Add a GVN pass, using the value numbering code I developed for GVNPRE and the

load elimination code from RedundantLoadElimination.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@40469 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 816 insertions, 0 deletions

diff --git a/lib/Transforms/Scalar/GVN.cpp b/lib/Transforms/Scalar/GVN.cpp
new file mode 100644
index 0000000..555a9f3
--- /dev/null
+++ b/lib/Transforms/Scalar/GVN.cpp
@@ -0,0 +1,816 @@
+//===- GVN.cpp - Eliminate redundant values and loads ------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file was developed by the Owen Anderson and 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.
+//
+//===----------------------------------------------------------------------===//
+
+#define DEBUG_TYPE "gvn"
+#include "llvm/Value.h"
+#include "llvm/Transforms/Scalar.h"
+#include "llvm/Instructions.h"
+#include "llvm/Function.h"
+#include "llvm/DerivedTypes.h"
+#include "llvm/Analysis/Dominators.h"
+#include "llvm/ADT/BitVector.h"
+#include "llvm/ADT/DenseMap.h"
+#include "llvm/ADT/DepthFirstIterator.h"
+#include "llvm/ADT/SmallPtrSet.h"
+#include "llvm/ADT/SmallVector.h"
+#include "llvm/ADT/Statistic.h"
+#include "llvm/Analysis/MemoryDependenceAnalysis.h"
+#include "llvm/Support/CFG.h"
+#include "llvm/Support/Compiler.h"
+using namespace llvm;
+
+//===----------------------------------------------------------------------===//
+//                         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, EMPTY,
+                            TOMBSTONE };
+
+    ExpressionOpcode opcode;
+    const Type* type;
+    uint32_t firstVN;
+    uint32_t secondVN;
+    uint32_t thirdVN;
+    SmallVector<uint32_t, 4> varargs;
+  
+    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 (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 {
+      if (opcode != other.opcode)
+        return true;
+      else if (opcode == EMPTY || opcode == TOMBSTONE)
+        return false;
+      else if (type != other.type)
+        return true;
+      else if (firstVN != other.firstVN)
+        return true;
+      else if (secondVN != other.secondVN)
+        return true;
+      else if (thirdVN != other.thirdVN)
+        return true;
+      else {
+        if (varargs.size() != other.varargs.size())
+          return true;
+      
+        for (size_t i = 0; i < varargs.size(); ++i)
+          if (varargs[i] != other.varargs[i])
+            return true;
+    
+          return false;
+      }
+    }
+  };
+  
+  class VISIBILITY_HIDDEN ValueTable {
+    private:
+      DenseMap<Value*, uint32_t> valueNumbering;
+      DenseMap<Expression, uint32_t> expressionNumbering;
+  
+      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);
+    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();
+  };
+}
+
+namespace llvm {
+template <> struct DenseMapKeyInfo<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;
+    
+    return hash;
+  }
+  static bool isPod() { return true; }
+};
+}
+
+//===----------------------------------------------------------------------===//
+//                     ValueTable Internal Functions
+//===----------------------------------------------------------------------===//
+Expression::ExpressionOpcode 
+                             ValueTable::getOpcode(BinaryOperator* BO) {
+  switch(BO->getOpcode()) {
+    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;
+    
+    // THIS SHOULD NEVER HAPPEN
+    default:
+      assert(0 && "Binary operator with unknown opcode?");
+      return Expression::ADD;
+  }
+}
+
+Expression::ExpressionOpcode ValueTable::getOpcode(CmpInst* C) {
+  if (C->getOpcode() == Instruction::ICmp) {
+    switch (C->getPredicate()) {
+      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;
+      
+      // THIS SHOULD NEVER HAPPEN
+      default:
+        assert(0 && "Comparison with unknown predicate?");
+        return Expression::ICMPEQ;
+    }
+  } else {
+    switch (C->getPredicate()) {
+      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;
+      
+      // THIS SHOULD NEVER HAPPEN
+      default:
+        assert(0 && "Comparison with unknown predicate?");
+        return Expression::FCMPOEQ;
+    }
+  }
+}
+
+Expression::ExpressionOpcode 
+                             ValueTable::getOpcode(CastInst* C) {
+  switch(C->getOpcode()) {
+    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;
+    
+    // THIS SHOULD NEVER HAPPEN
+    default:
+      assert(0 && "Cast operator with unknown opcode?");
+      return Expression::BITCAST;
+  }
+}
+
+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.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.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.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.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.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.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.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.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
