RegisterPressure: Make liveness tracking subregister aware

[MatzeB]

Summary

Some comments:

• I did not see any compiletime impact of this change if subregister/lanemask tracking is disabled
• Compiletime when subregister/lanemask tracking is affected, this is because the only way to see which lanes are actually dead or use an undefined value is to perform a liveness query. Unfortunately we have to perform this query for each register operand.

[atrick]

Nice. I can't claim to know if you've covered everything that needed to be changed, but the new code looks good.

[MatzeB]

Rebase patch onto RegisterOperand changes

include/llvm/CodeGen/MachineScheduler.h

protected:
 
   /// Move an instruction and update register pressure.
   void scheduleMI(SUnit *SU, bool IsTopNode);
 
   // Lesser helpers...
 
   void initRegPressure();
 
-  void updatePressureDiffs(ArrayRef<unsigned> LiveUses);
+  void updatePressureDiffs(ArrayRef<RegisterMaskPair> LiveUses);
 
   void updateScheduledPressure(const SUnit *SU,
                                const std::vector<unsigned> &NewMaxPressure);
 };
 
 //===----------------------------------------------------------------------===//
 ///
 /// Helpers for implementing custom MachineSchedStrategy classes. These take

include/llvm/CodeGen/RegisterPressure.h

 
 namespace llvm {
 
 class LiveIntervals;
 class LiveRange;
 class RegisterClassInfo;
 class MachineInstr;
 
+struct RegisterMaskPair {
+  unsigned RegUnit; ///< Virtual register or register unit.
+  LaneBitmask LaneMask;
+
+  RegisterMaskPair(unsigned RegUnit, LaneBitmask LaneMask)
+      : RegUnit(RegUnit), LaneMask(LaneMask) {}
+};
+
 /// Base class for register pressure results.
 struct RegisterPressure {
   /// Map of max reg pressure indexed by pressure set ID, not class ID.
   std::vector<unsigned> MaxSetPressure;
 
   /// List of live in virtual registers or physical register units.
-  SmallVector<unsigned,8> LiveInRegs;
-  SmallVector<unsigned,8> LiveOutRegs;
+  SmallVector<RegisterMaskPair,8> LiveInRegs;
+  SmallVector<RegisterMaskPair,8> LiveOutRegs;
 
   void dump(const TargetRegisterInfo *TRI) const;
 };
 
 /// RegisterPressure computed within a region of instructions delimited by
 /// TopIdx and BottomIdx.  During pressure computation, the maximum pressure per
 /// register pressure set is increased. Once pressure within a region is fully
 /// computed, the live-in and live-out sets are recorded.
void addPressureChange(unsigned RegUnit, bool IsDec,
                          const MachineRegisterInfo *MRI);
 
   LLVM_DUMP_METHOD void dump(const TargetRegisterInfo &TRI) const;
 };
 
 /// List of register defined and used by a machine instruction.
 class RegisterOperands {
 public:
-  SmallVector<unsigned, 8> Uses;
-  SmallVector<unsigned, 8> Defs;
-  SmallVector<unsigned, 8> DeadDefs;
+  SmallVector<RegisterMaskPair, 8> Uses;
+  SmallVector<RegisterMaskPair, 8> Defs;
+  SmallVector<RegisterMaskPair, 8> DeadDefs;
 
   void collect(const MachineInstr &MI, const TargetRegisterInfo &TRI,
-               const MachineRegisterInfo &MRI, bool IgnoreDead = false);
+               const MachineRegisterInfo &MRI, bool TrackLaneMasks,
+               bool IgnoreDead);
 
   /// Use liveness information to find dead defs not marked with a dead flag
   /// and move them to the DeadDefs vector.
   void detectDeadDefs(const MachineInstr &MI, const LiveIntervals &LIS);
+
+  /// Use liveness information to find out which uses/defs are partially
+  /// undefined/dead and adjust the RegisterMaskPairs accordingly.
+  void adjustLaneLiveness(const LiveIntervals &LIS,
+                          const MachineRegisterInfo &MRI, SlotIndex Pos);
+
 };
 
 /// Array of PressureDiffs.
 class PressureDiffs {
   PressureDiff *PDiffArray;
   unsigned Size;
   unsigned Max;
 public:

 };
 
 /// A set of live virtual registers and physical register units.
 ///
 /// This is a wrapper around a SparseSet which deals with mapping register unit
 /// and virtual register indexes to an index usable by the sparse set.
 class LiveRegSet {
 private:
-  SparseSet<unsigned> Regs;
+  struct IndexMaskPair {
+    unsigned Index;
+    LaneBitmask LaneMask;
+
+    IndexMaskPair(unsigned Index, LaneBitmask LaneMask)
+        : Index(Index), LaneMask(LaneMask) {}
+
+    unsigned getSparseSetIndex() const {
+      return Index;
+    }
+  };
+
+  typedef SparseSet<IndexMaskPair> RegSet;
+  RegSet Regs;
   unsigned NumRegUnits;
 
   unsigned getSparseIndexFromReg(unsigned Reg) const {
     if (TargetRegisterInfo::isVirtualRegister(Reg))
       return TargetRegisterInfo::virtReg2Index(Reg) + NumRegUnits;
     assert(Reg < NumRegUnits);
     return Reg;
   }
   unsigned getRegFromSparseIndex(unsigned SparseIndex) const {
     if (SparseIndex >= NumRegUnits)
       return TargetRegisterInfo::index2VirtReg(SparseIndex-NumRegUnits);
     return SparseIndex;
   }
 
 public:
   void clear();
   void init(const MachineRegisterInfo &MRI);
 
-  bool contains(unsigned Reg) const {
+  LaneBitmask contains(unsigned Reg) const {
     unsigned SparseIndex = getSparseIndexFromReg(Reg);
-    return Regs.count(SparseIndex);
-  }
-
-  bool insert(unsigned Reg) {
-    unsigned SparseIndex = getSparseIndexFromReg(Reg);
-    return Regs.insert(SparseIndex).second;
-  }
-
-  bool erase(unsigned Reg) {
-    unsigned SparseIndex = getSparseIndexFromReg(Reg);
-    return Regs.erase(SparseIndex);
+    RegSet::const_iterator I = Regs.find(SparseIndex);
+    if (I == Regs.end())
+      return 0;
+    return I->LaneMask;
+  }
+
+  /// Mark the \p Pair.LaneMask lanes of \p Pair.Reg as live.
+  /// Returns the previously live lanes of \p Pair.Reg.
+  LaneBitmask insert(RegisterMaskPair Pair) {
+    unsigned SparseIndex = getSparseIndexFromReg(Pair.RegUnit);
+    auto InsertRes = Regs.insert(IndexMaskPair(SparseIndex, Pair.LaneMask));
+    if (!InsertRes.second) {
+      unsigned PrevMask = InsertRes.first->LaneMask;
+      InsertRes.first->LaneMask |= Pair.LaneMask;
+      return PrevMask;
+    }
+    return 0;
+  }
+
+  /// Clears the \p Pair.LaneMask lanes of \p Pair.Reg (mark them as dead).
+  /// Returns the previously live lanes of \p Pair.Reg.
+  LaneBitmask erase(RegisterMaskPair Pair) {
+    unsigned SparseIndex = getSparseIndexFromReg(Pair.RegUnit);
+    RegSet::iterator I = Regs.find(SparseIndex);
+    if (I == Regs.end())
+      return 0;
+    unsigned PrevMask = I->LaneMask;
+    I->LaneMask &= ~Pair.LaneMask;
+    return PrevMask;
   }
 
   size_t size() const {
     return Regs.size();
   }
 
   template<typename ContainerT>
   void appendTo(ContainerT &To) const {
-    for (unsigned I : Regs) {
-      unsigned Reg = getRegFromSparseIndex(I);
-      To.push_back(Reg);
+    for (const IndexMaskPair &P : Regs) {
+      unsigned Reg = getRegFromSparseIndex(P.Index);
+      if (P.LaneMask != 0)
+        To.push_back(RegisterMaskPair(Reg, P.LaneMask));
     }
   }
 };
 
