e55c85341d
Currently, we do not check the module for requires directives, which means we'll miss these and not set them on the OpenMP module. Otherwise, due to the first come first serve method we currently check the symbols, there is certain formats that would mean the compiler would miss that a user had specified requires somewhere in the module. This is partially but not fully avoided by the Semantics layer pushing the requires on to the top most PFT symbol, as it is entirely possible to create a legal Fortran program where you could have two or more of these (e.g. module and main program in one file, standalone funcitons intermixed with modules or main program). Some examples of this are shown in the added Fortran test. This PR opts to resolve it by gathering all of the relevant symbols and processing them. Also removed gathering from BlockDataUnit as I don't think these symbols ever get the requires applied.
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.