git/diffcore-break.c
Jeff King 8282de94bc diffcore-break: save cnt_data for other phases
The "break" phase works by counting changes between two
blobs with the same path. We do this by splitting the file
into chunks (or lines for text oriented files) and then
keeping a count of chunk hashes.

The "rename" phase counts changes between blobs at two
different paths. However, it uses the exact same set of
chunk hashes (which are immutable for a given sha1).

The rename phase can therefore use the same hash data as
break. Unfortunately, we were throwing this data away after
computing it in the break phase. This patch instead attaches
it to the filespec and lets it live through the rename
phase, working under the assumption that most of the time
that breaks are being computed, renames will be too.

We only do this optimization for files which have actually
been broken, as those ones will be candidates for rename
detection (and it is a time-space tradeoff, so we don't want
to waste space keeping useless data).

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
2009-11-16 13:21:12 -08:00

297 lines
8.7 KiB
C

/*
* Copyright (C) 2005 Junio C Hamano
*/
#include "cache.h"
#include "diff.h"
#include "diffcore.h"
static int should_break(struct diff_filespec *src,
struct diff_filespec *dst,
int break_score,
int *merge_score_p)
{
/* dst is recorded as a modification of src. Are they so
* different that we are better off recording this as a pair
* of delete and create?
*
* There are two criteria used in this algorithm. For the
* purposes of helping later rename/copy, we take both delete
* and insert into account and estimate the amount of "edit".
* If the edit is very large, we break this pair so that
* rename/copy can pick the pieces up to match with other
* files.
*
* On the other hand, we would want to ignore inserts for the
* pure "complete rewrite" detection. As long as most of the
* existing contents were removed from the file, it is a
* complete rewrite, and if sizable chunk from the original
* still remains in the result, it is not a rewrite. It does
* not matter how much or how little new material is added to
* the file.
*
* The score we leave for such a broken filepair uses the
* latter definition so that later clean-up stage can find the
* pieces that should not have been broken according to the
* latter definition after rename/copy runs, and merge the
* broken pair that have a score lower than given criteria
* back together. The break operation itself happens
* according to the former definition.
*
* The minimum_edit parameter tells us when to break (the
* amount of "edit" required for us to consider breaking the
* pair). We leave the amount of deletion in *merge_score_p
* when we return.
*
* The value we return is 1 if we want the pair to be broken,
* or 0 if we do not.
*/
unsigned long delta_size, max_size;
unsigned long src_copied, literal_added, src_removed;
*merge_score_p = 0; /* assume no deletion --- "do not break"
* is the default.
*/
if (S_ISREG(src->mode) != S_ISREG(dst->mode)) {
*merge_score_p = (int)MAX_SCORE;
return 1; /* even their types are different */
}
if (src->sha1_valid && dst->sha1_valid &&
!hashcmp(src->sha1, dst->sha1))
return 0; /* they are the same */
if (diff_populate_filespec(src, 0) || diff_populate_filespec(dst, 0))
return 0; /* error but caught downstream */
max_size = ((src->size > dst->size) ? src->size : dst->size);
if (max_size < MINIMUM_BREAK_SIZE)
return 0; /* we do not break too small filepair */
if (diffcore_count_changes(src, dst,
&src->cnt_data, &dst->cnt_data,
0,
&src_copied, &literal_added))
return 0;
/* sanity */
if (src->size < src_copied)
src_copied = src->size;
if (dst->size < literal_added + src_copied) {
if (src_copied < dst->size)
literal_added = dst->size - src_copied;
else
literal_added = 0;
}
src_removed = src->size - src_copied;
/* Compute merge-score, which is "how much is removed
* from the source material". The clean-up stage will
* merge the surviving pair together if the score is
* less than the minimum, after rename/copy runs.
*/
*merge_score_p = (int)(src_removed * MAX_SCORE / src->size);
if (*merge_score_p > break_score)
return 1;
/* Extent of damage, which counts both inserts and
* deletes.
*/
delta_size = src_removed + literal_added;
if (delta_size * MAX_SCORE / max_size < break_score)
return 0;
/* If you removed a lot without adding new material, that is
* not really a rewrite.
*/
if ((src->size * break_score < src_removed * MAX_SCORE) &&
(literal_added * 20 < src_removed) &&
(literal_added * 20 < src_copied))
return 0;
return 1;
}
void diffcore_break(int break_score)
{
struct diff_queue_struct *q = &diff_queued_diff;
struct diff_queue_struct outq;
