[llvm] LICM: use PatternMatch, IRBuilder in hoist BO assoc (PR #106978)

[Nikita Popov via llvm-commits]

nikic wrote:

> > The change to use IRBuilder looks good to me, but the rest seems like it will make generalization harder, not easier.
> 
> I hope the PatternMatch change is fine.

It doesn't seem like an improvement, given that you still need to `cast<BinaryOperator>` for both afterwards.

https://github.com/llvm/llvm-project/pull/106978