 /// Track the current register pressure at some position in the instruction
 /// stream, and remember the high water mark within the region traversed. This
 /// does not automatically consider live-through ranges. The client may
 /// independently adjust for global liveness.
class RegPressureTracker {
 
   /// Run in two modes dependending on whether constructed with IntervalPressure
   /// or RegisterPressure. If requireIntervals is false, LIS are ignored.
   bool RequireIntervals;
 
   /// True if UntiedDefs will be populated.
   bool TrackUntiedDefs;
 
+  /// True if lanemasks should be tracked.
+  bool TrackLaneMasks;
+
   /// Register pressure corresponds to liveness before this instruction
   /// iterator. It may point to the end of the block or a DebugValue rather than
   /// an instruction.
   MachineBasicBlock::const_iterator CurrPos;
 
   /// Pressure map indexed by pressure set ID, not class ID.
   std::vector<unsigned> CurrSetPressure;
 
   /// Set of live registers.
   LiveRegSet LiveRegs;
 
   /// Set of vreg defs that start a live range.
   SparseSet<unsigned, VirtReg2IndexFunctor> UntiedDefs;
   /// Live-through pressure.
   std::vector<unsigned> LiveThruPressure;
 
 public:
   RegPressureTracker(IntervalPressure &rp) :
     MF(nullptr), TRI(nullptr), RCI(nullptr), LIS(nullptr), MBB(nullptr), P(rp),
-    RequireIntervals(true), TrackUntiedDefs(false) {}
+    RequireIntervals(true), TrackUntiedDefs(false), TrackLaneMasks(false) {}
 
   RegPressureTracker(RegionPressure &rp) :
     MF(nullptr), TRI(nullptr), RCI(nullptr), LIS(nullptr), MBB(nullptr), P(rp),
-    RequireIntervals(false), TrackUntiedDefs(false) {}
+    RequireIntervals(false), TrackUntiedDefs(false), TrackLaneMasks(false) {}
 
   void reset();
 
   void init(const MachineFunction *mf, const RegisterClassInfo *rci,
             const LiveIntervals *lis, const MachineBasicBlock *mbb,
             MachineBasicBlock::const_iterator pos,
-            bool ShouldTrackUntiedDefs = false);
+            bool TrackLaneMasks, bool TrackUntiedDefs);
 
   /// Force liveness of virtual registers or physical register
   /// units. Particularly useful to initialize the livein/out state of the
   /// tracker before the first call to advance/recede.
-  void addLiveRegs(ArrayRef<unsigned> Regs);
+  void addLiveRegs(ArrayRef<RegisterMaskPair> Regs);
 
   /// Get the MI position corresponding to this register pressure.
   MachineBasicBlock::const_iterator getPos() const { return CurrPos; }
 
   // Reset the MI position corresponding to the register pressure. This allows
   // schedulers to move instructions above the RegPressureTracker's
   // CurrPos. Since the pressure is computed before CurrPos, the iterator
   // position changes while pressure does not.
   void setPos(MachineBasicBlock::const_iterator Pos) { CurrPos = Pos; }
 
   /// Recede across the previous instruction.
-  void recede(SmallVectorImpl<unsigned> *LiveUses = nullptr);
+  void recede(SmallVectorImpl<RegisterMaskPair> *LiveUses = nullptr);
 
   /// Recede across the previous instruction.
   /// This "low-level" variant assumes that recedeSkipDebugValues() was
   /// called previously and takes precomputed RegisterOperands for the
   /// instruction.
   void recede(const RegisterOperands &RegOpers,
-              SmallVectorImpl<unsigned> *LiveUses = nullptr);
+              SmallVectorImpl<RegisterMaskPair> *LiveUses = nullptr);
 
   /// Recede until we find an instruction which is not a DebugValue.
   void recedeSkipDebugValues();
 
   /// Advance across the current instruction.
   void advance();
 
   /// Finalize the region boundaries and recored live ins and live outs.
public:
 
   bool hasUntiedDef(unsigned VirtReg) const {
     return UntiedDefs.count(VirtReg);
   }
 
   void dump() const;
 
 protected:
-  void discoverLiveOut(unsigned Reg);
-  void discoverLiveIn(unsigned Reg);
+  /// Add Reg to the live out set and increase max pressure.
+  void discoverLiveOut(RegisterMaskPair Pair);
+  /// Add Reg to the live in set and increase max pressure.
+  void discoverLiveIn(RegisterMaskPair Pair);
 
   /// \brief Get the SlotIndex for the first nondebug instruction including or
   /// after the current position.
   SlotIndex getCurrSlot() const;
 
-  void increaseRegPressure(ArrayRef<unsigned> Regs);
-  void decreaseRegPressure(ArrayRef<unsigned> Regs);
+  void increaseRegPressure(unsigned RegUnit, LaneBitmask PreviousMask,
+                           LaneBitmask NewMask);
+  void decreaseRegPressure(unsigned RegUnit, LaneBitmask PreviousMask,
+                           LaneBitmask NewMask);
+
+  void bumpDeadDefs(ArrayRef<RegisterMaskPair> DeadDefs);
 
   void bumpUpwardPressure(const MachineInstr *MI);
   void bumpDownwardPressure(const MachineInstr *MI);
+
+  void discoverLiveInOrOut(RegisterMaskPair Pair,
+                           SmallVectorImpl<RegisterMaskPair> &LiveInOrOut);
+
+  LaneBitmask getLastUsedLanes(unsigned RegUnit, SlotIndex Pos) const;
+  LaneBitmask getLiveLanesAt(unsigned RegUnit, SlotIndex Pos) const;
+  LaneBitmask getLiveThroughAt(unsigned RegUnit, SlotIndex Pos) const;
 };
 
 void dumpRegSetPressure(ArrayRef<unsigned> SetPressure,
                         const TargetRegisterInfo *TRI);
 } // end namespace llvm
 
 #endif

lib/CodeGen/MachineScheduler.cpp

void ScheduleDAGMILive::enterRegion(MachineBasicBlock *bb,
   SUPressureDiffs.clear();
 
   ShouldTrackPressure = SchedImpl->shouldTrackPressure();
 }
 
 // Setup the register pressure trackers for the top scheduled top and bottom
 // scheduled regions.
 void ScheduleDAGMILive::initRegPressure() {
-  TopRPTracker.init(&MF, RegClassInfo, LIS, BB, RegionBegin);
-  BotRPTracker.init(&MF, RegClassInfo, LIS, BB, LiveRegionEnd);
+  TopRPTracker.init(&MF, RegClassInfo, LIS, BB, RegionBegin, false, false);
+  BotRPTracker.init(&MF, RegClassInfo, LIS, BB, LiveRegionEnd, false, false);
 
   // Close the RPTracker to finalize live ins.
   RPTracker.closeRegion();
 
   DEBUG(RPTracker.dump());
 
   // Initialize the live ins and live outs.
   TopRPTracker.addLiveRegs(RPTracker.getPressure().LiveInRegs);
void ScheduleDAGMILive::initRegPressure() {
   };
 
   // For each live out vreg reduce the pressure change associated with other
   // uses of the same vreg below the live-out reaching def.
   updatePressureDiffs(RPTracker.getPressure().LiveOutRegs);
 
   // Account for liveness generated by the region boundary.
   if (LiveRegionEnd != RegionEnd) {
-    SmallVector<unsigned, 8> LiveUses;
+    SmallVector<RegisterMaskPair, 8> LiveUses;
     BotRPTracker.recede(&LiveUses);
     updatePressureDiffs(LiveUses);
   }
 
   DEBUG(
     dbgs() << "Top Pressure:\n";
     dumpRegSetPressure(TopRPTracker.getRegSetPressureAtPos(), TRI);
     dbgs() << "Bottom Pressure:\n";
if (NewMaxPressure[ID] >= Limit - 2) {
             << ((NewMaxPressure[ID] > Limit) ? " > " : " <= ") << Limit
             << "(+ " << BotRPTracker.getLiveThru()[ID] << " livethru)\n");
     }
   }
 }
 
