Combine the implementations of the core part of the SSAUpdater and

MachineSSAUpdater to avoid duplicating all the code.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@103060 91177308-0d34-0410-b5e6-96231b3b80d8

5 files changed, 680 insertions, 900 deletions

diff --git a/include/llvm/CodeGen/MachineSSAUpdater.h b/include/llvm/CodeGen/MachineSSAUpdater.h
index 979ef01..cbb45a7 100644
--- a/include/llvm/CodeGen/MachineSSAUpdater.h
+++ b/include/llvm/CodeGen/MachineSSAUpdater.h
@@ -23,6 +23,7 @@ namespace llvm {
   class TargetInstrInfo;
   class TargetRegisterClass;
   template<typename T> class SmallVectorImpl;
+  template<typename T> class SSAUpdaterTraits;
   class BumpPtrAllocator;
 
 /// MachineSSAUpdater - This class updates SSA form for a set of virtual
@@ -30,9 +31,7 @@ namespace llvm {
 /// or another unstructured transformation wants to rewrite a set of uses of one
 /// vreg with uses of a set of vregs.
 class MachineSSAUpdater {
-public:
-  class BBInfo;
-  typedef SmallVectorImpl<BBInfo*> BlockListTy;
+  friend class SSAUpdaterTraits<MachineSSAUpdater>;
 
 private:
   /// AvailableVals - This keeps track of which value to use on a per-block
@@ -40,11 +39,6 @@ private:
   //typedef DenseMap<MachineBasicBlock*, unsigned > AvailableValsTy;
   void *AV;
 
-  /// BBMap - The GetValueAtEndOfBlock method maintains this mapping from
-  /// basic blocks to BBInfo structures.
-  /// typedef DenseMap<MachineBasicBlock*, BBInfo*> BBMapTy;
-  void *BM;
-
   /// VR - Current virtual register whose uses are being updated.
   unsigned VR;
 
@@ -111,14 +105,6 @@ public:
 private:
   void ReplaceRegWith(unsigned OldReg, unsigned NewReg);
   unsigned GetValueAtEndOfBlockInternal(MachineBasicBlock *BB);
-  void BuildBlockList(MachineBasicBlock *BB, BlockListTy *BlockList,
-                      BumpPtrAllocator *Allocator);
-  void FindDominators(BlockListTy *BlockList);
-  void FindPHIPlacement(BlockListTy *BlockList);
-  void FindAvailableVals(BlockListTy *BlockList);
-  void FindExistingPHI(MachineBasicBlock *BB, BlockListTy *BlockList);
-  bool CheckIfPHIMatches(MachineInstr *PHI);
-  void RecordMatchingPHI(MachineInstr *PHI);
 
   void operator=(const MachineSSAUpdater&); // DO NOT IMPLEMENT
   MachineSSAUpdater(const MachineSSAUpdater&);     // DO NOT IMPLEMENT
diff --git a/include/llvm/Transforms/Utils/SSAUpdater.h b/include/llvm/Transforms/Utils/SSAUpdater.h
index 5b77ed6..ca98466 100644
--- a/include/llvm/Transforms/Utils/SSAUpdater.h
+++ b/include/llvm/Transforms/Utils/SSAUpdater.h
@@ -19,8 +19,8 @@ namespace llvm {
   class BasicBlock;
   class Use;
   class PHINode;
-  template<typename T>
-  class SmallVectorImpl;
+  template<typename T> class SmallVectorImpl;
+  template<typename T> class SSAUpdaterTraits;
   class BumpPtrAllocator;
 
 /// SSAUpdater - This class updates SSA form for a set of values defined in
@@ -28,9 +28,7 @@ namespace llvm {
 /// transformation wants to rewrite a set of uses of one value with uses of a
 /// set of values.
 class SSAUpdater {
-public:
-  class BBInfo;
-  typedef SmallVectorImpl<BBInfo*> BlockListTy;
+  friend class SSAUpdaterTraits<SSAUpdater>;
 
 private:
   /// AvailableVals - This keeps track of which value to use on a per-block
@@ -42,14 +40,10 @@ private:
   /// and a type for PHI nodes.
   Value *PrototypeValue;
 
-  /// BBMap - The GetValueAtEndOfBlock method maintains this mapping from
-  /// basic blocks to BBInfo structures.
-  /// typedef DenseMap<BasicBlock*, BBInfo*> BBMapTy;
-  void *BM;
-
   /// InsertedPHIs - If this is non-null, the SSAUpdater adds all PHI nodes that
   /// it creates to the vector.
   SmallVectorImpl<PHINode*> *InsertedPHIs;
+
 public:
   /// SSAUpdater constructor.  If InsertedPHIs is specified, it will be filled
   /// in with all PHI Nodes created by rewriting.
@@ -102,14 +96,6 @@ public:
 
 private:
   Value *GetValueAtEndOfBlockInternal(BasicBlock *BB);
-  void BuildBlockList(BasicBlock *BB, BlockListTy *BlockList,
-                      BumpPtrAllocator *Allocator);
-  void FindDominators(BlockListTy *BlockList);
-  void FindPHIPlacement(BlockListTy *BlockList);
-  void FindAvailableVals(BlockListTy *BlockList);
-  void FindExistingPHI(BasicBlock *BB, BlockListTy *BlockList);
-  bool CheckIfPHIMatches(PHINode *PHI);
-  void RecordMatchingPHI(PHINode *PHI);
 
