revision: parse "git log -<count>" more carefully

[git/git-svn.git] / revision.c

#include "cache.h"
#include "tag.h"
#include "blob.h"
#include "tree.h"
#include "commit.h"
#include "diff.h"
#include "refs.h"
#include "revision.h"
#include "graph.h"
#include "grep.h"
#include "reflog-walk.h"
#include "patch-ids.h"
#include "decorate.h"
#include "log-tree.h"
#include "string-list.h"
#include "line-log.h"
#include "mailmap.h"
#include "commit-slab.h"

volatile show_early_output_fn_t show_early_output;

char *path_name(const struct name_path *path, const char *name)
{
        const struct name_path *p;
        char *n, *m;
        int nlen = strlen(name);
        int len = nlen + 1;

        for (p = path; p; p = p->up) {
                if (p->elem_len)
                        len += p->elem_len + 1;
        }
        n = xmalloc(len);
        m = n + len - (nlen + 1);
        strcpy(m, name);
        for (p = path; p; p = p->up) {
                if (p->elem_len) {
                        m -= p->elem_len + 1;
                        memcpy(m, p->elem, p->elem_len);
                        m[p->elem_len] = '/';
                }
        }
        return n;
}

static int show_path_component_truncated(FILE *out, const char *name, int len)
{
        int cnt;
        for (cnt = 0; cnt < len; cnt++) {
                int ch = name[cnt];
                if (!ch || ch == '\n')
                        return -1;
                fputc(ch, out);
        }
        return len;
}

static int show_path_truncated(FILE *out, const struct name_path *path)
{
        int emitted, ours;

        if (!path)
                return 0;
        emitted = show_path_truncated(out, path->up);
        if (emitted < 0)
                return emitted;
        if (emitted)
                fputc('/', out);
        ours = show_path_component_truncated(out, path->elem, path->elem_len);
        if (ours < 0)
                return ours;
        return ours || emitted;
}

void show_object_with_name(FILE *out, struct object *obj,
                           const struct name_path *path, const char *component)
{
        struct name_path leaf;
        leaf.up = (struct name_path *)path;
        leaf.elem = component;
        leaf.elem_len = strlen(component);

        fprintf(out, "%s ", sha1_to_hex(obj->sha1));
        show_path_truncated(out, &leaf);
        fputc('\n', out);
}

void add_object(struct object *obj,
                struct object_array *p,
                struct name_path *path,
                const char *name)
{
        char *pn = path_name(path, name);
        add_object_array(obj, pn, p);
        free(pn);
}

static void mark_blob_uninteresting(struct blob *blob)
{
        if (!blob)
                return;
        if (blob->object.flags & UNINTERESTING)
                return;
        blob->object.flags |= UNINTERESTING;
}

static void mark_tree_contents_uninteresting(struct tree *tree)
{
        struct tree_desc desc;
        struct name_entry entry;
        struct object *obj = &tree->object;

        if (!has_sha1_file(obj->sha1))
                return;
        if (parse_tree(tree) < 0)
                die("bad tree %s", sha1_to_hex(obj->sha1));

        init_tree_desc(&desc, tree->buffer, tree->size);
        while (tree_entry(&desc, &entry)) {
                switch (object_type(entry.mode)) {
                case OBJ_TREE:
                        mark_tree_uninteresting(lookup_tree(entry.sha1));
                        break;
                case OBJ_BLOB:
                        mark_blob_uninteresting(lookup_blob(entry.sha1));
                        break;
                default:
                        /* Subproject commit - not in this repository */
                        break;
                }
        }

        /*
         * We don't care about the tree any more
         * after it has been marked uninteresting.
         */
        free_tree_buffer(tree);
}

void mark_tree_uninteresting(struct tree *tree)
{
        struct object *obj = &tree->object;

        if (!tree)
                return;
        if (obj->flags & UNINTERESTING)
                return;
        obj->flags |= UNINTERESTING;
        mark_tree_contents_uninteresting(tree);
}

void mark_parents_uninteresting(struct commit *commit)
{
        struct commit_list *parents = NULL, *l;

        for (l = commit->parents; l; l = l->next)
                commit_list_insert(l->item, &parents);

        while (parents) {
                struct commit *commit = parents->item;
                l = parents;
                parents = parents->next;
                free(l);

                while (commit) {
                        /*
                         * A missing commit is ok iff its parent is marked
                         * uninteresting.
                         *
                         * We just mark such a thing parsed, so that when
                         * it is popped next time around, we won't be trying
                         * to parse it and get an error.
                         */
                        if (!has_sha1_file(commit->object.sha1))
                                commit->object.parsed = 1;

                        if (commit->object.flags & UNINTERESTING)
                                break;

                        commit->object.flags |= UNINTERESTING;

                        /*
                         * Normally we haven't parsed the parent
                         * yet, so we won't have a parent of a parent
                         * here. However, it may turn out that we've
                         * reached this commit some other way (where it
                         * wasn't uninteresting), in which case we need
                         * to mark its parents recursively too..
                         */
                        if (!commit->parents)
                                break;

                        for (l = commit->parents->next; l; l = l->next)
                                commit_list_insert(l->item, &parents);
                        commit = commit->parents->item;
                }
        }
}

static void add_pending_object_with_mode(struct rev_info *revs,
                                         struct object *obj,
                                         const char *name, unsigned mode)
{
        if (!obj)
                return;
        if (revs->no_walk && (obj->flags & UNINTERESTING))
                revs->no_walk = 0;
        if (revs->reflog_info && obj->type == OBJ_COMMIT) {
                struct strbuf buf = STRBUF_INIT;
                int len = interpret_branch_name(name, 0, &buf);
                int st;

                if (0 < len && name[len] && buf.len)
                        strbuf_addstr(&buf, name + len);
                st = add_reflog_for_walk(revs->reflog_info,
                                         (struct commit *)obj,
                                         buf.buf[0] ? buf.buf: name);
                strbuf_release(&buf);
                if (st)
                        return;
        }
        add_object_array_with_mode(obj, name, &revs->pending, mode);
}

void add_pending_object(struct rev_info *revs,
                        struct object *obj, const char *name)
{
        add_pending_object_with_mode(revs, obj, name, S_IFINVALID);
}

void add_head_to_pending(struct rev_info *revs)
{
        unsigned char sha1[20];
        struct object *obj;
        if (get_sha1("HEAD", sha1))
                return;
        obj = parse_object(sha1);
        if (!obj)
                return;
        add_pending_object(revs, obj, "HEAD");
}

static struct object *get_reference(struct rev_info *revs, const char *name,
                                    const unsigned char *sha1,
                                    unsigned int flags)
{
        struct object *object;

        object = parse_object(sha1);
        if (!object) {
                if (revs->ignore_missing)
                        return object;
                die("bad object %s", name);
        }
        object->flags |= flags;
        return object;
}

void add_pending_sha1(struct rev_info *revs, const char *name,
                      const unsigned char *sha1, unsigned int flags)
{
        struct object *object = get_reference(revs, name, sha1, flags);
        add_pending_object(revs, object, name);
}

static struct commit *handle_commit(struct rev_info *revs,
                                    struct object *object, const char *name)
{
        unsigned long flags = object->flags;

        /*
         * Tag object? Look what it points to..
         */
        while (object->type == OBJ_TAG) {
                struct tag *tag = (struct tag *) object;
                if (revs->tag_objects && !(flags & UNINTERESTING))
                        add_pending_object(revs, object, tag->tag);
                if (!tag->tagged)
                        die("bad tag");
                object = parse_object(tag->tagged->sha1);
                if (!object) {
                        if (flags & UNINTERESTING)
                                return NULL;
                        die("bad object %s", sha1_to_hex(tag->tagged->sha1));
                }
                object->flags |= flags;
        }

        /*
         * Commit object? Just return it, we'll do all the complex
         * reachability crud.
         */
        if (object->type == OBJ_COMMIT) {
                struct commit *commit = (struct commit *)object;
                if (parse_commit(commit) < 0)
                        die("unable to parse commit %s", name);
                if (flags & UNINTERESTING) {
                        mark_parents_uninteresting(commit);
                        revs->limited = 1;
                }
                if (revs->show_source && !commit->util)
                        commit->util = (void *) name;
                return commit;
        }

        /*
         * Tree object? Either mark it uninteresting, or add it
         * to the list of objects to look at later..
         */
        if (object->type == OBJ_TREE) {
                struct tree *tree = (struct tree *)object;
                if (!revs->tree_objects)
                        return NULL;
                if (flags & UNINTERESTING) {
                        mark_tree_contents_uninteresting(tree);
                        return NULL;
                }
                add_pending_object(revs, object, "");
                return NULL;
        }

        /*
         * Blob object? You know the drill by now..
         */
        if (object->type == OBJ_BLOB) {
                if (!revs->blob_objects)
                        return NULL;
                if (flags & UNINTERESTING)
                        return NULL;
                add_pending_object(revs, object, "");
                return NULL;
        }
        die("%s is unknown object", name);
}

static int everybody_uninteresting(struct commit_list *orig)
{
        struct commit_list *list = orig;
        while (list) {
                struct commit *commit = list->item;
                list = list->next;
                if (commit->object.flags & UNINTERESTING)
                        continue;
                return 0;
        }
        return 1;
}

/*
 * A definition of "relevant" commit that we can use to simplify limited graphs
 * by eliminating side branches.
 *
 * A "relevant" commit is one that is !UNINTERESTING (ie we are including it
 * in our list), or that is a specified BOTTOM commit. Then after computing
 * a limited list, during processing we can generally ignore boundary merges
 * coming from outside the graph, (ie from irrelevant parents), and treat
 * those merges as if they were single-parent. TREESAME is defined to consider
 * only relevant parents, if any. If we are TREESAME to our on-graph parents,
 * we don't care if we were !TREESAME to non-graph parents.
 *
 * Treating bottom commits as relevant ensures that a limited graph's
 * connection to the actual bottom commit is not viewed as a side branch, but
 * treated as part of the graph. For example:
 *
 *   ....Z...A---X---o---o---B
 *        .     /
 *         W---Y
 *
 * When computing "A..B", the A-X connection is at least as important as
 * Y-X, despite A being flagged UNINTERESTING.
 *
 * And when computing --ancestry-path "A..B", the A-X connection is more
 * important than Y-X, despite both A and Y being flagged UNINTERESTING.
 */
static inline int relevant_commit(struct commit *commit)
{
        return (commit->object.flags & (UNINTERESTING | BOTTOM)) != UNINTERESTING;
}

/*
 * Return a single relevant commit from a parent list. If we are a TREESAME
 * commit, and this selects one of our parents, then we can safely simplify to
 * that parent.
 */
static struct commit *one_relevant_parent(const struct rev_info *revs,
                                          struct commit_list *orig)
{
        struct commit_list *list = orig;
        struct commit *relevant = NULL;

        if (!orig)
                return NULL;

        /*
         * For 1-parent commits, or if first-parent-only, then return that
         * first parent (even if not "relevant" by the above definition).
         * TREESAME will have been set purely on that parent.
         */
        if (revs->first_parent_only || !orig->next)
                return orig->item;

        /*
         * For multi-parent commits, identify a sole relevant parent, if any.
         * If we have only one relevant parent, then TREESAME will be set purely
         * with regard to that parent, and we can simplify accordingly.
         *
         * If we have more than one relevant parent, or no relevant parents
         * (and multiple irrelevant ones), then we can't select a parent here
         * and return NULL.
         */
        while (list) {
                struct commit *commit = list->item;
                list = list->next;
                if (relevant_commit(commit)) {
                        if (relevant)
                                return NULL;
                        relevant = commit;
                }
        }
        return relevant;
}

