Re: [PATCH v2] diff: disable rename detection with --quiet
On 11/10/25 6:54 PM, Jeff King wrote:
Show 10 quoted lines
>
> I wonder if we should _also_ take the hunk from v1 that teaches
> can_quit_early() to avoid triggering when copy detection is on. It's
> probably redundant now, but it feels to me like that's the place where
> the correctness check should kick in. And the patch here is just
> optimizing out the unnecessary work, but also happens to align things
> for correctness downstream.
>
> But I dunno. Maybe a check for a condition that we think can never be
> triggered becomes too confusing for later maintenance.
That check was only necessary because we queue unchanged filepairs for rename detection as if they were changes. With --quiet forcing rename detection off we won't run into this anymore, but it still feels like a trip hazard. Adding a check would help, but we could also stop doing that in the first place. Patch below.
René
--- >8 ---
Subject: [PATCH] diff-index: don't queue unchanged filepairs with diff_change()
diff_cache() queues unchanged filepairs if the flag find_copies_harder is set, and uses diff_change() for that. This function does a few things that are unnecessary for unchanged filepairs and always sets the diff_flag has_changes, which is simply misleading in this case.
Add a new streamlined function for queuing unchanged filepairs and use it in show_modified(), which is called by diff_cache() via oneway_diff() and do_oneway_diff(). It allocates only one half of each filepair, which has a measurable effect if there are a lot of them, like in the Linux repo:
Benchmark 1: ./git_v2.52.0 -C ../linux diff --cached --find-copies-harder
Time (mean ± σ): 31.8 ms ± 0.2 ms [User: 24.2 ms, System: 6.3 ms]
Range (min … max): 31.5 ms … 32.3 ms 85 runs
Benchmark 2: ./git -C ../linux diff --cached --find-copies-harder
Time (mean ± σ): 23.9 ms ± 0.2 ms [User: 18.1 ms, System: 4.6 ms]
Range (min … max): 23.5 ms … 24.4 ms 111 runs
Summary
./git -C ../linux diff --cached --find-copies-harder ran
1.33 ± 0.01 times faster than ./git_v2.52.0 -C ../linux diff --cached --find-copies-harderSigned-off-by: René Scharfe <l.s.r@web.de>
---
diff-lib.c | 13 ++++++-------
diff.c | 20 ++++++++++++++++++++
diff.h | 5 +++++
3 files changed, 31 insertions(+), 7 deletions(-)
diff --git a/diff-lib.c b/diff-lib.c
index b8f8f3bc31..8e624f38c6 100644
--- a/diff-lib.c
+++ b/diff-lib.c
@@ -418,13 +418,12 @@ static int show_modified(struct rev_info *revs,
}
oldmode = old_entry->ce_mode;
- if (mode == oldmode && oideq(oid, &old_entry->oid) && !dirty_submodule &&
- !revs->diffopt.flags.find_copies_harder)
- return 0;
-
- diff_change(&revs->diffopt, oldmode, mode,
- &old_entry->oid, oid, 1, !is_null_oid(oid),
- old_entry->name, 0, dirty_submodule);
+ if (mode != oldmode || !oideq(oid, &old_entry->oid) || dirty_submodule)
+ diff_change(&revs->diffopt, oldmode, mode,
+ &old_entry->oid, oid, 1, !is_null_oid(oid),
+ old_entry->name, 0, dirty_submodule);
+ else if (revs->diffopt.flags.find_copies_harder)
+ diff_same(&revs->diffopt, mode, oid, old_entry->name);
return 0;
}
diff --git a/diff.c b/diff.c
index efa8d9773c..e2a2927f8c 100644
--- a/diff.c
+++ b/diff.c
@@ -7349,6 +7349,26 @@ void diff_change(struct diff_options *options,
concatpath, old_dirty_submodule, new_dirty_submodule);
}
+void diff_same(struct diff_options *options,
+ unsigned mode,
+ const struct object_id *oid,
+ const char *concatpath)
+{
+ struct diff_filespec *one;
+
+ if (S_ISGITLINK(mode) && is_submodule_ignored(concatpath, options))
+ return;
+
+ if (options->prefix &&
+ strncmp(concatpath, options->prefix, options->prefix_length))
+ return;
+
+ one = alloc_filespec(concatpath);
+ fill_filespec(one, oid, 1, mode);
+ one->count++;
+ diff_queue(&diff_queued_diff, one, one);
+}
+
struct diff_filepair *diff_unmerge(struct diff_options *options, const char *path)
{
struct diff_filepair *pair;
diff --git a/diff.h b/diff.h
index 31eedd5c0c..e80503aebb 100644
--- a/diff.h
+++ b/diff.h
@@ -572,6 +572,11 @@ void diff_change(struct diff_options *,
const char *fullpath,
unsigned dirty_submodule1, unsigned dirty_submodule2);
+void diff_same(struct diff_options *,
+ unsigned mode,
+ const struct object_id *oid,
+ const char *fullpath);
+
struct diff_filepair *diff_unmerge(struct diff_options *, const char *path);
void compute_diffstat(struct diff_options *options, struct diffstat_t *diffstat,
--
2.52.0
D. Ben Knoble
