[PATCH] D72656: Specify branch probabilities for callbr dests

Mon Jan 13 22:25:45 PST 2020

nickdesaulniers added a comment.

Cool, IIRC when upstream kernel devs took a look (via some objtool bug reports) they mentioned that our block placement was backwards.  The `callbr-asm-branch-folding.ll` change makes the most sense to me; the indirect branch is moved out of the way. (Though I would have thought branch predictors assume forward branches are taken).  Did this result in any measurable performance difference?

================
Comment at: llvm/test/CodeGen/X86/callbr-asm.ll:81
 ; CHECK-NEXT:    # Child Loop BB2_4 Depth 4
-; CHECK-NEXT:    .p2align 4, 0x90
 ; CHECK-NEXT:  .Ltmp4: # Block address taken
----------------
The top of this file mentions `; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py`.  Did `update_llc_test_checks.py` really remove this `.p2align`?

Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D72656/new/

https://reviews.llvm.org/D72656