   void operator=(const SSAUpdater&); // DO NOT IMPLEMENT
   SSAUpdater(const SSAUpdater&);     // DO NOT IMPLEMENT
diff --git a/include/llvm/Transforms/Utils/SSAUpdaterImpl.h b/include/llvm/Transforms/Utils/SSAUpdaterImpl.h
new file mode 100644
index 0000000..8253796
--- /dev/null
+++ b/include/llvm/Transforms/Utils/SSAUpdaterImpl.h
@@ -0,0 +1,463 @@
+//===-- SSAUpdaterImpl.h - SSA Updater Implementation -----------*- C++ -*-===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This file provides a template that implements the core algorithm for the
+// SSAUpdater and MachineSSAUpdater.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_TRANSFORMS_UTILS_SSAUPDATERIMPL_H
+#define LLVM_TRANSFORMS_UTILS_SSAUPDATERIMPL_H
+
+namespace llvm {
+
+template<typename T> class SSAUpdaterTraits;
+
+template<typename UpdaterT>
+class SSAUpdaterImpl {
+private:
+  UpdaterT *Updater;
+
+  typedef SSAUpdaterTraits<UpdaterT> Traits;
+  typedef typename Traits::BlkT BlkT;
+  typedef typename Traits::ValT ValT;
+  typedef typename Traits::PhiT PhiT;
+
+  /// BBInfo - Per-basic block information used internally by SSAUpdaterImpl.
+  /// The predecessors of each block are cached here since pred_iterator is
+  /// slow and we need to iterate over the blocks at least a few times.
+  class BBInfo {
+  public:
+    BlkT *BB;          // Back-pointer to the corresponding block.
+    ValT AvailableVal; // Value to use in this block.
+    BBInfo *DefBB;     // Block that defines the available value.
+    int BlkNum;        // Postorder number.
+    BBInfo *IDom;      // Immediate dominator.
+    unsigned NumPreds; // Number of predecessor blocks.
+    BBInfo **Preds;    // Array[NumPreds] of predecessor blocks.
+    PhiT *PHITag;      // Marker for existing PHIs that match.
+
+    BBInfo(BlkT *ThisBB, ValT V)
+      : BB(ThisBB), AvailableVal(V), DefBB(V ? this : 0), BlkNum(0), IDom(0),
+      NumPreds(0), Preds(0), PHITag(0) { }
+  };
+
+  typedef DenseMap<BlkT*, ValT> AvailableValsTy;
+  AvailableValsTy *AvailableVals;
+
+  SmallVectorImpl<PhiT*> *InsertedPHIs;
+
+  typedef SmallVectorImpl<BBInfo*> BlockListTy;
+  typedef DenseMap<BlkT*, BBInfo*> BBMapTy;
+  BBMapTy BBMap;
+  BumpPtrAllocator Allocator;
+
+public:
+  explicit SSAUpdaterImpl(UpdaterT *U, AvailableValsTy *A,
+                          SmallVectorImpl<PhiT*> *Ins) :
+    Updater(U), AvailableVals(A), InsertedPHIs(Ins) { }
+
+  /// 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
+  /// calculating the required placement of PHIs and then inserting new PHIs
+  /// where needed.
+  ValT GetValue(BlkT *BB) {
+    SmallVector<BBInfo*, 100> BlockList;
+    BuildBlockList(BB, &BlockList);
+
+    // Special case: bail out if BB is unreachable.
+    if (BlockList.size() == 0) {
+      ValT V = Traits::GetUndefVal(BB, Updater);
+      (*AvailableVals)[BB] = V;
+      return V;
+    }
+
+    FindDominators(&BlockList);
+    FindPHIPlacement(&BlockList);
+    FindAvailableVals(&BlockList);
+
+    return BBMap[BB]->DefBB->AvailableVal;
+  }
+
+  /// 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
+  /// list.
+  void BuildBlockList(BlkT *BB, BlockListTy *BlockList) {
+    SmallVector<BBInfo*, 10> RootList;
+    SmallVector<BBInfo*, 64> WorkList;
+
+    BBInfo *Info = new (Allocator) BBInfo(BB, 0);
+    BBMap[BB] = Info;
+    WorkList.push_back(Info);
+
+    // Search backward from BB, creating BBInfos along the way and stopping
+    // when reaching blocks that define the value.  Record those defining
+    // blocks on the RootList.
+    SmallVector<BlkT*, 10> Preds;
+    while (!WorkList.empty()) {
+      Info = WorkList.pop_back_val();
+      Preds.clear();
+      Traits::FindPredecessorBlocks(Info->BB, &Preds);
+      Info->NumPreds = Preds.size();
+      Info->Preds = static_cast<BBInfo**>
+        (Allocator.Allocate(Info->NumPreds * sizeof(BBInfo*),
+                            AlignOf<BBInfo*>::Alignment));
+
+      // Treat an unreachable predecessor as a definition with 'undef'.
+      if (Info->NumPreds == 0) {
+        Info->AvailableVal = Traits::GetUndefVal(Info->BB, Updater);
+        Info->DefBB = Info;
+        RootList.push_back(Info);
+        continue;
+      }
+
+      for (unsigned p = 0; p != Info->NumPreds; ++p) {
+        BlkT *Pred = Preds[p];
+        // Check if BBMap already has a BBInfo for the predecessor block.
+        typename BBMapTy::value_type &BBMapBucket =
+          BBMap.FindAndConstruct(Pred);
+        if (BBMapBucket.second) {
+          Info->Preds[p] = BBMapBucket.second;
+          continue;
+        }
+
+        // Create a new BBInfo for the predecessor.
+        ValT PredVal = AvailableVals->lookup(Pred);
+        BBInfo *PredInfo = new (Allocator) BBInfo(Pred, PredVal);
+        BBMapBucket.second = PredInfo;
+        Info->Preds[p] = PredInfo;
+
+        if (PredInfo->AvailableVal) {
+          RootList.push_back(PredInfo);
+          continue;
+        }
+        WorkList.push_back(PredInfo);
+      }
+    }
+
+    // Now that we know what blocks are backwards-reachable from the starting
+    // block, do a forward depth-first traversal to assign postorder numbers
+    // to those blocks.
+    BBInfo *PseudoEntry = new (Allocator) BBInfo(0, 0);
+    unsigned BlkNum = 1;
+
+    // Initialize the worklist with the roots from the backward traversal.
+    while (!RootList.empty()) {
+      Info = RootList.pop_back_val();
+      Info->IDom = PseudoEntry;
+      Info->BlkNum = -1;
+      WorkList.push_back(Info);
+    }
+
+    while (!WorkList.empty()) {
+      Info = WorkList.back();
+
+      if (Info->BlkNum == -2) {
+        // All the successors have been handled; assign the postorder number.
+        Info->BlkNum = BlkNum++;
+        // If not a root, put it on the BlockList.
+        if (!Info->AvailableVal)
+          BlockList->push_back(Info);
+        WorkList.pop_back();
+        continue;
+      }
+
+      // Leave this entry on the worklist, but set its BlkNum to mark that its
+      // successors have been put on the worklist.  When it returns to the top
+      // the list, after handling its successors, it will be assigned a
+      // number.
+      Info->BlkNum = -2;
+
+      // Add unvisited successors to the work list.
+      for (typename Traits::BlkSucc_iterator SI =
+             Traits::BlkSucc_begin(Info->BB),
+             E = Traits::BlkSucc_end(Info->BB); SI != E; ++SI) {
+        BBInfo *SuccInfo = BBMap[*SI];
+        if (!SuccInfo || SuccInfo->BlkNum)
+          continue;
+        SuccInfo->BlkNum = -1;
+        WorkList.push_back(SuccInfo);
+      }
+    }
+    PseudoEntry->BlkNum = BlkNum;
+  }
+
+  /// IntersectDominators - This is the dataflow lattice "meet" operation for
+  /// finding dominators.  Given two basic blocks, it walks up the dominator
+  /// tree until it finds a common dominator of both.  It uses the postorder
+  /// number of the blocks to determine how to do that.
+  BBInfo *IntersectDominators(BBInfo *Blk1, BBInfo *Blk2) {
+    while (Blk1 != Blk2) {
+      while (Blk1->BlkNum < Blk2->BlkNum) {
+        Blk1 = Blk1->IDom;
+        if (!Blk1)
+          return Blk2;
+      }
+      while (Blk2->BlkNum < Blk1->BlkNum) {
+        Blk2 = Blk2->IDom;
+        if (!Blk2)
+          return Blk1;
+      }
+    }
+    return Blk1;
+  }
+
+  /// FindDominators - Calculate the dominator tree for the subset of the CFG
+  /// corresponding to the basic blocks on the BlockList.  This uses the
+  /// algorithm from: "A Simple, Fast Dominance Algorithm" by Cooper, Harvey
+  /// and Kennedy, published in Software--Practice and Experience, 2001,
+  /// 4:1-10.  Because the CFG subset does not include any edges leading into
+  /// blocks that define the value, the results are not the usual dominator
+  /// tree.  The CFG subset has a single pseudo-entry node with edges to a set
+  /// of root nodes for blocks that define the value.  The dominators for this
+  /// subset CFG are not the standard dominators but they are adequate for
+  /// placing PHIs within the subset CFG.
+  void FindDominators(BlockListTy *BlockList) {
+    bool Changed;
+    do {
+      Changed = false;
+      // Iterate over the list in reverse order, i.e., forward on CFG edges.
+      for (typename BlockListTy::reverse_iterator I = BlockList->rbegin(),
+             E = BlockList->rend(); I != E; ++I) {
+        BBInfo *Info = *I;
+
+        // Start with the first predecessor.
+        assert(Info->NumPreds > 0 && "unreachable block");
+        BBInfo *NewIDom = Info->Preds[0];
+
+        // Iterate through the block's other predecessors.
+        for (unsigned p = 1; p != Info->NumPreds; ++p) {
+          BBInfo *Pred = Info->Preds[p];
+          NewIDom = IntersectDominators(NewIDom, Pred);
+        }
+
+        // Check if the IDom value has changed.
+        if (NewIDom != Info->IDom) {
+          Info->IDom = NewIDom;
+          Changed = true;
+        }
+      }
+    } while (Changed);
+  }
+
+  /// IsDefInDomFrontier - Search up the dominator tree from Pred to IDom for
+  /// any blocks containing definitions of the value.  If one is found, then
+  /// the successor of Pred is in the dominance frontier for the definition,
+  /// and this function returns true.
+  bool IsDefInDomFrontier(const BBInfo *Pred, const BBInfo *IDom) {
+    for (; Pred != IDom; Pred = Pred->IDom) {
+      if (Pred->DefBB == Pred)
+        return true;
+    }
+    return false;
+  }
+
+  /// FindPHIPlacement - PHIs are needed in the iterated dominance frontiers
+  /// of the known definitions.  Iteratively add PHIs in the dom frontiers
+  /// until nothing changes.  Along the way, keep track of the nearest
+  /// dominating definitions for non-PHI blocks.
+  void FindPHIPlacement(BlockListTy *BlockList) {
+    bool Changed;
+    do {
+      Changed = false;
+      // Iterate over the list in reverse order, i.e., forward on CFG edges.
+      for (typename BlockListTy::reverse_iterator I = BlockList->rbegin(),
+             E = BlockList->rend(); I != E; ++I) {
+        BBInfo *Info = *I;
+
+        // If this block already needs a PHI, there is nothing to do here.
+        if (Info->DefBB == Info)
+          continue;
+
+        // Default to use the same def as the immediate dominator.
+        BBInfo *NewDefBB = Info->IDom->DefBB;
+        for (unsigned p = 0; p != Info->NumPreds; ++p) {
+          if (IsDefInDomFrontier(Info->Preds[p], Info->IDom)) {
+            // Need a PHI here.
+            NewDefBB = Info;
+            break;
+          }
+        }
+
+        // Check if anything changed.
+        if (NewDefBB != Info->DefBB) {
+          Info->DefBB = NewDefBB;
+          Changed = true;
+        }
+      }
+    } while (Changed);
+  }
+
+  /// FindAvailableVal - If this block requires a PHI, first check if an
+  /// existing PHI matches the PHI placement and reaching definitions computed
+  /// 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) {
+    // 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.
+    for (typename BlockListTy::iterator I = BlockList->begin(),
+           E = BlockList->end(); I != E; ++I) {
+      BBInfo *Info = *I;
+      // Check if there needs to be a PHI in BB.
+      if (Info->DefBB != Info)
+        continue;
+
+      // Look for an existing PHI.
+      FindExistingPHI(Info->BB, BlockList);
+      if (Info->AvailableVal)
+        continue;
+
+      ValT PHI = Traits::CreateEmptyPHI(Info->BB, Info->NumPreds, Updater);
+      Info->AvailableVal = PHI;
+      (*AvailableVals)[Info->BB] = PHI;
+    }
+
+    // Now go back through the worklist in reverse order to fill in the
+    // arguments for any new PHIs added in the forward traversal.
+    for (typename BlockListTy::reverse_iterator I = BlockList->rbegin(),
+           E = BlockList->rend(); I != E; ++I) {
+      BBInfo *Info = *I;
+
+      if (Info->DefBB != Info) {
+        // Record the available value at join nodes to speed up subsequent
+        // uses of this SSAUpdater for the same value.
+        if (Info->NumPreds > 1)
+          (*AvailableVals)[Info->BB] = Info->DefBB->AvailableVal;
+        continue;
+      }
+
+      // Check if this block contains a newly added PHI.
+      PhiT *PHI = Traits::ValueIsNewPHI(Info->AvailableVal, Updater);
+      if (!PHI)
+        continue;
+
+      // Iterate through the block's predecessors.
+      for (unsigned p = 0; p != Info->NumPreds; ++p) {
+        BBInfo *PredInfo = Info->Preds[p];
+        BlkT *Pred = PredInfo->BB;
+        // Skip to the nearest preceding definition.
+        if (PredInfo->DefBB != PredInfo)
+          PredInfo = PredInfo->DefBB;
+        Traits::AddPHIOperand(PHI, PredInfo->AvailableVal, Pred);
+      }
+
+      DEBUG(dbgs() << "  Inserted PHI: " << *PHI << "\n");
+
+      // If the client wants to know about all new instructions, tell it.
+      if (InsertedPHIs) InsertedPHIs->push_back(PHI);
+    }
+  }
+
+  /// FindExistingPHI - Look through the PHI nodes in a block to see if any of
+  /// them match what is needed.
+  void FindExistingPHI(BlkT *BB, BlockListTy *BlockList) {
+    for (typename BlkT::iterator BBI = BB->begin(), BBE = BB->end();
+         BBI != BBE; ++BBI) {
+      PhiT *SomePHI = Traits::InstrIsPHI(BBI);
+      if (!SomePHI)
+        break;
+      if (CheckIfPHIMatches(SomePHI)) {
+        RecordMatchingPHI(SomePHI);
+        break;
+      }
+      // Match failed: clear all the PHITag values.
+      for (typename BlockListTy::iterator I = BlockList->begin(),
+             E = BlockList->end(); I != E; ++I)
+        (*I)->PHITag = 0;
+    }
+  }
+
+  /// CheckIfPHIMatches - Check if a PHI node matches the placement and values
+  /// in the BBMap.
+  bool CheckIfPHIMatches(PhiT *PHI) {
+    SmallVector<PhiT*, 20> WorkList;
+    WorkList.push_back(PHI);
+
+    // Mark that the block containing this PHI has been visited.
+    BBMap[PHI->getParent()]->PHITag = PHI;
+
+    while (!WorkList.empty()) {
+      PHI = WorkList.pop_back_val();
+
+      // Iterate through the PHI's incoming values.
+      for (typename Traits::PHI_iterator I = Traits::PHI_begin(PHI),
+             E = Traits::PHI_end(PHI); I != E; ++I) {
+        ValT IncomingVal = I.getIncomingValue();
+        BBInfo *PredInfo = BBMap[I.getIncomingBlock()];
+        // Skip to the nearest preceding definition.
+        if (PredInfo->DefBB != PredInfo)
+          PredInfo = PredInfo->DefBB;
+
+        // Check if it matches the expected value.
+        if (PredInfo->AvailableVal) {
+          if (IncomingVal == PredInfo->AvailableVal)
+            continue;
+          return false;
+        }
+
+        // Check if the value is a PHI in the correct block.
+        PhiT *IncomingPHIVal = Traits::ValueIsPHI(IncomingVal, Updater);
+        if (!IncomingPHIVal || IncomingPHIVal->getParent() != PredInfo->BB)
+          return false;
+
+        // If this block has already been visited, check if this PHI matches.
+        if (PredInfo->PHITag) {
+          if (IncomingPHIVal == PredInfo->PHITag)
+            continue;
+          return false;
+        }
+        PredInfo->PHITag = IncomingPHIVal;
+
+        WorkList.push_back(IncomingPHIVal);
+      }
+    }
+    return true;
+  }
+
+  /// RecordMatchingPHI - For a PHI node that matches, record it and its input
+  /// PHIs in both the BBMap and the AvailableVals mapping.
+  void RecordMatchingPHI(PhiT *PHI) {
+    SmallVector<PhiT*, 20> WorkList;
+    WorkList.push_back(PHI);
+
+    // Record this PHI.
+    BlkT *BB = PHI->getParent();
+    ValT PHIVal = Traits::GetPHIValue(PHI);
+    (*AvailableVals)[BB] = PHIVal;
+    BBMap[BB]->AvailableVal = PHIVal;
+
+    while (!WorkList.empty()) {
+      PHI = WorkList.pop_back_val();
+
+      // Iterate through the PHI's incoming values.
+      for (typename Traits::PHI_iterator I = Traits::PHI_begin(PHI),
+             E = Traits::PHI_end(PHI); I != E; ++I) {
+        ValT IncomingVal = I.getIncomingValue();
+        PhiT *IncomingPHI = Traits::ValueIsPHI(IncomingVal, Updater);
+        if (!IncomingPHI) continue;
+        BB = IncomingPHI->getParent();
+        BBInfo *Info = BBMap[BB];
+        if (!Info || Info->AvailableVal)
+          continue;
+
+        // Record the PHI and add it to the worklist.
+        (*AvailableVals)[BB] = IncomingVal;
+        Info->AvailableVal = IncomingVal;
+        WorkList.push_back(IncomingPHI);
+      }
+    }
+  }
+};
+
+} // End llvm namespace
+
+#endif
diff --git a/lib/CodeGen/MachineSSAUpdater.cpp b/lib/CodeGen/MachineSSAUpdater.cpp
index b8996d4..99fb99a 100644
--- a/lib/CodeGen/MachineSSAUpdater.cpp
+++ b/lib/CodeGen/MachineSSAUpdater.cpp
@@ -26,39 +26,17 @@
 #include "llvm/Support/Debug.h"
 #include "llvm/Support/ErrorHandling.h"
 #include "llvm/Support/raw_ostream.h"
+#include "llvm/Transforms/Utils/SSAUpdaterImpl.h"
 using namespace llvm;
 
