The index might be aware that a file hasn't modified via fsmonitor, but
unpack-trees did not pay attention to it and checked via ie_match_stat which
can be inefficient on certain filesystems. This significantly slows down
commands that run oneway_merge, like checkout and reset --hard.

This patch makes oneway_merge check whether a file is considered unchanged
through fsmonitor and skips ie_match_stat on it. unpack-trees also now
correctly copies over fsmonitor validity state from the source index.
Finally, for correctness, we force a refresh of fsmonitor state in
tweak_fsmonitor.

After this change, commands like stash (that use reset --hard internally) go
from 8s or more to ~2s on a 250k file repository on a mac.

Signed-off-by: Utsav Shah utsav@dropbox.com [utsav@dropbox.com]

Utsav Shah (1):
  unpack-trees: skip stat on fsmonitor-valid files

 fsmonitor.c                       | 20 +++++++++++---------
 t/t7113-post-index-change-hook.sh |  3 ---
 t/t7519-status-fsmonitor.sh       |  9 +++++++--
 unpack-trees.c                    |  6 +++++-
 4 files changed, 23 insertions(+), 15 deletions(-)

base-commit: 566a1439f6f56c2171b8853ddbca0ad3f5098770

Submitted-As: https://public-inbox.org/git/pull.446.git.1572910885.gitgitgadget@gmail.com