diff --git a/lib/CodeGen/LiveRangeCalc.cpp b/lib/CodeGen/LiveRangeCalc.cpp
index a558e142e01..4433fb1aaa2 100644
--- a/lib/CodeGen/LiveRangeCalc.cpp
+++ b/lib/CodeGen/LiveRangeCalc.cpp
@@ -29,14 +29,75 @@ void LiveRangeCalc::reset(const MachineFunction *mf,
   DomTree = MDT;
   Alloc = VNIA;
 
-  unsigned N = MF->getNumBlockIDs();
-  Seen.clear();
-  Seen.resize(N);
-  LiveOut.resize(N);
+  MainLiveOutData.reset(MF->getNumBlockIDs());
   LiveIn.clear();
 }
 
 
+static SlotIndex getDefIndex(const SlotIndexes &Indexes, const MachineInstr &MI,
+                             bool EarlyClobber) {
+  // PHI defs begin at the basic block start index.
+  if (MI.isPHI())
+    return Indexes.getMBBStartIdx(MI.getParent());
+
+  // Instructions are either normal 'r', or early clobber 'e'.
+  return Indexes.getInstructionIndex(&MI).getRegSlot(EarlyClobber);
+}
+
+void LiveRangeCalc::createDeadDefs(LiveInterval &LI) {
+  assert(MRI && Indexes && "call reset() first");
+
+  // Visit all def operands. If the same instruction has multiple defs of Reg,
+  // LR.createDeadDef() will deduplicate.
+  const TargetRegisterInfo &TRI = *MRI->getTargetRegisterInfo();
+  unsigned Reg = LI.reg;
+  for (const MachineOperand &MO : MRI->def_operands(Reg)) {
+    const MachineInstr *MI = MO.getParent();
+    SlotIndex Idx = getDefIndex(*Indexes, *MI, MO.isEarlyClobber());
+    unsigned SubReg = MO.getSubReg();
+    if (SubReg != 0 || LI.hasSubRanges()) {
+      unsigned Mask = SubReg != 0 ? TRI.getSubRegIndexLaneMask(SubReg)
+                                  : MRI->getMaxLaneMaskForVReg(Reg);
+
+      // If this is the first time we see a subregister def, initialize
+      // subranges by creating a copy of the main range.
+      if (!LI.hasSubRanges() && !LI.empty()) {
+        unsigned ClassMask = MRI->getMaxLaneMaskForVReg(Reg);
+        LI.createSubRangeFrom(*Alloc, ClassMask, LI);
+      }
+
+      for (LiveInterval::subrange_iterator S = LI.subrange_begin(),
+           SE = LI.subrange_end(); S != SE; ++S) {
+        // A Mask for subregs common to the existing subrange and current def.
+        unsigned Common = S->LaneMask & Mask;
+        if (Common == 0)
+          continue;
+        // A Mask for subregs covered by the subrange but not the current def.
+        unsigned LRest = S->LaneMask & ~Mask;
+        LiveInterval::SubRange *CommonRange;
+        if (LRest != 0) {
+          // Split current subrange into Common and LRest ranges.
+          S->LaneMask = LRest;
+          CommonRange = LI.createSubRangeFrom(*Alloc, Common, *S);
+        } else {
+          assert(Common == S->LaneMask);
+          CommonRange = &*S;
+        }
+        CommonRange->createDeadDef(Idx, *Alloc);
+        Mask &= ~Common;
+      }
+      if (Mask != 0) {
+        LiveInterval::SubRange *SubRange = LI.createSubRange(*Alloc, Mask);
+        SubRange->createDeadDef(Idx, *Alloc);
+      }
+    }
+
+    // Create the def in LR. This may find an existing def.
+    LI.createDeadDef(Idx, *Alloc);
+  }
+}
+
+
 void LiveRangeCalc::createDeadDefs(LiveRange &LR, unsigned Reg) {
   assert(MRI && Indexes && "call reset() first");
 
