Plug the ort merge backend throughout the rest of the system, and
start testing it as a replacement for the recursive backend.
* en/ort-readiness:
Add testing with merge-ort merge strategy
t6423: mark remaining expected failure under merge-ort as such
Revert "merge-ort: ignore the directory rename split conflict for now"
merge-recursive: add a bunch of FIXME comments documenting known bugs
merge-ort: write $GIT_DIR/AUTO_MERGE whenever we hit a conflict
t: mark several submodule merging tests as fixed under merge-ort
merge-ort: implement CE_SKIP_WORKTREE handling with conflicted entries
t6428: new test for SKIP_WORKTREE handling and conflicts
merge-ort: support subtree shifting
merge-ort: let renormalization change modify/delete into clean delete
merge-ort: have ll_merge() use a special attr_index for renormalization
merge-ort: add a special minimal index just for renormalization
merge-ort: use STABLE_QSORT instead of QSORT where required
Various rename detection optimization to help "ort" merge strategy
backend.
* en/ort-perf-batch-10:
diffcore-rename: determine which relevant_sources are no longer relevant
merge-ort: record the reason that we want a rename for a file
diffcore-rename: add computation of number of unknown renames
diffcore-rename: check if we have enough renames for directories early on
diffcore-rename: only compute dir_rename_count for relevant directories
merge-ort: record the reason that we want a rename for a directory
merge-ort, diffcore-rename: tweak dirs_removed and relevant_source type
diffcore-rename: take advantage of "majority rules" to skip more renames
versions could be an empty string_list. In that case, versions->items is
NULL, and we shouldn't be trying to perform pointer arithmetic with it (as
that results in undefined behaviour).
Moreover we only use the results of this calculation once when calling
QSORT. Therefore we choose to skip creating relevant_entries and call
QSORT directly with our manipulated pointers (but only if there's data
requiring sorting). This lets us avoid abusing the string_list API,
and saves us from having to explain why this abuse is OK.
Finally, an assertion is added to make sure that write_tree() is called
with a valid offset.
This issue has probably existed since:
ee4012dcf9 (merge-ort: step 2 of tree writing -- function to create tree object, 2020-12-13)
But it only started occurring during tests since tests started using
merge-ort:
f3b964a07e (Add testing with merge-ort merge strategy, 2021-03-20)
For reference - here's the original UBSAN commit that implemented this
check, it sounds like this behaviour isn't actually likely to cause any
issues (but we might as well fix it regardless):
https://reviews.llvm.org/D67122
UBSAN output from t3404 or t5601:
merge-ort.c:2669:43: runtime error: applying zero offset to null pointer
#0 0x78bb53 in write_tree merge-ort.c:2669:43
#1 0x7856c9 in process_entries merge-ort.c:3303:2
#2 0x782317 in merge_ort_nonrecursive_internal merge-ort.c:3744:2
#3 0x77feef in merge_incore_nonrecursive merge-ort.c:3853:2
#4 0x6f6a5c in do_recursive_merge sequencer.c:640:3
#5 0x6f6a5c in do_pick_commit sequencer.c:2221:9
#6 0x6ef055 in single_pick sequencer.c:4814:9
#7 0x6ef055 in sequencer_pick_revisions sequencer.c:4867:10
#8 0x4fb392 in run_sequencer revert.c:225:9
#9 0x4fa5b0 in cmd_revert revert.c:235:8
#10 0x42abd7 in run_builtin git.c:453:11
#11 0x429531 in handle_builtin git.c:704:3
#12 0x4282fb in run_argv git.c:771:4
#13 0x4282fb in cmd_main git.c:902:19
#14 0x524b63 in main common-main.c:52:11
#15 0x7fc2ca340349 in __libc_start_main (/lib64/libc.so.6+0x24349)
#16 0x4072b9 in _start start.S:120
SUMMARY: UndefinedBehaviorSanitizer: undefined-behavior merge-ort.c:2669:43 in
Signed-off-by: Andrzej Hunt <ajrhunt@google.com>
Reviewed-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
The ort merge backend has been optimized by skipping irrelevant
renames.
* en/ort-perf-batch-9:
diffcore-rename: avoid doing basename comparisons for irrelevant sources
merge-ort: skip rename detection entirely if possible
merge-ort: use relevant_sources to filter possible rename sources
merge-ort: precompute whether directory rename detection is needed
merge-ort: introduce wrappers for alternate tree traversal
merge-ort: add data structures for an alternate tree traversal
merge-ort: precompute subset of sources for which we need rename detection
diffcore-rename: enable filtering possible rename sources
Rename detection rework continues.
