c91ba04328
Split some headers into headers for public and private declarations in preparation for #110217. Moving the runtime-private headers in runtime-private include directory will occur in #110298. * Do not use `sizeof(Descriptor)` in the compiler. The size of the descriptor is target-dependent while `sizeof(Descriptor)` is the size of the Descriptor for the host platform which might be too small when cross-compiling to a different platform. Another problem is that the emitted assembly ((cross-)compiling to the same target) is not identical between Flang's running on different systems. Moving the declaration of `class Descriptor` out of the included header will also reduce the amount of #included sources. * Do not use `sizeof(ArrayConstructorVector)` and `alignof(ArrayConstructorVector)` in the compiler. Same reason as with `Descriptor`. * Compute the descriptor's extra flags without instantiating a Descriptor. `Fortran::runtime::Descriptor` is defined in the runtime source, but not the compiler source. * Move `InquiryKeywordHashDecode` into runtime-private header. The function is defined in the runtime sources and trying to call it in the compiler would lead to a link-error. * Move allocator-kind magic numbers into common header. They are the only declarations out of `allocator-registry.h` in the compiler as well. This does not make Flang cross-compile ready yet, the main goal is to avoid transitive header dependencies from Flang to clang-rt. There are more assumptions that host platform is the same as the target platform.
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.