path: root/lib/Transforms/Scalar/EarlyCSE.cpp

//===- EarlyCSE.cpp - Simple and fast CSE pass ----------------------------===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This pass performs a simple dominator tree walk that eliminates trivially
// redundant instructions.
//
//===----------------------------------------------------------------------===//

#define DEBUG_TYPE "early-cse"
#include "llvm/Transforms/Scalar.h"
#include "llvm/Instructions.h"
#include "llvm/Pass.h"
#include "llvm/Analysis/Dominators.h"
#include "llvm/Analysis/InstructionSimplify.h"
#include "llvm/Target/TargetData.h"
#include "llvm/Transforms/Utils/Local.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/RecyclingAllocator.h"
#include "llvm/ADT/ScopedHashTable.h"
#include "llvm/ADT/Statistic.h"
using namespace llvm;

STATISTIC(NumSimplify, "Number of insts simplified or DCE'd");
STATISTIC(NumCSE,      "Number of insts CSE'd");
STATISTIC(NumCSEMem,   "Number of load and call insts CSE'd");

static unsigned getHash(const void *V) {
  return DenseMapInfo<const void*>::getHashValue(V);
}

//===----------------------------------------------------------------------===//
// SimpleValue 
//===----------------------------------------------------------------------===//

namespace {
  /// SimpleValue - Instances of this struct represent available values in the
  /// scoped hash table.
  struct SimpleValue {
    Instruction *Inst;
    
    bool isSentinel() const {
      return Inst == DenseMapInfo<Instruction*>::getEmptyKey() ||
             Inst == DenseMapInfo<Instruction*>::getTombstoneKey();
    }
    
    static bool canHandle(Instruction *Inst) {
      return isa<CastInst>(Inst) || isa<BinaryOperator>(Inst) ||
             isa<GetElementPtrInst>(Inst) || isa<CmpInst>(Inst) ||
             isa<SelectInst>(Inst) || isa<ExtractElementInst>(Inst) ||
             isa<InsertElementInst>(Inst) || isa<ShuffleVectorInst>(Inst) ||
             isa<ExtractValueInst>(Inst) || isa<InsertValueInst>(Inst);
    }
    
    static SimpleValue get(Instruction *I) {
      SimpleValue X; X.Inst = I;
      assert((X.isSentinel() || canHandle(I)) && "Inst can't be handled!");
      return X;
    }
  };
}

namespace llvm {
// SimpleValue is POD.
template<> struct isPodLike<SimpleValue> {
  static const bool value = true;
};

template<> struct DenseMapInfo<SimpleValue> {
  static inline SimpleValue getEmptyKey() {
    return SimpleValue::get(DenseMapInfo<Instruction*>::getEmptyKey());
  }
  static inline SimpleValue getTombstoneKey() {
    return SimpleValue::get(DenseMapInfo<Instruction*>::getTombstoneKey());
  }
  static unsigned getHashValue(SimpleValue Val);
  static bool isEqual(SimpleValue LHS, SimpleValue RHS);
};
}

unsigned DenseMapInfo<SimpleValue>::getHashValue(SimpleValue Val) {
  Instruction *Inst = Val.Inst;
  
  // Hash in all of the operands as pointers.
  unsigned Res = 0;
  for (unsigned i = 0, e = Inst->getNumOperands(); i != e; ++i)
    Res ^= getHash(Inst->getOperand(i)) << i;

  if (CastInst *CI = dyn_cast<CastInst>(Inst))
    Res ^= getHash(CI->getType());
  else if (CmpInst *CI = dyn_cast<CmpInst>(Inst))
    Res ^= CI->getPredicate();
  else if (const ExtractValueInst *EVI = dyn_cast<ExtractValueInst>(Inst)) {
    for (ExtractValueInst::idx_iterator I = EVI->idx_begin(),
         E = EVI->idx_end(); I != E; ++I)
      Res ^= *I;
  } else if (const InsertValueInst *IVI = dyn_cast<InsertValueInst>(Inst)) {
    for (InsertValueInst::idx_iterator I = IVI->idx_begin(),
         E = IVI->idx_end(); I != E; ++I)
      Res ^= *I;
  } else {
    // nothing extra to hash in.
    assert((isa<BinaryOperator>(Inst) || isa<GetElementPtrInst>(Inst) ||
            isa<SelectInst>(Inst) || isa<ExtractElementInst>(Inst) ||
            isa<InsertElementInst>(Inst) || isa<ShuffleVectorInst>(Inst)) &&
           "Invalid/unknown instruction");
  }

