diff --git a/llvm/include/llvm/CodeGen/LiveIntervalUnion.h b/llvm/include/llvm/CodeGen/LiveIntervalUnion.h
--- a/llvm/include/llvm/CodeGen/LiveIntervalUnion.h
+++ b/llvm/include/llvm/CodeGen/LiveIntervalUnion.h
@@ -114,12 +114,19 @@
     const LiveRange *LR = nullptr;
     LiveRange::const_iterator LRI;  ///< current position in LR
     ConstSegmentIter LiveUnionI;    ///< current position in LiveUnion
-    Optional<SmallVector<LiveInterval *, 4>> InterferingVRegs;
+    SmallVector<LiveInterval *, 4> InterferingVRegs;
     bool CheckedFirstInterference = false;
     bool SeenAllInterferences = false;
     unsigned Tag = 0;
     unsigned UserTag = 0;
 
+    // Count the virtual registers in this union that interfere with this
+    // query's live virtual register, up to maxInterferingRegs.
+    unsigned collectInterferingVRegs(unsigned MaxInterferingRegs);
+
+    // Was this virtual register visited during collectInterferingVRegs?
+    bool isSeenInterference(LiveInterval *VirtReg) const;
+
   public:
     Query() = default;
     Query(const LiveRange &LR, const LiveIntervalUnion &LIU)
@@ -131,7 +138,7 @@
                const LiveIntervalUnion &NewLiveUnion) {
       LiveUnion = &NewLiveUnion;
       LR = &NewLR;
-      InterferingVRegs = None;
+      InterferingVRegs.clear();
       CheckedFirstInterference = false;
       SeenAllInterferences = false;
       Tag = NewLiveUnion.getTag();
@@ -151,20 +158,12 @@
     // Does this live virtual register interfere with the union?
     bool checkInterference() { return collectInterferingVRegs(1); }
 
-    // Count the virtual registers in this union that interfere with this
-    // query's live virtual register, up to maxInterferingRegs.
-    unsigned collectInterferingVRegs(
-        unsigned MaxInterferingRegs = std::numeric_limits<unsigned>::max());
-
-    // Was this virtual register visited during collectInterferingVRegs?
-    bool isSeenInterference(LiveInterval *VirtReg) const;
-
-    // Did collectInterferingVRegs collect all interferences?
-    bool seenAllInterferences() const { return SeenAllInterferences; }
-
     // Vector generated by collectInterferingVRegs.
-    const SmallVectorImpl<LiveInterval*> &interferingVRegs() const {
-      return *InterferingVRegs;
+    const SmallVectorImpl<LiveInterval *> &interferingVRegs(
+        unsigned MaxInterferingRegs = std::numeric_limits<unsigned>::max()) {
+      if (!SeenAllInterferences || MaxInterferingRegs < InterferingVRegs.size())
+        collectInterferingVRegs(MaxInterferingRegs);
+      return InterferingVRegs;
     }
   };
 
diff --git a/llvm/lib/CodeGen/LiveIntervalUnion.cpp b/llvm/lib/CodeGen/LiveIntervalUnion.cpp
--- a/llvm/lib/CodeGen/LiveIntervalUnion.cpp
+++ b/llvm/lib/CodeGen/LiveIntervalUnion.cpp
@@ -112,7 +112,7 @@
 // Scan the vector of interfering virtual registers in this union. Assume it's
 // quite small.
 bool LiveIntervalUnion::Query::isSeenInterference(LiveInterval *VirtReg) const {
-  return is_contained(*InterferingVRegs, VirtReg);
+  return is_contained(InterferingVRegs, VirtReg);
 }
 
 // Collect virtual registers in this union that interfere with this
@@ -124,14 +124,11 @@
 // 2. SeenAllInterferences == true: InterferingVRegs complete, iterators unused.
 // 3. Iterators left at the last seen intersection.
 //
-unsigned LiveIntervalUnion::Query::
-collectInterferingVRegs(unsigned MaxInterferingRegs) {
-  if (!InterferingVRegs)
-    InterferingVRegs.emplace();
-
+unsigned
+LiveIntervalUnion::Query::collectInterferingVRegs(unsigned MaxInterferingRegs) {
   // Fast path return if we already have the desired information.
-  if (SeenAllInterferences || InterferingVRegs->size() >= MaxInterferingRegs)
-    return InterferingVRegs->size();
+  if (SeenAllInterferences || InterferingVRegs.size() >= MaxInterferingRegs)
+    return InterferingVRegs.size();
 
