4 files changed, 396 insertions, 480 deletions
diff --git a/lib/Transforms/IPO/Internalize.cpp b/lib/Transforms/IPO/Internalize.cpp
index 3d31932..47abb7d 100644
--- a/lib/Transforms/IPO/Internalize.cpp
+++ b/lib/Transforms/IPO/Internalize.cpp
@@ -156,6 +156,8 @@ bool InternalizePass::runOnModule(Module &M) {
   for (Module::global_iterator I = M.global_begin(), E = M.global_end();
        I != E; ++I)
     if (!I->isDeclaration() && !I->hasLocalLinkage() &&
+        // Available externally is really just a "declaration with a body".
+        !I->hasAvailableExternallyLinkage() &&
         !ExternalNames.count(I->getName())) {
       I->setLinkage(GlobalValue::InternalLinkage);
       Changed = true;
@@ -167,6 +169,8 @@ bool InternalizePass::runOnModule(Module &M) {
   for (Module::alias_iterator I = M.alias_begin(), E = M.alias_end();
        I != E; ++I)
     if (!I->isDeclaration() && !I->hasInternalLinkage() &&
+        // Available externally is really just a "declaration with a body".
+        !I->hasAvailableExternallyLinkage() &&
         !ExternalNames.count(I->getName())) {
       I->setLinkage(GlobalValue::InternalLinkage);
       Changed = true;
diff --git a/lib/Transforms/Scalar/IndVarSimplify.cpp b/lib/Transforms/Scalar/IndVarSimplify.cpp
index 988a4cb..6605666 100644
--- a/lib/Transforms/Scalar/IndVarSimplify.cpp
+++ b/lib/Transforms/Scalar/IndVarSimplify.cpp
@@ -510,6 +510,13 @@ void IndVarSimplify::RewriteIVExpressions(Loop *L, SCEVExpander &Rewriter) {
     // Now expand it into actual Instructions and patch it into place.
     Value *NewVal = Rewriter.expandCodeFor(AR, UseTy, InsertPt);
 
+    // Inform ScalarEvolution that this value is changing. The change doesn't
+    // affect its value, but it does potentially affect which use lists the
+    // value will be on after the replacement, which affects ScalarEvolution's
+    // ability to walk use lists and drop dangling pointers when a value is
+    // deleted.
+    SE->forgetValue(User);
+
     // Patch the new value into place.
     if (Op->hasName())
       NewVal->takeName(Op);
@@ -616,36 +623,18 @@ void IndVarSimplify::SinkUnusedInvariants(Loop *L) {
   }
 }
 
-/// Return true if it is OK to use SIToFPInst for an induction variable
-/// with given initial and exit values.
-static bool useSIToFPInst(ConstantFP &InitV, ConstantFP &ExitV,
-                          uint64_t intIV, uint64_t intEV) {
-
-  if (InitV.getValueAPF().isNegative() || ExitV.getValueAPF().isNegative())
-    return true;
-
-  // If the iteration range can be handled by SIToFPInst then use it.
-  APInt Max = APInt::getSignedMaxValue(32);
-  if (Max.getZExtValue() > static_cast<uint64_t>(abs64(intEV - intIV)))
-    return true;
-
-  return false;
-}
-
-/// convertToInt - Convert APF to an integer, if possible.
-static bool convertToInt(const APFloat &APF, uint64_t *intVal) {
-
+/// ConvertToSInt - Convert APF to an integer, if possible.
+static bool ConvertToSInt(const APFloat &APF, int64_t &IntVal) {
   bool isExact = false;
   if (&APF.getSemantics() == &APFloat::PPCDoubleDouble)
     return false;
-  if (APF.convertToInteger(intVal, 32, APF.isNegative(),
-                           APFloat::rmTowardZero, &isExact)
-      != APFloat::opOK)
-    return false;
-  if (!isExact)
+  // See if we can convert this to an int64_t
+  uint64_t UIntVal;
+  if (APF.convertToInteger(&UIntVal, 64, true, APFloat::rmTowardZero,
+                           &isExact) != APFloat::opOK || !isExact)
     return false;
+  IntVal = UIntVal;
   return true;
-
 }
 
 /// HandleFloatingPointIV - If the loop has floating induction variable
@@ -657,144 +646,200 @@ static bool convertToInt(const APFloat &APF, uint64_t *intVal) {
 /// for(int i = 0; i < 10000; ++i)
 ///   bar((double)i);
 ///
-void IndVarSimplify::HandleFloatingPointIV(Loop *L, PHINode *PH) {
-
-  unsigned IncomingEdge = L->contains(PH->getIncomingBlock(0));
+void IndVarSimplify::HandleFloatingPointIV(Loop *L, PHINode *PN) {
+  unsigned IncomingEdge = L->contains(PN->getIncomingBlock(0));
   unsigned BackEdge     = IncomingEdge^1;
 
   // Check incoming value.
-  ConstantFP *InitValue = dyn_cast<ConstantFP>(PH->getIncomingValue(IncomingEdge));
-  if (!InitValue) return;
-  uint64_t newInitValue =
-              Type::getInt32Ty(PH->getContext())->getPrimitiveSizeInBits();
-  if (!convertToInt(InitValue->getValueAPF(), &newInitValue))
+  ConstantFP *InitValueVal =
+    dyn_cast<ConstantFP>(PN->getIncomingValue(IncomingEdge));
+
+  int64_t InitValue;
+  if (!InitValueVal || !ConvertToSInt(InitValueVal->getValueAPF(), InitValue))
     return;
 
