vendor/llvm/llvm-r72732

1 files changed, 1738 insertions, 0 deletions

diff --git a/lib/Transforms/Scalar/GVN.cpp b/lib/Transforms/Scalar/GVN.cpp
new file mode 100644
index 0000000000000..733dfa97a1547
--- /dev/null
+++ b/lib/Transforms/Scalar/GVN.cpp
@@ -0,0 +1,1738 @@
+//===- GVN.cpp - Eliminate redundant values and loads ---------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This pass performs global value numbering to eliminate fully redundant
+// instructions.  It also performs simple dead load elimination.
+//
+// Note that this pass does the value numbering itself; it does not use the
+// ValueNumbering analysis passes.
+//
+//===----------------------------------------------------------------------===//
+
+#define DEBUG_TYPE "gvn"
+#include "llvm/Transforms/Scalar.h"
+#include "llvm/BasicBlock.h"
+#include "llvm/Constants.h"
+#include "llvm/DerivedTypes.h"
+#include "llvm/Function.h"
+#include "llvm/IntrinsicInst.h"
+#include "llvm/Value.h"
+#include "llvm/ADT/DenseMap.h"
+#include "llvm/ADT/DepthFirstIterator.h"
+#include "llvm/ADT/PostOrderIterator.h"
+#include "llvm/ADT/SmallPtrSet.h"
+#include "llvm/ADT/SmallVector.h"
+#include "llvm/ADT/Statistic.h"
+#include "llvm/Analysis/Dominators.h"
+#include "llvm/Analysis/AliasAnalysis.h"
+#include "llvm/Analysis/MemoryDependenceAnalysis.h"
+#include "llvm/Support/CFG.h"
+#include "llvm/Support/CommandLine.h"
+#include "llvm/Support/Compiler.h"
+#include "llvm/Support/Debug.h"
+#include "llvm/Transforms/Utils/BasicBlockUtils.h"
+#include <cstdio>
+using namespace llvm;
+
+STATISTIC(NumGVNInstr,  "Number of instructions deleted");
+STATISTIC(NumGVNLoad,   "Number of loads deleted");
+STATISTIC(NumGVNPRE,    "Number of instructions PRE'd");
+STATISTIC(NumGVNBlocks, "Number of blocks merged");
+STATISTIC(NumPRELoad,   "Number of loads PRE'd");
+
+static cl::opt<bool> EnablePRE("enable-pre",
+                               cl::init(true), cl::Hidden);
+cl::opt<bool> EnableLoadPRE("enable-load-pre", cl::init(true));
+
+//===----------------------------------------------------------------------===//
+//                         ValueTable Class
+//===----------------------------------------------------------------------===//
+
+/// This class holds the mapping between values and value numbers.  It is used
+/// as an efficient mechanism to determine the expression-wise equivalence of
+/// two values.
+namespace {
+  struct VISIBILITY_HIDDEN Expression {
+    enum ExpressionOpcode { ADD, SUB, MUL, UDIV, SDIV, FDIV, UREM, SREM, 
+                            FREM, SHL, LSHR, ASHR, AND, OR, XOR, ICMPEQ, 
+                            ICMPNE, ICMPUGT, ICMPUGE, ICMPULT, ICMPULE, 
+                            ICMPSGT, ICMPSGE, ICMPSLT, ICMPSLE, FCMPOEQ, 
+                            FCMPOGT, FCMPOGE, FCMPOLT, FCMPOLE, FCMPONE, 
+                            FCMPORD, FCMPUNO, FCMPUEQ, FCMPUGT, FCMPUGE, 
+                            FCMPULT, FCMPULE, FCMPUNE, EXTRACT, INSERT,
+                            SHUFFLE, SELECT, TRUNC, ZEXT, SEXT, FPTOUI,
+                            FPTOSI, UITOFP, SITOFP, FPTRUNC, FPEXT, 
+                            PTRTOINT, INTTOPTR, BITCAST, GEP, CALL, CONSTANT,
+                            EMPTY, TOMBSTONE };
+
+    ExpressionOpcode opcode;
+    const Type* type;
+    uint32_t firstVN;
+    uint32_t secondVN;
+    uint32_t thirdVN;
+    SmallVector<uint32_t, 4> varargs;
+    Value* function;
+  
+    Expression() { }
+    Expression(ExpressionOpcode o) : opcode(o) { }
+  
+    bool operator==(const Expression &other) const {
+      if (opcode != other.opcode)
+        return false;
+      else if (opcode == EMPTY || opcode == TOMBSTONE)
+        return true;
+      else if (type != other.type)
+        return false;
+      else if (function != other.function)
+        return false;
+      else if (firstVN != other.firstVN)
+        return false;
+      else if (secondVN != other.secondVN)
+        return false;
+      else if (thirdVN != other.thirdVN)
+        return false;
+      else {
+        if (varargs.size() != other.varargs.size())
+          return false;
+      
+        for (size_t i = 0; i < varargs.size(); ++i)
+          if (varargs[i] != other.varargs[i])
+            return false;
+    
+        return true;
+      }
+    }
+  
+    bool operator!=(const Expression &other) const {
+      return !(*this == other);
+    }
+  };
+  
+  class VISIBILITY_HIDDEN ValueTable {
+    private:
+      DenseMap<Value*, uint32_t> valueNumbering;
+      DenseMap<Expression, uint32_t> expressionNumbering;
+      AliasAnalysis* AA;
+      MemoryDependenceAnalysis* MD;
+      DominatorTree* DT;
+  
+      uint32_t nextValueNumber;
+    
+      Expression::ExpressionOpcode getOpcode(BinaryOperator* BO);
+      Expression::ExpressionOpcode getOpcode(CmpInst* C);
+      Expression::ExpressionOpcode getOpcode(CastInst* C);
+      Expression create_expression(BinaryOperator* BO);
+      Expression create_expression(CmpInst* C);
+      Expression create_expression(ShuffleVectorInst* V);
+      Expression create_expression(ExtractElementInst* C);
+      Expression create_expression(InsertElementInst* V);
+      Expression create_expression(SelectInst* V);
+      Expression create_expression(CastInst* C);
+      Expression create_expression(GetElementPtrInst* G);
+      Expression create_expression(CallInst* C);
+      Expression create_expression(Constant* C);
+    public:
+      ValueTable() : nextValueNumber(1) { }
+      uint32_t lookup_or_add(Value* V);
+      uint32_t lookup(Value* V) const;
+      void add(Value* V, uint32_t num);
+      void clear();
+      void erase(Value* v);
+      unsigned size();
+      void setAliasAnalysis(AliasAnalysis* A) { AA = A; }
+      AliasAnalysis *getAliasAnalysis() const { return AA; }
+      void setMemDep(MemoryDependenceAnalysis* M) { MD = M; }
+      void setDomTree(DominatorTree* D) { DT = D; }
+      uint32_t getNextUnusedValueNumber() { return nextValueNumber; }
+      void verifyRemoved(const Value *) const;
+  };
+}
+
+namespace llvm {
+template <> struct DenseMapInfo<Expression> {
+  static inline Expression getEmptyKey() {
+    return Expression(Expression::EMPTY);
+  }
+  
+  static inline Expression getTombstoneKey() {
+    return Expression(Expression::TOMBSTONE);
+  }
+  
+  static unsigned getHashValue(const Expression e) {
+    unsigned hash = e.opcode;
+    
+    hash = e.firstVN + hash * 37;
+    hash = e.secondVN + hash * 37;
+    hash = e.thirdVN + hash * 37;
+    
+    hash = ((unsigned)((uintptr_t)e.type >> 4) ^
+            (unsigned)((uintptr_t)e.type >> 9)) +
+           hash * 37;
+    
+    for (SmallVector<uint32_t, 4>::const_iterator I = e.varargs.begin(),
+         E = e.varargs.end(); I != E; ++I)
+      hash = *I + hash * 37;
+    
+    hash = ((unsigned)((uintptr_t)e.function >> 4) ^
+            (unsigned)((uintptr_t)e.function >> 9)) +
+           hash * 37;
+    
+    return hash;
+  }
+  static bool isEqual(const Expression &LHS, const Expression &RHS) {
+    return LHS == RHS;
+  }
+  static bool isPod() { return true; }
+};
+}
+
+//===----------------------------------------------------------------------===//
+//                     ValueTable Internal Functions
