rebase: use 'skip_cache_tree_update' option

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>
Signed-off-by: Taylor Blau <me@ttaylorr.com>

1 files changed, 1 insertions, 0 deletions

diff --git a/reset.c b/reset.c
index e3383a9334..5ded23611f 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;