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diffcore-rename: avoid doing basename comparisons for irrelevant sources 

The basename comparison optimization implemented in
find_basename_matches() is very beneficial since it allows a source to
sometimes only be compared with one other file instead of N other files.
When a match is found, both a source and destination can be removed from
the matrix of inexact rename comparisons.  In contrast, the irrelevant
source optimization only allows us to remove a source from the matrix of
inexact rename comparisons...but it has the advantage of allowing a
source file to not even be loaded into memory at all and be compared to
0 other files.  Generally, not even comparing is a bigger performance
win, so when both optimizations could apply, prefer to use the
irrelevant-source optimization.

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:        5.708 s ±  0.111 s     5.680 s ±  0.096 s
    mega-renames:    102.171 s ±  0.440 s    13.812 s ±  0.162 s
    just-one-mega:     3.471 s ±  0.015 s   506.0  ms ±  3.9  ms

Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
maint
Elijah Newren 2021-03-11 00:38:31 +00:00 committed by Junio C Hamano
parent f89b4f2bee
commit e4fd06e7e2
1 changed files with 33 additions and 4 deletions
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37
diffcore-rename.c
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@ -527,6 +527,7 @@ static void update_dir_rename_counts(struct dir_rename_info *info,
} }


static void initialize_dir_rename_info(struct dir_rename_info *info, static void initialize_dir_rename_info(struct dir_rename_info *info,
struct strset *relevant_sources,
struct strset *dirs_removed, struct strset *dirs_removed,
struct strmap *dir_rename_count) struct strmap *dir_rename_count)
{ {
@ -534,7 +535,7 @@ static void initialize_dir_rename_info(struct dir_rename_info *info,
struct strmap_entry *entry; struct strmap_entry *entry;
int i; int i;


if (!dirs_removed) { if (!dirs_removed && !relevant_sources) {
info->setup = 0; info->setup = 0;
return; return;
} }
@ -549,7 +550,20 @@ static void initialize_dir_rename_info(struct dir_rename_info *info,
strmap_init_with_options(&info->dir_rename_guess, NULL, 0); strmap_init_with_options(&info->dir_rename_guess, NULL, 0);


/* Setup info->relevant_source_dirs */ /* Setup info->relevant_source_dirs */
info->relevant_source_dirs = dirs_removed; info->relevant_source_dirs = NULL;
if (dirs_removed || !relevant_sources) {
info->relevant_source_dirs = dirs_removed; /* might be NULL */
} else {
info->relevant_source_dirs = xmalloc(sizeof(struct strintmap));
strset_init(info->relevant_source_dirs);
strset_for_each_entry(relevant_sources, &iter, entry) {
char *dirname = get_dirname(entry->key);
if (!dirs_removed ||
strset_contains(dirs_removed, dirname))
strset_add(info->relevant_source_dirs, dirname);
free(dirname);
}
}


/* /*
* Loop setting up both info->idx_map, and doing setup of * Loop setting up both info->idx_map, and doing setup of
@ -627,6 +641,13 @@ static void cleanup_dir_rename_info(struct dir_rename_info *info,
/* dir_rename_guess */ /* dir_rename_guess */
strmap_clear(&info->dir_rename_guess, 1); strmap_clear(&info->dir_rename_guess, 1);


/* relevant_source_dirs */
if (info->relevant_source_dirs &&
info->relevant_source_dirs != dirs_removed) {
strset_clear(info->relevant_source_dirs);
FREE_AND_NULL(info->relevant_source_dirs);
}

/* dir_rename_count */ /* dir_rename_count */
if (!keep_dir_rename_count) { if (!keep_dir_rename_count) {
partial_clear_dir_rename_count(info->dir_rename_count); partial_clear_dir_rename_count(info->dir_rename_count);
@ -749,6 +770,7 @@ static int idx_possible_rename(char *filename, struct dir_rename_info *info)
static int find_basename_matches(struct diff_options *options, static int find_basename_matches(struct diff_options *options,
int minimum_score, int minimum_score,
struct dir_rename_info *info, struct dir_rename_info *info,
struct strset *relevant_sources,
struct strset *dirs_removed) struct strset *dirs_removed)
{ {
/* /*
@ -839,6 +861,11 @@ static int find_basename_matches(struct diff_options *options,
intptr_t src_index; intptr_t src_index;
intptr_t dst_index; intptr_t dst_index;


/* Skip irrelevant sources */
if (relevant_sources &&
!strset_contains(relevant_sources, filename))
continue;

/* /*
* If the basename is unique among remaining sources, then * If the basename is unique among remaining sources, then
* src_index will equal 'i' and we can attempt to match it * src_index will equal 'i' and we can attempt to match it
@ -1164,7 +1191,7 @@ void diffcore_rename_extended(struct diff_options *options,


/* Preparation for basename-driven matching. */ /* Preparation for basename-driven matching. */
trace2_region_enter("diff", "dir rename setup", options->repo); trace2_region_enter("diff", "dir rename setup", options->repo);
initialize_dir_rename_info(&info, initialize_dir_rename_info(&info, relevant_sources,
dirs_removed, dir_rename_count); dirs_removed, dir_rename_count);
trace2_region_leave("diff", "dir rename setup", options->repo); trace2_region_leave("diff", "dir rename setup", options->repo);


@ -1172,7 +1199,9 @@ void diffcore_rename_extended(struct diff_options *options,
trace2_region_enter("diff", "basename matches", options->repo); trace2_region_enter("diff", "basename matches", options->repo);
rename_count += find_basename_matches(options, rename_count += find_basename_matches(options,
min_basename_score, min_basename_score,
&info, dirs_removed); &info,
relevant_sources,
dirs_removed);
trace2_region_leave("diff", "basename matches", options->repo); trace2_region_leave("diff", "basename matches", options->repo);


/* /*