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diffcore-rename: no point trying to find a match better than exact

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diffcore_rename() had some code to avoid having destination paths that
already had an exact rename detected from being re-checked for other
renames.  Source paths, however, were re-checked because we wanted to
allow the possibility of detecting copies.  But if copy detection isn't
turned on, then this merely amounts to attempting to find a
better-than-exact match, which naturally ends up being an expensive
no-op.  In particular, copy detection is never turned on by the merge
machinery.

For the testcases mentioned in commit 557ac0350d ("merge-ort: begin
performance work; instrument with trace2_region_* calls", 2020-10-28),
this change improves the performance as follows:

                            Before                  After
    no-renames:       14.263 s ±  0.053 s    14.119 s ±  0.101 s
    mega-renames:   5504.231 s ±  5.150 s  1802.044 s ±  0.828 s
    just-one-mega:   158.534 s ±  0.498 s    51.391 s ±  0.028 s

Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
This commit is contained in:
Elijah Newren 2021-02-03 20:03:46 +00:00 committed by Junio C Hamano
parent f011795891
commit f15eb7c1cf
1 changed files with 14 additions and 6 deletions
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20
diffcore-rename.c
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@ -463,9 +463,11 @@ 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, 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;
@ -502,7 +504,7 @@ void diffcore_rename(struct diff_options *options)
p->one->rename_used++;
register_rename_src(p);
}
else if (detect_rename == DIFF_DETECT_COPY) {
else if (want_copies) {
/*
* Increment the "rename_used" score by
* one, to indicate ourselves as a user.
@ -532,12 +534,15 @@ void diffcore_rename(struct diff_options *options)
* files still remain as options for rename/copies!)
*/
num_destinations = (rename_dst_nr - rename_count);
num_sources = rename_src_nr;
if (!want_copies)
num_sources -= rename_count;
/* All done? */
if (!num_destinations)
if (!num_destinations || !num_sources)
goto cleanup;
switch (too_many_rename_candidates(num_destinations, rename_src_nr,
switch (too_many_rename_candidates(num_destinations, num_sources,
options)) {
case 1:
goto cleanup;
@ -553,7 +558,7 @@ void diffcore_rename(struct diff_options *options)
if (options->show_rename_progress) {
progress = start_delayed_progress(
_("Performing inexact rename detection"),
(uint64_t)num_destinations * (uint64_t)rename_src_nr);
(uint64_t)num_destinations * (uint64_t)num_sources);
}
mx = xcalloc(st_mult(NUM_CANDIDATE_PER_DST, num_destinations),
@ -573,6 +578,9 @@ void diffcore_rename(struct diff_options *options)
struct diff_filespec *one = rename_src[j].p->one;
struct diff_score this_src;
if (one->rename_used && !want_copies)
continue;
if (skip_unmodified &&
diff_unmodified_pair(rename_src[j].p))
continue;
@ -594,7 +602,7 @@ void diffcore_rename(struct diff_options *options)
}
dst_cnt++;
display_progress(progress,
(uint64_t)dst_cnt * (uint64_t)rename_src_nr);
(uint64_t)dst_cnt * (uint64_t)num_sources);
}
stop_progress(&progress);
@ -602,7 +610,7 @@ void diffcore_rename(struct diff_options *options)
STABLE_QSORT(mx, dst_cnt * NUM_CANDIDATE_PER_DST, score_compare);
rename_count += find_renames(mx, dst_cnt, minimum_score, 0);
if (detect_rename == DIFF_DETECT_COPY)
if (want_copies)
rename_count += find_renames(mx, dst_cnt, minimum_score, 1);
free(mx);
trace2_region_leave("diff", "inexact renames", options->repo);