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tag: speed up --contains calculation 

When we want to know if commit A contains commit B (or any
one of a set of commits, B through Z), we generally
calculate the merge bases and see if B is a merge base of A
(or for a set, if any of the commits B through Z have that
property).

When we are going to check a series of commits A1 through An
to see whether each contains B (e.g., because we are
deciding which tags to show with "git tag --contains"), we
do a series of merge base calculations. This can be very
expensive, as we repeat a lot of traversal work.

Instead, let's leverage the fact that we are going to use
the same --contains list for each tag, and mark areas of the
commit graph is definitely containing those commits, or
definitely not containing those commits. Later tags can then
stop traversing as soon as they see a previously calculated
answer.

This sped up "git tag --contains HEAD~200" in the linux-2.6
repository from:

  real    0m15.417s
  user    0m15.197s
  sys     0m0.220s

to:

  real    0m5.329s
  user    0m5.144s
  sys     0m0.184s

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
This commit is contained in:
Jeff King 2011-06-11 19:04:08 +00:00 committed by Junio C Hamano
parent 45e9a825ed
commit ffc4b8012d
1 changed files with 45 additions and 1 deletions
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46
builtin/tag.c
View File

@ -12,6 +12,8 @@
#include "tag.h"
#include "run-command.h"
#include "parse-options.h"
#include "diff.h"
#include "revision.h"
static const char * const git_tag_usage[] = {
"git tag [-a|-s|-u <key-id>] [-f] [-m <msg>|-F <file>] <tagname> [<head>]",
@ -31,6 +33,48 @@ struct tag_filter {
#define PGP_SIGNATURE "-----BEGIN PGP SIGNATURE-----"
static int in_commit_list(const struct commit_list *want, struct commit *c)
{
for (; want; want = want->next)
if (!hashcmp(want->item->object.sha1, c->object.sha1))
return 1;
return 0;
}
static int contains_recurse(struct commit *candidate,
const struct commit_list *want)
{
struct commit_list *p;
/* was it previously marked as containing a want commit? */
if (candidate->object.flags & TMP_MARK)
return 1;
/* or marked as not possibly containing a want commit? */
if (candidate->object.flags & UNINTERESTING)
return 0;
/* or are we it? */
if (in_commit_list(want, candidate))
return 1;
if (parse_commit(candidate) < 0)
return 0;
/* Otherwise recurse and mark ourselves for future traversals. */
for (p = candidate->parents; p; p = p->next) {
if (contains_recurse(p->item, want)) {
candidate->object.flags |= TMP_MARK;
return 1;
}
}
candidate->object.flags |= UNINTERESTING;
return 0;
}
static int contains(struct commit *candidate, const struct commit_list *want)
{
return contains_recurse(candidate, want);
}
static int show_reference(const char *refname, const unsigned char *sha1,
int flag, void *cb_data)
{
@ -49,7 +93,7 @@ static int show_reference(const char *refname, const unsigned char *sha1,
commit = lookup_commit_reference_gently(sha1, 1);
if (!commit)
return 0;
if (!is_descendant_of(commit, filter->with_commit))
if (!contains(commit, filter->with_commit))
return 0;
}