[clang] [SimplifyCFG] Prevent merging cbranch to cbranch if the branch probability from the first to second is too low. (PR #69375)

[Valery Pykhtin via cfe-commits]

vpykhtin wrote:

@nikic or other reviewers, do you have objections to submit this patch?

https://github.com/llvm/llvm-project/pull/69375