 /// Update the PressureDiff array for liveness after scheduling this
 /// instruction.
-void ScheduleDAGMILive::updatePressureDiffs(ArrayRef<unsigned> LiveUses) {
-  for (unsigned LUIdx = 0, LUEnd = LiveUses.size(); LUIdx != LUEnd; ++LUIdx) {
+void ScheduleDAGMILive::updatePressureDiffs(
+    ArrayRef<RegisterMaskPair> LiveUses) {
+  for (const RegisterMaskPair &P : LiveUses) {
     /// FIXME: Currently assuming single-use physregs.
-    unsigned Reg = LiveUses[LUIdx];
+    unsigned Reg = P.RegUnit;
+    assert(P.LaneMask != 0);
     DEBUG(dbgs() << "  LiveReg: " << PrintVRegOrUnit(Reg, TRI) << "\n");
     if (!TRI->isVirtualRegister(Reg))
       continue;
 
     // This may be called before CurrentBottom has been initialized. However,
     // BotRPTracker must have a valid position. We want the value live into the
     // instruction or live out of the block, so ask for the previous
     // instruction's live-out.
if (!ShouldTrackPressure) {
     RPTracker.reset();
     RegionCriticalPSets.clear();
     buildSchedGraph(AA);
     return;
   }
 
   // Initialize the register pressure tracker used by buildSchedGraph.
   RPTracker.init(&MF, RegClassInfo, LIS, BB, LiveRegionEnd,
-                 /*TrackUntiedDefs=*/true);
+                 false, /*TrackUntiedDefs=*/true);
 
   // Account for liveness generate by the region boundary.
   if (LiveRegionEnd != RegionEnd)
     RPTracker.recede();
 
   // Build the DAG, and compute current register pressure.
   buildSchedGraph(AA, &RPTracker, &SUPressureDiffs);
 

 /// assuming LiveIntervals.
 unsigned ScheduleDAGMILive::computeCyclicCriticalPath() {
   // This only applies to single block loop.
   if (!BB->isSuccessor(BB))
     return 0;
 
   unsigned MaxCyclicLatency = 0;
   // Visit each live out vreg def to find def/use pairs that cross iterations.
-  ArrayRef<unsigned> LiveOuts = RPTracker.getPressure().LiveOutRegs;
-  for (ArrayRef<unsigned>::iterator RI = LiveOuts.begin(), RE = LiveOuts.end();
-       RI != RE; ++RI) {
-    unsigned Reg = *RI;
+  for (const RegisterMaskPair &P : RPTracker.getPressure().LiveOutRegs) {
+    unsigned Reg = P.RegUnit;
     if (!TRI->isVirtualRegister(Reg))
         continue;
     const LiveInterval &LI = LIS->getInterval(Reg);
     const VNInfo *DefVNI = LI.getVNInfoBefore(LIS->getMBBEndIdx(BB));
     if (!DefVNI)
       continue;
 
     MachineInstr *DefMI = LIS->getInstructionFromIndex(DefVNI->def);
else {
         CurrentTop = nextIfDebug(++CurrentTop, priorII);
         TopRPTracker.setPos(CurrentTop);
       }
       moveInstruction(MI, CurrentBottom);
       CurrentBottom = MI;
     }
     if (ShouldTrackPressure) {
       // Update bottom scheduled pressure.
-      SmallVector<unsigned, 8> LiveUses;
+      SmallVector<RegisterMaskPair, 8> LiveUses;
       BotRPTracker.recede(&LiveUses);
       assert(BotRPTracker.getPos() == CurrentBottom && "out of sync");
       DEBUG(
         dbgs() << "Bottom Pressure:\n";
         dumpRegSetPressure(BotRPTracker.getRegSetPressureAtPos(), TRI);
       );
 
       updateScheduledPressure(SU, BotRPTracker.getPressure().MaxSetPressure);

lib/CodeGen/RegisterPressure.cpp

 #include "llvm/CodeGen/RegisterClassInfo.h"
 #include "llvm/Support/Debug.h"
 #include "llvm/Support/raw_ostream.h"
 
 using namespace llvm;
 
 /// Increase pressure for each pressure set provided by TargetRegisterInfo.
 static void increaseSetPressure(std::vector<unsigned> &CurrSetPressure,
-                                PSetIterator PSetI) {
+                                const MachineRegisterInfo &MRI, unsigned Reg,
+                                LaneBitmask PrevMask, LaneBitmask NewMask) {
+  assert((PrevMask & ~NewMask) == 0 && "Must not remove bits");
+  if (PrevMask != 0 || NewMask == 0)
+    return;
+
+  PSetIterator PSetI = MRI.getPressureSets(Reg);
   unsigned Weight = PSetI.getWeight();
   for (; PSetI.isValid(); ++PSetI)
     CurrSetPressure[*PSetI] += Weight;
 }
 
 /// Decrease pressure for each pressure set provided by TargetRegisterInfo.
 static void decreaseSetPressure(std::vector<unsigned> &CurrSetPressure,
-                                PSetIterator PSetI) {
+                                const MachineRegisterInfo &MRI, unsigned Reg,
+                                LaneBitmask PrevMask, LaneBitmask NewMask) {
+  assert((NewMask & !PrevMask) == 0 && "Must not add bits");
+  if (NewMask != 0 || PrevMask == 0)
+    return;
+
+  PSetIterator PSetI = MRI.getPressureSets(Reg);
   unsigned Weight = PSetI.getWeight();
   for (; PSetI.isValid(); ++PSetI) {
     assert(CurrSetPressure[*PSetI] >= Weight && "register pressure underflow");
     CurrSetPressure[*PSetI] -= Weight;
   }
 }
 
 LLVM_DUMP_METHOD
if (Empty)
     dbgs() << "\n";
 }
 
 LLVM_DUMP_METHOD
 void RegisterPressure::dump(const TargetRegisterInfo *TRI) const {
   dbgs() << "Max Pressure: ";
   dumpRegSetPressure(MaxSetPressure, TRI);
   dbgs() << "Live In: ";
-  for (unsigned Reg : LiveInRegs)
-    dbgs() << PrintVRegOrUnit(Reg, TRI) << " ";
+  for (const RegisterMaskPair &P : LiveInRegs) {
+    dbgs() << PrintVRegOrUnit(P.RegUnit, TRI);
+    if (P.LaneMask != ~0u)
+      dbgs() << ':' << PrintLaneMask(P.LaneMask);
+    dbgs() << ' ';
+  }
   dbgs() << '\n';
   dbgs() << "Live Out: ";
-  for (unsigned Reg : LiveOutRegs)
-    dbgs() << PrintVRegOrUnit(Reg, TRI) << " ";
+  for (const RegisterMaskPair &P : LiveOutRegs) {
+    dbgs() << PrintVRegOrUnit(P.RegUnit, TRI);
+    if (P.LaneMask != ~0u)
+      dbgs() << ':' << PrintLaneMask(P.LaneMask);
+    dbgs() << ' ';
+  }
   dbgs() << '\n';
 }
 
 LLVM_DUMP_METHOD
 void RegPressureTracker::dump() const {
   if (!isTopClosed() || !isBottomClosed()) {
     dbgs() << "Curr Pressure: ";
     dumpRegSetPressure(CurrSetPressure, TRI);
   }
   P.dump(TRI);
 }
 
 void PressureDiff::dump(const TargetRegisterInfo &TRI) const {
   const char *sep = "";
   for (const PressureChange &Change : *this) {
     if (!Change.isValid())
       break;
     dbgs() << sep << TRI.getRegPressureSetName(Change.getPSet())
            << " " << Change.getUnitInc();
     sep = "    ";
   }
   dbgs() << '\n';
 }
 
-/// Increase the current pressure as impacted by these registers and bump
-/// the high water mark if needed.
-void RegPressureTracker::increaseRegPressure(ArrayRef<unsigned> RegUnits) {
-  for (unsigned RegUnit : RegUnits) {
-    PSetIterator PSetI = MRI->getPressureSets(RegUnit);
-    unsigned Weight = PSetI.getWeight();
-    for (; PSetI.isValid(); ++PSetI) {
-      CurrSetPressure[*PSetI] += Weight;
-      if (CurrSetPressure[*PSetI] > P.MaxSetPressure[*PSetI]) {
-        P.MaxSetPressure[*PSetI] = CurrSetPressure[*PSetI];
-      }
-    }
-  }
-}
+void RegPressureTracker::increaseRegPressure(unsigned RegUnit,
+                                             LaneBitmask PreviousMask,
+                                             LaneBitmask NewMask) {
+  if (PreviousMask != 0 || NewMask == 0)
+    return;
+
+    if (CurrSetPressure[*PSetI] > P.MaxSetPressure[*PSetI])
 
