7220fdad0c
Enabling volatility lowering by default revealed some issues in lowering and op verification. For example, given volatile variable of a nested type, accessing structure members of a structure member would result in a volatility mismatch when the inner structure member is designated (and thus a verification error at compile time). In other cases, I found correct codegen when the checks were disabled, also related to allocatable types and how we handle volatile references of boxes. This hides the strict verification of fir and hlfir ops behind a flag so I can iteratively improve lowering of volatile variables without causing compile-time failures, keeping the strict verification on when running tests.
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.