Latest version of Fil-C with -O1 is just around 50-100% slower than ASAN, very acceptable in my book. I'm actually more "bothered" by its compilation time (took roughly 8x time of clang with ASAN).
I’ve found Fil-C 0.670 to be around 30x slower than a regular build, with -O1 vs. -O2 not making much difference. Perhaps it is very dependent on the kind of code. IIRC the author of Fil-C (which I think is an incredible project, to be clear) wants it to be possible to run Fil-C builds in production, so I think the comparison to a regular non-ASAN build is relevant.
