[llvm] [SLPVectorizer][NFC] Avoid calling `calculateRtStride` twice. (PR #152359)

[Alexey Bataev via llvm-commits]

alexey-bataev wrote:

> > Why do you want to do this? It does not affect compile time much
> 
> Eventually I want to merge a patch addressing this missed opportunity: https://github.com/llvm/llvm-project/pull/152355/files#diff-91b6ce00bd8b5677cc498f099b45e1e98a714662c5e41793f58a8b7b97ab770fR530
> 
> That patch would look really ugly without this refactoring. Also, this is a good thing by itself I think. Simplifies the code somewhat

Could you try to post the patch without this change at first? It does not simplify the code, we have just 2 function calls, instead it will extra 8 bytes to all nodes, even non-load, for all targets, increasing memory footprint. 

https://github.com/llvm/llvm-project/pull/152359