@@ -44,22 +105,38 @@ void LiveRangeCalc::createDeadDefs(LiveRange &LR, unsigned Reg) {
   // LR.createDeadDef() will deduplicate.
   for (MachineOperand &MO : MRI->def_operands(Reg)) {
     const MachineInstr *MI = MO.getParent();
-    // Find the corresponding slot index.
-    SlotIndex Idx;
-    if (MI->isPHI())
-      // PHI defs begin at the basic block start index.
-      Idx = Indexes->getMBBStartIdx(MI->getParent());
-    else
-      // Instructions are either normal 'r', or early clobber 'e'.
-      Idx = Indexes->getInstructionIndex(MI)
-        .getRegSlot(MO.isEarlyClobber());
-
+    SlotIndex Idx = getDefIndex(*Indexes, *MI, MO.isEarlyClobber());
     // Create the def in LR. This may find an existing def.
     LR.createDeadDef(Idx, *Alloc);
   }
 }
 
 
+static SlotIndex getUseIndex(const SlotIndexes &Indexes,
+                             const MachineOperand &MO) {
+  const MachineInstr *MI = MO.getParent();
+  unsigned OpNo = (&MO - &MI->getOperand(0));
+  if (MI->isPHI()) {
+    assert(!MO.isDef() && "Cannot handle PHI def of partial register.");
+    // The actual place where a phi operand is used is the end of the pred MBB.
+    // PHI operands are paired: (Reg, PredMBB).
+    return Indexes.getMBBEndIdx(MI->getOperand(OpNo+1).getMBB());
+  }
+
+  // Check for early-clobber redefs.
+  bool isEarlyClobber = false;
+  unsigned DefIdx;
+  if (MO.isDef()) {
+    isEarlyClobber = MO.isEarlyClobber();
+  } else if (MI->isRegTiedToDefOperand(OpNo, &DefIdx)) {
+    // FIXME: This would be a lot easier if tied early-clobber uses also
+    // had an early-clobber flag.
+    isEarlyClobber = MI->getOperand(DefIdx).isEarlyClobber();
+  }
+  return Indexes.getInstructionIndex(MI).getRegSlot(isEarlyClobber);
+}
+
+
 void LiveRangeCalc::extendToUses(LiveRange &LR, unsigned Reg) {
   assert(MRI && Indexes && "call reset() first");
 
@@ -73,38 +150,86 @@ void LiveRangeCalc::extendToUses(LiveRange &LR, unsigned Reg) {
       continue;
     // MI is reading Reg. We may have visited MI before if it happens to be
     // reading Reg multiple times. That is OK, extend() is idempotent.
-    const MachineInstr *MI = MO.getParent();
-    unsigned OpNo = (&MO - &MI->getOperand(0));
-
-    // Find the SlotIndex being read.
-    SlotIndex Idx;
-    if (MI->isPHI()) {
-      assert(!MO.isDef() && "Cannot handle PHI def of partial register.");
-      // PHI operands are paired: (Reg, PredMBB).
-      // Extend the live range to be live-out from PredMBB.
-      Idx = Indexes->getMBBEndIdx(MI->getOperand(OpNo+1).getMBB());
-    } else {
-      // This is a normal instruction.
-      Idx = Indexes->getInstructionIndex(MI).getRegSlot();
-      // Check for early-clobber redefs.
-      unsigned DefIdx;
-      if (MO.isDef()) {
-        if (MO.isEarlyClobber())
-          Idx = Idx.getRegSlot(true);
-      } else if (MI->isRegTiedToDefOperand(OpNo, &DefIdx)) {
-        // FIXME: This would be a lot easier if tied early-clobber uses also
-        // had an early-clobber flag.
-        if (MI->getOperand(DefIdx).isEarlyClobber())
-          Idx = Idx.getRegSlot(true);
-      }
-    }
-    extend(LR, Idx, Reg);
+    SlotIndex Idx = getUseIndex(*Indexes, MO);
+    extend(LR, Idx, Reg, MainLiveOutData);
   }
 }
 
