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
@@ -26,8 +26,8 @@
 #include "llvm/IR/DebugInfoMetadata.h"
 #include "llvm/IR/DerivedTypes.h"
 #include "llvm/IR/Function.h"
-#include "llvm/IR/GlobalObject.h"
 #include "llvm/IR/GlobalIndirectSymbol.h"
+#include "llvm/IR/GlobalObject.h"
 #include "llvm/IR/GlobalVariable.h"
 #include "llvm/IR/InlineAsm.h"
 #include "llvm/IR/Instruction.h"
@@ -37,6 +37,7 @@
 #include "llvm/IR/Type.h"
 #include "llvm/IR/Value.h"
 #include "llvm/Support/Casting.h"
+#include "llvm/Support/Debug.h"
 #include <cassert>
 #include <limits>
 #include <memory>
@@ -44,6 +45,8 @@
 
 using namespace llvm;
 
+#define DEBUG_TYPE "value-mapper"
+
 // Out of line method to get vtable etc for class.
 void ValueMapTypeRemapper::anchor() {}
 void ValueMaterializer::anchor() {}
@@ -546,10 +549,16 @@
 MDNode *MDNodeMapper::mapDistinctNode(const MDNode &N) {
   assert(N.isDistinct() && "Expected a distinct node");
   assert(!M.getVM().getMappedMD(&N) && "Expected an unmapped node");
-  DistinctWorklist.push_back(
-      cast<MDNode>((M.Flags & RF_MoveDistinctMDs)
-                       ? M.mapToSelf(&N)
-                       : M.mapToMetadata(&N, cloneOrBuildODR(N))));
+  Metadata *NewM = nullptr;
+  if (M.Flags & RF_MoveDistinctMDs) {
+    NewM = M.mapToSelf(&N);
+  } else {
+    NewM = cloneOrBuildODR(N);
+    LLVM_DEBUG(dbgs() << "\nMap " << N << "\n"
+                      << "To  " << *NewM << "\n\n");
+    M.mapToMetadata(&N, NewM);
+  }
+  DistinctWorklist.push_back(cast<MDNode>(NewM));
   return DistinctWorklist.back();
 }
 
@@ -597,6 +606,9 @@
   for (unsigned I = 0, E = N.getNumOperands(); I != E; ++I) {
     Metadata *Old = N.getOperand(I);
     Metadata *New = mapOperand(Old);
+    if (Old != New)
+      LLVM_DEBUG(dbgs() << "Replacing Op " << Old << " with " << New << " in "
+                        << N << "\n");
 
     if (Old != New)
       N.replaceOperandWith(I, New);
@@ -716,6 +728,11 @@
     });
 
     auto *NewN = MDNode::replaceWithUniqued(std::move(ClonedN));
+    if (N && NewN && N != NewN) {
+      LLVM_DEBUG(dbgs() << "\nMap " << *N << "\n"
+                        << "To  " << *NewN << "\n\n");
+    }
+
     M.mapToMetadata(N, NewN);
 
     // Nodes that were referenced out of order in the POT are involved in a