[flang][runtime] Enable more code for offload device builds. (#67489)

I extended the "closure" of the device code containing the initial
transformational.cpp. The device side of the library should not be
complete at least for some APIs. For example, I tested with C OpenMP
code calling BesselJnX0 with a nullptr descriptor that failed with
a runtime error when executing on a GPU.

I added `--expt-relaxed-constexpr` for NVCC compiler to avoid multiple
warnings about missing `__attribute__((device))` on constexpr methods
coming from C++ header files.

GitOrigin-RevId: 4bdec5830bc398cecf6e775cc54d9dd511e6e237
12 files changed
tree: fa7860f9e0ee97b56feb306e0ab9e5ced0181af2
  1. cmake/
  2. docs/
  3. examples/
  4. include/
  5. lib/
  6. module/
  7. runtime/
  8. test/
  9. tools/
  10. unittests/
  11. .clang-format
  12. .clang-tidy
  13. .drone.star
  14. .gitignore
  15. CMakeLists.txt
  18. README.md


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.