Add a routine to swap branch instruction operands, and update any

profile metadata at the same time. Use it to preserve metadata attached
to a branch when re-writing it in InstCombine.

Add metadata to the canonicalize_branch InstCombine test, and check that
it is tranformed correctly.

Reviewed by Nick Lewycky!

llvm-svn: 142168

1 files changed, 21 insertions, 0 deletions

diff --git a/llvm/lib/VMCore/Instructions.cpp b/llvm/lib/VMCore/Instructions.cpp
index 82f883ad98a..b3a720527a8 100644
--- a/llvm/lib/VMCore/Instructions.cpp
+++ b/llvm/lib/VMCore/Instructions.cpp
@@ -785,6 +785,27 @@ BranchInst::BranchInst(const BranchInst &BI) :
   SubclassOptionalData = BI.SubclassOptionalData;
 }
 
+void BranchInst::swapSuccessors() {
+  assert(isConditional() &&
+         "Cannot swap successors of an unconditional branch");
+  Op<-1>().swap(Op<-2>());
+
+  // Update profile metadata if present and it matches our structural
+  // expectations.
+  MDNode *ProfileData = getMetadata(LLVMContext::MD_prof);
+  if (!ProfileData || ProfileData->getNumOperands() != 3)
+    return;
+
+  // The first operand is the name. Fetch them backwards and build a new one.
+  Value *Ops[] = {
+    ProfileData->getOperand(0),
+    ProfileData->getOperand(2),
+    ProfileData->getOperand(1)
+  };
+  setMetadata(LLVMContext::MD_prof,
+              MDNode::get(ProfileData->getContext(), Ops));
+}
+
 BasicBlock *BranchInst::getSuccessorV(unsigned idx) const {
   return getSuccessor(idx);
 }