-  // Check IV increment. Reject this PH if increment operation is not
+  // Check IV increment. Reject this PN if increment operation is not
   // an add or increment value can not be represented by an integer.
   BinaryOperator *Incr =
-    dyn_cast<BinaryOperator>(PH->getIncomingValue(BackEdge));
-  if (!Incr) return;
-  if (Incr->getOpcode() != Instruction::FAdd) return;
-  ConstantFP *IncrValue = NULL;
-  unsigned IncrVIndex = 1;
-  if (Incr->getOperand(1) == PH)
-    IncrVIndex = 0;
-  IncrValue = dyn_cast<ConstantFP>(Incr->getOperand(IncrVIndex));
-  if (!IncrValue) return;
-  uint64_t newIncrValue =
-              Type::getInt32Ty(PH->getContext())->getPrimitiveSizeInBits();
-  if (!convertToInt(IncrValue->getValueAPF(), &newIncrValue))
+    dyn_cast<BinaryOperator>(PN->getIncomingValue(BackEdge));
+  if (Incr == 0 || Incr->getOpcode() != Instruction::FAdd) return;
+  
+  // If this is not an add of the PHI with a constantfp, or if the constant fp
+  // is not an integer, bail out.
+  ConstantFP *IncValueVal = dyn_cast<ConstantFP>(Incr->getOperand(1));
+  int64_t IncValue;
+  if (IncValueVal == 0 || Incr->getOperand(0) != PN ||
+      !ConvertToSInt(IncValueVal->getValueAPF(), IncValue))
     return;
 
-  // Check Incr uses. One user is PH and the other users is exit condition used
-  // by the conditional terminator.
+  // Check Incr uses. One user is PN and the other user is an exit condition
+  // used by the conditional terminator.
   Value::use_iterator IncrUse = Incr->use_begin();
   Instruction *U1 = cast<Instruction>(IncrUse++);
   if (IncrUse == Incr->use_end()) return;
   Instruction *U2 = cast<Instruction>(IncrUse++);
   if (IncrUse != Incr->use_end()) return;
 
-  // Find exit condition.
-  FCmpInst *EC = dyn_cast<FCmpInst>(U1);
-  if (!EC)
-    EC = dyn_cast<FCmpInst>(U2);
-  if (!EC) return;
-
-  if (BranchInst *BI = dyn_cast<BranchInst>(EC->getParent()->getTerminator())) {
-    if (!BI->isConditional()) return;
-    if (BI->getCondition() != EC) return;
-  }
-
-  // Find exit value. If exit value can not be represented as an integer then
-  // do not handle this floating point PH.
-  ConstantFP *EV = NULL;
-  unsigned EVIndex = 1;
-  if (EC->getOperand(1) == Incr)
-    EVIndex = 0;
-  EV = dyn_cast<ConstantFP>(EC->getOperand(EVIndex));
-  if (!EV) return;
-  uint64_t intEV = Type::getInt32Ty(PH->getContext())->getPrimitiveSizeInBits();
-  if (!convertToInt(EV->getValueAPF(), &intEV))
+  // Find exit condition, which is an fcmp.  If it doesn't exist, or if it isn't
+  // only used by a branch, we can't transform it.
+  FCmpInst *Compare = dyn_cast<FCmpInst>(U1);
+  if (!Compare)
+    Compare = dyn_cast<FCmpInst>(U2);
+  if (Compare == 0 || !Compare->hasOneUse() ||
+      !isa<BranchInst>(Compare->use_back()))
     return;
-
+  
+  BranchInst *TheBr = cast<BranchInst>(Compare->use_back());
+
+  // We need to verify that the branch actually controls the iteration count
+  // of the loop.  If not, the new IV can overflow and no one will notice.
+  // The branch block must be in the loop and one of the successors must be out
+  // of the loop.
+  assert(TheBr->isConditional() && "Can't use fcmp if not conditional");
+  if (!L->contains(TheBr->getParent()) ||
+      (L->contains(TheBr->getSuccessor(0)) &&
+       L->contains(TheBr->getSuccessor(1))))
+    return;
+  
+  
+  // If it isn't a comparison with an integer-as-fp (the exit value), we can't
+  // transform it.
+  ConstantFP *ExitValueVal = dyn_cast<ConstantFP>(Compare->getOperand(1));
+  int64_t ExitValue;
+  if (ExitValueVal == 0 ||
+      !ConvertToSInt(ExitValueVal->getValueAPF(), ExitValue))
+    return;
+  
   // Find new predicate for integer comparison.
   CmpInst::Predicate NewPred = CmpInst::BAD_ICMP_PREDICATE;
-  switch (EC->getPredicate()) {
+  switch (Compare->getPredicate()) {
+  default: return;  // Unknown comparison.
   case CmpInst::FCMP_OEQ:
-  case CmpInst::FCMP_UEQ:
-    NewPred = CmpInst::ICMP_EQ;
-    break;
+  case CmpInst::FCMP_UEQ: NewPred = CmpInst::ICMP_EQ; break;
+  case CmpInst::FCMP_ONE:
+  case CmpInst::FCMP_UNE: NewPred = CmpInst::ICMP_NE; break;
   case CmpInst::FCMP_OGT:
-  case CmpInst::FCMP_UGT:
-    NewPred = CmpInst::ICMP_UGT;
-    break;
+  case CmpInst::FCMP_UGT: NewPred = CmpInst::ICMP_SGT; break;
   case CmpInst::FCMP_OGE:
-  case CmpInst::FCMP_UGE:
-    NewPred = CmpInst::ICMP_UGE;
-    break;
+  case CmpInst::FCMP_UGE: NewPred = CmpInst::ICMP_SGE; break;
   case CmpInst::FCMP_OLT:
-  case CmpInst::FCMP_ULT:
-    NewPred = CmpInst::ICMP_ULT;
-    break;
+  case CmpInst::FCMP_ULT: NewPred = CmpInst::ICMP_SLT; break;
   case CmpInst::FCMP_OLE:
-  case CmpInst::FCMP_ULE:
-    NewPred = CmpInst::ICMP_ULE;
-    break;
-  default:
-    break;
+  case CmpInst::FCMP_ULE: NewPred = CmpInst::ICMP_SLE; break;
   }
-  if (NewPred == CmpInst::BAD_ICMP_PREDICATE) return;
+  
+  // We convert the floating point induction variable to a signed i32 value if
+  // we can.  This is only safe if the comparison will not overflow in a way
+  // that won't be trapped by the integer equivalent operations.  Check for this
+  // now.
+  // TODO: We could use i64 if it is native and the range requires it.
+  
+  // The start/stride/exit values must all fit in signed i32.
+  if (!isInt<32>(InitValue) || !isInt<32>(IncValue) || !isInt<32>(ExitValue))
+    return;
+
+  // If not actually striding (add x, 0.0), avoid touching the code.
+  if (IncValue == 0)
+    return;
+
+  // Positive and negative strides have different safety conditions.
+  if (IncValue > 0) {
+    // If we have a positive stride, we require the init to be less than the
+    // exit value and an equality or less than comparison.
+    if (InitValue >= ExitValue ||
+        NewPred == CmpInst::ICMP_SGT || NewPred == CmpInst::ICMP_SGE)
+      return;
+    
+    uint32_t Range = uint32_t(ExitValue-InitValue);
+    if (NewPred == CmpInst::ICMP_SLE) {
+      // Normalize SLE -> SLT, check for infinite loop.
+      if (++Range == 0) return;  // Range overflows.
+    }
+    
+    unsigned Leftover = Range % uint32_t(IncValue);
+    
+    // If this is an equality comparison, we require that the strided value
+    // exactly land on the exit value, otherwise the IV condition will wrap
+    // around and do things the fp IV wouldn't.
+    if ((NewPred == CmpInst::ICMP_EQ || NewPred == CmpInst::ICMP_NE) &&
+        Leftover != 0)
+      return;
+    
+    // If the stride would wrap around the i32 before exiting, we can't
+    // transform the IV.
+    if (Leftover != 0 && int32_t(ExitValue+IncValue) < ExitValue)
+      return;
+    
+  } else {
+    // If we have a negative stride, we require the init to be greater than the
+    // exit value and an equality or greater than comparison.
+    if (InitValue >= ExitValue ||
+        NewPred == CmpInst::ICMP_SLT || NewPred == CmpInst::ICMP_SLE)
+      return;
+    
+    uint32_t Range = uint32_t(InitValue-ExitValue);
+    if (NewPred == CmpInst::ICMP_SGE) {
+      // Normalize SGE -> SGT, check for infinite loop.
+      if (++Range == 0) return;  // Range overflows.
+    }
+    
+    unsigned Leftover = Range % uint32_t(-IncValue);
+    
+    // If this is an equality comparison, we require that the strided value
+    // exactly land on the exit value, otherwise the IV condition will wrap
+    // around and do things the fp IV wouldn't.
+    if ((NewPred == CmpInst::ICMP_EQ || NewPred == CmpInst::ICMP_NE) &&
+        Leftover != 0)
+      return;
+    
+    // If the stride would wrap around the i32 before exiting, we can't
+    // transform the IV.
+    if (Leftover != 0 && int32_t(ExitValue+IncValue) > ExitValue)
+      return;
+  }
+  
+  const IntegerType *Int32Ty = Type::getInt32Ty(PN->getContext());
 
