[llvm-branch-commits] [flang] [flang][OpenMP] use attribute for delayed privatization barrier (PR #140092)

Thu May 15 09:08:18 PDT 2025

https://github.com/tblah created https://github.com/llvm/llvm-project/pull/140092

Fixes #136357

The barrier needs to go between the copying into firstprivate variables and the initialization call for the OpenMP construct (e.g. wsloop). There is no way of expressing this in MLIR because for delayed privatization that is all implicit (added in MLIR->LLVMIR conversion).

The previous approach put the barrier immediately before the wsloop (or similar). For delayed privatization, the firstprivate copy code would then be inserted after that, opening the possibility for the race observed in the bug report.

This patch solves the issue by instead setting an attribute on the mlir operation, which will instruct openmp dialect to llvm ir conversion to insert a barrier in the correct place.

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