-/// BBInfo - Per-basic block information used internally by MachineSSAUpdater.
-class MachineSSAUpdater::BBInfo {
-public:
-  MachineBasicBlock *BB; // Back-pointer to the corresponding block.
-  unsigned AvailableVal; // Value to use in this block.
-  BBInfo *DefBB;         // Block that defines the available value.
-  int BlkNum;            // Postorder number.
-  BBInfo *IDom;          // Immediate dominator.
-  unsigned NumPreds;     // Number of predecessor blocks.
-  BBInfo **Preds;        // Array[NumPreds] of predecessor blocks.
-  MachineInstr *PHITag;  // Marker for existing PHIs that match.
-
-  BBInfo(MachineBasicBlock *ThisBB, unsigned V)
-    : BB(ThisBB), AvailableVal(V), DefBB(V ? this : 0), BlkNum(0), IDom(0),
-      NumPreds(0), Preds(0), PHITag(0) { }
-};
-
-typedef DenseMap<MachineBasicBlock*, MachineSSAUpdater::BBInfo*> BBMapTy;
-
 typedef DenseMap<MachineBasicBlock*, unsigned> AvailableValsTy;
 static AvailableValsTy &getAvailableVals(void *AV) {
   return *static_cast<AvailableValsTy*>(AV);
 }
 
-static BBMapTy *getBBMap(void *BM) {
-  return static_cast<BBMapTy*>(BM);
-}
-
 MachineSSAUpdater::MachineSSAUpdater(MachineFunction &MF,
                                      SmallVectorImpl<MachineInstr*> *NewPHI)
-  : AV(0), BM(0), InsertedPHIs(NewPHI) {
+  : AV(0), InsertedPHIs(NewPHI) {
   TII = MF.getTarget().getInstrInfo();
   MRI = &MF.getRegInfo();
 }
@@ -134,7 +112,8 @@ static
 MachineInstr *InsertNewDef(unsigned Opcode,
                            MachineBasicBlock *BB, MachineBasicBlock::iterator I,
                            const TargetRegisterClass *RC,
-                           MachineRegisterInfo *MRI, const TargetInstrInfo *TII) {
+                           MachineRegisterInfo *MRI,
+                           const TargetInstrInfo *TII) {
   unsigned NewVR = MRI->createVirtualRegister(RC);
   return BuildMI(*BB, I, DebugLoc(), TII->get(Opcode), NewVR);
 }
@@ -263,438 +242,131 @@ void MachineSSAUpdater::ReplaceRegWith(unsigned OldReg, unsigned NewReg) {
       I->second = NewReg;
 }
 
-/// GetValueAtEndOfBlockInternal - Check to see if AvailableVals has an entry
-/// for the specified BB and if so, return it.  If not, construct SSA form by
-/// first calculating the required placement of PHIs and then inserting new
-/// PHIs where needed.
-unsigned MachineSSAUpdater::GetValueAtEndOfBlockInternal(MachineBasicBlock *BB){
-  AvailableValsTy &AvailableVals = getAvailableVals(AV);
-  if (unsigned V = AvailableVals[BB])
-    return V;
+/// MachinePHIiter - Iterator for PHI operands.  This is used for the
+/// PHI_iterator in the SSAUpdaterImpl template.
+namespace {
+  class MachinePHIiter {
+  private:
+    MachineInstr *PHI;
+    unsigned idx;
+ 
+  public:
+    explicit MachinePHIiter(MachineInstr *P) // begin iterator
+      : PHI(P), idx(1) {}
+    MachinePHIiter(MachineInstr *P, bool) // end iterator
+      : PHI(P), idx(PHI->getNumOperands()) {}
+
+    MachinePHIiter &operator++() { idx += 2; return *this; } 
+    bool operator==(const MachinePHIiter& x) const { return idx == x.idx; }
+    bool operator!=(const MachinePHIiter& x) const { return !operator==(x); }
+    unsigned getIncomingValue() { return PHI->getOperand(idx).getReg(); }
+    MachineBasicBlock *getIncomingBlock() {
+      return PHI->getOperand(idx+1).getMBB();
+    }
+  };
+}
 
