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/Analysis/Dominators.h"
#include "llvm/Pass.h"
using namespace llvm;

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:
  static char ID;
  explicit EarlyCSE()
      : FunctionPass(ID) {
    initializeEarlyCSEPass(*PassRegistry::getPassRegistry());
  }

  bool runOnFunction(Function &F);

private:
  // This transformation requires dominator postdominator info
  virtual void getAnalysisUsage(AnalysisUsage &AU) const {
    AU.addRequired<DominatorTree>();
    AU.setPreservesCFG();
  }
};
}

char EarlyCSE::ID = 0;

// createEarlyCSEPass - The public interface to this file.
FunctionPass *llvm::createEarlyCSEPass() {
  return new EarlyCSE();
}

INITIALIZE_PASS_BEGIN(EarlyCSE, "early-cse", "Early CSE", false, false)
INITIALIZE_PASS_DEPENDENCY(DominatorTree)
INITIALIZE_PASS_END(EarlyCSE, "early-cse", "Early CSE", false, false)

bool EarlyCSE::runOnFunction(Function &F) {
  DominatorTree &DT = getAnalysis<DominatorTree>();
  (void)DT;
  return false;
}