[llvm] [X86] EltsFromConsecutiveLoads - handle trunc(wideload()) patterns (PR #199371)

[Adam Scott via llvm-commits]

as4230 wrote:

> This seems to be be increasing the size of the load without checking that this is valid? I'd expect to see either a dereferenceability or alignment check (to ensure the page boundary is not crossed).

I was able to confirm this problem. The last wide load reads up to (stride - element) bytes past the last element. Reverting in #208960, with reproducer over there. Will put up reland shortly after revert merges. 

https://github.com/llvm/llvm-project/pull/199371