* en/ort-perf-batch-8:
diffcore-rename: compute dir_rename_guess from dir_rename_counts
diffcore-rename: limit dir_rename_counts computation to relevant dirs
diffcore-rename: compute dir_rename_counts in stages
diffcore-rename: extend cleanup_dir_rename_info()
diffcore-rename: move dir_rename_counts into dir_rename_info struct
diffcore-rename: add function for clearing dir_rename_count
Move computation of dir_rename_count from merge-ort to diffcore-rename
diffcore-rename: add a mapping of destination names to their indices
diffcore-rename: provide basic implementation of idx_possible_rename()
diffcore-rename: use directory rename guided basename comparisons
This reverts commit 5ced7c3da0, which was
put in place as a temporary measure to avoid optimizations unstably
erroring out on no destination having a majority of the necessary
renames for directories that had no new files and thus no need for
directory rename detection anyway. Now that optimizations are in place
to prevent us from trying to compute directory rename count computations
for directories that do not need it, we can undo this temporary measure.
Signed-off-by: Elijah Newren <newren@gmail.com>
Reviewed-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
There are a variety of questions users might ask while resolving
conflicts:
* What changes have been made since the previous (first) parent?
* What changes are staged?
* What is still unstaged? (or what is still conflicted?)
* What changes did I make to resolve conflicts so far?
The first three of these have simple answers:
* git diff HEAD
* git diff --cached
* git diff
There was no way to answer the final question previously. Adding one
is trivial in merge-ort, since it works by creating a tree representing
what should be written to the working copy complete with conflict
markers. Simply write that tree to .git/AUTO_MERGE, allowing users to
answer the fourth question with
* git diff AUTO_MERGE
I avoided using a name like "MERGE_AUTO", because that would be
merge-specific (much like MERGE_HEAD, REBASE_HEAD, REVERT_HEAD,
CHERRY_PICK_HEAD) and I wanted a name that didn't change depending on
which type of operation the merge was part of.
Ensure that paths which clean out other temporary operation-specific
files (e.g. CHERRY_PICK_HEAD, MERGE_MSG, rebase-merge/ state directory)
also clean out this AUTO_MERGE file.
Signed-off-by: Elijah Newren <newren@gmail.com>
Reviewed-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
When merge conflicts occur in paths removed by a sparse-checkout, we
need to unsparsify those paths (clear the SKIP_WORKTREE bit), and write
out the conflicted file to the working copy. In the very unlikely case
that someone manually put a file into the working copy at the location
of the SKIP_WORKTREE file, we need to avoid overwriting whatever edits
they have made and move that file to a different location first.
Signed-off-by: Elijah Newren <newren@gmail.com>
Reviewed-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
merge-recursive has some simple code to support subtree shifting; copy
it over to merge-ort. This fixes t6409.12 under
GIT_TEST_MERGE_ALGORITHM=ort.
Signed-off-by: Elijah Newren <newren@gmail.com>
Reviewed-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
When we have a modify/delete conflict, but the only change to the
modification is e.g. change of line endings, then if renormalization is
requested then we should be able to recognize such a case as a
not-modified/delete and resolve the conflict automatically.
This fixes t6418.10 under GIT_TEST_MERGE_ALGORITHM=ort.
Signed-off-by: Elijah Newren <newren@gmail.com>
Reviewed-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
ll_merge() needs an index when renormalization is requested. Create one
specifically for just this purpose with just the one needed entry. This
fixes t6418.4 and t6418.5 under GIT_TEST_MERGE_ALGORITHM=ort.
NOTE 1: Even if the user has a working copy or a real index (which is
not a given as merge-ort can be used in bare repositories), we
explicitly ignore any .gitattributes file from either of these
locations. merge-ort can be used to merge two branches that are
unrelated to HEAD, so .gitattributes from the working copy and current
index should not be considered relevant.
NOTE 2: Since we are in the middle of merging, there is a risk that
.gitattributes itself is conflicted...leaving us with an ill-defined
situation about how to perform the rest of the merge. It could be that
the .gitattributes file does not even exist on one of the sides of the
merge, or that it has been modified on both sides. If it's been
modified on both sides, it's possible that it could itself be merged
cleanly, though it's also possible that it only merges cleanly if you
use the right version of the .gitattributes file to drive the merge. It
gets kind of complicated. The only test we ever had that attempted to
test behavior in this area was seemingly unaware of the undefined
behavior, but knew the test wouldn't work for lack of attribute handling
support, marked it as test_expect_failure from the beginning, but
managed to fail for several reasons unrelated to attribute handling.
See commit 6f6e7cfb52 ("t6038: remove problematic test", 2020-08-03) for
details. So there are probably various ways to improve what
initialize_attr_index() picks in the case of a conflicted .gitattributes
but for now I just implemented something simple -- look for whatever
.gitattributes file we can find in any of the higher order stages and
use it.
Signed-off-by: Elijah Newren <newren@gmail.com>
Reviewed-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
renormalize_buffer() requires an index_state, which is something that
merge-ort does not operate with. However, all the renormalization code
needs is an index with a .gitattributes file...plus a little bit of
setup. Create such an index, along with the deallocation and
attr_direction handling.
A subsequent commit will add a function to finish the initialization
of this index.
