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//===- 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;
}
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