[llvm] [AArch64][TTI] Improve `LegalVF` when computing gather-loads cost (PR #69617)

[David Green via llvm-commits]

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@@ -2989,7 +2989,14 @@ InstructionCost AArch64TTIImpl::getGatherScatterOpCost(
       ElementCount::getScalable(1))
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davemgreen wrote:

I think it might be worth treating !LT.second.isVector() the same as 1 x scalable vectors. Either that or something should be checking that the element type isElementTypeLegalForScalableVector.

https://github.com/llvm/llvm-project/pull/69617