GVN.cpp

//===- 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/GlobalVariable.h"
#include "llvm/Function.h"
#include "llvm/IntrinsicInst.h"
#include "llvm/LLVMContext.h"
#include "llvm/Operator.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/AliasAnalysis.h"
#include "llvm/Analysis/ConstantFolding.h"
#include "llvm/Analysis/Dominators.h"
#include "llvm/Analysis/MemoryBuiltins.h"
#include "llvm/Analysis/MemoryDependenceAnalysis.h"
#include "llvm/Analysis/PHITransAddr.h"
#include "llvm/Support/CFG.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/GetElementPtrTypeIterator.h"
#include "llvm/Support/IRBuilder.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/Target/TargetData.h"
#include "llvm/Transforms/Utils/BasicBlockUtils.h"
#include "llvm/Transforms/Utils/Local.h"
#include "llvm/Transforms/Utils/SSAUpdater.h"
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);
static cl::opt<bool> EnableLoadPRE("enable-load-pre", cl::init(true));
static cl::opt<bool> EnableFullLoadPRE("enable-full-load-pre", cl::init(false));

//===----------------------------------------------------------------------===//
//                         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 Expression {
    enum ExpressionOpcode { 
      ADD = Instruction::Add,
      FADD = Instruction::FAdd,
      SUB = Instruction::Sub,
      FSUB = Instruction::FSub,
      MUL = Instruction::Mul,
      FMUL = Instruction::FMul,
      UDIV = Instruction::UDiv,
      SDIV = Instruction::SDiv,
      FDIV = Instruction::FDiv,
      UREM = Instruction::URem,
      SREM = Instruction::SRem,
      FREM = Instruction::FRem,
      SHL = Instruction::Shl,
      LSHR = Instruction::LShr,
      ASHR = Instruction::AShr,
      AND = Instruction::And,
      OR = Instruction::Or,
      XOR = Instruction::Xor,
      TRUNC = Instruction::Trunc,
      ZEXT = Instruction::ZExt,
      SEXT = Instruction::SExt,
      FPTOUI = Instruction::FPToUI,
      FPTOSI = Instruction::FPToSI,
      UITOFP = Instruction::UIToFP,
      SITOFP = Instruction::SIToFP,
      FPTRUNC = Instruction::FPTrunc,
      FPEXT = Instruction::FPExt,
      PTRTOINT = Instruction::PtrToInt,
      INTTOPTR = Instruction::IntToPtr,
      BITCAST = Instruction::BitCast,
      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, GEP, CALL, CONSTANT,
      INSERTVALUE, EXTRACTVALUE, EMPTY, TOMBSTONE };

    ExpressionOpcode opcode;
    const Type* type;
    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 (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 ValueTable {
    private:
      DenseMap<Value*, uint32_t> valueNumbering;
      DenseMap<Expression, uint32_t> expressionNumbering;
      AliasAnalysis* AA;
      MemoryDependenceAnalysis* MD;
      DominatorTree* DT;

      uint32_t nextValueNumber;

      Expression::ExpressionOpcode getOpcode(CmpInst* 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);
      Expression create_expression(ExtractValueInst* C);
      Expression create_expression(InsertValueInst* C);
      
      uint32_t lookup_or_add_call(CallInst* 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 = ((unsigned)((uintptr_t)e.type >> 4) ^
            (unsigned)((uintptr_t)e.type >> 9));

    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;
  }
};
  
template <>
struct isPodLike<Expression> { static const bool value = true; };

}

//===----------------------------------------------------------------------===//
//                     ValueTable Internal Functions
//===----------------------------------------------------------------------===//

Expression::ExpressionOpcode ValueTable::getOpcode(CmpInst* C) {
  if (isa<ICmpInst>(C)) {
    switch (C->getPredicate()) {
    default:  // THIS SHOULD NEVER HAPPEN
      llvm_unreachable("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;
    }
  } else {
    switch (C->getPredicate()) {
    default: // THIS SHOULD NEVER HAPPEN
      llvm_unreachable("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 ValueTable::create_expression(CallInst* C) {
  Expression e;

  e.type = C->getType();
  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.varargs.push_back(lookup_or_add(BO->getOperand(0)));
  e.varargs.push_back(lookup_or_add(BO->getOperand(1)));
  e.function = 0;
  e.type = BO->getType();
  e.opcode = static_cast<Expression::ExpressionOpcode>(BO->getOpcode());

  return e;
}

Expression ValueTable::create_expression(CmpInst* C) {
  Expression e;

