[PATCH v3 5/5] rebase: use 'skip_cache_tree_update' option

["Victoria Dye via GitGitGadget" <gitgitgadget@gmail.com>]

From: Victoria Dye <vdye@github.com>

Enable the 'skip_cache_tree_update' option in both 'do_reset()'
('sequencer.c') and 'reset_head()' ('reset.c'). Both of these callers invoke
'prime_cache_tree()' after 'unpack_trees()', so we can remove an unnecessary
cache tree rebuild by skipping 'cache_tree_update()'.

When testing with 'p3400-rebase.sh' and 'p3404-rebase-interactive.sh', the
performance change of this update was negligible, likely due to the
operation being dominated by more expensive operations (like checking out
trees). However, since the change doesn't harm performance, it's worth
keeping this 'unpack_trees()' usage consistent with others that subsequently
invoke 'prime_cache_tree()'.

Signed-off-by: Victoria Dye <vdye@github.com>
---
 reset.c     | 1 +
 sequencer.c | 1 +
 2 files changed, 2 insertions(+)

diff --git a/reset.c b/reset.c
index e3383a93343..5ded23611f3 100644
--- a/reset.c
+++ b/reset.c
@@ -128,6 +128,7 @@ int reset_head(struct repository *r, const struct reset_head_opts *opts)
 	unpack_tree_opts.update = 1;
 	unpack_tree_opts.merge = 1;
 	unpack_tree_opts.preserve_ignored = 0; /* FIXME: !overwrite_ignore */
+	unpack_tree_opts.skip_cache_tree_update = 1;
 	init_checkout_metadata(&unpack_tree_opts.meta, switch_to_branch, oid, NULL);
 	if (reset_hard)
 		unpack_tree_opts.reset = UNPACK_RESET_PROTECT_UNTRACKED;
diff --git a/sequencer.c b/sequencer.c
index e658df7e8ff..3f7a73ce4e1 100644
--- a/sequencer.c
+++ b/sequencer.c
@@ -3750,6 +3750,7 @@ static int do_reset(struct repository *r,
 	unpack_tree_opts.merge = 1;
 	unpack_tree_opts.update = 1;
 	unpack_tree_opts.preserve_ignored = 0; /* FIXME: !overwrite_ignore */
+	unpack_tree_opts.skip_cache_tree_update = 1;
 	init_checkout_metadata(&unpack_tree_opts.meta, name, &oid, NULL);
 
 	if (repo_read_index_unmerged(r)) {
-- 
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