diff --git a/llvm/include/llvm/CodeGen/SlotIndexes.h b/llvm/include/llvm/CodeGen/SlotIndexes.h
index 72f4a6876b6cb..2b437a0649aac 100644
--- a/llvm/include/llvm/CodeGen/SlotIndexes.h
+++ b/llvm/include/llvm/CodeGen/SlotIndexes.h
@@ -43,21 +43,40 @@ class raw_ostream;
   /// SlotIndex & SlotIndexes classes for the public interface to this
   /// information.
   class IndexListEntry : public ilist_node<IndexListEntry> {
-    MachineInstr *mi;
+#if NDEBUG
+    // Disable poison checks such that setPoison will do nothing and isPoisoned
+    // will return false.
+    static constexpr unsigned PoisonBits = 0;
+    static constexpr unsigned PoisonVal = 0;
+#else
+    static constexpr unsigned PoisonBits = 1;
+    static constexpr unsigned PoisonVal = 1;
+#endif
+
+    PointerIntPair<MachineInstr *, PoisonBits, unsigned> mi;
     unsigned index;
 
   public:
-    IndexListEntry(MachineInstr *mi, unsigned index) : mi(mi), index(index) {}
+    IndexListEntry(MachineInstr *mi, unsigned index) : mi(mi, 0), index(index) {
+    }
 
-    MachineInstr* getInstr() const { return mi; }
+    MachineInstr* getInstr() const { return mi.getPointer(); }
     void setInstr(MachineInstr *mi) {
-      this->mi = mi;
+      this->mi.setPointer(mi);
     }
 
     unsigned getIndex() const { return index; }
     void setIndex(unsigned index) {
       this->index = index;
     }
+
+    void setPoison() {
+      mi.setInt(PoisonVal);
+    }
+
+    bool isPoisoned() const {
+      return mi.getInt();
+    }
   };
 
   template <>
@@ -285,6 +304,10 @@ class raw_ostream;
     SlotIndex getPrevIndex() const {
       return SlotIndex(&*--listEntry()->getIterator(), getSlot());
     }
+
+    bool isPoisoned() const {
+      return listEntry()->isPoisoned();
+    }
   };
 
   inline raw_ostream& operator<<(raw_ostream &os, SlotIndex li) {
diff --git a/llvm/lib/CodeGen/LiveDebugVariables.cpp b/llvm/lib/CodeGen/LiveDebugVariables.cpp
index 9603c1f01e085..53d99058f9d69 100644
--- a/llvm/lib/CodeGen/LiveDebugVariables.cpp
+++ b/llvm/lib/CodeGen/LiveDebugVariables.cpp
@@ -491,6 +491,13 @@ class UserValue {
   /// Return DebugLoc of this UserValue.
   const DebugLoc &getDebugLoc() { return dl; }
 
+  void verify() const {
+    for (auto I = locInts.begin(), E = locInts.end(); I != E; ++I) {
+      assert(!I.start().isPoisoned());
+      assert(!I.stop().isPoisoned());
+    }
+  }
+
   void print(raw_ostream &, const TargetRegisterInfo *);
 };
 
@@ -654,6 +661,11 @@ class LDVImpl {
     ModifiedMF = false;
   }
 
+  void verify() const {
+    for (auto [DV, UV] : userVarMap)
+      UV->verify();
+  }
+
   /// Map virtual register to an equivalence class.
   void mapVirtReg(Register VirtReg, UserValue *EC);
 
@@ -1319,6 +1331,11 @@ void LiveDebugVariables::releaseMemory() {
     static_cast<LDVImpl*>(pImpl)->clear();
 }
 
+void LiveDebugVariables::verifyAnalysis() const {
+  if (pImpl)
+    static_cast<LDVImpl *>(pImpl)->verify();
+}
+
 LiveDebugVariables::~LiveDebugVariables() {
   if (pImpl)
     delete static_cast<LDVImpl*>(pImpl);
diff --git a/llvm/lib/CodeGen/LiveDebugVariables.h b/llvm/lib/CodeGen/LiveDebugVariables.h
index 9998ce9e8dad8..c99f11c8565a8 100644
--- a/llvm/lib/CodeGen/LiveDebugVariables.h
+++ b/llvm/lib/CodeGen/LiveDebugVariables.h
@@ -56,6 +56,7 @@ class LLVM_LIBRARY_VISIBILITY LiveDebugVariables : public MachineFunctionPass {
   bool runOnMachineFunction(MachineFunction &) override;
   void releaseMemory() override;
   void getAnalysisUsage(AnalysisUsage &) const override;
+  void verifyAnalysis() const override;
 
   MachineFunctionProperties getSetProperties() const override {
     return MachineFunctionProperties().set(
diff --git a/llvm/lib/CodeGen/SlotIndexes.cpp b/llvm/lib/CodeGen/SlotIndexes.cpp
index 65726f06dedb4..e8173c232516c 100644
--- a/llvm/lib/CodeGen/SlotIndexes.cpp
+++ b/llvm/lib/CodeGen/SlotIndexes.cpp
@@ -126,6 +126,7 @@ void SlotIndexes::removeMachineInstrFromMaps(MachineInstr &MI,
   mi2iMap.erase(mi2iItr);
   // FIXME: Eventually we want to actually delete these indexes.
   MIEntry.setInstr(nullptr);
+  MIEntry.setPoison();
 }
 
 void SlotIndexes::removeSingleMachineInstrFromMaps(MachineInstr &MI) {
@@ -152,6 +153,7 @@ void SlotIndexes::removeSingleMachineInstrFromMaps(MachineInstr &MI) {
   } else {
     // FIXME: Eventually we want to actually delete these indexes.
     MIEntry.setInstr(nullptr);
+    MIEntry.setPoison();
   }
 }