[X86] improve split-stack machine BB placement
Summary:
The conditional branch created to support -fsplit-stack for X86 is
left unbiased/unhinted, resulting in less than ideal block placement:
the __morestack call block is kept on the main hot path. Bias the
branch to insure that the stack allocation block is treated as a
"cold" block during machine basic block placement.
Subscribers: llvm-commits
Differential Revision: https://reviews.llvm.org/D54123
llvm-svn: 346336
diff --git a/llvm/lib/Target/X86/X86FrameLowering.cpp b/llvm/lib/Target/X86/X86FrameLowering.cpp
index 67ec867..e40b0f8 100644
--- a/llvm/lib/Target/X86/X86FrameLowering.cpp
+++ b/llvm/lib/Target/X86/X86FrameLowering.cpp
@@ -2471,8 +2471,8 @@
allocMBB->addSuccessor(&PrologueMBB);
- checkMBB->addSuccessor(allocMBB);
- checkMBB->addSuccessor(&PrologueMBB);
+ checkMBB->addSuccessor(allocMBB, BranchProbability::getZero());
+ checkMBB->addSuccessor(&PrologueMBB, BranchProbability::getOne());
#ifdef EXPENSIVE_CHECKS
MF.verify();