C++ SlotIndexes::getMBBFromIndex方法代码示例

// Add newly allocated physical registers to the MBB live in sets.
void RegAllocBase::addMBBLiveIns(MachineFunction *MF) {
  NamedRegionTimer T("MBB Live Ins", TimerGroupName, TimePassesIsEnabled);
  SlotIndexes *Indexes = LIS->getSlotIndexes();
  if (MF->size() <= 1)
    return;

  LiveIntervalUnion::SegmentIter SI;
  for (unsigned PhysReg = 0; PhysReg < PhysReg2LiveUnion.numRegs(); ++PhysReg) {
    LiveIntervalUnion &LiveUnion = PhysReg2LiveUnion[PhysReg];
    if (LiveUnion.empty())
      continue;
    MachineFunction::iterator MBB = llvm::next(MF->begin());
    MachineFunction::iterator MFE = MF->end();
    SlotIndex Start, Stop;
    tie(Start, Stop) = Indexes->getMBBRange(MBB);
    SI.setMap(LiveUnion.getMap());
    SI.find(Start);
    while (SI.valid()) {
      if (SI.start() <= Start) {
        if (!MBB->isLiveIn(PhysReg))
          MBB->addLiveIn(PhysReg);
      } else if (SI.start() > Stop)
        MBB = Indexes->getMBBFromIndex(SI.start().getPrevIndex());
      if (++MBB == MFE)
        break;
      tie(Start, Stop) = Indexes->getMBBRange(MBB);
      SI.advanceTo(Start);
    }
  }
}

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));
    }
  }
}

static void determineMissingVNIs(const SlotIndexes &Indexes, LiveInterval &LI) {
  SmallPtrSet<const MachineBasicBlock*, 5> Visited;

  LiveRange::iterator OutIt;
  VNInfo *PrevValNo = nullptr;
  for (LiveRange::iterator I = LI.begin(), E = LI.end(); I != E; ++I) {
    LiveRange::Segment &S = *I;
    // Determine final VNI if necessary.
    if (S.valno == nullptr) {
      // This can only happen at the begin of a basic block.
      assert(S.start.isBlock() && "valno should only be missing at block begin");

      Visited.clear();
      const MachineBasicBlock *MBB = Indexes.getMBBFromIndex(S.start);
      for (const MachineBasicBlock *Pred : MBB->predecessors()) {
        VNInfo *VNI = searchForVNI(Indexes, LI, Pred, Visited);
        if (VNI != nullptr) {
          S.valno = VNI;
          break;
        }
      }
      assert(S.valno != nullptr && "could not determine valno");
    }
    // Merge with previous segment if it has the same VNI.
    if (PrevValNo == S.valno && OutIt->end == S.start) {
      OutIt->end = S.end;
    } else {
      // Didn't merge. Move OutIt to next segment.
      if (PrevValNo == nullptr)
        OutIt = LI.begin();
      else
        ++OutIt;

      if (OutIt != I)
        *OutIt = *I;
      PrevValNo = S.valno;
    }
  }
  // If we merged some segments chop off the end.
  ++OutIt;
  LI.segments.erase(OutIt, LI.end());
}

bool LiveRangeCalc::isJointlyDominated(const MachineBasicBlock *MBB,
                                       ArrayRef<SlotIndex> Defs,
                                       const SlotIndexes &Indexes) {
  const MachineFunction &MF = *MBB->getParent();
  BitVector DefBlocks(MF.getNumBlockIDs());
  for (SlotIndex I : Defs)
    DefBlocks.set(Indexes.getMBBFromIndex(I)->getNumber());

  SetVector<unsigned> PredQueue;
  PredQueue.insert(MBB->getNumber());
  for (unsigned i = 0; i != PredQueue.size(); ++i) {
    unsigned BN = PredQueue[i];
    if (DefBlocks[BN])
      return true;
    const MachineBasicBlock *B = MF.getBlockNumbered(BN);
    for (const MachineBasicBlock *P : B->predecessors())
      PredQueue.insert(P->getNumber());
  }
  return false;
}

static void determineMissingVNIs(const SlotIndexes &Indexes, LiveInterval &LI) {
  SmallPtrSet<const MachineBasicBlock*, 5> Visited;
  for (LiveRange::Segment &S : LI.segments) {
    if (S.valno != nullptr)
      continue;
    // This can only happen at the begin of a basic block.
    assert(S.start.isBlock() && "valno should only be missing at block begin");

