[PATCH] D32293: InstructionSimplify: Simplify a shuffle with a undef mask to undef

[Jonathan Roelofs via Phabricator via llvm-commits]

jroelofs added a comment.

In https://reviews.llvm.org/D32293#732162, @jroelofs wrote:

> We are not allowed to fold `(select undef x y)` -> `undef`, but we can fold `(select undef x y)` to `x` or to `y`. Likewise, I think this transformation needs to be `(shufflevector x y undef)` -> `x`.


Wait, never mind, LangRef says: "If the shuffle mask is undef, the result vector is undef"


Repository:
  rL LLVM

https://reviews.llvm.org/D32293