cf602b95d1
fir.call side effects are hard to describe in a useful way using `MemoryEffectOpInterface` because it is impossible to list which memory location a user procedure read/write without doing a data flow analysis of its body (even PURE procedures may read from any module variable, Fortran SIMPLE procedure from F2023 will allow that, but they are far from common at that point). Fortran language specifications allow the compiler to deduce that a procedure call cannot access a variable in many cases This patch leverages this to extend `fir::AliasAnalysis::getModRef` to deal with fir.call. This will allow implementing "array = array_function()" optimization in a future patch.
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.