Merge branch 'tc/last-modified-active-paths-optimization' into next

"git last-modified" was optimized by narrowing the set of paths to
follow as it dug deeper in the history.

* tc/last-modified-active-paths-optimization:
  last-modified: implement faster algorithm

Author: gitster

builtin/last-modified.c

@@ -2,26 +2,32 @@
 #include "bloom.h"
 #include "builtin.h"
 #include "commit-graph.h"
+#include "commit-slab.h"
 #include "commit.h"
 #include "config.h"
-#include "environment.h"
 #include "diff.h"
 #include "diffcore.h"
 #include "environment.h"
+#include "ewah/ewok.h"
 #include "hashmap.h"
 #include "hex.h"
-#include "log-tree.h"
 #include "object-name.h"
 #include "object.h"
 #include "parse-options.h"
+#include "prio-queue.h"
 #include "quote.h"
 #include "repository.h"
 #include "revision.h"
 
+/* Remember to update object flag allocation in object.h */
+#define PARENT1 (1u<<16) /* used instead of SEEN */
+#define PARENT2 (1u<<17) /* used instead of BOTTOM, BOUNDARY */
+
 struct last_modified_entry {
 	struct hashmap_entry hashent;
 	struct object_id oid;
 	struct bloom_key key;
+	size_t diff_idx;
 	const char path[FLEX_ARRAY];
 };
 
@@ -37,13 +43,45 @@ static int last_modified_entry_hashcmp(const void *unused UNUSED,
 	return strcmp(ent1->path, path ? path : ent2->path);
 }
 
+/*
+ * Hold a bitmap for each commit we're working with. In the bitmap, each bit
+ * represents a path in `lm->all_paths`. An active bit indicates the path still
+ * needs to be associated to a commit.
+ */
+define_commit_slab(active_paths_for_commit, struct bitmap *);
+
 struct last_modified {
 	struct hashmap paths;
 	struct rev_info rev;
 	bool recursive;
 	bool show_trees;
+
+	const char **all_paths;
+	size_t all_paths_nr;
+	struct active_paths_for_commit active_paths;
+
+	/* 'scratch' to avoid allocating a bitmap every process_parent() */
+	struct bitmap *scratch;
 };
 
+static struct bitmap *active_paths_for(struct last_modified *lm, struct commit *c)
+{
+	struct bitmap **bitmap = active_paths_for_commit_at(&lm->active_paths, c);
+	if (!*bitmap)
+		*bitmap = bitmap_word_alloc(lm->all_paths_nr / BITS_IN_EWORD + 1);
+
+	return *bitmap;
+}
+
+static void active_paths_free(struct last_modified *lm, struct commit *c)
+{
+	struct bitmap **bitmap = active_paths_for_commit_at(&lm->active_paths, c);
+	if (*bitmap) {
+		bitmap_free(*bitmap);
+		*bitmap = NULL;
+	}
+}
+
 static void last_modified_release(struct last_modified *lm)
 {
 	struct hashmap_iter iter;
@@ -54,6 +92,8 @@ static void last_modified_release(struct last_modified *lm)
 
 	hashmap_clear_and_free(&lm->paths, struct last_modified_entry, hashent);
 	release_revisions(&lm->rev);
+
+	free(lm->all_paths);
 }
 
 struct last_modified_callback_data {
@@ -146,7 +186,7 @@ static void mark_path(const char *path, const struct object_id *oid,
 	 * Is it arriving at a version of interest, or is it from a side branch
 	 * which did not contribute to the final state?
 	 */
-	if (!oideq(oid, &ent->oid))
+	if (oid && !oideq(oid, &ent->oid))
 		return;
 
 	last_modified_emit(data->lm, path, data->commit);
@@ -196,7 +236,17 @@ static void last_modified_diff(struct diff_queue_struct *q,
 	}
 }
 
-static bool maybe_changed_path(struct last_modified *lm, struct commit *origin)
+static void pass_to_parent(struct bitmap *c,
+			   struct bitmap *p,
+			   size_t pos)
+{
+	bitmap_unset(c, pos);
+	bitmap_set(p, pos);
+}
+
+static bool maybe_changed_path(struct last_modified *lm,
+			       struct commit *origin,
+			       struct bitmap *active)
 {
 	struct bloom_filter *filter;
 	struct last_modified_entry *ent;
@@ -213,49 +263,212 @@ static bool maybe_changed_path(struct last_modified *lm, struct commit *origin)
 		return true;
 
 	hashmap_for_each_entry(&lm->paths, &iter, ent, hashent) {
+		if (active && !bitmap_get(active, ent->diff_idx))
+			continue;
+
 		if (bloom_filter_contains(filter, &ent->key,
 					  lm->rev.bloom_filter_settings))
 			return true;
 	}
 	return false;
 }
 
