[llvm] [X86] Don't always separate conditions in `(br (and/or cond0, cond1))` into separate branches (PR #81689)

[via llvm-commits]

goldsteinn wrote:

> Mostly there, my remaining concern is how this is supposed to interact with middle-end passes like SimplfyCFG which are handling something similar?

I would think this just works better to honor the middle-end's decisions.
I.e if SimplifyCFG breaks the two conditions, we aren't recombining here. If SimplifyCFG keeps them together, this patch adds backend knowledge that will either confirm that decision, or reject the decision (current default behavior).


https://github.com/llvm/llvm-project/pull/81689