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;

	/*
	 * If we don't do pruning, everything is interesting
	 */
	if (!revs->prune)
		return;

	if (!commit->tree)
		return;

	if (!commit->parents) {
		if (rev_same_tree_as_empty(revs, commit->tree))
			commit->object.flags |= TREESAME;
		return;
	}

	/*
	 * Normal non-merge commit? If we don't want to make the
	 * history dense, we consider it always to be a change..
	 */
	if (!revs->dense && !commit->parents->next)
		return;

	pp = &commit->parents;
	while ((parent = *pp) != NULL) {
		struct commit *p = parent->item;

		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->tree, commit->tree)) {
		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
				 * we are interested in, we do not want
				 * to lose the other branches of this
				 * merge, so we just keep going.
				 */
				pp = &parent->next;
				continue;
			}
			parent->next = NULL;
			commit->parents = parent;
			commit->object.flags |= TREESAME;
			return;

		case REV_TREE_NEW:
			if (revs->remove_empty_trees &&
			    rev_same_tree_as_empty(revs, p->tree)) {
				/* We are adding all the specified
				 * paths from this parent, so the
				 * history beyond this parent is not
				 * interesting.  Remove its parents
				 * (they are grandparents for us).
				 * IOW, we pretend this parent is a
				 * "root" commit.
				 */
				if (parse_commit(p) < 0)
					die("cannot simplify commit %s (invalid %s)",
					    sha1_to_hex(commit->object.sha1),
					    sha1_to_hex(p->object.sha1));
				p->parents = NULL;
			}
		/* fallthrough */
		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)
		return;
	commit->object.flags |= TREESAME;
}
Unknown