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A defined assignment generic interface for a given LHS/RHS type & rank combination may have a specific procedure with LHS dummy argument that is neither allocatable nor pointer, or specific procedure(s) whose LHS dummy arguments are allocatable or pointer. It is possible to have two specific procedures if one's LHS dummy argument is allocatable and the other's is pointer. However, the runtime doesn't work with LHS dummy arguments that are allocatable, and will crash with a mysterious "invalid descriptor" error message. Extend the list of special bindings to include ScalarAllocatableAssignment and ScalarPointerAssignment, use them when appropriate in the runtime type information tables, and handle them in Assign() in the runtime support library.
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.