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!

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@142168 91177308-0d34-0410-b5e6-96231b3b80d8

2 files changed, 24 insertions, 6 deletions

diff --git a/lib/Transforms/InstCombine/InstructionCombining.cpp b/lib/Transforms/InstCombine/InstructionCombining.cpp
index c66f423..92874b9 100644
--- a/lib/Transforms/InstCombine/InstructionCombining.cpp
+++ b/lib/Transforms/InstCombine/InstructionCombining.cpp
@@ -1190,8 +1190,7 @@ Instruction *InstCombiner::visitBranchInst(BranchInst &BI) {
       !isa<Constant>(X)) {
     // Swap Destinations and condition...
     BI.setCondition(X);
-    BI.setSuccessor(0, FalseDest);
-    BI.setSuccessor(1, TrueDest);
+    BI.swapSuccessors();
     return &BI;
   }
 
@@ -1206,8 +1205,7 @@ Instruction *InstCombiner::visitBranchInst(BranchInst &BI) {
       Cond->setPredicate(FCmpInst::getInversePredicate(FPred));
       
       // Swap Destinations and condition.
-      BI.setSuccessor(0, FalseDest);
-      BI.setSuccessor(1, TrueDest);
+      BI.swapSuccessors();
       Worklist.Add(Cond);
       return &BI;
     }
@@ -1223,8 +1221,7 @@ Instruction *InstCombiner::visitBranchInst(BranchInst &BI) {
       ICmpInst *Cond = cast<ICmpInst>(BI.getCondition());
       Cond->setPredicate(ICmpInst::getInversePredicate(IPred));
       // Swap Destinations and condition.
-      BI.setSuccessor(0, FalseDest);
-      BI.setSuccessor(1, TrueDest);
+      BI.swapSuccessors();
       Worklist.Add(Cond);
       return &BI;
     }
diff --git a/lib/VMCore/Instructions.cpp b/lib/VMCore/Instructions.cpp
index 82f883a..b3a7205 100644
--- a/lib/VMCore/Instructions.cpp
+++ b/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);
 }