1 files changed, 211 insertions, 30 deletions

diff --git a/revision.c b/revision.c
index 7f7a8ab7cb..64b86ae91e 100644
--- a/revision.c
+++ b/revision.c
@@ -429,10 +429,100 @@ static int rev_same_tree_as_empty(struct rev_info *revs, struct commit *commit)
 	return retval >= 0 && (tree_difference == REV_TREE_SAME);
 }
 
+struct treesame_state {
+	unsigned int nparents;
+	unsigned char treesame[FLEX_ARRAY];
+};
+
+static struct treesame_state *initialise_treesame(struct rev_info *revs, struct commit *commit)
+{
+	unsigned n = commit_list_count(commit->parents);
+	struct treesame_state *st = xcalloc(1, sizeof(*st) + n);
+	st->nparents = n;
+	add_decoration(&revs->treesame, &commit->object, st);
+	return st;
+}
+
+/*
+ * Must be called immediately after removing the nth_parent from a commit's
+ * parent list, if we are maintaining the per-parent treesame[] decoration.
+ * This does not recalculate the master TREESAME flag - update_treesame()
+ * should be called to update it after a sequence of treesame[] modifications
+ * that may have affected it.
+ */
+static int compact_treesame(struct rev_info *revs, struct commit *commit, unsigned nth_parent)
+{
+	struct treesame_state *st;
+	int old_same;
+
+	if (!commit->parents) {
+		/*
+		 * Have just removed the only parent from a non-merge.
+		 * Different handling, as we lack decoration.
+		 */
+		if (nth_parent != 0)
+			die("compact_treesame %u", nth_parent);
+		old_same = !!(commit->object.flags & TREESAME);
+		if (rev_same_tree_as_empty(revs, commit))
+			commit->object.flags |= TREESAME;
+		else
+			commit->object.flags &= ~TREESAME;
+		return old_same;
+	}
+
+	st = lookup_decoration(&revs->treesame, &commit->object);
+	if (!st || nth_parent >= st->nparents)
+		die("compact_treesame %u", nth_parent);
+
+	old_same = st->treesame[nth_parent];
+	memmove(st->treesame + nth_parent,
+		st->treesame + nth_parent + 1,
+		st->nparents - nth_parent - 1);
+
+	/*
+	 * If we've just become a non-merge commit, update TREESAME
+	 * immediately, and remove the no-longer-needed decoration.
+	 * If still a merge, defer update until update_treesame().
+	 */
+	if (--st->nparents == 1) {
+		if (commit->parents->next)
+			die("compact_treesame parents mismatch");
+		if (st->treesame[0] && revs->dense)
+			commit->object.flags |= TREESAME;
+		else
+			commit->object.flags &= ~TREESAME;
+		free(add_decoration(&revs->treesame, &commit->object, NULL));
+	}
+
+	return old_same;
+}
+
+static unsigned update_treesame(struct rev_info *revs, struct commit *commit)
+{
+	if (commit->parents && commit->parents->next) {
+		unsigned n;
+		struct treesame_state *st;
+
+		st = lookup_decoration(&revs->treesame, &commit->object);
+		if (!st)
+			die("update_treesame %s", sha1_to_hex(commit->object.sha1));
+		commit->object.flags |= TREESAME;
+		for (n = 0; n < st->nparents; n++) {
+			if (!st->treesame[n]) {
+				commit->object.flags &= ~TREESAME;
+				break;
+			}
+		}
+	}
+
+	return commit->object.flags & TREESAME;
+}
+
 static void try_to_simplify_commit(struct rev_info *revs, struct commit *commit)
 {
 	struct commit_list **pp, *parent;
-	int tree_changed = 0, tree_same = 0, nth_parent = 0;
+	struct treesame_state *ts = NULL;
+	int tree_changed = 0, nth_parent;
 
 	/*
 	 * If we don't do pruning, everything is interesting
@@ -456,25 +546,43 @@ static void try_to_simplify_commit(struct rev_info *revs, struct commit *commit)
 	if (!revs->dense && !commit->parents->next)
 		return;
 
-	pp = &commit->parents;
-	while ((parent = *pp) != NULL) {
+	for (pp = &commit->parents, nth_parent = 0;
+	     (parent = *pp) != NULL;
+	     pp = &parent->next, nth_parent++) {
 		struct commit *p = parent->item;
 