-  // Pool allocation used internally by GetValueAtEndOfBlock.
-  BumpPtrAllocator Allocator;
-  BBMapTy BBMapObj;
-  BM = &BBMapObj;
+/// SSAUpdaterTraits<MachineSSAUpdater> - Traits for the SSAUpdaterImpl
+/// template, specialized for MachineSSAUpdater.
+namespace llvm {
+template<>
+class SSAUpdaterTraits<MachineSSAUpdater> {
+public:
+  typedef MachineBasicBlock BlkT;
+  typedef unsigned ValT;
+  typedef MachineInstr PhiT;
+
+  typedef MachineBasicBlock::succ_iterator BlkSucc_iterator;
+  static BlkSucc_iterator BlkSucc_begin(BlkT *BB) { return BB->succ_begin(); }
+  static BlkSucc_iterator BlkSucc_end(BlkT *BB) { return BB->succ_end(); }
+
+  typedef MachinePHIiter PHI_iterator;
+  static inline PHI_iterator PHI_begin(PhiT *PHI) { return PHI_iterator(PHI); }
+  static inline PHI_iterator PHI_end(PhiT *PHI) {
+    return PHI_iterator(PHI, true);
+  }
 
-  SmallVector<BBInfo*, 100> BlockList;
-  BuildBlockList(BB, &BlockList, &Allocator);
+  /// FindPredecessorBlocks - Put the predecessors of BB into the Preds
+  /// vector.
+  static void FindPredecessorBlocks(MachineBasicBlock *BB,
+                                    SmallVectorImpl<MachineBasicBlock*> *Preds){
+    for (MachineBasicBlock::pred_iterator PI = BB->pred_begin(),
+           E = BB->pred_end(); PI != E; ++PI)
+      Preds->push_back(*PI);
+  }
 
-  // Special case: bail out if BB is unreachable.
-  if (BlockList.size() == 0) {
-    BM = 0;
+  /// GetUndefVal - Create an IMPLICIT_DEF instruction with a new register.
+  /// Add it into the specified block and return the register.
+  static unsigned GetUndefVal(MachineBasicBlock *BB,
+                              MachineSSAUpdater *Updater) {
     // Insert an implicit_def to represent an undef value.
     MachineInstr *NewDef = InsertNewDef(TargetOpcode::IMPLICIT_DEF,
                                         BB, BB->getFirstTerminator(),
-                                        VRC, MRI, TII);
-    unsigned V = NewDef->getOperand(0).getReg();
-    AvailableVals[BB] = V;
-    return V;
-  }
-
-  FindDominators(&BlockList);
-  FindPHIPlacement(&BlockList);
-  FindAvailableVals(&BlockList);
-
-  BM = 0;
-  return BBMapObj[BB]->DefBB->AvailableVal;
-}
-
-/// FindPredecessorBlocks - Put the predecessors of Info->BB into the Preds
-/// vector, set Info->NumPreds, and allocate space in Info->Preds.
-static void FindPredecessorBlocks(MachineSSAUpdater::BBInfo *Info,
-                                  SmallVectorImpl<MachineBasicBlock*> *Preds,
-                                  BumpPtrAllocator *Allocator) {
-  MachineBasicBlock *BB = Info->BB;
-  for (MachineBasicBlock::pred_iterator PI = BB->pred_begin(),
-         E = BB->pred_end(); PI != E; ++PI)
-    Preds->push_back(*PI);
-
-  Info->NumPreds = Preds->size();
-  Info->Preds = static_cast<MachineSSAUpdater::BBInfo**>
-    (Allocator->Allocate(Info->NumPreds * sizeof(MachineSSAUpdater::BBInfo*),
-                         AlignOf<MachineSSAUpdater::BBInfo*>::Alignment));
-}
-
-/// 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 list.
-void MachineSSAUpdater::BuildBlockList(MachineBasicBlock *BB,
-                                       BlockListTy *BlockList,
-                                       BumpPtrAllocator *Allocator) {
-  AvailableValsTy &AvailableVals = getAvailableVals(AV);
-  BBMapTy *BBMap = getBBMap(BM);
-  SmallVector<BBInfo*, 10> RootList;
-  SmallVector<BBInfo*, 64> WorkList;
-
-  BBInfo *Info = new (*Allocator) BBInfo(BB, 0);
-  (*BBMap)[BB] = Info;
-  WorkList.push_back(Info);
-
-  // Search backward from BB, creating BBInfos along the way and stopping when
-  // reaching blocks that define the value.  Record those defining blocks on
-  // the RootList.
-  SmallVector<MachineBasicBlock*, 10> Preds;
-  while (!WorkList.empty()) {
-    Info = WorkList.pop_back_val();
-    Preds.clear();
-    FindPredecessorBlocks(Info, &Preds, Allocator);
-
-    // Treat an unreachable predecessor as a definition with 'undef'.
-    if (Info->NumPreds == 0) {
-      // Insert an implicit_def to represent an undef value.
-      MachineInstr *NewDef = InsertNewDef(TargetOpcode::IMPLICIT_DEF,
-                                          Info->BB,
-                                          Info->BB->getFirstTerminator(),
-                                          VRC, MRI, TII);
-      Info->AvailableVal = NewDef->getOperand(0).getReg();
-      Info->DefBB = Info;
-      RootList.push_back(Info);
-      continue;
-    }
-
-    for (unsigned p = 0; p != Info->NumPreds; ++p) {
-      MachineBasicBlock *Pred = Preds[p];
-      // Check if BBMap already has a BBInfo for the predecessor block.
-      BBMapTy::value_type &BBMapBucket = BBMap->FindAndConstruct(Pred);
-      if (BBMapBucket.second) {
-        Info->Preds[p] = BBMapBucket.second;
-        continue;
-      }
-
-      // Create a new BBInfo for the predecessor.
-      unsigned PredVal = AvailableVals.lookup(Pred);
-      BBInfo *PredInfo = new (*Allocator) BBInfo(Pred, PredVal);
-      BBMapBucket.second = PredInfo;
-      Info->Preds[p] = PredInfo;
-
-      if (PredInfo->AvailableVal) {
-        RootList.push_back(PredInfo);
-        continue;
-      }
-      WorkList.push_back(PredInfo);
-    }
+                                        Updater->VRC, Updater->MRI,
+                                        Updater->TII);
+    return NewDef->getOperand(0).getReg();
   }
 
-  // Now that we know what blocks are backwards-reachable from the starting
-  // block, do a forward depth-first traversal to assign postorder numbers
-  // to those blocks.
-  BBInfo *PseudoEntry = new (*Allocator) BBInfo(0, 0);
-  unsigned BlkNum = 1;
-
-  // Initialize the worklist with the roots from the backward traversal.
-  while (!RootList.empty()) {
-    Info = RootList.pop_back_val();
-    Info->IDom = PseudoEntry;
-    Info->BlkNum = -1;
-    WorkList.push_back(Info);
+  /// CreateEmptyPHI - Create a PHI instruction that defines a new register.
+  /// Add it into the specified block and return the register.
+  static unsigned CreateEmptyPHI(MachineBasicBlock *BB, unsigned NumPreds,
+                                 MachineSSAUpdater *Updater) {
+    MachineBasicBlock::iterator Loc = BB->empty() ? BB->end() : BB->front();
+    MachineInstr *PHI = InsertNewDef(TargetOpcode::PHI, BB, Loc,
+                                     Updater->VRC, Updater->MRI,
+                                     Updater->TII);
+    return PHI->getOperand(0).getReg();
   }
 
-  while (!WorkList.empty()) {
-    Info = WorkList.back();
-
-    if (Info->BlkNum == -2) {
-      // All the successors have been handled; assign the postorder number.
-      Info->BlkNum = BlkNum++;
-      // If not a root, put it on the BlockList.
-      if (!Info->AvailableVal)
-        BlockList->push_back(Info);
-      WorkList.pop_back();
-      continue;
-    }
-
-    // Leave this entry on the worklist, but set its BlkNum to mark that its
-    // successors have been put on the worklist.  When it returns to the top
-    // the list, after handling its successors, it will be assigned a number.
-    Info->BlkNum = -2;
-
-    // Add unvisited successors to the work list.
-    for (MachineBasicBlock::succ_iterator SI = Info->BB->succ_begin(),
-           E = Info->BB->succ_end(); SI != E; ++SI) {
-      BBInfo *SuccInfo = (*BBMap)[*SI];
-      if (!SuccInfo || SuccInfo->BlkNum)
-        continue;
-      SuccInfo->BlkNum = -1;
-      WorkList.push_back(SuccInfo);
-    }
+  /// AddPHIOperand - Add the specified value as an operand of the PHI for
+  /// the specified predecessor block.
+  static void AddPHIOperand(MachineInstr *PHI, unsigned Val,
+                            MachineBasicBlock *Pred) {
+    PHI->addOperand(MachineOperand::CreateReg(Val, false));
+    PHI->addOperand(MachineOperand::CreateMBB(Pred));
   }
-  PseudoEntry->BlkNum = BlkNum;
-}
 