   // Insert new integer induction variable.
-  PHINode *NewPHI = PHINode::Create(Type::getInt32Ty(PH->getContext()),
-                                    PH->getName()+".int", PH);
-  NewPHI->addIncoming(ConstantInt::get(Type::getInt32Ty(PH->getContext()),
-                                       newInitValue),
-                      PH->getIncomingBlock(IncomingEdge));
-
-  Value *NewAdd = BinaryOperator::CreateAdd(NewPHI,
-                           ConstantInt::get(Type::getInt32Ty(PH->getContext()),
-                                                             newIncrValue),
-                                            Incr->getName()+".int", Incr);
-  NewPHI->addIncoming(NewAdd, PH->getIncomingBlock(BackEdge));
-
-  // The back edge is edge 1 of newPHI, whatever it may have been in the
-  // original PHI.
-  ConstantInt *NewEV = ConstantInt::get(Type::getInt32Ty(PH->getContext()),
-                                        intEV);
-  Value *LHS = (EVIndex == 1 ? NewPHI->getIncomingValue(1) : NewEV);
-  Value *RHS = (EVIndex == 1 ? NewEV : NewPHI->getIncomingValue(1));
-  ICmpInst *NewEC = new ICmpInst(EC->getParent()->getTerminator(),
-                                 NewPred, LHS, RHS, EC->getName());
-
-  // In the following deletions, PH may become dead and may be deleted.
+  PHINode *NewPHI = PHINode::Create(Int32Ty, PN->getName()+".int", PN);
+  NewPHI->addIncoming(ConstantInt::get(Int32Ty, InitValue),
+                      PN->getIncomingBlock(IncomingEdge));
+
+  Value *NewAdd =
+    BinaryOperator::CreateAdd(NewPHI, ConstantInt::get(Int32Ty, IncValue),
+                              Incr->getName()+".int", Incr);
+  NewPHI->addIncoming(NewAdd, PN->getIncomingBlock(BackEdge));
+
+  ICmpInst *NewCompare = new ICmpInst(TheBr, NewPred, NewAdd,
+                                      ConstantInt::get(Int32Ty, ExitValue),
+                                      Compare->getName());
+
+  // In the following deletions, PN may become dead and may be deleted.
   // Use a WeakVH to observe whether this happens.
-  WeakVH WeakPH = PH;
+  WeakVH WeakPH = PN;
 