/*
 * The goal is to get REV_TREE_NEW as the result only if the
 * diff consists of all '+' (and no other changes), REV_TREE_OLD
 * if the whole diff is removal of old data, and otherwise
 * REV_TREE_DIFFERENT (of course if the trees are the same we
 * want REV_TREE_SAME).
 * That means that once we get to REV_TREE_DIFFERENT, we do not
 * have to look any further.
 */
static int tree_difference = REV_TREE_SAME;

static void file_add_remove(struct diff_options *options,
                    int addremove, unsigned mode,
                    const unsigned char *sha1,
                    int sha1_valid,
                    const char *fullpath, unsigned dirty_submodule)
{
        int diff = addremove == '+' ? REV_TREE_NEW : REV_TREE_OLD;

        tree_difference |= diff;
        if (tree_difference == REV_TREE_DIFFERENT)
                DIFF_OPT_SET(options, HAS_CHANGES);
}

static void file_change(struct diff_options *options,
                 unsigned old_mode, unsigned new_mode,
                 const unsigned char *old_sha1,
                 const unsigned char *new_sha1,
                 int old_sha1_valid, int new_sha1_valid,
                 const char *fullpath,
                 unsigned old_dirty_submodule, unsigned new_dirty_submodule)
{
        tree_difference = REV_TREE_DIFFERENT;
        DIFF_OPT_SET(options, HAS_CHANGES);
}

static int rev_compare_tree(struct rev_info *revs,
                            struct commit *parent, struct commit *commit)
{
        struct tree *t1 = parent->tree;
        struct tree *t2 = commit->tree;

        if (!t1)
                return REV_TREE_NEW;
        if (!t2)
                return REV_TREE_OLD;

        if (revs->simplify_by_decoration) {
                /*
                 * If we are simplifying by decoration, then the commit
                 * is worth showing if it has a tag pointing at it.
                 */
                if (lookup_decoration(&name_decoration, &commit->object))
                        return REV_TREE_DIFFERENT;
                /*
                 * A commit that is not pointed by a tag is uninteresting
                 * if we are not limited by path.  This means that you will
                 * see the usual "commits that touch the paths" plus any
                 * tagged commit by specifying both --simplify-by-decoration
                 * and pathspec.
                 */
                if (!revs->prune_data.nr)
                        return REV_TREE_SAME;
        }

        tree_difference = REV_TREE_SAME;
        DIFF_OPT_CLR(&revs->pruning, HAS_CHANGES);
        if (diff_tree_sha1(t1->object.sha1, t2->object.sha1, "",
                           &revs->pruning) < 0)
                return REV_TREE_DIFFERENT;
        return tree_difference;
}

static int rev_same_tree_as_empty(struct rev_info *revs, struct commit *commit)
{
        int retval;
        void *tree;
        unsigned long size;
        struct tree_desc empty, real;
        struct tree *t1 = commit->tree;

        if (!t1)
                return 0;

        tree = read_object_with_reference(t1->object.sha1, tree_type, &size, NULL);
        if (!tree)
                return 0;
        init_tree_desc(&real, tree, size);
        init_tree_desc(&empty, "", 0);

        tree_difference = REV_TREE_SAME;
        DIFF_OPT_CLR(&revs->pruning, HAS_CHANGES);
        retval = diff_tree(&empty, &real, "", &revs->pruning);
        free(tree);

        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;
                struct commit_list *p;
                unsigned relevant_parents;
                unsigned relevant_change, irrelevant_change;

                st = lookup_decoration(&revs->treesame, &commit->object);
                if (!st)
                        die("update_treesame %s", sha1_to_hex(commit->object.sha1));
                relevant_parents = 0;
                relevant_change = irrelevant_change = 0;
                for (p = commit->parents, n = 0; p; n++, p = p->next) {
                        if (relevant_commit(p->item)) {
                                relevant_change |= !st->treesame[n];
                                relevant_parents++;
                        } else
                                irrelevant_change |= !st->treesame[n];
                }
                if (relevant_parents ? relevant_change : irrelevant_change)
                        commit->object.flags &= ~TREESAME;
                else
                        commit->object.flags |= TREESAME;
        }

        return commit->object.flags & TREESAME;
}

static inline int limiting_can_increase_treesame(const struct rev_info *revs)
{
        /*
         * TREESAME is irrelevant unless prune && dense;
         * if simplify_history is set, we can't have a mixture of TREESAME and
         *    !TREESAME INTERESTING parents (and we don't have treesame[]
         *    decoration anyway);
         * if first_parent_only is set, then the TREESAME flag is locked
         *    against the first parent (and again we lack treesame[] decoration).
         */
        return revs->prune && revs->dense &&
               !revs->simplify_history &&
               !revs->first_parent_only;
}

static void try_to_simplify_commit(struct rev_info *revs, struct commit *commit)
{
        struct commit_list **pp, *parent;
        struct treesame_state *ts = NULL;
        int relevant_change = 0, irrelevant_change = 0;
        int relevant_parents, nth_parent;

        /*
         * 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))
                        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;

        for (pp = &commit->parents, nth_parent = 0, relevant_parents = 0;
             (parent = *pp) != NULL;
             pp = &parent->next, nth_parent++) {
                struct commit *p = parent->item;
                if (relevant_commit(p))
                        relevant_parents++;

                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 (!(irrelevant_change || relevant_change))
                                        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:
                        if (!revs->simplify_history || !relevant_commit(p)) {
                                /* 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.
                                 */
                                if (ts)
                                        ts->treesame[nth_parent] = 1;
                                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)) {
                                /* 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_OLD:
                case REV_TREE_DIFFERENT:
                        if (relevant_commit(p))
                                relevant_change = 1;
                        else
                                irrelevant_change = 1;
                        continue;
                }
                die("bad tree compare for commit %s", sha1_to_hex(commit->object.sha1));
        }

        /*
         * TREESAME is straightforward for single-parent commits. For merge
         * commits, it is most useful to define it so that "irrelevant"
         * parents cannot make us !TREESAME - if we have any relevant
         * parents, then we only consider TREESAMEness with respect to them,
         * allowing irrelevant merges from uninteresting branches to be
         * simplified away. Only if we have only irrelevant parents do we
         * base TREESAME on them. Note that this logic is replicated in
         * update_treesame, which should be kept in sync.
         */
        if (relevant_parents ? !relevant_change : !irrelevant_change)
                commit->object.flags |= TREESAME;
}

static void commit_list_insert_by_date_cached(struct commit *p, struct commit_list **head,
                    struct commit_list *cached_base, struct commit_list **cache)
{
        struct commit_list *new_entry;

        if (cached_base && p->date < cached_base->item->date)
                new_entry = commit_list_insert_by_date(p, &cached_base->next);
        else
                new_entry = commit_list_insert_by_date(p, head);

        if (cache && (!*cache || p->date < (*cache)->item->date))
                *cache = new_entry;
}

static int add_parents_to_list(struct rev_info *revs, struct commit *commit,
                    struct commit_list **list, struct commit_list **cache_ptr)
{
        struct commit_list *parent = commit->parents;
        unsigned left_flag;
        struct commit_list *cached_base = cache_ptr ? *cache_ptr : NULL;

        if (commit->object.flags & ADDED)
                return 0;
        commit->object.flags |= ADDED;

        /*
         * If the commit is uninteresting, don't try to
         * prune parents - we want the maximal uninteresting
         * set.
         *
         * Normally we haven't parsed the parent
         * yet, so we won't have a parent of a parent
         * here. However, it may turn out that we've
         * reached this commit some other way (where it
         * wasn't uninteresting), in which case we need
         * to mark its parents recursively too..
         */
        if (commit->object.flags & UNINTERESTING) {
                while (parent) {
                        struct commit *p = parent->item;
                        parent = parent->next;
                        if (p)
                                p->object.flags |= UNINTERESTING;
                        if (parse_commit(p) < 0)
                                continue;
                        if (p->parents)
                                mark_parents_uninteresting(p);
                        if (p->object.flags & SEEN)
                                continue;
                        p->object.flags |= SEEN;
                        commit_list_insert_by_date_cached(p, list, cached_base, cache_ptr);
                }
                return 0;
        }

        /*
         * Ok, the commit wasn't uninteresting. Try to
         * simplify the commit history and find the parent
         * that has no differences in the path set if one exists.
         */
        try_to_simplify_commit(revs, commit);

        if (revs->no_walk)
                return 0;

        left_flag = (commit->object.flags & SYMMETRIC_LEFT);

        for (parent = commit->parents; parent; parent = parent->next) {
                struct commit *p = parent->item;

                if (parse_commit(p) < 0)
                        return -1;
                if (revs->show_source && !p->util)
                        p->util = commit->util;
                p->object.flags |= left_flag;
                if (!(p->object.flags & SEEN)) {
                        p->object.flags |= SEEN;
                        commit_list_insert_by_date_cached(p, list, cached_base, cache_ptr);
                }
                if (revs->first_parent_only)
                        break;
        }
        return 0;
}

static void cherry_pick_list(struct commit_list *list, struct rev_info *revs)
{
        struct commit_list *p;
        int left_count = 0, right_count = 0;
        int left_first;
        struct patch_ids ids;
        unsigned cherry_flag;

        /* First count the commits on the left and on the right */
        for (p = list; p; p = p->next) {
                struct commit *commit = p->item;
                unsigned flags = commit->object.flags;
                if (flags & BOUNDARY)
                        ;
                else if (flags & SYMMETRIC_LEFT)
                        left_count++;
                else
                        right_count++;
        }

        if (!left_count || !right_count)
                return;

        left_first = left_count < right_count;
        init_patch_ids(&ids);
        ids.diffopts.pathspec = revs->diffopt.pathspec;

        /* Compute patch-ids for one side */
        for (p = list; p; p = p->next) {
                struct commit *commit = p->item;
                unsigned flags = commit->object.flags;

                if (flags & BOUNDARY)
                        continue;
                /*
                 * If we have fewer left, left_first is set and we omit
                 * commits on the right branch in this loop.  If we have
                 * fewer right, we skip the left ones.
                 */
                if (left_first != !!(flags & SYMMETRIC_LEFT))
                        continue;
                commit->util = add_commit_patch_id(commit, &ids);
        }

        /* either cherry_mark or cherry_pick are true */
        cherry_flag = revs->cherry_mark ? PATCHSAME : SHOWN;

        /* Check the other side */
        for (p = list; p; p = p->next) {
                struct commit *commit = p->item;
                struct patch_id *id;
                unsigned flags = commit->object.flags;

                if (flags & BOUNDARY)
                        continue;
                /*
                 * If we have fewer left, left_first is set and we omit
                 * commits on the left branch in this loop.
                 */
                if (left_first == !!(flags & SYMMETRIC_LEFT))
                        continue;

                /*
                 * Have we seen the same patch id?
                 */
                id = has_commit_patch_id(commit, &ids);
                if (!id)
                        continue;
                id->seen = 1;
                commit->object.flags |= cherry_flag;
        }

        /* Now check the original side for seen ones */
        for (p = list; p; p = p->next) {
                struct commit *commit = p->item;
                struct patch_id *ent;

                ent = commit->util;
                if (!ent)
                        continue;
                if (ent->seen)
                        commit->object.flags |= cherry_flag;
                commit->util = NULL;
        }

        free_patch_ids(&ids);
}

/* How many extra uninteresting commits we want to see.. */
#define SLOP 5

static int still_interesting(struct commit_list *src, unsigned long date, int slop)
{
        /*
         * No source list at all? We're definitely done..
         */
        if (!src)
                return 0;

        /*
         * Does the destination list contain entries with a date
         * before the source list? Definitely _not_ done.
         */
        if (date <= src->item->date)
                return SLOP;

        /*
         * Does the source list still have interesting commits in
         * it? Definitely not done..
         */
        if (!everybody_uninteresting(src))
                return SLOP;

