[llvm] [PredicateInfo] Support existing `PredicateType` by adding `PredicatePHI` when needing introduction of phi nodes (PR #151132)

[Nikita Popov via llvm-commits]

nikic wrote:

I'm not sure I fully understand what you mean here. Is this about renaming uses so that the inserted phis get used?

The phis do need to be integrated with renaming, but treating them like a plain predicate is not quite right. If you do that, then you'll introduce a bitcast (formerly ssa.copy). But we should not be inserting a bitcast, things should directly use the phi nodes.

https://github.com/llvm/llvm-project/pull/151132