+//===----------------------------------------------------------------------===//
+
+/// 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 (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);
+  if (VI != valueNumbering.end())
+    return VI->second;
+  else
+    assert(0 && "Value not numbered?");
+  
+  return 0;
+}
+
+/// clear - Remove all entries from the ValueTable
+void ValueTable::clear() {
+  valueNumbering.clear();
+  expressionNumbering.clear();
+  nextValueNumber = 1;
+}
+
+//===----------------------------------------------------------------------===//
+//                       ValueNumberedSet Class
+//===----------------------------------------------------------------------===//
+namespace {
+class ValueNumberedSet {
+  private:
+    SmallPtrSet<Value*, 8> contents;
+    BitVector numbers;
+  public:
+    ValueNumberedSet() { numbers.resize(1); }
+    ValueNumberedSet(const ValueNumberedSet& other) {
+      numbers = other.numbers;
+      contents = other.contents;
+    }
+    
+    typedef SmallPtrSet<Value*, 8>::iterator iterator;
+    
+    iterator begin() { return contents.begin(); }
+    iterator end() { return contents.end(); }
+    
+    bool insert(Value* v) { return contents.insert(v); }
+    void insert(iterator I, iterator E) { contents.insert(I, E); }
+    void erase(Value* v) { contents.erase(v); }
+    unsigned count(Value* v) { return contents.count(v); }
+    size_t size() { return contents.size(); }
+    
+    void set(unsigned i)  {
+      if (i >= numbers.size())
+        numbers.resize(i+1);
+      
+      numbers.set(i);
+    }
+    
+    void operator=(const ValueNumberedSet& other) {
+      contents = other.contents;
+      numbers = other.numbers;
+    }
+    
+    void reset(unsigned i)  {
+      if (i < numbers.size())
+        numbers.reset(i);
+    }
+    
+    bool test(unsigned i)  {
+      if (i >= numbers.size())
+        return false;
+      
+      return numbers.test(i);
+    }
+    
+    void clear() {
+      contents.clear();
+      numbers.clear();
+    }
+};
+}
+
+//===----------------------------------------------------------------------===//
+//                         GVN Pass
+//===----------------------------------------------------------------------===//
+
+namespace {
+
+  class VISIBILITY_HIDDEN GVN : public FunctionPass {
+    bool runOnFunction(Function &F);
+  public:
+    static char ID; // Pass identification, replacement for typeid
+    GVN() : FunctionPass((intptr_t)&ID) { }
+
+  private:
+    ValueTable VN;
+    
+    DenseMap<BasicBlock*, ValueNumberedSet> availableOut;
+    
+    // This transformation requires dominator postdominator info
+    virtual void getAnalysisUsage(AnalysisUsage &AU) const {
+      AU.setPreservesCFG();
+      AU.addRequired<DominatorTree>();
+      AU.addRequired<MemoryDependenceAnalysis>();
+      AU.addPreserved<MemoryDependenceAnalysis>();
+    }
+  
+    // Helper fuctions
+    // FIXME: eliminate or document these better
+    Value* find_leader(ValueNumberedSet& vals, uint32_t v) ;
+    void val_insert(ValueNumberedSet& s, Value* v);
+    bool processLoad(LoadInst* L,
+                     DenseMap<Value*, LoadInst*>& lastLoad,
+                     SmallVector<Instruction*, 4>& toErase);
+    bool processInstruction(Instruction* I,
+                            ValueNumberedSet& currAvail,
+                            DenseMap<Value*, LoadInst*>& lastSeenLoad,
+                            SmallVector<Instruction*, 4>& toErase);
+  };
+  
+  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");
+
+STATISTIC(NumGVNInstr, "Number of instructions deleted");
+STATISTIC(NumGVNLoad, "Number of loads deleted");
+
+/// find_leader - Given a set and a value number, return the first
+/// element of the set with that value number, or 0 if no such element
+/// is present
+Value* GVN::find_leader(ValueNumberedSet& vals, uint32_t v) {
+  if (!vals.test(v))
+    return 0;
+  
+  for (ValueNumberedSet::iterator I = vals.begin(), E = vals.end();
+       I != E; ++I)
+    if (v == VN.lookup(*I))
+      return *I;
+  
+  assert(0 && "No leader found, but present bit is set?");
+  return 0;
+}
+
+/// val_insert - Insert a value into a set only if there is not a value
+/// with the same value number already in the set
+void GVN::val_insert(ValueNumberedSet& s, Value* v) {
+  uint32_t num = VN.lookup(v);
+  if (!s.test(num))
+    s.insert(v);
+}
+
+bool GVN::processLoad(LoadInst* L,
+                         DenseMap<Value*, LoadInst*>& lastLoad,
+                         SmallVector<Instruction*, 4>& toErase) {
+  if (L->isVolatile()) {
+    lastLoad[L->getPointerOperand()] = L;
+    return false;
+  }
+  
+  Value* pointer = L->getPointerOperand();
+  LoadInst*& last = lastLoad[pointer];
+  
+  // ... to a pointer that has been loaded from before...