-/// Simply decrease the current pressure as impacted by these registers.
-void RegPressureTracker::decreaseRegPressure(ArrayRef<unsigned> RegUnits) {
-  for (unsigned RegUnit : RegUnits)
-    decreaseSetPressure(CurrSetPressure, MRI->getPressureSets(RegUnit));
+void RegPressureTracker::decreaseRegPressure(unsigned RegUnit,
+                                             LaneBitmask PreviousMask,
+                                             LaneBitmask NewMask) {
+  decreaseSetPressure(CurrSetPressure, *MRI, RegUnit, PreviousMask, NewMask);
 }
 
 /// Clear the result so it can be used for another round of pressure tracking.
 void IntervalPressure::reset() {
   TopIdx = BottomIdx = SlotIndex();
   MaxSetPressure.clear();
   LiveInRegs.clear();
   LiveOutRegs.clear();

 /// Setup the RegPressureTracker.
 ///
 /// TODO: Add support for pressure without LiveIntervals.
 void RegPressureTracker::init(const MachineFunction *mf,
                               const RegisterClassInfo *rci,
                               const LiveIntervals *lis,
                               const MachineBasicBlock *mbb,
                               MachineBasicBlock::const_iterator pos,
-                              bool ShouldTrackUntiedDefs)
-{
+                              bool TrackLaneMasks, bool TrackUntiedDefs) {
   reset();
 
   MF = mf;
   TRI = MF->getSubtarget().getRegisterInfo();
   RCI = rci;
   MRI = &MF->getRegInfo();
   MBB = mbb;
-  TrackUntiedDefs = ShouldTrackUntiedDefs;
+  this->TrackUntiedDefs = TrackUntiedDefs;
+  this->TrackLaneMasks = TrackLaneMasks;
 
   if (RequireIntervals) {
     assert(lis && "IntervalPressure requires LiveIntervals");
     LIS = lis;
   }
 
   CurrPos = pos;
   CurrSetPressure.assign(TRI->getNumRegPressureSets(), 0);

 
 /// The register tracker is unaware of global liveness so ignores normal
 /// live-thru ranges. However, two-address or coalesced chains can also lead
 /// to live ranges with no holes. Count these to inform heuristics that we
 /// can never drop below this pressure.
 void RegPressureTracker::initLiveThru(const RegPressureTracker &RPTracker) {
   LiveThruPressure.assign(TRI->getNumRegPressureSets(), 0);
   assert(isBottomClosed() && "need bottom-up tracking to intialize.");
-  for (unsigned Reg : P.LiveOutRegs) {
-    if (TargetRegisterInfo::isVirtualRegister(Reg)
-        && !RPTracker.hasUntiedDef(Reg)) {
-      increaseSetPressure(LiveThruPressure, MRI->getPressureSets(Reg));
-    }
-  }
+  for (const RegisterMaskPair &Pair : P.LiveOutRegs) {
+    unsigned RegUnit = Pair.RegUnit;
+    if (TargetRegisterInfo::isVirtualRegister(RegUnit)
+        && !RPTracker.hasUntiedDef(RegUnit))
+      increaseSetPressure(LiveThruPressure, *MRI, RegUnit, 0, Pair.LaneMask);
+  }
+}
+
+static unsigned getRegLanes(ArrayRef<RegisterMaskPair> RegUnits,
+                            unsigned RegUnit) {
+  auto I = std::find_if(RegUnits.begin(), RegUnits.end(),
+                        [RegUnit](const RegisterMaskPair Other) {
+                        return Other.RegUnit == RegUnit;
+                        });
+  if (I == RegUnits.end())
+    return 0;
+  return I->LaneMask;
+}
+
+static void addRegLanes(SmallVectorImpl<RegisterMaskPair> &RegUnits,
+                        RegisterMaskPair Pair) {
+  unsigned RegUnit = Pair.RegUnit;
+  assert(Pair.LaneMask != 0);
+  auto I = std::find_if(RegUnits.begin(), RegUnits.end(),
+                        [RegUnit](const RegisterMaskPair Other) {
+                          return Other.RegUnit == RegUnit;
+                        });
+  if (I == RegUnits.end()) {
+    RegUnits.push_back(Pair);
+  } else {
+    I->LaneMask |= Pair.LaneMask;
+
+static void removeRegLanes(SmallVectorImpl<RegisterMaskPair> &RegUnits,
+                           RegisterMaskPair Pair) {
+  unsigned RegUnit = Pair.RegUnit;
+  assert(Pair.LaneMask != 0);
+  auto I = std::find_if(RegUnits.begin(), RegUnits.end(),
+                        [RegUnit](const RegisterMaskPair Other) {
+                          return Other.RegUnit == RegUnit;
+                        });
+  if (I != RegUnits.end()) {
+    I->LaneMask &= ~Pair.LaneMask;
+    if (I->LaneMask == 0)
+      RegUnits.erase(I);
+  }
 }
 
-/// \brief Convenient wrapper for checking membership in RegisterOperands.
-/// (std::count() doesn't have an early exit).
-static bool containsReg(ArrayRef<unsigned> RegUnits, unsigned RegUnit) {
-  return std::find(RegUnits.begin(), RegUnits.end(), RegUnit) != RegUnits.end();
+static LaneBitmask getLanesWithProperty(const LiveIntervals &LIS,
+    const MachineRegisterInfo &MRI, bool TrackLaneMasks, unsigned RegUnit,
+    SlotIndex Pos,
+    bool(*Property)(const LiveRange &LR, SlotIndex Pos)) {
+  if (TargetRegisterInfo::isVirtualRegister(RegUnit)) {
+    const LiveInterval &LI = LIS.getInterval(RegUnit);
+    LaneBitmask Result = 0;
+    if (TrackLaneMasks && LI.hasSubRanges()) {
+      for (const LiveInterval::SubRange &SR : LI.subranges()) {
+        if (Property(SR, Pos))
+          Result |= SR.LaneMask;
       }
+    } else if (Property(LI, Pos))
+      Result = MRI.getMaxLaneMaskForVReg(RegUnit);
+
+    return Result;
+  } else {
+    const LiveRange *LR = LIS.getCachedRegUnit(RegUnit);
+    // Be prepared for missing liveranges: We usually do not compute liveranges
+    // for physical registers on targets with many registers (GPUs).
+    if (LR == nullptr)
+      return 0;
+    return Property(*LR, Pos) ? ~0u : 0;
+  }
+}
+
+static LaneBitmask getLiveLanesAt(const LiveIntervals &LIS,
+                                  const MachineRegisterInfo &MRI,
+                                  bool TrackLaneMasks, unsigned RegUnit,
+                                  SlotIndex Pos) {
+  return getLanesWithProperty(LIS, MRI, TrackLaneMasks, RegUnit, Pos,
+                              [](const LiveRange &LR, SlotIndex Pos) {
+                                return LR.liveAt(Pos);
+                              });
+}
+
 
 namespace {
 
 /// Collect this instruction's unique uses and defs into SmallVectors for
 /// processing defs and uses in order.
 ///
 /// FIXME: always ignore tied opers
 class RegisterOperandsCollector {
   RegisterOperands &RegOpers;
   const TargetRegisterInfo &TRI;
   const MachineRegisterInfo &MRI;
+  bool TrackLaneMasks;
   bool IgnoreDead;
 
   RegisterOperandsCollector(RegisterOperands &RegOpers,
                             const TargetRegisterInfo &TRI,
                             const MachineRegisterInfo &MRI,
-                            bool IgnoreDead)
-    : RegOpers(RegOpers), TRI(TRI), MRI(MRI), IgnoreDead(IgnoreDead) {}
+                            bool TrackLaneMasks, bool IgnoreDead)
+    : RegOpers(RegOpers), TRI(TRI), MRI(MRI),
+      TrackLaneMasks(TrackLaneMasks), IgnoreDead(IgnoreDead) {}
 
   void collectInstr(const MachineInstr &MI) const {
     for (ConstMIBundleOperands OperI(&MI); OperI.isValid(); ++OperI)
       collectOperand(*OperI);
 