 
-// Transfer information from the LiveIn vector to the live ranges.
-void LiveRangeCalc::updateLiveIns() {
+void LiveRangeCalc::extendToUses(LiveInterval &LI) {
+  assert(MRI && Indexes && "call reset() first");
+
+  const TargetRegisterInfo &TRI = *MRI->getTargetRegisterInfo();
+  SmallVector<LiveOutData,2> LiveOuts;
+  unsigned NumSubRanges = 0;
+  for (LiveInterval::subrange_iterator S = LI.subrange_begin(),
+       SE = LI.subrange_end(); S != SE; ++S, ++NumSubRanges) {
+    LiveOuts.push_back(LiveOutData());
+    LiveOuts.back().reset(MF->getNumBlockIDs());
+  }
+
+  // Visit all operands that read Reg. This may include partial defs.
+  unsigned Reg = LI.reg;
+  for (MachineOperand &MO : MRI->reg_nodbg_operands(Reg)) {
+    // Clear all kill flags. They will be reinserted after register allocation
+    // by LiveIntervalAnalysis::addKillFlags().
+    if (MO.isUse())
+      MO.setIsKill(false);
+    if (!MO.readsReg())
+      continue;
+    SlotIndex Idx = getUseIndex(*Indexes, MO);
+    unsigned SubReg = MO.getSubReg();
+    if (MO.isUse() && (LI.hasSubRanges() || SubReg != 0)) {
+      unsigned Mask = SubReg != 0
+        ? TRI.getSubRegIndexLaneMask(SubReg)
+        : Mask = MRI->getMaxLaneMaskForVReg(Reg);
+
+      // If this is the first time we see a subregister def/use. Initialize
+      // subranges by creating a copy of the main range.
+      if (!LI.hasSubRanges()) {
+        unsigned ClassMask = MRI->getMaxLaneMaskForVReg(Reg);
+        LI.createSubRangeFrom(*Alloc, ClassMask, LI);
+        LiveOuts.insert(LiveOuts.begin(), LiveOutData());
+        LiveOuts.front().reset(MF->getNumBlockIDs());
+        ++NumSubRanges;
+      }
+      unsigned SubRangeIdx = 0;
+      for (LiveInterval::subrange_iterator S = LI.subrange_begin(),
+           SE = LI.subrange_end(); S != SE; ++S, ++SubRangeIdx) {
+        // A Mask for subregs common to the existing subrange and current def.
+        unsigned Common = S->LaneMask & Mask;
+        if (Common == 0)
+          continue;
+        // A Mask for subregs covered by the subrange but not the current def.
+        unsigned LRest = S->LaneMask & ~Mask;
+        LiveInterval::SubRange *CommonRange;
+        unsigned CommonRangeIdx;
+        if (LRest != 0) {
+          // Split current subrange into Common and LRest ranges.
+          S->LaneMask = LRest;
+          CommonRange = LI.createSubRangeFrom(*Alloc, Common, *S);
+          CommonRangeIdx = 0;
+          LiveOuts.insert(LiveOuts.begin(), LiveOutData());
+          LiveOuts.front().reset(MF->getNumBlockIDs());
+          ++NumSubRanges;
+          ++SubRangeIdx;
+        } else {
+          // The subrange and current def lanemasks match completely.
+          assert(Common == S->LaneMask);
+          CommonRange = &*S;
+          CommonRangeIdx = SubRangeIdx;
+        }
+        extend(*CommonRange, Idx, Reg, LiveOuts[CommonRangeIdx]);
+        Mask &= ~Common;
+      }
+      assert(SubRangeIdx == NumSubRanges);
+    }
+    extend(LI, Idx, Reg, MainLiveOutData);
+  }
+}
+
+
+void LiveRangeCalc::updateFromLiveIns(LiveOutData &LiveOuts) {
   LiveRangeUpdater Updater;
   for (SmallVectorImpl<LiveInBlock>::iterator I = LiveIn.begin(),
          E = LiveIn.end(); I != E; ++I) {
@@ -121,8 +246,8 @@ void LiveRangeCalc::updateLiveIns() {
     else {
       // The value is live-through, update LiveOut as well.
       // Defer the Domtree lookup until it is needed.
-      assert(Seen.test(MBB->getNumber()));
-      LiveOut[MBB] = LiveOutPair(I->Value, (MachineDomTreeNode *)nullptr);
+      assert(LiveOuts.Seen.test(MBB->getNumber()));
+      LiveOuts.Map[MBB] = LiveOutPair(I->Value, nullptr);
     }
     Updater.setDest(&I->LR);
     Updater.add(Start, End, I->Value);
@@ -131,7 +256,8 @@ void LiveRangeCalc::updateLiveIns() {
 }
 