+//===----------------------------------------------------------------------===//
+Expression::ExpressionOpcode ValueTable::getOpcode(BinaryOperator* BO) {
+  switch(BO->getOpcode()) {
+  default: // THIS SHOULD NEVER HAPPEN
+    assert(0 && "Binary operator with unknown opcode?");
+  case Instruction::Add:  return Expression::ADD;
+  case Instruction::Sub:  return Expression::SUB;
+  case Instruction::Mul:  return Expression::MUL;
+  case Instruction::UDiv: return Expression::UDIV;
+  case Instruction::SDiv: return Expression::SDIV;
+  case Instruction::FDiv: return Expression::FDIV;
+  case Instruction::URem: return Expression::UREM;
+  case Instruction::SRem: return Expression::SREM;
+  case Instruction::FRem: return Expression::FREM;
+  case Instruction::Shl:  return Expression::SHL;
+  case Instruction::LShr: return Expression::LSHR;
+  case Instruction::AShr: return Expression::ASHR;
+  case Instruction::And:  return Expression::AND;
+  case Instruction::Or:   return Expression::OR;
+  case Instruction::Xor:  return Expression::XOR;
+  }
+}
+
+Expression::ExpressionOpcode ValueTable::getOpcode(CmpInst* C) {
+  if (isa<ICmpInst>(C) || isa<VICmpInst>(C)) {
+    switch (C->getPredicate()) {
+    default:  // THIS SHOULD NEVER HAPPEN
+      assert(0 && "Comparison with unknown predicate?");
+    case ICmpInst::ICMP_EQ:  return Expression::ICMPEQ;
+    case ICmpInst::ICMP_NE:  return Expression::ICMPNE;
+    case ICmpInst::ICMP_UGT: return Expression::ICMPUGT;
+    case ICmpInst::ICMP_UGE: return Expression::ICMPUGE;
+    case ICmpInst::ICMP_ULT: return Expression::ICMPULT;
+    case ICmpInst::ICMP_ULE: return Expression::ICMPULE;
+    case ICmpInst::ICMP_SGT: return Expression::ICMPSGT;
+    case ICmpInst::ICMP_SGE: return Expression::ICMPSGE;
+    case ICmpInst::ICMP_SLT: return Expression::ICMPSLT;
+    case ICmpInst::ICMP_SLE: return Expression::ICMPSLE;
+    }
+  }
+  assert((isa<FCmpInst>(C) || isa<VFCmpInst>(C)) && "Unknown compare");
+  switch (C->getPredicate()) {
+  default: // THIS SHOULD NEVER HAPPEN
+    assert(0 && "Comparison with unknown predicate?");
+  case FCmpInst::FCMP_OEQ: return Expression::FCMPOEQ;
+  case FCmpInst::FCMP_OGT: return Expression::FCMPOGT;
+  case FCmpInst::FCMP_OGE: return Expression::FCMPOGE;
+  case FCmpInst::FCMP_OLT: return Expression::FCMPOLT;
+  case FCmpInst::FCMP_OLE: return Expression::FCMPOLE;
+  case FCmpInst::FCMP_ONE: return Expression::FCMPONE;
+  case FCmpInst::FCMP_ORD: return Expression::FCMPORD;
+  case FCmpInst::FCMP_UNO: return Expression::FCMPUNO;
+  case FCmpInst::FCMP_UEQ: return Expression::FCMPUEQ;
+  case FCmpInst::FCMP_UGT: return Expression::FCMPUGT;
+  case FCmpInst::FCMP_UGE: return Expression::FCMPUGE;
+  case FCmpInst::FCMP_ULT: return Expression::FCMPULT;
+  case FCmpInst::FCMP_ULE: return Expression::FCMPULE;
+  case FCmpInst::FCMP_UNE: return Expression::FCMPUNE;
+  }
+}
+
+Expression::ExpressionOpcode ValueTable::getOpcode(CastInst* C) {
+  switch(C->getOpcode()) {
+  default: // THIS SHOULD NEVER HAPPEN
+    assert(0 && "Cast operator with unknown opcode?");
+  case Instruction::Trunc:    return Expression::TRUNC;
+  case Instruction::ZExt:     return Expression::ZEXT;
+  case Instruction::SExt:     return Expression::SEXT;
+  case Instruction::FPToUI:   return Expression::FPTOUI;
+  case Instruction::FPToSI:   return Expression::FPTOSI;
+  case Instruction::UIToFP:   return Expression::UITOFP;
+  case Instruction::SIToFP:   return Expression::SITOFP;
+  case Instruction::FPTrunc:  return Expression::FPTRUNC;
+  case Instruction::FPExt:    return Expression::FPEXT;
+  case Instruction::PtrToInt: return Expression::PTRTOINT;
+  case Instruction::IntToPtr: return Expression::INTTOPTR;
+  case Instruction::BitCast:  return Expression::BITCAST;
+  }
+}
+
+Expression ValueTable::create_expression(CallInst* C) {
+  Expression e;
+  
+  e.type = C->getType();
+  e.firstVN = 0;
+  e.secondVN = 0;
+  e.thirdVN = 0;
+  e.function = C->getCalledFunction();
+  e.opcode = Expression::CALL;
+  
+  for (CallInst::op_iterator I = C->op_begin()+1, E = C->op_end();
+       I != E; ++I)
+    e.varargs.push_back(lookup_or_add(*I));
+  
+  return e;
+}
+
+Expression ValueTable::create_expression(BinaryOperator* BO) {
+  Expression e;
+    
+  e.firstVN = lookup_or_add(BO->getOperand(0));
+  e.secondVN = lookup_or_add(BO->getOperand(1));
+  e.thirdVN = 0;
+  e.function = 0;
+  e.type = BO->getType();
+  e.opcode = getOpcode(BO);
+  
+  return e;
+}
+
+Expression ValueTable::create_expression(CmpInst* C) {
+  Expression e;
+    
+  e.firstVN = lookup_or_add(C->getOperand(0));
+  e.secondVN = lookup_or_add(C->getOperand(1));
+  e.thirdVN = 0;
+  e.function = 0;
+  e.type = C->getType();
+  e.opcode = getOpcode(C);
+  
+  return e;
+}
+
+Expression ValueTable::create_expression(CastInst* C) {
+  Expression e;
+    
+  e.firstVN = lookup_or_add(C->getOperand(0));
+  e.secondVN = 0;
+  e.thirdVN = 0;
+  e.function = 0;
+  e.type = C->getType();
+  e.opcode = getOpcode(C);
+  
+  return e;
+}
+
+Expression ValueTable::create_expression(ShuffleVectorInst* S) {
+  Expression e;
+    
+  e.firstVN = lookup_or_add(S->getOperand(0));
+  e.secondVN = lookup_or_add(S->getOperand(1));
+  e.thirdVN = lookup_or_add(S->getOperand(2));
+  e.function = 0;
+  e.type = S->getType();
+  e.opcode = Expression::SHUFFLE;
+  
+  return e;
+}
+
+Expression ValueTable::create_expression(ExtractElementInst* E) {
+  Expression e;
+    
+  e.firstVN = lookup_or_add(E->getOperand(0));
+  e.secondVN = lookup_or_add(E->getOperand(1));
+  e.thirdVN = 0;
+  e.function = 0;
+  e.type = E->getType();
+  e.opcode = Expression::EXTRACT;
+  
+  return e;
+}
+
+Expression ValueTable::create_expression(InsertElementInst* I) {
+  Expression e;
+    
+  e.firstVN = lookup_or_add(I->getOperand(0));
+  e.secondVN = lookup_or_add(I->getOperand(1));
+  e.thirdVN = lookup_or_add(I->getOperand(2));
+  e.function = 0;
+  e.type = I->getType();
+  e.opcode = Expression::INSERT;
+  
+  return e;
+}
+
+Expression ValueTable::create_expression(SelectInst* I) {
+  Expression e;
+    
+  e.firstVN = lookup_or_add(I->getCondition());
+  e.secondVN = lookup_or_add(I->getTrueValue());
+  e.thirdVN = lookup_or_add(I->getFalseValue());
+  e.function = 0;
+  e.type = I->getType();
+  e.opcode = Expression::SELECT;
+  
+  return e;
+}
+
+Expression ValueTable::create_expression(GetElementPtrInst* G) {
+  Expression e;
+  
+  e.firstVN = lookup_or_add(G->getPointerOperand());
+  e.secondVN = 0;
+  e.thirdVN = 0;
+  e.function = 0;
+  e.type = G->getType();
+  e.opcode = Expression::GEP;
+  
+  for (GetElementPtrInst::op_iterator I = G->idx_begin(), E = G->idx_end();
+       I != E; ++I)
+    e.varargs.push_back(lookup_or_add(*I));
+  
+  return e;
+}
+
+//===----------------------------------------------------------------------===//
+//                     ValueTable External Functions
+//===----------------------------------------------------------------------===//
+
+/// add - Insert a value into the table with a specified value number.
+void ValueTable::add(Value* V, uint32_t num) {
+  valueNumbering.insert(std::make_pair(V, num));
+}
+
+/// lookup_or_add - Returns the value number for the specified value, assigning
+/// it a new number if it did not have one before.
