From: Derrick Stolee <stolee@gmail.com>
The 'git rev-list --maximal-only' option filters the output to only independent commits. A commit is independent if it is not reachable from other listed commits. Currently this is implemented by doing a full revision walk and marking parents with CHILD_VISITED to skip non-maximal commits.
The 'git merge-base --independent' command computes the same result using reduce_heads(), which uses the more efficient remove_redundant() algorithm. This is significantly faster because it avoids walking the entire commit graph.
Add a fast path in rev-list that detects when --maximal-only is the only interesting option and all input commits are positive (no revision ranges). In this case, use reduce_heads() directly instead of doing a full revision walk.
In order to preserve the rest of the output filtering, this computation is done opportunistically in a new prepare_maximal_independent() method when possible. If successful, it populates revs->commits with the list of independent commits and set revs->no_walk to prevent any other walk from occurring. This allows us to have any custom output be handled using the existing output code hidden inside traverse_commit_list_filtered(). A new test is added to demonstrate that this output is preserved.
The fast path is only used when no other flags complicate the walk or output format: no UNINTERESTING commits, no limiting options (max-count, age filters, path filters, grep filters), no output formatting beyond plain OIDs, and no object listing flags.
Running the p6011 performance test for my copy of git.git, I see the following improvement with this change:
Test HEAD~1 HEAD
------------------------------------------------------------
6011.2: merge-base --independent 0.03 0.03 +0.0%
6011.3: rev-list --maximal-only 0.06 0.03 -50.0%
6011.4: rev-list --maximal-only --since 0.06 0.06 +0.0%
And for a fresh clone of the Linux kernel repository, I see:
Test HEAD~1 HEAD
------------------------------------------------------------
6011.2: merge-base --independent 0.00 0.00 =
6011.3: rev-list --maximal-only 0.70 0.00 -100.0%
6011.4: rev-list --maximal-only --since 0.70 0.70 +0.0%
In both cases, the performance is indeed matching the behavior of 'git merge-base --independent', as expected.
Signed-off-by: Derrick Stolee <stolee@gmail.com>
---
builtin/rev-list.c | 59 ++++++++++++++++++++++++++++++++++++++++
t/t6000-rev-list-misc.sh | 31 +++++++++++++++++++++
2 files changed, 90 insertions(+)
Show changes to 2 files +90 −0
builtin/rev-list.c, t/t6000-rev-list-misc.sh
diff --git a/builtin/rev-list.c b/builtin/rev-list.c
index 854d82ece3..8f63003709 100644
--- a/builtin/rev-list.c
+++ b/builtin/rev-list.c
@@ -25,6 +25,7 @@
#include "oidset.h"
#include "oidmap.h"
#include "packfile.h"
+#include "commit-reach.h"
#include "quote.h"
#include "strbuf.h"
@@ -633,6 +634,61 @@ static int try_bitmap_disk_usage(struct rev_info *revs,
return 0;
}
+/*
+ * If revs->maximal_only is set and no other walk modifiers are provided,
+ * run a faster computation to filter the independent commits and prepare
+ * them for output. Set revs->no_walk to prevent later walking.
+ *
+ * If this algorithm doesn't apply, then no changes are made to revs.
+ */
+static void prepare_maximal_independent(struct rev_info *revs)
+{
+ struct commit_list *c;
+
+ if (!revs->maximal_only)
+ return;
+
+ for (c = revs->commits; c; c = c->next) {
+ if (c->item->object.flags & UNINTERESTING)
+ return;
+ }
+
+ if (revs->limited ||
+ revs->topo_order ||
+ revs->first_parent_only ||
+ revs->reverse ||
+ revs->max_count >= 0 ||
+ revs->skip_count >= 0 ||
+ revs->min_age != (timestamp_t)-1 ||
+ revs->max_age != (timestamp_t)-1 ||
+ revs->min_parents > 0 ||
+ revs->max_parents >= 0 ||
+ revs->prune_data.nr ||
+ revs->count ||
+ revs->left_right ||
+ revs->boundary ||
+ revs->tag_objects ||
+ revs->tree_objects ||
+ revs->blob_objects ||
+ revs->filter.choice ||
+ revs->reflog_info ||
+ revs->diff ||
+ revs->grep_filter.pattern_list ||
+ revs->grep_filter.header_list ||
+ revs->verbose_header ||
+ revs->print_parents ||
+ revs->edge_hint ||
+ revs->unpacked ||
+ revs->no_kept_objects ||
+ revs->line_level_traverse)
+ return;
+
+ reduce_heads_replace(&revs->commits);
+
+ /* Modify 'revs' to only output this commit list. */
+ revs->no_walk = 1;
+}
+
int cmd_rev_list(int argc,
const char **argv,
const char *prefix,
@@ -875,6 +931,9 @@ int cmd_rev_list(int argc,
if (prepare_revision_walk(&revs))
die("revision walk setup failed");
+
+ prepare_maximal_independent(&revs);
+
if (revs.tree_objects)
mark_edges_uninteresting(&revs, show_edge, 0);
diff --git a/t/t6000-rev-list-misc.sh b/t/t6000-rev-list-misc.sh
index d0a2a86610..a95ba576fa 100755
--- a/t/t6000-rev-list-misc.sh
+++ b/t/t6000-rev-list-misc.sh
@@ -263,4 +263,35 @@ test_expect_success 'rev-list --boundary incompatible with --maximal-only' '
test_grep "cannot be used together" err
'
+test_expect_success 'rev-list --maximal-only and --pretty' '
+ test_when_finished rm -rf repo &&
+
+ git init repo &&
+ test_commit -C repo 1 &&
+ oid1=$(git -C repo rev-parse HEAD) &&
+ test_commit -C repo 2 &&
+ oid2=$(git -C repo rev-parse HEAD) &&
+ git -C repo checkout --detach HEAD~1 &&
+ test_commit -C repo 3 &&
+ oid3=$(git -C repo rev-parse HEAD) &&
+
+ cat >expect <<-EOF &&
+ commit $oid3
+ $oid3
+ commit $oid2
+ $oid2
+ EOF
+
+ git -C repo rev-list --pretty="%H" --maximal-only $oid1 $oid2 $oid3 >out &&
+ test_cmp expect out &&
+
+ cat >expect <<-EOF &&
+ $oid3
+ $oid2
+ EOF
+
+ git -C repo log --pretty="%H" --maximal-only $oid1 $oid2 $oid3 >out &&
+ test_cmp expect out
+'
+
test_done