diff --git a/llvm/lib/CodeGen/AssignmentTrackingAnalysis.cpp b/llvm/lib/CodeGen/AssignmentTrackingAnalysis.cpp
--- a/llvm/lib/CodeGen/AssignmentTrackingAnalysis.cpp
+++ b/llvm/lib/CodeGen/AssignmentTrackingAnalysis.cpp
@@ -1630,6 +1630,10 @@
   unsigned IntersectSize = Join.size();
   (void)IntersectSize;
 
+  // Check if A and B contain the same variables.
+  if (SymmetricDifference.empty() && A.size() == B.size())
+    return Join;
+
   // Add the elements in B with variables that are not in A into
   // SymmetricDifference.
   for (const auto &Pair : B) {
@@ -1721,6 +1725,10 @@
   unsigned IntersectSize = Join.size();
   (void)IntersectSize;
 
+  // Check if A and B contain the same variables.
+  if (SymmetricDifference.empty() && A.size() == B.size())
+    return Join;
+
   // Add the elements in B with variables that are not in A into
   // SymmetricDifference.
   for (const auto &Pair : B) {