Wow thanks for the pointer! That seems unfortunate, I wonder if there is a way to evaluate whether the extra jump is actually worth it, and whether this optimization could be allowed.
I'm dubious about the whole thing though. Seems like it may day from when branching "down" vs. "up" mattered to branch prediction.
https://github.com/llvm/llvm-project/blob/535df472b04208d6ae...
https://reviews.llvm.org/D29856
added the comment.
If I remove the check for `OptForSize` and `PredTBB == MBB`, we can optimize OP's report, but seem to regress basic tests like llvm/test/CodeGen/X86/conditional-tailcall.ll, literally flipping the branches incorrectly IIUC.