mclow.lists added a comment. There are no uses of `_LIBCPP_UNROLL_LOOPS` in LLVM (other than the ones in `<algorithm>`. Googling for `_LIBCPP_UNROLL_LOOPS` on github finds the ones in libc++, and no others. I think I'll just take it out, and see what happens. https://reviews.llvm.org/D26991