  e.varargs.push_back(lookup_or_add(C->getOperand(0)));
  e.varargs.push_back(lookup_or_add(C->getOperand(1)));
  e.function = 0;
  e.type = C->getType();
  e.opcode = getOpcode(C);

  return e;
}

Expression ValueTable::create_expression(CastInst* C) {
  Expression e;

  e.varargs.push_back(lookup_or_add(C->getOperand(0)));
  e.function = 0;
  e.type = C->getType();
  e.opcode = static_cast<Expression::ExpressionOpcode>(C->getOpcode());

  return e;
}

Expression ValueTable::create_expression(ShuffleVectorInst* S) {
  Expression e;

  e.varargs.push_back(lookup_or_add(S->getOperand(0)));
  e.varargs.push_back(lookup_or_add(S->getOperand(1)));
  e.varargs.push_back(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.varargs.push_back(lookup_or_add(E->getOperand(0)));
  e.varargs.push_back(lookup_or_add(E->getOperand(1)));
  e.function = 0;
  e.type = E->getType();
  e.opcode = Expression::EXTRACT;

  return e;
}

Expression ValueTable::create_expression(InsertElementInst* I) {
  Expression e;

  e.varargs.push_back(lookup_or_add(I->getOperand(0)));
  e.varargs.push_back(lookup_or_add(I->getOperand(1)));
  e.varargs.push_back(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.varargs.push_back(lookup_or_add(I->getCondition()));
  e.varargs.push_back(lookup_or_add(I->getTrueValue()));
  e.varargs.push_back(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.varargs.push_back(lookup_or_add(G->getPointerOperand()));
  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;
}

Expression ValueTable::create_expression(ExtractValueInst* E) {
  Expression e;

  e.varargs.push_back(lookup_or_add(E->getAggregateOperand()));
  for (ExtractValueInst::idx_iterator II = E->idx_begin(), IE = E->idx_end();
       II != IE; ++II)
    e.varargs.push_back(*II);
  e.function = 0;
  e.type = E->getType();
  e.opcode = Expression::EXTRACTVALUE;

  return e;
}

Expression ValueTable::create_expression(InsertValueInst* E) {
  Expression e;

  e.varargs.push_back(lookup_or_add(E->getAggregateOperand()));
  e.varargs.push_back(lookup_or_add(E->getInsertedValueOperand()));
  for (InsertValueInst::idx_iterator II = E->idx_begin(), IE = E->idx_end();
       II != IE; ++II)
    e.varargs.push_back(*II);
  e.function = 0;
  e.type = E->getType();
  e.opcode = Expression::INSERTVALUE;

  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));
}

uint32_t ValueTable::lookup_or_add_call(CallInst* C) {
  if (AA->doesNotAccessMemory(C)) {
    Expression exp = create_expression(C);
    uint32_t& e = expressionNumbering[exp];
    if (!e) e = nextValueNumber++;
    valueNumbering[C] = e;
    return e;
  } else if (AA->onlyReadsMemory(C)) {
    Expression exp = create_expression(C);
    uint32_t& e = expressionNumbering[exp];
    if (!e) {
      e = nextValueNumber++;
      valueNumbering[C] = e;
      return e;
    }
    if (!MD) {
      e = nextValueNumber++;
      valueNumbering[C] = e;
      return e;
    }

    MemDepResult local_dep = MD->getDependency(C);

    if (!local_dep.isDef() && !local_dep.isNonLocal()) {
      valueNumbering[C] =  nextValueNumber;
      return nextValueNumber++;
    }

    if (local_dep.isDef()) {
      CallInst* local_cdep = cast<CallInst>(local_dep.getInst());

      if (local_cdep->getNumOperands() != C->getNumOperands()) {
        valueNumbering[C] = 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[C] = nextValueNumber;
          return nextValueNumber++;
        }
      }

      uint32_t v = lookup_or_add(local_cdep);
      valueNumbering[C] = 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 NonLocalDepEntry *I = &deps[i];
      // Ignore non-local dependencies.
      if (I->getResult().isNonLocal())
        continue;

      // We don't handle non-depedencies.  If we already have a call, reject
      // instruction dependencies.
      if (I->getResult().isClobber() || cdep != 0) {
        cdep = 0;
        break;
      }

