Fourth batch for 2.19 cycle

[git.git] / shallow.c

#include "cache.h"
#include "repository.h"
#include "tempfile.h"
#include "lockfile.h"
#include "object-store.h"
#include "commit.h"
#include "tag.h"
#include "pkt-line.h"
#include "remote.h"
#include "refs.h"
#include "sha1-array.h"
#include "diff.h"
#include "revision.h"
#include "commit-slab.h"
#include "revision.h"
#include "list-objects.h"
#include "commit-slab.h"
#include "repository.h"

void set_alternate_shallow_file(struct repository *r, const char *path, int override)
{
        if (r->parsed_objects->is_shallow != -1)
                BUG("is_repository_shallow must not be called before set_alternate_shallow_file");
        if (r->parsed_objects->alternate_shallow_file && !override)
                return;
        free(r->parsed_objects->alternate_shallow_file);
        r->parsed_objects->alternate_shallow_file = xstrdup_or_null(path);
}

int register_shallow(struct repository *r, const struct object_id *oid)
{
        struct commit_graft *graft =
                xmalloc(sizeof(struct commit_graft));
        struct commit *commit = lookup_commit(oid);

        oidcpy(&graft->oid, oid);
        graft->nr_parent = -1;
        if (commit && commit->object.parsed)
                commit->parents = NULL;
        return register_commit_graft(r, graft, 0);
}

int is_repository_shallow(struct repository *r)
{
        FILE *fp;
        char buf[1024];
        const char *path = r->parsed_objects->alternate_shallow_file;

        if (r->parsed_objects->is_shallow >= 0)
                return r->parsed_objects->is_shallow;

        if (!path)
                path = git_path_shallow(r);
        /*
         * fetch-pack sets '--shallow-file ""' as an indicator that no
         * shallow file should be used. We could just open it and it
         * will likely fail. But let's do an explicit check instead.
         */
        if (!*path || (fp = fopen(path, "r")) == NULL) {
                stat_validity_clear(r->parsed_objects->shallow_stat);
                r->parsed_objects->is_shallow = 0;
                return r->parsed_objects->is_shallow;
        }
        stat_validity_update(r->parsed_objects->shallow_stat, fileno(fp));
        r->parsed_objects->is_shallow = 1;

        while (fgets(buf, sizeof(buf), fp)) {
                struct object_id oid;
                if (get_oid_hex(buf, &oid))
                        die("bad shallow line: %s", buf);
                register_shallow(r, &oid);
        }
        fclose(fp);
        return r->parsed_objects->is_shallow;
}

/*
 * TODO: use "int" elemtype instead of "int *" when/if commit-slab
 * supports a "valid" flag.
 */
define_commit_slab(commit_depth, int *);
struct commit_list *get_shallow_commits(struct object_array *heads, int depth,
                int shallow_flag, int not_shallow_flag)
{
        int i = 0, cur_depth = 0;
        struct commit_list *result = NULL;
        struct object_array stack = OBJECT_ARRAY_INIT;
        struct commit *commit = NULL;
        struct commit_graft *graft;
        struct commit_depth depths;

        init_commit_depth(&depths);
        while (commit || i < heads->nr || stack.nr) {
                struct commit_list *p;
                if (!commit) {
                        if (i < heads->nr) {
                                int **depth_slot;
                                commit = (struct commit *)
                                        deref_tag(heads->objects[i++].item, NULL, 0);
                                if (!commit || commit->object.type != OBJ_COMMIT) {
                                        commit = NULL;
                                        continue;
                                }
                                depth_slot = commit_depth_at(&depths, commit);
                                if (!*depth_slot)
                                        *depth_slot = xmalloc(sizeof(int));
                                **depth_slot = 0;
                                cur_depth = 0;
                        } else {
                                commit = (struct commit *)
                                        object_array_pop(&stack);
                                cur_depth = **commit_depth_at(&depths, commit);
                        }
                }
                parse_commit_or_die(commit);
                cur_depth++;
                if ((depth != INFINITE_DEPTH && cur_depth >= depth) ||
                    (is_repository_shallow(the_repository) && !commit->parents &&
                     (graft = lookup_commit_graft(the_repository, &commit->object.oid)) != NULL &&
                     graft->nr_parent < 0)) {
                        commit_list_insert(commit, &result);
                        commit->object.flags |= shallow_flag;
                        commit = NULL;
                        continue;
                }
                commit->object.flags |= not_shallow_flag;
                for (p = commit->parents, commit = NULL; p; p = p->next) {
                        int **depth_slot = commit_depth_at(&depths, p->item);
                        if (!*depth_slot) {
                                *depth_slot = xmalloc(sizeof(int));
                                **depth_slot = cur_depth;
                        } else {
                                if (cur_depth >= **depth_slot)
                                        continue;
                                **depth_slot = cur_depth;
                        }
                        if (p->next)
                                add_object_array(&p->item->object,
                                                NULL, &stack);
                        else {
                                commit = p->item;
                                cur_depth = **commit_depth_at(&depths, commit);
                        }
                }
        }
        for (i = 0; i < depths.slab_count; i++) {
                int j;

