Index: include/llvm/Transforms/Utils/SSAUpdater.h
===================================================================
--- include/llvm/Transforms/Utils/SSAUpdater.h
+++ include/llvm/Transforms/Utils/SSAUpdater.h
@@ -55,6 +55,9 @@
   /// the vector.
   SmallVectorImpl<PHINode*> *InsertedPHIs;
 
+  /// False if we should not create new Phis but only find an existing.
+  bool AllowPhiCreation;
+
 public:
   /// If InsertedPHIs is specified, it will be filled
   /// in with all PHI Nodes created by rewriting.
@@ -69,6 +72,9 @@
   /// PHI nodes get a name based on 'Name'.
   void Initialize(Type *Ty, StringRef Name);
 
+  /// \brief Sets whether we are allowed creation new Phi node.
+  void SetAllowPhiCreation(bool Val) { AllowPhiCreation = Val; }
+
   /// \brief Indicate that a rewritten value is available in the specified block
   /// with the specified value.
   void AddAvailableValue(BasicBlock *BB, Value *V);
Index: include/llvm/Transforms/Utils/SSAUpdaterImpl.h
===================================================================
--- include/llvm/Transforms/Utils/SSAUpdaterImpl.h
+++ include/llvm/Transforms/Utils/SSAUpdaterImpl.h
@@ -68,11 +68,13 @@
   typedef DenseMap<BlkT*, BBInfo*> BBMapTy;
   BBMapTy BBMap;
   BumpPtrAllocator Allocator;
+  bool AllowPhiCreation;
 
 public:
   explicit SSAUpdaterImpl(UpdaterT *U, AvailableValsTy *A,
-                          SmallVectorImpl<PhiT*> *Ins) :
-    Updater(U), AvailableVals(A), InsertedPHIs(Ins) { }
+                          SmallVectorImpl<PhiT *> *Ins, bool APC = true)
+      : Updater(U), AvailableVals(A), InsertedPHIs(Ins), AllowPhiCreation(APC) {
+  }
 
   /// GetValue - Check to see if AvailableVals has an entry for the specified
   /// BB and if so, return it.  If not, construct SSA form by first
@@ -91,11 +93,13 @@
 
     FindDominators(&BlockList, PseudoEntry);
     FindPHIPlacement(&BlockList);
-    FindAvailableVals(&BlockList);
+    if (!FindAvailableVals(&BlockList))
+      return Traits::GetUndefVal(BB, Updater);
 
     return BBMap[BB]->DefBB->AvailableVal;
   }
 
+private:
   /// BuildBlockList - Starting from the specified basic block, traverse back
   /// through its predecessors until reaching blocks with known values.
   /// Create BBInfo structures for the blocks and append them to the block
@@ -316,7 +320,9 @@
   /// earlier, and if not, create a new PHI.  Visit all the block's
   /// predecessors to calculate the available value for each one and fill in
   /// the incoming values for a new PHI.
-  void FindAvailableVals(BlockListTy *BlockList) {
+  /// Return false if new Phi creation is required but we are not allowed to do
+  /// that.
+  bool FindAvailableVals(BlockListTy *BlockList) {
     // Go through the worklist in forward order (i.e., backward through the CFG)
     // and check if existing PHIs can be used.  If not, create empty PHIs where
     // they are needed.
@@ -332,6 +338,10 @@
       if (Info->AvailableVal)
         continue;
 
+      // If we are not allowed to create a new Phi then bail out.
+      if (!AllowPhiCreation)
+        return false;
+
       ValT PHI = Traits::CreateEmptyPHI(Info->BB, Info->NumPreds, Updater);
       Info->AvailableVal = PHI;
       (*AvailableVals)[Info->BB] = PHI;
@@ -371,6 +381,7 @@
       // If the client wants to know about all new instructions, tell it.
       if (InsertedPHIs) InsertedPHIs->push_back(PHI);
     }
+    return true;
   }
 
   /// FindExistingPHI - Look through the PHI nodes in a block to see if any of
Index: lib/Transforms/Utils/SSAUpdater.cpp
===================================================================
--- lib/Transforms/Utils/SSAUpdater.cpp
+++ lib/Transforms/Utils/SSAUpdater.cpp
@@ -44,8 +44,8 @@
   return *static_cast<AvailableValsTy*>(AV);
 }
 
-SSAUpdater::SSAUpdater(SmallVectorImpl<PHINode*> *NewPHI)
-  : InsertedPHIs(NewPHI) {}
+SSAUpdater::SSAUpdater(SmallVectorImpl<PHINode *> *NewPHI)
+    : InsertedPHIs(NewPHI), AllowPhiCreation(true) {}
 
 SSAUpdater::~SSAUpdater() {
   delete static_cast<AvailableValsTy*>(AV);
@@ -155,6 +155,9 @@
     }
   }
 
+  if (!AllowPhiCreation)
+    return UndefValue::get(ProtoType);
+
   // Ok, we have no way out, insert a new one now.
   PHINode *InsertedPHI = PHINode::Create(ProtoType, PredValues.size(),
                                          ProtoName, &BB->front());
@@ -324,7 +327,8 @@
   if (Value *V = AvailableVals[BB])
     return V;
 
-  SSAUpdaterImpl<SSAUpdater> Impl(this, &AvailableVals, InsertedPHIs);
+  SSAUpdaterImpl<SSAUpdater> Impl(this, &AvailableVals, InsertedPHIs,
+                                  AllowPhiCreation);
   return Impl.GetValue(BB);
 }