        /* Ok, we're closing in.. */
        return slop-1;
}

/*
 * "rev-list --ancestry-path A..B" computes commits that are ancestors
 * of B but not ancestors of A but further limits the result to those
 * that are descendants of A.  This takes the list of bottom commits and
 * the result of "A..B" without --ancestry-path, and limits the latter
 * further to the ones that can reach one of the commits in "bottom".
 */
static void limit_to_ancestry(struct commit_list *bottom, struct commit_list *list)
{
        struct commit_list *p;
        struct commit_list *rlist = NULL;
        int made_progress;

        /*
         * Reverse the list so that it will be likely that we would
         * process parents before children.
         */
        for (p = list; p; p = p->next)
                commit_list_insert(p->item, &rlist);

        for (p = bottom; p; p = p->next)
                p->item->object.flags |= TMP_MARK;

        /*
         * Mark the ones that can reach bottom commits in "list",
         * in a bottom-up fashion.
         */
        do {
                made_progress = 0;
                for (p = rlist; p; p = p->next) {
                        struct commit *c = p->item;
                        struct commit_list *parents;
                        if (c->object.flags & (TMP_MARK | UNINTERESTING))
                                continue;
                        for (parents = c->parents;
                             parents;
                             parents = parents->next) {
                                if (!(parents->item->object.flags & TMP_MARK))
                                        continue;
                                c->object.flags |= TMP_MARK;
                                made_progress = 1;
                                break;
                        }
                }
        } while (made_progress);

        /*
         * NEEDSWORK: decide if we want to remove parents that are
         * not marked with TMP_MARK from commit->parents for commits
         * in the resulting list.  We may not want to do that, though.
         */

        /*
         * The ones that are not marked with TMP_MARK are uninteresting
         */
        for (p = list; p; p = p->next) {
                struct commit *c = p->item;
                if (c->object.flags & TMP_MARK)
                        continue;
                c->object.flags |= UNINTERESTING;
        }

        /* We are done with the TMP_MARK */
        for (p = list; p; p = p->next)
                p->item->object.flags &= ~TMP_MARK;
        for (p = bottom; p; p = p->next)
                p->item->object.flags &= ~TMP_MARK;
        free_commit_list(rlist);
}

/*
 * Before walking the history, keep the set of "negative" refs the
 * caller has asked to exclude.
 *
 * This is used to compute "rev-list --ancestry-path A..B", as we need
 * to filter the result of "A..B" further to the ones that can actually
 * reach A.
 */
static struct commit_list *collect_bottom_commits(struct commit_list *list)
{
        struct commit_list *elem, *bottom = NULL;
        for (elem = list; elem; elem = elem->next)
                if (elem->item->object.flags & BOTTOM)
                        commit_list_insert(elem->item, &bottom);
        return bottom;
}

/* Assumes either left_only or right_only is set */
static void limit_left_right(struct commit_list *list, struct rev_info *revs)
{
        struct commit_list *p;

        for (p = list; p; p = p->next) {
                struct commit *commit = p->item;

                if (revs->right_only) {
                        if (commit->object.flags & SYMMETRIC_LEFT)
                                commit->object.flags |= SHOWN;
                } else  /* revs->left_only is set */
                        if (!(commit->object.flags & SYMMETRIC_LEFT))
                                commit->object.flags |= SHOWN;
        }
}

static int limit_list(struct rev_info *revs)
{
        int slop = SLOP;
        unsigned long date = ~0ul;
        struct commit_list *list = revs->commits;
        struct commit_list *newlist = NULL;
        struct commit_list **p = &newlist;
        struct commit_list *bottom = NULL;

        if (revs->ancestry_path) {
                bottom = collect_bottom_commits(list);
                if (!bottom)
                        die("--ancestry-path given but there are no bottom commits");
        }

        while (list) {
                struct commit_list *entry = list;
                struct commit *commit = list->item;
                struct object *obj = &commit->object;
                show_early_output_fn_t show;

                list = list->next;
                free(entry);

                if (revs->max_age != -1 && (commit->date < revs->max_age))
                        obj->flags |= UNINTERESTING;
                if (add_parents_to_list(revs, commit, &list, NULL) < 0)
                        return -1;
                if (obj->flags & UNINTERESTING) {
                        mark_parents_uninteresting(commit);
                        if (revs->show_all)
                                p = &commit_list_insert(commit, p)->next;
                        slop = still_interesting(list, date, slop);
                        if (slop)
                                continue;
                        /* If showing all, add the whole pending list to the end */
                        if (revs->show_all)
                                *p = list;
                        break;
                }
                if (revs->min_age != -1 && (commit->date > revs->min_age))
                        continue;
                date = commit->date;
                p = &commit_list_insert(commit, p)->next;

                show = show_early_output;
                if (!show)
                        continue;

                show(revs, newlist);
                show_early_output = NULL;
        }
        if (revs->cherry_pick || revs->cherry_mark)
                cherry_pick_list(newlist, revs);

        if (revs->left_only || revs->right_only)
                limit_left_right(newlist, revs);

        if (bottom) {
                limit_to_ancestry(bottom, newlist);
                free_commit_list(bottom);
        }

        /*
         * Check if any commits have become TREESAME by some of their parents
         * becoming UNINTERESTING.
         */
        if (limiting_can_increase_treesame(revs))
                for (list = newlist; list; list = list->next) {
                        struct commit *c = list->item;
                        if (c->object.flags & (UNINTERESTING | TREESAME))
                                continue;
                        update_treesame(revs, c);
                }

        revs->commits = newlist;
        return 0;
}

/*
 * Add an entry to refs->cmdline with the specified information.
 * *name is copied.
 */
static void add_rev_cmdline(struct rev_info *revs,
                            struct object *item,
                            const char *name,
                            int whence,
                            unsigned flags)
{
        struct rev_cmdline_info *info = &revs->cmdline;
        int nr = info->nr;

        ALLOC_GROW(info->rev, nr + 1, info->alloc);
        info->rev[nr].item = item;
        info->rev[nr].name = xstrdup(name);
        info->rev[nr].whence = whence;
        info->rev[nr].flags = flags;
        info->nr++;
}

static void add_rev_cmdline_list(struct rev_info *revs,
                                 struct commit_list *commit_list,
                                 int whence,
                                 unsigned flags)
{
        while (commit_list) {
                struct object *object = &commit_list->item->object;
                add_rev_cmdline(revs, object, sha1_to_hex(object->sha1),
                                whence, flags);
                commit_list = commit_list->next;
        }
}

struct all_refs_cb {
        int all_flags;
        int warned_bad_reflog;
        struct rev_info *all_revs;
        const char *name_for_errormsg;
};

static int handle_one_ref(const char *path, const unsigned char *sha1, int flag, void *cb_data)
{
        struct all_refs_cb *cb = cb_data;
        struct object *object = get_reference(cb->all_revs, path, sha1,
                                              cb->all_flags);
        add_rev_cmdline(cb->all_revs, object, path, REV_CMD_REF, cb->all_flags);
        add_pending_sha1(cb->all_revs, path, sha1, cb->all_flags);
        return 0;
}

static void init_all_refs_cb(struct all_refs_cb *cb, struct rev_info *revs,
        unsigned flags)
{
        cb->all_revs = revs;
        cb->all_flags = flags;
}

static void handle_refs(const char *submodule, struct rev_info *revs, unsigned flags,
                int (*for_each)(const char *, each_ref_fn, void *))
{
        struct all_refs_cb cb;
        init_all_refs_cb(&cb, revs, flags);
        for_each(submodule, handle_one_ref, &cb);
}

static void handle_one_reflog_commit(unsigned char *sha1, void *cb_data)
{
        struct all_refs_cb *cb = cb_data;
        if (!is_null_sha1(sha1)) {
                struct object *o = parse_object(sha1);
                if (o) {
                        o->flags |= cb->all_flags;
                        /* ??? CMDLINEFLAGS ??? */
                        add_pending_object(cb->all_revs, o, "");
                }
                else if (!cb->warned_bad_reflog) {
                        warning("reflog of '%s' references pruned commits",
                                cb->name_for_errormsg);
                        cb->warned_bad_reflog = 1;
                }
        }
}

static int handle_one_reflog_ent(unsigned char *osha1, unsigned char *nsha1,
                const char *email, unsigned long timestamp, int tz,
                const char *message, void *cb_data)
{
        handle_one_reflog_commit(osha1, cb_data);
        handle_one_reflog_commit(nsha1, cb_data);
        return 0;
}

static int handle_one_reflog(const char *path, const unsigned char *sha1, int flag, void *cb_data)
{
        struct all_refs_cb *cb = cb_data;
        cb->warned_bad_reflog = 0;
        cb->name_for_errormsg = path;
        for_each_reflog_ent(path, handle_one_reflog_ent, cb_data);
        return 0;
}

static void handle_reflog(struct rev_info *revs, unsigned flags)
{
        struct all_refs_cb cb;
        cb.all_revs = revs;
        cb.all_flags = flags;
        for_each_reflog(handle_one_reflog, &cb);
}

static int add_parents_only(struct rev_info *revs, const char *arg_, int flags)
{
        unsigned char sha1[20];
        struct object *it;
        struct commit *commit;
        struct commit_list *parents;
        const char *arg = arg_;

        if (*arg == '^') {
                flags ^= UNINTERESTING | BOTTOM;
                arg++;
        }
        if (get_sha1_committish(arg, sha1))
                return 0;
        while (1) {
                it = get_reference(revs, arg, sha1, 0);
                if (!it && revs->ignore_missing)
                        return 0;
                if (it->type != OBJ_TAG)
                        break;
                if (!((struct tag*)it)->tagged)
                        return 0;
                hashcpy(sha1, ((struct tag*)it)->tagged->sha1);
        }
        if (it->type != OBJ_COMMIT)
                return 0;
        commit = (struct commit *)it;
        for (parents = commit->parents; parents; parents = parents->next) {
                it = &parents->item->object;
                it->flags |= flags;
                add_rev_cmdline(revs, it, arg_, REV_CMD_PARENTS_ONLY, flags);
                add_pending_object(revs, it, arg);
        }
        return 1;
}

void init_revisions(struct rev_info *revs, const char *prefix)
{
        memset(revs, 0, sizeof(*revs));

        revs->abbrev = DEFAULT_ABBREV;
        revs->ignore_merges = 1;
        revs->simplify_history = 1;
        DIFF_OPT_SET(&revs->pruning, RECURSIVE);
        DIFF_OPT_SET(&revs->pruning, QUICK);
        revs->pruning.add_remove = file_add_remove;
        revs->pruning.change = file_change;
        revs->sort_order = REV_SORT_IN_GRAPH_ORDER;
        revs->dense = 1;
        revs->prefix = prefix;
        revs->max_age = -1;
        revs->min_age = -1;
        revs->skip_count = -1;
        revs->max_count = -1;
        revs->max_parents = -1;

        revs->commit_format = CMIT_FMT_DEFAULT;

        init_grep_defaults();
        grep_init(&revs->grep_filter, prefix);
        revs->grep_filter.status_only = 1;
        revs->grep_filter.regflags = REG_NEWLINE;

        diff_setup(&revs->diffopt);
        if (prefix && !revs->diffopt.prefix) {
                revs->diffopt.prefix = prefix;
                revs->diffopt.prefix_length = strlen(prefix);
        }

        revs->notes_opt.use_default_notes = -1;
}

static void add_pending_commit_list(struct rev_info *revs,
                                    struct commit_list *commit_list,
                                    unsigned int flags)
{
        while (commit_list) {
                struct object *object = &commit_list->item->object;
                object->flags |= flags;
                add_pending_object(revs, object, sha1_to_hex(object->sha1));
                commit_list = commit_list->next;
        }
}