   // Set up iterators on the first call.
   if (!CheckedFirstInterference) {
@@ -160,14 +157,14 @@
       LiveInterval *VReg = LiveUnionI.value();
       if (VReg != RecentReg && !isSeenInterference(VReg)) {
         RecentReg = VReg;
-        InterferingVRegs->push_back(VReg);
-        if (InterferingVRegs->size() >= MaxInterferingRegs)
-          return InterferingVRegs->size();
+        InterferingVRegs.push_back(VReg);
+        if (InterferingVRegs.size() >= MaxInterferingRegs)
+          return InterferingVRegs.size();
       }
       // This LiveUnion segment is no longer interesting.
       if (!(++LiveUnionI).valid()) {
         SeenAllInterferences = true;
-        return InterferingVRegs->size();
+        return InterferingVRegs.size();
       }
     }
 
@@ -188,7 +185,7 @@
     LiveUnionI.advanceTo(LRI->start);
   }
   SeenAllInterferences = true;
-  return InterferingVRegs->size();
+  return InterferingVRegs.size();
 }
 
 void LiveIntervalUnion::Array::init(LiveIntervalUnion::Allocator &Alloc,
diff --git a/llvm/lib/CodeGen/RegAllocBasic.cpp b/llvm/lib/CodeGen/RegAllocBasic.cpp
--- a/llvm/lib/CodeGen/RegAllocBasic.cpp
+++ b/llvm/lib/CodeGen/RegAllocBasic.cpp
@@ -217,9 +217,7 @@
   // Collect interferences assigned to any alias of the physical register.
   for (MCRegUnitIterator Units(PhysReg, TRI); Units.isValid(); ++Units) {
     LiveIntervalUnion::Query &Q = Matrix->query(VirtReg, *Units);
-    Q.collectInterferingVRegs();
-    for (unsigned i = Q.interferingVRegs().size(); i; --i) {
-      LiveInterval *Intf = Q.interferingVRegs()[i - 1];
+    for (auto *Intf : reverse(Q.interferingVRegs())) {
       if (!Intf->isSpillable() || Intf->weight() > VirtReg.weight())
         return false;
       Intfs.push_back(Intf);
diff --git a/llvm/lib/CodeGen/RegAllocGreedy.cpp b/llvm/lib/CodeGen/RegAllocGreedy.cpp
--- a/llvm/lib/CodeGen/RegAllocGreedy.cpp
+++ b/llvm/lib/CodeGen/RegAllocGreedy.cpp
@@ -955,11 +955,12 @@
   for (MCRegUnitIterator Units(PhysReg, TRI); Units.isValid(); ++Units) {
     LiveIntervalUnion::Query &Q = Matrix->query(VirtReg, *Units);
     // If there is 10 or more interferences, chances are one is heavier.
-    if (Q.collectInterferingVRegs(10) >= 10)
+    const auto &Interferences = Q.interferingVRegs(10);
+    if (Interferences.size() >= 10)
       return false;
 
     // Check if any interfering live range is heavier than MaxWeight.
-    for (LiveInterval *Intf : reverse(Q.interferingVRegs())) {
+    for (LiveInterval *Intf : reverse(Interferences)) {
       assert(Register::isVirtualRegister(Intf->reg()) &&
              "Only expecting virtual register interference from query");
 
@@ -1037,7 +1038,6 @@
 
   for (MCRegUnitIterator Units(PhysReg, TRI); Units.isValid(); ++Units) {
     LiveIntervalUnion::Query &Q = Matrix->query(VirtReg, *Units);
-    Q.collectInterferingVRegs();
 
     // Check if any interfering live range is heavier than MaxWeight.
     for (const LiveInterval *Intf : reverse(Q.interferingVRegs())) {
@@ -1127,7 +1127,6 @@
     // should be fast, we may need to recalculate if when different physregs
     // overlap the same register unit so we had different SubRanges queried
     // against it.
-    Q.collectInterferingVRegs();
     ArrayRef<LiveInterval*> IVR = Q.interferingVRegs();
     Intfs.append(IVR.begin(), IVR.end());
   }
@@ -2547,8 +2546,9 @@
     LiveIntervalUnion::Query &Q = Matrix->query(VirtReg, *Units);
     // If there is LastChanceRecoloringMaxInterference or more interferences,
     // chances are one would not be recolorable.
-    if (Q.collectInterferingVRegs(LastChanceRecoloringMaxInterference) >=
-        LastChanceRecoloringMaxInterference && !ExhaustiveSearch) {
+    if (Q.interferingVRegs(LastChanceRecoloringMaxInterference).size() >=
+            LastChanceRecoloringMaxInterference &&
+        !ExhaustiveSearch) {
       LLVM_DEBUG(dbgs() << "Early abort: too many interferences.\n");
       CutOffInfo |= CO_Interf;
       return false;