+uint32_t ValueTable::lookup_or_add(Value* V) {
+  DenseMap<Value*, uint32_t>::iterator VI = valueNumbering.find(V);
+  if (VI != valueNumbering.end())
+    return VI->second;
+  
+  if (CallInst* C = dyn_cast<CallInst>(V)) {
+    if (AA->doesNotAccessMemory(C)) {
+      Expression e = create_expression(C);
+    
+      DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e);
+      if (EI != expressionNumbering.end()) {
+        valueNumbering.insert(std::make_pair(V, EI->second));
+        return EI->second;
+      } else {
+        expressionNumbering.insert(std::make_pair(e, nextValueNumber));
+        valueNumbering.insert(std::make_pair(V, nextValueNumber));
+      
+        return nextValueNumber++;
+      }
+    } else if (AA->onlyReadsMemory(C)) {
+      Expression e = create_expression(C);
+      
+      if (expressionNumbering.find(e) == expressionNumbering.end()) {
+        expressionNumbering.insert(std::make_pair(e, nextValueNumber));
+        valueNumbering.insert(std::make_pair(V, nextValueNumber));
+        return nextValueNumber++;
+      }
+      
+      MemDepResult local_dep = MD->getDependency(C);
+      
+      if (!local_dep.isDef() && !local_dep.isNonLocal()) {
+        valueNumbering.insert(std::make_pair(V, nextValueNumber));
+        return nextValueNumber++;
+      }
+
+      if (local_dep.isDef()) {
+        CallInst* local_cdep = cast<CallInst>(local_dep.getInst());
+        
+        if (local_cdep->getNumOperands() != C->getNumOperands()) {
+          valueNumbering.insert(std::make_pair(V, nextValueNumber));
+          return nextValueNumber++;
+        }
+          
+        for (unsigned i = 1; i < C->getNumOperands(); ++i) {
+          uint32_t c_vn = lookup_or_add(C->getOperand(i));
+          uint32_t cd_vn = lookup_or_add(local_cdep->getOperand(i));
+          if (c_vn != cd_vn) {
+            valueNumbering.insert(std::make_pair(V, nextValueNumber));
+            return nextValueNumber++;
+          }
+        }
+      
+        uint32_t v = lookup_or_add(local_cdep);
+        valueNumbering.insert(std::make_pair(V, v));
+        return v;
+      }
+
+      // Non-local case.
+      const MemoryDependenceAnalysis::NonLocalDepInfo &deps = 
+        MD->getNonLocalCallDependency(CallSite(C));
+      // FIXME: call/call dependencies for readonly calls should return def, not
+      // clobber!  Move the checking logic to MemDep!
+      CallInst* cdep = 0;
+      
+      // Check to see if we have a single dominating call instruction that is
+      // identical to C.
+      for (unsigned i = 0, e = deps.size(); i != e; ++i) {
+        const MemoryDependenceAnalysis::NonLocalDepEntry *I = &deps[i];
+        // Ignore non-local dependencies.
+        if (I->second.isNonLocal())
+          continue;
+
+        // We don't handle non-depedencies.  If we already have a call, reject
+        // instruction dependencies.
+        if (I->second.isClobber() || cdep != 0) {
+          cdep = 0;
+          break;
+        }
+        
+        CallInst *NonLocalDepCall = dyn_cast<CallInst>(I->second.getInst());
+        // FIXME: All duplicated with non-local case.
+        if (NonLocalDepCall && DT->properlyDominates(I->first, C->getParent())){
+          cdep = NonLocalDepCall;
+          continue;
+        }
+        
+        cdep = 0;
+        break;
+      }
+      
+      if (!cdep) {
+        valueNumbering.insert(std::make_pair(V, nextValueNumber));
+        return nextValueNumber++;
+      }
+      
+      if (cdep->getNumOperands() != C->getNumOperands()) {
+        valueNumbering.insert(std::make_pair(V, nextValueNumber));
+        return nextValueNumber++;
+      }
+      for (unsigned i = 1; i < C->getNumOperands(); ++i) {
+        uint32_t c_vn = lookup_or_add(C->getOperand(i));
+        uint32_t cd_vn = lookup_or_add(cdep->getOperand(i));
+        if (c_vn != cd_vn) {
+          valueNumbering.insert(std::make_pair(V, nextValueNumber));
+          return nextValueNumber++;
+        }
+      }
+      
+      uint32_t v = lookup_or_add(cdep);
+      valueNumbering.insert(std::make_pair(V, v));
+      return v;
+      
+    } else {
+      valueNumbering.insert(std::make_pair(V, nextValueNumber));
+      return nextValueNumber++;
+    }
+  } else if (BinaryOperator* BO = dyn_cast<BinaryOperator>(V)) {
+    Expression e = create_expression(BO);
+    
+    DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e);
+    if (EI != expressionNumbering.end()) {
+      valueNumbering.insert(std::make_pair(V, EI->second));
+      return EI->second;
+    } else {
+      expressionNumbering.insert(std::make_pair(e, nextValueNumber));
+      valueNumbering.insert(std::make_pair(V, nextValueNumber));
+      
+      return nextValueNumber++;
+    }
+  } else if (CmpInst* C = dyn_cast<CmpInst>(V)) {
+    Expression e = create_expression(C);
+    
+    DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e);
+    if (EI != expressionNumbering.end()) {
+      valueNumbering.insert(std::make_pair(V, EI->second));
+      return EI->second;
+    } else {
+      expressionNumbering.insert(std::make_pair(e, nextValueNumber));
+      valueNumbering.insert(std::make_pair(V, nextValueNumber));
+      
+      return nextValueNumber++;
+    }
+  } else if (ShuffleVectorInst* U = dyn_cast<ShuffleVectorInst>(V)) {
+    Expression e = create_expression(U);
+    
+    DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e);
+    if (EI != expressionNumbering.end()) {
+      valueNumbering.insert(std::make_pair(V, EI->second));
+      return EI->second;
+    } else {
+      expressionNumbering.insert(std::make_pair(e, nextValueNumber));
+      valueNumbering.insert(std::make_pair(V, nextValueNumber));
+      
+      return nextValueNumber++;
+    }
+  } else if (ExtractElementInst* U = dyn_cast<ExtractElementInst>(V)) {
+    Expression e = create_expression(U);
+    
+    DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e);
+    if (EI != expressionNumbering.end()) {
+      valueNumbering.insert(std::make_pair(V, EI->second));
+      return EI->second;
+    } else {
+      expressionNumbering.insert(std::make_pair(e, nextValueNumber));
+      valueNumbering.insert(std::make_pair(V, nextValueNumber));
+      
+      return nextValueNumber++;
+    }
+  } else if (InsertElementInst* U = dyn_cast<InsertElementInst>(V)) {
+    Expression e = create_expression(U);
+    
+    DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e);
+    if (EI != expressionNumbering.end()) {
+      valueNumbering.insert(std::make_pair(V, EI->second));
+      return EI->second;
+    } else {
+      expressionNumbering.insert(std::make_pair(e, nextValueNumber));
+      valueNumbering.insert(std::make_pair(V, nextValueNumber));
+      
+      return nextValueNumber++;
+    }
+  } else if (SelectInst* U = dyn_cast<SelectInst>(V)) {
+    Expression e = create_expression(U);
+    
+    DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e);
+    if (EI != expressionNumbering.end()) {
+      valueNumbering.insert(std::make_pair(V, EI->second));
+      return EI->second;
+    } else {
+      expressionNumbering.insert(std::make_pair(e, nextValueNumber));
+      valueNumbering.insert(std::make_pair(V, nextValueNumber));
+      
+      return nextValueNumber++;
+    }
+  } else if (CastInst* U = dyn_cast<CastInst>(V)) {
+    Expression e = create_expression(U);
+    
+    DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e);
+    if (EI != expressionNumbering.end()) {
+      valueNumbering.insert(std::make_pair(V, EI->second));
+      return EI->second;
+    } else {
+      expressionNumbering.insert(std::make_pair(e, nextValueNumber));
+      valueNumbering.insert(std::make_pair(V, nextValueNumber));
+      
+      return nextValueNumber++;
+    }
+  } else if (GetElementPtrInst* U = dyn_cast<GetElementPtrInst>(V)) {
+    Expression e = create_expression(U);
+    
+    DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e);
+    if (EI != expressionNumbering.end()) {
+      valueNumbering.insert(std::make_pair(V, EI->second));
+      return EI->second;
+    } else {
+      expressionNumbering.insert(std::make_pair(e, nextValueNumber));
+      valueNumbering.insert(std::make_pair(V, nextValueNumber));
+      
+      return nextValueNumber++;
+    }
+  } else {
+    valueNumbering.insert(std::make_pair(V, nextValueNumber));
+    return nextValueNumber++;
+  }
+}
+
+/// lookup - Returns the value number of the specified value. Fails if
+/// the value has not yet been numbered.