                for (j = 0; j < depths.slab_size; j++)
                        free(depths.slab[i][j]);
        }
        clear_commit_depth(&depths);

        return result;
}

static void show_commit(struct commit *commit, void *data)
{
        commit_list_insert(commit, data);
}

/*
 * Given rev-list arguments, run rev-list. All reachable commits
 * except border ones are marked with not_shallow_flag. Border commits
 * are marked with shallow_flag. The list of border/shallow commits
 * are also returned.
 */
struct commit_list *get_shallow_commits_by_rev_list(int ac, const char **av,
                                                    int shallow_flag,
                                                    int not_shallow_flag)
{
        struct commit_list *result = NULL, *p;
        struct commit_list *not_shallow_list = NULL;
        struct rev_info revs;
        int both_flags = shallow_flag | not_shallow_flag;

        /*
         * SHALLOW (excluded) and NOT_SHALLOW (included) should not be
         * set at this point. But better be safe than sorry.
         */
        clear_object_flags(both_flags);

        is_repository_shallow(the_repository); /* make sure shallows are read */

        init_revisions(&revs, NULL);
        save_commit_buffer = 0;
        setup_revisions(ac, av, &revs, NULL);

        if (prepare_revision_walk(&revs))
                die("revision walk setup failed");
        traverse_commit_list(&revs, show_commit, NULL, &not_shallow_list);

        if (!not_shallow_list)
                die("no commits selected for shallow requests");

        /* Mark all reachable commits as NOT_SHALLOW */
        for (p = not_shallow_list; p; p = p->next)
                p->item->object.flags |= not_shallow_flag;

        /*
         * mark border commits SHALLOW + NOT_SHALLOW.
         * We cannot clear NOT_SHALLOW right now. Imagine border
         * commit A is processed first, then commit B, whose parent is
         * A, later. If NOT_SHALLOW on A is cleared at step 1, B
         * itself is considered border at step 2, which is incorrect.
         */
        for (p = not_shallow_list; p; p = p->next) {
                struct commit *c = p->item;
                struct commit_list *parent;

                if (parse_commit(c))
                        die("unable to parse commit %s",
                            oid_to_hex(&c->object.oid));

                for (parent = c->parents; parent; parent = parent->next)
                        if (!(parent->item->object.flags & not_shallow_flag)) {
                                c->object.flags |= shallow_flag;
                                commit_list_insert(c, &result);
                                break;
                        }
        }
        free_commit_list(not_shallow_list);

        /*
         * Now we can clean up NOT_SHALLOW on border commits. Having
         * both flags set can confuse the caller.
         */
        for (p = result; p; p = p->next) {
                struct object *o = &p->item->object;
                if ((o->flags & both_flags) == both_flags)
                        o->flags &= ~not_shallow_flag;
        }
        return result;
}

static void check_shallow_file_for_update(struct repository *r)
{
        if (r->parsed_objects->is_shallow == -1)
                BUG("shallow must be initialized by now");

        if (!stat_validity_check(r->parsed_objects->shallow_stat, git_path_shallow(the_repository)))
                die("shallow file has changed since we read it");
}