static void prepare_show_merge(struct rev_info *revs)
{
        struct commit_list *bases;
        struct commit *head, *other;
        unsigned char sha1[20];
        const char **prune = NULL;
        int i, prune_num = 1; /* counting terminating NULL */

        if (get_sha1("HEAD", sha1))
                die("--merge without HEAD?");
        head = lookup_commit_or_die(sha1, "HEAD");
        if (get_sha1("MERGE_HEAD", sha1))
                die("--merge without MERGE_HEAD?");
        other = lookup_commit_or_die(sha1, "MERGE_HEAD");
        add_pending_object(revs, &head->object, "HEAD");
        add_pending_object(revs, &other->object, "MERGE_HEAD");
        bases = get_merge_bases(head, other, 1);
        add_rev_cmdline_list(revs, bases, REV_CMD_MERGE_BASE, UNINTERESTING | BOTTOM);
        add_pending_commit_list(revs, bases, UNINTERESTING | BOTTOM);
        free_commit_list(bases);
        head->object.flags |= SYMMETRIC_LEFT;

        if (!active_nr)
                read_cache();
        for (i = 0; i < active_nr; i++) {
                const struct cache_entry *ce = active_cache[i];
                if (!ce_stage(ce))
                        continue;
                if (ce_path_match(ce, &revs->prune_data)) {
                        prune_num++;
                        prune = xrealloc(prune, sizeof(*prune) * prune_num);
                        prune[prune_num-2] = ce->name;
                        prune[prune_num-1] = NULL;
                }
                while ((i+1 < active_nr) &&
                       ce_same_name(ce, active_cache[i+1]))
                        i++;
        }
        free_pathspec(&revs->prune_data);
        parse_pathspec(&revs->prune_data, PATHSPEC_ALL_MAGIC & ~PATHSPEC_LITERAL,
                       PATHSPEC_PREFER_FULL | PATHSPEC_LITERAL_PATH, "", prune);
        revs->limited = 1;
}

int handle_revision_arg(const char *arg_, struct rev_info *revs, int flags, unsigned revarg_opt)
{
        struct object_context oc;
        char *dotdot;
        struct object *object;
        unsigned char sha1[20];
        int local_flags;
        const char *arg = arg_;
        int cant_be_filename = revarg_opt & REVARG_CANNOT_BE_FILENAME;
        unsigned get_sha1_flags = 0;

        flags = flags & UNINTERESTING ? flags | BOTTOM : flags & ~BOTTOM;

        dotdot = strstr(arg, "..");
        if (dotdot) {
                unsigned char from_sha1[20];
                const char *next = dotdot + 2;
                const char *this = arg;
                int symmetric = *next == '.';
                unsigned int flags_exclude = flags ^ (UNINTERESTING | BOTTOM);
                static const char head_by_default[] = "HEAD";
                unsigned int a_flags;

                *dotdot = 0;
                next += symmetric;

                if (!*next)
                        next = head_by_default;
                if (dotdot == arg)
                        this = head_by_default;
                if (this == head_by_default && next == head_by_default &&
                    !symmetric) {
                        /*
                         * Just ".."?  That is not a range but the
                         * pathspec for the parent directory.
                         */
                        if (!cant_be_filename) {
                                *dotdot = '.';
                                return -1;
                        }
                }
                if (!get_sha1_committish(this, from_sha1) &&
                    !get_sha1_committish(next, sha1)) {
                        struct object *a_obj, *b_obj;

                        if (!cant_be_filename) {
                                *dotdot = '.';
                                verify_non_filename(revs->prefix, arg);
                        }

                        a_obj = parse_object(from_sha1);
                        b_obj = parse_object(sha1);
                        if (!a_obj || !b_obj) {
                        missing:
                                if (revs->ignore_missing)
                                        return 0;
                                die(symmetric
                                    ? "Invalid symmetric difference expression %s"
                                    : "Invalid revision range %s", arg);
                        }

                        if (!symmetric) {
                                /* just A..B */
                                a_flags = flags_exclude;
                        } else {
                                /* A...B -- find merge bases between the two */
                                struct commit *a, *b;
                                struct commit_list *exclude;

                                a = (a_obj->type == OBJ_COMMIT
                                     ? (struct commit *)a_obj
                                     : lookup_commit_reference(a_obj->sha1));
                                b = (b_obj->type == OBJ_COMMIT
                                     ? (struct commit *)b_obj
                                     : lookup_commit_reference(b_obj->sha1));
                                if (!a || !b)
                                        goto missing;
                                exclude = get_merge_bases(a, b, 1);
                                add_rev_cmdline_list(revs, exclude,
                                                     REV_CMD_MERGE_BASE,
                                                     flags_exclude);
                                add_pending_commit_list(revs, exclude,
                                                        flags_exclude);
                                free_commit_list(exclude);

                                a_flags = flags | SYMMETRIC_LEFT;
                        }

                        a_obj->flags |= a_flags;
                        b_obj->flags |= flags;
                        add_rev_cmdline(revs, a_obj, this,
                                        REV_CMD_LEFT, a_flags);
                        add_rev_cmdline(revs, b_obj, next,
                                        REV_CMD_RIGHT, flags);
                        add_pending_object(revs, a_obj, this);
                        add_pending_object(revs, b_obj, next);
                        return 0;
                }
                *dotdot = '.';
        }
        dotdot = strstr(arg, "^@");
        if (dotdot && !dotdot[2]) {
                *dotdot = 0;
                if (add_parents_only(revs, arg, flags))
                        return 0;
                *dotdot = '^';
        }
        dotdot = strstr(arg, "^!");
        if (dotdot && !dotdot[2]) {
                *dotdot = 0;
                if (!add_parents_only(revs, arg, flags ^ (UNINTERESTING | BOTTOM)))
                        *dotdot = '^';
        }

        local_flags = 0;
        if (*arg == '^') {
                local_flags = UNINTERESTING | BOTTOM;
                arg++;
        }

        if (revarg_opt & REVARG_COMMITTISH)
                get_sha1_flags = GET_SHA1_COMMITTISH;

        if (get_sha1_with_context(arg, get_sha1_flags, sha1, &oc))
                return revs->ignore_missing ? 0 : -1;
        if (!cant_be_filename)
                verify_non_filename(revs->prefix, arg);
        object = get_reference(revs, arg, sha1, flags ^ local_flags);
        add_rev_cmdline(revs, object, arg_, REV_CMD_REV, flags ^ local_flags);
        add_pending_object_with_mode(revs, object, arg, oc.mode);
        return 0;
}

struct cmdline_pathspec {
        int alloc;
        int nr;
        const char **path;
};

static void append_prune_data(struct cmdline_pathspec *prune, const char **av)
{
        while (*av) {
                ALLOC_GROW(prune->path, prune->nr + 1, prune->alloc);
                prune->path[prune->nr++] = *(av++);
        }
}

static void read_pathspec_from_stdin(struct rev_info *revs, struct strbuf *sb,
                                     struct cmdline_pathspec *prune)
{
        while (strbuf_getwholeline(sb, stdin, '\n') != EOF) {
                int len = sb->len;
                if (len && sb->buf[len - 1] == '\n')
                        sb->buf[--len] = '\0';
                ALLOC_GROW(prune->path, prune->nr + 1, prune->alloc);
                prune->path[prune->nr++] = xstrdup(sb->buf);
        }
}

static void read_revisions_from_stdin(struct rev_info *revs,
                                      struct cmdline_pathspec *prune)
{
        struct strbuf sb;
        int seen_dashdash = 0;

        strbuf_init(&sb, 1000);
        while (strbuf_getwholeline(&sb, stdin, '\n') != EOF) {
                int len = sb.len;
                if (len && sb.buf[len - 1] == '\n')
                        sb.buf[--len] = '\0';
                if (!len)
                        break;
                if (sb.buf[0] == '-') {
                        if (len == 2 && sb.buf[1] == '-') {
                                seen_dashdash = 1;
                                break;
                        }
                        die("options not supported in --stdin mode");
                }
                if (handle_revision_arg(sb.buf, revs, 0,
                                        REVARG_CANNOT_BE_FILENAME))
                        die("bad revision '%s'", sb.buf);
        }
        if (seen_dashdash)
                read_pathspec_from_stdin(revs, &sb, prune);
        strbuf_release(&sb);
}

static void add_grep(struct rev_info *revs, const char *ptn, enum grep_pat_token what)
{
        append_grep_pattern(&revs->grep_filter, ptn, "command line", 0, what);
}

static void add_header_grep(struct rev_info *revs, enum grep_header_field field, const char *pattern)
{
        append_header_grep_pattern(&revs->grep_filter, field, pattern);
}

static void add_message_grep(struct rev_info *revs, const char *pattern)
{
        add_grep(revs, pattern, GREP_PATTERN_BODY);
}

static int handle_revision_opt(struct rev_info *revs, int argc, const char **argv,
                               int *unkc, const char **unkv)
{
        const char *arg = argv[0];
        const char *optarg;
        int argcount;

        /* pseudo revision arguments */
        if (!strcmp(arg, "--all") || !strcmp(arg, "--branches") ||
            !strcmp(arg, "--tags") || !strcmp(arg, "--remotes") ||
            !strcmp(arg, "--reflog") || !strcmp(arg, "--not") ||
            !strcmp(arg, "--no-walk") || !strcmp(arg, "--do-walk") ||
            !strcmp(arg, "--bisect") || !prefixcmp(arg, "--glob=") ||
            !prefixcmp(arg, "--branches=") || !prefixcmp(arg, "--tags=") ||
            !prefixcmp(arg, "--remotes=") || !prefixcmp(arg, "--no-walk="))
        {
                unkv[(*unkc)++] = arg;
                return 1;
        }

