13cd7a29e8
When a `GoTo` inside an ACC region (`acc.loop`, `acc.data`, `acc.parallel`, etc.) targets a label outside that region, the lowering generated an illegal cross-region `cf.br`. This caused MLIR verification failures or stack overflows in `runRegionDCE`'s recursive `propagateLiveness`. This patch addresses the issue with a generalized approach: - Add `genOpenACCRegionExitBranch` helper that detects cross-region branches from any ACC region op and generates the appropriate terminator (`acc.yield` for compute/loop ops, `acc.terminator` for data ops). The helper verifies that `parentOp` is an ACC operation, so it does not interfere with branches inside `scf.execute_region` or other non-ACC regions. - In `genBranch`, when a cross-region exit from an ACC region is detected, store a unique exit ID into a selector variable and generate the region terminator. After the ACC op, a jump table dispatches to the correct target based on the selector. This correctly handles GOTOs that skip intermediate code between the loop end and the target label. - Emit a TODO diagnostic for GOTOs that cross multiple nested ACC region boundaries. - Fix `acc.data` creation when the construct has no data clauses but contains unstructured control flow: skip the early return in `genACCDataOp` so the `acc.data` region is created and blocks are properly managed.
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.