Updating the list with some progress: Alexander narrowed it down to pgaio_io_wait() being inlined into pgaio_io_was_recycled(). It seems to have some instructions in the wrong order, and that can be reproduced standalone, so I've asked about it here:
https://github.com/llvm/llvm-project/issues/164194 I'm not seeing how that could be our fault, but let's see...
