//===- LoopExtractor.cpp - Extract each loop into a new function ----------===//
// 
//                     The LLVM Compiler Infrastructure
//
// This file was developed by the LLVM research group and is distributed under
// the University of Illinois Open Source License. See LICENSE.TXT for details.
// 
//===----------------------------------------------------------------------===//
//
// A pass wrapper around the ExtractLoop() scalar transformation to extract each
// top-level loop into its own new function. If the loop is the ONLY loop in a
// given function, it is not touched. This is a pass most useful for debugging
// via bugpoint.
//
//===----------------------------------------------------------------------===//

#include "llvm/Transforms/IPO.h"
#include "llvm/Module.h"
#include "llvm/Pass.h"
#include "llvm/Analysis/LoopInfo.h"
#include "llvm/Transforms/Scalar.h"
#include "llvm/Transforms/Utils/FunctionUtils.h"
using namespace llvm;

namespace {
  // FIXME: This is not a function pass, but the PassManager doesn't allow
  // Module passes to require FunctionPasses, so we can't get loop info if we're
  // not a function pass.
  struct LoopExtractor : public FunctionPass {
    unsigned NumLoops;

    LoopExtractor(unsigned numLoops = ~0) : NumLoops(numLoops) {}

    virtual bool runOnFunction(Function &F);
    
    virtual void getAnalysisUsage(AnalysisUsage &AU) const {
      AU.addRequired<LoopInfo>();
      AU.addRequiredID(LoopSimplifyID);
    }
  };

  RegisterOpt<LoopExtractor> 
  X("loop-extract", "Extract loops into new functions");

  /// SingleLoopExtractor - For bugpoint.
  struct SingleLoopExtractor : public LoopExtractor {
    SingleLoopExtractor() : LoopExtractor(1) {}
  };

  RegisterOpt<SingleLoopExtractor> 
  Y("loop-extract-single", "Extract at most one loop into a new function");
} // End anonymous namespace 

bool LoopExtractor::runOnFunction(Function &F) {
  LoopInfo &LI = getAnalysis<LoopInfo>();

  // We don't want to keep extracting the only loop of a function into a new one
  if (LI.begin() == LI.end() || LI.begin() + 1 == LI.end())
    return false;

  bool Changed = false;

  // Try to move each loop out of the code into separate function
  for (LoopInfo::iterator i = LI.begin(), e = LI.end(); i != e; ++i) {
    if (NumLoops == 0) return Changed;
    --NumLoops;
    Changed |= (ExtractLoop(*i) != 0);
  }

  return Changed;
}

// createSingleLoopExtractorPass - This pass extracts one natural loop from the
// program into a function if it can.  This is used by bugpoint.
//
Pass *llvm::createSingleLoopExtractorPass() {
  return new SingleLoopExtractor();
}