[llvm] [SLP] Add store-to-load forwarding conflict cost for widened store chains (PR #199606)

[Milin Bhade via llvm-commits]

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mbhade-amd wrote:

Done — moved into the Load case and removed the post-trim block so it's charged once. Sized the penalty with Scalars.size() (per your earlier comment) instead of the ambient VecTy.

https://github.com/llvm/llvm-project/pull/199606