diff --git a/llvm/include/llvm/CodeGen/MachineRegisterInfo.h b/llvm/include/llvm/CodeGen/MachineRegisterInfo.h
index 09d9a0b4ec402f..2367d8d04787d9 100644
--- a/llvm/include/llvm/CodeGen/MachineRegisterInfo.h
+++ b/llvm/include/llvm/CodeGen/MachineRegisterInfo.h
@@ -801,6 +801,7 @@ class MachineRegisterInfo {
   /// of an earlier hint it will be overwritten.
   void setRegAllocationHint(Register VReg, unsigned Type, Register PrefReg) {
     assert(VReg.isVirtual());
+    RegAllocHints.grow(Register::index2VirtReg(getNumVirtRegs()));
     RegAllocHints[VReg].first  = Type;
     RegAllocHints[VReg].second.clear();
     RegAllocHints[VReg].second.push_back(PrefReg);
@@ -810,6 +811,7 @@ class MachineRegisterInfo {
   /// vector for VReg.
   void addRegAllocationHint(Register VReg, Register PrefReg) {
     assert(VReg.isVirtual());
+    RegAllocHints.grow(Register::index2VirtReg(getNumVirtRegs()));
     RegAllocHints[VReg].second.push_back(PrefReg);
   }
 
@@ -822,7 +824,8 @@ class MachineRegisterInfo {
   void clearSimpleHint(Register VReg) {
     assert (!RegAllocHints[VReg].first &&
             "Expected to clear a non-target hint!");
-    RegAllocHints[VReg].second.clear();
+    if (RegAllocHints.inBounds(VReg))
+      RegAllocHints[VReg].second.clear();
   }
 
   /// getRegAllocationHint - Return the register allocation hint for the
@@ -830,6 +833,8 @@ class MachineRegisterInfo {
   /// one with the greatest weight.
   std::pair<unsigned, Register> getRegAllocationHint(Register VReg) const {
     assert(VReg.isVirtual());
+    if (!RegAllocHints.inBounds(VReg))
+      return {0, Register()};
     Register BestHint = (RegAllocHints[VReg.id()].second.size() ?
                          RegAllocHints[VReg.id()].second[0] : Register());
     return {RegAllocHints[VReg.id()].first, BestHint};
@@ -845,10 +850,10 @@ class MachineRegisterInfo {
 
   /// getRegAllocationHints - Return a reference to the vector of all
   /// register allocation hints for VReg.
-  const std::pair<unsigned, SmallVector<Register, 4>> &
+  const std::pair<unsigned, SmallVector<Register, 4>> *
   getRegAllocationHints(Register VReg) const {
     assert(VReg.isVirtual());
-    return RegAllocHints[VReg];
+    return RegAllocHints.inBounds(VReg) ? &RegAllocHints[VReg] : nullptr;
   }
 
   /// markUsesInDebugValueAsUndef - Mark every DBG_VALUE referencing the
diff --git a/llvm/lib/CodeGen/MachineRegisterInfo.cpp b/llvm/lib/CodeGen/MachineRegisterInfo.cpp
index 3caa96cd5e55d4..fcedb302d228c4 100644
--- a/llvm/lib/CodeGen/MachineRegisterInfo.cpp
+++ b/llvm/lib/CodeGen/MachineRegisterInfo.cpp
@@ -47,7 +47,6 @@ MachineRegisterInfo::MachineRegisterInfo(MachineFunction *MF)
                                : MF->getSubtarget().enableSubRegLiveness()) {
   unsigned NumRegs = getTargetRegisterInfo()->getNumRegs();
   VRegInfo.reserve(256);
-  RegAllocHints.reserve(256);
   UsedPhysRegMask.resize(NumRegs);
   PhysRegUseDefLists.reset(new MachineOperand*[NumRegs]());
   TheDelegates.clear();
@@ -147,7 +146,6 @@ MachineRegisterInfo::recomputeRegClass(Register Reg) {
 Register MachineRegisterInfo::createIncompleteVirtualRegister(StringRef Name) {
   Register Reg = Register::index2VirtReg(getNumVirtRegs());
   VRegInfo.grow(Reg);
-  RegAllocHints.grow(Reg);
   insertVRegByName(Name, Reg);
   return Reg;
 }
diff --git a/llvm/lib/CodeGen/TargetRegisterInfo.cpp b/llvm/lib/CodeGen/TargetRegisterInfo.cpp
index ffc8055dd27e8f..16dab974efacb2 100644
--- a/llvm/lib/CodeGen/TargetRegisterInfo.cpp
+++ b/llvm/lib/CodeGen/TargetRegisterInfo.cpp
@@ -421,13 +421,16 @@ bool TargetRegisterInfo::getRegAllocationHints(
     SmallVectorImpl<MCPhysReg> &Hints, const MachineFunction &MF,
     const VirtRegMap *VRM, const LiveRegMatrix *Matrix) const {
   const MachineRegisterInfo &MRI = MF.getRegInfo();
-  const std::pair<unsigned, SmallVector<Register, 4>> &Hints_MRI =
+  const std::pair<unsigned, SmallVector<Register, 4>> *Hints_MRI =
       MRI.getRegAllocationHints(VirtReg);
 
