Re: [PATCH 2/2] diffcore-rename: filter rename_src list when possible

> +static int remove_unneeded_paths_from_src(int num_src,
> +					  int detecting_copies)
> +{
> +	int i, new_num_src;
> +
> +	/*
> +	 * Note on reasons why we cull unneeded sources but not destinations:
> +	 *   1) Pairings are stored in rename_dst (not rename_src), which we
> +	 *      need to keep around.  So, we just can't cull rename_dst even
> +	 *      if we wanted to.  But doing so wouldn't help because...
> +	 *
> +	 *   2) There is a matrix pairwise comparison that follows the
> +	 *      "Performing inexact rename detection" progress message.
> +	 *      Iterating over the destinations is done in the outer loop,
> +	 *      hence we only iterate over each of those once and we can
> +	 *      easily skip the outer loop early if the destination isn't
> +	 *      relevant.  That's only one check per destination path to
> +	 *      skip.
> +	 *
> +	 *      By contrast, the sources are iterated in the inner loop; if
> +	 *      we check whether a source can be skipped, then we'll be
> +	 *      checking it N separate times, once for each destination.
> +	 *      We don't want to have to iterate over known-not-needed
> +	 *      sources N times each, so avoid that by removing the sources
> +	 *      from rename_src here.
> +	 */
> +	if (detecting_copies)
> +		return num_src; /* nothing to remove */
> +	if (break_idx)
> +		return num_src; /* culling incompatbile with break detection */
> +
> +	for (i = 0, new_num_src = 0; i < num_src; i++) {
> +		/*
> +		 * renames are stored in rename_dst, so if a rename has
> +		 * already been detected using this source, we can just
> +		 * remove the source knowing rename_dst has its info.
> +		 */
> +		if (rename_src[i].p->one->rename_used)
> +			continue;
> +
> +		if (new_num_src < i)
> +			memcpy(&rename_src[new_num_src], &rename_src[i],
> +			       sizeof(struct diff_rename_src));
> +		new_num_src++;
> +	}
> +
> +	return new_num_src;
> +}

>  void diffcore_rename(struct diff_options *options)
>  {
>  	int detect_rename = options->detect_rename;
> @@ -463,10 +512,11 @@ void diffcore_rename(struct diff_options *options)
>  	struct diff_score *mx;
>  	int i, j, rename_count, skip_unmodified = 0;
>  	int num_destinations, dst_cnt;
> -	int num_sources;
> +	int num_sources, want_copies;
>  	struct progress *progress = NULL;
>  
>  	trace2_region_enter("diff", "setup", options->repo);
> +	want_copies = (detect_rename == DIFF_DETECT_COPY);
>  	if (!minimum_score)
>  		minimum_score = DEFAULT_RENAME_SCORE;
>  
> @@ -529,13 +579,10 @@ void diffcore_rename(struct diff_options *options)
>  		goto cleanup;
>  
>  	/*
> -	 * Calculate how many renames are left (but all the source
> -	 * files still remain as options for rename/copies!)
> +	 * Calculate how many renames are left
>  	 */
>  	num_destinations = (rename_dst_nr - rename_count);
> -	num_sources = rename_src_nr;
> -	if (detect_rename != DIFF_DETECT_COPY)
> -		num_sources -= rename_count;
> +	num_sources = remove_unneeded_paths_from_src(rename_src_nr, want_copies);