-  // Delete old, floating point, exit comparison instruction.
-  NewEC->takeName(EC);
-  EC->replaceAllUsesWith(NewEC);
-  RecursivelyDeleteTriviallyDeadInstructions(EC);
+  // Delete the old floating point exit comparison.  The branch starts using the
+  // new comparison.
+  NewCompare->takeName(Compare);
+  Compare->replaceAllUsesWith(NewCompare);
+  RecursivelyDeleteTriviallyDeadInstructions(Compare);
 
-  // Delete old, floating point, increment instruction.
+  // Delete the old floating point increment.
   Incr->replaceAllUsesWith(UndefValue::get(Incr->getType()));
   RecursivelyDeleteTriviallyDeadInstructions(Incr);
 
-  // Replace floating induction variable, if it isn't already deleted.
-  // Give SIToFPInst preference over UIToFPInst because it is faster on
-  // platforms that are widely used.
-  if (WeakPH && !PH->use_empty()) {
-    if (useSIToFPInst(*InitValue, *EV, newInitValue, intEV)) {
-      SIToFPInst *Conv = new SIToFPInst(NewPHI, PH->getType(), "indvar.conv",
-                                        PH->getParent()->getFirstNonPHI());
-      PH->replaceAllUsesWith(Conv);
-    } else {
-      UIToFPInst *Conv = new UIToFPInst(NewPHI, PH->getType(), "indvar.conv",
-                                        PH->getParent()->getFirstNonPHI());
-      PH->replaceAllUsesWith(Conv);
-    }
-    RecursivelyDeleteTriviallyDeadInstructions(PH);
+  // If the FP induction variable still has uses, this is because something else
+  // in the loop uses its value.  In order to canonicalize the induction
+  // variable, we chose to eliminate the IV and rewrite it in terms of an
+  // int->fp cast.
+  //
+  // We give preference to sitofp over uitofp because it is faster on most
+  // platforms.
+  if (WeakPH) {
+    Value *Conv = new SIToFPInst(NewPHI, PN->getType(), "indvar.conv",
+                                 PN->getParent()->getFirstNonPHI());
+    PN->replaceAllUsesWith(Conv);
+    RecursivelyDeleteTriviallyDeadInstructions(PN);
   }
 
   // Add a new IVUsers entry for the newly-created integer PHI.
diff --git a/lib/Transforms/Scalar/LoopUnswitch.cpp b/lib/Transforms/Scalar/LoopUnswitch.cpp
index e3b809e..27fd2ef 100644
--- a/lib/Transforms/Scalar/LoopUnswitch.cpp
+++ b/lib/Transforms/Scalar/LoopUnswitch.cpp
@@ -415,46 +415,44 @@ bool LoopUnswitch::UnswitchIfProfitable(Value *LoopCond, Constant *Val) {
 
   Function *F = loopHeader->getParent();
 
-  // If the condition is trivial, always unswitch.  There is no code growth for
-  // this case.
-  if (!IsTrivialUnswitchCondition(LoopCond)) {
-    // Check to see if it would be profitable to unswitch current loop.
+  Constant *CondVal = 0;
+  BasicBlock *ExitBlock = 0;
+  if (IsTrivialUnswitchCondition(LoopCond, &CondVal, &ExitBlock)) {
+    // If the condition is trivial, always unswitch. There is no code growth
+    // for this case.
+    UnswitchTrivialCondition(currentLoop, LoopCond, CondVal, ExitBlock);
+    return true;
+  }
 
-    // Do not do non-trivial unswitch while optimizing for size.
-    if (OptimizeForSize || F->hasFnAttr(Attribute::OptimizeForSize))
-      return false;
+  // Check to see if it would be profitable to unswitch current loop.
 
-    // FIXME: This is overly conservative because it does not take into
-    // consideration code simplification opportunities and code that can
-    // be shared by the resultant unswitched loops.
-    CodeMetrics Metrics;
-    for (Loop::block_iterator I = currentLoop->block_begin(), 
-           E = currentLoop->block_end();
-         I != E; ++I)
-      Metrics.analyzeBasicBlock(*I);
-
-    // Limit the number of instructions to avoid causing significant code
-    // expansion, and the number of basic blocks, to avoid loops with
-    // large numbers of branches which cause loop unswitching to go crazy.
-    // This is a very ad-hoc heuristic.
-    if (Metrics.NumInsts > Threshold ||
-        Metrics.NumBlocks * 5 > Threshold ||
-        Metrics.NeverInline) {
-      DEBUG(dbgs() << "NOT unswitching loop %"
-            << currentLoop->getHeader()->getName() << ", cost too high: "
-            << currentLoop->getBlocks().size() << "\n");
-      return false;
-    }
-  }
+  // Do not do non-trivial unswitch while optimizing for size.
+  if (OptimizeForSize || F->hasFnAttr(Attribute::OptimizeForSize))
+    return false;
 
-  Constant *CondVal;
-  BasicBlock *ExitBlock;
-  if (IsTrivialUnswitchCondition(LoopCond, &CondVal, &ExitBlock)) {
-    UnswitchTrivialCondition(currentLoop, LoopCond, CondVal, ExitBlock);
-  } else {
-    UnswitchNontrivialCondition(LoopCond, Val, currentLoop);
+  // FIXME: This is overly conservative because it does not take into
+  // consideration code simplification opportunities and code that can
+  // be shared by the resultant unswitched loops.
+  CodeMetrics Metrics;
+  for (Loop::block_iterator I = currentLoop->block_begin(), 
+         E = currentLoop->block_end();
+       I != E; ++I)
+    Metrics.analyzeBasicBlock(*I);
+
+  // Limit the number of instructions to avoid causing significant code
+  // expansion, and the number of basic blocks, to avoid loops with
+  // large numbers of branches which cause loop unswitching to go crazy.
+  // This is a very ad-hoc heuristic.
+  if (Metrics.NumInsts > Threshold ||
+      Metrics.NumBlocks * 5 > Threshold ||
+      Metrics.NeverInline) {
+    DEBUG(dbgs() << "NOT unswitching loop %"
+          << currentLoop->getHeader()->getName() << ", cost too high: "
+          << currentLoop->getBlocks().size() << "\n");
+    return false;
   }
 
