Comment by chandlerc1024

5 years ago

At the very least, can check when the target isn't a basic block and thus it's a clear win. Will fix your case.

I'm dubious about the whole thing though. Seems like it may day from when branching "down" vs. "up" mattered to branch prediction.

2 comments

chandlerc1024

pyler 5 years ago

It seems that that code handles just the case when target is function.

https://github.com/llvm/llvm-project/blob/535df472b04208d6ae...

ndesaulniers 5 years ago

commit a468601e0ead ("[X86] Re-enable conditional tail calls and fix PR31257.")

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.

Filed: https://bugs.llvm.org/show_bug.cgi?id=50130