Signed-off-by: Elijah Newren <newren@gmail.com>
Reviewed-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
rename/rename conflict handling depends on the fact that if both sides
renamed the same path, that the one on the MERGE_SIDE1 will appear first
in the combined diff_queue_struct passed to process_renames(). Since we
add all pairs from MERGE_SIDE1 to combined first, and then all pairs
from MERGE_SIDE2, and then sort based on filename, this will only be
true if the sort used is stable. This was found due to the fact that
Mac, unlike Linux, apparently has a system-defined qsort that is not
stable.
While we are at it, review the other callers of QSORT and add comments
about why they can remain as calls to QSORT instead of being modified
to call STABLE_QSORT.
Signed-off-by: Elijah Newren <newren@gmail.com>
Reviewed-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
There are two different reasons we might want a rename for a file -- for
three-way content merging or as part of directory rename detection.
Record the reason. diffcore-rename will potentially be able to filter
some of the ones marked as needed only for directory rename detection,
if it can determine those directory renames based solely on renames
found via exact rename detection and basename-guided rename detection.
Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
The previous commit can only be effective if we have a computation of
the number of paths under a given directory which are still have pending
renames, and expected this number to be recorded in the dir_rename_count
map under the key UNKNOWN_DIR. Add the code necessary to compute these
values.
Note that this change means dir_rename_count might have a directory
whose only entry (for UNKNOWN_DIR) was removed by the time merge-ort
goes to check it. To account for this, merge-ort needs to check for the
case where the max count is 0.
With this change we are now computing the necessary value for each
directory in dirs_removed, but are not using that value anywhere. The
next two commits will make use of the values stored in dirs_removed in
order to compute whether each relevant_source (that is needed only for
directory rename detection) has become unnecessary.
Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
When one side of history renames a directory, and the other side of
history added files to the old directory, directory rename detection is
used to warn about the location of the added files so the user can
move them to the old directory or keep them with the new one.
This sets up three different types of directories:
* directories that had new files added to them
* directories underneath a directory that had new files added to them
* directories where no new files were added to it or any leading path
Save this information in dirs_removed; the next several commits will
make use of this information.
Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
As noted in the previous commit, we want to be able to take advantage of
the "majority rules" portion of directory rename detection to avoid
detecting more renames than necessary. However, for diffcore-rename to
take advantage of that, it needs to know whether a rename source file
was needed for just directory rename detection reasons, or if it is
wanted for potential three-way content merging. Modify relevant_sources
from a strset to a strintmap, so we can encode additional information.
We also modify dirs_removed from a strset to a strintmap at the same
time because trying to determine what files are needed for directory
rename detection will require us tracking a bit more information for
each directory.
This commit only changes the types of the two variables from strset to
strintmap; it does not actually store any special values yet and for now
only checks for presence of entries in the strintmap. Thus, the code is
functionally identical to how it behaved before. Future commits will
start associating values with each key for these two maps.
Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Add and apply a semantic patch for converting code that open-codes
CALLOC_ARRAY to use it instead. It shortens the code and infers the
element size automatically.
Signed-off-by: René Scharfe <l.s.r@web.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
diffcore_rename_extended() will do a bunch of setup, then check for
exact renames, then abort before inexact rename detection if there are
no more sources or destinations that need to be matched. It will
sometimes be the case, however, that either
* we start with neither any sources or destinations
* we start with no *relevant* sources
In the first of these two cases, the setup and exact rename detection
will be very cheap since there are 0 files to operate on. In the second
case, it is quite possible to have thousands of files with none of the
source ones being relevant. Avoid calling diffcore_rename_extended() or
even some of the setup before diffcore_rename_extended() when we can
determine that rename detection is unnecessary.
For the testcases mentioned in commit 557ac0350d ("merge-ort: begin
performance work; instrument with trace2_region_* calls", 2020-10-28),
this change improves the performance as follows:
Before After
no-renames: 6.003 s ± 0.048 s 5.708 s ± 0.111 s
mega-renames: 114.009 s ± 0.236 s 102.171 s ± 0.440 s
just-one-mega: 3.489 s ± 0.017 s 3.471 s ± 0.015 s
Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
The past several commits determined conditions when rename sources might
be needed, and filled a relevant_sources strset with those paths. Pass
these along to diffcore_rename_extended() to use to limit the sources
that we need to detect renames for.
For the testcases mentioned in commit 557ac0350d ("merge-ort: begin
performance work; instrument with trace2_region_* calls", 2020-10-28),
this change improves the performance as follows:
Before After
no-renames: 12.596 s ± 0.061 s 6.003 s ± 0.048 s
mega-renames: 130.465 s ± 0.259 s 114.009 s ± 0.236 s
just-one-mega: 3.958 s ± 0.010 s 3.489 s ± 0.017 s
Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
The point of directory rename detection is that if one side of history
renames a directory, and the other side adds new files under the old
directory, then the merge can move those new files into the new
directory. This leads to the following important observation:
* If the other side does not add any new files under the old
directory, we do not need to detect any renames for that directory.