+uint32_t ValueTable::lookup(Value* V) const {
+  DenseMap<Value*, uint32_t>::iterator VI = valueNumbering.find(V);
+  assert(VI != valueNumbering.end() && "Value not numbered?");
+  return VI->second;
+}
+
+/// clear - Remove all entries from the ValueTable
+void ValueTable::clear() {
+  valueNumbering.clear();
+  expressionNumbering.clear();
+  nextValueNumber = 1;
+}
+
+/// erase - Remove a value from the value numbering
+void ValueTable::erase(Value* V) {
+  valueNumbering.erase(V);
+}
+
+/// verifyRemoved - Verify that the value is removed from all internal data
+/// structures.
+void ValueTable::verifyRemoved(const Value *V) const {
+  for (DenseMap<Value*, uint32_t>::iterator
+         I = valueNumbering.begin(), E = valueNumbering.end(); I != E; ++I) {
+    assert(I->first != V && "Inst still occurs in value numbering map!");
+  }
+}
+
+//===----------------------------------------------------------------------===//
+//                                GVN Pass
+//===----------------------------------------------------------------------===//
+
+namespace {
+  struct VISIBILITY_HIDDEN ValueNumberScope {
+    ValueNumberScope* parent;
+    DenseMap<uint32_t, Value*> table;
+    
+    ValueNumberScope(ValueNumberScope* p) : parent(p) { }
+  };
+}
+
+namespace {
+
+  class VISIBILITY_HIDDEN GVN : public FunctionPass {
+    bool runOnFunction(Function &F);
+  public:
+    static char ID; // Pass identification, replacement for typeid
+    GVN() : FunctionPass(&ID) { }
+
+  private:
+    MemoryDependenceAnalysis *MD;
+    DominatorTree *DT;
+
+    ValueTable VN;
+    DenseMap<BasicBlock*, ValueNumberScope*> localAvail;
+    
+    typedef DenseMap<Value*, SmallPtrSet<Instruction*, 4> > PhiMapType;
+    PhiMapType phiMap;
+    
+    
+    // This transformation requires dominator postdominator info
+    virtual void getAnalysisUsage(AnalysisUsage &AU) const {
+      AU.addRequired<DominatorTree>();
+      AU.addRequired<MemoryDependenceAnalysis>();
+      AU.addRequired<AliasAnalysis>();
+      
+      AU.addPreserved<DominatorTree>();
+      AU.addPreserved<AliasAnalysis>();
+    }
+  
+    // Helper fuctions
+    // FIXME: eliminate or document these better
+    bool processLoad(LoadInst* L,
+                     SmallVectorImpl<Instruction*> &toErase);
+    bool processInstruction(Instruction* I,
+                            SmallVectorImpl<Instruction*> &toErase);
+    bool processNonLocalLoad(LoadInst* L,
+                             SmallVectorImpl<Instruction*> &toErase);
+    bool processBlock(BasicBlock* BB);
+    Value *GetValueForBlock(BasicBlock *BB, Instruction* orig,
+                            DenseMap<BasicBlock*, Value*> &Phis,
+                            bool top_level = false);
+    void dump(DenseMap<uint32_t, Value*>& d);
+    bool iterateOnFunction(Function &F);
+    Value* CollapsePhi(PHINode* p);
+    bool isSafeReplacement(PHINode* p, Instruction* inst);
+    bool performPRE(Function& F);
+    Value* lookupNumber(BasicBlock* BB, uint32_t num);
+    bool mergeBlockIntoPredecessor(BasicBlock* BB);
+    Value* AttemptRedundancyElimination(Instruction* orig, unsigned valno);
+    void cleanupGlobalSets();
+    void verifyRemoved(const Instruction *I) const;
+  };
+  
+  char GVN::ID = 0;
+}
+
+// createGVNPass - The public interface to this file...
+FunctionPass *llvm::createGVNPass() { return new GVN(); }
+
+static RegisterPass<GVN> X("gvn",
+                           "Global Value Numbering");
+
+void GVN::dump(DenseMap<uint32_t, Value*>& d) {
+  printf("{\n");
+  for (DenseMap<uint32_t, Value*>::iterator I = d.begin(),
+       E = d.end(); I != E; ++I) {
+      printf("%d\n", I->first);
+      I->second->dump();
+  }
+  printf("}\n");
+}
+
+Value* GVN::CollapsePhi(PHINode* p) {
+  Value* constVal = p->hasConstantValue();
+  if (!constVal) return 0;
+  
+  Instruction* inst = dyn_cast<Instruction>(constVal);
+  if (!inst)
+    return constVal;
+    
+  if (DT->dominates(inst, p))
+    if (isSafeReplacement(p, inst))
+      return inst;
+  return 0;
+}
+
+bool GVN::isSafeReplacement(PHINode* p, Instruction* inst) {
+  if (!isa<PHINode>(inst))
+    return true;
+  
+  for (Instruction::use_iterator UI = p->use_begin(), E = p->use_end();
+       UI != E; ++UI)
+    if (PHINode* use_phi = dyn_cast<PHINode>(UI))
+      if (use_phi->getParent() == inst->getParent())
+        return false;
+  
+  return true;
+}
+
+/// GetValueForBlock - Get the value to use within the specified basic block.
+/// available values are in Phis.
+Value *GVN::GetValueForBlock(BasicBlock *BB, Instruction* orig,
+                             DenseMap<BasicBlock*, Value*> &Phis,
+                             bool top_level) { 
+                                 
+  // If we have already computed this value, return the previously computed val.
+  DenseMap<BasicBlock*, Value*>::iterator V = Phis.find(BB);
+  if (V != Phis.end() && !top_level) return V->second;
+  
+  // If the block is unreachable, just return undef, since this path
+  // can't actually occur at runtime.
+  if (!DT->isReachableFromEntry(BB))
+    return Phis[BB] = UndefValue::get(orig->getType());
+  
+  if (BasicBlock *Pred = BB->getSinglePredecessor()) {
+    Value *ret = GetValueForBlock(Pred, orig, Phis);
+    Phis[BB] = ret;
+    return ret;
+  }
+
+  // Get the number of predecessors of this block so we can reserve space later.
+  // If there is already a PHI in it, use the #preds from it, otherwise count.
+  // Getting it from the PHI is constant time.
+  unsigned NumPreds;
+  if (PHINode *ExistingPN = dyn_cast<PHINode>(BB->begin()))
+    NumPreds = ExistingPN->getNumIncomingValues();
+  else
+    NumPreds = std::distance(pred_begin(BB), pred_end(BB));
+  
+  // Otherwise, the idom is the loop, so we need to insert a PHI node.  Do so
+  // now, then get values to fill in the incoming values for the PHI.
+  PHINode *PN = PHINode::Create(orig->getType(), orig->getName()+".rle",
+                                BB->begin());
+  PN->reserveOperandSpace(NumPreds);
+  
+  Phis.insert(std::make_pair(BB, PN));
+  
+  // Fill in the incoming values for the block.
+  for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
+    Value* val = GetValueForBlock(*PI, orig, Phis);
+    PN->addIncoming(val, *PI);
+  }
+  
+  VN.getAliasAnalysis()->copyValue(orig, PN);
+  
+  // Attempt to collapse PHI nodes that are trivially redundant
+  Value* v = CollapsePhi(PN);
+  if (!v) {
+    // Cache our phi construction results
+    if (LoadInst* L = dyn_cast<LoadInst>(orig))
+      phiMap[L->getPointerOperand()].insert(PN);
+    else
+      phiMap[orig].insert(PN);
+    
+    return PN;
+  }
+    
+  PN->replaceAllUsesWith(v);
+  if (isa<PointerType>(v->getType()))
+    MD->invalidateCachedPointerInfo(v);
+
+  for (DenseMap<BasicBlock*, Value*>::iterator I = Phis.begin(),
+       E = Phis.end(); I != E; ++I)
+    if (I->second == PN)
+      I->second = v;
+
+  DEBUG(cerr << "GVN removed: " << *PN);
+  MD->removeInstruction(PN);
+  PN->eraseFromParent();
+  DEBUG(verifyRemoved(PN));
+
+  Phis[BB] = v;
+  return v;
+}
+
+/// IsValueFullyAvailableInBlock - Return true if we can prove that the value
+/// we're analyzing is fully available in the specified block.  As we go, keep
+/// track of which blocks we know are fully alive in FullyAvailableBlocks.  This
+/// map is actually a tri-state map with the following values:
+///   0) we know the block *is not* fully available.
+///   1) we know the block *is* fully available.
+///   2) we do not know whether the block is fully available or not, but we are
+///      currently speculating that it will be.
+///   3) we are speculating for this block and have used that to speculate for
+///      other blocks.
+static bool IsValueFullyAvailableInBlock(BasicBlock *BB, 
+                            DenseMap<BasicBlock*, char> &FullyAvailableBlocks) {
+  // Optimistically assume that the block is fully available and check to see
+  // if we already know about this block in one lookup.
