[llvm] [IR] Add support for ignoring poisons in `getSplatValue` (PR #89155)

[Nikita Popov via llvm-commits]

nikic wrote:

I don't think this is the change we want to do. I've posted an alternative at https://github.com/llvm/llvm-project/pull/89159.

Basically:

 * In the spirit of https://github.com/llvm/llvm-project/pull/88217, we should remove support for undef splats to the degree possible, not support both.
 * Allowing poison splats by default in m_APInt/m_APFloat is a separate change, and requires at least some due diligence (at least a cursory review of select combines, where this is most likely to cause issues.)

https://github.com/llvm/llvm-project/pull/89155