Similarly, directory rename detection had an important requirement:
* If a directory still exists on one side of history, it has not been
renamed on that side of history. (See section 4 of t6423 or
Documentation/technical/directory-rename-detection.txt for more
details).
Using these two bits of information, we note that directory rename
detection is only needed in cases where (1) directories exist in the
merge base and on one side of history (i.e. dirmask == 3 or dirmask ==
5), and (2) where there is some new file added to that directory on the
side where it still exists (thus where the file has filemask == 2 or
filemask == 4, respectively). This has to be done in two steps, because
we have the dirmask when we are first considering the directory, and
won't get the filemasks for the files within it until we recurse into
that directory. So, we save
dir_rename_mask = dirmask - 1
when we hit a directory that is missing on one side, and then later look
for cases of
filemask == dir_rename_mask
One final note is that as soon as we hit a directory that needs
directory rename detection, we will need to detect renames in all
subdirectories of that directory as well due to the "majority rules"
decision when files are renamed into different directory hierarchies.
We arbitrarily use the special value of 0x07 to record when we've hit
such a directory.
The combination of all the above mean that we introduce a variable
named dir_rename_mask (couldn't think of a better name) which has one
of the following values as we traverse into a directory:
* 0x00: directory rename detection not needed
* 0x02 or 0x04: directory rename detection only needed if files added
* 0x07: directory rename detection definitely needed
We then pass this value through to add_pairs() so that it can mark
location_relevant as true only when dir_rename_mask is 0x07.
Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Add traverse_trees_wrapper() and traverse_trees_wrapper_callback()
functions. The former runs traverse_trees() with info->fn set to
traverse_trees_wrapper_callback, in order to simply save all the entries
without processing or recursing into any of them. This step allows
extra computation to be done (e.g. checking some condition across all
files) that can be used later. Then, after that is completed, it
iterates over all the saved entries and calls the original info->fn
callback with the saved data.
Currently, this does nothing more than marginally slowing down the tree
traversal since we do not take advantage of the opportunity to compute
anything special in traverse_trees_wrapper_callback(), and thus the real
callback will be called identically as it would have been without this
extra wrapper. However, a subsequent commit will add some special
computation of some values that the real callback will be able to use.
Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
In order to determine whether directory rename detection is needed, we
as a pre-requisite need a way to traverse through all the files in a
given tree before visiting any directories within that tree.
traverse_trees() only iterates through the entries in the order they
appear, so add some data structures that will store all the entries as
we iterate through them in traverse_trees(), which will allow us to
re-traverse them in our desired order.
Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
rename detection works by trying to pair all file deletions (or
"sources") with all file additions (or "destinations"), checking
similarity, and then marking the sufficiently similar ones as renames.
This can be expensive if there are many sources and destinations on a
given side of history as it results in an N x M comparison matrix.
However, there are many cases where we can compute in advance that
detecting renames for some of the sources provides no useful information
and thus that we can exclude those sources from the matrix.
To see why, first note that the merge machinery uses detected renames in
two ways:
* directory rename detection: when one side of history renames a
directory, and the other side of history adds new files to that
directory, we want to be able to warn the user about the need to
chose whether those new files stay in the old directory or move
to the new one.
* three-way content merging: in order to do three-way content merging
of files, we need three different file versions. If one side of
history renamed a file, then some of the content for the file is
found under a different path than in the merge base or on the
other side of history.
Add a simple testcase showing the two kinds of reasons renames are
relevant; it's a testcase that will only pass if we detect both kinds of
needed renames.
Other than the testcase added above, this commit concentrates just on
the three-way content merging; it will punt and mark all sources as
needed for directory rename detection, and leave it to future commits to
narrow that down more.
The point of three-way content merging is to reconcile changes made on
*both* sides of history. What if the file wasn't modified on both
sides? There are two possibilities:
* If it wasn't modified on the renamed side:
-> then we get to do exact rename detection, which is cheap.
* If it wasn't modified on the unrenamed side:
-> then detection of a rename for that source file is irrelevant
That latter claim might be surprising at first, so let's walk through a
case to show why rename detection for that source file is irrelevant.
Let's use two filenames, old.c & new.c, with the following abbreviated
object ids (and where the value '000000' is used to denote that the file
is missing in that commit):
old.c new.c
MERGE_BASE: 01d01d 000000
MERGE_SIDE1: 01d01d 000000
MERGE_SIDE2: 000000 5e1ec7
If the rename *isn't* detected:
then old.c looks like it was unmodified on one side and deleted on
the other and should thus be removed. new.c looks like a new file we
should keep as-is.
If the rename *is* detected:
then a three-way content merge is done. Since the version of the
file in MERGE_BASE and MERGE_SIDE1 are identical, the three-way merge
will produce exactly the version of the file whose abbreviated
object id is 5e1ec7. It will record that file at the path new.c,
while removing old.c from the directory.