+  UnswitchNontrivialCondition(LoopCond, Val, currentLoop);
   return true;
 }
 
diff --git a/lib/Transforms/Utils/SSAUpdater.cpp b/lib/Transforms/Utils/SSAUpdater.cpp
index 292332e..a31235a 100644
--- a/lib/Transforms/Utils/SSAUpdater.cpp
+++ b/lib/Transforms/Utils/SSAUpdater.cpp
@@ -14,82 +14,31 @@
 #include "llvm/Transforms/Utils/SSAUpdater.h"
 #include "llvm/Instructions.h"
 #include "llvm/ADT/DenseMap.h"
-#include "llvm/Support/AlignOf.h"
-#include "llvm/Support/Allocator.h"
 #include "llvm/Support/CFG.h"
 #include "llvm/Support/Debug.h"
+#include "llvm/Support/ValueHandle.h"
 #include "llvm/Support/raw_ostream.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:
-  Value *AvailableVal; // Value to use in this block.
-  BasicBlock *DefBB;   // Block that defines the available value.
-  unsigned NumPreds;   // Number of predecessor blocks.
-  BasicBlock **Preds;  // Array[NumPreds] of predecessor blocks.
-  unsigned Counter;    // Marker to identify blocks already visited.
-  PHINode *PHITag;     // Marker for existing PHIs that match.
-
-  BBInfo(BasicBlock *BB, Value *V, BumpPtrAllocator *Allocator);
-};
-typedef DenseMap<BasicBlock*, SSAUpdater::BBInfo*> BBMapTy;
-
-SSAUpdater::BBInfo::BBInfo(BasicBlock *BB, Value *V,
-                           BumpPtrAllocator *Allocator)
-  : AvailableVal(V), DefBB(0), NumPreds(0), Preds(0), Counter(0), PHITag(0) {
-  // If this block has a known value, don't bother finding its predecessors.
-  if (V) {
-    DefBB = BB;
-    return;
-  }
-
-  // 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())) {
-    NumPreds = SomePhi->getNumIncomingValues();
-    Preds = static_cast<BasicBlock**>
-      (Allocator->Allocate(NumPreds * sizeof(BasicBlock*),
-                           AlignOf<BasicBlock*>::Alignment));
-    for (unsigned pi = 0; pi != NumPreds; ++pi)
-      Preds[pi] = SomePhi->getIncomingBlock(pi);
-    return;
-  }
-
-  // Stash the predecessors in a temporary vector until we know how much space
-  // to allocate for them.
-  SmallVector<BasicBlock*, 10> TmpPreds;
-  for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
-    TmpPreds.push_back(*PI);
-    ++NumPreds;
-  }
-  Preds = static_cast<BasicBlock**>
-    (Allocator->Allocate(NumPreds * sizeof(BasicBlock*),
-                         AlignOf<BasicBlock*>::Alignment));
-  memcpy(Preds, TmpPreds.data(), NumPreds * sizeof(BasicBlock*));
-}
+typedef DenseMap<BasicBlock*, TrackingVH<Value> > AvailableValsTy;
+typedef std::vector<std::pair<BasicBlock*, TrackingVH<Value> > >
+                IncomingPredInfoTy;
 
-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);
+static IncomingPredInfoTy &getIncomingPredInfo(void *IPI) {
+  return *static_cast<IncomingPredInfoTy*>(IPI);
 }
 
-static BumpPtrAllocator *getAllocator(void *BPA) {
-  return static_cast<BumpPtrAllocator*>(BPA);
-}
 
 SSAUpdater::SSAUpdater(SmallVectorImpl<PHINode*> *NewPHI)
-  : AV(0), PrototypeValue(0), BM(0), BPA(0), InsertedPHIs(NewPHI) {}
+  : AV(0), PrototypeValue(0), IPI(0), InsertedPHIs(NewPHI) {}
 
 SSAUpdater::~SSAUpdater() {
   delete &getAvailableVals(AV);
+  delete &getIncomingPredInfo(IPI);
 }
 
 /// Initialize - Reset this object to get ready for a new set of SSA
@@ -99,6 +48,11 @@ void SSAUpdater::Initialize(Value *ProtoValue) {
     AV = new AvailableValsTy();
   else
     getAvailableVals(AV).clear();
+
+  if (IPI == 0)
+    IPI = new IncomingPredInfoTy();
+  else
+    getIncomingPredInfo(IPI).clear();
   PrototypeValue = ProtoValue;
 }
 
@@ -119,7 +73,7 @@ void SSAUpdater::AddAvailableValue(BasicBlock *BB, Value *V) {
 
 /// IsEquivalentPHI - Check if PHI has the same incoming value as specified
 /// in ValueMapping for each predecessor block.
-static bool IsEquivalentPHI(PHINode *PHI,
+static bool IsEquivalentPHI(PHINode *PHI, 
                             DenseMap<BasicBlock*, Value*> &ValueMapping) {
   unsigned PHINumValues = PHI->getNumIncomingValues();
   if (PHINumValues != ValueMapping.size())
@@ -135,12 +89,38 @@ static bool IsEquivalentPHI(PHINode *PHI,
   return true;
 }
 