        if ((argcount = parse_long_opt("max-count", argv, &optarg))) {
                revs->max_count = atoi(optarg);
                revs->no_walk = 0;
                return argcount;
        } else if ((argcount = parse_long_opt("skip", argv, &optarg))) {
                revs->skip_count = atoi(optarg);
                return argcount;
        } else if ((*arg == '-') && isdigit(arg[1])) {
                /* accept -<digit>, like traditional "head" */
                if (strtol_i(arg + 1, 10, &revs->max_count) < 0 ||
                    revs->max_count < 0)
                        die("'%s': not a non-negative integer", arg + 1);
                revs->no_walk = 0;
        } else if (!strcmp(arg, "-n")) {
                if (argc <= 1)
                        return error("-n requires an argument");
                revs->max_count = atoi(argv[1]);
                revs->no_walk = 0;
                return 2;
        } else if (!prefixcmp(arg, "-n")) {
                revs->max_count = atoi(arg + 2);
                revs->no_walk = 0;
        } else if ((argcount = parse_long_opt("max-age", argv, &optarg))) {
                revs->max_age = atoi(optarg);
                return argcount;
        } else if ((argcount = parse_long_opt("since", argv, &optarg))) {
                revs->max_age = approxidate(optarg);
                return argcount;
        } else if ((argcount = parse_long_opt("after", argv, &optarg))) {
                revs->max_age = approxidate(optarg);
                return argcount;
        } else if ((argcount = parse_long_opt("min-age", argv, &optarg))) {
                revs->min_age = atoi(optarg);
                return argcount;
        } else if ((argcount = parse_long_opt("before", argv, &optarg))) {
                revs->min_age = approxidate(optarg);
                return argcount;
        } else if ((argcount = parse_long_opt("until", argv, &optarg))) {
                revs->min_age = approxidate(optarg);
                return argcount;
        } else if (!strcmp(arg, "--first-parent")) {
                revs->first_parent_only = 1;
        } else if (!strcmp(arg, "--ancestry-path")) {
                revs->ancestry_path = 1;
                revs->simplify_history = 0;
                revs->limited = 1;
        } else if (!strcmp(arg, "-g") || !strcmp(arg, "--walk-reflogs")) {
                init_reflog_walk(&revs->reflog_info);
        } else if (!strcmp(arg, "--default")) {
                if (argc <= 1)
                        return error("bad --default argument");
                revs->def = argv[1];
                return 2;
        } else if (!strcmp(arg, "--merge")) {
                revs->show_merge = 1;
        } else if (!strcmp(arg, "--topo-order")) {
                revs->sort_order = REV_SORT_IN_GRAPH_ORDER;
                revs->topo_order = 1;
        } else if (!strcmp(arg, "--simplify-merges")) {
                revs->simplify_merges = 1;
                revs->topo_order = 1;
                revs->rewrite_parents = 1;
                revs->simplify_history = 0;
                revs->limited = 1;
        } else if (!strcmp(arg, "--simplify-by-decoration")) {
                revs->simplify_merges = 1;
                revs->topo_order = 1;
                revs->rewrite_parents = 1;
                revs->simplify_history = 0;
                revs->simplify_by_decoration = 1;
                revs->limited = 1;
                revs->prune = 1;
                load_ref_decorations(DECORATE_SHORT_REFS);
        } else if (!strcmp(arg, "--date-order")) {
                revs->sort_order = REV_SORT_BY_COMMIT_DATE;
                revs->topo_order = 1;
        } else if (!strcmp(arg, "--author-date-order")) {
                revs->sort_order = REV_SORT_BY_AUTHOR_DATE;
                revs->topo_order = 1;
        } else if (!prefixcmp(arg, "--early-output")) {
                int count = 100;
                switch (arg[14]) {
                case '=':
                        count = atoi(arg+15);
                        /* Fallthrough */
                case 0:
                        revs->topo_order = 1;
                       revs->early_output = count;
                }
        } else if (!strcmp(arg, "--parents")) {
                revs->rewrite_parents = 1;
                revs->print_parents = 1;
        } else if (!strcmp(arg, "--dense")) {
                revs->dense = 1;
        } else if (!strcmp(arg, "--sparse")) {
                revs->dense = 0;
        } else if (!strcmp(arg, "--show-all")) {
                revs->show_all = 1;
        } else if (!strcmp(arg, "--remove-empty")) {
                revs->remove_empty_trees = 1;
        } else if (!strcmp(arg, "--merges")) {
                revs->min_parents = 2;
        } else if (!strcmp(arg, "--no-merges")) {
                revs->max_parents = 1;
        } else if (!prefixcmp(arg, "--min-parents=")) {
                revs->min_parents = atoi(arg+14);
        } else if (!prefixcmp(arg, "--no-min-parents")) {
                revs->min_parents = 0;
        } else if (!prefixcmp(arg, "--max-parents=")) {
                revs->max_parents = atoi(arg+14);
        } else if (!prefixcmp(arg, "--no-max-parents")) {
                revs->max_parents = -1;
        } else if (!strcmp(arg, "--boundary")) {
                revs->boundary = 1;
        } else if (!strcmp(arg, "--left-right")) {
                revs->left_right = 1;
        } else if (!strcmp(arg, "--left-only")) {
                if (revs->right_only)
                        die("--left-only is incompatible with --right-only"
                            " or --cherry");
                revs->left_only = 1;
        } else if (!strcmp(arg, "--right-only")) {
                if (revs->left_only)
                        die("--right-only is incompatible with --left-only");
                revs->right_only = 1;
        } else if (!strcmp(arg, "--cherry")) {
                if (revs->left_only)
                        die("--cherry is incompatible with --left-only");
                revs->cherry_mark = 1;
                revs->right_only = 1;
                revs->max_parents = 1;
                revs->limited = 1;
        } else if (!strcmp(arg, "--count")) {
                revs->count = 1;
        } else if (!strcmp(arg, "--cherry-mark")) {
                if (revs->cherry_pick)
                        die("--cherry-mark is incompatible with --cherry-pick");
                revs->cherry_mark = 1;
                revs->limited = 1; /* needs limit_list() */
        } else if (!strcmp(arg, "--cherry-pick")) {
                if (revs->cherry_mark)
                        die("--cherry-pick is incompatible with --cherry-mark");
                revs->cherry_pick = 1;
                revs->limited = 1;
        } else if (!strcmp(arg, "--objects")) {
                revs->tag_objects = 1;
                revs->tree_objects = 1;
                revs->blob_objects = 1;
        } else if (!strcmp(arg, "--objects-edge")) {
                revs->tag_objects = 1;
                revs->tree_objects = 1;
                revs->blob_objects = 1;
                revs->edge_hint = 1;
        } else if (!strcmp(arg, "--verify-objects")) {
                revs->tag_objects = 1;
                revs->tree_objects = 1;
                revs->blob_objects = 1;
                revs->verify_objects = 1;
        } else if (!strcmp(arg, "--unpacked")) {
                revs->unpacked = 1;
        } else if (!prefixcmp(arg, "--unpacked=")) {
                die("--unpacked=<packfile> no longer supported.");
        } else if (!strcmp(arg, "-r")) {
                revs->diff = 1;
                DIFF_OPT_SET(&revs->diffopt, RECURSIVE);
        } else if (!strcmp(arg, "-t")) {
                revs->diff = 1;
                DIFF_OPT_SET(&revs->diffopt, RECURSIVE);
                DIFF_OPT_SET(&revs->diffopt, TREE_IN_RECURSIVE);
        } else if (!strcmp(arg, "-m")) {
                revs->ignore_merges = 0;
        } else if (!strcmp(arg, "-c")) {
                revs->diff = 1;
                revs->dense_combined_merges = 0;
                revs->combine_merges = 1;
        } else if (!strcmp(arg, "--cc")) {
                revs->diff = 1;
                revs->dense_combined_merges = 1;
                revs->combine_merges = 1;
        } else if (!strcmp(arg, "-v")) {
                revs->verbose_header = 1;
        } else if (!strcmp(arg, "--pretty")) {
                revs->verbose_header = 1;
                revs->pretty_given = 1;
                get_commit_format(arg+8, revs);
        } else if (!prefixcmp(arg, "--pretty=") || !prefixcmp(arg, "--format=")) {
                /*
                 * Detached form ("--pretty X" as opposed to "--pretty=X")
                 * not allowed, since the argument is optional.
                 */
                revs->verbose_header = 1;
                revs->pretty_given = 1;
                get_commit_format(arg+9, revs);
        } else if (!strcmp(arg, "--show-notes") || !strcmp(arg, "--notes")) {
                revs->show_notes = 1;
                revs->show_notes_given = 1;
                revs->notes_opt.use_default_notes = 1;
        } else if (!strcmp(arg, "--show-signature")) {
                revs->show_signature = 1;
        } else if (!prefixcmp(arg, "--show-notes=") ||
                   !prefixcmp(arg, "--notes=")) {
                struct strbuf buf = STRBUF_INIT;
                revs->show_notes = 1;
                revs->show_notes_given = 1;
                if (!prefixcmp(arg, "--show-notes")) {
                        if (revs->notes_opt.use_default_notes < 0)
                                revs->notes_opt.use_default_notes = 1;
                        strbuf_addstr(&buf, arg+13);
                }
                else
                        strbuf_addstr(&buf, arg+8);
                expand_notes_ref(&buf);
                string_list_append(&revs->notes_opt.extra_notes_refs,
                                   strbuf_detach(&buf, NULL));
        } else if (!strcmp(arg, "--no-notes")) {
                revs->show_notes = 0;
                revs->show_notes_given = 1;
                revs->notes_opt.use_default_notes = -1;
                /* we have been strdup'ing ourselves, so trick
                 * string_list into free()ing strings */
                revs->notes_opt.extra_notes_refs.strdup_strings = 1;
                string_list_clear(&revs->notes_opt.extra_notes_refs, 0);
                revs->notes_opt.extra_notes_refs.strdup_strings = 0;
        } else if (!strcmp(arg, "--standard-notes")) {
                revs->show_notes_given = 1;
                revs->notes_opt.use_default_notes = 1;
        } else if (!strcmp(arg, "--no-standard-notes")) {
                revs->notes_opt.use_default_notes = 0;
        } else if (!strcmp(arg, "--oneline")) {
                revs->verbose_header = 1;
                get_commit_format("oneline", revs);
                revs->pretty_given = 1;
                revs->abbrev_commit = 1;
        } else if (!strcmp(arg, "--graph")) {
                revs->topo_order = 1;
                revs->rewrite_parents = 1;
                revs->graph = graph_init(revs);
        } else if (!strcmp(arg, "--root")) {
                revs->show_root_diff = 1;
        } else if (!strcmp(arg, "--no-commit-id")) {
                revs->no_commit_id = 1;
        } else if (!strcmp(arg, "--always")) {
                revs->always_show_header = 1;
        } else if (!strcmp(arg, "--no-abbrev")) {
                revs->abbrev = 0;
        } else if (!strcmp(arg, "--abbrev")) {
                revs->abbrev = DEFAULT_ABBREV;
        } else if (!prefixcmp(arg, "--abbrev=")) {
                revs->abbrev = strtoul(arg + 9, NULL, 10);
                if (revs->abbrev < MINIMUM_ABBREV)
                        revs->abbrev = MINIMUM_ABBREV;
                else if (revs->abbrev > 40)
                        revs->abbrev = 40;
        } else if (!strcmp(arg, "--abbrev-commit")) {
                revs->abbrev_commit = 1;
                revs->abbrev_commit_given = 1;
        } else if (!strcmp(arg, "--no-abbrev-commit")) {
                revs->abbrev_commit = 0;
        } else if (!strcmp(arg, "--full-diff")) {
                revs->diff = 1;
                revs->full_diff = 1;
        } else if (!strcmp(arg, "--full-history")) {
                revs->simplify_history = 0;
        } else if (!strcmp(arg, "--relative-date")) {
                revs->date_mode = DATE_RELATIVE;
                revs->date_mode_explicit = 1;
        } else if ((argcount = parse_long_opt("date", argv, &optarg))) {
                revs->date_mode = parse_date_format(optarg);
                revs->date_mode_explicit = 1;
                return argcount;
        } else if (!strcmp(arg, "--log-size")) {
                revs->show_log_size = 1;
        }
        /*
         * Grepping the commit log
         */
        else if ((argcount = parse_long_opt("author", argv, &optarg))) {
                add_header_grep(revs, GREP_HEADER_AUTHOR, optarg);
                return argcount;
        } else if ((argcount = parse_long_opt("committer", argv, &optarg))) {
                add_header_grep(revs, GREP_HEADER_COMMITTER, optarg);
                return argcount;
        } else if ((argcount = parse_long_opt("grep-reflog", argv, &optarg))) {
                add_header_grep(revs, GREP_HEADER_REFLOG, optarg);
                return argcount;
        } else if ((argcount = parse_long_opt("grep", argv, &optarg))) {
                add_message_grep(revs, optarg);
                return argcount;
        } else if (!strcmp(arg, "--grep-debug")) {
                revs->grep_filter.debug = 1;
        } else if (!strcmp(arg, "--basic-regexp")) {
                grep_set_pattern_type_option(GREP_PATTERN_TYPE_BRE, &revs->grep_filter);
        } else if (!strcmp(arg, "--extended-regexp") || !strcmp(arg, "-E")) {
                grep_set_pattern_type_option(GREP_PATTERN_TYPE_ERE, &revs->grep_filter);
        } else if (!strcmp(arg, "--regexp-ignore-case") || !strcmp(arg, "-i")) {
                revs->grep_filter.regflags |= REG_ICASE;
                DIFF_OPT_SET(&revs->diffopt, PICKAXE_IGNORE_CASE);
        } else if (!strcmp(arg, "--fixed-strings") || !strcmp(arg, "-F")) {
                grep_set_pattern_type_option(GREP_PATTERN_TYPE_FIXED, &revs->grep_filter);
        } else if (!strcmp(arg, "--perl-regexp")) {
                grep_set_pattern_type_option(GREP_PATTERN_TYPE_PCRE, &revs->grep_filter);
        } else if (!strcmp(arg, "--all-match")) {
                revs->grep_filter.all_match = 1;
        } else if ((argcount = parse_long_opt("encoding", argv, &optarg))) {
                if (strcmp(optarg, "none"))
                        git_log_output_encoding = xstrdup(optarg);
                else
                        git_log_output_encoding = "";
                return argcount;
        } else if (!strcmp(arg, "--reverse")) {
                revs->reverse ^= 1;
        } else if (!strcmp(arg, "--children")) {
                revs->children.name = "children";
                revs->limited = 1;
        } else if (!strcmp(arg, "--ignore-missing")) {
                revs->ignore_missing = 1;
        } else {
                int opts = diff_opt_parse(&revs->diffopt, argv, argc);
                if (!opts)
                        unkv[(*unkc)++] = arg;
                return opts;
        }