Note that these two results are identical -- a single file named 'new.c'
with object id 5e1ec7. In other words, it doesn't matter if the rename
is detected in the case where the file is unmodified on the unrenamed
side.
Use this information to compute whether we need rename detection for
each source created in add_pair().
It's probably worth noting that there used to be a few other edge or
corner cases besides three-way content merges and directory rename
detection where lack of rename detection could have affected the result,
but those cases actually highlighted where conflict resolution methods
were not consistent with each other. Fixing those inconsistencies were
thus critically important to enabling this optimization. That work
involved the following:
* bringing consistency to add/add, rename/add, and rename/rename
conflict types, as done back in the topic merged at commit
ac193e0e0a ("Merge branch 'en/merge-path-collision'", 2019-01-04),
and further extended in commits 2a7c16c980 ("t6422, t6426: be more
flexible for add/add conflicts involving renames", 2020-08-10) and
e8eb99d4a6 ("t642[23]: be more flexible for add/add conflicts
involving pair renames", 2020-08-10)
* making rename/delete more consistent with modify/delete
as done in commits 1f3c9ba707 ("t6425: be more flexible with
rename/delete conflict messages", 2020-08-10) and 727c75b23f
("t6404, t6423: expect improved rename/delete handling in ort
backend", 2020-10-26)
Since the set of relevant_sources we compute has not yet been narrowed
down for directory rename detection, we do not pass it to
diffcore_rename_extended() yet. That will be done after subsequent
commits narrow down the list of relevant_sources needed for directory
rename detection reasons.
Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Add the ability to diffcore_rename_extended() to allow external callers
to declare that they only need renames detected for a subset of source
files, and use that information to skip detecting renames for them.
There are two important pieces to this optimization that may not be
obvious at first glance:
* We do not require callers to just filter the filepairs out
to remove the non-relevant sources, because exact rename detection
is fast and when it finds a match it can remove both a source and a
destination whereas the relevant_sources filter can only remove a
source.
* We need to filter out the source pairs in a preliminary pass instead
of adding a
strset_contains(relevant_sources, one->path)
check within the nested matrix loop. The reason for that is if we
have 30k renames, doing 30k * 30k = 900M strset_contains() calls
becomes extraordinarily expensive and defeats the performance gains
from this change; we only want to do 30k such calls instead.
If callers pass NULL for relevant_sources, that is special cases to
treat all sources as relevant. Since all callers currently pass NULL,
this optimization does not yet have any effect. Subsequent commits will
have merge-ort compute a set of relevant_sources to restrict which
sources we detect renames for, and have merge-ort pass that set of
relevant_sources to diffcore_rename_extended().
A note about filtering order:
Some may be curious why we don't filter out irrelevant sources at the
same time we filter out exact renames. While that technically could be
done at this point, there are two reasons to defer it:
First, was to reinforce a lesson that was too easy to forget. As I
mentioned above, in the past I filtered irrelevant sources out before
exact rename checking, and then discovered that exact renames' ability
to remove both sources and destinations was an important consideration
and thus doing the filtering after exact rename checking would speed
things up. Then at some point I realized that basename matching could
also remove both sources and destinations, and decided to put irrelevant
source filtering after basename filtering. That slowed things down a
lot. But, despite learning about this important ordering, in later
restructuring I forgot and made the same mistake of putting the
filtering after basename guided rename detection again. So, I have this
series of patches structured to do the irrelevant filtering last to
start to show how much extra it costs, and then add relevant filtering
in to find_basename_matches() to show how much it speeds things up.
Basically, it's a way to reinforce something that apparently was too
easy to forget, and make sure the commit messages record this lesson.
Second, the items in the "relevant_sources" in this patch series will
include all sources that *might be* relevant. It has to be conservative
and catch anything that might need a rename, but in the patch series
after this one we'll find ways to weed out more of the *might be*
relevant ones. Unfortunately, merge-ort does not have sufficient
information to weed those ones out, and there isn't enough information
at the time of filtering exact renames out to remove the extra ones
either. It has to be deferred. So the deferral is in part to simplify
some later additions.
Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
As we adjust the usage of dir_rename_count we want to have a function
for clearing, or partially clearing it out. Add a
partial_clear_dir_rename_count() function for this purpose.
Reviewed-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Move the computation of dir_rename_count from merge-ort.c to
diffcore-rename.c, making slight adjustments to the data structures
based on the move. While the diffstat looks large, viewing this commit
with --color-moved makes it clear that only about 20 lines changed.
With this patch, the computation of dir_rename_count is still only done
after inexact rename detection, but subsequent commits will add a
preliminary computation of dir_rename_count after exact rename
detection, followed by some updates after inexact rename detection.