+static void process_parent(struct last_modified *lm,
+			   struct prio_queue *queue,
+			   struct commit *c, struct bitmap *active_c,
+			   struct commit *parent, int parent_i)
+{
+	struct bitmap *active_p;
+
+	repo_parse_commit(lm->rev.repo, parent);
+	active_p = active_paths_for(lm, parent);
+
+	/*
+	 * The first time entering this function for this commit (i.e. first parent)
+	 * see if Bloom filters will tell us it's worth to do the diff.
+	 */
+	if (parent_i || maybe_changed_path(lm, c, active_c)) {
+		diff_tree_oid(&parent->object.oid,
+			      &c->object.oid, "", &lm->rev.diffopt);
+		diffcore_std(&lm->rev.diffopt);
+	}
+
+	/*
+	 * Test each path for TREESAME-ness against the parent. If a path is
+	 * TREESAME, pass it on to this parent.
+	 *
+	 * First, collect all paths that are *not* TREESAME in 'scratch'.
+	 * Then, pass paths that *are* TREESAME and active to the parent.
+	 */
+	for (int i = 0; i < diff_queued_diff.nr; i++) {
+		struct diff_filepair *fp = diff_queued_diff.queue[i];
+		const char *path = fp->two->path;
+		struct last_modified_entry *ent =
+			hashmap_get_entry_from_hash(&lm->paths, strhash(path), path,
+						    struct last_modified_entry, hashent);
+		if (ent) {
+			size_t k = ent->diff_idx;
+			if (bitmap_get(active_c, k))
+				bitmap_set(lm->scratch, k);
+		}
+	}
+	for (size_t i = 0; i < lm->all_paths_nr; i++) {
+		if (bitmap_get(active_c, i) && !bitmap_get(lm->scratch, i))
+			pass_to_parent(active_c, active_p, i);
+	}
+
+	/*
+	 * If parent has any active paths, put it on the queue (if not already).
+	 */
+	if (!bitmap_is_empty(active_p) && !(parent->object.flags & PARENT1)) {
+		parent->object.flags |= PARENT1;
+		prio_queue_put(queue, parent);
+	}
+	if (!(parent->object.flags & PARENT1))
+		active_paths_free(lm, parent);
+
+	memset(lm->scratch->words, 0x0, lm->scratch->word_alloc);
+	diff_queue_clear(&diff_queued_diff);
+}
+
 static int last_modified_run(struct last_modified *lm)
 {
+	int max_count, queue_popped = 0;
+	struct prio_queue queue = { compare_commits_by_gen_then_commit_date };
+	struct prio_queue not_queue = { compare_commits_by_gen_then_commit_date };
+	struct commit_list *list;
 	struct last_modified_callback_data data = { .lm = lm };
 
 	lm->rev.diffopt.output_format = DIFF_FORMAT_CALLBACK;
 	lm->rev.diffopt.format_callback = last_modified_diff;
 	lm->rev.diffopt.format_callback_data = &data;
+	lm->rev.no_walk = 1;
 
 	prepare_revision_walk(&lm->rev);
 
-	while (hashmap_get_size(&lm->paths)) {
-		data.commit = get_revision(&lm->rev);
-		if (!data.commit)
-			BUG("paths remaining beyond boundary in last-modified");
+	max_count = lm->rev.max_count;
+
+	init_active_paths_for_commit(&lm->active_paths);
+	lm->scratch = bitmap_word_alloc(lm->all_paths_nr);
+
+	/*
+	 * lm->rev.commits holds the set of boundary commits for our walk.
+	 *
+	 * Loop through each such commit, and place it in the appropriate queue.
+	 */
+	for (list = lm->rev.commits; list; list = list->next) {
+		struct commit *c = list->item;
+
+		if (c->object.flags & BOTTOM) {
+			prio_queue_put(&not_queue, c);
+			c->object.flags |= PARENT2;
+		} else if (!(c->object.flags & PARENT1)) {
+			/*
+			 * If the commit is a starting point (and hasn't been
+			 * seen yet), then initialize the set of interesting
+			 * paths, too.
+			 */
+			struct bitmap *active;
+
+			prio_queue_put(&queue, c);
+			c->object.flags |= PARENT1;
+
+			active = active_paths_for(lm, c);
+			for (size_t i = 0; i < lm->all_paths_nr; i++)
+				bitmap_set(active, i);
+		}
+	}
 