-		/*
-		 * Do not compare with later parents when we care only about
-		 * the first parent chain, in order to avoid derailing the
-		 * traversal to follow a side branch that brought everything
-		 * in the path we are limited to by the pathspec.
-		 */
-		if (revs->first_parent_only && nth_parent++)
-			break;
+		if (nth_parent == 1) {
+			/*
+			 * This our second loop iteration - so we now know
+			 * we're dealing with a merge.
+			 *
+			 * Do not compare with later parents when we care only about
+			 * the first parent chain, in order to avoid derailing the
+			 * traversal to follow a side branch that brought everything
+			 * in the path we are limited to by the pathspec.
+			 */
+			if (revs->first_parent_only)
+				break;
+			/*
+			 * If this will remain a potentially-simplifiable
+			 * merge, remember per-parent treesame if needed.
+			 * Initialise the array with the comparison from our
+			 * first iteration.
+			 */
+			if (revs->treesame.name &&
+			    !revs->simplify_history &&
+			    !(commit->object.flags & UNINTERESTING)) {
+				ts = initialise_treesame(revs, commit);
+				if (!tree_changed)
+					ts->treesame[0] = 1;
+			}
+		}
 		if (parse_commit(p) < 0)
 			die("cannot simplify commit %s (because of %s)",
 			    sha1_to_hex(commit->object.sha1),
 			    sha1_to_hex(p->object.sha1));
 		switch (rev_compare_tree(revs, p, commit)) {
 		case REV_TREE_SAME:
-			tree_same = 1;
 			if (!revs->simplify_history || (p->object.flags & UNINTERESTING)) {
 				/* Even if a merge with an uninteresting
 				 * side branch brought the entire change
@@ -482,7 +590,8 @@ static void try_to_simplify_commit(struct rev_info *revs, struct commit *commit)
 				 * to lose the other branches of this
 				 * merge, so we just keep going.
 				 */
-				pp = &parent->next;
+				if (ts)
+					ts->treesame[nth_parent] = 1;
 				continue;
 			}
 			parent->next = NULL;
@@ -511,12 +620,11 @@ static void try_to_simplify_commit(struct rev_info *revs, struct commit *commit)
 		case REV_TREE_OLD:
 		case REV_TREE_DIFFERENT:
 			tree_changed = 1;
-			pp = &parent->next;
 			continue;
 		}
 		die("bad tree compare for commit %s", sha1_to_hex(commit->object.sha1));
 	}
-	if (tree_changed && !tree_same)
+	if (tree_changed)
 		return;
 	commit->object.flags |= TREESAME;
 }
@@ -1947,28 +2055,32 @@ static void add_child(struct rev_info *revs, struct commit *parent, struct commi
 	l->next = add_decoration(&revs->children, &parent->object, l);
 }
 
-static int remove_duplicate_parents(struct commit *commit)
+static int remove_duplicate_parents(struct rev_info *revs, struct commit *commit)
 {
+	struct treesame_state *ts = lookup_decoration(&revs->treesame, &commit->object);
 	struct commit_list **pp, *p;
 	int surviving_parents;
 
 	/* Examine existing parents while marking ones we have seen... */
 	pp = &commit->parents;
+	surviving_parents = 0;
 	while ((p = *pp) != NULL) {
 		struct commit *parent = p->item;
 		if (parent->object.flags & TMP_MARK) {
 			*pp = p->next;
+			if (ts)
+				compact_treesame(revs, commit, surviving_parents);
 			continue;
 		}
 		parent->object.flags |= TMP_MARK;
+		surviving_parents++;
 		pp = &p->next;
 	}
-	/* count them while clearing the temporary mark */
-	surviving_parents = 0;
+	/* clear the temporary mark */
 	for (p = commit->parents; p; p = p->next) {
 		p->item->object.flags &= ~TMP_MARK;
-		surviving_parents++;
 	}
+	/* no update_treesame() - removing duplicates can't affect TREESAME */
 	return surviving_parents;
 }
 
@@ -1988,6 +2100,70 @@ static struct merge_simplify_state *locate_simplify_state(struct rev_info *revs,
 	return st;
 }
 
