96d1baedef
Remove the FLANG_INCLUDE_RUNTIME option which was replaced by LLVM_ENABLE_RUNTIMES=flang-rt. The FLANG_INCLUDE_RUNTIME option was added in #122336 which disables the non-runtimes build instructions for the Flang runtime so they do not conflict with the LLVM_ENABLE_RUNTIMES=flang-rt option added in #110217. In order to not maintain multiple build instructions for the same thing, this PR completely removes the old build instructions (effectively forcing FLANG_INCLUDE_RUNTIME=OFF). As per discussion in https://discourse.llvm.org/t/buildbot-changes-with-llvm-enable-runtimes-flang-rt/83571/2 we now implicitly add LLVM_ENABLE_RUNTIMES=flang-rt whenever Flang is compiled in a bootstrapping (non-standalone) build. Because it is possible to build Flang-RT separately, this behavior can be disabled using `-DFLANG_ENABLE_FLANG_RT=OFF`. Also see the discussion an implicitly adding runtimes/projects in #123964.
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.