[PATCH] D109676: [HardwareLoops] put +1 for loop count before zero extension

[Sam Parker via Phabricator via llvm-commits]

samparker added subscribers: samtebbs, dmgreen.
samparker added a comment.

I would like to start a top-level discussion so everything isn't lost within the review comments, and pull in the Arm people who still work on this... @dmgreen @samtebbs

It appears as though PPC and Arm have different semantics for their loop backedge control. To summarize @shchenz, PPC will 'Decrement CTR and branch if it is still nonzero'. On Arm, AFAICT, we don't perform the decrement when the counter (LR) is <= 1.

So, do we need to tighten the semantics of the loop intrinsics for their overflow behaviour? Arm and PPC use different intrinsics so I can't see why defining them slightly differently would anyone.


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https://reviews.llvm.org/D109676