d67947162f
The HAS_DEVICE_ADDR indicates that the object(s) listed exists at an address that is a valid device address. Specifically, `has_device_addr(x)` means that (in C/C++ terms) `&x` is a device address. When entering a target region, `x` does not need to be allocated on the device, or have its contents copied over (in the absence of additional mapping clauses). Passing its address verbatim to the region for use is sufficient, and is the intended goal of the clause. Some Fortran objects use descriptors in their in-memory representation. If `x` had a descriptor, both the descriptor and the contents of `x` would be located in the device memory. However, the descriptors are managed by the compiler, and can be regenerated at various points as needed. The address of the effective descriptor may change, hence it's not safe to pass the address of the descriptor to the target region. Instead, the descriptor itself is always copied, but for objects like `x`, no further mapping takes place (as this keeps the storage pointer in the descriptor unchanged). --------- Co-authored-by: Sergio Afonso <safonsof@amd.com>
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.