 
-void LiveRangeCalc::extend(LiveRange &LR, SlotIndex Kill, unsigned PhysReg) {
+void LiveRangeCalc::extend(LiveRange &LR, SlotIndex Kill, unsigned PhysReg,
+                           LiveOutData &LiveOuts) {
   assert(Kill.isValid() && "Invalid SlotIndex");
   assert(Indexes && "Missing SlotIndexes");
   assert(DomTree && "Missing dominator tree");
@@ -147,27 +273,28 @@ void LiveRangeCalc::extend(LiveRange &LR, SlotIndex Kill, unsigned PhysReg) {
   // multiple values, and we may need to create even more phi-defs to preserve
   // VNInfo SSA form.  Perform a search for all predecessor blocks where we
   // know the dominating VNInfo.
-  if (findReachingDefs(LR, *KillMBB, Kill, PhysReg))
+  if (findReachingDefs(LR, *KillMBB, Kill, PhysReg, LiveOuts))
     return;
 
   // When there were multiple different values, we may need new PHIs.
-  calculateValues();
+  calculateValues(LiveOuts);
 }
 
 
 // This function is called by a client after using the low-level API to add
 // live-out and live-in blocks.  The unique value optimization is not
 // available, SplitEditor::transferValues handles that case directly anyway.
-void LiveRangeCalc::calculateValues() {
+void LiveRangeCalc::calculateValues(LiveOutData &LiveOuts) {
   assert(Indexes && "Missing SlotIndexes");
   assert(DomTree && "Missing dominator tree");
-  updateSSA();
-  updateLiveIns();
+  updateSSA(LiveOuts);
+  updateFromLiveIns(LiveOuts);
 }
 
 
 bool LiveRangeCalc::findReachingDefs(LiveRange &LR, MachineBasicBlock &KillMBB,
-                                     SlotIndex Kill, unsigned PhysReg) {
+                                     SlotIndex Kill, unsigned PhysReg,
+                                     LiveOutData &LiveOuts) {
   unsigned KillMBBNum = KillMBB.getNumber();
 
   // Block numbers where LR should be live-in.
@@ -201,8 +328,8 @@ bool LiveRangeCalc::findReachingDefs(LiveRange &LR, MachineBasicBlock &KillMBB,
        MachineBasicBlock *Pred = *PI;
 
        // Is this a known live-out block?
-       if (Seen.test(Pred->getNumber())) {
-         if (VNInfo *VNI = LiveOut[Pred].first) {
+       if (LiveOuts.Seen.test(Pred->getNumber())) {
+         if (VNInfo *VNI = LiveOuts.Map[Pred].first) {
            if (TheVNI && TheVNI != VNI)
              UniqueVNI = false;
            TheVNI = VNI;
@@ -216,7 +343,7 @@ bool LiveRangeCalc::findReachingDefs(LiveRange &LR, MachineBasicBlock &KillMBB,
        // First time we see Pred.  Try to determine the live-out value, but set
        // it as null if Pred is live-through with an unknown value.
        VNInfo *VNI = LR.extendInBlock(Start, End);
-       setLiveOutValue(Pred, VNI);
+       LiveOuts.setLiveOutValue(Pred, VNI);
        if (VNI) {
          if (TheVNI && TheVNI != VNI)
            UniqueVNI = false;
@@ -251,7 +378,7 @@ bool LiveRangeCalc::findReachingDefs(LiveRange &LR, MachineBasicBlock &KillMBB,
        if (*I == KillMBBNum && Kill.isValid())
          End = Kill;
        else
-         LiveOut[MF->getBlockNumbered(*I)] =
+         LiveOuts.Map[MF->getBlockNumbered(*I)] =
            LiveOutPair(TheVNI, nullptr);
        Updater.add(Start, End, TheVNI);
     }
@@ -275,7 +402,7 @@ bool LiveRangeCalc::findReachingDefs(LiveRange &LR, MachineBasicBlock &KillMBB,
 
