GVN.cpp

//===- 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/Transforms/Scalar.h"
#include "llvm/BasicBlock.h"
#include "llvm/Constants.h"
#include "llvm/DerivedTypes.h"
#include "llvm/Function.h"
#include "llvm/Instructions.h"
#include "llvm/Value.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: