[llvm] [SimplifyCFG] Enable MergeBlockIntoPredecessor with two successors (PR #143766)

[via llvm-commits]

HighW4y2H3ll wrote:

Still have a lot of unit testing failures that needs to be double checked... but would like to hear some feedbacks on this if possible... thx :)

https://github.com/llvm/llvm-project/pull/143766