-/// IntersectDominators - This is the dataflow lattice "meet" operation for
-/// finding dominators.  Given two basic blocks, it walks up the dominator
-/// tree until it finds a common dominator of both.  It uses the postorder
-/// number of the blocks to determine how to do that.
-static MachineSSAUpdater::BBInfo *
-IntersectDominators(MachineSSAUpdater::BBInfo *Blk1,
-                    MachineSSAUpdater::BBInfo *Blk2) {
-  while (Blk1 != Blk2) {
-    while (Blk1->BlkNum < Blk2->BlkNum) {
-      Blk1 = Blk1->IDom;
-      if (!Blk1)
-        return Blk2;
-    }
-    while (Blk2->BlkNum < Blk1->BlkNum) {
-      Blk2 = Blk2->IDom;
-      if (!Blk2)
-        return Blk1;
-    }
-  }
-  return Blk1;
-}
-
-/// FindDominators - Calculate the dominator tree for the subset of the CFG
-/// corresponding to the basic blocks on the BlockList.  This uses the
-/// algorithm from: "A Simple, Fast Dominance Algorithm" by Cooper, Harvey and
-/// Kennedy, published in Software--Practice and Experience, 2001, 4:1-10.
-/// Because the CFG subset does not include any edges leading into blocks that
-/// define the value, the results are not the usual dominator tree.  The CFG
-/// subset has a single pseudo-entry node with edges to a set of root nodes
-/// for blocks that define the value.  The dominators for this subset CFG are
-/// not the standard dominators but they are adequate for placing PHIs within
-/// the subset CFG.
-void MachineSSAUpdater::FindDominators(BlockListTy *BlockList) {
-  bool Changed;
-  do {
-    Changed = false;
-    // Iterate over the list in reverse order, i.e., forward on CFG edges.
-    for (BlockListTy::reverse_iterator I = BlockList->rbegin(),
-           E = BlockList->rend(); I != E; ++I) {
-      BBInfo *Info = *I;
-
-      // Start with the first predecessor.
-      assert(Info->NumPreds > 0 && "unreachable block");
-      BBInfo *NewIDom = Info->Preds[0];
-
-      // Iterate through the block's other predecessors.
-      for (unsigned p = 1; p != Info->NumPreds; ++p) {
-        BBInfo *Pred = Info->Preds[p];
-        NewIDom = IntersectDominators(NewIDom, Pred);
-      }
-
-      // Check if the IDom value has changed.
-      if (NewIDom != Info->IDom) {
-        Info->IDom = NewIDom;
-        Changed = true;
-      }
-    }
-  } while (Changed);
-}
-
-/// IsDefInDomFrontier - Search up the dominator tree from Pred to IDom for
-/// any blocks containing definitions of the value.  If one is found, then the
-/// successor of Pred is in the dominance frontier for the definition, and
-/// this function returns true.
-static bool IsDefInDomFrontier(const MachineSSAUpdater::BBInfo *Pred,
-                               const MachineSSAUpdater::BBInfo *IDom) {
-  for (; Pred != IDom; Pred = Pred->IDom) {
-    if (Pred->DefBB == Pred)
-      return true;
+  /// InstrIsPHI - Check if an instruction is a PHI.
+  ///
+  static MachineInstr *InstrIsPHI(MachineInstr *I) {
+    if (I->isPHI())
+      return I;
+    return 0;
   }
-  return false;
-}
-
-/// FindPHIPlacement - PHIs are needed in the iterated dominance frontiers of
-/// the known definitions.  Iteratively add PHIs in the dom frontiers until
-/// nothing changes.  Along the way, keep track of the nearest dominating
-/// definitions for non-PHI blocks.
-void MachineSSAUpdater::FindPHIPlacement(BlockListTy *BlockList) {
-  bool Changed;
-  do {
-    Changed = false;
-    // Iterate over the list in reverse order, i.e., forward on CFG edges.
-    for (BlockListTy::reverse_iterator I = BlockList->rbegin(),
-           E = BlockList->rend(); I != E; ++I) {
-      BBInfo *Info = *I;
-
-      // If this block already needs a PHI, there is nothing to do here.
-      if (Info->DefBB == Info)
-        continue;
-
-      // Default to use the same def as the immediate dominator.
-      BBInfo *NewDefBB = Info->IDom->DefBB;
-      for (unsigned p = 0; p != Info->NumPreds; ++p) {
-        if (IsDefInDomFrontier(Info->Preds[p], Info->IDom)) {
-          // Need a PHI here.
-          NewDefBB = Info;
-          break;
-        }
-      }
 
-      // Check if anything changed.
-      if (NewDefBB != Info->DefBB) {
-        Info->DefBB = NewDefBB;
-        Changed = true;
-      }
-    }
-  } while (Changed);
-}
-
-/// FindAvailableVal - If this block requires a PHI, first check if an existing
-/// PHI matches the PHI placement and reaching definitions computed 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 MachineSSAUpdater::FindAvailableVals(BlockListTy *BlockList) {
-  AvailableValsTy &AvailableVals = getAvailableVals(AV);
-
-  // 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.
-  for (BlockListTy::iterator I = BlockList->begin(), E = BlockList->end();
-       I != E; ++I) {
-    BBInfo *Info = *I;
-    // Check if there needs to be a PHI in BB.
-    if (Info->DefBB != Info)
-      continue;
-
-    // Look for an existing PHI.
-    FindExistingPHI(Info->BB, BlockList);
-    if (Info->AvailableVal)
-      continue;
-
-    MachineBasicBlock::iterator Loc =
-      Info->BB->empty() ? Info->BB->end() : Info->BB->front();
-    MachineInstr *InsertedPHI = InsertNewDef(TargetOpcode::PHI, Info->BB, Loc,
-                                             VRC, MRI, TII);
-    unsigned PHI = InsertedPHI->getOperand(0).getReg();
-    Info->AvailableVal = PHI;
-    AvailableVals[Info->BB] = PHI;
+  /// ValueIsPHI - Check if the instruction that defines the specified register
+  /// is a PHI instruction.
+  static MachineInstr *ValueIsPHI(unsigned Val, MachineSSAUpdater *Updater) {
+    return InstrIsPHI(Updater->MRI->getVRegDef(Val));
   }
 
-  // Now go back through the worklist in reverse order to fill in the arguments
-  // for any new PHIs added in the forward traversal.
-  for (BlockListTy::reverse_iterator I = BlockList->rbegin(),
-         E = BlockList->rend(); I != E; ++I) {
-    BBInfo *Info = *I;
-
-    if (Info->DefBB != Info) {
-      // Record the available value at join nodes to speed up subsequent
-      // uses of this SSAUpdater for the same value.
-      if (Info->NumPreds > 1)
-        AvailableVals[Info->BB] = Info->DefBB->AvailableVal;
-      continue;
-    }
-
-    // Check if this block contains a newly added PHI.
-    unsigned PHI = Info->AvailableVal;
-    MachineInstr *InsertedPHI = MRI->getVRegDef(PHI);
-    if (!InsertedPHI->isPHI() || InsertedPHI->getNumOperands() > 1)
-      continue;
-
-    // Iterate through the block's predecessors.
-    MachineInstrBuilder MIB(InsertedPHI);
-    for (unsigned p = 0; p != Info->NumPreds; ++p) {
-      BBInfo *PredInfo = Info->Preds[p];
-      MachineBasicBlock *Pred = PredInfo->BB;
-      // Skip to the nearest preceding definition.
-      if (PredInfo->DefBB != PredInfo)
-        PredInfo = PredInfo->DefBB;
-      MIB.addReg(PredInfo->AvailableVal).addMBB(Pred);
-    }
-
-    DEBUG(dbgs() << "  Inserted PHI: " << *InsertedPHI << "\n");
-
-    // If the client wants to know about all new instructions, tell it.
-    if (InsertedPHIs) InsertedPHIs->push_back(InsertedPHI);
+  /// ValueIsNewPHI - Like ValueIsPHI but also check if the PHI has no source
+  /// operands, i.e., it was just added.
+  static MachineInstr *ValueIsNewPHI(unsigned Val, MachineSSAUpdater *Updater) {
+    MachineInstr *PHI = ValueIsPHI(Val, Updater);
+    if (PHI && PHI->getNumOperands() <= 1)
+      return PHI;
+    return 0;
   }
-}
 
-/// FindExistingPHI - Look through the PHI nodes in a block to see if any of
-/// them match what is needed.
-void MachineSSAUpdater::FindExistingPHI(MachineBasicBlock *BB,
-                                        BlockListTy *BlockList) {
-  for (MachineBasicBlock::iterator BBI = BB->begin(), BBE = BB->end();
-       BBI != BBE && BBI->isPHI(); ++BBI) {
-    if (CheckIfPHIMatches(BBI)) {
-      RecordMatchingPHI(BBI);
-      break;
-    }
-    // Match failed: clear all the PHITag values.
-    for (BlockListTy::iterator I = BlockList->begin(), E = BlockList->end();
-         I != E; ++I)
-      (*I)->PHITag = 0;
+  /// GetPHIValue - For the specified PHI instruction, return the register
+  /// that it defines.
+  static unsigned GetPHIValue(MachineInstr *PHI) {
+    return PHI->getOperand(0).getReg();
   }
-}
-
-/// CheckIfPHIMatches - Check if a PHI node matches the placement and values
-/// in the BBMap.
-bool MachineSSAUpdater::CheckIfPHIMatches(MachineInstr *PHI) {
-  BBMapTy *BBMap = getBBMap(BM);
-  SmallVector<MachineInstr*, 20> WorkList;
-  WorkList.push_back(PHI);
-
-  // Mark that the block containing this PHI has been visited.
-  (*BBMap)[PHI->getParent()]->PHITag = PHI;
-
-  while (!WorkList.empty()) {
-    PHI = WorkList.pop_back_val();
-
-    // Iterate through the PHI's incoming values.
-    for (unsigned i = 1, e = PHI->getNumOperands(); i != e; i += 2) {
-      unsigned IncomingVal = PHI->getOperand(i).getReg();
-      BBInfo *PredInfo = (*BBMap)[PHI->getOperand(i+1).getMBB()];
-      // Skip to the nearest preceding definition.
-      if (PredInfo->DefBB != PredInfo)
-        PredInfo = PredInfo->DefBB;
-
-      // Check if it matches the expected value.
-      if (PredInfo->AvailableVal) {
-        if (IncomingVal == PredInfo->AvailableVal)
-          continue;
-        return false;
-      }
-
-      // Check if the value is a PHI in the correct block.
-      MachineInstr *IncomingPHIVal = MRI->getVRegDef(IncomingVal);
-      if (!IncomingPHIVal->isPHI() ||
-          IncomingPHIVal->getParent() != PredInfo->BB)
-        return false;
-
-      // If this block has already been visited, check if this PHI matches.
-      if (PredInfo->PHITag) {
-        if (IncomingPHIVal == PredInfo->PHITag)
-          continue;
-        return false;
-      }
-      PredInfo->PHITag = IncomingPHIVal;
+};
 