#define SEEN_ONLY 1
#define VERBOSE   2

struct write_shallow_data {
        struct strbuf *out;
        int use_pack_protocol;
        int count;
        unsigned flags;
};

static int write_one_shallow(const struct commit_graft *graft, void *cb_data)
{
        struct write_shallow_data *data = cb_data;
        const char *hex = oid_to_hex(&graft->oid);
        if (graft->nr_parent != -1)
                return 0;
        if (data->flags & SEEN_ONLY) {
                struct commit *c = lookup_commit(&graft->oid);
                if (!c || !(c->object.flags & SEEN)) {
                        if (data->flags & VERBOSE)
                                printf("Removing %s from .git/shallow\n",
                                       oid_to_hex(&c->object.oid));
                        return 0;
                }
        }
        data->count++;
        if (data->use_pack_protocol)
                packet_buf_write(data->out, "shallow %s", hex);
        else {
                strbuf_addstr(data->out, hex);
                strbuf_addch(data->out, '\n');
        }
        return 0;
}

static int write_shallow_commits_1(struct strbuf *out, int use_pack_protocol,
                                   const struct oid_array *extra,
                                   unsigned flags)
{
        struct write_shallow_data data;
        int i;
        data.out = out;
        data.use_pack_protocol = use_pack_protocol;
        data.count = 0;
        data.flags = flags;
        for_each_commit_graft(write_one_shallow, &data);
        if (!extra)
                return data.count;
        for (i = 0; i < extra->nr; i++) {
                strbuf_addstr(out, oid_to_hex(extra->oid + i));
                strbuf_addch(out, '\n');
                data.count++;
        }
        return data.count;
}

int write_shallow_commits(struct strbuf *out, int use_pack_protocol,
                          const struct oid_array *extra)
{
        return write_shallow_commits_1(out, use_pack_protocol, extra, 0);
}

const char *setup_temporary_shallow(const struct oid_array *extra)
{
        struct tempfile *temp;
        struct strbuf sb = STRBUF_INIT;

        if (write_shallow_commits(&sb, 0, extra)) {
                temp = xmks_tempfile(git_path("shallow_XXXXXX"));

                if (write_in_full(temp->fd, sb.buf, sb.len) < 0 ||
                    close_tempfile_gently(temp) < 0)
                        die_errno("failed to write to %s",
                                  get_tempfile_path(temp));
                strbuf_release(&sb);
                return get_tempfile_path(temp);
        }
        /*
         * is_repository_shallow() sees empty string as "no shallow
         * file".
         */
        return "";
}

void setup_alternate_shallow(struct lock_file *shallow_lock,
                             const char **alternate_shallow_file,
                             const struct oid_array *extra)
{
        struct strbuf sb = STRBUF_INIT;
        int fd;

        fd = hold_lock_file_for_update(shallow_lock,
                                       git_path_shallow(the_repository),
                                       LOCK_DIE_ON_ERROR);
        check_shallow_file_for_update(the_repository);
        if (write_shallow_commits(&sb, 0, extra)) {
                if (write_in_full(fd, sb.buf, sb.len) < 0)
                        die_errno("failed to write to %s",
                                  get_lock_file_path(shallow_lock));
                *alternate_shallow_file = get_lock_file_path(shallow_lock);
        } else
                /*
                 * is_repository_shallow() sees empty string as "no
                 * shallow file".
                 */
                *alternate_shallow_file = "";
        strbuf_release(&sb);
}

static int advertise_shallow_grafts_cb(const struct commit_graft *graft, void *cb)
{
        int fd = *(int *)cb;
        if (graft->nr_parent == -1)
                packet_write_fmt(fd, "shallow %s\n", oid_to_hex(&graft->oid));
        return 0;
}

void advertise_shallow_grafts(int fd)
{
        if (!is_repository_shallow(the_repository))
                return;
        for_each_commit_graft(advertise_shallow_grafts_cb, &fd);
}

/*
 * mark_reachable_objects() should have been run prior to this and all
 * reachable commits marked as "SEEN".
 */
void prune_shallow(int show_only)
{
        struct lock_file shallow_lock = LOCK_INIT;
        struct strbuf sb = STRBUF_INIT;
        int fd;

        if (show_only) {
                write_shallow_commits_1(&sb, 0, NULL, SEEN_ONLY | VERBOSE);
                strbuf_release(&sb);
                return;
        }
        fd = hold_lock_file_for_update(&shallow_lock,
                                       git_path_shallow(the_repository),
                                       LOCK_DIE_ON_ERROR);
        check_shallow_file_for_update(the_repository);
        if (write_shallow_commits_1(&sb, 0, NULL, SEEN_ONLY)) {
                if (write_in_full(fd, sb.buf, sb.len) < 0)
                        die_errno("failed to write to %s",
                                  get_lock_file_path(&shallow_lock));
                commit_lock_file(&shallow_lock);
        } else {
                unlink(git_path_shallow(the_repository));
                rollback_lock_file(&shallow_lock);
        }
        strbuf_release(&sb);
}

struct trace_key trace_shallow = TRACE_KEY_INIT(SHALLOW);