     // Remove redundant physreg dead defs.
-    SmallVectorImpl<unsigned>::iterator I =
-      std::remove_if(RegOpers.DeadDefs.begin(), RegOpers.DeadDefs.end(),
-                     std::bind1st(std::ptr_fun(containsReg), RegOpers.Defs));
-    RegOpers.DeadDefs.erase(I, RegOpers.DeadDefs.end());
+    for (const RegisterMaskPair &P : RegOpers.Defs)
+      removeRegLanes(RegOpers.DeadDefs, P);
   }
 
   /// Push this operand's register onto the correct vectors.
   void collectOperand(const MachineOperand &MO) const {
     if (!MO.isReg() || !MO.getReg())
       return;
     unsigned Reg = MO.getReg();
-    if (MO.readsReg())
-      pushRegUnits(Reg, RegOpers.Uses);
-    if (MO.isDef()) {
+    unsigned SubRegIdx = MO.getSubReg();
+    if (MO.isUse()) {
+      if (!MO.isUndef() && !MO.isInternalRead())
+        pushRegUnits(Reg, SubRegIdx, RegOpers.Uses);
+    } else {
+      assert(MO.isDef());
+      if (MO.isUndef()) {
+        // Treat read-undef subreg defs as definitions of the whole register.
+        SubRegIdx = 0;
+      } else if (!TrackLaneMasks && SubRegIdx != 0 && !MO.isInternalRead()) {
+        // Interpret the subregister def as read-modify-store: A use+def of the
+        // full register.
+        pushRegUnits(Reg, SubRegIdx, RegOpers.Uses);
+      }
+
       if (MO.isDead()) {
         if (!IgnoreDead)
-          pushRegUnits(Reg, RegOpers.DeadDefs);
+          pushRegUnits(Reg, SubRegIdx, RegOpers.DeadDefs);
       } else
-        pushRegUnits(Reg, RegOpers.Defs);
+        pushRegUnits(Reg, SubRegIdx, RegOpers.Defs);
     }
   }
 
-  void pushRegUnits(unsigned Reg, SmallVectorImpl<unsigned> &RegUnits) const {
+  void pushRegUnits(unsigned Reg, unsigned SubRegIdx,
+                    SmallVectorImpl<RegisterMaskPair> &RegUnits) const {
     if (TargetRegisterInfo::isVirtualRegister(Reg)) {
-      if (containsReg(RegUnits, Reg))
-        return;
-      RegUnits.push_back(Reg);
+      LaneBitmask LaneMask = TrackLaneMasks && SubRegIdx != 0
+                           ? TRI.getSubRegIndexLaneMask(SubRegIdx)
+                           : MRI.getMaxLaneMaskForVReg(Reg);
+      addRegLanes(RegUnits, RegisterMaskPair(Reg, LaneMask));
     } else if (MRI.isAllocatable(Reg)) {
-      for (MCRegUnitIterator Units(Reg, &TRI); Units.isValid(); ++Units) {
-        if (containsReg(RegUnits, *Units))
-          continue;
-        RegUnits.push_back(*Units);
-      }
+      for (MCRegUnitIterator Units(Reg, &TRI); Units.isValid(); ++Units)
+        addRegLanes(RegUnits, RegisterMaskPair(*Units, ~0u));
     }
   }
 
   friend class llvm::RegisterOperands;
 };
 
 } // namespace
 
 void RegisterOperands::collect(const MachineInstr &MI,
                                const TargetRegisterInfo &TRI,
                                const MachineRegisterInfo &MRI,
-                               bool IgnoreDead) {
-  RegisterOperandsCollector Collector(*this, TRI, MRI, IgnoreDead);
+                               bool TrackLaneMasks, bool IgnoreDead) {
+  RegisterOperandsCollector Collector(*this, TRI, MRI, TrackLaneMasks,
+                                      IgnoreDead);
   Collector.collectInstr(MI);
 }
 
 void RegisterOperands::detectDeadDefs(const MachineInstr &MI,
                                       const LiveIntervals &LIS) {
   SlotIndex SlotIdx = LIS.getInstructionIndex(&MI);
-  for (SmallVectorImpl<unsigned>::iterator RI = Defs.begin();
-       RI != Defs.end(); /*empty*/) {
-    unsigned Reg = *RI;
+  for (auto RI = Defs.begin(); RI != Defs.end(); /*empty*/) {
+    unsigned Reg = RI->RegUnit;
     const LiveRange *LR = getLiveRange(LIS, Reg);
     if (LR != nullptr) {
       LiveQueryResult LRQ = LR->Query(SlotIdx);
       if (LRQ.isDeadDef()) {
         // LiveIntervals knows this is a dead even though it's MachineOperand is
         // not flagged as such.
-        DeadDefs.push_back(Reg);
+        DeadDefs.push_back(*RI);
         RI = Defs.erase(RI);
         continue;
       }
     }
     ++RI;
   }
 }
 
+void RegisterOperands::adjustLaneLiveness(const LiveIntervals &LIS,
+                                          const MachineRegisterInfo &MRI,
+                                          SlotIndex Pos) {
+  for (auto I = Defs.begin(); I != Defs.end(); ) {
+    LaneBitmask LiveAfter = getLiveLanesAt(LIS, MRI, true, I->RegUnit,
+                                           Pos.getDeadSlot());
+#if 0
+    unsigned DeadDef = I->LaneMask & ~LiveAfter;
+    if (DeadDef != 0)
+      addRegLanes(DeadDefs, RegisterMaskPair(I->RegUnit, DeadDef));
+#endif
+    unsigned LaneMask = I->LaneMask & LiveAfter;
+    if (LaneMask == 0)
+      I = Defs.erase(I);
+    else {
+      I->LaneMask = LaneMask;
+      ++I;
+    }
+  }
+  for (auto I = Uses.begin(); I != Uses.end(); ) {
+    LaneBitmask LiveBefore = getLiveLanesAt(LIS, MRI, true, I->RegUnit,
+                                            Pos.getBaseIndex());
+    unsigned LaneMask = I->LaneMask & LiveBefore;
+    if (LaneMask == 0) {
+      I = Uses.erase(I);
+    } else {
+      I->LaneMask = LaneMask;
+      ++I;
+    }
+  }
+}
+
 /// Initialize an array of N PressureDiffs.
 void PressureDiffs::init(unsigned N) {
   Size = N;
   if (N <= Max) {
     memset(PDiffArray, 0, N * sizeof(PressureDiff));
     return;
   }
   Max = Size;
   free(PDiffArray);
   PDiffArray = reinterpret_cast<PressureDiff*>(calloc(N, sizeof(PressureDiff)));
 }
 
 void PressureDiffs::addInstruction(unsigned Idx,
                                    const RegisterOperands &RegOpers,
                                    const MachineRegisterInfo &MRI) {
   PressureDiff &PDiff = (*this)[Idx];
   assert(!PDiff.begin()->isValid() && "stale PDiff");
-  for (unsigned Reg : RegOpers.Defs)
-    PDiff.addPressureChange(Reg, true, &MRI);
+  for (const RegisterMaskPair &P : RegOpers.Defs)
+    PDiff.addPressureChange(P.RegUnit, true, &MRI);
 
-  for (unsigned Reg : RegOpers.Uses)
-    PDiff.addPressureChange(Reg, false, &MRI);
+  for (const RegisterMaskPair &P : RegOpers.Uses)
+    PDiff.addPressureChange(P.RegUnit, false, &MRI);
 }
 
 /// Add a change in pressure to the pressure diff of a given instruction.
 void PressureDiff::addPressureChange(unsigned RegUnit, bool IsDec,
                                      const MachineRegisterInfo *MRI) {
   PSetIterator PSetI = MRI->getPressureSets(RegUnit);
   int Weight = IsDec ? -PSetI.getWeight() : PSetI.getWeight();
   for (; PSetI.isValid(); ++PSetI) {
if (NewUnitInc != 0) {
         *I = *J;
       if (J != E)
         *I = *J;
     }
   }
 }
 