        return 1;
}

void parse_revision_opt(struct rev_info *revs, struct parse_opt_ctx_t *ctx,
                        const struct option *options,
                        const char * const usagestr[])
{
        int n = handle_revision_opt(revs, ctx->argc, ctx->argv,
                                    &ctx->cpidx, ctx->out);
        if (n <= 0) {
                error("unknown option `%s'", ctx->argv[0]);
                usage_with_options(usagestr, options);
        }
        ctx->argv += n;
        ctx->argc -= n;
}

static int for_each_bad_bisect_ref(const char *submodule, each_ref_fn fn, void *cb_data)
{
        return for_each_ref_in_submodule(submodule, "refs/bisect/bad", fn, cb_data);
}

static int for_each_good_bisect_ref(const char *submodule, each_ref_fn fn, void *cb_data)
{
        return for_each_ref_in_submodule(submodule, "refs/bisect/good", fn, cb_data);
}

static int handle_revision_pseudo_opt(const char *submodule,
                                struct rev_info *revs,
                                int argc, const char **argv, int *flags)
{
        const char *arg = argv[0];
        const char *optarg;
        int argcount;

        /*
         * NOTE!
         *
         * Commands like "git shortlog" will not accept the options below
         * unless parse_revision_opt queues them (as opposed to erroring
         * out).
         *
         * When implementing your new pseudo-option, remember to
         * register it in the list at the top of handle_revision_opt.
         */
        if (!strcmp(arg, "--all")) {
                handle_refs(submodule, revs, *flags, for_each_ref_submodule);
                handle_refs(submodule, revs, *flags, head_ref_submodule);
        } else if (!strcmp(arg, "--branches")) {
                handle_refs(submodule, revs, *flags, for_each_branch_ref_submodule);
        } else if (!strcmp(arg, "--bisect")) {
                handle_refs(submodule, revs, *flags, for_each_bad_bisect_ref);
                handle_refs(submodule, revs, *flags ^ (UNINTERESTING | BOTTOM), for_each_good_bisect_ref);
                revs->bisect = 1;
        } else if (!strcmp(arg, "--tags")) {
                handle_refs(submodule, revs, *flags, for_each_tag_ref_submodule);
        } else if (!strcmp(arg, "--remotes")) {
                handle_refs(submodule, revs, *flags, for_each_remote_ref_submodule);
        } else if ((argcount = parse_long_opt("glob", argv, &optarg))) {
                struct all_refs_cb cb;
                init_all_refs_cb(&cb, revs, *flags);
                for_each_glob_ref(handle_one_ref, optarg, &cb);
                return argcount;
        } else if (!prefixcmp(arg, "--branches=")) {
                struct all_refs_cb cb;
                init_all_refs_cb(&cb, revs, *flags);
                for_each_glob_ref_in(handle_one_ref, arg + 11, "refs/heads/", &cb);
        } else if (!prefixcmp(arg, "--tags=")) {
                struct all_refs_cb cb;
                init_all_refs_cb(&cb, revs, *flags);
                for_each_glob_ref_in(handle_one_ref, arg + 7, "refs/tags/", &cb);
        } else if (!prefixcmp(arg, "--remotes=")) {
                struct all_refs_cb cb;
                init_all_refs_cb(&cb, revs, *flags);
                for_each_glob_ref_in(handle_one_ref, arg + 10, "refs/remotes/", &cb);
        } else if (!strcmp(arg, "--reflog")) {
                handle_reflog(revs, *flags);
        } else if (!strcmp(arg, "--not")) {
                *flags ^= UNINTERESTING | BOTTOM;
        } else if (!strcmp(arg, "--no-walk")) {
                revs->no_walk = REVISION_WALK_NO_WALK_SORTED;
        } else if (!prefixcmp(arg, "--no-walk=")) {
                /*
                 * Detached form ("--no-walk X" as opposed to "--no-walk=X")
                 * not allowed, since the argument is optional.
                 */
                if (!strcmp(arg + 10, "sorted"))
                        revs->no_walk = REVISION_WALK_NO_WALK_SORTED;
                else if (!strcmp(arg + 10, "unsorted"))
                        revs->no_walk = REVISION_WALK_NO_WALK_UNSORTED;
                else
                        return error("invalid argument to --no-walk");
        } else if (!strcmp(arg, "--do-walk")) {
                revs->no_walk = 0;
        } else {
                return 0;
        }

        return 1;
}

/*
 * Parse revision information, filling in the "rev_info" structure,
 * and removing the used arguments from the argument list.
 *
 * Returns the number of arguments left that weren't recognized
 * (which are also moved to the head of the argument list)
 */
int setup_revisions(int argc, const char **argv, struct rev_info *revs, struct setup_revision_opt *opt)
{
        int i, flags, left, seen_dashdash, read_from_stdin, got_rev_arg = 0, revarg_opt;
        struct cmdline_pathspec prune_data;
        const char *submodule = NULL;

        memset(&prune_data, 0, sizeof(prune_data));
        if (opt)
                submodule = opt->submodule;

        /* First, search for "--" */
        if (opt && opt->assume_dashdash) {
                seen_dashdash = 1;
        } else {
                seen_dashdash = 0;
                for (i = 1; i < argc; i++) {
                        const char *arg = argv[i];
                        if (strcmp(arg, "--"))
                                continue;
                        argv[i] = NULL;
                        argc = i;
                        if (argv[i + 1])
                                append_prune_data(&prune_data, argv + i + 1);
                        seen_dashdash = 1;
                        break;
                }
        }

        /* Second, deal with arguments and options */
        flags = 0;
        revarg_opt = opt ? opt->revarg_opt : 0;
        if (seen_dashdash)
                revarg_opt |= REVARG_CANNOT_BE_FILENAME;
        read_from_stdin = 0;
        for (left = i = 1; i < argc; i++) {
                const char *arg = argv[i];
                if (*arg == '-') {
                        int opts;

                        opts = handle_revision_pseudo_opt(submodule,
                                                revs, argc - i, argv + i,
                                                &flags);
                        if (opts > 0) {
                                i += opts - 1;
                                continue;
                        }

                        if (!strcmp(arg, "--stdin")) {
                                if (revs->disable_stdin) {
                                        argv[left++] = arg;
                                        continue;
                                }
                                if (read_from_stdin++)
                                        die("--stdin given twice?");
                                read_revisions_from_stdin(revs, &prune_data);
                                continue;
                        }

                        opts = handle_revision_opt(revs, argc - i, argv + i, &left, argv);
                        if (opts > 0) {
                                i += opts - 1;
                                continue;
                        }
                        if (opts < 0)
                                exit(128);
                        continue;
                }


                if (handle_revision_arg(arg, revs, flags, revarg_opt)) {
                        int j;
                        if (seen_dashdash || *arg == '^')
                                die("bad revision '%s'", arg);

                        /* If we didn't have a "--":
                         * (1) all filenames must exist;
                         * (2) all rev-args must not be interpretable
                         *     as a valid filename.
                         * but the latter we have checked in the main loop.
                         */
                        for (j = i; j < argc; j++)
                                verify_filename(revs->prefix, argv[j], j == i);

                        append_prune_data(&prune_data, argv + i);
                        break;
                }
                else
                        got_rev_arg = 1;
        }

        if (prune_data.nr) {
                /*
                 * If we need to introduce the magic "a lone ':' means no
                 * pathspec whatsoever", here is the place to do so.
                 *
                 * if (prune_data.nr == 1 && !strcmp(prune_data[0], ":")) {
                 *      prune_data.nr = 0;
                 *      prune_data.alloc = 0;
                 *      free(prune_data.path);
                 *      prune_data.path = NULL;
                 * } else {
                 *      terminate prune_data.alloc with NULL and
                 *      call init_pathspec() to set revs->prune_data here.
                 * }
                 */
                ALLOC_GROW(prune_data.path, prune_data.nr + 1, prune_data.alloc);
                prune_data.path[prune_data.nr++] = NULL;
                parse_pathspec(&revs->prune_data, 0, 0,
                               revs->prefix, prune_data.path);
        }

        if (revs->def == NULL)
                revs->def = opt ? opt->def : NULL;
        if (opt && opt->tweak)
                opt->tweak(revs, opt);
        if (revs->show_merge)
                prepare_show_merge(revs);
        if (revs->def && !revs->pending.nr && !got_rev_arg) {
                unsigned char sha1[20];
                struct object *object;
                struct object_context oc;
                if (get_sha1_with_context(revs->def, 0, sha1, &oc))
                        die("bad default revision '%s'", revs->def);
                object = get_reference(revs, revs->def, sha1, 0);
                add_pending_object_with_mode(revs, object, revs->def, oc.mode);
        }

        /* Did the user ask for any diff output? Run the diff! */
        if (revs->diffopt.output_format & ~DIFF_FORMAT_NO_OUTPUT)
                revs->diff = 1;

        /* Pickaxe, diff-filter and rename following need diffs */
        if (revs->diffopt.pickaxe ||
            revs->diffopt.filter ||
            DIFF_OPT_TST(&revs->diffopt, FOLLOW_RENAMES))
                revs->diff = 1;

        if (revs->topo_order)
                revs->limited = 1;

        if (revs->prune_data.nr) {
                copy_pathspec(&revs->pruning.pathspec, &revs->prune_data);
                /* Can't prune commits with rename following: the paths change.. */
                if (!DIFF_OPT_TST(&revs->diffopt, FOLLOW_RENAMES))
                        revs->prune = 1;
                if (!revs->full_diff)
                        copy_pathspec(&revs->diffopt.pathspec,
                                      &revs->prune_data);
        }
        if (revs->combine_merges)
                revs->ignore_merges = 0;
        revs->diffopt.abbrev = revs->abbrev;

        if (revs->line_level_traverse) {
                revs->limited = 1;
                revs->topo_order = 1;
        }

        diff_setup_done(&revs->diffopt);

        grep_commit_pattern_type(GREP_PATTERN_TYPE_UNSPECIFIED,
                                 &revs->grep_filter);
        compile_grep_patterns(&revs->grep_filter);

        if (revs->reverse && revs->reflog_info)
                die("cannot combine --reverse with --walk-reflogs");
        if (revs->rewrite_parents && revs->children.name)
                die("cannot combine --parents and --children");

        /*
         * Limitations on the graph functionality
         */
        if (revs->reverse && revs->graph)
                die("cannot combine --reverse with --graph");

        if (revs->reflog_info && revs->graph)
                die("cannot combine --walk-reflogs with --graph");
        if (!revs->reflog_info && revs->grep_filter.use_reflog_filter)
                die("cannot use --grep-reflog without --walk-reflogs");

        return left;
}

static void add_child(struct rev_info *revs, struct commit *parent, struct commit *child)
{
        struct commit_list *l = xcalloc(1, sizeof(*l));

        l->item = child;
        l->next = add_decoration(&revs->children, &parent->object, l);
}

