@matheusbsbs / matheus-bagliano / commits / a3540ed20e

line-log: avoid unnecessary tree diffs when processing merge commits

In process_ranges_merge_commit(), the line-level log first creates an array of diff queues by iterating over all parents of a merge commit and computing a tree diff for each. Then in a second loop it iterates over those diff queues, and if it finds that none of the interesting paths were modified in one of them, then it will return early. This means that when none of the interesting paths were modified between a merge and its first parent, then the tree diff between the merge and its second (Nth...) parent was computed in vain. Unify these two loops, so when it iterates over all parents of a merge commit, then it first computes the tree diff between the merge and that particular parent and then processes the resulting diff queue right away. This way we can spare some tree diff computing, thereby speeding up line-level log in repositories with mergy history: # git.git, 25.8% of commits are merges: Benchmark 1: ./git_v2.51.0 -C ~/src/git log -L:'lookup_commit(':commit.c v2.51.0 Time (mean ± σ): 1.001 s ± 0.009 s [User: 0.906 s, System: 0.095 s] Range (min … max): 0.991 s … 1.023 s 10 runs Benchmark 2: ./git -C ~/src/git log -L:'lookup_commit(':commit.c v2.51.0 Time (mean ± σ): 445.5 ms ± 3.4 ms [User: 358.8 ms, System: 84.3 ms] Range (min … max): 440.1 ms … 450.3 ms 10 runs Summary './git -C ~/src/git log -L:'lookup_commit(':commit.c v2.51.0' ran 2.25 ± 0.03 times faster than './git_v2.51.0 -C ~/src/git log -L:'lookup_commit(':commit.c v2.51.0' # linux.git, 7.5% of commits are merges: Benchmark 1: ./git_v2.51.0 -C ~/src/linux.git log -L:build_restore_work_registers:arch/mips/mm/tlbex.c v6.16 Time (mean ± σ): 3.246 s ± 0.007 s [User: 2.835 s, System: 0.409 s] Range (min … max): 3.232 s … 3.255 s 10 runs Benchmark 2: ./git -C ~/src/linux.git log -L:build_restore_work_registers:arch/mips/mm/tlbex.c v6.16 Time (mean ± σ): 2.467 s ± 0.014 s [User: 2.113 s, System: 0.353 s] Range (min … max): 2.455 s … 2.505 s 10 runs Summary './git -C ~/src/linux.git log -L:build_restore_work_registers:arch/mips/mm/tlbex.c v6.16' ran 1.32 ± 0.01 times faster than './git_v2.51.0 -C ~/src/linux.git log -L:build_restore_work_registers:arch/mips/mm/tlbex.c v6.16' And since now each iteration computes a tree diff and processes its result, there is no reason to store the diff queues for each merge parent anymore, so replace that diff queue array with a loop-local diff queue variable. With this change the static free_diffqueues() helper function in 'line-log.c' has no more callers left, remove it. Signed-off-by: SZEDER Gábor <szeder.dev@gmail.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>

SZEDER Gábor committed Aug 24, 2025 at 21:06 UTC a3540ed20efad4e1aebb71edac2fc74604f2122e

1 file changed +5 -15

line-log.c

+5 -15

@@ -1087,13 +1087,6 @@ static struct diff_filepair *diff_filepair_dup(struct diff_filepair *pair)

1087 return new_filepair;

1088 }

1089

1090 -static void free_diffqueues(int n, struct diff_queue_struct *dq)

1091 -{

1092 - for (int i = 0; i < n; i++)

1093 - diff_queue_clear(&dq[i]);

1094 - free(dq);

1095 -}

1096 -

1090 static int process_all_files(struct line_log_data **range_out,

1091 struct rev_info *rev,

1092 struct diff_queue_struct *queue,

@@ -1209,7 +1202,6 @@ static int process_ranges_ordinary_commit(struct rev_info *rev, struct commit *c

1202 static int process_ranges_merge_commit(struct rev_info *rev, struct commit *commit,

1203 struct line_log_data *range)

1204 {

1212 - struct diff_queue_struct *diffqueues;

1205 struct line_log_data **cand;

1206 struct commit **parents;

1207 struct commit_list *p;

@@ -1220,20 +1212,19 @@ static int process_ranges_merge_commit(struct rev_info *rev, struct commit *comm

1212 if (nparents > 1 && rev->first_parent_only)

1213 nparents = 1;

1214

1223 - ALLOC_ARRAY(diffqueues, nparents);

1215 CALLOC_ARRAY(cand, nparents);

1216 ALLOC_ARRAY(parents, nparents);

1217

1218 p = commit->parents;

1219 for (i = 0; i < nparents; i++) {

1220 + struct diff_queue_struct diffqueue = DIFF_QUEUE_INIT;

1221 + int changed;

1222 parents[i] = p->item;

1223 p = p->next;

1231 - queue_diffs(range, &rev->diffopt, &diffqueues[i], commit, parents[i]);

1232 - }

1224 + queue_diffs(range, &rev->diffopt, &diffqueue, commit, parents[i]);

1225

1234 - for (i = 0; i < nparents; i++) {

1235 - int changed;

1236 - changed = process_all_files(&cand[i], rev, &diffqueues[i], range);

1226 + changed = process_all_files(&cand[i], rev, &diffqueue, range);

1227 + diff_queue_clear(&diffqueue);

1228 if (!changed) {

1229 /*

1230 * This parent can take all the blame, so we

@@ -1267,7 +1258,6 @@ out:

1258 free(cand[i]);

1259 }

1260 free(cand);

1270 - free_diffqueues(nparents, diffqueues);

1261 return ret;

1262

1263 /* NEEDSWORK evil merge detection stuff */