4 ms·

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 optimi

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.

chandlerc1024 6y 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.
- pyler 6y ago
  It seems that that code handles just the case when target is function. https://github.com/llvm/llvm-project/blob/535df472b04208d6ae88e017c8f1d831fb239346/llvm/lib/Target/X86/X86InstrInfo.cpp#L2870 https://github.com/llvm/llvm-project/blob/535df472b04208d6ae...
- ndesaulniers 6y ago
  commit a468601e0ead ("[X86] Re-enable conditional tail calls and fix PR31257.") https://reviews.llvm.org/D29856 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 https://bugs.llvm.org/show_bug.cgi?id=50130