SplitKit.cpp

  // Now check if any registers were separated into multiple components.
  ConnectedVNInfoEqClasses ConEQ(LIS);
  for (unsigned i = 0, e = Edit.size(); i != e; ++i) {
    // Don't use iterators, they are invalidated by create() below.
    LiveInterval *li = Edit.get(i);
    unsigned NumComp = ConEQ.Classify(li);
    if (NumComp <= 1)
      continue;
    DEBUG(dbgs() << "  " << NumComp << " components: " << *li << '\n');
    SmallVector<LiveInterval*, 8> dups;
    dups.push_back(li);
    for (unsigned i = 1; i != NumComp; ++i)
      dups.push_back(&Edit.create(MRI, LIS, VRM));
    rewriteComponents(dups, ConEQ);
    ConEQ.Distribute(&dups[0]);
  }

  // Calculate spill weight and allocation hints for new intervals.
  VirtRegAuxInfo vrai(VRM.getMachineFunction(), LIS, sa_.Loops);
  for (LiveRangeEdit::iterator I = Edit.begin(), E = Edit.end(); I != E; ++I){
    LiveInterval &li = **I;
    vrai.CalculateRegClass(li.reg);
    vrai.CalculateWeightAndHint(li);
    DEBUG(dbgs() << "  new interval " << MRI.getRegClass(li.reg)->getName()
                 << ":" << li << '\n');
  }
}


//===----------------------------------------------------------------------===//
//                               Loop Splitting
//===----------------------------------------------------------------------===//

void SplitEditor::splitAroundLoop(const MachineLoop *Loop) {
  SplitAnalysis::LoopBlocks Blocks;
  sa_.getLoopBlocks(Loop, Blocks);

  DEBUG({
    dbgs() << "  splitAround"; sa_.print(Blocks, dbgs()); dbgs() << '\n';
  });

  // Break critical edges as needed.
  SplitAnalysis::BlockPtrSet CriticalExits;
  sa_.getCriticalExits(Blocks, CriticalExits);
  assert(CriticalExits.empty() && "Cannot break critical exits yet");

  // Create new live interval for the loop.
  openIntv();

  // Insert copies in the predecessors if live-in to the header.
  if (LIS.isLiveInToMBB(Edit.getParent(), Loop->getHeader())) {
    for (SplitAnalysis::BlockPtrSet::iterator I = Blocks.Preds.begin(),
           E = Blocks.Preds.end(); I != E; ++I) {
      MachineBasicBlock &MBB = const_cast<MachineBasicBlock&>(**I);
      enterIntvAtEnd(MBB);
    }
  }

  // Switch all loop blocks.
  for (SplitAnalysis::BlockPtrSet::iterator I = Blocks.Loop.begin(),
       E = Blocks.Loop.end(); I != E; ++I)
     useIntv(**I);

  // Insert back copies in the exit blocks.
  for (SplitAnalysis::BlockPtrSet::iterator I = Blocks.Exits.begin(),
       E = Blocks.Exits.end(); I != E; ++I) {
    MachineBasicBlock &MBB = const_cast<MachineBasicBlock&>(**I);
    leaveIntvAtTop(MBB);
  }

  // Done.
  closeIntv();
  finish();
}


//===----------------------------------------------------------------------===//
//                            Single Block Splitting
//===----------------------------------------------------------------------===//

/// getMultiUseBlocks - if CurLI has more than one use in a basic block, it
/// may be an advantage to split CurLI for the duration of the block.
bool SplitAnalysis::getMultiUseBlocks(BlockPtrSet &Blocks) {
  // If CurLI is local to one block, there is no point to splitting it.
  if (UsingBlocks.size() <= 1)
    return false;
  // Add blocks with multiple uses.
  for (BlockCountMap::iterator I = UsingBlocks.begin(), E = UsingBlocks.end();
       I != E; ++I)
    switch (I->second) {
    case 0:
    case 1:
      continue;
    case 2: {
      // When there are only two uses and CurLI is both live in and live out,
      // we don't really win anything by isolating the block since we would be
      // inserting two copies.
      // The remaing register would still have two uses in the block. (Unless it
      // separates into disconnected components).
      if (LIS.isLiveInToMBB(*CurLI, I->first) &&
          LIS.isLiveOutOfMBB(*CurLI, I->first))
        continue;
    } // Fall through.
    default:
      Blocks.insert(I->first);
    }
  return !Blocks.empty();
}

