[llvm] [AArch64][LV] Reduce cost of scaled reduction extends (PR #134074)

[David Sherwood via llvm-commits]

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david-arm wrote:

Do you know why we don't see any differences in the chained variants? Perhaps your pattern matching doesn't kick in for chains due to single-use constraints? Not suggesting you fix this in your patch - we can always improve this in a follow-on patch.

https://github.com/llvm/llvm-project/pull/134074