diff --git a/llvm/include/llvm/Analysis/ScalarEvolution.h b/llvm/include/llvm/Analysis/ScalarEvolution.h
--- a/llvm/include/llvm/Analysis/ScalarEvolution.h
+++ b/llvm/include/llvm/Analysis/ScalarEvolution.h
@@ -1032,6 +1032,9 @@
   /// Test whether the given SCEV has Op as a direct or indirect operand.
   bool hasOperand(const SCEV *S, const SCEV *Op) const;
 
+  /// Test whether the given SCEV has a SCEVUnknown that has been nulled.
+  bool hasNulledUnknown(const SCEV *S) const;
+
   /// Return the size of an element read or written by Inst.
   const SCEV *getElementSize(Instruction *Inst);
 
diff --git a/llvm/lib/Analysis/ScalarEvolution.cpp b/llvm/lib/Analysis/ScalarEvolution.cpp
--- a/llvm/lib/Analysis/ScalarEvolution.cpp
+++ b/llvm/lib/Analysis/ScalarEvolution.cpp
@@ -12461,6 +12461,13 @@
   return SCEVExprContains(S, [&](const SCEV *Expr) { return Expr == Op; });
 }
 
+bool ScalarEvolution::hasNulledUnknown(const SCEV *S) const {
+  return SCEVExprContains(S, [&](const SCEV *Expr) {
+    auto U = dyn_cast<SCEVUnknown>(Expr);
+    return U && !U->getValPtr();
+  });
+}
+
 bool ScalarEvolution::ExitLimit::hasOperand(const SCEV *S) const {
   auto IsS = [&](const SCEV *X) { return S == X; };
   auto ContainsS = [&](const SCEV *X) {
diff --git a/llvm/lib/Transforms/Scalar/LoopStrengthReduce.cpp b/llvm/lib/Transforms/Scalar/LoopStrengthReduce.cpp
--- a/llvm/lib/Transforms/Scalar/LoopStrengthReduce.cpp
+++ b/llvm/lib/Transforms/Scalar/LoopStrengthReduce.cpp
@@ -5843,6 +5843,8 @@
       auto DbgDIExpr = std::get<DIExpression *>(D);
       if (!isa<UndefValue>(DbgValue->getVariableLocation()))
         continue;
+      if (SE.hasNulledUnknown(DbgValueSCEV))
+        continue;
       for (PHINode &Phi : L->getHeader()->phis()) {
         if (DbgValueType != Phi.getType())
           continue;