-      WorkList.push_back(IncomingPHIVal);
-    }
-  }
-  return true;
-}
+} // End llvm namespace
 
-/// RecordMatchingPHI - For a PHI node that matches, record it and its input
-/// PHIs in both the BBMap and the AvailableVals mapping.
-void MachineSSAUpdater::RecordMatchingPHI(MachineInstr *PHI) {
-  BBMapTy *BBMap = getBBMap(BM);
+/// GetValueAtEndOfBlockInternal - Check to see if AvailableVals has an entry
+/// for the specified BB and if so, return it.  If not, construct SSA form by
+/// first calculating the required placement of PHIs and then inserting new
+/// PHIs where needed.
+unsigned MachineSSAUpdater::GetValueAtEndOfBlockInternal(MachineBasicBlock *BB){
   AvailableValsTy &AvailableVals = getAvailableVals(AV);
-  SmallVector<MachineInstr*, 20> WorkList;
-  WorkList.push_back(PHI);
-
-  // Record this PHI.
-  MachineBasicBlock *BB = PHI->getParent();
-  AvailableVals[BB] = PHI->getOperand(0).getReg();
-  (*BBMap)[BB]->AvailableVal = PHI->getOperand(0).getReg();
-
-  while (!WorkList.empty()) {
-    PHI = WorkList.pop_back_val();
-
-    // Iterate through the PHI's incoming values.
-    for (unsigned i = 1, e = PHI->getNumOperands(); i != e; i += 2) {
-      unsigned IncomingVal = PHI->getOperand(i).getReg();
-      MachineInstr *IncomingPHIVal = MRI->getVRegDef(IncomingVal);
-      if (!IncomingPHIVal->isPHI()) continue;
-      BB = IncomingPHIVal->getParent();
-      BBInfo *Info = (*BBMap)[BB];
-      if (!Info || Info->AvailableVal)
-        continue;
-
-      // Record the PHI and add it to the worklist.
-      AvailableVals[BB] = IncomingVal;
-      Info->AvailableVal = IncomingVal;
-      WorkList.push_back(IncomingPHIVal);
-    }
-  }
+  if (unsigned V = AvailableVals[BB])
+    return V;
+
+  SSAUpdaterImpl<MachineSSAUpdater> Impl(this, &AvailableVals, InsertedPHIs);
+  return Impl.GetValue(BB);
 }
diff --git a/lib/Transforms/Utils/SSAUpdater.cpp b/lib/Transforms/Utils/SSAUpdater.cpp
index 25d50db..f4bdb52 100644
--- a/lib/Transforms/Utils/SSAUpdater.cpp
+++ b/lib/Transforms/Utils/SSAUpdater.cpp
@@ -12,7 +12,6 @@
 //===----------------------------------------------------------------------===//
 
 #define DEBUG_TYPE "ssaupdater"
-#include "llvm/Transforms/Utils/SSAUpdater.h"
 #include "llvm/Instructions.h"
 #include "llvm/ADT/DenseMap.h"
 #include "llvm/Support/AlignOf.h"
@@ -20,40 +19,17 @@
 #include "llvm/Support/CFG.h"
 #include "llvm/Support/Debug.h"
 #include "llvm/Support/raw_ostream.h"
+#include "llvm/Transforms/Utils/SSAUpdater.h"
+#include "llvm/Transforms/Utils/SSAUpdaterImpl.h"
 using namespace llvm;
 
-/// BBInfo - Per-basic block information used internally by SSAUpdater.
-/// The predecessors of each block are cached here since pred_iterator is
-/// slow and we need to iterate over the blocks at least a few times.
-class SSAUpdater::BBInfo {
-public:
-  BasicBlock *BB;      // Back-pointer to the corresponding block.
-  Value *AvailableVal; // Value to use in this block.
-  BBInfo *DefBB;       // Block that defines the available value.
-  int BlkNum;          // Postorder number.
-  BBInfo *IDom;        // Immediate dominator.
-  unsigned NumPreds;   // Number of predecessor blocks.
-  BBInfo **Preds;      // Array[NumPreds] of predecessor blocks.
-  PHINode *PHITag;     // Marker for existing PHIs that match.
-
-  BBInfo(BasicBlock *ThisBB, Value *V)
-    : BB(ThisBB), AvailableVal(V), DefBB(V ? this : 0), BlkNum(0), IDom(0),
-      NumPreds(0), Preds(0), PHITag(0) { }
-};
-
-typedef DenseMap<BasicBlock*, SSAUpdater::BBInfo*> BBMapTy;
-
 typedef DenseMap<BasicBlock*, Value*> AvailableValsTy;
 static AvailableValsTy &getAvailableVals(void *AV) {
   return *static_cast<AvailableValsTy*>(AV);
 }
 
-static BBMapTy *getBBMap(void *BM) {
-  return static_cast<BBMapTy*>(BM);
-}
-
 SSAUpdater::SSAUpdater(SmallVectorImpl<PHINode*> *NewPHI)
-  : AV(0), PrototypeValue(0), BM(0), InsertedPHIs(NewPHI) {}
+  : AV(0), PrototypeValue(0), InsertedPHIs(NewPHI) {}
 
 SSAUpdater::~SSAUpdater() {
   delete &getAvailableVals(AV);
@@ -105,9 +81,7 @@ static bool IsEquivalentPHI(PHINode *PHI,
 /// GetValueAtEndOfBlock - Construct SSA form, materializing a value that is
 /// live at the end of the specified block.
 Value *SSAUpdater::GetValueAtEndOfBlock(BasicBlock *BB) {
-  assert(BM == 0 && "Unexpected Internal State");
   Value *Res = GetValueAtEndOfBlockInternal(BB);
-  assert(BM == 0 && "Unexpected Internal State");
   return Res;
 }
 
@@ -231,427 +205,126 @@ void SSAUpdater::RewriteUse(Use &U) {
   U.set(V);
 }
 
-/// GetValueAtEndOfBlockInternal - Check to see if AvailableVals has an entry
-/// for the specified BB and if so, return it.  If not, construct SSA form by
-/// first calculating the required placement of PHIs and then inserting new
-/// PHIs where needed.
-Value *SSAUpdater::GetValueAtEndOfBlockInternal(BasicBlock *BB) {
-  AvailableValsTy &AvailableVals = getAvailableVals(AV);
-  if (Value *V = AvailableVals[BB])
-    return V;
-
-  // Pool allocation used internally by GetValueAtEndOfBlock.
-  BumpPtrAllocator Allocator;
-  BBMapTy BBMapObj;
-  BM = &BBMapObj;
-
-  SmallVector<BBInfo*, 100> BlockList;
-  BuildBlockList(BB, &BlockList, &Allocator);
-
-  // Special case: bail out if BB is unreachable.
-  if (BlockList.size() == 0) {
-    BM = 0;
-    return UndefValue::get(PrototypeValue->getType());
-  }
-
-  FindDominators(&BlockList);
-  FindPHIPlacement(&BlockList);
-  FindAvailableVals(&BlockList);
-
-  BM = 0;
-  return BBMapObj[BB]->DefBB->AvailableVal;
+/// PHIiter - Iterator for PHI operands.  This is used for the PHI_iterator
+/// in the SSAUpdaterImpl template.
+namespace {
+  class PHIiter {
+  private:
+    PHINode *PHI;
+    unsigned idx;
+
+  public:
+    explicit PHIiter(PHINode *P) // begin iterator
+      : PHI(P), idx(0) {}
+    PHIiter(PHINode *P, bool) // end iterator
+      : PHI(P), idx(PHI->getNumIncomingValues()) {}
+
+    PHIiter &operator++() { ++idx; return *this; } 
+    bool operator==(const PHIiter& x) const { return idx == x.idx; }
+    bool operator!=(const PHIiter& x) const { return !operator==(x); }
+    Value *getIncomingValue() { return PHI->getIncomingValue(idx); }
+    BasicBlock *getIncomingBlock() { return PHI->getIncomingBlock(idx); }
+  };
 }
 
-/// FindPredecessorBlocks - Put the predecessors of Info->BB into the Preds
-/// vector, set Info->NumPreds, and allocate space in Info->Preds.
-static void FindPredecessorBlocks(SSAUpdater::BBInfo *Info,
-                                  SmallVectorImpl<BasicBlock*> *Preds,
-                                  BumpPtrAllocator *Allocator) {
-  // We can get our predecessor info by walking the pred_iterator list,
-  // but it is relatively slow.  If we already have PHI nodes in this
-  // block, walk one of them to get the predecessor list instead.
-  BasicBlock *BB = Info->BB;
-  if (PHINode *SomePhi = dyn_cast<PHINode>(BB->begin())) {
-    for (unsigned PI = 0, E = SomePhi->getNumIncomingValues(); PI != E; ++PI)
-      Preds->push_back(SomePhi->getIncomingBlock(PI));
-  } else {
-    for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI)
-      Preds->push_back(*PI);
+/// SSAUpdaterTraits<SSAUpdater> - Traits for the SSAUpdaterImpl template,
+/// specialized for SSAUpdater.
+namespace llvm {
+template<>
+class SSAUpdaterTraits<SSAUpdater> {
+public:
+  typedef BasicBlock BlkT;
+  typedef Value *ValT;
+  typedef PHINode PhiT;
+
+  typedef succ_iterator BlkSucc_iterator;
+  static BlkSucc_iterator BlkSucc_begin(BlkT *BB) { return succ_begin(BB); }
+  static BlkSucc_iterator BlkSucc_end(BlkT *BB) { return succ_end(BB); }
+
+  typedef PHIiter PHI_iterator;
+  static inline PHI_iterator PHI_begin(PhiT *PHI) { return PHI_iterator(PHI); }
+  static inline PHI_iterator PHI_end(PhiT *PHI) {
+    return PHI_iterator(PHI, true);
   }
 