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;
        }
        /* clear the temporary mark */
        for (p = commit->parents; p; p = p->next) {
                p->item->object.flags &= ~TMP_MARK;
        }
        /* no update_treesame() - removing duplicates can't affect TREESAME */
        return surviving_parents;
}

struct merge_simplify_state {
        struct commit *simplified;
};

static struct merge_simplify_state *locate_simplify_state(struct rev_info *revs, struct commit *commit)
{
        struct merge_simplify_state *st;

        st = lookup_decoration(&revs->merge_simplification, &commit->object);
        if (!st) {
                st = xcalloc(1, sizeof(*st));
                add_decoration(&revs->merge_simplification, &commit->object, st);
        }
        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 mark_treesame_root_parents(struct rev_info *revs, struct commit *commit)
{
        struct commit_list *p;
        int marked = 0;

        for (p = commit->parents; p; p = p->next) {
                struct commit *parent = p->item;
                if (!parent->parents && (parent->object.flags & TREESAME)) {
                        parent->object.flags |= TMP_MARK;
                        marked++;
                }
        }

        return marked;
}

/*
 * Awkward naming - this means one parent we are TREESAME to.
 * cf mark_treesame_root_parents: root parents that are TREESAME (to an
 * empty tree). Better name suggestions?
 */
static int leave_one_treesame_to_parent(struct rev_info *revs, struct commit *commit)
{
        struct treesame_state *ts = lookup_decoration(&revs->treesame, &commit->object);
        struct commit *unmarked = NULL, *marked = NULL;
        struct commit_list *p;
        unsigned n;

        for (p = commit->parents, n = 0; p; p = p->next, n++) {
                if (ts->treesame[n]) {
                        if (p->item->object.flags & TMP_MARK) {
                                if (!marked)
                                        marked = p->item;
                        } else {
                                if (!unmarked) {
                                        unmarked = p->item;
                                        break;
                                }
                        }
                }
        }

        /*
         * If we are TREESAME to a marked-for-deletion parent, but not to any
         * unmarked parents, unmark the first TREESAME parent. This is the
         * parent that the default simplify_history==1 scan would have followed,
         * and it doesn't make sense to omit that path when asking for a
         * simplified full history. Retaining it improves the chances of
         * understanding odd missed merges that took an old version of a file.
         *
         * Example:
         *
         *   I--------*X       A modified the file, but mainline merge X used
         *    \       /        "-s ours", so took the version from I. X is
         *     `-*A--'         TREESAME to I and !TREESAME to A.
         *
         * Default log from X would produce "I". Without this check,
         * --full-history --simplify-merges would produce "I-A-X", showing
         * the merge commit X and that it changed A, but not making clear that
         * it had just taken the I version. With this check, the topology above
         * is retained.
         *
         * Note that it is possible that the simplification chooses a different
         * TREESAME parent from the default, in which case this test doesn't
         * activate, and we _do_ drop the default parent. Example:
         *
         *   I------X         A modified the file, but it was reverted in B,
         *    \    /          meaning mainline merge X is TREESAME to both
         *    *A-*B           parents.
         *
         * Default log would produce "I" by following the first parent;
         * --full-history --simplify-merges will produce "I-A-B". But this is a
         * reasonable result - it presents a logical full history leading from
         * I to X, and X is not an important merge.
         */
        if (!unmarked && marked) {
                marked->object.flags &= ~TMP_MARK;
                return 1;
        }

        return 0;
}

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;
        struct commit *parent;
        struct merge_simplify_state *st, *pst;
        int cnt;

        st = locate_simplify_state(revs, commit);

        /*
         * Have we handled this one?
         */
        if (st->simplified)
                return tail;

        /*
         * An UNINTERESTING commit simplifies to itself, so does a
         * root commit.  We do not rewrite parents of such commit
         * anyway.
         */
        if ((commit->object.flags & UNINTERESTING) || !commit->parents) {
                st->simplified = commit;
                return tail;
        }

        /*
         * Do we know what commit all of our parents that matter
         * should be rewritten to?  Otherwise we are not ready to
         * rewrite this one yet.
         */
        for (cnt = 0, p = commit->parents; p; p = p->next) {
                pst = locate_simplify_state(revs, p->item);
                if (!pst->simplified) {
                        tail = &commit_list_insert(p->item, tail)->next;
                        cnt++;
                }
                if (revs->first_parent_only)
                        break;
        }
        if (cnt) {
                tail = &commit_list_insert(commit, tail)->next;
                return tail;
        }

        /*
         * 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);
                p->item = pst->simplified;
                if (revs->first_parent_only)
                        break;
        }

        if (revs->first_parent_only)
                cnt = 1;
        else
                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 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, a merge of an independent branch that doesn't
         * touch the path will reduce to a treesame root parent:
         *
         *  ----o----X          X: the commit we are looking at;
         *          /           o: a commit that touches the paths;
         *         r            r: a root commit not touching the paths
         *
         * Detect and simplify both cases.
         */
        if (1 < cnt) {
                int marked = mark_redundant_parents(revs, commit);
                marked += mark_treesame_root_parents(revs, commit);
                if (marked)
                        marked -= leave_one_treesame_to_parent(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 don't simplify to one relevant commit
         * (the first two cases are already handled at the beginning of
         * this function).
         *
         * Otherwise, it simplifies to what its sole relevant parent
         * simplifies to.
         */
        if (!cnt ||
            (commit->object.flags & UNINTERESTING) ||
            !(commit->object.flags & TREESAME) ||
            (parent = one_relevant_parent(revs, commit->parents)) == NULL)
                st->simplified = commit;
        else {
                pst = locate_simplify_state(revs, parent);
                st->simplified = pst->simplified;
        }
        return tail;
}

static void simplify_merges(struct rev_info *revs)
{
        struct commit_list *list, *next;
        struct commit_list *yet_to_do, **tail;
        struct commit *commit;

        if (!revs->prune)
                return;

        /* feed the list reversed */
        yet_to_do = NULL;
        for (list = revs->commits; list; list = next) {
                commit = list->item;
                next = list->next;
                /*
                 * Do not free(list) here yet; the original list
                 * is used later in this function.
                 */
                commit_list_insert(commit, &yet_to_do);
        }
        while (yet_to_do) {
                list = yet_to_do;
                yet_to_do = NULL;
                tail = &yet_to_do;
                while (list) {
                        commit = list->item;
                        next = list->next;
                        free(list);
                        list = next;
                        tail = simplify_one(revs, commit, tail);
                }
        }

        /* clean up the result, removing the simplified ones */
        list = revs->commits;
        revs->commits = NULL;
        tail = &revs->commits;
        while (list) {
                struct merge_simplify_state *st;

                commit = list->item;
                next = list->next;
                free(list);
                list = next;
                st = locate_simplify_state(revs, commit);
                if (st->simplified == commit)
                        tail = &commit_list_insert(commit, tail)->next;
        }
}

static void set_children(struct rev_info *revs)
{
        struct commit_list *l;
        for (l = revs->commits; l; l = l->next) {
                struct commit *commit = l->item;
                struct commit_list *p;

                for (p = commit->parents; p; p = p->next)
                        add_child(revs, p->item, commit);
        }
}

void reset_revision_walk(void)
{
        clear_object_flags(SEEN | ADDED | SHOWN);
}

int prepare_revision_walk(struct rev_info *revs)
{
        int nr = revs->pending.nr;
        struct object_array_entry *e, *list;
        struct commit_list **next = &revs->commits;

        e = list = revs->pending.objects;
        revs->pending.nr = 0;
        revs->pending.alloc = 0;
        revs->pending.objects = NULL;
        while (--nr >= 0) {
                struct commit *commit = handle_commit(revs, e->item, e->name);
                if (commit) {
                        if (!(commit->object.flags & SEEN)) {
                                commit->object.flags |= SEEN;
                                next = commit_list_append(commit, next);
                        }
                }
                e++;
        }
        if (!revs->leak_pending)
                free(list);

        /* Signal whether we need per-parent treesame decoration */
        if (revs->simplify_merges ||
            (revs->limited && limiting_can_increase_treesame(revs)))
                revs->treesame.name = "treesame";

        if (revs->no_walk != REVISION_WALK_NO_WALK_UNSORTED)
                commit_list_sort_by_date(&revs->commits);
        if (revs->no_walk)
                return 0;
        if (revs->limited)
                if (limit_list(revs) < 0)
                        return -1;
        if (revs->topo_order)
                sort_in_topological_order(&revs->commits, revs->sort_order);
        if (revs->line_level_traverse)
                line_log_filter(revs);
        if (revs->simplify_merges)
                simplify_merges(revs);
        if (revs->children.name)
                set_children(revs);
        return 0;
}

static enum rewrite_result rewrite_one(struct rev_info *revs, struct commit **pp)
{
        struct commit_list *cache = NULL;

        for (;;) {
                struct commit *p = *pp;
                if (!revs->limited)
                        if (add_parents_to_list(revs, p, &revs->commits, &cache) < 0)
                                return rewrite_one_error;
                if (p->object.flags & UNINTERESTING)
                        return rewrite_one_ok;
                if (!(p->object.flags & TREESAME))
                        return rewrite_one_ok;
                if (!p->parents)
                        return rewrite_one_noparents;
                if ((p = one_relevant_parent(revs, p->parents)) == NULL)
                        return rewrite_one_ok;
                *pp = p;
        }
}

int rewrite_parents(struct rev_info *revs, struct commit *commit,
        rewrite_parent_fn_t rewrite_parent)
{
        struct commit_list **pp = &commit->parents;
        while (*pp) {
                struct commit_list *parent = *pp;
                switch (rewrite_parent(revs, &parent->item)) {
                case rewrite_one_ok:
                        break;
                case rewrite_one_noparents:
                        *pp = parent->next;
                        continue;
                case rewrite_one_error:
                        return -1;
                }
                pp = &parent->next;
        }
        remove_duplicate_parents(revs, commit);
        return 0;
}

static int commit_rewrite_person(struct strbuf *buf, const char *what, struct string_list *mailmap)
{
        char *person, *endp;
        size_t len, namelen, maillen;
        const char *name;
        const char *mail;
        struct ident_split ident;

        person = strstr(buf->buf, what);
        if (!person)
                return 0;

        person += strlen(what);
        endp = strchr(person, '\n');
        if (!endp)
                return 0;

        len = endp - person;

        if (split_ident_line(&ident, person, len))
                return 0;

        mail = ident.mail_begin;
        maillen = ident.mail_end - ident.mail_begin;
        name = ident.name_begin;
        namelen = ident.name_end - ident.name_begin;

        if (map_user(mailmap, &mail, &maillen, &name, &namelen)) {
                struct strbuf namemail = STRBUF_INIT;

                strbuf_addf(&namemail, "%.*s <%.*s>",
                            (int)namelen, name, (int)maillen, mail);

                strbuf_splice(buf, ident.name_begin - buf->buf,
                              ident.mail_end - ident.name_begin + 1,
                              namemail.buf, namemail.len);

                strbuf_release(&namemail);

                return 1;
        }

        return 0;
}

static int commit_match(struct commit *commit, struct rev_info *opt)
{
        int retval;
        const char *encoding;
        char *message;
        struct strbuf buf = STRBUF_INIT;

        if (!opt->grep_filter.pattern_list && !opt->grep_filter.header_list)
                return 1;

        /* Prepend "fake" headers as needed */
        if (opt->grep_filter.use_reflog_filter) {
                strbuf_addstr(&buf, "reflog ");
                get_reflog_message(&buf, opt->reflog_info);
                strbuf_addch(&buf, '\n');
        }

