[PATCH] D48893: [Constants, InstCombine] allow RHS (operand 1) identity constants for binops

[Nuno Lopes via Phabricator via llvm-commits]

nlopes added a comment.

`shl %x, undef` is poison; we don't want more undefs :)
So this transformation for shifts is not correct. The way to make it correct would be to introduce a `poison` value and use it in the shuffle instructions instead of undef. I suggest we finally go ahead and do that.


https://reviews.llvm.org/D48893