diff --git a/llvm/include/llvm/CodeGen/LiveRegUnits.h b/llvm/include/llvm/CodeGen/LiveRegUnits.h
--- a/llvm/include/llvm/CodeGen/LiveRegUnits.h
+++ b/llvm/include/llvm/CodeGen/LiveRegUnits.h
@@ -93,7 +93,7 @@
   void addRegMasked(MCPhysReg Reg, LaneBitmask Mask) {
     for (MCRegUnitMaskIterator Unit(Reg, TRI); Unit.isValid(); ++Unit) {
       LaneBitmask UnitMask = (*Unit).second;
-      if (UnitMask.none() || (UnitMask & Mask).any())
+      if ((UnitMask & Mask).any())
         Units.set((*Unit).first);
     }
   }
diff --git a/llvm/lib/CodeGen/MachineSink.cpp b/llvm/lib/CodeGen/MachineSink.cpp
--- a/llvm/lib/CodeGen/MachineSink.cpp
+++ b/llvm/lib/CodeGen/MachineSink.cpp
@@ -1704,10 +1704,9 @@
   for (auto U : UsedOpsInCopy) {
     Register SrcReg = MI->getOperand(U).getReg();
     LaneBitmask Mask;
-    for (MCRegUnitMaskIterator S(SrcReg, TRI); S.isValid(); ++S) {
+    for (MCRegUnitMaskIterator S(SrcReg, TRI); S.isValid(); ++S)
       Mask |= (*S).second;
-    }
-    SuccBB->addLiveIn(SrcReg, Mask.any() ? Mask : LaneBitmask::getAll());
+    SuccBB->addLiveIn(SrcReg, Mask);
   }
   SuccBB->sortUniqueLiveIns();
 }
diff --git a/llvm/lib/CodeGen/RDFRegisters.cpp b/llvm/lib/CodeGen/RDFRegisters.cpp
--- a/llvm/lib/CodeGen/RDFRegisters.cpp
+++ b/llvm/lib/CodeGen/RDFRegisters.cpp
@@ -61,14 +61,7 @@
         std::pair<uint32_t, LaneBitmask> P = *I;
         UnitInfo &UI = UnitInfos[P.first];
         UI.Reg = F;
-        if (P.second.any()) {
-          UI.Mask = P.second;
-        } else {
-          if (const TargetRegisterClass *RC = RegInfos[F].RegClass)
-            UI.Mask = RC->LaneMask;
-          else
-            UI.Mask = LaneBitmask::getAll();
-        }
+        UI.Mask = P.second;
       }
     }
   }
@@ -141,7 +134,7 @@
       return Units; // Empty
     for (MCRegUnitMaskIterator UM(RR.idx(), &TRI); UM.isValid(); ++UM) {
       auto [U, M] = *UM;
-      if (M.none() || (M & RR.Mask).any())
+      if ((M & RR.Mask).any())
         Units.insert(U);
     }
     return Units;
@@ -200,13 +193,6 @@
     auto [AReg, AMask] = *AI;
     auto [BReg, BMask] = *BI;
 
-    // Lane masks are "none" for units that don't correspond to subregs
-    // e.g. a single unit in a leaf register, or aliased unit.
-    if (AMask.none())
-      AMask = LaneBitmask::getAll();
-    if (BMask.none())
-      BMask = LaneBitmask::getAll();
-
     // If both iterators point to a unit contained in both A and B, then
     // compare the units.
     if ((AMask & A.Mask).any() && (BMask & B.Mask).any()) {
@@ -245,13 +231,6 @@
     auto [AReg, AMask] = *AI;
     auto [BReg, BMask] = *BI;
 