/*
 * Step 1, split sender shallow commits into "ours" and "theirs"
 * Step 2, clean "ours" based on .git/shallow
 */
void prepare_shallow_info(struct shallow_info *info, struct oid_array *sa)
{
        int i;
        trace_printf_key(&trace_shallow, "shallow: prepare_shallow_info\n");
        memset(info, 0, sizeof(*info));
        info->shallow = sa;
        if (!sa)
                return;
        ALLOC_ARRAY(info->ours, sa->nr);
        ALLOC_ARRAY(info->theirs, sa->nr);
        for (i = 0; i < sa->nr; i++) {
                if (has_object_file(sa->oid + i)) {
                        struct commit_graft *graft;
                        graft = lookup_commit_graft(the_repository,
                                                    &sa->oid[i]);
                        if (graft && graft->nr_parent < 0)
                                continue;
                        info->ours[info->nr_ours++] = i;
                } else
                        info->theirs[info->nr_theirs++] = i;
        }
}

void clear_shallow_info(struct shallow_info *info)
{
        free(info->ours);
        free(info->theirs);
}

/* Step 4, remove non-existent ones in "theirs" after getting the pack */

void remove_nonexistent_theirs_shallow(struct shallow_info *info)
{
        struct object_id *oid = info->shallow->oid;
        int i, dst;
        trace_printf_key(&trace_shallow, "shallow: remove_nonexistent_theirs_shallow\n");
        for (i = dst = 0; i < info->nr_theirs; i++) {
                if (i != dst)
                        info->theirs[dst] = info->theirs[i];
                if (has_object_file(oid + info->theirs[i]))
                        dst++;
        }
        info->nr_theirs = dst;
}

define_commit_slab(ref_bitmap, uint32_t *);

#define POOL_SIZE (512 * 1024)

struct paint_info {
        struct ref_bitmap ref_bitmap;
        unsigned nr_bits;
        char **pools;
        char *free, *end;
        unsigned pool_count;
};

static uint32_t *paint_alloc(struct paint_info *info)
{
        unsigned nr = DIV_ROUND_UP(info->nr_bits, 32);
        unsigned size = nr * sizeof(uint32_t);
        void *p;
        if (!info->pool_count || size > info->end - info->free) {
                if (size > POOL_SIZE)
                        BUG("pool size too small for %d in paint_alloc()",
                            size);
                info->pool_count++;
                REALLOC_ARRAY(info->pools, info->pool_count);
                info->free = xmalloc(POOL_SIZE);
                info->pools[info->pool_count - 1] = info->free;
                info->end = info->free + POOL_SIZE;
        }
        p = info->free;
        info->free += size;
        return p;
}

/*
 * Given a commit SHA-1, walk down to parents until either SEEN,
 * UNINTERESTING or BOTTOM is hit. Set the id-th bit in ref_bitmap for
 * all walked commits.
 */
static void paint_down(struct paint_info *info, const struct object_id *oid,
                       unsigned int id)
{
        unsigned int i, nr;
        struct commit_list *head = NULL;
        int bitmap_nr = DIV_ROUND_UP(info->nr_bits, 32);
        size_t bitmap_size = st_mult(sizeof(uint32_t), bitmap_nr);
        struct commit *c = lookup_commit_reference_gently(oid, 1);
        uint32_t *tmp; /* to be freed before return */
        uint32_t *bitmap;

        if (!c)
                return;

        tmp = xmalloc(bitmap_size);
        bitmap = paint_alloc(info);
        memset(bitmap, 0, bitmap_size);
        bitmap[id / 32] |= (1U << (id % 32));
        commit_list_insert(c, &head);
        while (head) {
                struct commit_list *p;
                struct commit *c = pop_commit(&head);
                uint32_t **refs = ref_bitmap_at(&info->ref_bitmap, c);

