[llvm] [WebAssembly] getMemoryOpCost and getCastInstrCost (PR #122896)

[Sam Parker via llvm-commits]

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sparker-arm wrote:

It doesn't actually change this test, I don't think these loops are complicated enough. But I want the test in for this and future patches, including #123207 , which will play more with the vectorizer and Wasm TTI. 

https://github.com/llvm/llvm-project/pull/122896