+  std::pair<DenseMap<BasicBlock*, char>::iterator, char> IV = 
+    FullyAvailableBlocks.insert(std::make_pair(BB, 2));
+
+  // If the entry already existed for this block, return the precomputed value.
+  if (!IV.second) {
+    // If this is a speculative "available" value, mark it as being used for
+    // speculation of other blocks.
+    if (IV.first->second == 2)
+      IV.first->second = 3;
+    return IV.first->second != 0;
+  }
+  
+  // Otherwise, see if it is fully available in all predecessors.
+  pred_iterator PI = pred_begin(BB), PE = pred_end(BB);
+  
+  // If this block has no predecessors, it isn't live-in here.
+  if (PI == PE)
+    goto SpeculationFailure;
+  
+  for (; PI != PE; ++PI)
+    // If the value isn't fully available in one of our predecessors, then it
+    // isn't fully available in this block either.  Undo our previous
+    // optimistic assumption and bail out.
+    if (!IsValueFullyAvailableInBlock(*PI, FullyAvailableBlocks))
+      goto SpeculationFailure;
+  
+  return true;
+  
+// SpeculationFailure - If we get here, we found out that this is not, after
+// all, a fully-available block.  We have a problem if we speculated on this and
+// used the speculation to mark other blocks as available.
+SpeculationFailure:
+  char &BBVal = FullyAvailableBlocks[BB];
+  
+  // If we didn't speculate on this, just return with it set to false.
+  if (BBVal == 2) {
+    BBVal = 0;
+    return false;
+  }
+
+  // If we did speculate on this value, we could have blocks set to 1 that are
+  // incorrect.  Walk the (transitive) successors of this block and mark them as
+  // 0 if set to one.
+  SmallVector<BasicBlock*, 32> BBWorklist;
+  BBWorklist.push_back(BB);
+  
+  while (!BBWorklist.empty()) {
+    BasicBlock *Entry = BBWorklist.pop_back_val();
+    // Note that this sets blocks to 0 (unavailable) if they happen to not
+    // already be in FullyAvailableBlocks.  This is safe.
+    char &EntryVal = FullyAvailableBlocks[Entry];
+    if (EntryVal == 0) continue;  // Already unavailable.
+
+    // Mark as unavailable.
+    EntryVal = 0;
+    
+    for (succ_iterator I = succ_begin(Entry), E = succ_end(Entry); I != E; ++I)
+      BBWorklist.push_back(*I);
+  }
+  
+  return false;
+}
+
+/// processNonLocalLoad - Attempt to eliminate a load whose dependencies are
+/// non-local by performing PHI construction.
+bool GVN::processNonLocalLoad(LoadInst *LI,
+                              SmallVectorImpl<Instruction*> &toErase) {
+  // Find the non-local dependencies of the load.
+  SmallVector<MemoryDependenceAnalysis::NonLocalDepEntry, 64> Deps; 
+  MD->getNonLocalPointerDependency(LI->getOperand(0), true, LI->getParent(),
+                                   Deps);
+  //DEBUG(cerr << "INVESTIGATING NONLOCAL LOAD: " << Deps.size() << *LI);
+  
+  // If we had to process more than one hundred blocks to find the
+  // dependencies, this load isn't worth worrying about.  Optimizing
+  // it will be too expensive.
+  if (Deps.size() > 100)
+    return false;
+
+  // If we had a phi translation failure, we'll have a single entry which is a
+  // clobber in the current block.  Reject this early.
+  if (Deps.size() == 1 && Deps[0].second.isClobber())
+    return false;
+  
+  // Filter out useless results (non-locals, etc).  Keep track of the blocks
+  // where we have a value available in repl, also keep track of whether we see
+  // dependencies that produce an unknown value for the load (such as a call
+  // that could potentially clobber the load).
+  SmallVector<std::pair<BasicBlock*, Value*>, 16> ValuesPerBlock;
+  SmallVector<BasicBlock*, 16> UnavailableBlocks;
+  
+  for (unsigned i = 0, e = Deps.size(); i != e; ++i) {
+    BasicBlock *DepBB = Deps[i].first;
+    MemDepResult DepInfo = Deps[i].second;
+    
+    if (DepInfo.isClobber()) {
+      UnavailableBlocks.push_back(DepBB);
+      continue;
+    }
+    
+    Instruction *DepInst = DepInfo.getInst();
+    
+    // Loading the allocation -> undef.
+    if (isa<AllocationInst>(DepInst)) {
+      ValuesPerBlock.push_back(std::make_pair(DepBB, 
+                                              UndefValue::get(LI->getType())));
+      continue;
+    }
+  
+    if (StoreInst* S = dyn_cast<StoreInst>(DepInst)) {
+      // Reject loads and stores that are to the same address but are of 
+      // different types.
+      // NOTE: 403.gcc does have this case (e.g. in readonly_fields_p) because
+      // of bitfield access, it would be interesting to optimize for it at some
+      // point.
+      if (S->getOperand(0)->getType() != LI->getType()) {
+        UnavailableBlocks.push_back(DepBB);
+        continue;
+      }
+      
+      ValuesPerBlock.push_back(std::make_pair(DepBB, S->getOperand(0)));
+      
+    } else if (LoadInst* LD = dyn_cast<LoadInst>(DepInst)) {
+      if (LD->getType() != LI->getType()) {
+        UnavailableBlocks.push_back(DepBB);
+        continue;
+      }
+      ValuesPerBlock.push_back(std::make_pair(DepBB, LD));
+    } else {
+      UnavailableBlocks.push_back(DepBB);
+      continue;
+    }
+  }
+  
+  // If we have no predecessors that produce a known value for this load, exit
+  // early.
+  if (ValuesPerBlock.empty()) return false;
+  
+  // If all of the instructions we depend on produce a known value for this
+  // load, then it is fully redundant and we can use PHI insertion to compute
+  // its value.  Insert PHIs and remove the fully redundant value now.
+  if (UnavailableBlocks.empty()) {
+    // Use cached PHI construction information from previous runs
+    SmallPtrSet<Instruction*, 4> &p = phiMap[LI->getPointerOperand()];
+    // FIXME: What does phiMap do? Are we positive it isn't getting invalidated?
+    for (SmallPtrSet<Instruction*, 4>::iterator I = p.begin(), E = p.end();
+         I != E; ++I) {
+      if ((*I)->getParent() == LI->getParent()) {
+        DEBUG(cerr << "GVN REMOVING NONLOCAL LOAD #1: " << *LI);
+        LI->replaceAllUsesWith(*I);
+        if (isa<PointerType>((*I)->getType()))
+          MD->invalidateCachedPointerInfo(*I);
+        toErase.push_back(LI);
+        NumGVNLoad++;
+        return true;
+      }
+      
+      ValuesPerBlock.push_back(std::make_pair((*I)->getParent(), *I));
+    }
+    
+    DEBUG(cerr << "GVN REMOVING NONLOCAL LOAD: " << *LI);
+    
+    DenseMap<BasicBlock*, Value*> BlockReplValues;
+    BlockReplValues.insert(ValuesPerBlock.begin(), ValuesPerBlock.end());
+    // Perform PHI construction.
+    Value* v = GetValueForBlock(LI->getParent(), LI, BlockReplValues, true);
+    LI->replaceAllUsesWith(v);
+    
+    if (isa<PHINode>(v))
+      v->takeName(LI);
+    if (isa<PointerType>(v->getType()))
+      MD->invalidateCachedPointerInfo(v);
+    toErase.push_back(LI);
+    NumGVNLoad++;
+    return true;
+  }
+  
+  if (!EnablePRE || !EnableLoadPRE)
+    return false;
+
+  // Okay, we have *some* definitions of the value.  This means that the value
+  // is available in some of our (transitive) predecessors.  Lets think about
+  // doing PRE of this load.  This will involve inserting a new load into the
+  // predecessor when it's not available.  We could do this in general, but
+  // prefer to not increase code size.  As such, we only do this when we know
+  // that we only have to insert *one* load (which means we're basically moving
+  // the load, not inserting a new one).
+  
+  SmallPtrSet<BasicBlock *, 4> Blockers;
+  for (unsigned i = 0, e = UnavailableBlocks.size(); i != e; ++i)
+    Blockers.insert(UnavailableBlocks[i]);
+
+  // Lets find first basic block with more than one predecessor.  Walk backwards
+  // through predecessors if needed.
+  BasicBlock *LoadBB = LI->getParent();
+  BasicBlock *TmpBB = LoadBB;
+
+  bool isSinglePred = false;
+  while (TmpBB->getSinglePredecessor()) {
+    isSinglePred = true;
+    TmpBB = TmpBB->getSinglePredecessor();
+    if (!TmpBB) // If haven't found any, bail now.
