reduce_heads(): reimplement on top of remove_redundant()

This is used by "git merge" and "git merge-base --independent" but
used to use a similar N*(N-1) traversals to reject commits that are
ancestors of other commits.

Reimplement it on top of remove_redundant().  Note that the callers
of this function are allowed to pass the same commit more than once,
but remove_redundant() is designed to be fed each commit only once.
The function removes duplicates before calling remove_redundant().

Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/commit.c b/commit.c
index 2ff5061c122300c55e4499c0067ad936266f7ee0..69af37014fd07d30408c959f40357493ca21e7d4 100644 (file)
--- a/commit.c
+++ b/commit.c
@@ -842,51 +842,31 @@ struct commit_list *reduce_heads(struct commit_list *heads)
 {
        struct commit_list *p;
        struct commit_list *result = NULL, **tail = &result;
-       struct commit **other;
-       size_t num_head, num_other;
+       struct commit **array;
+       int num_head, i;
 
        if (!heads)
                return NULL;
 
-       /* Avoid unnecessary reallocations */
-       for (p = heads, num_head = 0; p; p = p->next)
-               num_head++;
-       other = xcalloc(sizeof(*other), num_head);
-
-       /* For each commit, see if it can be reached by others */
-       for (p = heads; p; p = p->next) {
-               struct commit_list *q, *base;
-
-               /* Do we already have this in the result? */
-               for (q = result; q; q = q->next)
-                       if (p->item == q->item)
-                               break;
-               if (q)
+       /* Uniquify */
+       for (p = heads; p; p = p->next)
+               p->item->object.flags &= ~STALE;
+       for (p = heads, num_head = 0; p; p = p->next) {
+               if (p->item->object.flags & STALE)
                        continue;
-
-               num_other = 0;
-               for (q = heads; q; q = q->next) {
-                       if (p->item == q->item)
-                               continue;
-                       other[num_other++] = q->item;
+               p->item->object.flags |= STALE;
+               num_head++;
+       }
+       array = xcalloc(sizeof(*array), num_head);
+       for (p = heads, i = 0; p; p = p->next) {
+               if (p->item->object.flags & STALE) {
+                       array[i++] = p->item;
+                       p->item->object.flags &= ~STALE;
                }
-               if (num_other)
-                       base = get_merge_bases_many(p->item, num_other, other, 1);
-               else
-                       base = NULL;
-               /*
-                * If p->item does not have anything common with other
-                * commits, there won't be any merge base.  If it is
-                * reachable from some of the others, p->item will be
-                * the merge base.  If its history is connected with
-                * others, but p->item is not reachable by others, we
-                * will get something other than p->item back.
-                */
-               if (!base || (base->item != p->item))
-                       tail = &(commit_list_insert(p->item, tail)->next);
-               free_commit_list(base);
        }
-       free(other);
+       num_head = remove_redundant(array, num_head);
+       for (i = 0; i < num_head; i++)
+               tail = &commit_list_insert(array[i], tail)->next;
        return result;
 }