Subject: Re: [PATCH v2 2/5] commit-reach: use one walk in remove_redundant()

From: René Scharfe. <[email-masked]>
Date: Mon, 1 Feb 2021 17:12:37 +0100

Am 01.02.21 um 13:47 schrieb Derrick Stolee via GitGitGadget:
> @@ -210,12 +204,110 @@ static int remove_redundant(struct repository *r, struct commit **array, int cnt
>  	for (i = filled = 0; i < cnt; i++)
>  		if (!redundant[i])
>  			array[filled++] = work[i];
> +	for (j = filled, i = 0; i < cnt; i++)
> +		if (redundant[i])
> +			array[j++] = work[i];

This puts the loop back in that you removed in the previous commit.
Intentionally?

>  	free(work);
>  	free(redundant);
>  	free(filled_index);
>  	return filled;
>  }
>
> +static int remove_redundant_with_gen(struct repository *r,
> +				     struct commit **array, int cnt)
> +{
> +	int i, count_non_stale = 0;
> +	timestamp_t min_generation = GENERATION_NUMBER_INFINITY;
> +	struct commit **walk_start;
> +	size_t walk_start_nr = 0, walk_start_alloc = cnt;
> +	struct prio_queue queue = { compare_commits_by_gen_then_commit_date };
> +
> +	ALLOC_ARRAY(walk_start, walk_start_alloc);
> +
> +	/* Mark all parents of the input as STALE */
> +	for (i = 0; i < cnt; i++) {
> +		struct commit_list *parents;
> +		timestamp_t generation;
> +
> +		repo_parse_commit(r, array[i]);
> +		parents = array[i]->parents;
> +
> +		while (parents) {
> +			repo_parse_commit(r, parents->item);
> +			if (!(parents->item->object.flags & STALE)) {
> +				parents->item->object.flags |= STALE;
> +				ALLOC_GROW(walk_start, walk_start_nr + 1, walk_start_alloc);
> +				walk_start[walk_start_nr++] = parents->item;
> +				prio_queue_put(&queue, parents->item);
> +			}
> +			parents = parents->next;
> +		}
> +
> +		generation = commit_graph_generation(array[i]);
> +
> +		if (generation < min_generation)
> +			min_generation = generation;
> +	}
> +
> +	/* push the STALE bits up to min generation */
> +	while (queue.nr) {
> +		struct commit_list *parents;
> +		struct commit *c = prio_queue_get(&queue);
> +
> +		repo_parse_commit(r, c);
> +
> +		if (commit_graph_generation(c) < min_generation)
> +			continue;
> +
> +		parents = c->parents;
> +		while (parents) {
> +			if (!(parents->item->object.flags & STALE)) {
> +				parents->item->object.flags |= STALE;
> +				prio_queue_put(&queue, parents->item);
> +			}
> +			parents = parents->next;
> +		}
> +	}
> +
> +	/* rearrange array */
> +	for (i = count_non_stale = 0; i < cnt; i++) {
> +		if (!(array[i]->object.flags & STALE))

Here I would have added another condition, count_non_stale != i, to
avoid self-assignment (array[x] = array[x]).  The code works without
it, though.  Not sure if there is a performance benefit to be had --
branch vs. pointer copy.  Probably not worth it..

> +			array[count_non_stale++] = array[i];
> +	}
> +
> +	/* clear marks */
> +	for (i = 0; i < walk_start_nr; i++)
> +		clear_commit_marks(walk_start[i], STALE);

You can replace this loop with a call to clear_commit_marks_many().

> +	free(walk_start);
> +
> +	return count_non_stale;
> +}
> +
> +static int remove_redundant(struct repository *r, struct commit **array, int cnt)
> +{
> +	/*
> +	 * Some commit in the array may be an ancestor of
> +	 * another commit.  Move the independent commits to the
> +	 * beginning of 'array' and return their number. Callers
> +	 * should not rely upon the contents of 'array' after
> +	 * that number.
> +	 */
> +	if (generation_numbers_enabled(r)) {
> +		int i;
> +
> +		/*
> +		 * If we have a single commit with finite generation
> +		 * number, then the _with_gen algorithm is preferred.
> +		 */
> +		for (i = 0; i < cnt; i++) {
> +			if (commit_graph_generation(array[i]) < GENERATION_NUMBER_INFINITY)
> +				return remove_redundant_with_gen(r, array, cnt);
> +		}
> +	}
> +
> +	return remove_redundant_no_gen(r, array, cnt);
> +}
> +
>  static struct commit_list *get_merge_bases_many_0(struct repository *r,
>  						  struct commit *one,
>  						  int n,
>