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Follow-up to #132003, in particular, see https://github.com/llvm/llvm-project/pull/132003#issuecomment-2739701936. This PR extends reduction support for `loop` directives. Consider the following scenario: ```fortran subroutine bar implicit none integer :: x, i !$omp teams loop reduction(+: x) DO i = 1, 5 call foo() END DO end subroutine ``` Note the following: * According to the spec, the `reduction` clause will be attached to `loop` during earlier stages in the compiler. * Additionally, `loop` cannot be mapped to `distribute parallel for` due to the call to a foreign function inside the loop's body. * Therefore, `loop` must be mapped to `distribute`. * However, `distribute` does not have `reduction` clauses. * As a result, we have to move the `reduction`s from the `loop` to its parent `teams` directive, which is what is done by this PR.
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.