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The parser will accept a wide variety of illegal attempts at forming an ATOMIC construct, leaving it to the semantic analysis to diagnose any issues. This consolidates the analysis into one place and allows us to produce more informative diagnostics. The parser's outcome will be parser::OpenMPAtomicConstruct object holding the directive, parser::Body, and an optional end-directive. The prior variety of OmpAtomicXyz classes, as well as OmpAtomicClause have been removed. READ, WRITE, etc. are now proper clauses. The semantic analysis consistently operates on "evaluation" representations, mainly evaluate::Expr (as SomeExpr) and evaluate::Assignment. The results of the semantic analysis are stored in a mutable member of the OpenMPAtomicConstruct node. This follows a precedent of having `typedExpr` member in parser::Expr, for example. This allows the lowering code to avoid duplicated handling of AST nodes. Using a BLOCK construct containing multiple statements for an ATOMIC construct that requires multiple statements is now allowed. In fact, any nesting of such BLOCK constructs is allowed. This implementation will parse, and perform semantic checks for both conditional-update and conditional-update-capture, although no MLIR will be generated for those. Instead, a TODO error will be issues prior to lowering. The allowed forms of the ATOMIC construct were based on the OpenMP 6.0 spec.
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.