I use a M1 Macbook air. I know @certik uses Apple Silicon as well.
I know about Questions 1 and 3.
- Gfortran generates native ARM code. It works with OpenMP. There are a few corner cases where Gfortran does not work properly. For example, currently, homebrew gfortran release so not work with nested functions. This has been fixed by GCC developers, but binaries are not released yet (see here). It sounds like a much updated Gfortran version should come out with the release of GCC 12, which I’ve heard somewhere should be around April 2022.
I have used Intel ifort compiler via rosetta. It seems to work. But I had issues with C/Fortran interoperability with the Intel compilers.
- I’ve done multithreading across all 8 cores on my M1. Seems to scale as well as my old intel with 6 cores. I haven’t look too carefully at this though.