        /*
         * We grep in the user's output encoding, under the assumption that it
         * is the encoding they are most likely to write their grep pattern
         * for. In addition, it means we will match the "notes" encoding below,
         * so we will not end up with a buffer that has two different encodings
         * in it.
         */
        encoding = get_log_output_encoding();
        message = logmsg_reencode(commit, NULL, encoding);

        /* Copy the commit to temporary if we are using "fake" headers */
        if (buf.len)
                strbuf_addstr(&buf, message);

        if (opt->grep_filter.header_list && opt->mailmap) {
                if (!buf.len)
                        strbuf_addstr(&buf, message);

                commit_rewrite_person(&buf, "\nauthor ", opt->mailmap);
                commit_rewrite_person(&buf, "\ncommitter ", opt->mailmap);
        }

        /* Append "fake" message parts as needed */
        if (opt->show_notes) {
                if (!buf.len)
                        strbuf_addstr(&buf, message);
                format_display_notes(commit->object.sha1, &buf, encoding, 1);
        }

        /* Find either in the original commit message, or in the temporary */
        if (buf.len)
                retval = grep_buffer(&opt->grep_filter, buf.buf, buf.len);
        else
                retval = grep_buffer(&opt->grep_filter,
                                     message, strlen(message));
        strbuf_release(&buf);
        logmsg_free(message, commit);
        return retval;
}

static inline int want_ancestry(const struct rev_info *revs)
{
        return (revs->rewrite_parents || revs->children.name);
}

enum commit_action get_commit_action(struct rev_info *revs, struct commit *commit)
{
        if (commit->object.flags & SHOWN)
                return commit_ignore;
        if (revs->unpacked && has_sha1_pack(commit->object.sha1))
                return commit_ignore;
        if (revs->show_all)
                return commit_show;
        if (commit->object.flags & UNINTERESTING)
                return commit_ignore;
        if (revs->min_age != -1 && (commit->date > revs->min_age))
                return commit_ignore;
        if (revs->min_parents || (revs->max_parents >= 0)) {
                int n = commit_list_count(commit->parents);
                if ((n < revs->min_parents) ||
                    ((revs->max_parents >= 0) && (n > revs->max_parents)))
                        return commit_ignore;
        }
        if (!commit_match(commit, revs))
                return commit_ignore;
        if (revs->prune && revs->dense) {
                /* Commit without changes? */
                if (commit->object.flags & TREESAME) {
                        int n;
                        struct commit_list *p;
                        /* drop merges unless we want parenthood */
                        if (!want_ancestry(revs))
                                return commit_ignore;
                        /*
                         * If we want ancestry, then need to keep any merges
                         * between relevant commits to tie together topology.
                         * For consistency with TREESAME and simplification
                         * use "relevant" here rather than just INTERESTING,
                         * to treat bottom commit(s) as part of the topology.
                         */
                        for (n = 0, p = commit->parents; p; p = p->next)
                                if (relevant_commit(p->item))
                                        if (++n >= 2)
                                                return commit_show;
                        return commit_ignore;
                }
        }
        return commit_show;
}

enum commit_action simplify_commit(struct rev_info *revs, struct commit *commit)
{
        enum commit_action action = get_commit_action(revs, commit);

        if (action == commit_show &&
            !revs->show_all &&
            revs->prune && revs->dense && want_ancestry(revs)) {
                /*
                 * --full-diff on simplified parents is no good: it
                 * will show spurious changes from the commits that
                 * were elided.  So we save the parents on the side
                 * when --full-diff is in effect.
                 */
                if (revs->full_diff)
                        save_parents(revs, commit);
                if (rewrite_parents(revs, commit, rewrite_one) < 0)
                        return commit_error;
        }
        return action;
}

static struct commit *get_revision_1(struct rev_info *revs)
{
        if (!revs->commits)
                return NULL;

        do {
                struct commit_list *entry = revs->commits;
                struct commit *commit = entry->item;

                revs->commits = entry->next;
                free(entry);

                if (revs->reflog_info) {
                        save_parents(revs, commit);
                        fake_reflog_parent(revs->reflog_info, commit);
                        commit->object.flags &= ~(ADDED | SEEN | SHOWN);
                }

                /*
                 * If we haven't done the list limiting, we need to look at
                 * the parents here. We also need to do the date-based limiting
                 * that we'd otherwise have done in limit_list().
                 */
                if (!revs->limited) {
                        if (revs->max_age != -1 &&
                            (commit->date < revs->max_age))
                                continue;
                        if (add_parents_to_list(revs, commit, &revs->commits, NULL) < 0)
                                die("Failed to traverse parents of commit %s",
                                    sha1_to_hex(commit->object.sha1));
                }

                switch (simplify_commit(revs, commit)) {
                case commit_ignore:
                        continue;
                case commit_error:
                        die("Failed to simplify parents of commit %s",
                            sha1_to_hex(commit->object.sha1));
                default:
                        return commit;
                }
        } while (revs->commits);
        return NULL;
}

/*
 * Return true for entries that have not yet been shown.  (This is an
 * object_array_each_func_t.)
 */
static int entry_unshown(struct object_array_entry *entry, void *cb_data_unused)
{
        return !(entry->item->flags & SHOWN);
}

/*
 * If array is on the verge of a realloc, garbage-collect any entries
 * that have already been shown to try to free up some space.
 */
static void gc_boundary(struct object_array *array)
{
        if (array->nr == array->alloc)
                object_array_filter(array, entry_unshown, NULL);
}

static void create_boundary_commit_list(struct rev_info *revs)
{
        unsigned i;
        struct commit *c;
        struct object_array *array = &revs->boundary_commits;
        struct object_array_entry *objects = array->objects;

        /*
         * If revs->commits is non-NULL at this point, an error occurred in
         * get_revision_1().  Ignore the error and continue printing the
         * boundary commits anyway.  (This is what the code has always
         * done.)
         */
        if (revs->commits) {
                free_commit_list(revs->commits);
                revs->commits = NULL;
        }

        /*
         * Put all of the actual boundary commits from revs->boundary_commits
         * into revs->commits
         */
        for (i = 0; i < array->nr; i++) {
                c = (struct commit *)(objects[i].item);
                if (!c)
                        continue;
                if (!(c->object.flags & CHILD_SHOWN))
                        continue;
                if (c->object.flags & (SHOWN | BOUNDARY))
                        continue;
                c->object.flags |= BOUNDARY;
                commit_list_insert(c, &revs->commits);
        }

        /*
         * If revs->topo_order is set, sort the boundary commits
         * in topological order
         */
        sort_in_topological_order(&revs->commits, revs->sort_order);
}

static struct commit *get_revision_internal(struct rev_info *revs)
{
        struct commit *c = NULL;
        struct commit_list *l;

        if (revs->boundary == 2) {
                /*
                 * All of the normal commits have already been returned,
                 * and we are now returning boundary commits.
                 * create_boundary_commit_list() has populated
                 * revs->commits with the remaining commits to return.
                 */
                c = pop_commit(&revs->commits);
                if (c)
                        c->object.flags |= SHOWN;
                return c;
        }

        /*
         * If our max_count counter has reached zero, then we are done. We
         * don't simply return NULL because we still might need to show
         * boundary commits. But we want to avoid calling get_revision_1, which
         * might do a considerable amount of work finding the next commit only
         * for us to throw it away.
         *
         * If it is non-zero, then either we don't have a max_count at all
         * (-1), or it is still counting, in which case we decrement.
         */
        if (revs->max_count) {
                c = get_revision_1(revs);
                if (c) {
                        while (revs->skip_count > 0) {
                                revs->skip_count--;
                                c = get_revision_1(revs);
                                if (!c)
                                        break;
                        }
                }

                if (revs->max_count > 0)
                        revs->max_count--;
        }

        if (c)
                c->object.flags |= SHOWN;

        if (!revs->boundary)
                return c;

        if (!c) {
                /*
                 * get_revision_1() runs out the commits, and
                 * we are done computing the boundaries.
                 * switch to boundary commits output mode.
                 */
                revs->boundary = 2;

                /*
                 * Update revs->commits to contain the list of
                 * boundary commits.
                 */
                create_boundary_commit_list(revs);

                return get_revision_internal(revs);
        }

        /*
         * boundary commits are the commits that are parents of the
         * ones we got from get_revision_1() but they themselves are
         * not returned from get_revision_1().  Before returning
         * 'c', we need to mark its parents that they could be boundaries.
         */

        for (l = c->parents; l; l = l->next) {
                struct object *p;
                p = &(l->item->object);
                if (p->flags & (CHILD_SHOWN | SHOWN))
                        continue;
                p->flags |= CHILD_SHOWN;
                gc_boundary(&revs->boundary_commits);
                add_object_array(p, NULL, &revs->boundary_commits);
        }

        return c;
}

struct commit *get_revision(struct rev_info *revs)
{
        struct commit *c;
        struct commit_list *reversed;

        if (revs->reverse) {
                reversed = NULL;
                while ((c = get_revision_internal(revs)))
                        commit_list_insert(c, &reversed);
                revs->commits = reversed;
                revs->reverse = 0;
                revs->reverse_output_stage = 1;
        }

        if (revs->reverse_output_stage)
                return pop_commit(&revs->commits);

        c = get_revision_internal(revs);
        if (c && revs->graph)
                graph_update(revs->graph, c);
        if (!c)
                free_saved_parents(revs);
        return c;
}

char *get_revision_mark(const struct rev_info *revs, const struct commit *commit)
{
        if (commit->object.flags & BOUNDARY)
                return "-";
        else if (commit->object.flags & UNINTERESTING)
                return "^";
        else if (commit->object.flags & PATCHSAME)
                return "=";
        else if (!revs || revs->left_right) {
                if (commit->object.flags & SYMMETRIC_LEFT)
                        return "<";
                else
                        return ">";
        } else if (revs->graph)
                return "*";
        else if (revs->cherry_mark)
                return "+";
        return "";
}

void put_revision_mark(const struct rev_info *revs, const struct commit *commit)
{
        char *mark = get_revision_mark(revs, commit);
        if (!strlen(mark))
                return;
        fputs(mark, stdout);
        putchar(' ');
}

define_commit_slab(saved_parents, struct commit_list *);

#define EMPTY_PARENT_LIST ((struct commit_list *)-1)

void save_parents(struct rev_info *revs, struct commit *commit)
{
        struct commit_list **pp;

        if (!revs->saved_parents_slab) {
                revs->saved_parents_slab = xmalloc(sizeof(struct saved_parents));
                init_saved_parents(revs->saved_parents_slab);
        }

        pp = saved_parents_at(revs->saved_parents_slab, commit);

        /*
         * When walking with reflogs, we may visit the same commit
         * several times: once for each appearance in the reflog.
         *
         * In this case, save_parents() will be called multiple times.
         * We want to keep only the first set of parents.  We need to
         * store a sentinel value for an empty (i.e., NULL) parent
         * list to distinguish it from a not-yet-saved list, however.
         */
        if (*pp)
                return;
        if (commit->parents)
                *pp = copy_commit_list(commit->parents);
        else
                *pp = EMPTY_PARENT_LIST;
}

struct commit_list *get_saved_parents(struct rev_info *revs, const struct commit *commit)
{
        struct commit_list *parents;

        if (!revs->saved_parents_slab)
                return commit->parents;

        parents = *saved_parents_at(revs->saved_parents_slab, commit);
        if (parents == EMPTY_PARENT_LIST)
                return NULL;
        return parents;
}

void free_saved_parents(struct rev_info *revs)
{
        if (revs->saved_parents_slab)
                clear_saved_parents(revs->saved_parents_slab);
}