[PATCH] D130618: [AArch64][LoopVectorize] Enable tail-folding by default for SVE

[David Sherwood via Phabricator via llvm-commits]

david-arm added a comment.

Hi @dmgreen, we had exactly the same thought process as you. We have already explored unrolling tail-folded loops with reductions and even with the best code quality it makes zero difference to performance on these cores. Sadly it doesn't make the loops faster in the slightest - there appears to be a fundamental bottleneck that cannot be surpassed. No amount of unrolling (using LLVM or by hand) helps in the case of reductions or first-order recurrences. I have also tried unrolling plus manually rescheduling instructions in different ways, but to no avail. We were also very suprised by this, and wish it were different!


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  https://reviews.llvm.org/D130618/new/

https://reviews.llvm.org/D130618