+      return false;
+    if (TmpBB == LoadBB) // Infinite (unreachable) loop.
+      return false;
+    if (Blockers.count(TmpBB))
+      return false;
+  }
+  
+  assert(TmpBB);
+  LoadBB = TmpBB;
+  
+  // If we have a repl set with LI itself in it, this means we have a loop where
+  // at least one of the values is LI.  Since this means that we won't be able
+  // to eliminate LI even if we insert uses in the other predecessors, we will
+  // end up increasing code size.  Reject this by scanning for LI.
+  for (unsigned i = 0, e = ValuesPerBlock.size(); i != e; ++i)
+    if (ValuesPerBlock[i].second == LI)
+      return false;
+  
+  if (isSinglePred) {
+    bool isHot = false;
+    for (unsigned i = 0, e = ValuesPerBlock.size(); i != e; ++i)
+      if (Instruction *I = dyn_cast<Instruction>(ValuesPerBlock[i].second))
+	// "Hot" Instruction is in some loop (because it dominates its dep. 
+	// instruction).
+	if (DT->dominates(LI, I)) { 
+	  isHot = true;
+	  break;
+	}
+
+    // We are interested only in "hot" instructions. We don't want to do any
+    // mis-optimizations here.
+    if (!isHot)
+      return false;
+  }
+
+  // Okay, we have some hope :).  Check to see if the loaded value is fully
+  // available in all but one predecessor.
+  // FIXME: If we could restructure the CFG, we could make a common pred with
+  // all the preds that don't have an available LI and insert a new load into
+  // that one block.
+  BasicBlock *UnavailablePred = 0;
+
+  DenseMap<BasicBlock*, char> FullyAvailableBlocks;
+  for (unsigned i = 0, e = ValuesPerBlock.size(); i != e; ++i)
+    FullyAvailableBlocks[ValuesPerBlock[i].first] = true;
+  for (unsigned i = 0, e = UnavailableBlocks.size(); i != e; ++i)
+    FullyAvailableBlocks[UnavailableBlocks[i]] = false;
+
+  for (pred_iterator PI = pred_begin(LoadBB), E = pred_end(LoadBB);
+       PI != E; ++PI) {
+    if (IsValueFullyAvailableInBlock(*PI, FullyAvailableBlocks))
+      continue;
+    
+    // If this load is not available in multiple predecessors, reject it.
+    if (UnavailablePred && UnavailablePred != *PI)
+      return false;
+    UnavailablePred = *PI;
+  }
+  
+  assert(UnavailablePred != 0 &&
+         "Fully available value should be eliminated above!");
+  
+  // If the loaded pointer is PHI node defined in this block, do PHI translation
+  // to get its value in the predecessor.
+  Value *LoadPtr = LI->getOperand(0)->DoPHITranslation(LoadBB, UnavailablePred);
+  
+  // Make sure the value is live in the predecessor.  If it was defined by a
+  // non-PHI instruction in this block, we don't know how to recompute it above.
+  if (Instruction *LPInst = dyn_cast<Instruction>(LoadPtr))
+    if (!DT->dominates(LPInst->getParent(), UnavailablePred)) {
+      DEBUG(cerr << "COULDN'T PRE LOAD BECAUSE PTR IS UNAVAILABLE IN PRED: "
+                 << *LPInst << *LI << "\n");
+      return false;
+    }
+  
+  // We don't currently handle critical edges :(
+  if (UnavailablePred->getTerminator()->getNumSuccessors() != 1) {
+    DEBUG(cerr << "COULD NOT PRE LOAD BECAUSE OF CRITICAL EDGE '"
+                << UnavailablePred->getName() << "': " << *LI);
+    return false;
+  }
+  
+  // Okay, we can eliminate this load by inserting a reload in the predecessor
+  // and using PHI construction to get the value in the other predecessors, do
+  // it.
+  DEBUG(cerr << "GVN REMOVING PRE LOAD: " << *LI);
+  
+  Value *NewLoad = new LoadInst(LoadPtr, LI->getName()+".pre", false,
+                                LI->getAlignment(),
+                                UnavailablePred->getTerminator());
+  
+  SmallPtrSet<Instruction*, 4> &p = phiMap[LI->getPointerOperand()];
+  for (SmallPtrSet<Instruction*, 4>::iterator I = p.begin(), E = p.end();
+       I != E; ++I)
+    ValuesPerBlock.push_back(std::make_pair((*I)->getParent(), *I));
+  
+  DenseMap<BasicBlock*, Value*> BlockReplValues;
+  BlockReplValues.insert(ValuesPerBlock.begin(), ValuesPerBlock.end());
+  BlockReplValues[UnavailablePred] = NewLoad;
+  
+  // Perform PHI construction.
+  Value* v = GetValueForBlock(LI->getParent(), LI, BlockReplValues, true);
+  LI->replaceAllUsesWith(v);
+  if (isa<PHINode>(v))
+    v->takeName(LI);
+  if (isa<PointerType>(v->getType()))
+    MD->invalidateCachedPointerInfo(v);
+  toErase.push_back(LI);
+  NumPRELoad++;
+  return true;
+}
+
+/// processLoad - Attempt to eliminate a load, first by eliminating it
+/// locally, and then attempting non-local elimination if that fails.
+bool GVN::processLoad(LoadInst *L, SmallVectorImpl<Instruction*> &toErase) {
+  if (L->isVolatile())
+    return false;
+  
+  Value* pointer = L->getPointerOperand();
+
+  // ... to a pointer that has been loaded from before...
+  MemDepResult dep = MD->getDependency(L);
+  
+  // If the value isn't available, don't do anything!
+  if (dep.isClobber()) {
+    DEBUG(
+      // fast print dep, using operator<< on instruction would be too slow
+      DOUT << "GVN: load ";
+      WriteAsOperand(*DOUT.stream(), L);
+      Instruction *I = dep.getInst();
+      DOUT << " is clobbered by " << *I;
+    );
+    return false;
+  }
+
+  // If it is defined in another block, try harder.
+  if (dep.isNonLocal())
+    return processNonLocalLoad(L, toErase);
+
+  Instruction *DepInst = dep.getInst();
+  if (StoreInst *DepSI = dyn_cast<StoreInst>(DepInst)) {
+    // Only forward substitute stores to loads of the same type.
+    // FIXME: Could do better!
+    if (DepSI->getPointerOperand()->getType() != pointer->getType())
+      return false;
+    
+    // Remove it!
+    L->replaceAllUsesWith(DepSI->getOperand(0));
+    if (isa<PointerType>(DepSI->getOperand(0)->getType()))
+      MD->invalidateCachedPointerInfo(DepSI->getOperand(0));
+    toErase.push_back(L);
+    NumGVNLoad++;
+    return true;
+  }
+
+  if (LoadInst *DepLI = dyn_cast<LoadInst>(DepInst)) {
+    // Only forward substitute stores to loads of the same type.
+    // FIXME: Could do better! load i32 -> load i8 -> truncate on little endian.
+    if (DepLI->getType() != L->getType())
+      return false;
+    
+    // Remove it!
+    L->replaceAllUsesWith(DepLI);
+    if (isa<PointerType>(DepLI->getType()))
+      MD->invalidateCachedPointerInfo(DepLI);
+    toErase.push_back(L);
+    NumGVNLoad++;
+    return true;
+  }
+  
+  // If this load really doesn't depend on anything, then we must be loading an
+  // undef value.  This can happen when loading for a fresh allocation with no
+  // intervening stores, for example.
+  if (isa<AllocationInst>(DepInst)) {
+    L->replaceAllUsesWith(UndefValue::get(L->getType()));
+    toErase.push_back(L);
+    NumGVNLoad++;
+    return true;
+  }
+
+  return false;
+}
+
+Value* GVN::lookupNumber(BasicBlock* BB, uint32_t num) {
+  DenseMap<BasicBlock*, ValueNumberScope*>::iterator I = localAvail.find(BB);
+  if (I == localAvail.end())
+    return 0;
+  
+  ValueNumberScope* locals = I->second;
+  
+  while (locals) {
+    DenseMap<uint32_t, Value*>::iterator I = locals->table.find(num);
+    if (I != locals->table.end())
+      return I->second;
+    else
+      locals = locals->parent;
+  }
+  
+  return 0;
+}
+
+/// AttemptRedundancyElimination - If the "fast path" of redundancy elimination
+/// by inheritance from the dominator fails, see if we can perform phi 
+/// construction to eliminate the redundancy.
+Value* GVN::AttemptRedundancyElimination(Instruction* orig, unsigned valno) {
+  BasicBlock* BaseBlock = orig->getParent();
+  
+  SmallPtrSet<BasicBlock*, 4> Visited;
+  SmallVector<BasicBlock*, 8> Stack;
+  Stack.push_back(BaseBlock);
+  
+  DenseMap<BasicBlock*, Value*> Results;
+  
+  // Walk backwards through our predecessors, looking for instances of the
+  // value number we're looking for.  Instances are recorded in the Results
+  // map, which is then used to perform phi construction.