/* When the filepair has this much edit (insert and delete),
* it is first considered to be a rewrite and broken into a
* create and delete filepair. This is to help breaking a
* file that had too much new stuff added, possibly from
* moving contents from another file, so that rename/copy can
* match it with the other file.
*
* int break_score; we reuse incoming parameter for this.
*/
/* After a pair is broken according to break_score and
* subjected to rename/copy, both of them may survive intact,
* due to lack of suitable rename/copy peer. Or, the caller
* may be calling us without using rename/copy. When that
* happens, we merge the broken pieces back into one
* modification together if the pair did not have more than
* this much delete. For this computation, we do not take
* insert into account at all. If you start from a 100-line
* file and delete 97 lines of it, it does not matter if you
* add 27 lines to it to make a new 30-line file or if you add
* 997 lines to it to make a 1000-line file. Either way what
* you did was a rewrite of 97%. On the other hand, if you
* delete 3 lines, keeping 97 lines intact, it does not matter
* if you add 3 lines to it to make a new 100-line file or if
* you add 903 lines to it to make a new 1000-line file.
* Either way you did a lot of additions and not a rewrite.
* This merge happens to catch the latter case. A merge_score
* of 80% would be a good default value (a broken pair that
* has score lower than merge_score will be merged back
* together).
*/
int merge_score;
int i;
/* See comment on DEFAULT_BREAK_SCORE and
* DEFAULT_MERGE_SCORE in diffcore.h
*/
merge_score = (break_score >> 16) & 0xFFFF;
break_score = (break_score & 0xFFFF);
if (!break_score)
break_score = DEFAULT_BREAK_SCORE;
if (!merge_score)
merge_score = DEFAULT_MERGE_SCORE;
outq.nr = outq.alloc = 0;
outq.queue = NULL;
for (i = 0; i < q->nr; i++) {
struct diff_filepair *p = q->queue[i];
int score;
/*
* We deal only with in-place edit of blobs.
* We do not break anything else.
*/
if (DIFF_FILE_VALID(p->one) && DIFF_FILE_VALID(p->two) &&
object_type(p->one->mode) == OBJ_BLOB &&
object_type(p->two->mode) == OBJ_BLOB &&
!strcmp(p->one->path, p->two->path)) {
if (should_break(p->one, p->two,
break_score, &score)) {
/* Split this into delete and create */
struct diff_filespec *null_one, *null_two;
struct diff_filepair *dp;
/* Set score to 0 for the pair that
* needs to be merged back together
* should they survive rename/copy.
* Also we do not want to break very
* small files.
*/
if (score < merge_score)
score = 0;
/* deletion of one */
null_one = alloc_filespec(p->one->path);
dp = diff_queue(&outq, p->one, null_one);
dp->score = score;
dp->broken_pair = 1;
/* creation of two */
null_two = alloc_filespec(p->two->path);
dp = diff_queue(&outq, null_two, p->two);
dp->score = score;
dp->broken_pair = 1;
diff_free_filespec_blob(p->one);
diff_free_filespec_blob(p->two);
free(p); /* not diff_free_filepair(), we are
* reusing one and two here.
*/
continue;
}
}
diff_free_filespec_data(p->one);
diff_free_filespec_data(p->two);
diff_q(&outq, p);
}
free(q->queue);
*q = outq;
return;
}
static void merge_broken(struct diff_filepair *p,
struct diff_filepair *pp,
struct diff_queue_struct *outq)
{
/* p and pp are broken pairs we want to merge */
struct diff_filepair *c = p, *d = pp, *dp;
if (DIFF_FILE_VALID(p->one)) {
/* this must be a delete half */
d = p; c = pp;
}
/* Sanity check */
if (!DIFF_FILE_VALID(d->one))
die("internal error in merge #1");
if (DIFF_FILE_VALID(d->two))
die("internal error in merge #2");
if (DIFF_FILE_VALID(c->one))
die("internal error in merge #3");
if (!DIFF_FILE_VALID(c->two))
die("internal error in merge #4");
dp = diff_queue(outq, d->one, c->two);
dp->score = p->score;
diff_free_filespec_data(d->two);
diff_free_filespec_data(c->one);
free(d);
free(c);
}
void diffcore_merge_broken(void)
{
struct diff_queue_struct *q = &diff_queued_diff;
struct diff_queue_struct outq;
int i, j;
outq.nr = outq.alloc = 0;
outq.queue = NULL;
for (i = 0; i < q->nr; i++) {
struct diff_filepair *p = q->queue[i];
if (!p)
/* we already merged this with its peer */
continue;
else if (p->broken_pair &&
!strcmp(p->one->path, p->two->path)) {
/* If the peer also survived rename/copy, then
* we merge them back together.
*/
for (j = i + 1; j < q->nr; j++) {
struct diff_filepair *pp = q->queue[j];
if (pp->broken_pair &&
!strcmp(pp->one->path, pp->two->path) &&
!strcmp(p->one->path, pp->two->path)) {
/* Peer survived. Merge them */
merge_broken(p, pp, &outq);
q->queue[j] = NULL;
break;
}
}
if (q->nr <= j)
/* The peer did not survive, so we keep
* it in the output.
*/
diff_q(&outq, p);
}
else
diff_q(&outq, p);
}
free(q->queue);
*q = outq;
return;
}