6dc23b7009
The expansion of a SCEVUnknown is trivial (it's just the wrapped value). If we try to reuse an existing value it might be a more complex expression that simplifies to the SCEVUnknown. This is inspired by https://github.com/llvm/llvm-project/issues/114879, because SCEVExpander replacing a constant with a phi node is just silly. (I don't consider this a fix for that issue though.)