Re: [PATCH v2 08/13] merge-ort: add code to check for whether cached renames can be reused

Signed-off-by: Elijah Newren <redacted>
---
 merge-ort.c | 66 +++++++++++++++++++++++++++++++++++++++++++++++++++--
 1 file changed, 64 insertions(+), 2 deletions(-)

diff --git a/merge-ort.c b/merge-ort.c
index 5523fc9e86b3..a342cc6344fd 100644
--- a/merge-ort.c
+++ b/merge-ort.c

@@ -140,6 +140,30 @@ struct rename_info {
 	int callback_data_nr, callback_data_alloc;
 	char *callback_data_traverse_path;
 
+	/*
+	 * merge_trees: trees passed to the merge algorithm for the merge
+	 *
+	 * merge_trees records the trees passed to the merge algorithm.  But,
+	 * this data also is stored in merge_result->priv.  If a sequence of
+	 * merges are being done (such as when cherry-picking or rebasing),
+	 * the next merge can look at this and re-use information from
+	 * previous merges under certain cirumstances.

+	 *
+	 * See also all the cached_* variables.
+	 */
+	struct tree *merge_trees[3];
+
+	/*
+	 * cached_pairs_valid_side: which side's cached info can be reused
+	 *
+	 * See the description for merge_trees.  For repeated merges, at most
+	 * only one side's cached information can be used.  Valid values:
+	 *   MERGE_SIDE2: cached data from side2 can be reused
+	 *   MERGE_SIDE1: cached data from side1 can be reused
+	 *   0:           no cached data can be reused
+	 */
+	int cached_pairs_valid_side;

+static void merge_check_renames_reusable(struct merge_options *opt,
+					 struct merge_result *result,
+					 struct tree *merge_base,
+					 struct tree *side1,
+					 struct tree *side2)
+{
+	struct rename_info *renames;
+	struct tree **merge_trees;
+	struct merge_options_internal *opti = result->priv;
+
+	if (!opti)
+		return;
+
+	renames = &opti->renames;
+	merge_trees = renames->merge_trees;
+	/* merge_trees[0..2] will only be NULL if opti is */
+	assert(merge_trees[0] && merge_trees[1] && merge_trees[2]);
+
+	/* Check if we meet a condition for re-using cached_pairs */
+	if (     oideq(&merge_base->object.oid, &merge_trees[2]->object.oid) &&
+		 oideq(     &side1->object.oid, &result->tree->object.oid))
+		renames->cached_pairs_valid_side = MERGE_SIDE1;
+	else if (oideq(&merge_base->object.oid, &merge_trees[1]->object.oid) &&
+		 oideq(     &side2->object.oid, &result->tree->object.oid))

+		renames->cached_pairs_valid_side = MERGE_SIDE2;
+	else
+		renames->cached_pairs_valid_side = 0; /* neither side valid */
+}
+
 /*** Function Grouping: merge_incore_*() and their internal variants ***/
 
 /*

@@ -3949,7 +4002,16 @@ void merge_incore_nonrecursive(struct merge_options *opt,
 
 	trace2_region_enter("merge", "merge_start", opt->repo);
 	assert(opt->ancestor != NULL);
+	merge_check_renames_reusable(opt, result, merge_base, side1, side2);
 	merge_start(opt, result);
+	/*
+	 * Record the trees used in this merge, so if there's a next merge in
+	 * a cherry-pick or rebase sequence it might be able to take advantage
+	 * of the cached_pairs in that next merge.
+	 */
+	opt->priv->renames.merge_trees[0] = merge_base;
+	opt->priv->renames.merge_trees[1] = side1;
+	opt->priv->renames.merge_trees[2] = side2;
 	trace2_region_leave("merge", "merge_start", opt->repo);