[jcranmer]

For extra fun, "flang" actually refers to three different projects, one of which also completely rebuilt its frontend, so there are four separate "flang" frontends to LLVM. And I know of at least one proprietary LLVM-based Fortran compiler that's not based on any of the flags, and I suspect there are a few more lurking about.

The short answer as to why there are so many different LLVM Fortran frontends is that open source community took a long time to find someone willing to commit to a Fortran frontend to LLVM, and even when that happened, the initial results weren't particularly usable--it's not until I want to say late 2020 or early 2021 that there's an in-LLVM-tree flang project, and the exe isn't renamed from flang-new to flang until 2024.

[pklausler]

I started writing the new "f18" Fortran front-end at NVIDIA in the summer of '17, and it was added to LLVM as "flang" in June 2020. There were already at least three other "flang"s at the time, one of which was our open-sourced llvm-targeting pgifortran compiler.

I still call this latest one "flang-new" myself just because that's the only unambiguous name for it. The name confusion is not my fault, I promise.