C++ LiveRange::getVNInfoBefore方法代码示例

static void extendSegmentsToUses(LiveRange &LR, const SlotIndexes &Indexes,
                                 ShrinkToUsesWorkList &WorkList,
                                 const LiveRange &OldRange) {
  // Keep track of the PHIs that are in use.
  SmallPtrSet<VNInfo*, 8> UsedPHIs;
  // Blocks that have already been added to WorkList as live-out.
  SmallPtrSet<MachineBasicBlock*, 16> LiveOut;

  // Extend intervals to reach all uses in WorkList.
  while (!WorkList.empty()) {
    SlotIndex Idx = WorkList.back().first;
    VNInfo *VNI = WorkList.back().second;
    WorkList.pop_back();
    const MachineBasicBlock *MBB = Indexes.getMBBFromIndex(Idx.getPrevSlot());
    SlotIndex BlockStart = Indexes.getMBBStartIdx(MBB);

    // Extend the live range for VNI to be live at Idx.
    if (VNInfo *ExtVNI = LR.extendInBlock(BlockStart, Idx)) {
      assert(ExtVNI == VNI && "Unexpected existing value number");
      (void)ExtVNI;
      // Is this a PHIDef we haven't seen before?
      if (!VNI->isPHIDef() || VNI->def != BlockStart ||
          !UsedPHIs.insert(VNI).second)
        continue;
      // The PHI is live, make sure the predecessors are live-out.
      for (auto &Pred : MBB->predecessors()) {
        if (!LiveOut.insert(Pred).second)
          continue;
        SlotIndex Stop = Indexes.getMBBEndIdx(Pred);
        // A predecessor is not required to have a live-out value for a PHI.
        if (VNInfo *PVNI = OldRange.getVNInfoBefore(Stop))
          WorkList.push_back(std::make_pair(Stop, PVNI));
      }
      continue;
    }

    // VNI is live-in to MBB.
    DEBUG(dbgs() << " live-in at " << BlockStart << '\n');
    LR.addSegment(LiveRange::Segment(BlockStart, Idx, VNI));

    // Make sure VNI is live-out from the predecessors.
    for (auto &Pred : MBB->predecessors()) {
      if (!LiveOut.insert(Pred).second)
        continue;
      SlotIndex Stop = Indexes.getMBBEndIdx(Pred);
      assert(OldRange.getVNInfoBefore(Stop) == VNI &&
             "Wrong value out of predecessor");
      WorkList.push_back(std::make_pair(Stop, VNI));
    }
  }
}

unsigned ConnectedVNInfoEqClasses::Classify(const LiveRange &LR) {
  // Create initial equivalence classes.
  EqClass.clear();
  EqClass.grow(LR.getNumValNums());

  const VNInfo *used = nullptr, *unused = nullptr;

  // Determine connections.
  for (const VNInfo *VNI : LR.valnos) {
    // Group all unused values into one class.
    if (VNI->isUnused()) {
      if (unused)
        EqClass.join(unused->id, VNI->id);
      unused = VNI;
      continue;
    }
    used = VNI;
    if (VNI->isPHIDef()) {
      const MachineBasicBlock *MBB = LIS.getMBBFromIndex(VNI->def);
      assert(MBB && "Phi-def has no defining MBB");
      // Connect to values live out of predecessors.
      for (MachineBasicBlock::const_pred_iterator PI = MBB->pred_begin(),
           PE = MBB->pred_end(); PI != PE; ++PI)
        if (const VNInfo *PVNI = LR.getVNInfoBefore(LIS.getMBBEndIdx(*PI)))
          EqClass.join(VNI->id, PVNI->id);
    } else {
      // Normal value defined by an instruction. Check for two-addr redef.
      // FIXME: This could be coincidental. Should we really check for a tied
      // operand constraint?
      // Note that VNI->def may be a use slot for an early clobber def.
      if (const VNInfo *UVNI = LR.getVNInfoBefore(VNI->def))
        EqClass.join(VNI->id, UVNI->id);
    }
  }

  // Lump all the unused values in with the last used value.
  if (used && unused)
    EqClass.join(used->id, unused->id);

  EqClass.compress();
  return EqClass.getNumClasses();
}