 /// Force liveness of registers.
-void RegPressureTracker::addLiveRegs(ArrayRef<unsigned> Regs) {
-  for (unsigned Reg : Regs) {
-    if (LiveRegs.insert(Reg))
-      increaseRegPressure(Reg);
+void RegPressureTracker::addLiveRegs(ArrayRef<RegisterMaskPair> Regs) {
+  for (const RegisterMaskPair &P : Regs) {
+    unsigned PrevMask = LiveRegs.insert(P);
+    unsigned NewMask = PrevMask | P.LaneMask;
+    increaseRegPressure(P.RegUnit, PrevMask, NewMask);
   }
 }
 
-/// Add Reg to the live in set and increase max pressure.
-void RegPressureTracker::discoverLiveIn(unsigned Reg) {
-  assert(!LiveRegs.contains(Reg) && "avoid bumping max pressure twice");
-  if (containsReg(P.LiveInRegs, Reg))
+void RegPressureTracker::discoverLiveInOrOut(RegisterMaskPair Pair,
+    SmallVectorImpl<RegisterMaskPair> &LiveInOrOut) {
+  if (Pair.LaneMask == 0)
     return;
 
-  // At live in discovery, unconditionally increase the high water mark.
-  P.LiveInRegs.push_back(Reg);
-  increaseSetPressure(P.MaxSetPressure, MRI->getPressureSets(Reg));
+  unsigned RegUnit = Pair.RegUnit;
+  auto I = std::find_if(LiveInOrOut.begin(), LiveInOrOut.end(),
+                        [RegUnit](const RegisterMaskPair &Other) {
+                          return Other.RegUnit == RegUnit;
+                        });
+  LaneBitmask PrevMask;
+  LaneBitmask NewMask;
+  if (I == LiveInOrOut.end()) {
+    PrevMask = 0;
+    NewMask = Pair.LaneMask;
+    LiveInOrOut.push_back(Pair);
+  } else {
+    PrevMask = I->LaneMask;
+    NewMask = PrevMask | Pair.LaneMask;
+    I->LaneMask = NewMask;
+  }
+  increaseSetPressure(P.MaxSetPressure, *MRI, RegUnit, PrevMask, NewMask);
 }
 
-/// Add Reg to the live out set and increase max pressure.
-void RegPressureTracker::discoverLiveOut(unsigned Reg) {
-  assert(!LiveRegs.contains(Reg) && "avoid bumping max pressure twice");
-  if (containsReg(P.LiveOutRegs, Reg))
-    return;
+void RegPressureTracker::discoverLiveIn(RegisterMaskPair Pair) {
+  discoverLiveInOrOut(Pair, P.LiveInRegs);
+}
 
-  // At live out discovery, unconditionally increase the high water mark.
-  P.LiveOutRegs.push_back(Reg);
-  increaseSetPressure(P.MaxSetPressure, MRI->getPressureSets(Reg));
+void RegPressureTracker::discoverLiveOut(RegisterMaskPair Pair) {
+  discoverLiveInOrOut(Pair, P.LiveOutRegs);
+}
+
+void RegPressureTracker::bumpDeadDefs(ArrayRef<RegisterMaskPair> DeadDefs) {
+  for (const RegisterMaskPair &P : DeadDefs) {
+    unsigned Reg = P.RegUnit;
+    LaneBitmask LiveMask = LiveRegs.contains(Reg);
+    LaneBitmask BumpedMask = LiveMask | P.LaneMask;
+    increaseRegPressure(Reg, LiveMask, BumpedMask);
+  }
+  for (const RegisterMaskPair &P : DeadDefs) {
+    unsigned Reg = P.RegUnit;
+    LaneBitmask LiveMask = LiveRegs.contains(Reg);
+    LaneBitmask BumpedMask = LiveMask | P.LaneMask;
+    decreaseRegPressure(Reg, BumpedMask, LiveMask);
+  }
 }
 
 /// Recede across the previous instruction. If LiveUses is provided, record any
 /// RegUnits that are made live by the current instruction's uses. This includes
 /// registers that are both defined and used by the instruction.  If a pressure
 /// difference pointer is provided record the changes is pressure caused by this
 /// instruction independent of liveness.
 void RegPressureTracker::recede(const RegisterOperands &RegOpers,
-                                SmallVectorImpl<unsigned> *LiveUses) {
+                                SmallVectorImpl<RegisterMaskPair> *LiveUses) {
   assert(!CurrPos->isDebugValue());
 
   // Boost pressure for all dead defs together.
-  increaseRegPressure(RegOpers.DeadDefs);
-  decreaseRegPressure(RegOpers.DeadDefs);
+  bumpDeadDefs(RegOpers.DeadDefs);
 
   // Kill liveness at live defs.
   // TODO: consider earlyclobbers?
-  for (unsigned Reg : RegOpers.Defs) {
-    if (LiveRegs.erase(Reg))
-      decreaseRegPressure(Reg);
-    else
-      discoverLiveOut(Reg);
+  for (const RegisterMaskPair &Def : RegOpers.Defs) {
+    unsigned Reg = Def.RegUnit;
+
+    LaneBitmask PreviousMask = LiveRegs.erase(Def);
+    LaneBitmask NewMask = PreviousMask & ~Def.LaneMask;
+
+    LaneBitmask LiveOut = Def.LaneMask & ~PreviousMask;
+    if (LiveOut != 0) {
+      discoverLiveOut(RegisterMaskPair(Reg, LiveOut));
+      // Retroactively model effects on pressure of the live out lanes.
+      increaseSetPressure(CurrSetPressure, *MRI, Reg, 0, LiveOut);
+      PreviousMask = LiveOut;
+    }
+
+    decreaseRegPressure(Reg, PreviousMask, NewMask);
   }
 
   SlotIndex SlotIdx;
   if (RequireIntervals)
     SlotIdx = LIS->getInstructionIndex(CurrPos).getRegSlot();
 
   // Generate liveness for uses.
-  for (unsigned Reg : RegOpers.Uses) {
-    if (!LiveRegs.contains(Reg)) {
-      // Adjust liveouts if LiveIntervals are available.
-      if (RequireIntervals) {
-        const LiveRange *LR = getLiveRange(*LIS, Reg);
-        if (LR) {
-          LiveQueryResult LRQ = LR->Query(SlotIdx);
-          if (!LRQ.isKill() && !LRQ.valueDefined())
-            discoverLiveOut(Reg);
-        }
+  for (const RegisterMaskPair &Use : RegOpers.Uses) {
+    unsigned Reg = Use.RegUnit;
+    assert(Use.LaneMask != 0);
+    LaneBitmask PreviousMask = LiveRegs.insert(Use);
+    LaneBitmask NewMask = PreviousMask | Use.LaneMask;
+    if (NewMask == PreviousMask)
+      continue;
+
+    // Did the register just become live?
+    if (PreviousMask == 0) {
+      if (LiveUses != nullptr) {
+        unsigned NewLanes = NewMask & ~PreviousMask;
+        addRegLanes(*LiveUses, RegisterMaskPair(Reg, NewLanes));
       }
-      increaseRegPressure(Reg);
-      LiveRegs.insert(Reg);
-      if (LiveUses && !containsReg(*LiveUses, Reg))
-        LiveUses->push_back(Reg);
+
+      // Discover live outs if this may be the first occurance of this register.
+      LaneBitmask LiveOut = getLiveThroughAt(Reg, SlotIdx);
+      discoverLiveOut(RegisterMaskPair(Reg, LiveOut));
     }
+
+    increaseRegPressure(Reg, PreviousMask, NewMask);
   }
   if (TrackUntiedDefs) {
-    for (unsigned Reg : RegOpers.Defs) {
-      if (TargetRegisterInfo::isVirtualRegister(Reg) && !LiveRegs.contains(Reg))
-        UntiedDefs.insert(Reg);
+    for (const RegisterMaskPair &Def : RegOpers.Defs) {
+      unsigned RegUnit = Def.RegUnit;
+      if (TargetRegisterInfo::isVirtualRegister(RegUnit) &&
+          (LiveRegs.contains(RegUnit) & Def.LaneMask) == 0)
+        UntiedDefs.insert(RegUnit);
     }
   }
 }
 
 void RegPressureTracker::recedeSkipDebugValues() {
   assert(CurrPos != MBB->begin());
   if (!isBottomClosed())
     closeBottom();
void RegPressureTracker::recedeSkipDebugValues() {
   if (RequireIntervals)
     SlotIdx = LIS->getInstructionIndex(CurrPos).getRegSlot();
 