-		if (data.commit->object.flags & BOUNDARY) {
+	while (queue.nr) {
+		int parent_i;
+		struct commit_list *p;
+		struct commit *c = prio_queue_get(&queue);
+		struct bitmap *active_c = active_paths_for(lm, c);
+
+		if ((0 <= max_count && max_count < ++queue_popped) ||
+		    (c->object.flags & PARENT2)) {
+			/*
+			 * Either a boundary commit, or we have already seen too
+			 * many others. Either way, stop here.
+			 */
+			c->object.flags |= PARENT2 | BOUNDARY;
+			data.commit = c;
 			diff_tree_oid(lm->rev.repo->hash_algo->empty_tree,
-				      &data.commit->object.oid, "",
-				      &lm->rev.diffopt);
+				      &c->object.oid,
+				      "", &lm->rev.diffopt);
 			diff_flush(&lm->rev.diffopt);
+			goto cleanup;
+		}
 
-			break;
+		/*
+		 * Otherwise, make sure that 'c' isn't reachable from anything
+		 * in the '--not' queue.
+		 */
+		repo_parse_commit(lm->rev.repo, c);
+
+		while (not_queue.nr) {
+			struct commit_list *np;
+			struct commit *n = prio_queue_get(&not_queue);
+
+			repo_parse_commit(lm->rev.repo, n);
+
+			for (np = n->parents; np; np = np->next) {
+				if (!(np->item->object.flags & PARENT2)) {
+					prio_queue_put(&not_queue, np->item);
+					np->item->object.flags |= PARENT2;
+				}
+			}
+
+			if (commit_graph_generation(n) < commit_graph_generation(c))
+				break;
 		}
 
-		if (!maybe_changed_path(lm, data.commit))
-			continue;
+		/*
+		 * Look at each parent and pass on each path that's TREESAME
+		 * with that parent. Stop early when no active paths remain.
+		 */
+		for (p = c->parents, parent_i = 0; p; p = p->next, parent_i++) {
+			process_parent(lm, &queue,
+				       c, active_c,
+				       p->item, parent_i);
+
+			if (bitmap_is_empty(active_c))
+				break;
+		}
+
+		/*
+		 * Paths that remain active, or not TREESAME with any parent,
+		 * were changed by 'c'.
+		 */
+		if (!bitmap_is_empty(active_c))  {
+			data.commit = c;
+			for (size_t i = 0; i < lm->all_paths_nr; i++) {
+				if (bitmap_get(active_c, i))
+					mark_path(lm->all_paths[i], NULL, &data);
+			}
+		}
 
-		log_tree_commit(&lm->rev, data.commit);
+cleanup:
+		active_paths_free(lm, c);
 	}
 
+	if (hashmap_get_size(&lm->paths))
+		BUG("paths remaining beyond boundary in last-modified");
+
+	clear_prio_queue(&not_queue);
+	clear_prio_queue(&queue);
+	clear_active_paths_for_commit(&lm->active_paths);
+	bitmap_free(lm->scratch);
+
 	return 0;
 }
 
 static int last_modified_init(struct last_modified *lm, struct repository *r,
 			      const char *prefix, int argc, const char **argv)
 {
+	struct hashmap_iter iter;
+	struct last_modified_entry *ent;
+
 	hashmap_init(&lm->paths, last_modified_entry_hashcmp, NULL, 0);
 
 	repo_init_revisions(r, &lm->rev, prefix);
@@ -280,6 +493,13 @@ static int last_modified_init(struct last_modified *lm, struct repository *r,
 	if (populate_paths_from_revs(lm) < 0)
 		return error(_("unable to setup last-modified"));
 
+	CALLOC_ARRAY(lm->all_paths, hashmap_get_size(&lm->paths));
+	lm->all_paths_nr = 0;
+	hashmap_for_each_entry(&lm->paths, &iter, ent, hashent) {
+		ent->diff_idx = lm->all_paths_nr++;
+		lm->all_paths[ent->diff_idx] = ent->path;
+	}
+
 	return 0;
 }
 

object.h

@@ -75,6 +75,7 @@ void object_array_init(struct object_array *array);
  * http-push.c:                          11-----14
  * commit-graph.c:                                15
  * commit-reach.c:                                  16-----19
+ * builtin/last-modified.c:                         1617
  * sha1-name.c:                                              20
  * list-objects-filter.c:                                      21
  * bloom.c:                                                    2122

t/t8020-last-modified.sh

@@ -57,9 +57,9 @@ test_expect_success 'last-modified recursive' '
 
 test_expect_success 'last-modified recursive with show-trees' '
 	check_last_modified -r -t <<-\EOF
-	3 a
 	3 a/b
 	3 a/b/file
+	3 a
 	2 a/file
 	1 file
 	EOF