      CallInst *NonLocalDepCall = dyn_cast<CallInst>(I->getResult().getInst());
      // FIXME: All duplicated with non-local case.
      if (NonLocalDepCall && DT->properlyDominates(I->getBB(), C->getParent())){
        cdep = NonLocalDepCall;
        continue;
      }

      cdep = 0;
      break;
    }

    if (!cdep) {
      valueNumbering[C] = nextValueNumber;
      return nextValueNumber++;
    }

    if (cdep->getNumOperands() != C->getNumOperands()) {
      valueNumbering[C] = 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[C] = nextValueNumber;
        return nextValueNumber++;
      }
    }

    uint32_t v = lookup_or_add(cdep);
    valueNumbering[C] = v;
    return v;

  } else {
    valueNumbering[C] = nextValueNumber;
    return nextValueNumber++;
  }
}

/// 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 (!isa<Instruction>(V)) {
    valueNumbering[V] = nextValueNumber;
    return nextValueNumber++;
  }
  
  Instruction* I = cast<Instruction>(V);
  Expression exp;
  switch (I->getOpcode()) {
    case Instruction::Call:
      return lookup_or_add_call(cast<CallInst>(I));
    case Instruction::Add:
    case Instruction::FAdd:
    case Instruction::Sub:
    case Instruction::FSub:
    case Instruction::Mul:
    case Instruction::FMul:
    case Instruction::UDiv:
    case Instruction::SDiv:
    case Instruction::FDiv:
    case Instruction::URem:
    case Instruction::SRem:
    case Instruction::FRem:
    case Instruction::Shl:
    case Instruction::LShr:
    case Instruction::AShr:
    case Instruction::And:
    case Instruction::Or :
    case Instruction::Xor:
      exp = create_expression(cast<BinaryOperator>(I));
      break;
    case Instruction::ICmp:
    case Instruction::FCmp:
      exp = create_expression(cast<CmpInst>(I));
      break;
    case Instruction::Trunc:
    case Instruction::ZExt:
    case Instruction::SExt:
    case Instruction::FPToUI:
    case Instruction::FPToSI:
    case Instruction::UIToFP:
    case Instruction::SIToFP:
    case Instruction::FPTrunc:
    case Instruction::FPExt:
    case Instruction::PtrToInt:
    case Instruction::IntToPtr:
    case Instruction::BitCast:
      exp = create_expression(cast<CastInst>(I));
      break;
    case Instruction::Select:
      exp = create_expression(cast<SelectInst>(I));
      break;
    case Instruction::ExtractElement:
      exp = create_expression(cast<ExtractElementInst>(I));
      break;
    case Instruction::InsertElement:
      exp = create_expression(cast<InsertElementInst>(I));
      break;
    case Instruction::ShuffleVector:
      exp = create_expression(cast<ShuffleVectorInst>(I));
      break;
    case Instruction::ExtractValue:
      exp = create_expression(cast<ExtractValueInst>(I));
      break;
    case Instruction::InsertValue:
      exp = create_expression(cast<InsertValueInst>(I));
      break;      
    case Instruction::GetElementPtr:
      exp = create_expression(cast<GetElementPtrInst>(I));
      break;
    default:
      valueNumbering[V] = nextValueNumber;
      return nextValueNumber++;
  }

  uint32_t& e = expressionNumbering[exp];
  if (!e) e = nextValueNumber++;
  valueNumbering[V] = e;
  return e;
}

/// 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>::const_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>::const_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 ValueNumberScope {
    ValueNumberScope* parent;
    DenseMap<uint32_t, Value*> table;

    ValueNumberScope(ValueNumberScope* p) : parent(p) { }
  };
}

namespace {

  class GVN : public FunctionPass {
    bool runOnFunction(Function &F);
  public:
    static char ID; // Pass identification, replacement for typeid
    explicit GVN(bool nopre = false, bool noloads = false)
      : FunctionPass(&ID), NoPRE(nopre), NoLoads(noloads), MD(0) { }

  private:
    bool NoPRE;
    bool NoLoads;
    MemoryDependenceAnalysis *MD;
    DominatorTree *DT;

    ValueTable VN;
    DenseMap<BasicBlock*, ValueNumberScope*> localAvail;

