[llvm] [ConstantFolding] Add folding for [de]interleave2, insert and extract (PR #141301)

[Yingwei Zheng via llvm-commits]

https://github.com/dtcxzyw commented:

Can you add some constexpr tests? `getAggregateElement` may return null.


https://github.com/llvm/llvm-project/pull/141301