From: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Subject: [PATCH 4/6] copy vs rename detection: avoid unnecessary O(n*m) loops
The core rename detection had some rather stupid code to check if a
pathname was used by a later modification or rename, which basically
walked the whole pathname space for all renames for each rename, in
order to tell whether it was a pure rename (no remaining users) or
should be considered a copy (other users of the source file remaining).
That's really silly, since we can just keep a count of users around, and
replace all those complex and expensive loops with just testing that
simple counter (but this all depends on the previous commit that shared
the diff_filespec data structure by using a separate reference count).
Note that the reference count is not the same as the rename count: they
behave otherwise rather similarly, but the reference count is tied to
the allocation (and decremented at de-allocation, so that when it turns
zero we can get rid of the memory), while the rename count is tied to
the renames and is decremented when we find a rename (so that when it
turns zero we know that it was a rename, not a copy).
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
---
This fixes the generic diffcode infrastructure, but doesn't do the actual
*detection* any faster. But as you can tell, it's a huge cleanup on its
own, and basically removes the "incidental" and stupid support costs of
rename detection.
diff.c | 40 +++++++++++++------------------
diffcore-rename.c | 68 +++++++++++++---------------------------------------
diffcore.h | 2 +-
3 files changed, 35 insertions(+), 75 deletions(-)
diff --git a/diff.c b/diff.c
index 0b320f6..af85b94 100644
--- a/diff.c
+++ b/diff.c
@@ -2597,9 +2597,9 @@ void diff_debug_filepair(const struct diff_filepair *p, int i)
{
diff_debug_filespec(p->one, i, "one");
diff_debug_filespec(p->two, i, "two");
- fprintf(stderr, "score %d, status %c stays %d broken %d\n",
+ fprintf(stderr, "score %d, status %c rename_used %d broken %d\n",
p->score, p->status ? p->status : '?',
- p->source_stays, p->broken_pair);
+ p->one->rename_used, p->broken_pair);
}
void diff_debug_queue(const char *msg, struct diff_queue_struct *q)
@@ -2617,8 +2617,8 @@ void diff_debug_queue(const char *msg, struct diff_queue_struct *q)
static void diff_resolve_rename_copy(void)
{
- int i, j;
- struct diff_filepair *p, *pp;
+ int i;
+ struct diff_filepair *p;
struct diff_queue_struct *q = &diff_queued_diff;
diff_debug_queue("resolve-rename-copy", q);
@@ -2640,27 +2640,21 @@ static void diff_resolve_rename_copy(void)
* either in-place edit or rename/copy edit.
*/
else if (DIFF_PAIR_RENAME(p)) {
- if (p->source_stays) {
- p->status = DIFF_STATUS_COPIED;
- continue;
- }
- /* See if there is some other filepair that
- * copies from the same source as us. If so
- * we are a copy. Otherwise we are either a
- * copy if the path stays, or a rename if it
- * does not, but we already handled "stays" case.
+ /*
+ * A rename might have re-connected a broken
+ * pair up, causing the pathnames to be the
+ * same again. If so, that's not a rename at
+ * all, just a modification..
+ *
+ * Otherwise, see if this source was used for
+ * multiple renames, in which case we decrement
+ * the count, and call it a copy.
*/
- for (j = i + 1; j < q->nr; j++) {
- pp = q->queue[j];
- if (strcmp(pp->one->path, p->one->path))
- continue; /* not us */
- if (!DIFF_PAIR_RENAME(pp))
- continue; /* not a rename/copy */
- /* pp is a rename/copy from the same source */
+ if (!strcmp(p->one->path, p->two->path))
+ p->status = DIFF_STATUS_MODIFIED;
+ else if (--p->one->rename_used > 0)
p->status = DIFF_STATUS_COPIED;
- break;
- }
- if (!p->status)
+ else
p->status = DIFF_STATUS_RENAMED;
}
else if (hashcmp(p->one->sha1, p->two->sha1) ||
diff --git a/diffcore-rename.c b/diffcore-rename.c
index 3da06b7..edb2424 100644
--- a/diffcore-rename.c
+++ b/diffcore-rename.c
@@ -55,12 +55,10 @@ static struct diff_rename_dst *locate_rename_dst(struct diff_filespec *two,
static struct diff_rename_src {
struct diff_filespec *one;
unsigned short score; /* to remember the break score */
- unsigned src_path_left : 1;
} *rename_src;
static int rename_src_nr, rename_src_alloc;
static struct diff_rename_src *register_rename_src(struct diff_filespec *one,
- int src_path_left,
unsigned short score)
{
int first, last;
@@ -92,7 +90,6 @@ static struct diff_rename_src *register_rename_src(struct diff_filespec *one,
(rename_src_nr - first - 1) * sizeof(*rename_src));
rename_src[first].one = one;
rename_src[first].score = score;
- rename_src[first].src_path_left = src_path_left;
return &(rename_src[first]);
}
@@ -216,6 +213,7 @@ static void record_rename_pair(int dst_index, int src_index, int score)
die("internal error: dst already matched.");
src = rename_src[src_index].one;
+ src->rename_used++;
src->count++;
dst = rename_dst[dst_index].two;
@@ -227,7 +225,6 @@ static void record_rename_pair(int dst_index, int src_index, int score)
dp->score = rename_src[src_index].score;
else
dp->score = score;
- dp->source_stays = rename_src[src_index].src_path_left;
rename_dst[dst_index].pair = dp;
}
@@ -245,21 +242,6 @@ static int score_compare(const void *a_, const void *b_)
return b->score - a->score;
}
-static int compute_stays(struct diff_queue_struct *q,
- struct diff_filespec *one)
-{
- int i;
- for (i = 0; i < q->nr; i++) {
- struct diff_filepair *p = q->queue[i];
- if (strcmp(one->path, p->two->path))
- continue;
- if (DIFF_PAIR_RENAME(p)) {
- return 0; /* something else is renamed into this */
- }
- }
- return 1;
-}
-
/*
* Find exact renames first.
