C++ LiveRange::removeSegment方法代码示例

void LiveIntervals::pruneValue(LiveRange &LR, SlotIndex Kill,
                               SmallVectorImpl<SlotIndex> *EndPoints) {
  LiveQueryResult LRQ = LR.Query(Kill);
  VNInfo *VNI = LRQ.valueOutOrDead();
  if (!VNI)
    return;

  MachineBasicBlock *KillMBB = Indexes->getMBBFromIndex(Kill);
  SlotIndex MBBEnd = Indexes->getMBBEndIdx(KillMBB);

  // If VNI isn't live out from KillMBB, the value is trivially pruned.
  if (LRQ.endPoint() < MBBEnd) {
    LR.removeSegment(Kill, LRQ.endPoint());
    if (EndPoints) EndPoints->push_back(LRQ.endPoint());
    return;
  }

  // VNI is live out of KillMBB.
  LR.removeSegment(Kill, MBBEnd);
  if (EndPoints) EndPoints->push_back(MBBEnd);

  // Find all blocks that are reachable from KillMBB without leaving VNI's live
  // range. It is possible that KillMBB itself is reachable, so start a DFS
  // from each successor.
  typedef SmallPtrSet<MachineBasicBlock*, 9> VisitedTy;
  VisitedTy Visited;
  for (MachineBasicBlock::succ_iterator
       SuccI = KillMBB->succ_begin(), SuccE = KillMBB->succ_end();
       SuccI != SuccE; ++SuccI) {
    for (df_ext_iterator<MachineBasicBlock*, VisitedTy>
         I = df_ext_begin(*SuccI, Visited), E = df_ext_end(*SuccI, Visited);
         I != E;) {
      MachineBasicBlock *MBB = *I;

      // Check if VNI is live in to MBB.
      SlotIndex MBBStart, MBBEnd;
      std::tie(MBBStart, MBBEnd) = Indexes->getMBBRange(MBB);
      LiveQueryResult LRQ = LR.Query(MBBStart);
      if (LRQ.valueIn() != VNI) {
        // This block isn't part of the VNI segment. Prune the search.
        I.skipChildren();
        continue;
      }

      // Prune the search if VNI is killed in MBB.
      if (LRQ.endPoint() < MBBEnd) {
        LR.removeSegment(MBBStart, LRQ.endPoint());
        if (EndPoints) EndPoints->push_back(LRQ.endPoint());
        I.skipChildren();
        continue;
      }

      // VNI is live through MBB.
      LR.removeSegment(MBBStart, MBBEnd);
      if (EndPoints) EndPoints->push_back(MBBEnd);
      ++I;
    }
  }
}

//.........这里部分代码省略.........
        }
        // Special case: An early-clobber tied operand reads and writes the
        // register one slot early.
        if (VNInfo *DefVNI = LRQ.valueDefined())
            Idx = DefVNI->def;

        WorkList.push_back(std::make_pair(Idx, VNI));
    }

    // Create new live ranges with only minimal live segments per def.
    LiveRange NewLR;
    for (LiveInterval::vni_iterator I = li->vni_begin(), E = li->vni_end();
            I != E; ++I) {
        VNInfo *VNI = *I;
        if (VNI->isUnused())
            continue;
        NewLR.addSegment(LiveRange::Segment(VNI->def, VNI->def.getDeadSlot(), VNI));
    }

    // Keep track of the PHIs that are in use.
    SmallPtrSet<VNInfo*, 8> UsedPHIs;

    // 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 = getMBBFromIndex(Idx.getPrevSlot());
        SlotIndex BlockStart = getMBBStartIdx(MBB);

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

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

        // Make sure VNI is live-out from the predecessors.
        for (MachineBasicBlock::const_pred_iterator PI = MBB->pred_begin(),
                PE = MBB->pred_end(); PI != PE; ++PI) {
            if (!LiveOut.insert(*PI))
                continue;
            SlotIndex Stop = getMBBEndIdx(*PI);
            assert(li->getVNInfoBefore(Stop) == VNI &&
                   "Wrong value out of predecessor");
            WorkList.push_back(std::make_pair(Stop, VNI));
        }
    }

    // Handle dead values.
    bool CanSeparate = false;
    for (LiveInterval::vni_iterator I = li->vni_begin(), E = li->vni_end();
            I != E; ++I) {
        VNInfo *VNI = *I;
        if (VNI->isUnused())
            continue;
        LiveRange::iterator LRI = NewLR.FindSegmentContaining(VNI->def);
        assert(LRI != NewLR.end() && "Missing segment for PHI");
        if (LRI->end != VNI->def.getDeadSlot())
            continue;
        if (VNI->isPHIDef()) {
            // This is a dead PHI. Remove it.
            VNI->markUnused();
            NewLR.removeSegment(LRI->start, LRI->end);
            DEBUG(dbgs() << "Dead PHI at " << VNI->def << " may separate interval\n");
            CanSeparate = true;
        } else {
            // This is a dead def. Make sure the instruction knows.
            MachineInstr *MI = getInstructionFromIndex(VNI->def);
            assert(MI && "No instruction defining live value");
            MI->addRegisterDead(li->reg, TRI);
            if (dead && MI->allDefsAreDead()) {
                DEBUG(dbgs() << "All defs dead: " << VNI->def << '\t' << *MI);
                dead->push_back(MI);
            }
        }
    }

    // Move the trimmed segments back.
    li->segments.swap(NewLR.segments);
    DEBUG(dbgs() << "Shrunk: " << *li << '\n');
    return CanSeparate;
}