 // This is essentially the same iterative algorithm that SSAUpdater uses,
 // except we already have a dominator tree, so we don't have to recompute it.
-void LiveRangeCalc::updateSSA() {
+void LiveRangeCalc::updateSSA(LiveOutData &LiveOuts) {
   assert(Indexes && "Missing SlotIndexes");
   assert(DomTree && "Missing dominator tree");
 
@@ -297,22 +424,23 @@ void LiveRangeCalc::updateSSA() {
 
       // We need a live-in value to a block with no immediate dominator?
       // This is probably an unreachable block that has survived somehow.
-      bool needPHI = !IDom || !Seen.test(IDom->getBlock()->getNumber());
+      bool needPHI = !IDom
+                  || !LiveOuts.Seen.test(IDom->getBlock()->getNumber());
 
       // IDom dominates all of our predecessors, but it may not be their
       // immediate dominator. Check if any of them have live-out values that are
       // properly dominated by IDom. If so, we need a phi-def here.
       if (!needPHI) {
-        IDomValue = LiveOut[IDom->getBlock()];
+        IDomValue = LiveOuts.Map[IDom->getBlock()];
 
         // Cache the DomTree node that defined the value.
         if (IDomValue.first && !IDomValue.second)
-          LiveOut[IDom->getBlock()].second = IDomValue.second =
+          LiveOuts.Map[IDom->getBlock()].second = IDomValue.second =
             DomTree->getNode(Indexes->getMBBFromIndex(IDomValue.first->def));
 
         for (MachineBasicBlock::pred_iterator PI = MBB->pred_begin(),
                PE = MBB->pred_end(); PI != PE; ++PI) {
-          LiveOutPair &Value = LiveOut[*PI];
+          LiveOutPair &Value = LiveOuts.Map[*PI];
           if (!Value.first || Value.first == IDomValue.first)
             continue;
 
@@ -334,7 +462,7 @@ void LiveRangeCalc::updateSSA() {
       // The value may be live-through even if Kill is set, as can happen when
       // we are called from extendRange. In that case LiveOutSeen is true, and
       // LiveOut indicates a foreign or missing value.
-      LiveOutPair &LOP = LiveOut[MBB];
+      LiveOutPair &LOP = LiveOuts.Map[MBB];
 
       // Create a phi-def if required.
       if (needPHI) {
@@ -348,7 +476,7 @@ void LiveRangeCalc::updateSSA() {
         // This block is done, we know the final value.
         I->DomNode = nullptr;
 
-        // Add liveness since updateLiveIns now skips this node.
+        // Add liveness since updateFromLiveIns now skips this node.
         if (I->Kill.isValid())
           LR.addSegment(LiveInterval::Segment(Start, I->Kill, VNI));
         else {
diff --git a/lib/CodeGen/LiveRangeCalc.h b/lib/CodeGen/LiveRangeCalc.h
index 345d6c43081..fd494797918 100644
--- a/lib/CodeGen/LiveRangeCalc.h
+++ b/lib/CodeGen/LiveRangeCalc.h
@@ -40,12 +40,6 @@ class LiveRangeCalc {
   MachineDominatorTree *DomTree;
   VNInfo::Allocator *Alloc;
 