    // This transformation requires dominator postdominator info
    virtual void getAnalysisUsage(AnalysisUsage &AU) const {
      AU.addRequired<DominatorTree>();
      if (!NoLoads)
        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);
    void dump(DenseMap<uint32_t, Value*>& d);
    bool iterateOnFunction(Function &F);
    Value *CollapsePhi(PHINode* p);
    bool performPRE(Function& F);
    Value *lookupNumber(BasicBlock *BB, uint32_t num);
    void cleanupGlobalSets();
    void verifyRemoved(const Instruction *I) const;
  };

  char GVN::ID = 0;
}

// createGVNPass - The public interface to this file...
FunctionPass *llvm::createGVNPass(bool NoPRE, bool NoLoads) {
  return new GVN(NoPRE, NoLoads);
}

static RegisterPass<GVN> X("gvn",
                           "Global Value Numbering");

void GVN::dump(DenseMap<uint32_t, Value*>& d) {
  errs() << "{\n";
  for (DenseMap<uint32_t, Value*>::iterator I = d.begin(),
       E = d.end(); I != E; ++I) {
      errs() << I->first << "\n";
      I->second->dump();
  }
  errs() << "}\n";
}

static bool 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;
}

Value *GVN::CollapsePhi(PHINode *PN) {
  Value *ConstVal = PN->hasConstantValue(DT);
  if (!ConstVal) return 0;

  Instruction *Inst = dyn_cast<Instruction>(ConstVal);
  if (!Inst)
    return ConstVal;

  if (DT->dominates(Inst, PN))
    if (isSafeReplacement(PN, Inst))
      return Inst;
  return 0;
}

/// 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);

  do {
    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);
  } while (!BBWorklist.empty());

  return false;
}


/// CanCoerceMustAliasedValueToLoad - Return true if
/// CoerceAvailableValueToLoadType will succeed.
static bool CanCoerceMustAliasedValueToLoad(Value *StoredVal,
                                            const Type *LoadTy,
                                            const TargetData &TD) {
  // If the loaded or stored value is an first class array or struct, don't try
  // to transform them.  We need to be able to bitcast to integer.
  if (LoadTy->isStructTy() || LoadTy->isArrayTy() ||
      StoredVal->getType()->isStructTy() ||
      StoredVal->getType()->isArrayTy())
    return false;
  
  // The store has to be at least as big as the load.
  if (TD.getTypeSizeInBits(StoredVal->getType()) <
        TD.getTypeSizeInBits(LoadTy))
    return false;
  
  return true;
}
  

/// CoerceAvailableValueToLoadType - If we saw a store of a value to memory, and
/// then a load from a must-aliased pointer of a different type, try to coerce
/// the stored value.  LoadedTy is the type of the load we want to replace and
/// InsertPt is the place to insert new instructions.
///
/// If we can't do it, return null.
static Value *CoerceAvailableValueToLoadType(Value *StoredVal, 
                                             const Type *LoadedTy,
                                             Instruction *InsertPt,
                                             const TargetData &TD) {
  if (!CanCoerceMustAliasedValueToLoad(StoredVal, LoadedTy, TD))
    return 0;
  
  const Type *StoredValTy = StoredVal->getType();
  
  uint64_t StoreSize = TD.getTypeSizeInBits(StoredValTy);
  uint64_t LoadSize = TD.getTypeSizeInBits(LoadedTy);
  
  // If the store and reload are the same size, we can always reuse it.
  if (StoreSize == LoadSize) {
    if (StoredValTy->isPointerTy() && LoadedTy->isPointerTy()) {
      // Pointer to Pointer -> use bitcast.
      return new BitCastInst(StoredVal, LoadedTy, "", InsertPt);
    }
    
    // Convert source pointers to integers, which can be bitcast.
    if (StoredValTy->isPointerTy()) {
      StoredValTy = TD.getIntPtrType(StoredValTy->getContext());
      StoredVal = new PtrToIntInst(StoredVal, StoredValTy, "", InsertPt);
    }
    
    const Type *TypeToCastTo = LoadedTy;
    if (TypeToCastTo->isPointerTy())
      TypeToCastTo = TD.getIntPtrType(StoredValTy->getContext());
    
    if (StoredValTy != TypeToCastTo)
      StoredVal = new BitCastInst(StoredVal, TypeToCastTo, "", InsertPt);
    
    // Cast to pointer if the load needs a pointer type.
    if (LoadedTy->isPointerTy())
      StoredVal = new IntToPtrInst(StoredVal, LoadedTy, "", InsertPt);
    
    return StoredVal;
  }
  
  // If the loaded value is smaller than the available value, then we can
  // extract out a piece from it.  If the available value is too small, then we
  // can't do anything.
  assert(StoreSize >= LoadSize && "CanCoerceMustAliasedValueToLoad fail");
  
  // Convert source pointers to integers, which can be manipulated.
  if (StoredValTy->isPointerTy()) {
    StoredValTy = TD.getIntPtrType(StoredValTy->getContext());
    StoredVal = new PtrToIntInst(StoredVal, StoredValTy, "", InsertPt);
  }
  