*
@@ -338,15 +320,25 @@ void diffcore_rename(struct diff_options *options)
locate_rename_dst(p->two, 1);
}
else if (!DIFF_FILE_VALID(p->two)) {
- /* If the source is a broken "delete", and
+ /*
+ * If the source is a broken "delete", and
* they did not really want to get broken,
* that means the source actually stays.
+ * So we increment the "rename_used" score
+ * by one, to indicate ourselves as a user
+ */
+ if (p->broken_pair && !p->score)
+ p->one->rename_used++;
+ register_rename_src(p->one, p->score);
+ }
+ else if (detect_rename == DIFF_DETECT_COPY) {
+ /*
+ * Increment the "rename_used" score by
+ * one, to indicate ourselves as a user.
*/
- int stays = (p->broken_pair && !p->score);
- register_rename_src(p->one, stays, p->score);
+ p->one->rename_used++;
+ register_rename_src(p->one, p->score);
}
- else if (detect_rename == DIFF_DETECT_COPY)
- register_rename_src(p->one, 1, p->score);
}
if (rename_dst_nr == 0 || rename_src_nr == 0)
goto cleanup; /* nothing to do */
@@ -472,16 +464,7 @@ void diffcore_rename(struct diff_options *options)
pair_to_free = p;
}
else {
- for (j = 0; j < rename_dst_nr; j++) {
- if (!rename_dst[j].pair)
- continue;
- if (strcmp(rename_dst[j].pair->
- one->path,
- p->one->path))
- continue;
- break;
- }
- if (j < rename_dst_nr)
+ if (p->one->rename_used)
/* this path remains */
pair_to_free = p;
}
@@ -507,23 +490,6 @@ void diffcore_rename(struct diff_options *options)
*q = outq;
diff_debug_queue("done collapsing", q);
- /* We need to see which rename source really stays here;
- * earlier we only checked if the path is left in the result,
- * but even if a path remains in the result, if that is coming
- * from copying something else on top of it, then the original
- * source is lost and does not stay.
- */
- for (i = 0; i < q->nr; i++) {
- struct diff_filepair *p = q->queue[i];
- if (DIFF_PAIR_RENAME(p) && p->source_stays) {
- /* If one appears as the target of a rename-copy,
- * then mark p->source_stays = 0; otherwise
- * leave it as is.
- */
- p->source_stays = compute_stays(q, p->one);
- }
- }
-
for (i = 0; i < rename_dst_nr; i++)
free_filespec(rename_dst[i].two);
diff --git a/diffcore.h b/diffcore.h
index 30055ac..cc96c20 100644
--- a/diffcore.h
+++ b/diffcore.h
@@ -31,6 +31,7 @@ struct diff_filespec {
unsigned long size;
int count; /* Reference count */
int xfrm_flags; /* for use by the xfrm */
+ int rename_used; /* Count of rename users */
unsigned short mode; /* file mode */
unsigned sha1_valid : 1; /* if true, use sha1 and trust mode;
* if false, use the name and read from
@@ -58,7 +59,6 @@ struct diff_filepair {
struct diff_filespec *two;
unsigned short int score;
char status; /* M C R N D U (see Documentation/diff-format.txt) */
- unsigned source_stays : 1; /* all of R/C are copies */
unsigned broken_pair : 1;
unsigned renamed_pair : 1;
unsigned is_unmerged : 1;
--
1.5.3.4.330.g1dec6
-
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