llvm-project/polly/lib/RegionSimplify.cpp

//===- RegionSimplify.cpp -------------------------------------------------===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file converts refined regions detected by the RegionInfo analysis
// into simple regions.
//
//===----------------------------------------------------------------------===//

#include "polly/LinkAllPasses.h"

#include "llvm/Instructions.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/Analysis/AliasAnalysis.h"
#include "llvm/Analysis/Dominators.h"
#include "llvm/Analysis/LoopInfo.h"
#include "llvm/Analysis/RegionPass.h"
#include "llvm/Analysis/RegionInfo.h"
#include "llvm/Transforms/Scalar.h"
#include "llvm/Transforms/Utils/BasicBlockUtils.h"

#define DEBUG_TYPE "region-simplify"
#include "llvm/Support/Debug.h"

using namespace llvm;

STATISTIC(NumEntries, "The # of created entry edges");
STATISTIC(NumExits, "The # of created exit edges");

namespace {
class RegionSimplify: public RegionPass {
  // Remember the modified region.
  Region *r;
  void createSingleEntryEdge(Region *R);
  void createSingleExitEdge(Region *R);
public:
  static char ID;
  explicit RegionSimplify() : RegionPass(ID), r(0) {}

  virtual void print(raw_ostream &O, const Module *M) const;

  virtual bool runOnRegion(Region *R, RGPassManager &RGM);
  virtual void getAnalysisUsage(AnalysisUsage &AU) const;
};
}

static RegisterPass<RegionSimplify>
X("polly-region-simplify", "Transform refined regions into simple regions");

char RegionSimplify::ID = 0;
namespace polly {
  Pass *createRegionSimplifyPass() {
    return new RegionSimplify();
  }
}

void RegionSimplify::print(raw_ostream &O, const Module *M) const {
  if (r == 0) return;

  BasicBlock *enteringBlock = r->getEnteringBlock();
  BasicBlock *exitingBlock = r->getExitingBlock();

  O << "Region: " << r->getNameStr() << " Edges:\t";

  if (enteringBlock)
    O << "Entering: [" << enteringBlock->getNameStr() << " -> "
      << r->getEntry()->getName() << "], ";

  if (exitingBlock) {
    O << "Exiting: [" << exitingBlock->getNameStr() << " -> ";
    if (r->getExit())
      O << r->getExit()->getName();
    else
      O << "<return>";
    O << "]";
  }

  O << "\n";
}

void RegionSimplify::getAnalysisUsage(AnalysisUsage &AU) const {
  // Function SplitBlockPredecessors currently updates/preserves AliasAnalysis,
  /// DominatorTree, LoopInfo, and LCCSA but no other analyses.
  //AU.addPreserved<AliasAnalysis>(); Break SCEV-AA
  AU.addPreserved<DominatorTree> ();
  AU.addPreserved<LoopInfo>();
  AU.addPreservedID(LCSSAID);

  AU.addPreserved<RegionInfo> ();
  AU.addRequired<RegionInfo> ();
}

// createSingleEntryEdge - Split the entry basic block of the given
// region after the last PHINode to form a single entry edge.
void RegionSimplify::createSingleEntryEdge(Region *R) {
  BasicBlock *oldEntry = R->getEntry();
  SmallVector<BasicBlock*, 4> Preds;
  for (pred_iterator PI = pred_begin(oldEntry), PE = pred_end(oldEntry);
       PI != PE; ++PI)
    if (!R->contains(*PI))
      Preds.push_back(*PI);

  assert(Preds.size() && "This region has already a single entry edge");

  BasicBlock *newEntry = SplitBlockPredecessors(oldEntry,
                                                Preds.data(), Preds.size(),
                                                ".single_entry", this);

  RegionInfo *RI = &getAnalysis<RegionInfo> ();
  // We do not update entry node for children of this region.
  // This make it easier to extract children regions because they do not share
  // the entry node with their parents.
  // all parent regions whose entry is oldEntry are updated with newEntry
  Region *r = R->getParent();

  // Put the new entry to R's parent.
  RI->setRegionFor(newEntry,r);

  while (r->getEntry() == oldEntry && !r->isTopLevelRegion()) {
    r->replaceEntry(newEntry);
    r = r->getParent();
  }

  // We do not update exit node for children of this region for the same reason
  // of not updating entry node.
  // All other regions whose exit is oldEntry are updated with new exit node
  r = RI->getTopLevelRegion();
  std::vector<Region *> RQ;
  RQ.push_back(r);

  while (!RQ.empty()){
    r = RQ.back();
    RQ.pop_back();

    for (Region::const_iterator RI = r->begin(), RE = r->end(); RI!=RE; ++RI)
      RQ.push_back(*RI);

    if (r->getExit() == oldEntry && !R->contains(r))
      r->replaceExit(newEntry);
  }

}

// createSingleExitEdge - Split the exit basic of the given region
// to form a single exit edge.
void RegionSimplify::createSingleExitEdge(Region *R) {
  BasicBlock *oldExit = R->getExit();

  SmallVector<BasicBlock*, 4> Preds;
  for (pred_iterator PI = pred_begin(oldExit), PE = pred_end(oldExit);
      PI != PE; ++PI)
    if (R->contains(*PI))
      Preds.push_back(*PI);

  DEBUG(dbgs() << "Going to create single exit for:\n");
  DEBUG(R->print(dbgs(), true, 0, Region::PrintRN));
  BasicBlock *newExit =  SplitBlockPredecessors(oldExit,
                                                Preds.data(), Preds.size(),
                                                ".single_exit", this);
  RegionInfo *RI = &getAnalysis<RegionInfo>();

  // We do not need to update entry nodes because this split happens inside
  // this region and it affects only this region and all of its children.
  // The new split node belongs to this region
  RI->setRegionFor(newExit,R);
  DEBUG(dbgs() << "Adding new exiting block: " << newExit->getName() << '\n');

  // all children of this region whose exit is oldExit is changed to newExit
  std::vector<Region *> RQ;
  for (Region::const_iterator RI = R->begin(), RE = R->end(); RI!=RE; ++RI)
    RQ.push_back(*RI);

  while (!RQ.empty()){
    R = RQ.back();
    RQ.pop_back();

    if (R->getExit() != oldExit)
      continue;

    for (Region::const_iterator RI = R->begin(), RE = R->end(); RI!=RE; ++RI)
      RQ.push_back(*RI);

    R->replaceExit(newExit);
    DEBUG(dbgs() << "Replacing exit for:\n");
    DEBUG(R->print(dbgs(), true, 0, Region::PrintRN));
  }

  DEBUG(dbgs() << "After split exit:\n");
  DEBUG(R->print(dbgs(), true, 0, Region::PrintRN));
}

bool RegionSimplify::runOnRegion(Region *R, RGPassManager &RGM) {
  r = 0;

  if (!R->isTopLevelRegion()) {

    // split entry node if the region has multiple entry edges
    if (!(R->getEnteringBlock())
        && (pred_begin(R->getEntry()) != pred_end(R->getEntry()))) {
      createSingleEntryEdge(R);
      r = R;
      ++NumEntries;
    }

    // split exit node if the region has multiple exit edges
    if (!(R->getExitingBlock())) {
      createSingleExitEdge(R);
      r = R;
      ++NumExits;
    }
  }

  return r != 0;
}