+  while (!Stack.empty()) {
+    BasicBlock* Current = Stack.back();
+    Stack.pop_back();
+    
+    // If we've walked all the way to a proper dominator, then give up. Cases
+    // where the instance is in the dominator will have been caught by the fast
+    // path, and any cases that require phi construction further than this are
+    // probably not worth it anyways.  Note that this is a SIGNIFICANT compile
+    // time improvement.
+    if (DT->properlyDominates(Current, orig->getParent())) return 0;
+    
+    DenseMap<BasicBlock*, ValueNumberScope*>::iterator LA =
+                                                       localAvail.find(Current);
+    if (LA == localAvail.end()) return 0;
+    DenseMap<uint32_t, Value*>::iterator V = LA->second->table.find(valno);
+    
+    if (V != LA->second->table.end()) {
+      // Found an instance, record it.
+      Results.insert(std::make_pair(Current, V->second));
+      continue;
+    }
+    
+    // If we reach the beginning of the function, then give up.
+    if (pred_begin(Current) == pred_end(Current))
+      return 0;
+    
+    for (pred_iterator PI = pred_begin(Current), PE = pred_end(Current);
+         PI != PE; ++PI)
+      if (Visited.insert(*PI))
+        Stack.push_back(*PI);
+  }
+  
+  // If we didn't find instances, give up.  Otherwise, perform phi construction.
+  if (Results.size() == 0)
+    return 0;
+  else
+    return GetValueForBlock(BaseBlock, orig, Results, true);
+}
+
+/// processInstruction - When calculating availability, handle an instruction
+/// by inserting it into the appropriate sets
+bool GVN::processInstruction(Instruction *I,
+                             SmallVectorImpl<Instruction*> &toErase) {
+  if (LoadInst* L = dyn_cast<LoadInst>(I)) {
+    bool changed = processLoad(L, toErase);
+    
+    if (!changed) {
+      unsigned num = VN.lookup_or_add(L);
+      localAvail[I->getParent()]->table.insert(std::make_pair(num, L));
+    }
+    
+    return changed;
+  }
+  
+  uint32_t nextNum = VN.getNextUnusedValueNumber();
+  unsigned num = VN.lookup_or_add(I);
+  
+  if (BranchInst* BI = dyn_cast<BranchInst>(I)) {
+    localAvail[I->getParent()]->table.insert(std::make_pair(num, I));
+    
+    if (!BI->isConditional() || isa<Constant>(BI->getCondition()))
+      return false;
+    
+    Value* branchCond = BI->getCondition();
+    uint32_t condVN = VN.lookup_or_add(branchCond);
+    
+    BasicBlock* trueSucc = BI->getSuccessor(0);
+    BasicBlock* falseSucc = BI->getSuccessor(1);
+    
+    if (trueSucc->getSinglePredecessor())
+      localAvail[trueSucc]->table[condVN] = ConstantInt::getTrue();
+    if (falseSucc->getSinglePredecessor())
+      localAvail[falseSucc]->table[condVN] = ConstantInt::getFalse();
+
+    return false;
+    
+  // Allocations are always uniquely numbered, so we can save time and memory
+  // by fast failing them.  
+  } else if (isa<AllocationInst>(I) || isa<TerminatorInst>(I)) {
+    localAvail[I->getParent()]->table.insert(std::make_pair(num, I));
+    return false;
+  }
+  
+  // Collapse PHI nodes
+  if (PHINode* p = dyn_cast<PHINode>(I)) {
+    Value* constVal = CollapsePhi(p);
+    
+    if (constVal) {
+      for (PhiMapType::iterator PI = phiMap.begin(), PE = phiMap.end();
+           PI != PE; ++PI)
+        PI->second.erase(p);
+        
+      p->replaceAllUsesWith(constVal);
+      if (isa<PointerType>(constVal->getType()))
+        MD->invalidateCachedPointerInfo(constVal);
+      VN.erase(p);
+      
+      toErase.push_back(p);
+    } else {
+      localAvail[I->getParent()]->table.insert(std::make_pair(num, I));
+    }
+  
+  // If the number we were assigned was a brand new VN, then we don't
+  // need to do a lookup to see if the number already exists
+  // somewhere in the domtree: it can't!
+  } else if (num == nextNum) {
+    localAvail[I->getParent()]->table.insert(std::make_pair(num, I));
+    
+  // Perform fast-path value-number based elimination of values inherited from
+  // dominators.
+  } else if (Value* repl = lookupNumber(I->getParent(), num)) {
+    // Remove it!
+    VN.erase(I);
+    I->replaceAllUsesWith(repl);
+    if (isa<PointerType>(repl->getType()))
+      MD->invalidateCachedPointerInfo(repl);
+    toErase.push_back(I);
+    return true;
+
+#if 0
+  // Perform slow-pathvalue-number based elimination with phi construction.
+  } else if (Value* repl = AttemptRedundancyElimination(I, num)) {
+    // Remove it!
+    VN.erase(I);
+    I->replaceAllUsesWith(repl);
+    if (isa<PointerType>(repl->getType()))
+      MD->invalidateCachedPointerInfo(repl);
+    toErase.push_back(I);
+    return true;
+#endif
+  } else {
+    localAvail[I->getParent()]->table.insert(std::make_pair(num, I));
+  }
+  
+  return false;
+}
+
+/// runOnFunction - This is the main transformation entry point for a function.
+bool GVN::runOnFunction(Function& F) {
+  MD = &getAnalysis<MemoryDependenceAnalysis>();
+  DT = &getAnalysis<DominatorTree>();
+  VN.setAliasAnalysis(&getAnalysis<AliasAnalysis>());
+  VN.setMemDep(MD);
+  VN.setDomTree(DT);
+  
+  bool changed = false;
+  bool shouldContinue = true;
+  
+  // Merge unconditional branches, allowing PRE to catch more
+  // optimization opportunities.
+  for (Function::iterator FI = F.begin(), FE = F.end(); FI != FE; ) {
+    BasicBlock* BB = FI;
+    ++FI;
+    bool removedBlock = MergeBlockIntoPredecessor(BB, this);
+    if (removedBlock) NumGVNBlocks++;
+    
+    changed |= removedBlock;
+  }
+  
+  unsigned Iteration = 0;
+  
+  while (shouldContinue) {
+    DEBUG(cerr << "GVN iteration: " << Iteration << "\n");
+    shouldContinue = iterateOnFunction(F);
+    changed |= shouldContinue;
+    ++Iteration;
+  }
+  
+  if (EnablePRE) {
+    bool PREChanged = true;
+    while (PREChanged) {
+      PREChanged = performPRE(F);
+      changed |= PREChanged;
+    }
+  }
+  // FIXME: Should perform GVN again after PRE does something.  PRE can move
+  // computations into blocks where they become fully redundant.  Note that
+  // we can't do this until PRE's critical edge splitting updates memdep.
+  // Actually, when this happens, we should just fully integrate PRE into GVN.
+
+  cleanupGlobalSets();
+
+  return changed;
+}
+
+
+bool GVN::processBlock(BasicBlock* BB) {
+  // FIXME: Kill off toErase by doing erasing eagerly in a helper function (and
+  // incrementing BI before processing an instruction).
+  SmallVector<Instruction*, 8> toErase;
+  bool changed_function = false;
+  
+  for (BasicBlock::iterator BI = BB->begin(), BE = BB->end();
+       BI != BE;) {
+    changed_function |= processInstruction(BI, toErase);
+    if (toErase.empty()) {
+      ++BI;
+      continue;
+    }
+    
+    // If we need some instructions deleted, do it now.
+    NumGVNInstr += toErase.size();
+    
+    // Avoid iterator invalidation.
+    bool AtStart = BI == BB->begin();
+    if (!AtStart)
+      --BI;
+
+    for (SmallVector<Instruction*, 4>::iterator I = toErase.begin(),
+         E = toErase.end(); I != E; ++I) {
+      DEBUG(cerr << "GVN removed: " << **I);
+      MD->removeInstruction(*I);
+      (*I)->eraseFromParent();
+      DEBUG(verifyRemoved(*I));
+    }
+    toErase.clear();
+
+    if (AtStart)
+      BI = BB->begin();
+    else
+      ++BI;
+  }
+  
+  return changed_function;
+}
+
+/// performPRE - Perform a purely local form of PRE that looks for diamond
+/// control flow patterns and attempts to perform simple PRE at the join point.
+bool GVN::performPRE(Function& F) {
+  bool Changed = false;
+  SmallVector<std::pair<TerminatorInst*, unsigned>, 4> toSplit;
+  DenseMap<BasicBlock*, Value*> predMap;
+  for (df_iterator<BasicBlock*> DI = df_begin(&F.getEntryBlock()),
+       DE = df_end(&F.getEntryBlock()); DI != DE; ++DI) {
+    BasicBlock* CurrentBlock = *DI;
+    
+    // Nothing to PRE in the entry block.
