b55f7512a7
Extract Flang's runtime library to use the LLVM_ENABLE_RUNTIME mechanism. It will only become active when `LLVM_ENABLE_RUNTIMES=flang-rt` is used, which also changes the `FLANG_INCLUDE_RUNTIME` to `OFF` so the old runtime build rules do not conflict. This also means that unless `LLVM_ENABLE_RUNTIMES=flang-rt` is passed, nothing changes with the current build process. Motivation: * Consistency with LLVM's other runtime libraries (compiler-rt, libc, libcxx, openmp offload, ...) * Allows compiling the runtime for multiple targets at once using the LLVM_RUNTIME_TARGETS configuration options * Installs the runtime into the compiler's per-target resource directory so it can be automatically found even when cross-compiling Also see RFC discussion at https://discourse.llvm.org/t/rfc-use-llvm-enable-runtimes-for-flangs-runtime/80826
Flang
Flang is a ground-up implementation of a Fortran front end written in modern C++. It started off as the f18 project (https://github.com/flang-compiler/f18) with an aim to replace the previous flang project (https://github.com/flang-compiler/flang) and address its various deficiencies. F18 was subsequently accepted into the LLVM project and rechristened as Flang.
Please note that flang is not ready yet for production usage.
Getting Started
Read more about flang in the docs directory. Start with the compiler overview.
To better understand Fortran as a language and the specific grammar accepted by flang, read Fortran For C Programmers and flang's specifications of the Fortran grammar and the OpenMP grammar.
Treatment of language extensions is covered in this document.
To understand the compilers handling of intrinsics, see the discussion of intrinsics.
To understand how a flang program communicates with libraries at runtime, see the discussion of runtime descriptors.
If you're interested in contributing to the compiler, read the style guide and also review how flang uses modern C++ features.
If you are interested in writing new documentation, follow LLVM's Markdown style guide.
Consult the Getting Started with Flang for information on building and running flang.