4376fbd793
Summary: We use this `dyn_ptr` argument in Clang/OpenMP to handle the `KernelLaunchEnvironment`. This is a per-kernel argument used to share some information. Currenetly, it's prepended to the argument list and we generate storage for it in the runtime. This is bad for a few reasons: 1. It changes the ABI by shifting user arguments 2. It cannot be trivially be left uninitialized if unused 3. The runtime must allocate its own memory for it This PR changes it to be appended instead. Additionally, space for this is always emitted. This means the OMPIRBuilder itself will provide the storage, we simply need to populate it in the runtime if it is used. This means that if it's unused we don't always pay the cost and it's easier for non-OpenMP users to ignore it. Backward compatibility is maintained by auto-upgrading the kernel arguments. In `libomptarget` we completely allocate a new buffer to store this in the new format. The plugins still need to respect the old ABI of the called device object, so we simply rotate it if it's the old version.
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.