-  Info->NumPreds = Preds->size();
-  Info->Preds = static_cast<SSAUpdater::BBInfo**>
-    (Allocator->Allocate(Info->NumPreds * sizeof(SSAUpdater::BBInfo*),
-                         AlignOf<SSAUpdater::BBInfo*>::Alignment));
-}
-
-/// 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 list.
-void SSAUpdater::BuildBlockList(BasicBlock *BB, BlockListTy *BlockList,
-                                BumpPtrAllocator *Allocator) {
-  AvailableValsTy &AvailableVals = getAvailableVals(AV);
-  BBMapTy *BBMap = getBBMap(BM);
-  SmallVector<BBInfo*, 10> RootList;
-  SmallVector<BBInfo*, 64> WorkList;
-
-  BBInfo *Info = new (*Allocator) BBInfo(BB, 0);
-  (*BBMap)[BB] = Info;
-  WorkList.push_back(Info);
-
-  // Search backward from BB, creating BBInfos along the way and stopping when
-  // reaching blocks that define the value.  Record those defining blocks on
-  // the RootList.
-  SmallVector<BasicBlock*, 10> Preds;
-  while (!WorkList.empty()) {
-    Info = WorkList.pop_back_val();
-    Preds.clear();
-    FindPredecessorBlocks(Info, &Preds, Allocator);
-
-    // Treat an unreachable predecessor as a definition with 'undef'.
-    if (Info->NumPreds == 0) {
-      Info->AvailableVal = UndefValue::get(PrototypeValue->getType());
-      Info->DefBB = Info;
-      RootList.push_back(Info);
-      continue;
-    }
-
-    for (unsigned p = 0; p != Info->NumPreds; ++p) {
-      BasicBlock *Pred = Preds[p];
-      // Check if BBMap already has a BBInfo for the predecessor block.
-      BBMapTy::value_type &BBMapBucket = BBMap->FindAndConstruct(Pred);
-      if (BBMapBucket.second) {
-        Info->Preds[p] = BBMapBucket.second;
-        continue;
-      }
-
-      // Create a new BBInfo for the predecessor.
-      Value *PredVal = AvailableVals.lookup(Pred);
-      BBInfo *PredInfo = new (*Allocator) BBInfo(Pred, PredVal);
-      BBMapBucket.second = PredInfo;
-      Info->Preds[p] = PredInfo;
-
-      if (PredInfo->AvailableVal) {
-        RootList.push_back(PredInfo);
-        continue;
-      }
-      WorkList.push_back(PredInfo);
+  /// FindPredecessorBlocks - Put the predecessors of Info->BB into the Preds
+  /// vector, set Info->NumPreds, and allocate space in Info->Preds.
+  static void FindPredecessorBlocks(BasicBlock *BB,
+                                    SmallVectorImpl<BasicBlock*> *Preds) {
+    // We can get our predecessor info by walking the pred_iterator list,
+    // but it is relatively slow.  If we already have PHI nodes in this
+    // block, walk one of them to get the predecessor list instead.
+    if (PHINode *SomePhi = dyn_cast<PHINode>(BB->begin())) {
+      for (unsigned PI = 0, E = SomePhi->getNumIncomingValues(); PI != E; ++PI)
+        Preds->push_back(SomePhi->getIncomingBlock(PI));
+    } else {
+      for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI)
+        Preds->push_back(*PI);
     }
   }
 
-  // Now that we know what blocks are backwards-reachable from the starting
-  // block, do a forward depth-first traversal to assign postorder numbers
-  // to those blocks.
-  BBInfo *PseudoEntry = new (*Allocator) BBInfo(0, 0);
-  unsigned BlkNum = 1;
-
-  // Initialize the worklist with the roots from the backward traversal.
-  while (!RootList.empty()) {
-    Info = RootList.pop_back_val();
-    Info->IDom = PseudoEntry;
-    Info->BlkNum = -1;
-    WorkList.push_back(Info);
+  /// GetUndefVal - Get an undefined value of the same type as the value
+  /// being handled.
+  static Value *GetUndefVal(BasicBlock *BB, SSAUpdater *Updater) {
+    return UndefValue::get(Updater->PrototypeValue->getType());
   }
 
-  while (!WorkList.empty()) {
-    Info = WorkList.back();
-
-    if (Info->BlkNum == -2) {
-      // All the successors have been handled; assign the postorder number.
-      Info->BlkNum = BlkNum++;
-      // If not a root, put it on the BlockList.
-      if (!Info->AvailableVal)
-        BlockList->push_back(Info);
-      WorkList.pop_back();
-      continue;
-    }
-
-    // Leave this entry on the worklist, but set its BlkNum to mark that its
-    // successors have been put on the worklist.  When it returns to the top
-    // the list, after handling its successors, it will be assigned a number.
-    Info->BlkNum = -2;
-
-    // Add unvisited successors to the work list.
-    for (succ_iterator SI = succ_begin(Info->BB), E = succ_end(Info->BB);
-         SI != E; ++SI) {
-      BBInfo *SuccInfo = (*BBMap)[*SI];
-      if (!SuccInfo || SuccInfo->BlkNum)
-        continue;
-      SuccInfo->BlkNum = -1;
-      WorkList.push_back(SuccInfo);
-    }
+  /// CreateEmptyPHI - Create a new PHI instruction in the specified block.
+  /// Reserve space for the operands but do not fill them in yet.
+  static Value *CreateEmptyPHI(BasicBlock *BB, unsigned NumPreds,
+                               SSAUpdater *Updater) {
+    PHINode *PHI = PHINode::Create(Updater->PrototypeValue->getType(),
+                                   Updater->PrototypeValue->getName(),
+                                   &BB->front());
+    PHI->reserveOperandSpace(NumPreds);
+    return PHI;
   }
-  PseudoEntry->BlkNum = BlkNum;
-}
 
-/// IntersectDominators - This is the dataflow lattice "meet" operation for
-/// finding dominators.  Given two basic blocks, it walks up the dominator
-/// tree until it finds a common dominator of both.  It uses the postorder
-/// number of the blocks to determine how to do that.
-static SSAUpdater::BBInfo *IntersectDominators(SSAUpdater::BBInfo *Blk1,
-                                               SSAUpdater::BBInfo *Blk2) {
-  while (Blk1 != Blk2) {
-    while (Blk1->BlkNum < Blk2->BlkNum) {
-      Blk1 = Blk1->IDom;
-      if (!Blk1)
-        return Blk2;
-    }
-    while (Blk2->BlkNum < Blk1->BlkNum) {
-      Blk2 = Blk2->IDom;
-      if (!Blk2)
-        return Blk1;
-    }
+  /// AddPHIOperand - Add the specified value as an operand of the PHI for
+  /// the specified predecessor block.
+  static void AddPHIOperand(PHINode *PHI, Value *Val, BasicBlock *Pred) {
+    PHI->addIncoming(Val, Pred);
   }
-  return Blk1;
-}
 
-/// FindDominators - Calculate the dominator tree for the subset of the CFG
-/// corresponding to the basic blocks on the BlockList.  This uses the
-/// algorithm from: "A Simple, Fast Dominance Algorithm" by Cooper, Harvey and
-/// Kennedy, published in Software--Practice and Experience, 2001, 4:1-10.
-/// Because the CFG subset does not include any edges leading into blocks that
-/// define the value, the results are not the usual dominator tree.  The CFG
-/// subset has a single pseudo-entry node with edges to a set of root nodes
-/// for blocks that define the value.  The dominators for this subset CFG are
-/// not the standard dominators but they are adequate for placing PHIs within
-/// the subset CFG.
-void SSAUpdater::FindDominators(BlockListTy *BlockList) {
-  bool Changed;
-  do {
-    Changed = false;
-    // Iterate over the list in reverse order, i.e., forward on CFG edges.
-    for (BlockListTy::reverse_iterator I = BlockList->rbegin(),
-           E = BlockList->rend(); I != E; ++I) {
-      BBInfo *Info = *I;
-
-      // Start with the first predecessor.
-      assert(Info->NumPreds > 0 && "unreachable block");
-      BBInfo *NewIDom = Info->Preds[0];
-
-      // Iterate through the block's other predecessors.
-      for (unsigned p = 1; p != Info->NumPreds; ++p) {
-        BBInfo *Pred = Info->Preds[p];
-        NewIDom = IntersectDominators(NewIDom, Pred);
-      }
-
-      // Check if the IDom value has changed.
-      if (NewIDom != Info->IDom) {
-        Info->IDom = NewIDom;
-        Changed = true;
-      }
-    }
-  } while (Changed);
-}
-
-/// IsDefInDomFrontier - Search up the dominator tree from Pred to IDom for
-/// any blocks containing definitions of the value.  If one is found, then the
-/// successor of Pred is in the dominance frontier for the definition, and
-/// this function returns true.
-static bool IsDefInDomFrontier(const SSAUpdater::BBInfo *Pred,
-                               const SSAUpdater::BBInfo *IDom) {
-  for (; Pred != IDom; Pred = Pred->IDom) {
-    if (Pred->DefBB == Pred)
-      return true;
+  /// InstrIsPHI - Check if an instruction is a PHI.
+  ///
+  static PHINode *InstrIsPHI(Instruction *I) {
+    return dyn_cast<PHINode>(I);
   }
-  return false;
-}
-
-/// FindPHIPlacement - PHIs are needed in the iterated dominance frontiers of
-/// the known definitions.  Iteratively add PHIs in the dom frontiers until
-/// nothing changes.  Along the way, keep track of the nearest dominating
-/// definitions for non-PHI blocks.
-void SSAUpdater::FindPHIPlacement(BlockListTy *BlockList) {
-  bool Changed;
-  do {
-    Changed = false;
-    // Iterate over the list in reverse order, i.e., forward on CFG edges.
-    for (BlockListTy::reverse_iterator I = BlockList->rbegin(),
-           E = BlockList->rend(); I != E; ++I) {
-      BBInfo *Info = *I;
-
-      // If this block already needs a PHI, there is nothing to do here.
-      if (Info->DefBB == Info)
-        continue;
-
-      // Default to use the same def as the immediate dominator.
-      BBInfo *NewDefBB = Info->IDom->DefBB;
-      for (unsigned p = 0; p != Info->NumPreds; ++p) {
-        if (IsDefInDomFrontier(Info->Preds[p], Info->IDom)) {
-          // Need a PHI here.
-          NewDefBB = Info;
-          break;
-        }
-      }
-
-      // Check if anything changed.
-      if (NewDefBB != Info->DefBB) {
-        Info->DefBB = NewDefBB;
-        Changed = true;
-      }
-    }
-  } while (Changed);
-}
-
-/// FindAvailableVal - If this block requires a PHI, first check if an existing
-/// PHI matches the PHI placement and reaching definitions computed 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 SSAUpdater::FindAvailableVals(BlockListTy *BlockList) {
-  AvailableValsTy &AvailableVals = getAvailableVals(AV);
 
