add: speed up cmd_add() by utilizing read_cache_preload()

During an "add", a call is made to run_diff_files() which calls
check_removed() for each index-entry.  The preload_index() code
distributes some of the costs across multiple threads.

Because the files checked are restricted to pathspec, adding
individual files makes no measurable impact but on a Windows repo
with ~200K files, 'git add .' drops from 6.3 seconds to 3.3 seconds
for a 47% savings.

Signed-off-by: Ben Peart <benpeart@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/builtin/add.c b/builtin/add.c
index ad49806ebf92208e25a69ac9bff3f0e0a3b96570..f65c1722993b62e93feb85e506dffbc77b7ce921 100644 (file)
--- a/builtin/add.c
+++ b/builtin/add.c
@@ -445,11 +445,6 @@ int cmd_add(int argc, const char **argv, const char *prefix)
                return 0;
        }
 
-       if (read_cache() < 0)
-               die(_("index file corrupt"));
-
-       die_in_unpopulated_submodule(&the_index, prefix);
-
        /*
         * Check the "pathspec '%s' did not match any files" block
         * below before enabling new magic.
@@ -459,6 +454,10 @@ int cmd_add(int argc, const char **argv, const char *prefix)
                       PATHSPEC_SYMLINK_LEADING_PATH,
                       prefix, argv);
 
+       if (read_cache_preload(&pathspec) < 0)
+               die(_("index file corrupt"));
+
+       die_in_unpopulated_submodule(&the_index, prefix);
        die_path_inside_submodule(&the_index, &pathspec);
 
        if (add_new_files) {