diff --git a/llvm/lib/Transforms/Utils/ValueMapper.cpp
 b/llvm/lib/Transforms/Utils/ValueMapper.cpp
--- a/llvm/lib/Transforms/Utils/ValueMapper.cpp
+++ b/llvm/lib/Transforms/Utils/ValueMapper.cpp
@@ -398,13 +398,17 @@
       SmallVector<ValueAsMetadata *, 4> MappedArgs;
       for (auto *VAM : AL->getArgs()) {
         // Map both Local and Constant VAMs here; they will both ultimately
-        // be mapped via mapValue (apart from constants when we have no
-        // module level changes, which have an identity mapping).
+        // be mapped via mapValue. The exceptions are constants when we have no
+        // module level changes and locals when they have no existing mapped
+        // value and RF_IgnoreMissingLocals is set; these have identity
+        // mappings.
         if ((Flags & RF_NoModuleLevelChanges) && isa<ConstantAsMetadata>(VAM)) {
           MappedArgs.push_back(VAM);
         } else if (Value *LV = mapValue(VAM->getValue())) {
           MappedArgs.push_back(
               LV == VAM->getValue() ? VAM : ValueAsMetadata::get(LV));
+        } else if ((Flags & RF_IgnoreMissingLocals) && isa<LocalAsMetadata>(VAM)) {
+            MappedArgs.push_back(VAM);
         } else {
           // If we cannot map the value, set the argument as undef.
           MappedArgs.push_back(ValueAsMetadata::get(
diff --git a/llvm/unittests/Transforms/Utils/ValueMapperTest.cpp
 b/llvm/unittests/Transforms/Utils/ValueMapperTest.cpp
--- a/llvm/unittests/Transforms/Utils/ValueMapperTest.cpp
+++ b/llvm/unittests/Transforms/Utils/ValueMapperTest.cpp
@@ -8,6 +8,7 @@
 
 #include "llvm/Transforms/Utils/ValueMapper.h"
 #include "llvm/IR/Constants.h"
+#include "llvm/IR/DebugInfoMetadata.h"
 #include "llvm/IR/Function.h"
 #include "llvm/IR/GlobalVariable.h"
 #include "llvm/IR/LLVMContext.h"
@@ -291,7 +292,11 @@
   Argument &A = *F->arg_begin();
 
   auto *LAM = LocalAsMetadata::get(&A);
-  auto *MAV = MetadataAsValue::get(C, LAM);
+  auto *MAV0 = MetadataAsValue::get(C, LAM);
+  std::vector<ValueAsMetadata*> Elts;
+  Elts.push_back(LAM);
+  auto *ArgList = DIArgList::get(C, Elts);
+  auto *MAV1 = MetadataAsValue::get(C, ArgList);
 
   // The principled answer to a LocalAsMetadata of an unmapped SSA value would
   // be to return nullptr (regardless of RF_IgnoreMissingLocals).
@@ -301,26 +306,45 @@
   // such as "metadata i32 %x" don't currently successfully maintain that
   // property.  To keep RemapInstruction from crashing we need a non-null
   // return here, but we also shouldn't reference the unmapped local.  Use
-  // "metadata !{}".
+  // "metadata !{}" for direct LocalAsMetadata, and undef for uses in a
+  // DIArgList.
   auto *N0 = MDTuple::get(C, None);
   auto *N0AV = MetadataAsValue::get(C, N0);
+  auto *N1 = UndefValue::get(Type::getInt8Ty(C));
+  auto *N1AM = ValueAsMetadata::get(N1);
+  std::vector<ValueAsMetadata*> N1Elts;
+  N1Elts.push_back(N1AM);
+  auto *N1ArgList = DIArgList::get(C, N1Elts);
+  auto *N1AV = MetadataAsValue::get(C, N1ArgList);
   ValueToValueMapTy VM;
-  EXPECT_EQ(N0AV, ValueMapper(VM).mapValue(*MAV));
-  EXPECT_EQ(nullptr, ValueMapper(VM, RF_IgnoreMissingLocals).mapValue(*MAV));
-  EXPECT_FALSE(VM.count(MAV));
+  EXPECT_EQ(N0AV, ValueMapper(VM).mapValue(*MAV0));
+  EXPECT_EQ(nullptr, ValueMapper(VM, RF_IgnoreMissingLocals).mapValue(*MAV0));
+  EXPECT_EQ(N1AV, ValueMapper(VM).mapValue(*MAV1));
+  EXPECT_EQ(MAV1, ValueMapper(VM, RF_IgnoreMissingLocals).mapValue(*MAV1));
+  EXPECT_FALSE(VM.count(MAV0));
+  EXPECT_FALSE(VM.count(MAV1));
   EXPECT_FALSE(VM.count(&A));
   EXPECT_EQ(None, VM.getMappedMD(LAM));
-
-  VM[MAV] = MAV;
-  EXPECT_EQ(MAV, ValueMapper(VM).mapValue(*MAV));
-  EXPECT_EQ(MAV, ValueMapper(VM, RF_IgnoreMissingLocals).mapValue(*MAV));
-  EXPECT_TRUE(VM.count(MAV));
+  EXPECT_EQ(None, VM.getMappedMD(ArgList));
+
+  VM[MAV0] = MAV0;
+  VM[MAV1] = MAV1;
+  EXPECT_EQ(MAV0, ValueMapper(VM).mapValue(*MAV0));
+  EXPECT_EQ(MAV0, ValueMapper(VM, RF_IgnoreMissingLocals).mapValue(*MAV0));
+  EXPECT_EQ(MAV1, ValueMapper(VM).mapValue(*MAV1));
+  EXPECT_EQ(MAV1, ValueMapper(VM, RF_IgnoreMissingLocals).mapValue(*MAV1));
+  EXPECT_TRUE(VM.count(MAV0));
+  EXPECT_TRUE(VM.count(MAV1));
   EXPECT_FALSE(VM.count(&A));
 
-  VM[MAV] = &A;
-  EXPECT_EQ(&A, ValueMapper(VM).mapValue(*MAV));
-  EXPECT_EQ(&A, ValueMapper(VM, RF_IgnoreMissingLocals).mapValue(*MAV));
-  EXPECT_TRUE(VM.count(MAV));
+  VM[MAV0] = &A;
+  VM[MAV1] = &A;
+  EXPECT_EQ(&A, ValueMapper(VM).mapValue(*MAV0));
+  EXPECT_EQ(&A, ValueMapper(VM, RF_IgnoreMissingLocals).mapValue(*MAV0));
+  EXPECT_EQ(&A, ValueMapper(VM).mapValue(*MAV1));
+  EXPECT_EQ(&A, ValueMapper(VM, RF_IgnoreMissingLocals).mapValue(*MAV1));
+  EXPECT_TRUE(VM.count(MAV0));
+  EXPECT_TRUE(VM.count(MAV1));
   EXPECT_FALSE(VM.count(&A));
 }