[llvm] [SLP]Add cost estimation for gather node reshuffling (PR #115201)

[Alexey Bataev via llvm-commits]

alexey-bataev wrote:

> The reproducer @joanahalili mentioned above: https://godbolt.org/z/Eq36rPKc3
> 
> And a partially reduced standalone version in case it's more convenient to work with: https://gcc.godbolt.org/z/vKWrzc7KP

Thanks, will investigate it ASAP. Generally speaking, this patch itself could not introduce a bug, it just adds extra cost estimation, so most probably some previously existed issue was revealed

https://github.com/llvm/llvm-project/pull/115201