f1178815d2
This PR adds an initial implementation for the map modifiers close, present and ompx_hold, primarily just required adding the appropriate map type flags to the map type bits. In the case of ompx_hold it required adding the map type to the OpenMP dialect. Close has a bit of a problem when utilised with the ALWAYS map type on descriptors, so it is likely we'll have to make sure close and always are not applied to the descriptor simultaneously in the future when we apply always to the descriptors to facilitate movement of descriptor information to device for consistency, however, we may find an alternative to this with further investigation. For the moment, it is a TODO/Note to keep track of it.
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.