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================ Comment at: include/clang/Basic/AttrDocs.td:2677-2678 +`language extensions +<http://clang.llvm.org/docs/LanguageExtensions.html#extensions-for-loop-hint-optimizations>`_ +for further details, including limitations of the pipeline hints. + }]; ---------------- aaron.ballman wrote: > There is nothing in the linked documentation that describes pipeline > initiation intervals, so I'm still left wondering how to pick a value for the > attribute argument. I think the docs need a bit more detail for what that > value means and how it impacts the user's code. How about this variant : Software Pipelining optimization is a technique used to optimize loops by utilizing instructions level parallelism. It reorders loop instructions to overlap iterations. As the result new iteration started before previous have finished. The Modulo Scheduling technique creates schedule for one iteration such that when repeating at regular interval no inter-iteration dependence violated. This constant interval(in cycles) between the start of iterations called initiation interval. Cycles number of one iteration of newly generated loop matches with Initiation Interval. For further details see https://en.wikipedia.org/wiki/Software_pipelining and "Swing Modulo Scheduling: A Lifetime-Sensitive Approach", by J. Llosa, A. Gonzalez, E. Ayguade, and M. Valero. ``#pragma clang loop pipeline`` and `#pragma loop pipeline_initiation_interval`` could be used as hints for Software Pipelining optimization. Using ``#pragma clang loop pipeline(disable)`` avoids software pipelining optimization. The disable state can only be specified: .. code-block:: c++ #pragma clang loop pipeline(disable) for (...) { ... } Using ``#pragma loop pipeline_initiation_interval`` instructs the software pipeliner to check the specified initiation interval. If schedule found the result loop iteration would have specified cycle count: .. code-block:: c++ #pragma loop pipeline_initiation_interval(10) for (...) { ... } CHANGES SINCE LAST ACTION https://reviews.llvm.org/D55710/new/ https://reviews.llvm.org/D55710 _______________________________________________ cfe-commits mailing list cfe-commits@lists.llvm.org http://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
