[llvm] [InstCombine] Move extends across identity shuffles. (PR #146901)

[Philip Reames via llvm-commits]

https://github.com/preames commented:

Not an objection, but a possible point of concern.  We canonicalize shuffles after binary operators, and unary operators.  Having the shuffle canonicalized before the casts seems slightly inconsistent.  We should canonicalize one direction or the other, but is pulling the shuffle early the right choice?  I have no strong opinion here, just raising the question for consideration.  

https://github.com/llvm/llvm-project/pull/146901