[llvm] [AArch64] Guard against getRegisterBitWidth returning zero in vector instr cost. (PR #117749)

[Sander de Smalen via llvm-commits]

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@@ -3277,13 +3276,15 @@ InstructionCost AArch64TTIImpl::getVectorInstrCostHelper(
         // important.
         UserToExtractIdx[U];
       }
+      if (UserToExtractIdx.empty())
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sdesmalen-arm wrote:

I don't see the link with the change in `IsExtractLaneEquivalentToZero`, is this related?

https://github.com/llvm/llvm-project/pull/117749