Before the patch:
$ env LC_ALL=en_US.UTF-8 time src/grep -i ＦＯＯＢＡＲ ../k
Command exited with non-zero status 1
0.88user 0.31system 0:01.22elapsed 97%CPU (0avgtext+0avgdata 3072maxresident)k
0inputs+0outputs (0major+216minor)pagefaults 0swaps
$ env LC_ALL=ja_JP.eucJP time src/grep -i ＦＯＯＢＡＲ ../k
Command exited with non-zero status 1
20.84user 6.38system 0:27.81elapsed 97%CPU (0avgtext+0avgdata 3232maxresident)k
0inputs+0outputs (0major+12740minor)pagefaults 0swaps

After the patch:
$ env LC_ALL=en_US.UTF-8 time src/grep -i ＦＯＯＢＡＲ ../k
Command exited with non-zero status 1
0.13user 0.30system 0:00.43elapsed 99%CPU (0avgtext+0avgdata 3312maxresident)k
0inputs+0outputs (0major+232minor)pagefaults 0swaps
$ env LC_ALL=ja_JP.eucJP time src/grep -i ＦＯＯＢＡＲ ../k
Command exited with non-zero status 1
0.10user 0.25system 0:00.36elapsed 98%CPU (0avgtext+0avgdata 3328maxresident)k
0inputs+0outputs (0major+234minor)pagefaults 0swaps