diff --git a/llvm/include/llvm/Analysis/IRSimilarityIdentifier.h b/llvm/include/llvm/Analysis/IRSimilarityIdentifier.h
--- a/llvm/include/llvm/Analysis/IRSimilarityIdentifier.h
+++ b/llvm/include/llvm/Analysis/IRSimilarityIdentifier.h
@@ -46,6 +46,8 @@
 namespace llvm {
 namespace IRSimilarity {
 
+struct IRInstructionDataList;
+
 /// This represents what is and is not supported when finding similarity in
 /// Instructions.
 ///
@@ -112,7 +114,7 @@
   /// operands. This extra information allows for similarity matching to make
   /// assertions that allow for more flexibility when checking for whether an
   /// Instruction performs the same operation.
-  IRInstructionData(Instruction &I, bool Legality);
+  IRInstructionData(Instruction &I, bool Legality, IRInstructionDataList &IDL);
 
   /// Hashes \p Value based on its opcode, types, and operand types.
   /// Two IRInstructionData instances produce the same hash when they perform
@@ -147,8 +149,12 @@
         hash_value(Value.Inst->getType()),
         hash_combine_range(Value.OperTypes.begin(), Value.OperTypes.end()));
   }
+
+  IRInstructionDataList *IDL = nullptr;
 };
 
+struct IRInstructionDataList : simple_ilist<IRInstructionData> {};
+
 /// Compare one IRInstructionData class to another IRInstructionData class for
 /// whether they are performing a the same operation, and can mapped to the
 /// same value. For regular instructions if the hash value is the same, then
@@ -256,6 +262,8 @@
   /// with the information.
   BumpPtrAllocator *InstDataAllocator = nullptr;
 
+  IRInstructionDataList *IDL = nullptr;
+
   /// Maps the Instructions in a BasicBlock \p BB to legal or illegal integers
   /// determined by \p InstrType. Two Instructions are mapped to the same value
   /// if they are close as defined by the InstructionData class above.
@@ -289,24 +297,16 @@
       BasicBlock::iterator &It, std::vector<unsigned> &UnsignedVecForBB,
       std::vector<IRInstructionData *> &InstrListForBB, bool End = false);
 
-  IRInstructionMapper(){
-    // Make sure that the implementation of DenseMapInfo<unsigned> hasn't
-    // changed.
-    assert(DenseMapInfo<unsigned>::getEmptyKey() == (unsigned)-1 &&
-           "DenseMapInfo<unsigned>'s empty key isn't -1!");
-    assert(DenseMapInfo<unsigned>::getTombstoneKey() == (unsigned)-2 &&
-           "DenseMapInfo<unsigned>'s tombstone key isn't -2!");
-  }
-
-  IRInstructionMapper(BumpPtrAllocator *IDA)
-      : InstDataAllocator(IDA){
+  IRInstructionMapper(BumpPtrAllocator *IDA) : InstDataAllocator(IDA){
     // Make sure that the implementation of DenseMapInfo<unsigned> hasn't
     // changed.
     assert(DenseMapInfo<unsigned>::getEmptyKey() == (unsigned)-1 &&
            "DenseMapInfo<unsigned>'s empty key isn't -1!");
     assert(DenseMapInfo<unsigned>::getTombstoneKey() == (unsigned)-2 &&
            "DenseMapInfo<unsigned>'s tombstone key isn't -2!");
-  }
+    IDL = new (InstDataAllocator->Allocate<IRInstructionDataList>())
+        IRInstructionDataList();
+  };
 
   /// Custom InstVisitor to classify different instructions for whether it can
   /// be analyzed for similarity.
@@ -359,4 +359,4 @@
 } // end namespace IRSimilarity
 } // end namespace llvm
 
-#endif // LLVM_ANALYSIS_IRSIMILARITYIDENTIFIER_H
\ No newline at end of file
+#endif // LLVM_ANALYSIS_IRSIMILARITYIDENTIFIER_H
diff --git a/llvm/lib/Analysis/IRSimilarityIdentifier.cpp b/llvm/lib/Analysis/IRSimilarityIdentifier.cpp
--- a/llvm/lib/Analysis/IRSimilarityIdentifier.cpp
+++ b/llvm/lib/Analysis/IRSimilarityIdentifier.cpp
@@ -20,8 +20,9 @@
 using namespace llvm;
 using namespace IRSimilarity;
 
-IRInstructionData::IRInstructionData(Instruction &I, bool Legality)
-    : Inst(&I), Legal(Legality) {
+IRInstructionData::IRInstructionData(Instruction &I, bool Legality,
+                                     IRInstructionDataList &IDList)
+    : Inst(&I), Legal(Legality), IDL(&IDList) {
   // Here we collect the operands and their types for determining whether
   // the structure of the operand use matches between two different candidates.
   for (Use &OI : I.operands()) {
@@ -71,6 +72,9 @@
 
   if (HaveLegalRange) {
     mapToIllegalUnsigned(It, UnsignedVecForBB, InstrListForBB, true);
+    for_each(InstrListForBB, [this](IRInstructionData *ID){
+      this->IDL->push_back(*ID);
+    });
     InstrList.insert(InstrList.end(), InstrListForBB.begin(),
                      InstrListForBB.end());
     UnsignedVec.insert(UnsignedVec.end(), UnsignedVecForBB.begin(),
@@ -96,7 +100,7 @@
   // Get the integer for this instruction or give it the current
   // LegalInstrNumber.
   IRInstructionData *ID = new (InstDataAllocator->Allocate<IRInstructionData>())
-      IRInstructionData(*It, true);
+      IRInstructionData(*It, true, *IDL);
   InstrListForBB.push_back(ID);
 
   // Add to the instruction list
@@ -140,7 +144,7 @@
   IRInstructionData *ID = nullptr;
   if (!End)
     ID = new (InstDataAllocator->Allocate<IRInstructionData>())
-        IRInstructionData(*It, false);
+        IRInstructionData(*It, false, *IDL);
   InstrListForBB.push_back(ID);
 
   // Remember that we added an illegal number last time.
@@ -158,4 +162,4 @@
          "IllegalInstrNumber cannot be DenseMap tombstone or empty key!");
 
   return INumber;
-}
\ No newline at end of file
+}