-  /// Seen - Bit vector of active entries in LiveOut, also used as a visited
-  /// set by findReachingDefs.  One entry per basic block, indexed by block
-  /// number.  This is kept as a separate bit vector because it can be cleared
-  /// quickly when switching live ranges.
-  BitVector Seen;
-
   /// LiveOutPair - A value and the block that defined it.  The domtree node is
   /// redundant, it can be computed as: MDT[Indexes.getMBBFromIndex(VNI->def)].
   typedef std::pair<VNInfo*, MachineDomTreeNode*> LiveOutPair;
@@ -53,24 +47,44 @@ class LiveRangeCalc {
   /// LiveOutMap - Map basic blocks to the value leaving the block.
   typedef IndexedMap<LiveOutPair, MBB2NumberFunctor> LiveOutMap;
 
-  /// LiveOut - Map each basic block where a live range is live out to the
-  /// live-out value and its defining block.
-  ///
-  /// For every basic block, MBB, one of these conditions shall be true:
-  ///
-  ///  1. !Seen.count(MBB->getNumber())
-  ///     Blocks without a Seen bit are ignored.
-  ///  2. LiveOut[MBB].second.getNode() == MBB
-  ///     The live-out value is defined in MBB.
-  ///  3. forall P in preds(MBB): LiveOut[P] == LiveOut[MBB]
-  ///     The live-out value passses through MBB. All predecessors must carry
-  ///     the same value.
-  ///
-  /// The domtree node may be null, it can be computed.
-  ///
-  /// The map can be shared by multiple live ranges as long as no two are
-  /// live-out of the same block.
-  LiveOutMap LiveOut;
+  struct LiveOutData {
+    /// Seen - Bit vector of active entries in LiveOut, also used as a visited
+    /// set by findReachingDefs.  One entry per basic block, indexed by block
+    /// number.  This is kept as a separate bit vector because it can be cleared
+    /// quickly when switching live ranges.
+    BitVector Seen;
+
+    /// LiveOut - Map each basic block where a live range is live out to the
+    /// live-out value and its defining block.
+    ///
+    /// For every basic block, MBB, one of these conditions shall be true:
+    ///
+    ///  1. !Seen.count(MBB->getNumber())
+    ///     Blocks without a Seen bit are ignored.
+    ///  2. LiveOut[MBB].second.getNode() == MBB
+    ///     The live-out value is defined in MBB.
+    ///  3. forall P in preds(MBB): LiveOut[P] == LiveOut[MBB]
+    ///     The live-out value passses through MBB. All predecessors must carry
+    ///     the same value.
+    ///
+    /// The domtree node may be null, it can be computed.
+    ///
+    /// The map can be shared by multiple live ranges as long as no two are
+    /// live-out of the same block.
+    LiveOutMap Map;
+
+    void reset(unsigned NumBlocks) {
+      Seen.clear();
+      Seen.resize(NumBlocks);
+      Map.resize(NumBlocks);
+    }
+
+    void setLiveOutValue(MachineBasicBlock *MBB, VNInfo *VNI) {
+      Seen.set(MBB->getNumber());
+      Map[MBB] = LiveOutPair(VNI, nullptr);
+    }
+  };
+  LiveOutData MainLiveOutData;
 
   /// LiveInBlock - Information about a basic block where a live range is known
   /// to be live-in, but the value has not yet been determined.
@@ -112,17 +126,19 @@ class LiveRangeCalc {
   ///
   /// PhysReg, when set, is used to verify live-in lists on basic blocks.
   bool findReachingDefs(LiveRange &LR, MachineBasicBlock &KillMBB,
-                        SlotIndex Kill, unsigned PhysReg);
+                        SlotIndex Kill, unsigned PhysReg,
+                        LiveOutData &LiveOuts);
 
