[llvm] [AArch64] Disable Xor merging for certain neoverse cores (PR #165393)

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Lukacma wrote:

No not really. This was done as we saw value in keeping the eor separate for cores with V0 vector pipeline bandwidth . I agree with you that the benefit is situational and really depends on the surrounding code, but we thought it would be better default to keep it separate, as the throughput hit in case V0 is full would be higher than 1 extra latency cycle. In any case, this is my first time doing this kind of work and I am not sure what is the best to implement this kind of cpu tuning, so I would appreciate advice on how to best do this. Would I need to write some kind of pass which will analyze surrounding code to make this decision ?  

https://github.com/llvm/llvm-project/pull/165393