[llvm] [GlobalISel] Fold instructions with fully-known bits to a constant. (PR #224254)

[Matt Arsenault via llvm-commits]

https://github.com/arsenm commented:

This is *not* simplify demanded bits. IIRC there's still an open PR to introduce SimplifyDemanded* optimizations in GIsel. 

I don't think this is a likely to be worthwhile optimization on its own, only something that you can do if it happens to work out in SimplifyDemanded*

https://github.com/llvm/llvm-project/pull/224254