  // Convert vectors and fp to integer, which can be manipulated.
  if (!StoredValTy->isIntegerTy()) {
    StoredValTy = IntegerType::get(StoredValTy->getContext(), StoreSize);
    StoredVal = new BitCastInst(StoredVal, StoredValTy, "", InsertPt);
  }
  
  // If this is a big-endian system, we need to shift the value down to the low
  // bits so that a truncate will work.
  if (TD.isBigEndian()) {
    Constant *Val = ConstantInt::get(StoredVal->getType(), StoreSize-LoadSize);
    StoredVal = BinaryOperator::CreateLShr(StoredVal, Val, "tmp", InsertPt);
  }
  
  // Truncate the integer to the right size now.
  const Type *NewIntTy = IntegerType::get(StoredValTy->getContext(), LoadSize);
  StoredVal = new TruncInst(StoredVal, NewIntTy, "trunc", InsertPt);
  
  if (LoadedTy == NewIntTy)
    return StoredVal;
  
  // If the result is a pointer, inttoptr.
  if (LoadedTy->isPointerTy())
    return new IntToPtrInst(StoredVal, LoadedTy, "inttoptr", InsertPt);
  
  // Otherwise, bitcast.
  return new BitCastInst(StoredVal, LoadedTy, "bitcast", InsertPt);
}

/// GetBaseWithConstantOffset - Analyze the specified pointer to see if it can
/// be expressed as a base pointer plus a constant offset.  Return the base and
/// offset to the caller.
static Value *GetBaseWithConstantOffset(Value *Ptr, int64_t &Offset,
                                        const TargetData &TD) {
  Operator *PtrOp = dyn_cast<Operator>(Ptr);
  if (PtrOp == 0) return Ptr;
  
  // Just look through bitcasts.
  if (PtrOp->getOpcode() == Instruction::BitCast)
    return GetBaseWithConstantOffset(PtrOp->getOperand(0), Offset, TD);
  
  // If this is a GEP with constant indices, we can look through it.
  GEPOperator *GEP = dyn_cast<GEPOperator>(PtrOp);
  if (GEP == 0 || !GEP->hasAllConstantIndices()) return Ptr;
  
  gep_type_iterator GTI = gep_type_begin(GEP);
  for (User::op_iterator I = GEP->idx_begin(), E = GEP->idx_end(); I != E;
       ++I, ++GTI) {
    ConstantInt *OpC = cast<ConstantInt>(*I);
    if (OpC->isZero()) continue;
    
    // Handle a struct and array indices which add their offset to the pointer.
    if (const StructType *STy = dyn_cast<StructType>(*GTI)) {
      Offset += TD.getStructLayout(STy)->getElementOffset(OpC->getZExtValue());
    } else {
      uint64_t Size = TD.getTypeAllocSize(GTI.getIndexedType());
      Offset += OpC->getSExtValue()*Size;
    }
  }
  
  // Re-sign extend from the pointer size if needed to get overflow edge cases
  // right.
  unsigned PtrSize = TD.getPointerSizeInBits();
  if (PtrSize < 64)
    Offset = (Offset << (64-PtrSize)) >> (64-PtrSize);
  
  return GetBaseWithConstantOffset(GEP->getPointerOperand(), Offset, TD);
}


/// AnalyzeLoadFromClobberingWrite - This function is called when we have a
/// memdep query of a load that ends up being a clobbering memory write (store,
/// memset, memcpy, memmove).  This means that the write *may* provide bits used
/// by the load but we can't be sure because the pointers don't mustalias.
///
/// Check this case to see if there is anything more we can do before we give
/// up.  This returns -1 if we have to give up, or a byte number in the stored
/// value of the piece that feeds the load.
static int AnalyzeLoadFromClobberingWrite(const Type *LoadTy, Value *LoadPtr,
                                          Value *WritePtr,
                                          uint64_t WriteSizeInBits,
                                          const TargetData &TD) {
  // If the loaded or stored value is an first class array or struct, don't try
  // to transform them.  We need to be able to bitcast to integer.
  if (LoadTy->isStructTy() || LoadTy->isArrayTy())
    return -1;
  
  int64_t StoreOffset = 0, LoadOffset = 0;
  Value *StoreBase = GetBaseWithConstantOffset(WritePtr, StoreOffset, TD);
  Value *LoadBase = 
    GetBaseWithConstantOffset(LoadPtr, LoadOffset, TD);
  if (StoreBase != LoadBase)
    return -1;