    Visited.clear();
    const MachineBasicBlock *MBB = Indexes.getMBBFromIndex(S.start);
    for (const MachineBasicBlock *Pred : MBB->predecessors()) {
      VNInfo *VNI = searchForVNI(Indexes, LI, Pred, Visited);
      if (VNI != nullptr) {
        S.valno = VNI;
        break;
      }
    }
    assert(S.valno != nullptr && "could not determine valno");
  }
}

//.........这里部分代码省略.........
        ++I;
      if (I == SR.end())
        continue;
      if ((ActiveMask & SR.LaneMask) == 0 &&
          Pos <= I->start && I->start <= NextPos) {
        // Merge multiple begins at the same position.
        if (I->start == NextPos && Event == BEGIN_SEGMENT) {
          EventMask |= SR.LaneMask;
          IsDef |= I->valno->def == I->start;
        } else if (I->start < NextPos || Event != END_SEGMENT) {
          Event = BEGIN_SEGMENT;
          NextPos = I->start;
          EventMask = SR.LaneMask;
          IsDef = I->valno->def == I->start;
        }
      }
      if ((ActiveMask & SR.LaneMask) != 0 &&
          Pos <= I->end && I->end <= NextPos) {
        // Merge multiple ends at the same position.
        if (I->end == NextPos && Event == END_SEGMENT)
          EventMask |= SR.LaneMask;
        else {
          Event = END_SEGMENT;
          NextPos = I->end;
          EventMask = SR.LaneMask;
        }
      }
    }

    // Advance scan position.
    Pos = NextPos;
    if (Event == BEGIN_SEGMENT) {
      if (ConstructingSegment && IsDef) {
        // Finish previous segment because we have to start a new one.
        CurrentSegment.end = Pos;
        append(CurrentSegment);
        ConstructingSegment = false;
      }

      // Start a new segment if necessary.
      if (!ConstructingSegment) {
        // Determine value number for the segment.
        VNInfo *VNI;
        if (IsDef) {
          VNI = getNextValue(Pos, VNIAllocator);
        } else {
          // We have to reuse an existing value number, if we are lucky
          // then we already passed one of the predecessor blocks and determined
          // its value number (with blocks in reverse postorder this would be
          // always true but we have no such guarantee).
          assert(Pos.isBlock());
          const MachineBasicBlock *MBB = Indexes.getMBBFromIndex(Pos);
          // See if any of the predecessor blocks has a lower number and a VNI
          for (const MachineBasicBlock *Pred : MBB->predecessors()) {
            SlotIndex PredEnd = Indexes.getMBBEndIdx(Pred);
            VNI = getVNInfoBefore(PredEnd);
            if (VNI != nullptr)
              break;
          }
          // Def will come later: We have to do an extra fixup pass.
          if (VNI == nullptr)
            NeedVNIFixup = true;
        }

        // In rare cases we can produce adjacent segments with the same value
        // number (if they come from different subranges, but happen to have
        // the same defining instruction). VNIFixup will fix those cases.
        if (!empty() && segments.back().end == Pos &&
            segments.back().valno == VNI)
          NeedVNIFixup = true;
        CurrentSegment.start = Pos;
        CurrentSegment.valno = VNI;
        ConstructingSegment = true;
      }
      ActiveMask |= EventMask;
    } else if (Event == END_SEGMENT) {
      assert(ConstructingSegment);
      // Finish segment if no lane is active anymore.
      ActiveMask &= ~EventMask;
      if (ActiveMask == 0) {
        CurrentSegment.end = Pos;
        append(CurrentSegment);
        ConstructingSegment = false;
      }
    } else {
      // We reached the end of the last subranges and can stop.
      assert(Event == NOTHING);
      break;
    }
  }

  // We might not be able to assign new valnos for all segments if the basic
  // block containing the definition comes after a segment using the valno.
  // Do a fixup pass for this uncommon case.
  if (NeedVNIFixup)
    determineMissingVNIs(Indexes, *this);

  assert(ActiveMask == 0 && !ConstructingSegment && "all segments ended");
  verify();
}