+static int mark_redundant_parents(struct rev_info *revs, struct commit *commit)
+{
+	struct commit_list *h = reduce_heads(commit->parents);
+	int i = 0, marked = 0;
+	struct commit_list *po, *pn;
+
+	/* Want these for sanity-checking only */
+	int orig_cnt = commit_list_count(commit->parents);
+	int cnt = commit_list_count(h);
+
+	/*
+	 * Not ready to remove items yet, just mark them for now, based
+	 * on the output of reduce_heads(). reduce_heads outputs the reduced
+	 * set in its original order, so this isn't too hard.
+	 */
+	po = commit->parents;
+	pn = h;
+	while (po) {
+		if (pn && po->item == pn->item) {
+			pn = pn->next;
+			i++;
+		} else {
+			po->item->object.flags |= TMP_MARK;
+			marked++;
+		}
+		po=po->next;
+	}
+
+	if (i != cnt || cnt+marked != orig_cnt)
+		die("mark_redundant_parents %d %d %d %d", orig_cnt, cnt, i, marked);
+
+	free_commit_list(h);
+
+	return marked;
+}
+
+static int remove_marked_parents(struct rev_info *revs, struct commit *commit)
+{
+	struct commit_list **pp, *p;
+	int nth_parent, removed = 0;
+
+	pp = &commit->parents;
+	nth_parent = 0;
+	while ((p = *pp) != NULL) {
+		struct commit *parent = p->item;
+		if (parent->object.flags & TMP_MARK) {
+			parent->object.flags &= ~TMP_MARK;
+			*pp = p->next;
+			free(p);
+			removed++;
+			compact_treesame(revs, commit, nth_parent);
+			continue;
+		}
+		pp = &p->next;
+		nth_parent++;
+	}
+
+	/* Removing parents can only increase TREESAMEness */
+	if (removed && !(commit->object.flags & TREESAME))
+		update_treesame(revs, commit);
+
+	return nth_parent;
+}
+
 static struct commit_list **simplify_one(struct rev_info *revs, struct commit *commit, struct commit_list **tail)
 {
 	struct commit_list *p;
@@ -2032,7 +2208,9 @@ static struct commit_list **simplify_one(struct rev_info *revs, struct commit *c
 	}
 
 	/*
-	 * Rewrite our list of parents.
+	 * Rewrite our list of parents. Note that this cannot
+	 * affect our TREESAME flags in any way - a commit is
+	 * always TREESAME to its simplification.
 	 */
 	for (p = commit->parents; p; p = p->next) {
 		pst = locate_simplify_state(revs, p->item);
@@ -2044,31 +2222,30 @@ static struct commit_list **simplify_one(struct rev_info *revs, struct commit *c
 	if (revs->first_parent_only)
 		cnt = 1;
 	else
-		cnt = remove_duplicate_parents(commit);
+		cnt = remove_duplicate_parents(revs, commit);
 
 	/*
 	 * It is possible that we are a merge and one side branch
 	 * does not have any commit that touches the given paths;
-	 * in such a case, the immediate parents will be rewritten
-	 * to different commits.
+	 * in such a case, the immediate parent from that branch
+	 * will be rewritten to be the merge base.
 	 *
 	 *      o----X		X: the commit we are looking at;
 	 *     /    /		o: a commit that touches the paths;
 	 * ---o----'
 	 *
-	 * Further reduce the parents by removing redundant parents.
+	 * Detect and simplify this case.
 	 */
 	if (1 < cnt) {
-		struct commit_list *h = reduce_heads(commit->parents);
-		cnt = commit_list_count(h);
-		free_commit_list(commit->parents);
-		commit->parents = h;
+		int marked = mark_redundant_parents(revs, commit);
+		if (marked)
+			cnt = remove_marked_parents(revs, commit);
 	}
 
 	/*
 	 * A commit simplifies to itself if it is a root, if it is
 	 * UNINTERESTING, if it touches the given paths, or if it is a
-	 * merge and its parents simplifies to more than one commits
+	 * merge and its parents simplify to more than one commit
 	 * (the first two cases are already handled at the beginning of
 	 * this function).
 	 *
@@ -2176,6 +2353,10 @@ int prepare_revision_walk(struct rev_info *revs)
 	if (!revs->leak_pending)
 		free(list);
 
+	/* Signal whether we need per-parent treesame decoration */
+	if (revs->simplify_merges)
+		revs->treesame.name = "treesame";
+
 	if (revs->no_walk != REVISION_WALK_NO_WALK_UNSORTED)
 		commit_list_sort_by_date(&revs->commits);
 	if (revs->no_walk)
@@ -2235,7 +2416,7 @@ static int rewrite_parents(struct rev_info *revs, struct commit *commit)
 		}
 		pp = &parent->next;
 	}
-	remove_duplicate_parents(commit);
+	remove_duplicate_parents(revs, commit);
 	return 0;
 }