f486cc4417
Flang currently adds loop metadata to a conditional branch in the loop preheader, while clang adds it to the loop latch's branch instruction. Langref says: > Currently, loop metadata is implemented as metadata attached to the branch instruction in the loop latch block. > > https://llvm.org/docs/LangRef.html#llvm-loop I misread langref a couple times, but I think this is the appropriate branch op for the LoopAnnotationAttr. In a couple examples I found that the metadata was lost entirely during canonicalization. This patch makes the codegen look more like clang's and the annotations persist through codegen. * current clang: https://godbolt.org/z/8WhbcrnG3 * current flang: https://godbolt.org/z/TrPboqqcn
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.