don't load objects needlessly when repacking

If no delta is attempted on some objects then it is useless to load them
in memory, neither create any delta index for them.  The best thing to
do is therefore to load and index them only when really needed.

Signed-off-by: Nicolas Pitre <nico@cam.org>
Signed-off-by: Junio C Hamano <junkio@cox.net>

pack-objects.c

diff --git a/pack-objects.c b/pack-objects.c
index 47da33b..b486ea5 100644
--- a/pack-objects.c
+++ b/pack-objects.c
@@ -970,11 +970,12 @@
  * one.
  */
 static int try_delta(struct unpacked *trg, struct unpacked *src,
-		     struct delta_index *src_index, unsigned max_depth)
+		     unsigned max_depth)
 {
 	struct object_entry *trg_entry = trg->entry;
 	struct object_entry *src_entry = src->entry;
-	unsigned long size, src_size, delta_size, sizediff, max_size;
+	unsigned long trg_size, src_size, delta_size, sizediff, max_size, sz;
+	char type[10];
 	void *delta_buf;
 
 	/* Don't bother doing diffs between different types */
@@ -1009,19 +1010,38 @@
 		return 0;
 
 	/* Now some size filtering heuristics. */
-	size = trg_entry->size;
-	max_size = size/2 - 20;
+	trg_size = trg_entry->size;
+	max_size = trg_size/2 - 20;
 	max_size = max_size * (max_depth - src_entry->depth) / max_depth;
 	if (max_size == 0)
 		return 0;
 	if (trg_entry->delta && trg_entry->delta_size <= max_size)
 		max_size = trg_entry->delta_size-1;
 	src_size = src_entry->size;
-	sizediff = src_size < size ? size - src_size : 0;
+	sizediff = src_size < trg_size ? trg_size - src_size : 0;
 	if (sizediff >= max_size)
 		return 0;
 
-	delta_buf = create_delta(src_index, trg->data, size, &delta_size, max_size);
+	/* Load data if not already done */
+	if (!trg->data) {
+		trg->data = read_sha1_file(trg_entry->sha1, type, &sz);
+		if (sz != trg_size)
+			die("object %s inconsistent object length (%lu vs %lu)",
+			    sha1_to_hex(trg_entry->sha1), sz, trg_size);
+	}
+	if (!src->data) {
+		src->data = read_sha1_file(src_entry->sha1, type, &sz);
+		if (sz != src_size)
+			die("object %s inconsistent object length (%lu vs %lu)",
+			    sha1_to_hex(src_entry->sha1), sz, src_size);
+	}
+	if (!src->index) {
+		src->index = create_delta_index(src->data, src_size);
+		if (!src->index)
+			die("out of memory");
+	}
+
+	delta_buf = create_delta(src->index, trg->data, trg_size, &delta_size, max_size);
 	if (!delta_buf)
 		return 0;
 
@@ -1054,8 +1074,6 @@
 	while (--i >= 0) {
 		struct object_entry *entry = list[i];
 		struct unpacked *n = array + idx;
-		unsigned long size;
-		char type[10];
 		int j;
 
 		if (!entry->preferred_base)
@@ -1082,11 +1100,8 @@
 		free_delta_index(n->index);
 		n->index = NULL;
 		free(n->data);
+		n->data = NULL;
 		n->entry = entry;
-		n->data = read_sha1_file(entry->sha1, type, &size);
-		if (size != entry->size)
-			die("object %s inconsistent object length (%lu vs %lu)",
-			    sha1_to_hex(entry->sha1), size, entry->size);
 
 		j = window;
 		while (--j > 0) {
@@ -1097,7 +1112,7 @@
 			m = array + other_idx;
 			if (!m->entry)
 				break;
-			if (try_delta(n, m, m->index, depth) < 0)
+			if (try_delta(n, m, depth) < 0)
 				break;
 		}
 		/* if we made n a delta, and if n is already at max
@@ -1107,10 +1122,6 @@
 		if (entry->delta && depth <= entry->depth)
 			continue;
 
-		n->index = create_delta_index(n->data, size);
-		if (!n->index)
-			die("out of memory");
-
 		idx++;
 		if (idx >= window)
 			idx = 0;