4 files changed, 13 insertions, 11 deletions

diff --git a/llvm/lib/CodeGen/LiveIntervalAnalysis.cpp b/llvm/lib/CodeGen/LiveIntervalAnalysis.cpp
index a3122763806..4195f007d43 100644
--- a/llvm/lib/CodeGen/LiveIntervalAnalysis.cpp
+++ b/llvm/lib/CodeGen/LiveIntervalAnalysis.cpp
@@ -506,20 +506,19 @@ void LiveIntervals::shrinkToUses(LiveInterval::SubRange &SR, unsigned Reg) {
 
   // Visit all instructions reading Reg.
   SlotIndex LastIdx;
-  for (MachineOperand &MO : MRI->reg_operands(Reg)) {
-    MachineInstr *UseMI = MO.getParent();
-    if (UseMI->isDebugValue() || !MO.readsReg())
+  for (MachineOperand &MO : MRI->use_nodbg_operands(Reg)) {
+    // Skip "undef" uses.
+    if (!MO.readsReg())
       continue;
     // Maybe the operand is for a subregister we don't care about.
     unsigned SubReg = MO.getSubReg();
     if (SubReg != 0) {
       LaneBitmask LaneMask = TRI->getSubRegIndexLaneMask(SubReg);
-      if (MO.isDef())
-        LaneMask = ~LaneMask & MRI->getMaxLaneMaskForVReg(Reg);
       if ((LaneMask & SR.LaneMask) == 0)
         continue;
     }
     // We only need to visit each instruction once.
+    MachineInstr *UseMI = MO.getParent();
     SlotIndex Idx = getInstructionIndex(*UseMI).getRegSlot();
     if (Idx == LastIdx)
       continue;
diff --git a/llvm/lib/CodeGen/LiveRangeCalc.cpp b/llvm/lib/CodeGen/LiveRangeCalc.cpp
index 25d22a02d33..98022d99cf2 100644
--- a/llvm/lib/CodeGen/LiveRangeCalc.cpp
+++ b/llvm/lib/CodeGen/LiveRangeCalc.cpp
@@ -163,13 +163,18 @@ void LiveRangeCalc::extendToUses(LiveRange &LR, unsigned Reg, LaneBitmask Mask,
     LI->computeSubRangeUndefs(Undefs, Mask, *MRI, *Indexes);
 
   // Visit all operands that read Reg. This may include partial defs.
+  bool IsSubRange = (Mask != ~0U);
   const TargetRegisterInfo &TRI = *MRI->getTargetRegisterInfo();
   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())
+    // MO::readsReg returns "true" for subregister defs. This is for keeping
+    // liveness of the entire register (i.e. for the main range of the live
+    // interval). For subranges, definitions of non-overlapping subregisters
+    // do not count as uses.
+    if (!MO.readsReg() || (IsSubRange && MO.isDef()))
       continue;
 
     unsigned SubReg = MO.getSubReg();
diff --git a/llvm/lib/CodeGen/LiveRangeCalc.h b/llvm/lib/CodeGen/LiveRangeCalc.h
index 84cc1cb2be7..892f535a5ae 100644
--- a/llvm/lib/CodeGen/LiveRangeCalc.h
+++ b/llvm/lib/CodeGen/LiveRangeCalc.h
@@ -160,6 +160,7 @@ class LiveRangeCalc {
   /// all uses must be jointly dominated by the definitions from @p LR
   /// together with definitions of other lanes where @p LR becomes undefined
   /// (via <def,read-undef> operands).
+  /// If @p LR is a main range, the @p LaneMask should be set to ~0.
   void extendToUses(LiveRange &LR, unsigned Reg, LaneBitmask LaneMask,
                     LiveInterval *LI = nullptr);
 
diff --git a/llvm/lib/CodeGen/SplitKit.cpp b/llvm/lib/CodeGen/SplitKit.cpp
index 6d59f85d35f..e06bc4a3614 100644
--- a/llvm/lib/CodeGen/SplitKit.cpp
+++ b/llvm/lib/CodeGen/SplitKit.cpp
@@ -1206,7 +1206,8 @@ void SplitEditor::rewriteAssigned(bool ExtendRanges) {
       // defining the register. This is because a <def,read-undef> operand
       // will create an "undef" point, and we cannot extend any subranges
       // until all of them have been accounted for.
-      ExtPoints.push_back(ExtPoint(MO, RegIdx, Next));
+      if (MO.isUse())
+        ExtPoints.push_back(ExtPoint(MO, RegIdx, Next));
     } else {
       LiveRangeCalc &LRC = getLRCalc(RegIdx);
       LRC.extend(LI, Next, 0, ArrayRef<SlotIndex>());
@@ -1221,10 +1222,6 @@ void SplitEditor::rewriteAssigned(bool ExtendRanges) {
     unsigned Reg = EP.MO.getReg(), Sub = EP.MO.getSubReg();
     LaneBitmask LM = Sub != 0 ? TRI.getSubRegIndexLaneMask(Sub)
                               : MRI.getMaxLaneMaskForVReg(Reg);
-    // If this is a non-read-undef definition of a sub-register, extend
-    // subranges for everything except that sub-register.
-    if (Sub != 0 && EP.MO.isDef())
-      LM = MRI.getMaxLaneMaskForVReg(Reg) & ~LM;
     for (LiveInterval::SubRange &S : LI.subranges()) {
       if (!(S.LaneMask & LM))
         continue;