Do not ask for objects known to be complete.

On top of optimization by Linus not to ask refs that already match, we
can walk our refs and not issue "want" for things that are known to be
reachable from them.

Signed-off-by: Junio C Hamano <junkio@cox.net>

fetch-pack.c

@@ -1,6 +1,9 @@
 #include "cache.h"
 #include "refs.h"
 #include "pkt-line.h"
+#include "commit.h"
+#include "tag.h"
+#include <time.h>
 #include <sys/wait.h>
 
 static int quiet;
@@ -78,16 +81,73 @@ static int find_common(int fd[2], unsigned char *result_sha1,
 	return retval;
 }
 
+#define COMPLETE	(1U << 0)
+static struct commit_list *complete = NULL;
+
+static int mark_complete(const char *path, const unsigned char *sha1)
+{
+	struct object *o = parse_object(sha1);
+
+	while (o && o->type == tag_type) {
+		o->flags |= COMPLETE;
+		o = parse_object(((struct tag *)o)->tagged->sha1);
+	}
+	if (o->type == commit_type) {
+		struct commit *commit = (struct commit *)o;
+		commit->object.flags |= COMPLETE;
+		insert_by_date(commit, &complete);
+	}
+	return 0;
+}
+
+static void mark_recent_complete_commits(unsigned long cutoff)
+{
+	while (complete && cutoff <= complete->item->date) {
+		if (verbose)
+			fprintf(stderr, "Marking %s as complete\n",
+				sha1_to_hex(complete->item->object.sha1));
+		pop_most_recent_commit(&complete, COMPLETE);
+	}
+}
+
 static int everything_local(struct ref *refs)
 {
+	struct ref *ref;
 	int retval;
+	unsigned long cutoff = 0;
+
+	track_object_refs = 0;
+	save_commit_buffer = 0;
+
+	for (ref = refs; ref; ref = ref->next) {
+		struct object *o;
+
+		o = parse_object(ref->old_sha1);
+		if (!o)
+			continue;
+
+		/* We already have it -- which may mean that we were
+		 * in sync with the other side at some time after
+		 * that (it is OK if we guess wrong here).
+		 */
+		if (o->type == commit_type) {
+			struct commit *commit = (struct commit *)o;
+			if (!cutoff || cutoff < commit->date)
+				cutoff = commit->date;
+		}
+	}
+
+	for_each_ref(mark_complete);
+	if (cutoff)
+		mark_recent_complete_commits(cutoff);
 
 	for (retval = 1; refs ; refs = refs->next) {
 		const unsigned char *remote = refs->old_sha1;
 		unsigned char local[20];
+		struct object *o;
 
-		if (read_ref(git_path("%s", refs->name), local) < 0 ||
+		o = parse_object(remote);
-		    memcmp(remote, local, 20)) {
+		if (!o || !(o->flags & COMPLETE)) {
 			retval = 0;
 			if (!verbose)
 				continue;