+    if (CurrentBlock == &F.getEntryBlock()) continue;
+    
+    for (BasicBlock::iterator BI = CurrentBlock->begin(),
+         BE = CurrentBlock->end(); BI != BE; ) {
+      Instruction *CurInst = BI++;
+
+      if (isa<AllocationInst>(CurInst) || isa<TerminatorInst>(CurInst) ||
+          isa<PHINode>(CurInst) || (CurInst->getType() == Type::VoidTy) ||
+          CurInst->mayReadFromMemory() || CurInst->mayHaveSideEffects() ||
+          isa<DbgInfoIntrinsic>(CurInst))
+        continue;
+
+      uint32_t valno = VN.lookup(CurInst);
+      
+      // Look for the predecessors for PRE opportunities.  We're
+      // only trying to solve the basic diamond case, where
+      // a value is computed in the successor and one predecessor,
+      // but not the other.  We also explicitly disallow cases
+      // where the successor is its own predecessor, because they're
+      // more complicated to get right.
+      unsigned numWith = 0;
+      unsigned numWithout = 0;
+      BasicBlock* PREPred = 0;
+      predMap.clear();
+
+      for (pred_iterator PI = pred_begin(CurrentBlock),
+           PE = pred_end(CurrentBlock); PI != PE; ++PI) {
+        // We're not interested in PRE where the block is its
+        // own predecessor, on in blocks with predecessors
+        // that are not reachable.
+        if (*PI == CurrentBlock) {
+          numWithout = 2;
+          break;
+        } else if (!localAvail.count(*PI))  {
+          numWithout = 2;
+          break;
+        }
+        
+        DenseMap<uint32_t, Value*>::iterator predV = 
+                                            localAvail[*PI]->table.find(valno);
+        if (predV == localAvail[*PI]->table.end()) {
+          PREPred = *PI;
+          numWithout++;
+        } else if (predV->second == CurInst) {
+          numWithout = 2;
+        } else {
+          predMap[*PI] = predV->second;
+          numWith++;
+        }
+      }
+      
+      // Don't do PRE when it might increase code size, i.e. when
+      // we would need to insert instructions in more than one pred.
+      if (numWithout != 1 || numWith == 0)
+        continue;
+      
+      // We can't do PRE safely on a critical edge, so instead we schedule
+      // the edge to be split and perform the PRE the next time we iterate
+      // on the function.
+      unsigned succNum = 0;
+      for (unsigned i = 0, e = PREPred->getTerminator()->getNumSuccessors();
+           i != e; ++i)
+        if (PREPred->getTerminator()->getSuccessor(i) == CurrentBlock) {
+          succNum = i;
+          break;
+        }
+        
+      if (isCriticalEdge(PREPred->getTerminator(), succNum)) {
+        toSplit.push_back(std::make_pair(PREPred->getTerminator(), succNum));
+        continue;
+      }
+      
+      // Instantiate the expression the in predecessor that lacked it.
+      // Because we are going top-down through the block, all value numbers
+      // will be available in the predecessor by the time we need them.  Any
+      // that weren't original present will have been instantiated earlier
+      // in this loop.
+      Instruction* PREInstr = CurInst->clone();
+      bool success = true;
+      for (unsigned i = 0, e = CurInst->getNumOperands(); i != e; ++i) {
+        Value *Op = PREInstr->getOperand(i);
+        if (isa<Argument>(Op) || isa<Constant>(Op) || isa<GlobalValue>(Op))
+          continue;
+        
+        if (Value *V = lookupNumber(PREPred, VN.lookup(Op))) {
+          PREInstr->setOperand(i, V);
+        } else {
+          success = false;
+          break;
+        }
+      }
+      
+      // Fail out if we encounter an operand that is not available in
+      // the PRE predecessor.  This is typically because of loads which 
+      // are not value numbered precisely.
+      if (!success) {
+        delete PREInstr;
+        DEBUG(verifyRemoved(PREInstr));
+        continue;
+      }
+      
+      PREInstr->insertBefore(PREPred->getTerminator());
+      PREInstr->setName(CurInst->getName() + ".pre");
+      predMap[PREPred] = PREInstr;
+      VN.add(PREInstr, valno);
+      NumGVNPRE++;
+      
+      // Update the availability map to include the new instruction.
+      localAvail[PREPred]->table.insert(std::make_pair(valno, PREInstr));
+      
+      // Create a PHI to make the value available in this block.
+      PHINode* Phi = PHINode::Create(CurInst->getType(),
+                                     CurInst->getName() + ".pre-phi",
+                                     CurrentBlock->begin());
+      for (pred_iterator PI = pred_begin(CurrentBlock),
+           PE = pred_end(CurrentBlock); PI != PE; ++PI)
+        Phi->addIncoming(predMap[*PI], *PI);
+      
+      VN.add(Phi, valno);
+      localAvail[CurrentBlock]->table[valno] = Phi;
+      
+      CurInst->replaceAllUsesWith(Phi);
+      if (isa<PointerType>(Phi->getType()))
+        MD->invalidateCachedPointerInfo(Phi);
+      VN.erase(CurInst);
+      
+      DEBUG(cerr << "GVN PRE removed: " << *CurInst);
+      MD->removeInstruction(CurInst);
+      CurInst->eraseFromParent();
+      DEBUG(verifyRemoved(CurInst));
+      Changed = true;
+    }
+  }
+  
+  for (SmallVector<std::pair<TerminatorInst*, unsigned>, 4>::iterator
+       I = toSplit.begin(), E = toSplit.end(); I != E; ++I)
+    SplitCriticalEdge(I->first, I->second, this);
+  
+  return Changed || toSplit.size();
+}
+
+/// iterateOnFunction - Executes one iteration of GVN
+bool GVN::iterateOnFunction(Function &F) {
+  cleanupGlobalSets();
+
+  for (df_iterator<DomTreeNode*> DI = df_begin(DT->getRootNode()),
+       DE = df_end(DT->getRootNode()); DI != DE; ++DI) {
+    if (DI->getIDom())
+      localAvail[DI->getBlock()] =
+                   new ValueNumberScope(localAvail[DI->getIDom()->getBlock()]);
+    else
+      localAvail[DI->getBlock()] = new ValueNumberScope(0);
+  }
+
+  // Top-down walk of the dominator tree
+  bool changed = false;
+#if 0
+  // Needed for value numbering with phi construction to work.
+  ReversePostOrderTraversal<Function*> RPOT(&F);
+  for (ReversePostOrderTraversal<Function*>::rpo_iterator RI = RPOT.begin(),
+       RE = RPOT.end(); RI != RE; ++RI)
+    changed |= processBlock(*RI);
+#else
+  for (df_iterator<DomTreeNode*> DI = df_begin(DT->getRootNode()),
+       DE = df_end(DT->getRootNode()); DI != DE; ++DI)
+    changed |= processBlock(DI->getBlock());
+#endif
+
+  return changed;
+}
+
+void GVN::cleanupGlobalSets() {
+  VN.clear();
+  phiMap.clear();
+
+  for (DenseMap<BasicBlock*, ValueNumberScope*>::iterator
+       I = localAvail.begin(), E = localAvail.end(); I != E; ++I)
+    delete I->second;
+  localAvail.clear();
+}
+
+/// verifyRemoved - Verify that the specified instruction does not occur in our
+/// internal data structures.
+void GVN::verifyRemoved(const Instruction *Inst) const {
+  VN.verifyRemoved(Inst);
+
+  // Walk through the PHI map to make sure the instruction isn't hiding in there
+  // somewhere.
+  for (PhiMapType::iterator
+         I = phiMap.begin(), E = phiMap.end(); I != E; ++I) {
+    assert(I->first != Inst && "Inst is still a key in PHI map!");
+
+    for (SmallPtrSet<Instruction*, 4>::iterator
+           II = I->second.begin(), IE = I->second.end(); II != IE; ++II) {
+      assert(*II != Inst && "Inst is still a value in PHI map!");
+    }
+  }
+
+  // Walk through the value number scope to make sure the instruction isn't
+  // ferreted away in it.
+  for (DenseMap<BasicBlock*, ValueNumberScope*>::iterator
+         I = localAvail.begin(), E = localAvail.end(); I != E; ++I) {
+    const ValueNumberScope *VNS = I->second;
+
+    while (VNS) {
+      for (DenseMap<uint32_t, Value*>::iterator
+             II = VNS->table.begin(), IE = VNS->table.end(); II != IE; ++II) {
+        assert(II->second != Inst && "Inst still in value numbering scope!");
+      }
+
+      VNS = VNS->parent;
+    }
+  }
+}