   /// updateSSA - Compute the values that will be live in to all requested
   /// blocks in LiveIn.  Create PHI-def values as required to preserve SSA form.
   ///
   /// Every live-in block must be jointly dominated by the added live-out
   /// blocks.  No values are read from the live ranges.
-  void updateSSA();
+  void updateSSA(LiveOutData &LiveOuts);
 
-  /// Add liveness as specified in the LiveIn vector.
-  void updateLiveIns();
+  /// Transfer information from the LiveIn vector to the live ranges and update
+  /// the given @p LiveOuts.
+  void updateFromLiveIns(LiveOutData &LiveOuts);
 
 public:
   LiveRangeCalc() : MF(nullptr), MRI(nullptr), Indexes(nullptr),
@@ -160,17 +176,25 @@ public:
   /// single existing value, Alloc may be null.
   ///
   /// PhysReg, when set, is used to verify live-in lists on basic blocks.
-  void extend(LiveRange &LR, SlotIndex Kill, unsigned PhysReg = 0);
+  void extend(LiveRange &LR, SlotIndex Kill, unsigned PhysReg,
+              LiveOutData &LiveOuts);
+
+  void extend(LiveRange &LR, SlotIndex Kill) {
+    extend(LR, Kill, 0, MainLiveOutData);
+  }
 
   /// createDeadDefs - Create a dead def in LI for every def operand of Reg.
   /// Each instruction defining Reg gets a new VNInfo with a corresponding
   /// minimal live range.
   void createDeadDefs(LiveRange &LR, unsigned Reg);
 
-  /// createDeadDefs - Create a dead def in LI for every def of LI->reg.
-  void createDeadDefs(LiveInterval &LI) {
-    createDeadDefs(LI, LI.reg);
-  }
+  /// Subregister aware version of createDeadDefs(LiveRange &LR, unsigned Reg).
+  /// If subregister liveness tracking is enabled new subranges are created as
+  /// necessary when subregister defs are found. As with
+  /// createDeadDefs(LiveRange &LR, unsigned Reg) new short live segments are
+  /// created for every def of LI.reg. The new segments start and end at the
+  /// defining instruction (hence the name "DeadDef").
+  void createDeadDefs(LiveInterval &LI);
 
   /// extendToUses - Extend the live range of LI to reach all uses of Reg.
   ///
@@ -178,10 +202,13 @@ public:
   /// inserted as needed to preserve SSA form.
   void extendToUses(LiveRange &LR, unsigned Reg);
 
-  /// extendToUses - Extend the live range of LI to reach all uses of LI->reg.
-  void extendToUses(LiveInterval &LI) {
-    extendToUses(LI, LI.reg);
-  }
+  /// Subregister aware version of extendToUses(LiveRange &LR, unsigned Reg).
+  /// If subregister liveness tracking is enabled new subranges are created
+  /// as necessary when subregister uses are found. As with
+  /// extendToUses(LiveRange &LR, unsigned Reg) the segments existing at the
+  /// defs are extend until they reach all uses. New value numbers are created
+  /// at CFG joins as necessary (SSA construction).
+  void extendToUses(LiveInterval &LI);
 
   //===--------------------------------------------------------------------===//
   // Low-level interface.
@@ -203,8 +230,7 @@ public:
   /// VNI may be null only if MBB is a live-through block also passed to
   /// addLiveInBlock().
   void setLiveOutValue(MachineBasicBlock *MBB, VNInfo *VNI) {
-    Seen.set(MBB->getNumber());
-    LiveOut[MBB] = LiveOutPair(VNI, nullptr);
+    MainLiveOutData.setLiveOutValue(MBB, VNI);
   }
 
   /// addLiveInBlock - Add a block with an unknown live-in value.  This
@@ -229,7 +255,11 @@ public:
   ///
   /// Every predecessor of a live-in block must have been given a value with
   /// setLiveOutValue, the value may be null for live-trough blocks.
-  void calculateValues();
+  void calculateValues(LiveOutData &LiveOuts);
+
+  void calculateValues() {
+    calculateValues(MainLiveOutData);
+  }
 };
 
 } // end namespace llvm