->real_type == OBJ_REF_DELTA) {
+			struct base_data result;
+			resolve_delta(child, base, &result);
+			if (i == ref_last && ofs_last == -1)
+				free_base_data(base);
+			find_unresolved_deltas(&result, base);
 		}
 	}
 
-	if (ofs) {
-		for (i = ofs_first; i <= ofs_last; i++) {
-			struct object_entry *child = objects + deltas[i].obj_no;
-			if (child->real_type == OBJ_OFS_DELTA) {
-				struct base_data result;
-				resolve_delta(child, base, &result);
-				find_unresolved_deltas(&result, base);
-			}
+	for (i = ofs_first; i <= ofs_last; i++) {
+		struct object_entry *child = objects + deltas[i].obj_no;
+		if (child->real_type == OBJ_OFS_DELTA) {
+			struct base_data result;
+			resolve_delta(child, base, &result);
+			if (i == ofs_last)
+				free_base_data(base);
+			find_unresolved_deltas(&result, base);
 		}
 	}