                /* XXX check "UNINTERESTING" from pack bitmaps if available */
                if (c->object.flags & (SEEN | UNINTERESTING))
                        continue;
                else
                        c->object.flags |= SEEN;

                if (*refs == NULL)
                        *refs = bitmap;
                else {
                        memcpy(tmp, *refs, bitmap_size);
                        for (i = 0; i < bitmap_nr; i++)
                                tmp[i] |= bitmap[i];
                        if (memcmp(tmp, *refs, bitmap_size)) {
                                *refs = paint_alloc(info);
                                memcpy(*refs, tmp, bitmap_size);
                        }
                }

                if (c->object.flags & BOTTOM)
                        continue;

                if (parse_commit(c))
                        die("unable to parse commit %s",
                            oid_to_hex(&c->object.oid));

                for (p = c->parents; p; p = p->next) {
                        if (p->item->object.flags & SEEN)
                                continue;
                        commit_list_insert(p->item, &head);
                }
        }

        nr = get_max_object_index();
        for (i = 0; i < nr; i++) {
                struct object *o = get_indexed_object(i);
                if (o && o->type == OBJ_COMMIT)
                        o->flags &= ~SEEN;
        }

        free(tmp);
}

static int mark_uninteresting(const char *refname, const struct object_id *oid,
                              int flags, void *cb_data)
{
        struct commit *commit = lookup_commit_reference_gently(oid, 1);
        if (!commit)
                return 0;
        commit->object.flags |= UNINTERESTING;
        mark_parents_uninteresting(commit);
        return 0;
}

static void post_assign_shallow(struct shallow_info *info,
                                struct ref_bitmap *ref_bitmap,
                                int *ref_status);
/*
 * Step 6(+7), associate shallow commits with new refs
 *
 * info->ref must be initialized before calling this function.
 *
 * If used is not NULL, it's an array of info->shallow->nr
 * bitmaps. The n-th bit set in the m-th bitmap if ref[n] needs the
 * m-th shallow commit from info->shallow.
 *
 * If used is NULL, "ours" and "theirs" are updated. And if ref_status
 * is not NULL it's an array of ref->nr ints. ref_status[i] is true if
 * the ref needs some shallow commits from either info->ours or
 * info->theirs.
 */
void assign_shallow_commits_to_refs(struct shallow_info *info,
                                    uint32_t **used, int *ref_status)
{
        struct object_id *oid = info->shallow->oid;
        struct oid_array *ref = info->ref;
        unsigned int i, nr;
        int *shallow, nr_shallow = 0;
        struct paint_info pi;

        trace_printf_key(&trace_shallow, "shallow: assign_shallow_commits_to_refs\n");
        ALLOC_ARRAY(shallow, info->nr_ours + info->nr_theirs);
        for (i = 0; i < info->nr_ours; i++)
                shallow[nr_shallow++] = info->ours[i];
        for (i = 0; i < info->nr_theirs; i++)
                shallow[nr_shallow++] = info->theirs[i];

        /*
         * Prepare the commit graph to track what refs can reach what
         * (new) shallow commits.
         */
        nr = get_max_object_index();
        for (i = 0; i < nr; i++) {
                struct object *o = get_indexed_object(i);
                if (!o || o->type != OBJ_COMMIT)
                        continue;

                o->flags &= ~(UNINTERESTING | BOTTOM | SEEN);
        }

        memset(&pi, 0, sizeof(pi));
        init_ref_bitmap(&pi.ref_bitmap);
        pi.nr_bits = ref->nr;

        /*
         * "--not --all" to cut short the traversal if new refs
         * connect to old refs. If not (e.g. force ref updates) it'll
         * have to go down to the current shallow commits.
         */
        head_ref(mark_uninteresting, NULL);
        for_each_ref(mark_uninteresting, NULL);

        /* Mark potential bottoms so we won't go out of bound */
        for (i = 0; i < nr_shallow; i++) {
                struct commit *c = lookup_commit(&oid[shallow[i]]);
                c->object.flags |= BOTTOM;
        }

        for (i = 0; i < ref->nr; i++)
                paint_down(&pi, ref->oid + i, i);