  // Mix in the opcode.
  return (Res << 1) ^ Inst->getOpcode();
}

bool DenseMapInfo<SimpleValue>::isEqual(SimpleValue LHS, SimpleValue RHS) {
  Instruction *LHSI = LHS.Inst, *RHSI = RHS.Inst;

  if (LHS.isSentinel() || RHS.isSentinel())
    return LHSI == RHSI;
  
  if (LHSI->getOpcode() != RHSI->getOpcode()) return false;
  return LHSI->isIdenticalTo(RHSI);
}

//===----------------------------------------------------------------------===//
// MemoryValue 
//===----------------------------------------------------------------------===//

namespace {
  /// MemoryValue - Instances of this struct represent available load and call
  /// values in the scoped hash table.
  struct MemoryValue {
    Instruction *Inst;
    
    bool isSentinel() const {
      return Inst == DenseMapInfo<Instruction*>::getEmptyKey() ||
             Inst == DenseMapInfo<Instruction*>::getTombstoneKey();
    }
    
    static bool canHandle(Instruction *Inst) {
      if (LoadInst *LI = dyn_cast<LoadInst>(Inst))
        return !LI->isVolatile();
      if (CallInst *CI = dyn_cast<CallInst>(Inst))
        return CI->onlyReadsMemory();
      return false;
    }
    
    static MemoryValue get(Instruction *I) {
      MemoryValue X; X.Inst = I;
      assert((X.isSentinel() || canHandle(I)) && "Inst can't be handled!");
      return X;
    }
  };
}

namespace llvm {
  // MemoryValue is POD.
  template<> struct isPodLike<MemoryValue> {
    static const bool value = true;
  };
  
  template<> struct DenseMapInfo<MemoryValue> {
    static inline MemoryValue getEmptyKey() {
      return MemoryValue::get(DenseMapInfo<Instruction*>::getEmptyKey());
    }
    static inline MemoryValue getTombstoneKey() {
      return MemoryValue::get(DenseMapInfo<Instruction*>::getTombstoneKey());
    }
    static unsigned getHashValue(MemoryValue Val);
    static bool isEqual(MemoryValue LHS, MemoryValue RHS);
  };
}
unsigned DenseMapInfo<MemoryValue>::getHashValue(MemoryValue Val) {
  Instruction *Inst = Val.Inst;
  // Hash in all of the operands as pointers.
  unsigned Res = 0;
  for (unsigned i = 0, e = Inst->getNumOperands(); i != e; ++i)
    Res ^= getHash(Inst->getOperand(i)) << i;
  // Mix in the opcode.
  return (Res << 1) ^ Inst->getOpcode();
}

bool DenseMapInfo<MemoryValue>::isEqual(MemoryValue LHS, MemoryValue RHS) {
  Instruction *LHSI = LHS.Inst, *RHSI = RHS.Inst;
  
  if (LHS.isSentinel() || RHS.isSentinel())
    return LHSI == RHSI;
  
  if (LHSI->getOpcode() != RHSI->getOpcode()) return false;
  return LHSI->isIdenticalTo(RHSI);
}


//===----------------------------------------------------------------------===//
// EarlyCSE pass. 
//===----------------------------------------------------------------------===//

namespace {
  
/// EarlyCSE - This pass does a simple depth-first walk over the dominator
/// tree, eliminating trivially redundant instructions and using instsimplify
/// to canonicalize things as it goes.  It is intended to be fast and catch
/// obvious cases so that instcombine and other passes are more effective.  It
/// is expected that a later pass of GVN will catch the interesting/hard
/// cases.
class EarlyCSE : public FunctionPass {
public:
  const TargetData *TD;
  DominatorTree *DT;
  typedef RecyclingAllocator