[RFC] Defining thread convergence in C++ languages such as HIP, CUDA, OpenCL

[ssahasra]

Hi all,

Cross-posting an RFC from Clang to attract more attention. Although this talks about high-level languages and their treatment in Clang, convergence is a topic relevant to all of LLVM.

[RFC] Define thread convergence in C++ languages such as HIP, CUDA, OpenCL

This is a stack of two changes: The proposed definition closely follows the existing definition of convergence in LLVM IR, but using C++ terms to describe language constructs. There is no undefined behaviour. For each situation, convergence is either fully specified or implementation-defined. Two important limitations where LLVM IR requires convergence control tokens to correctly express the convergence specified here: Some combinations of loops, continue and break statements have differ…

Sameer.