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Previously, a bug in the MemCptOpt LLVM IR pass caused issues with adding alias tags for locally allocated objects for Fortran code. However, the bug has now been fixed (https://github.com/llvm/llvm-project/pull/129537 ), and we can safely enable alias tags for these objects. This change should improve the accuracy of the alias analysis. More accurate alias analysis assumes that Cray pointers do not alias with other variables. This assumption is common among other compilers. If the code violates this assumption, it can lead to incorrect results (see: https://github.com/llvm/llvm-project/issues/141928)
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.