diff --git a/lib/IR/Function.cpp b/lib/IR/Function.cpp
index bf9d949..a64a4fa 100644
--- a/lib/IR/Function.cpp
+++ b/lib/IR/Function.cpp
@@ -276,6 +276,9 @@
   // blockaddresses, but BasicBlock's destructor takes care of those.
   while (!BasicBlocks.empty())
     BasicBlocks.begin()->eraseFromParent();
+
+  // Prefix data is stored in a side table.
+  setPrefixData(0);
 }
 
 void Function::addAttribute(unsigned i, Attribute::AttrKind attr) {
@@ -351,6 +354,10 @@
     setGC(SrcF->getGC());
   else
     clearGC();
+  if (SrcF->hasPrefixData())
+    setPrefixData(SrcF->getPrefixData());
+  else
+    setPrefixData(0);
 }
 
 /// getIntrinsicID - This method returns the ID number of the specified
@@ -720,3 +727,32 @@
 
   return false;
 }
+
+Constant *Function::getPrefixData() const {
+  assert(hasPrefixData());
+  const LLVMContextImpl::PrefixDataMapTy &PDMap =
+      getContext().pImpl->PrefixDataMap;
+  assert(PDMap.find(this) != PDMap.end());
+  return cast<Constant>(PDMap.find(this)->second->getReturnValue());
+}
+
+void Function::setPrefixData(Constant *PrefixData) {
+  if (!PrefixData && !hasPrefixData())
+    return;
+
+  unsigned SCData = getSubclassDataFromValue();
+  LLVMContextImpl::PrefixDataMapTy &PDMap = getContext().pImpl->PrefixDataMap;
+  ReturnInst *&PDHolder = PDMap[this];
+  if (PrefixData) {
+    if (PDHolder)
+      PDHolder->setOperand(0, PrefixData);
+    else
+      PDHolder = ReturnInst::Create(getContext(), PrefixData);
+    SCData |= 2;
+  } else {
+    delete PDHolder;
+    PDMap.erase(this);
+    SCData &= ~2;
+  }
+  setValueSubclassData(SCData);
+}