+  MemoryDependenceAnalysis& MD = getAnalysis<MemoryDependenceAnalysis>();
+  Instruction* dep = MD.getDependency(L);
+  bool deletedLoad = false;
+  
+  while (dep != MemoryDependenceAnalysis::None &&
+         dep != MemoryDependenceAnalysis::NonLocal &&
+         (isa<LoadInst>(dep) || isa<StoreInst>(dep))) {
+    // ... that depends on a store ...
+    if (StoreInst* S = dyn_cast<StoreInst>(dep)) {
+      if (S->getPointerOperand() == pointer) {
+        // Remove it!
+        MD.removeInstruction(L);
+        
+        L->replaceAllUsesWith(S->getOperand(0));
+        toErase.push_back(L);
+        deletedLoad = true;
+        NumGVNLoad++;
+      }
+      
+      // Whether we removed it or not, we can't
+      // go any further
+      break;
+    } else if (!last) {
+      // If we don't depend on a store, and we haven't
+      // been loaded before, bail.
+      break;
+    } else if (dep == last) {
+      // Remove it!
+      MD.removeInstruction(L);
+      
+      L->replaceAllUsesWith(last);
+      toErase.push_back(L);
+      deletedLoad = true;
+      NumGVNLoad++;
+        
+      break;
+    } else {
+      dep = MD.getDependency(L, dep);
+    }
+  }
+  
+  if (!deletedLoad)
+    last = L;
+  
+  return deletedLoad;
+}
+
+/// buildsets_availout - When calculating availability, handle an instruction
+/// by inserting it into the appropriate sets
+bool GVN::processInstruction(Instruction* I,
+                                ValueNumberedSet& currAvail,
+                                DenseMap<Value*, LoadInst*>& lastSeenLoad,
+                                SmallVector<Instruction*, 4>& toErase) {
+  if (LoadInst* L = dyn_cast<LoadInst>(I)) {
+    return processLoad(L, lastSeenLoad, toErase);
+  }
+  
+  unsigned num = VN.lookup_or_add(I);
+  
+  if (currAvail.test(num)) {
+    Value* repl = find_leader(currAvail, num);
+    
+    I->replaceAllUsesWith(repl);
+    toErase.push_back(I);
+    return true;
+  } else if (!I->isTerminator()) {
+    currAvail.set(num);
+    currAvail.insert(I);
+  }
+  
+  return false;
+}
+
+// GVN::runOnFunction - This is the main transformation entry point for a
+// function.
+//
+bool GVN::runOnFunction(Function &F) {
+  // Clean out global sets from any previous functions
+  VN.clear();
+  availableOut.clear();
+ 
+  bool changed_function = false;
+  
+  DominatorTree &DT = getAnalysis<DominatorTree>();   
+  
+  SmallVector<Instruction*, 4> toErase;
+  
+  // Top-down walk of the dominator tree
+  for (df_iterator<DomTreeNode*> DI = df_begin(DT.getRootNode()),
+         E = df_end(DT.getRootNode()); DI != E; ++DI) {
+    
+    // Get the set to update for this block
+    ValueNumberedSet& currAvail = availableOut[DI->getBlock()];     
+    DenseMap<Value*, LoadInst*> lastSeenLoad;
+    
+    BasicBlock* BB = DI->getBlock();
+  
+    // A block inherits AVAIL_OUT from its dominator
+    if (DI->getIDom() != 0)
+      currAvail = availableOut[DI->getIDom()->getBlock()];
+
+    for (BasicBlock::iterator BI = BB->begin(), BE = BB->end();
+         BI != BE; ++BI) {
+      processInstruction(BI, currAvail, lastSeenLoad, toErase);
+    }
+  }
+  
+  NumGVNInstr = toErase.size();
+  
+  for (SmallVector<Instruction*, 4>::iterator I = toErase.begin(),
+       E = toErase.end(); I != E; ++I)
+    (*I)->eraseFromParent();
+  
+  return changed_function;
+}