/// splitSingleBlocks - Split CurLI into a separate live interval inside each
/// basic block in Blocks.
void SplitEditor::splitSingleBlocks(const SplitAnalysis::BlockPtrSet &Blocks) {
  DEBUG(dbgs() << "  splitSingleBlocks for " << Blocks.size() << " blocks.\n");
  // Determine the first and last instruction using CurLI in each block.
  typedef std::pair<SlotIndex,SlotIndex> IndexPair;
  typedef DenseMap<const MachineBasicBlock*,IndexPair> IndexPairMap;
  IndexPairMap MBBRange;
  for (SplitAnalysis::InstrPtrSet::const_iterator I = sa_.UsingInstrs.begin(),
       E = sa_.UsingInstrs.end(); I != E; ++I) {
    const MachineBasicBlock *MBB = (*I)->getParent();
    if (!Blocks.count(MBB))
      continue;
    SlotIndex Idx = LIS.getInstructionIndex(*I);
    DEBUG(dbgs() << "  BB#" << MBB->getNumber() << '\t' << Idx << '\t' << **I);
    IndexPair &IP = MBBRange[MBB];
    if (!IP.first.isValid() || Idx < IP.first)
      IP.first = Idx;
    if (!IP.second.isValid() || Idx > IP.second)
      IP.second = Idx;
  }

  // Create a new interval for each block.
  for (SplitAnalysis::BlockPtrSet::const_iterator I = Blocks.begin(),
       E = Blocks.end(); I != E; ++I) {
    IndexPair &IP = MBBRange[*I];
    DEBUG(dbgs() << "  splitting for BB#" << (*I)->getNumber() << ": ["
                 << IP.first << ';' << IP.second << ")\n");
    assert(IP.first.isValid() && IP.second.isValid());

    openIntv();
    useIntv(enterIntvBefore(IP.first), leaveIntvAfter(IP.second));
    closeIntv();
  }
  finish();
}


//===----------------------------------------------------------------------===//
//                            Sub Block Splitting
//===----------------------------------------------------------------------===//

/// getBlockForInsideSplit - If CurLI is contained inside a single basic block,
/// and it wou pay to subdivide the interval inside that block, return it.
/// Otherwise return NULL. The returned block can be passed to
/// SplitEditor::splitInsideBlock.
const MachineBasicBlock *SplitAnalysis::getBlockForInsideSplit() {
  // The interval must be exclusive to one block.
  if (UsingBlocks.size() != 1)
    return 0;
  // Don't to this for less than 4 instructions. We want to be sure that
  // splitting actually reduces the instruction count per interval.
  if (UsingInstrs.size() < 4)
    return 0;
  return UsingBlocks.begin()->first;
}

/// splitInsideBlock - Split CurLI into multiple intervals inside MBB.
void SplitEditor::splitInsideBlock(const MachineBasicBlock *MBB) {
  SmallVector<SlotIndex, 32> Uses;
  Uses.reserve(sa_.UsingInstrs.size());
  for (SplitAnalysis::InstrPtrSet::const_iterator I = sa_.UsingInstrs.begin(),
       E = sa_.UsingInstrs.end(); I != E; ++I)
    if ((*I)->getParent() == MBB)
      Uses.push_back(LIS.getInstructionIndex(*I));
  DEBUG(dbgs() << "  splitInsideBlock BB#" << MBB->getNumber() << " for "
               << Uses.size() << " instructions.\n");
  assert(Uses.size() >= 3 && "Need at least 3 instructions");
  array_pod_sort(Uses.begin(), Uses.end());

  // Simple algorithm: Find the largest gap between uses as determined by slot
  // indices. Create new intervals for instructions before the gap and after the
  // gap.
  unsigned bestPos = 0;
  int bestGap = 0;
  DEBUG(dbgs() << "    dist (" << Uses[0]);
  for (unsigned i = 1, e = Uses.size(); i != e; ++i) {
    int g = Uses[i-1].distance(Uses[i]);
    DEBUG(dbgs() << ") -" << g << "- (" << Uses[i]);
    if (g > bestGap)
      bestPos = i, bestGap = g;
  }
  DEBUG(dbgs() << "), best: -" << bestGap << "-\n");

  // bestPos points to the first use after the best gap.
  assert(bestPos > 0 && "Invalid gap");

  // FIXME: Don't create intervals for low densities.

  // First interval before the gap. Don't create single-instr intervals.
  if (bestPos > 1) {
    openIntv();
    useIntv(enterIntvBefore(Uses.front()), leaveIntvAfter(Uses[bestPos-1]));
    closeIntv();
  }

  // Second interval after the gap.
  if (bestPos < Uses.size()-1) {
    openIntv();
    useIntv(enterIntvBefore(Uses[bestPos]), leaveIntvAfter(Uses.back()));
    closeIntv();
  }

  finish();
}