   // Open the top of the region using slot indexes.
   if (RequireIntervals && isTopClosed())
     static_cast<IntervalPressure&>(P).openTop(SlotIdx);
 }
 
-void RegPressureTracker::recede(SmallVectorImpl<unsigned> *LiveUses) {
+void RegPressureTracker::recede(SmallVectorImpl<RegisterMaskPair> *LiveUses) {
   recedeSkipDebugValues();
 
   const MachineInstr &MI = *CurrPos;
   RegisterOperands RegOpers;
-  RegOpers.collect(MI, *TRI, *MRI);
-  if (RequireIntervals)
+  RegOpers.collect(MI, *TRI, *MRI, TrackLaneMasks, false);
+  if (TrackLaneMasks) {
+    SlotIndex SlotIdx = LIS->getInstructionIndex(CurrPos).getRegSlot();
+    RegOpers.adjustLaneLiveness(*LIS, *MRI, SlotIdx);
+  } else if (RequireIntervals) {
     RegOpers.detectDeadDefs(MI, *LIS);
+  }
 
   recede(RegOpers, LiveUses);
 }
 
 /// Advance across the current instruction.
 void RegPressureTracker::advance() {
   assert(!TrackUntiedDefs && "unsupported mode");
 
void RegPressureTracker::advance() {
   if (isBottomClosed()) {
     if (RequireIntervals)
       static_cast<IntervalPressure&>(P).openBottom(SlotIdx);
     else
       static_cast<RegionPressure&>(P).openBottom(CurrPos);
   }
 
   RegisterOperands RegOpers;
-  RegOpers.collect(*CurrPos, *TRI, *MRI);
-
-  for (unsigned Reg : RegOpers.Uses) {
-    // Discover live-ins.
-    bool isLive = LiveRegs.contains(Reg);
-    if (!isLive)
-      discoverLiveIn(Reg);
+  RegOpers.collect(*CurrPos, *TRI, *MRI, TrackLaneMasks, false);
+  if (TrackLaneMasks)
+    RegOpers.adjustLaneLiveness(*LIS, *MRI, SlotIdx);
+
+  for (const RegisterMaskPair &Use : RegOpers.Uses) {
+    unsigned Reg = Use.RegUnit;
+    LaneBitmask LiveMask = LiveRegs.contains(Reg);
+    LaneBitmask LiveIn = Use.LaneMask & ~LiveMask;
+    if (LiveIn != 0) {
+      discoverLiveIn(RegisterMaskPair(Reg, LiveIn));
+      increaseRegPressure(Reg, LiveMask, LiveMask | LiveIn);
+      LiveRegs.insert(RegisterMaskPair(Reg, LiveIn));
+    }
     // Kill liveness at last uses.
-    bool lastUse = false;
-    if (RequireIntervals) {
-      const LiveRange *LR = getLiveRange(*LIS, Reg);
-      lastUse = LR && LR->Query(SlotIdx).isKill();
-    } else {
-      // Allocatable physregs are always single-use before register rewriting.
-      lastUse = !TargetRegisterInfo::isVirtualRegister(Reg);
+    LaneBitmask LastUseMask = getLastUsedLanes(Reg, SlotIdx);
+    if (LastUseMask != 0) {
+      LiveRegs.erase(RegisterMaskPair(Reg, LastUseMask));
+      decreaseRegPressure(Reg, LiveMask, LiveMask & ~LastUseMask);
     }
-    if (lastUse && isLive) {
-      LiveRegs.erase(Reg);
-      decreaseRegPressure(Reg);
-    } else if (!lastUse && !isLive)
-      increaseRegPressure(Reg);
   }
 
   // Generate liveness for defs.
-  for (unsigned Reg : RegOpers.Defs) {
-    if (LiveRegs.insert(Reg))
-      increaseRegPressure(Reg);
+  for (const RegisterMaskPair &Def : RegOpers.Defs) {
+    LaneBitmask PreviousMask = LiveRegs.insert(Def);
+    LaneBitmask NewMask = PreviousMask | Def.LaneMask;
+    increaseRegPressure(Def.RegUnit, PreviousMask, NewMask);
   }
 
   // Boost pressure for all dead defs together.
-  increaseRegPressure(RegOpers.DeadDefs);
-  decreaseRegPressure(RegOpers.DeadDefs);
+  bumpDeadDefs(RegOpers.DeadDefs);
 
   // Find the next instruction.
   do
     ++CurrPos;
   while (CurrPos != MBB->end() && CurrPos->isDebugValue());
 }
 
 /// Find the max change in excess pressure across all sets.

 /// pressure. Unlike the advance/recede pressure tracking interface, this does
 /// not discover live in/outs.
 ///
 /// This is intended for speculative queries. It leaves pressure inconsistent
 /// with the current position, so must be restored by the caller.
 void RegPressureTracker::bumpUpwardPressure(const MachineInstr *MI) {
   assert(!MI->isDebugValue() && "Expect a nondebug instruction.");
 
+  SlotIndex SlotIdx;
+  if (RequireIntervals)
+    SlotIdx = LIS->getInstructionIndex(MI).getRegSlot();
+
   // Account for register pressure similar to RegPressureTracker::recede().
   RegisterOperands RegOpers;
-  RegOpers.collect(*MI, *TRI, *MRI, /*IgnoreDead=*/true);
+  RegOpers.collect(*MI, *TRI, *MRI, TrackLaneMasks, /*IgnoreDead=*/true);
   assert(RegOpers.DeadDefs.size() == 0);
-  if (RequireIntervals)
+  if (TrackLaneMasks)
+    RegOpers.adjustLaneLiveness(*LIS, *MRI, SlotIdx);
+  else if (RequireIntervals)
     RegOpers.detectDeadDefs(*MI, *LIS);
 
+  // Boost max pressure for all dead defs together.
+  // Since CurrSetPressure and MaxSetPressure
+  bumpDeadDefs(RegOpers.DeadDefs);
+
   // Kill liveness at live defs.
-  for (unsigned Reg : RegOpers.Defs) {
-    if (!containsReg(RegOpers.Uses, Reg))
-      decreaseRegPressure(Reg);
+  for (const RegisterMaskPair &P : RegOpers.Defs) {
+    unsigned Reg = P.RegUnit;
+    LaneBitmask LiveLanes = LiveRegs.contains(Reg);
+    LaneBitmask UseLanes = getRegLanes(RegOpers.Uses, Reg);
+    LaneBitmask DefLanes = P.LaneMask;
+    LaneBitmask LiveAfter = (LiveLanes & ~DefLanes) | UseLanes;
+    decreaseRegPressure(Reg, LiveLanes, LiveAfter);
   }
   // Generate liveness for uses.
-  for (unsigned Reg : RegOpers.Uses) {
-    if (!LiveRegs.contains(Reg))
-      increaseRegPressure(Reg);
+  for (const RegisterMaskPair &P : RegOpers.Uses) {
+    unsigned Reg = P.RegUnit;
+    LaneBitmask LiveLanes = LiveRegs.contains(Reg);
+    LaneBitmask LiveAfter = LiveLanes | P.LaneMask;
+    increaseRegPressure(Reg, LiveLanes, LiveAfter);
   }
 }
 
 /// Consider the pressure increase caused by traversing this instruction
 /// bottom-up. Find the pressure set with the most change beyond its pressure
 /// limit based on the tracker's current pressure, and return the change in
 /// number of register units of that pressure set introduced by this
 /// instruction.
for (PressureDiff::const_iterator
     if (!Delta.CurrentMax.isValid() && MNew > MaxPressureLimit[PSetID]) {
       Delta.CurrentMax = PressureChange(PSetID);
       Delta.CurrentMax.setUnitInc(MNew - MOld);
     }
   }
 }
 
