What is the exact difference between LLVM Flang and …
The classic Flang frontend ( GitHub - flang-compiler/flang: Flang is a Fortran language front-end designed for integration with LLVM.) continues to be developed and is the base of at least the Arm, AMD and Huawei Fortran compilers. The plan is to eventually move to using the F18 (or llvm/flang) frontend when it becomes ready.