Reviewed-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
We want to pass additional information to diffcore_rename() (or some
variant thereof) without plumbing that extra information through
diff_tree_oid() and diffcore_std(). Further, since we will need to
gather additional special information related to diffs and are walking
the trees anyway in collect_merge_info(), it seems odd to have
diff_tree_oid()/diffcore_std() repeat those tree walks. And there may
be times where we can avoid traversing into a subtree in
collect_merge_info() (based on additional information at our disposal),
that the basic diff logic would be unable to take advantage of. For all
these reasons, just create the add and delete pairs ourself and then
call diffcore_rename() directly.
This change is primarily about enabling future optimizations; the
advantage of avoiding extra tree traversals is small compared to the
cost of rename detection, and the advantage of avoiding the extra tree
traversals is somewhat offset by the extra time spent in
collect_merge_info() collecting the additional data anyway. However...
For the testcases mentioned in commit 557ac0350d ("merge-ort: begin
performance work; instrument with trace2_region_* calls", 2020-10-28),
this change improves the performance as follows:
Before After
no-renames: 13.294 s ± 0.103 s 12.775 s ± 0.062 s
mega-renames: 187.248 s ± 0.882 s 188.754 s ± 0.284 s
just-one-mega: 5.557 s ± 0.017 s 5.599 s ± 0.019 s
Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Add some timing instrumentation for both merge-ort and diffcore-rename;
I used these to measure and optimize performance in both, and several
future patch series will build on these to reduce the timings of some
select testcases.
=== Setup ===
The primary testcase I used involved rebasing a random topic in the
linux kernel (consisting of 35 patches) against an older version. I
added two variants, one where I rename a toplevel directory, and another
where I only rebase one patch instead of the whole topic. The setup is
as follows:
$ git clone git://git.kernel.org/pub/scm/linux/kernel/git/stable/linux-stable.git
$ git branch hwmon-updates fd8bdb23b91876ac1e624337bb88dc1dcc21d67e
$ git branch hwmon-just-one fd8bdb23b91876ac1e624337bb88dc1dcc21d67e~34
$ git branch base 4703d9119972bf586d2cca76ec6438f819ffa30e
$ git switch -c 5.4-renames v5.4
$ git mv drivers pilots # Introduce over 26,000 renames
$ git commit -m "Rename drivers/ to pilots/"
$ git config merge.renameLimit 30000
$ git config merge.directoryRenames true
=== Testcases ===
Now with REBASE standing for either "git rebase [--merge]" (using
merge-recursive) or "test-tool fast-rebase" (using merge-ort), the
testcases are:
Testcase #1: no-renames
$ git checkout v5.4^0
$ REBASE --onto HEAD base hwmon-updates
Note: technically the name is misleading; there are some renames, but
very few. Rename detection only takes about half the overall time.
Testcase #2: mega-renames
$ git checkout 5.4-renames^0
$ REBASE --onto HEAD base hwmon-updates
Testcase #3: just-one-mega
$ git checkout 5.4-renames^0
$ REBASE --onto HEAD base hwmon-just-one
=== Timing results ===
Overall timings, using hyperfine (1 warmup run, 3 runs for mega-renames,
10 runs for the other two cases):
merge-recursive merge-ort
no-renames: 18.912 s ± 0.174 s 14.263 s ± 0.053 s
mega-renames: 5964.031 s ± 10.459 s 5504.231 s ± 5.150 s
just-one-mega: 149.583 s ± 0.751 s 158.534 s ± 0.498 s
A single re-run of each with some breakdowns:
--- no-renames ---
merge-recursive merge-ort
overall runtime: 19.302 s 14.257 s
inexact rename detection: 7.603 s 7.906 s
everything else: 11.699 s 6.351 s
--- mega-renames ---
merge-recursive merge-ort
overall runtime: 5950.195 s 5499.672 s
inexact rename detection: 5746.309 s 5487.120 s
everything else: 203.886 s 17.552 s
--- just-one-mega ---
merge-recursive merge-ort
overall runtime: 151.001 s 158.582 s
inexact rename detection: 143.448 s 157.835 s
everything else: 7.553 s 0.747 s
=== Timing observations ===
0) Maximum speedup
The "everything else" row represents the maximum speedup we could
achieve if we were to somehow infinitely parallelize inexact rename
detection, but leave everything else alone. The fact that this is so
much smaller than the real runtime (even in the case with virtually no
renames) makes it clear just how overwhelmingly large the time spent on
rename detection can be.
1) no-renames
1a) merge-ort is faster than merge-recursive, which is nice. However,
this still should not be considered good enough. Although the "merge"
backend to rebase (merge-recursive) is sometimes faster than the "apply"
backend, this is one of those cases where it is not. In fact, even
merge-ort is slower. The "apply" backend can complete this testcase in
6.940 s ± 0.485 s
which is about 2x faster than merge-ort and 3x faster than
merge-recursive. One goal of the merge-ort performance work will be to
make it faster than git-am on this (and similar) testcases.