        if (used) {
                int bitmap_size = DIV_ROUND_UP(pi.nr_bits, 32) * sizeof(uint32_t);
                memset(used, 0, sizeof(*used) * info->shallow->nr);
                for (i = 0; i < nr_shallow; i++) {
                        const struct commit *c = lookup_commit(&oid[shallow[i]]);
                        uint32_t **map = ref_bitmap_at(&pi.ref_bitmap, c);
                        if (*map)
                                used[shallow[i]] = xmemdupz(*map, bitmap_size);
                }
                /*
                 * unreachable shallow commits are not removed from
                 * "ours" and "theirs". The user is supposed to run
                 * step 7 on every ref separately and not trust "ours"
                 * and "theirs" any more.
                 */
        } else
                post_assign_shallow(info, &pi.ref_bitmap, ref_status);

        clear_ref_bitmap(&pi.ref_bitmap);
        for (i = 0; i < pi.pool_count; i++)
                free(pi.pools[i]);
        free(pi.pools);
        free(shallow);
}

struct commit_array {
        struct commit **commits;
        int nr, alloc;
};

static int add_ref(const char *refname, const struct object_id *oid,
                   int flags, void *cb_data)
{
        struct commit_array *ca = cb_data;
        ALLOC_GROW(ca->commits, ca->nr + 1, ca->alloc);
        ca->commits[ca->nr] = lookup_commit_reference_gently(oid, 1);
        if (ca->commits[ca->nr])
                ca->nr++;
        return 0;
}

static void update_refstatus(int *ref_status, int nr, uint32_t *bitmap)
{
        unsigned int i;
        if (!ref_status)
                return;
        for (i = 0; i < nr; i++)
                if (bitmap[i / 32] & (1U << (i % 32)))
                        ref_status[i]++;
}

/*
 * Step 7, reachability test on "ours" at commit level
 */
static void post_assign_shallow(struct shallow_info *info,
                                struct ref_bitmap *ref_bitmap,
                                int *ref_status)
{
        struct object_id *oid = info->shallow->oid;
        struct commit *c;
        uint32_t **bitmap;
        int dst, i, j;
        int bitmap_nr = DIV_ROUND_UP(info->ref->nr, 32);
        struct commit_array ca;

        trace_printf_key(&trace_shallow, "shallow: post_assign_shallow\n");
        if (ref_status)
                memset(ref_status, 0, sizeof(*ref_status) * info->ref->nr);

        /* Remove unreachable shallow commits from "theirs" */
        for (i = dst = 0; i < info->nr_theirs; i++) {
                if (i != dst)
                        info->theirs[dst] = info->theirs[i];
                c = lookup_commit(&oid[info->theirs[i]]);
                bitmap = ref_bitmap_at(ref_bitmap, c);
                if (!*bitmap)
                        continue;
                for (j = 0; j < bitmap_nr; j++)
                        if (bitmap[0][j]) {
                                update_refstatus(ref_status, info->ref->nr, *bitmap);
                                dst++;
                                break;
                        }
        }
        info->nr_theirs = dst;

        memset(&ca, 0, sizeof(ca));
        head_ref(add_ref, &ca);
        for_each_ref(add_ref, &ca);

        /* Remove unreachable shallow commits from "ours" */
        for (i = dst = 0; i < info->nr_ours; i++) {
                if (i != dst)
                        info->ours[dst] = info->ours[i];
                c = lookup_commit(&oid[info->ours[i]]);
                bitmap = ref_bitmap_at(ref_bitmap, c);
                if (!*bitmap)
                        continue;
                for (j = 0; j < bitmap_nr; j++)
                        if (bitmap[0][j] &&
                            /* Step 7, reachability test at commit level */
                            !in_merge_bases_many(c, ca.nr, ca.commits)) {
                                update_refstatus(ref_status, info->ref->nr, *bitmap);
                                dst++;
                                break;
                        }
        }
        info->nr_ours = dst;

        free(ca.commits);
}

/* (Delayed) step 7, reachability test at commit level */
int delayed_reachability_test(struct shallow_info *si, int c)
{
        if (si->need_reachability_test[c]) {
                struct commit *commit = lookup_commit(&si->shallow->oid[c]);

                if (!si->commits) {
                        struct commit_array ca;

                        memset(&ca, 0, sizeof(ca));
                        head_ref(add_ref, &ca);
                        for_each_ref(add_ref, &ca);
                        si->commits = ca.commits;
                        si->nr_commits = ca.nr;
                }

                si->reachable[c] = in_merge_bases_many(commit,
                                                       si->nr_commits,
                                                       si->commits);
                si->need_reachability_test[c] = 0;
        }
        return si->reachable[c];
}