 /// Helper to find a vreg use between two indices [PriorUseIdx, NextUseIdx).
-static bool findUseBetween(unsigned Reg, SlotIndex PriorUseIdx,
-                           SlotIndex NextUseIdx, const MachineRegisterInfo &MRI,
+/// The query starts with a lane bitmask which gets lanes/bits removed for every
+/// use we find.
+static LaneBitmask findUseBetween(unsigned Reg, LaneBitmask LastUseMask,
+                                  SlotIndex PriorUseIdx, SlotIndex NextUseIdx,
+                                  const MachineRegisterInfo &MRI,
                                   const LiveIntervals *LIS) {
-  for (const MachineInstr &MI : MRI.use_nodbg_instructions(Reg)) {
-    SlotIndex InstSlot = LIS->getInstructionIndex(&MI).getRegSlot();
-    if (InstSlot >= PriorUseIdx && InstSlot < NextUseIdx)
-      return true;
-  }
-  return false;
+  const TargetRegisterInfo &TRI = *MRI.getTargetRegisterInfo();
+  for (const MachineOperand &MO : MRI.use_nodbg_operands(Reg)) {
+    if (MO.isUndef())
+      continue;
+    const MachineInstr *MI = MO.getParent();
+    SlotIndex InstSlot = LIS->getInstructionIndex(MI).getRegSlot();
+    if (InstSlot >= PriorUseIdx && InstSlot < NextUseIdx) {
+      unsigned SubRegIdx = MO.getSubReg();
+      LaneBitmask UseMask = TRI.getSubRegIndexLaneMask(SubRegIdx);
+      LastUseMask &= ~UseMask;
+      if (LastUseMask == 0)
+        return 0;
+    }
+  }
+  return LastUseMask;
+}
+
+LaneBitmask RegPressureTracker::getLiveLanesAt(unsigned RegUnit,
+                                               SlotIndex Pos) const {
+  if (!RequireIntervals)
+    return 0;
+
+  return getLanesWithProperty(*LIS, *MRI, TrackLaneMasks, RegUnit, Pos,
+      [](const LiveRange &LR, SlotIndex Pos) {
+        return LR.liveAt(Pos);
+      });
+}
+
+LaneBitmask RegPressureTracker::getLastUsedLanes(unsigned RegUnit,
+                                                 SlotIndex Pos) const {
+  if (!RequireIntervals)
+    return 0;
+
+  return getLanesWithProperty(*LIS, *MRI, TrackLaneMasks, RegUnit,
+                              Pos.getBaseIndex(),
+      [](const LiveRange &LR, SlotIndex Pos) {
+        const LiveRange::Segment *S = LR.getSegmentContaining(Pos);
+        return S != nullptr && S->end == Pos.getRegSlot();
+      });
+}
+
+LaneBitmask RegPressureTracker::getLiveThroughAt(unsigned RegUnit,
+                                                 SlotIndex Pos) const {
+  if (!RequireIntervals)
+    return 0;
+
+  return getLanesWithProperty(*LIS, *MRI, TrackLaneMasks, RegUnit, Pos,
+      [](const LiveRange &LR, SlotIndex Pos) {
+        const LiveRange::Segment *S = LR.getSegmentContaining(Pos);
+        return S != nullptr && S->start < Pos.getRegSlot(true) &&
+               S->end != Pos.getDeadSlot();
+      });
 }
 
 /// Record the downward impact of a single instruction on current register
 /// pressure. Unlike the advance/recede pressure tracking interface, this does
 /// not discover live in/outs.
 ///
 /// This is intended for speculative queries. It leaves pressure inconsistent
 /// with the current position, so must be restored by the caller.
 void RegPressureTracker::bumpDownwardPressure(const MachineInstr *MI) {
   assert(!MI->isDebugValue() && "Expect a nondebug instruction.");
 
-  // Account for register pressure similar to RegPressureTracker::recede().
-  RegisterOperands RegOpers;
-  RegOpers.collect(*MI, *TRI, *MRI);
-
-  // Kill liveness at last uses. Assume allocatable physregs are single-use
-  // rather than checking LiveIntervals.
   SlotIndex SlotIdx;
   if (RequireIntervals)
     SlotIdx = LIS->getInstructionIndex(MI).getRegSlot();
 
-  for (unsigned Reg : RegOpers.Uses) {
+  // Account for register pressure similar to RegPressureTracker::recede().
+  RegisterOperands RegOpers;
+  RegOpers.collect(*MI, *TRI, *MRI, TrackLaneMasks, false);
+  if (TrackLaneMasks)
+    RegOpers.adjustLaneLiveness(*LIS, *MRI, SlotIdx);
+
+  for (const RegisterMaskPair &Use : RegOpers.Uses) {
+    unsigned Reg = Use.RegUnit;
+    LaneBitmask LastUseMask = getLastUsedLanes(Reg, SlotIdx);
+    if (LastUseMask == 0)
+      continue;
     if (RequireIntervals) {
+      // The LastUseMask is queried from the liveness information of instruction
+      // which may be further down the schedule. Some lanes may actually not be
+      // last uses for the current position.
       // FIXME: allow the caller to pass in the list of vreg uses that remain
       // to be bottom-scheduled to avoid searching uses at each query.
       SlotIndex CurrIdx = getCurrSlot();
-      const LiveRange *LR = getLiveRange(*LIS, Reg);
-      if (LR) {
-        LiveQueryResult LRQ = LR->Query(SlotIdx);
-        if (LRQ.isKill() && !findUseBetween(Reg, CurrIdx, SlotIdx, *MRI, LIS))
-          decreaseRegPressure(Reg);
-      }
-    } else if (!TargetRegisterInfo::isVirtualRegister(Reg)) {
-      // Allocatable physregs are always single-use before register rewriting.
-      decreaseRegPressure(Reg);
+      LastUseMask
+        = findUseBetween(Reg, LastUseMask, CurrIdx, SlotIdx, *MRI, LIS);
+      if (LastUseMask == 0)
+        continue;
     }
+
+    LaneBitmask LiveMask = LiveRegs.contains(Reg);
+    LaneBitmask NewMask = LiveMask & ~LastUseMask;
+    decreaseRegPressure(Reg, LiveMask, NewMask);
   }
 
   // Generate liveness for defs.
-  increaseRegPressure(RegOpers.Defs);
+  for (const RegisterMaskPair &Def : RegOpers.Defs) {
+    unsigned Reg = Def.RegUnit;
+    LaneBitmask LiveMask = LiveRegs.contains(Reg);
+    LaneBitmask NewMask = LiveMask | Def.LaneMask;
+    increaseRegPressure(Reg, LiveMask, NewMask);
+  }
 
   // Boost pressure for all dead defs together.
-  increaseRegPressure(RegOpers.DeadDefs);
-  decreaseRegPressure(RegOpers.DeadDefs);
+  bumpDeadDefs(RegOpers.DeadDefs);
 }
 
 /// Consider the pressure increase caused by traversing this instruction
 /// top-down. Find the register class with the most change in its pressure limit
 /// based on the tracker's current pressure, and return the number of excess
 /// register units of that pressure set introduced by this instruction.
 ///
 /// This assumes that the current LiveIn set is sufficient.

lib/CodeGen/ScheduleDAGInstrs.cpp

for (MachineBasicBlock::iterator MII = RegionEnd, MIE = RegionBegin;
     }
     SUnit *SU = MISUnitMap[MI];
     assert(SU && "No SUnit mapped to this MI");
 
     if (RPTracker) {
       collectVRegUses(SU);
 
       RegisterOperands RegOpers;
-      RegOpers.collect(*MI, *TRI, MRI);
+      RegOpers.collect(*MI, *TRI, MRI, TrackLaneMasks, false);
       if (PDiffs != nullptr)
         PDiffs->addInstruction(SU->NodeNum, RegOpers, MRI);
 
       RPTracker->recedeSkipDebugValues();
       assert(&*RPTracker->getPos() == MI && "RPTracker in sync");
       RPTracker->recede(RegOpers);
     }