Re: [PATCH 2/2] line-log: avoid unnecessary full tree diffs

> On Wed, Aug 21, 2019 at 07:35:15PM +0200, SZEDER Gábor wrote:
>> So line-level log clearly computes a lot less diffs than
>> '--full-history', though still about 50% more than a regular
>> pathspec-limited history traversal.  Looking at the commit-parent
>> pairs in the output, it appears that the difference comes mostly from
>> merge commits, because line-level log compares a merge commit with all
>> of its parents.
> 
>> It seems there is still more room for improvements by avoiding
>> commit-non_first_parent diffs when the first parent is TREESAME, and
>> doing so could hopefully avoid triggering rename detection in those
>> subtree merges or in case of your evil path.
> 
> Well, that fruit hung much lower than I though, just look at the size
> of the WIP patch below.  I just hope that there are no unexpected
> surprises, but FWIW it produces the exact same output for all files up
> to 't/t5515' in v2.23.0 as the previous patch.
> 
> Can't wait to see how it fares with that evil Windows path :)

>   --- >8 ---
> 
> Subject: [PATCH 3/2] WIP line-log: stop diff-ing after first TREESAME merge parent
> 
>   # git.git, ~25% of all commits are merges
>   $ time git --no-pager log -L:read_alternate_refs:sha1-file.c v2.23.0
> 
>   Before:
> 
>     real    0m2.516s
>     user    0m2.456s
>     sys     0m0.060s
> 
>   After:
> 
>     real    0m1.132s
>     user    0m1.096s
>     sys     0m0.036s
> 
>   # linux.git, ~7% of all commits are merges
>   $ time ~/src/git/git --no-pager log \
>     -L:build_restore_work_registers:arch/mips/mm/tlbex.c v5.2
> 
>   Before:
> 
>     real    0m2.599s
>     user    0m2.466s
>     sys     0m0.157s
> 
>   After:
> 
>     real    0m1.976s
>     user    0m1.856s
>     sys     0m0.121s
> 
> [TODO: get rid of unnecessary arrays, tests?, write commit message...]
> ---
>  line-log.c | 6 ++----
>  1 file changed, 2 insertions(+), 4 deletions(-)
> 
> diff --git a/line-log.c b/line-log.c
> index 9010e00950..a4b032f83a 100644
> --- a/line-log.c
> +++ b/line-log.c
> @@ -1184,13 +1184,11 @@ static int process_ranges_merge_commit(struct rev_info *rev, struct commit *comm
>  
>  	p = commit->parents;
>  	for (i = 0; i < nparents; i++) {
> +		int changed;
>  		parents[i] = p->item;
>  		p = p->next;
>  		queue_diffs(range, &rev->diffopt, &diffqueues[i], commit, parents[i]);
> -	}
>  
> -	for (i = 0; i < nparents; i++) {
> -		int changed;
>  		cand[i] = NULL;
>  		changed = process_all_files(&cand[i], rev, &diffqueues[i], range);
>  		if (!changed) {

> @@ -1203,7 +1201,7 @@ static int process_ranges_merge_commit(struct rev_info *rev, struct commit *comm
>  			commit_list_append(parents[i], &commit->parents);
>  			free(parents);
>  			free(cand);
> -			free_diffqueues(nparents, diffqueues);
> +			free_diffqueues(i, diffqueues);