4 files changed, 48 insertions, 0 deletions
diff --git a/lib/IR/AsmWriter.cpp b/lib/IR/AsmWriter.cpp
index f275305cd9..6e3b853b39 100644
--- a/lib/IR/AsmWriter.cpp
+++ b/lib/IR/AsmWriter.cpp
@@ -1647,6 +1647,10 @@ void AssemblyWriter::printFunction(const Function *F) {
     Out << " align " << F->getAlignment();
   if (F->hasGC())
     Out << " gc \"" << F->getGC() << '"';
+  if (F->hasPrefixData()) {
+    Out << " prefix ";
+    writeOperand(F->getPrefixData(), true);
+  }
   if (F->isDeclaration()) {
     Out << '\n';
   } else {
diff --git a/lib/IR/Function.cpp b/lib/IR/Function.cpp
index bf9d949b89..a64a4fa64f 100644
--- a/lib/IR/Function.cpp
+++ b/lib/IR/Function.cpp
@@ -276,6 +276,9 @@ void Function::dropAllReferences() {
   // 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 @@ void Function::copyAttributesFrom(const GlobalValue *Src) {
     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 @@ bool Function::callsFunctionThatReturnsTwice() const {
 
   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);
+}
diff --git a/lib/IR/LLVMContextImpl.h b/lib/IR/LLVMContextImpl.h
index 0c659b81b7..407b985689 100644
--- a/lib/IR/LLVMContextImpl.h
+++ b/lib/IR/LLVMContextImpl.h
@@ -355,6 +355,11 @@ public:
   typedef DenseMap<const Function*, unsigned> IntrinsicIDCacheTy;
   IntrinsicIDCacheTy IntrinsicIDCache;
 
+  /// \brief Mapping from a function to its prefix data, which is stored as the
+  /// operand of an unparented ReturnInst so that the prefix data has a Use.
+  typedef DenseMap<const Function *, ReturnInst *> PrefixDataMapTy;
+  PrefixDataMapTy PrefixDataMap;
+
   int getOrAddScopeRecordIdxEntry(MDNode *N, int ExistingIdx);
   int getOrAddScopeInlinedAtIdxEntry(MDNode *Scope, MDNode *IA,int ExistingIdx);
   
diff --git a/lib/IR/TypeFinder.cpp b/lib/IR/TypeFinder.cpp
index d5e6203507..dd933026ea 100644
--- a/lib/IR/TypeFinder.cpp
+++ b/lib/IR/TypeFinder.cpp
@@ -44,6 +44,9 @@ void TypeFinder::run(const Module &M, bool onlyNamed) {
   for (Module::const_iterator FI = M.begin(), E = M.end(); FI != E; ++FI) {
     incorporateType(FI->getType());
 
+    if (FI->hasPrefixData())
+      incorporateValue(FI->getPrefixData());
+
     // First incorporate the arguments.
     for (Function::const_arg_iterator AI = FI->arg_begin(),
            AE = FI->arg_end(); AI != AE; ++AI)