-    // Lane masks are "none" for units that don't correspond to subregs
-    // e.g. a single unit in a leaf register, or aliased unit.
-    if (AMask.none())
-      AMask = LaneBitmask::getAll();
-    if (BMask.none())
-      BMask = LaneBitmask::getAll();
-
     // If both iterators point to a unit contained in both A and B, then
     // compare the units.
     if ((AMask & A.Mask).any() && (BMask & B.Mask).any()) {
@@ -303,7 +282,7 @@
 
   for (MCRegUnitMaskIterator U(RR.Reg, &PRI.getTRI()); U.isValid(); ++U) {
     std::pair<uint32_t, LaneBitmask> P = *U;
-    if (P.second.none() || (P.second & RR.Mask).any())
+    if ((P.second & RR.Mask).any())
       if (Units.test(P.first))
         return true;
   }
@@ -318,7 +297,7 @@
 
   for (MCRegUnitMaskIterator U(RR.Reg, &PRI.getTRI()); U.isValid(); ++U) {
     std::pair<uint32_t, LaneBitmask> P = *U;
-    if (P.second.none() || (P.second & RR.Mask).any())
+    if ((P.second & RR.Mask).any())
       if (!Units.test(P.first))
         return false;
   }
@@ -333,7 +312,7 @@
 
   for (MCRegUnitMaskIterator U(RR.Reg, &PRI.getTRI()); U.isValid(); ++U) {
     std::pair<uint32_t, LaneBitmask> P = *U;
-    if (P.second.none() || (P.second & RR.Mask).any())
+    if ((P.second & RR.Mask).any())
       Units.set(P.first);
   }
   return *this;
@@ -407,7 +386,7 @@
   for (MCRegUnitMaskIterator I(F, &PRI.getTRI()); I.isValid(); ++I) {
     std::pair<uint32_t, LaneBitmask> P = *I;
     if (Units.test(P.first))
-      M |= P.second.none() ? LaneBitmask::getAll() : P.second;
+      M |= P.second;
   }
   return RegisterRef(F, M);
 }
diff --git a/llvm/utils/TableGen/CodeGenRegisters.cpp b/llvm/utils/TableGen/CodeGenRegisters.cpp
--- a/llvm/utils/TableGen/CodeGenRegisters.cpp
+++ b/llvm/utils/TableGen/CodeGenRegisters.cpp
@@ -2123,8 +2123,8 @@
   for (auto &Register : Registers) {
     // Create an initial lane mask for all register units.
     const auto &RegUnits = Register.getRegUnits();
-    CodeGenRegister::RegUnitLaneMaskList
-        RegUnitLaneMasks(RegUnits.count(), LaneBitmask::getNone());
+    CodeGenRegister::RegUnitLaneMaskList RegUnitLaneMasks(
+        RegUnits.count(), LaneBitmask::getAll());
     // Iterate through SubRegisters.
     typedef CodeGenRegister::SubRegMap SubRegMap;
     const SubRegMap &SubRegs = Register.getSubRegs();
@@ -2143,7 +2143,7 @@
         unsigned u = 0;
         for (unsigned RU : RegUnits) {
           if (SUI == RU) {
-            RegUnitLaneMasks[u] |= LaneMask;
+            RegUnitLaneMasks[u] &= LaneMask;
             assert(!Found);
             Found = true;
           }
diff --git a/llvm/utils/TableGen/RegisterInfoEmitter.cpp b/llvm/utils/TableGen/RegisterInfoEmitter.cpp
--- a/llvm/utils/TableGen/RegisterInfoEmitter.cpp
+++ b/llvm/utils/TableGen/RegisterInfoEmitter.cpp
@@ -931,12 +931,6 @@
     MaskVec &LaneMaskVec = RegUnitLaneMasks[i];
     assert(LaneMaskVec.empty());
     llvm::append_range(LaneMaskVec, RUMasks);
-    // Terminator mask should not be used inside of the list.
-#ifndef NDEBUG
-    for (LaneBitmask M : LaneMaskVec) {
-      assert(!M.all() && "terminator mask should not be part of the list");
-    }
-#endif
     LaneMaskSeqs.add(LaneMaskVec);
   }
 
@@ -956,6 +950,8 @@
 
   // Emit the shared table of regunit lane mask sequences.
   OS << "extern const LaneBitmask " << TargetName << "LaneMaskLists[] = {\n";
+  // TODO: Omit the terminator since it is never used. The length of this list
+  // is known implicitly from the corresponding reg unit list.
   LaneMaskSeqs.emit(OS, printMask, "LaneBitmask::getAll()");
   OS << "};\n\n";