+/// GetExistingPHI - Check if BB already contains a phi node that is equivalent
+/// to the specified mapping from predecessor blocks to incoming values.
+static Value *GetExistingPHI(BasicBlock *BB,
+                             DenseMap<BasicBlock*, Value*> &ValueMapping) {
+  PHINode *SomePHI;
+  for (BasicBlock::iterator It = BB->begin();
+       (SomePHI = dyn_cast<PHINode>(It)); ++It) {
+    if (IsEquivalentPHI(SomePHI, ValueMapping))
+      return SomePHI;
+  }
+  return 0;
+}
+
+/// GetExistingPHI - Check if BB already contains an equivalent phi node.
+/// The InputIt type must be an iterator over std::pair<BasicBlock*, Value*>
+/// objects that specify the mapping from predecessor blocks to incoming values.
+template<typename InputIt>
+static Value *GetExistingPHI(BasicBlock *BB, const InputIt &I,
+                             const InputIt &E) {
+  // Avoid create the mapping if BB has no phi nodes at all.
+  if (!isa<PHINode>(BB->begin()))
+    return 0;
+  DenseMap<BasicBlock*, Value*> ValueMapping(I, E);
+  return GetExistingPHI(BB, ValueMapping);
+}
+
 /// 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 && BPA == 0 && "Unexpected Internal State");
+  assert(getIncomingPredInfo(IPI).empty() && "Unexpected Internal State");
   Value *Res = GetValueAtEndOfBlockInternal(BB);
-  assert(BM == 0 && BPA == 0 && "Unexpected Internal State");
+  assert(getIncomingPredInfo(IPI).empty() && "Unexpected Internal State");
   return Res;
 }
 
@@ -166,7 +146,7 @@ Value *SSAUpdater::GetValueAtEndOfBlock(BasicBlock *BB) {
 Value *SSAUpdater::GetValueInMiddleOfBlock(BasicBlock *BB) {
   // If there is no definition of the renamed variable in this block, just use
   // GetValueAtEndOfBlock to do our work.
-  if (!HasValueForBlock(BB))
+  if (!getAvailableVals(AV).count(BB))
     return GetValueAtEndOfBlock(BB);
 
   // Otherwise, we have the hard case.  Get the live-in values for each
@@ -213,18 +193,10 @@ Value *SSAUpdater::GetValueInMiddleOfBlock(BasicBlock *BB) {
   if (SingularValue != 0)
     return SingularValue;
 
-  // Otherwise, we do need a PHI: check to see if we already have one available
-  // in this block that produces the right value.
-  if (isa<PHINode>(BB->begin())) {
-    DenseMap<BasicBlock*, Value*> ValueMapping(PredValues.begin(),
-                                               PredValues.end());
-    PHINode *SomePHI;
-    for (BasicBlock::iterator It = BB->begin();
-         (SomePHI = dyn_cast<PHINode>(It)); ++It) {
-      if (IsEquivalentPHI(SomePHI, ValueMapping))
-        return SomePHI;
-    }
-  }
+  // Otherwise, we do need a PHI.
+  if (Value *ExistingPHI = GetExistingPHI(BB, PredValues.begin(),
+                                          PredValues.end()))
+    return ExistingPHI;
 
   // Ok, we have no way out, insert a new one now.
   PHINode *InsertedPHI = PHINode::Create(PrototypeValue->getType(),
@@ -254,7 +226,7 @@ Value *SSAUpdater::GetValueInMiddleOfBlock(BasicBlock *BB) {
 /// which use their value in the corresponding predecessor.
 void SSAUpdater::RewriteUse(Use &U) {
   Instruction *User = cast<Instruction>(U.getUser());
-
+  
   Value *V;
   if (PHINode *UserPN = dyn_cast<PHINode>(User))
     V = GetValueAtEndOfBlock(UserPN->getIncomingBlock(U));
@@ -264,264 +236,161 @@ 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.
+/// walking predecessors inserting PHI nodes as needed until we get to a block
+/// where the value is available.
+///
 Value *SSAUpdater::GetValueAtEndOfBlockInternal(BasicBlock *BB) {
   AvailableValsTy &AvailableVals = getAvailableVals(AV);
-  if (Value *V = AvailableVals[BB])
-    return V;
-
-  // Pool allocation used internally by GetValueAtEndOfBlock.
-  BumpPtrAllocator AllocatorObj;
-  BBMapTy BBMapObj;
-  BPA = &AllocatorObj;
-  BM = &BBMapObj;
-
-  BBInfo *Info = new (AllocatorObj) BBInfo(BB, 0, &AllocatorObj);
-  BBMapObj[BB] = Info;
-
-  bool Changed;
-  unsigned Counter = 1;
-  do {
-    Changed = false;
-    FindPHIPlacement(BB, Info, Changed, Counter);
-    ++Counter;
-  } while (Changed);
-
-  FindAvailableVal(BB, Info, Counter);
-
-  BPA = 0;
-  BM = 0;
-  return Info->AvailableVal;
-}
 
-/// FindPHIPlacement - Recursively visit the predecessors of a block to find
-/// the reaching definition for each predecessor and then determine whether
-/// a PHI is needed in this block.
-void SSAUpdater::FindPHIPlacement(BasicBlock *BB, BBInfo *Info, bool &Changed,
-                                  unsigned Counter) {
-  AvailableValsTy &AvailableVals = getAvailableVals(AV);
-  BBMapTy *BBMap = getBBMap(BM);
-  BumpPtrAllocator *Allocator = getAllocator(BPA);
-  bool BBNeedsPHI = false;
-  BasicBlock *SamePredDefBB = 0;
-
-  // If there are no predecessors, then we must have found an unreachable
-  // block.  Treat it as a definition with 'undef'.
-  if (Info->NumPreds == 0) {
-    Info->AvailableVal = UndefValue::get(PrototypeValue->getType());
-    Info->DefBB = BB;
-    return;
+  // Query AvailableVals by doing an insertion of null.
+  std::pair<AvailableValsTy::iterator, bool> InsertRes =
+    AvailableVals.insert(std::make_pair(BB, TrackingVH<Value>()));
+
+  // Handle the case when the insertion fails because we have already seen BB.
+  if (!InsertRes.second) {
+    // If the insertion failed, there are two cases.  The first case is that the
+    // value is already available for the specified block.  If we get this, just
+    // return the value.
+    if (InsertRes.first->second != 0)
+      return InsertRes.first->second;
+
+    // Otherwise, if the value we find is null, then this is the value is not
+    // known but it is being computed elsewhere in our recursion.  This means
+    // that we have a cycle.  Handle this by inserting a PHI node and returning
+    // it.  When we get back to the first instance of the recursion we will fill
+    // in the PHI node.
+    return InsertRes.first->second =
+      PHINode::Create(PrototypeValue->getType(), PrototypeValue->getName(),
+                      &BB->front());
   }
 