2) mega-renames
2a) Obviously rename detection is a huge cost; it's where most the time
is spent. We need to cut that down. If we could somehow infinitely
parallelize it and drive its time to 0, the merge-recursive time would
drop to about 204s, and the merge-ort time would drop to about 17s. I
think this particular stat shows I've subtly baked a couple performance
improvements into merge-ort and into fast-rebase already.
3) just-one-mega
3a) not much to say here, it just gives some flavor for how rebasing
only one patch compares to rebasing 35.
=== Goals ===
This patch is obviously just the beginning. Here are some of my goals
that this measurement will help us achieve:
* Drive the cost of rename detection down considerably for merges
* After the above has been achieved, see if there are other slowness
factors (which would have previously been overshadowed by rename
detection costs) which we can then focus on and also optimize.
* Ensure our rebase testcase that requires little rename detection
is noticeably faster with merge-ort than with apply-based rebase.
Signed-off-by: Elijah Newren <newren@gmail.com>
Acked-by: Taylor Blau <ttaylorr@github.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
get_provisional_directory_renames() has code to detect directories being
evenly split between different locations. However, as noted previously,
if there are no new files added to that directory that was split evenly,
our inability to determine where the directory was renamed to doesn't
matter since there are no new files to try to move into the new
location. Unfortunately, that code is unaware of whether there are new
files under the directory in question and we just ignore that, causing
us to fail t6423 test 2b but pass test 2a; turn off the error for now,
swapping which tests pass and fail.
The motivating reason for switching this off as a temporary measure is
that as we add optimizations, we'll start looking at only subsets of
renames, and subsets of renames can start switching the result we get
when this error is (wrongly) on. Once we get enough optimizations,
however, we can prevent that code from even running when there are no
new files added to the relevant directory, at which point we can revert
this commit and then both testcases 2a and 2b will pass simultaneously.
Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
When a series of merges was performed (such as for a rebase or series of
cherry-picks), only the data structures allocated by the final merge
operation were being freed. The problem was that while picking out
pieces of merge-ort to upstream, I previously misread a certain section
of merge_start() and assumed it was associated with a later
optimization. Include that section now, which ensures that if there was
a previous merge operation, that we clear out result->priv and then
re-use it for opt->priv, and otherwise we allocate opt->priv.
Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
* en/ort-directory-rename: (28 commits)
merge-ort: fix a directory rename detection bug
merge-ort: process_renames() now needs more defensiveness
merge-ort: implement apply_directory_rename_modifications()
merge-ort: add a new toplevel_dir field
merge-ort: implement handle_path_level_conflicts()
merge-ort: implement check_for_directory_rename()
merge-ort: implement apply_dir_rename() and check_dir_renamed()
merge-ort: implement compute_collisions()
merge-ort: modify collect_renames() for directory rename handling
merge-ort: implement handle_directory_level_conflicts()
merge-ort: implement compute_rename_counts()
merge-ort: copy get_renamed_dir_portion() from merge-recursive.c
merge-ort: add outline of get_provisional_directory_renames()
merge-ort: add outline for computing directory renames
merge-ort: collect which directories are removed in dirs_removed
merge-ort: initialize and free new directory rename data structures
merge-ort: add new data structures for directory rename detection
merge-ort: add implementation of type-changed rename handling
merge-ort: add implementation of normal rename handling
merge-ort: add implementation of rename collisions
...
As noted in commit 902c521a35 ("t6423: more involved directory rename
test", 2020-10-15), when we have a case where
* dir/subdir/ has several files
* almost all files in dir/subdir/ are renamed to folder/subdir/
* one of the files in dir/subdir/ is renamed to folder/subdir/newsubdir/
* the other side of history (that doesn't do the renames) adds a
new file to dir/subdir/
Then for the majority of the file renames, the directory rename of
dir/subdir/ -> folder/subdir/
is actually not represented that way but as
dir/ -> folder/
We also had one rename that was represented as
dir/subdir/ -> folder/subdir/newsubdir/
Now, since there's a new file in dir/subdir/, where does it go? Well,
there's only one rule for dir/subdir/, so the code previously noted that
this rule had the "majority" of the one "relevant" rename and thus
erroneously used it to place the file in folder/subdir/newsubdir/. We
really want the heavy weight associated with dir/ -> folder/ to also be
treated as dir/subdir/ -> folder/subdir/, so that we correctly place the
file in folder/subdir/.
Add a bunch of logic to make sure that we use all relevant renamings in
directory rename detection.
Note that testcase 12f of t6423 still fails after this, but it gets
further than merge-recursive does. There are some performance related
bits in that testcase (the region_enter messages) that do not yet
succeed, but the rest of the testcase works after this patch.
Subsequent patch series will fix up the performance side.
Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Since directory rename detection adds new paths to opt->priv->paths and
removes old ones, process_renames() needs to now check whether
pair->one->path actually exists in opt->priv->paths instead of just
assuming it does.
Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
This function roughly follows the same outline as the function of the
same name from merge-recursive.c, but the code diverges in multiple
ways due to some special considerations:
* merge-ort's version needs to update opt->priv->paths with any new
paths (and opt->priv->paths points to struct conflict_infos which
track quite a bit of metadata for each path); merge-recursive's
version would directly update the index
* merge-ort requires that opt->priv->paths has any leading directories
of any relevant files also be included in the set of paths. And
due to pointer equality requirements on merged_info.directory_name,
we have to be careful how we compute and insert these.
* due to the above requirements on opt->priv->paths, merge-ort's
version starts with a long comment to explain all the special
considerations that need to be handled
* merge-ort can use the full data stored in opt->priv->paths to avoid
making expensive get_tree_entry() calls to regather the necessary
data.
* due to messages being deferred automatically in merge-ort, this is
the best place to handle conflict messages whereas in
merge-recursive.c they are deferred manually so that processing of
entries does all the printing
Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Due to the string-equality-iff-pointer-equality requirements placed on
merged_info.directory_name, apply_directory_rename_modifications() will
need to have access to the exact toplevel directory name string pointer
and can't just use a new empty string. Store it in a field that we can
use.
Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
This is copied from merge-recursive.c, with minor tweaks due to:
* using strmap API
* merge-ort not using the non_unique_new_dir field, since it'll
obviate its need entirely later with performance improvements
* adding a new path_in_way() function that uses opt->priv->paths
instead of doing an expensive tree_has_path() lookup to see if
a tree has a given path.
Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
This is copied from merge-recursive.c, with minor tweaks due to using strmap
API and the fact that it can use opt->priv->paths to get all pathnames that
exist instead of taking a tree object.
This depends on a new function, handle_path_level_conflicts(), which
just has a placeholder die-not-yet-implemented implementation for now; a
subsequent patch will implement it.
Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Both of these are copied from merge-recursive.c, with just minor tweaks
due to using strmap API and not having a non_unique_new_dir field.
Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
This is nearly a wholesale copy of compute_collisions() from
merge-recursive.c, and the logic remains the same, but it has been
tweaked slightly due to:
* using strmap.h API (instead of direct hashmaps)
* allocation/freeing of data structures were done separately in
merge_start() and clear_or_reinit_internal_opts() in an earlier
patch in this series
* there is no non_unique_new_dir data field in merge-ort; that will
be handled a different way
It does depend on two new functions, apply_dir_rename() and
check_dir_renamed() which were introduced with simple
die-not-yet-implemented shells and will be implemented in subsequent
patches.
Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
collect_renames() is similar to merge-recursive.c's get_renames(), but
lacks the directory rename handling found in the latter. Port that code
structure over to merge-ort. This introduces three new
die-not-yet-implemented functions that will be defined in future
commits.
Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
This is modelled on the version of handle_directory_level_conflicts()
from merge-recursive.c, but is massively simplified due to the following
factors:
* strmap API provides simplifications over using direct hashmap
* we have a dirs_removed field in struct rename_info that we have an
easy way to populate from collect_merge_info(); this was already
used in compute_rename_counts() and thus we do not need to check
for condition #2.
* The removal of condition #2 by handling it earlier in the code also
obviates the need to check for condition #3 -- if both sides renamed
a directory, meaning that the directory no longer exists on either
side, then neither side could have added any new files to that
directory, and thus there are no files whose locations we need to
move due to such a directory rename.
In fact, the same logic that makes condition #3 irrelevant means
condition #1 is also irrelevant so we could drop this function.
However, it is cheap to check if both sides rename the same directory,
and doing so can save future computation. So, simply remove any
directories that both sides renamed from the list of directory renames.
Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
This function is based on the first half of get_directory_renames() from
merge-recursive.c; as part of the implementation, factor out a routine,
increment_count(), to update the bookkeeping to track the number of
items renamed into new directories.
Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
This function is based on merge-recursive.c's get_directory_renames(),
except that the first half has been split out into a not-yet-implemented
compute_rename_counts(). The primary difference here is our lack of the
non_unique_new_dir boolean in our strmap. The lack of that field will
at first cause us to fail testcase 2b of t6423; however, future
optimizations will obviate the need for that ugly field so we have just
left it out.
Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Port some directory rename handling changes from merge-recursive.c's
detect_and_process_renames() to the same-named function of merge-ort.c.
This does not yet add any use or handling of directory renames, just the
outline for where we start to compute them. Thus, a future patch will
add port additional changes to merge-ort's detect_and_process_renames().
Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
* en/ort-conflict-handling:
merge-ort: add handling for different types of files at same path
merge-ort: copy find_first_merges() implementation from merge-recursive.c
merge-ort: implement format_commit()
merge-ort: copy and adapt merge_submodule() from merge-recursive.c
merge-ort: copy and adapt merge_3way() from merge-recursive.c
merge-ort: flesh out implementation of handle_content_merge()
merge-ort: handle book-keeping around two- and three-way content merge
merge-ort: implement unique_path() helper
merge-ort: handle directory/file conflicts that remain
merge-ort: handle D/F conflict where directory disappears due to merge
