Since 2015, NVIDIA has supported Flang: a Fortran compiler frontend to LLVM. The first Flang was based on the PGI compiler, with proprietary optimizations removed. However, the C-based decade-plus of cruft led Flang developers and management to a ground-up rewrite in C++17. This new Flang f18 targets Fortran 2018 syntax and is implemented in C++17 internally. Flang became part of LLVM 11. Flang is growing in features and may not be sufficiently feature-complete for modern Fortran until later LLVM releases.
Building the LLVM Flang Fortran compiler from source is a resource-intensive process. A moderately powerful PC is needed to compile Flang with > 100 GB of free space on the drive you build Flang on. While the Flang install is small, the Flang build process requires a lot of drive space.