I somehow do not think this is correct. I expect
cd t && git grep -e foo -- :^perf/
to look into things in 't' except for things in 't/perf', but the
above will grab hits from ../Documentation/ etc. We need to pay
attention to PATHSPEC_PREFER_CWD bit in the flags word, I think.
Ok, that's easy enough.
Two-patch series to follow.
Linus