+  if (!Hints_MRI)
+    return false;
+
   SmallSet<Register, 32> HintedRegs;
   // First hint may be a target hint.
-  bool Skip = (Hints_MRI.first != 0);
-  for (auto Reg : Hints_MRI.second) {
+  bool Skip = (Hints_MRI->first != 0);
+  for (auto Reg : Hints_MRI->second) {
     if (Skip) {
       Skip = false;
       continue;
diff --git a/llvm/tools/llvm-reduce/ReducerWorkItem.cpp b/llvm/tools/llvm-reduce/ReducerWorkItem.cpp
index 3d36d80f82315e..3fa49cbef4ec23 100644
--- a/llvm/tools/llvm-reduce/ReducerWorkItem.cpp
+++ b/llvm/tools/llvm-reduce/ReducerWorkItem.cpp
@@ -306,9 +306,10 @@ static std::unique_ptr<MachineFunction> cloneMF(MachineFunction *SrcMF,
       DstMRI->setType(NewReg, RegTy);
 
     // Copy register allocation hints.
-    const auto &Hints = SrcMRI->getRegAllocationHints(Reg);
-    for (Register PrefReg : Hints.second)
-      DstMRI->addRegAllocationHint(NewReg, PrefReg);
+    const auto *Hints = SrcMRI->getRegAllocationHints(Reg);
+    if (Hints)
+      for (Register PrefReg : Hints->second)
+        DstMRI->addRegAllocationHint(NewReg, PrefReg);
   }
 
   const TargetSubtargetInfo &STI = DstMF->getSubtarget();
@@ -530,7 +531,8 @@ static uint64_t computeMIRComplexityScoreImpl(const MachineFunction &MF) {
   const MachineRegisterInfo &MRI = MF.getRegInfo();
   for (unsigned I = 0, E = MRI.getNumVirtRegs(); I != E; ++I) {
     Register Reg = Register::index2VirtReg(I);
-    Score += MRI.getRegAllocationHints(Reg).second.size();
+    if (const auto *Hints = MRI.getRegAllocationHints(Reg))
+      Score += Hints->second.size();
   }
 
   for (const MachineBasicBlock &MBB : MF) {
diff --git a/llvm/tools/llvm-reduce/deltas/ReduceVirtualRegisters.cpp b/llvm/tools/llvm-reduce/deltas/ReduceVirtualRegisters.cpp
index 2b97e65bbf0938..3ec9555c0f2f5f 100644
--- a/llvm/tools/llvm-reduce/deltas/ReduceVirtualRegisters.cpp
+++ b/llvm/tools/llvm-reduce/deltas/ReduceVirtualRegisters.cpp
@@ -23,9 +23,9 @@ static void dropRegisterHintsFromFunction(Oracle &O, MachineFunction &MF) {
   for (unsigned I = 0, E = MRI.getNumVirtRegs(); I != E; ++I) {
     Register Reg = Register::index2VirtReg(I);
 
-    const std::pair<unsigned, SmallVector<Register, 4>> &Hints =
+    const std::pair<unsigned, SmallVector<Register, 4>> *Hints =
         MRI.getRegAllocationHints(Reg);
-    if (Hints.second.empty())
+    if (!Hints || Hints->second.empty())
       continue;
 
     if (!O.shouldKeep())