-  // 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.
-  for (BlockListTy::iterator I = BlockList->begin(), E = BlockList->end();
-       I != E; ++I) {
-    BBInfo *Info = *I;
-    // Check if there needs to be a PHI in BB.
-    if (Info->DefBB != Info)
-      continue;
-
-    // Look for an existing PHI.
-    FindExistingPHI(Info->BB, BlockList);
-    if (Info->AvailableVal)
-      continue;
-
-    PHINode *PHI = PHINode::Create(PrototypeValue->getType(),
-                                   PrototypeValue->getName(),
-                                   &Info->BB->front());
-    PHI->reserveOperandSpace(Info->NumPreds);
-    Info->AvailableVal = PHI;
-    AvailableVals[Info->BB] = PHI;
+  /// ValueIsPHI - Check if a value is a PHI.
+  ///
+  static PHINode *ValueIsPHI(Value *Val, SSAUpdater *Updater) {
+    return dyn_cast<PHINode>(Val);
   }
 
-  // Now go back through the worklist in reverse order to fill in the arguments
-  // for any new PHIs added in the forward traversal.
-  for (BlockListTy::reverse_iterator I = BlockList->rbegin(),
-         E = BlockList->rend(); I != E; ++I) {
-    BBInfo *Info = *I;
-
-    if (Info->DefBB != Info) {
-      // Record the available value at join nodes to speed up subsequent
-      // uses of this SSAUpdater for the same value.
-      if (Info->NumPreds > 1)
-        AvailableVals[Info->BB] = Info->DefBB->AvailableVal;
-      continue;
-    }
-
-    // Check if this block contains a newly added PHI.
-    PHINode *PHI = dyn_cast<PHINode>(Info->AvailableVal);
-    if (!PHI || PHI->getNumIncomingValues() == Info->NumPreds)
-      continue;
-
-    // Iterate through the block's predecessors.
-    for (unsigned p = 0; p != Info->NumPreds; ++p) {
-      BBInfo *PredInfo = Info->Preds[p];
-      BasicBlock *Pred = PredInfo->BB;
-      // Skip to the nearest preceding definition.
-      if (PredInfo->DefBB != PredInfo)
-        PredInfo = PredInfo->DefBB;
-      PHI->addIncoming(PredInfo->AvailableVal, Pred);
-    }
-
-    DEBUG(dbgs() << "  Inserted PHI: " << *PHI << "\n");
-
-    // If the client wants to know about all new instructions, tell it.
-    if (InsertedPHIs) InsertedPHIs->push_back(PHI);
+  /// ValueIsNewPHI - Like ValueIsPHI but also check if the PHI has no source
+  /// operands, i.e., it was just added.
+  static PHINode *ValueIsNewPHI(Value *Val, SSAUpdater *Updater) {
+    PHINode *PHI = ValueIsPHI(Val, Updater);
+    if (PHI && PHI->getNumIncomingValues() == 0)
+      return PHI;
+    return 0;
   }
-}
 
-/// FindExistingPHI - Look through the PHI nodes in a block to see if any of
-/// them match what is needed.
-void SSAUpdater::FindExistingPHI(BasicBlock *BB, BlockListTy *BlockList) {
-  PHINode *SomePHI;
-  for (BasicBlock::iterator It = BB->begin();
-       (SomePHI = dyn_cast<PHINode>(It)); ++It) {
-    if (CheckIfPHIMatches(SomePHI)) {
-      RecordMatchingPHI(SomePHI);
-      break;
-    }
-    // Match failed: clear all the PHITag values.
-    for (BlockListTy::iterator I = BlockList->begin(), E = BlockList->end();
-         I != E; ++I)
-      (*I)->PHITag = 0;
+  /// GetPHIValue - For the specified PHI instruction, return the value
+  /// that it defines.
+  static Value *GetPHIValue(PHINode *PHI) {
+    return PHI;
   }
-}
+};
 
-/// CheckIfPHIMatches - Check if a PHI node matches the placement and values
-/// in the BBMap.
-bool SSAUpdater::CheckIfPHIMatches(PHINode *PHI) {
-  BBMapTy *BBMap = getBBMap(BM);
-  SmallVector<PHINode*, 20> WorkList;
-  WorkList.push_back(PHI);
-
-  // Mark that the block containing this PHI has been visited.
-  (*BBMap)[PHI->getParent()]->PHITag = PHI;
-
-  while (!WorkList.empty()) {
-    PHI = WorkList.pop_back_val();
-
-    // Iterate through the PHI's incoming values.
-    for (unsigned i = 0, e = PHI->getNumIncomingValues(); i != e; ++i) {
-      Value *IncomingVal = PHI->getIncomingValue(i);
-      BBInfo *PredInfo = (*BBMap)[PHI->getIncomingBlock(i)];
-      // Skip to the nearest preceding definition.
-      if (PredInfo->DefBB != PredInfo)
-        PredInfo = PredInfo->DefBB;
-
-      // Check if it matches the expected value.
-      if (PredInfo->AvailableVal) {
-        if (IncomingVal == PredInfo->AvailableVal)
-          continue;
-        return false;
-      }
-
-      // Check if the value is a PHI in the correct block.
-      PHINode *IncomingPHIVal = dyn_cast<PHINode>(IncomingVal);
-      if (!IncomingPHIVal || IncomingPHIVal->getParent() != PredInfo->BB)
-        return false;
-
-      // If this block has already been visited, check if this PHI matches.
-      if (PredInfo->PHITag) {
-        if (IncomingPHIVal == PredInfo->PHITag)
-          continue;
-        return false;
-      }
-      PredInfo->PHITag = IncomingPHIVal;
-
-      WorkList.push_back(IncomingPHIVal);
-    }
-  }
-  return true;
-}
+} // End llvm namespace
 
-/// RecordMatchingPHI - For a PHI node that matches, record it and its input
-/// PHIs in both the BBMap and the AvailableVals mapping.
-void SSAUpdater::RecordMatchingPHI(PHINode *PHI) {
-  BBMapTy *BBMap = getBBMap(BM);
+/// GetValueAtEndOfBlockInternal - Check to see if AvailableVals has an entry
+/// for the specified BB and if so, return it.  If not, construct SSA form by
+/// first calculating the required placement of PHIs and then inserting new
+/// PHIs where needed.
+Value *SSAUpdater::GetValueAtEndOfBlockInternal(BasicBlock *BB) {
   AvailableValsTy &AvailableVals = getAvailableVals(AV);
-  SmallVector<PHINode*, 20> WorkList;
-  WorkList.push_back(PHI);
-
-  // Record this PHI.
-  BasicBlock *BB = PHI->getParent();
-  AvailableVals[BB] = PHI;
-  (*BBMap)[BB]->AvailableVal = PHI;
-
-  while (!WorkList.empty()) {
-    PHI = WorkList.pop_back_val();
-
-    // Iterate through the PHI's incoming values.
-    for (unsigned i = 0, e = PHI->getNumIncomingValues(); i != e; ++i) {
-      PHINode *IncomingPHIVal = dyn_cast<PHINode>(PHI->getIncomingValue(i));
-      if (!IncomingPHIVal) continue;
-      BB = IncomingPHIVal->getParent();
-      BBInfo *Info = (*BBMap)[BB];
-      if (!Info || Info->AvailableVal)
-        continue;
-
-      // Record the PHI and add it to the worklist.
-      AvailableVals[BB] = IncomingPHIVal;
-      Info->AvailableVal = IncomingPHIVal;
-      WorkList.push_back(IncomingPHIVal);
-    }
-  }
+  if (Value *V = AvailableVals[BB])
+    return V;
+
+  SSAUpdaterImpl<SSAUpdater> Impl(this, &AvailableVals, InsertedPHIs);
+  return Impl.GetValue(BB);
 }