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This is another attempt at a change that Jean made to Phabricator in https://reviews.llvm.org/D116934. That attempt ran into problems with building on Windows. This change improves the messages that are produced when running into invalid arguments during constant folding. Note that the original attempt at implementing this contained additional code in .../llvm-project/flang/test/Evaluate/folding04.f90: ``` !WARN: warning: argument 'x' must be strictly positive real(8), parameter :: nan_r8_dlog1 = dlog(-0.1_8) TEST_ISNAN(nan_r8_dlog1) ``` For reasons I don't understand, this additional code caused the Windows build to fail. So this new version of the update does not contain that code.
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.