db5cd626b9
This is a follow-up fix for commit 0f5e9bee. Only write effects to thread-local memory should be considered safe to parallelize in workshare lowering, not reads. When both reads and writes were safe, the cascading effect in moveToSingle could cause entire SingleRegions to become fully parallelized, eliminating the omp.single and its implicit barrier. This removed synchronization points needed to keep threads coordinated inside sequential loops containing workshared operations, causing race conditions in forall-workshare patterns. This was exposed by the Fujitsu Test Suite and made the following tests regress: FAIL: test-suite :: Fujitsu/Fortran/0398/Fujitsu-Fortran-0398_0031.test FAIL: test-suite :: Fujitsu/Fortran/0398/Fujitsu-Fortran-0398_0013.test FAIL: test-suite :: Fujitsu/Fortran/0398/Fujitsu-Fortran-0398_0030.test FAIL: test-suite :: Fujitsu/Fortran/0398/Fujitsu-Fortran-0398_0014.test Updates #143330
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.