-  Info->Counter = Counter;
-  for (unsigned pi = 0; pi != Info->NumPreds; ++pi) {
-    BasicBlock *Pred = Info->Preds[pi];
-    BBMapTy::value_type &BBMapBucket = BBMap->FindAndConstruct(Pred);
-    if (!BBMapBucket.second) {
-      Value *PredVal = AvailableVals.lookup(Pred);
-      BBMapBucket.second = new (*Allocator) BBInfo(Pred, PredVal, Allocator);
-    }
-    BBInfo *PredInfo = BBMapBucket.second;
-    BasicBlock *DefBB = 0;
-    if (!PredInfo->AvailableVal) {
-      if (PredInfo->Counter != Counter)
-        FindPHIPlacement(Pred, PredInfo, Changed, Counter);
-
-      // Ignore back edges where the value is not yet known.
-      if (!PredInfo->DefBB)
-        continue;
+  // Okay, the value isn't in the map and we just inserted a null in the entry
+  // to indicate that we're processing the block.  Since we have no idea what
+  // value is in this block, we have to recurse through our predecessors.
+  //
+  // While we're walking our predecessors, we keep track of them in a vector,
+  // then insert a PHI node in the end if we actually need one.  We could use a
+  // smallvector here, but that would take a lot of stack space for every level
+  // of the recursion, just use IncomingPredInfo as an explicit stack.
+  IncomingPredInfoTy &IncomingPredInfo = getIncomingPredInfo(IPI);
+  unsigned FirstPredInfoEntry = IncomingPredInfo.size();
+
+  // As we're walking the predecessors, keep track of whether they are all
+  // producing the same value.  If so, this value will capture it, if not, it
+  // will get reset to null.  We distinguish the no-predecessor case explicitly
+  // below.
+  TrackingVH<Value> ExistingValue;
+
+  // 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 i = 0, e = SomePhi->getNumIncomingValues(); i != e; ++i) {
+      BasicBlock *PredBB = SomePhi->getIncomingBlock(i);
+      Value *PredVal = GetValueAtEndOfBlockInternal(PredBB);
+      IncomingPredInfo.push_back(std::make_pair(PredBB, PredVal));
+
+      // Set ExistingValue to singular value from all predecessors so far.
+      if (i == 0)
+        ExistingValue = PredVal;
+      else if (PredVal != ExistingValue)
+        ExistingValue = 0;
     }
-    DefBB = PredInfo->DefBB;
+  } else {
+    bool isFirstPred = true;
+    for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
+      BasicBlock *PredBB = *PI;
+      Value *PredVal = GetValueAtEndOfBlockInternal(PredBB);
+      IncomingPredInfo.push_back(std::make_pair(PredBB, PredVal));
 
-    if (!SamePredDefBB)
-      SamePredDefBB = DefBB;
-    else if (DefBB != SamePredDefBB)
-      BBNeedsPHI = true;
+      // Set ExistingValue to singular value from all predecessors so far.
+      if (isFirstPred) {
+        ExistingValue = PredVal;
+        isFirstPred = false;
+      } else if (PredVal != ExistingValue)
+        ExistingValue = 0;
+    }
   }
 
-  BasicBlock *NewDefBB = (BBNeedsPHI ? BB : SamePredDefBB);
-  if (Info->DefBB != NewDefBB) {
-    Changed = true;
-    Info->DefBB = NewDefBB;
-  }
-}
+  // If there are no predecessors, then we must have found an unreachable block
+  // just return 'undef'.  Since there are no predecessors, InsertRes must not
+  // be invalidated.
+  if (IncomingPredInfo.size() == FirstPredInfoEntry)
+    return InsertRes.first->second = UndefValue::get(PrototypeValue->getType());
+
+  /// Look up BB's entry in AvailableVals.  'InsertRes' may be invalidated.  If
+  /// this block is involved in a loop, a no-entry PHI node will have been
+  /// inserted as InsertedVal.  Otherwise, we'll still have the null we inserted
+  /// above.
+  TrackingVH<Value> &InsertedVal = AvailableVals[BB];
+
+  // If the predecessor values are not all the same, then check to see if there
+  // is an existing PHI that can be used.
+  if (!ExistingValue)
+    ExistingValue = GetExistingPHI(BB,
+                                   IncomingPredInfo.begin()+FirstPredInfoEntry,
+                                   IncomingPredInfo.end());
+
+  // If there is an existing value we can use, then we don't need to insert a
+  // PHI.  This is the simple and common case.
+  if (ExistingValue) {
+    // If a PHI node got inserted, replace it with the existing value and delete
+    // it.
+    if (InsertedVal) {
+      PHINode *OldVal = cast<PHINode>(InsertedVal);
+      // Be careful about dead loops.  These RAUW's also update InsertedVal.
+      if (InsertedVal != ExistingValue)
+        OldVal->replaceAllUsesWith(ExistingValue);
+      else
+        OldVal->replaceAllUsesWith(UndefValue::get(InsertedVal->getType()));
+      OldVal->eraseFromParent();
+    } else {
+      InsertedVal = ExistingValue;
+    }
 
