Fix withForeignPtr (#17746)
First try: marking withForeignPtr NOINLINE
- fix the bug
- kills performance (up to 2600% in some tests IIRC)
Second (current) try:
- use a with# helper that doesn't retain the full
ForeignPtrbut onlyForeignPtrContents - seems better but still regresses a lot
Edited by Sylvain Henry