[PATCH] D79175: [ARM][MVE] Tail-Predication: use @llvm.get.active.lane.mask to get the BTC

[Sjoerd Meijer via Phabricator via llvm-commits]

SjoerdMeijer added a comment.

Many thanks @efriedma and @samparker for all your help, really appreciated, will also mention that in the commit message.

And many thanks for your thoughts on the overflow behaviour. Looks like I will need to explore a few different strategies. Easiest would be if SCEV just understands our expressions. When I debugged SCEV, and while I didn't yet get fully to the bottom of it, my impression is that SCEV (its different helpers) is doing a lot of pattern matching, tries different strategies, and finally compares the expression against the loop guard expression. So, I don't know yet how easy or feasible it is to fit this analysis in. That's why I would tend to have a preference for revising the definition of llvm.get.active.lane.mask, because that looks easier. I appreciate that is somewhat working around SCEV limitations, which may or may not be a strong argument.


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