-/// 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::FindAvailableVal(BasicBlock *BB, BBInfo *Info,
-                                  unsigned Counter) {
-  if (Info->AvailableVal || Info->Counter == Counter)
-    return;
+    // Either path through the 'if' should have set InsertedVal -> ExistingVal.
+    assert((InsertedVal == ExistingValue || isa<UndefValue>(InsertedVal)) &&
+           "RAUW didn't change InsertedVal to be ExistingValue");
 
-  AvailableValsTy &AvailableVals = getAvailableVals(AV);
-  BBMapTy *BBMap = getBBMap(BM);
-
-  // Check if there needs to be a PHI in BB.
-  PHINode *NewPHI = 0;
-  if (Info->DefBB == BB) {
-    // Look for an existing PHI.
-    FindExistingPHI(BB);
-    if (!Info->AvailableVal) {
-      NewPHI = PHINode::Create(PrototypeValue->getType(),
-                               PrototypeValue->getName(), &BB->front());
-      NewPHI->reserveOperandSpace(Info->NumPreds);
-      Info->AvailableVal = NewPHI;
-      AvailableVals[BB] = NewPHI;
-    }
+    // Drop the entries we added in IncomingPredInfo to restore the stack.
+    IncomingPredInfo.erase(IncomingPredInfo.begin()+FirstPredInfoEntry,
+                           IncomingPredInfo.end());
+    return ExistingValue;
   }
 
-  // Iterate through the block's predecessors.
-  Info->Counter = Counter;
-  for (unsigned pi = 0; pi != Info->NumPreds; ++pi) {
-    BasicBlock *Pred = Info->Preds[pi];
-    BBInfo *PredInfo = (*BBMap)[Pred];
-    FindAvailableVal(Pred, PredInfo, Counter);
-    if (NewPHI) {
-      // Skip to the nearest preceding definition.
-      if (PredInfo->DefBB != Pred)
-        PredInfo = (*BBMap)[PredInfo->DefBB];
-      NewPHI->addIncoming(PredInfo->AvailableVal, Pred);
-    } else if (!Info->AvailableVal)
-      Info->AvailableVal = PredInfo->AvailableVal;
-  }
+  // Otherwise, we do need a PHI: insert one now if we don't already have one.
+  if (InsertedVal == 0)
+    InsertedVal = PHINode::Create(PrototypeValue->getType(),
+                                  PrototypeValue->getName(), &BB->front());
 
-  if (NewPHI) {
-    DEBUG(dbgs() << "  Inserted PHI: " << *NewPHI << "\n");
+  PHINode *InsertedPHI = cast<PHINode>(InsertedVal);
+  InsertedPHI->reserveOperandSpace(IncomingPredInfo.size()-FirstPredInfoEntry);
 
-    // If the client wants to know about all new instructions, tell it.
-    if (InsertedPHIs) InsertedPHIs->push_back(NewPHI);
-  }
-}
+  // Fill in all the predecessors of the PHI.
+  for (IncomingPredInfoTy::iterator I =
+         IncomingPredInfo.begin()+FirstPredInfoEntry,
+       E = IncomingPredInfo.end(); I != E; ++I)
+    InsertedPHI->addIncoming(I->second, I->first);
 
-/// FindExistingPHI - Look through the PHI nodes in a block to see if any of
-/// them match what is needed.
-void SSAUpdater::FindExistingPHI(BasicBlock *BB) {
-  PHINode *SomePHI;
-  for (BasicBlock::iterator It = BB->begin();
-       (SomePHI = dyn_cast<PHINode>(It)); ++It) {
-    if (CheckIfPHIMatches(SomePHI)) {
-      RecordMatchingPHI(SomePHI);
-      break;
-    }
-    ClearPHITags(SomePHI);
-  }
-}
+  // Drop the entries we added in IncomingPredInfo to restore the stack.
+  IncomingPredInfo.erase(IncomingPredInfo.begin()+FirstPredInfoEntry,
+                         IncomingPredInfo.end());
 
-/// 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);
-      BasicBlock *Pred = PHI->getIncomingBlock(i);
-      BBInfo *PredInfo = (*BBMap)[Pred];
-      // Skip to the nearest preceding definition.
-      if (PredInfo->DefBB != Pred) {
-        Pred = PredInfo->DefBB;
-        PredInfo = (*BBMap)[Pred];
-      }
-
-      // 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() != Pred)
-        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;
-}
+  // See if the PHI node can be merged to a single value.  This can happen in
+  // loop cases when we get a PHI of itself and one other value.
+  if (Value *ConstVal = InsertedPHI->hasConstantValue()) {
+    InsertedPHI->replaceAllUsesWith(ConstVal);
+    InsertedPHI->eraseFromParent();
+    InsertedVal = ConstVal;
+  } else {
+    DEBUG(dbgs() << "  Inserted PHI: " << *InsertedPHI << "\n");
 
-/// 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);
-  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 the client wants to know about all new instructions, tell it.
+    if (InsertedPHIs) InsertedPHIs->push_back(InsertedPHI);
   }
-}
 
-/// ClearPHITags - When one of the existing PHI nodes fails to match, clear
-/// the PHITag values that were stored in the BBMap when checking to see if
-/// it matched.
-void SSAUpdater::ClearPHITags(PHINode *PHI) {
-  BBMapTy *BBMap = getBBMap(BM);
-  SmallVector<PHINode*, 20> WorkList;
-  WorkList.push_back(PHI);
-
-  // Clear the tag for this PHI.
-  (*BBMap)[PHI->getParent()]->PHITag = 0;
-
-  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;
-      BasicBlock *BB = IncomingPHIVal->getParent();
-      BBInfo *Info = (*BBMap)[BB];
-      if (!Info || Info->AvailableVal || !Info->PHITag)
-        continue;
-
-      // Clear the tag and add the PHI to the worklist.
-      Info->PHITag = 0;
-      WorkList.push_back(IncomingPHIVal);
-    }
-  }
+  return InsertedVal;
 }