Index: lib/IR/AsmWriter.cpp
===================================================================
--- lib/IR/AsmWriter.cpp
+++ lib/IR/AsmWriter.cpp
@@ -872,7 +872,8 @@
   SmallVector<std::pair<unsigned, MDNode *>, 4> MDs;
   I.getAllMetadata(MDs);
   for (auto &MD : MDs)
-    CreateMetadataSlot(MD.second);
+    if (MD.second)
+      CreateMetadataSlot(MD.second);
 }
 
 /// Clean up after incorporating a function. This is the only way to get out of
@@ -1965,6 +1966,11 @@
                                    TypePrinting *TypePrinter,
                                    SlotTracker *Machine, const Module *Context,
                                    bool FromValue) {
+  if (!MD) {
+    Out << "<null>";
+    return;
+  }
+
   if (const MDNode *N = dyn_cast<MDNode>(MD)) {
     std::unique_ptr<SlotTracker> MachineStorage;
     if (!Machine) {
@@ -3120,7 +3126,9 @@
   if (MDs.empty())
     return;
 
-  if (MDNames.empty())
+  // Second should not be null in well formed, IR, but this is also
+  // called from the Verifier, so be permissive.
+  if (MDNames.empty() && MDs[0].second)
     MDs[0].second->getContext().getMDKindNames(MDNames);
 
   for (const auto &I : MDs) {
Index: lib/IR/TypeFinder.cpp
===================================================================
--- lib/IR/TypeFinder.cpp
+++ lib/IR/TypeFinder.cpp
@@ -71,7 +71,8 @@
         // Incorporate types hiding in metadata.
         I.getAllMetadataOtherThanDebugLoc(MDForInst);
         for (unsigned i = 0, e = MDForInst.size(); i != e; ++i)
-          incorporateMDNode(MDForInst[i].second);
+          if (MDForInst[i].second)
+            incorporateMDNode(MDForInst[i].second);
 
         MDForInst.clear();
       }
Index: lib/IR/Verifier.cpp
===================================================================
--- lib/IR/Verifier.cpp
+++ lib/IR/Verifier.cpp
@@ -3462,6 +3462,12 @@
     }
   }
 
+  SmallVector<std::pair<unsigned, MDNode *>, 4> InstMD;
+  I.getAllMetadata(InstMD);
+  for (auto MD : InstMD) {
+    Assert(MD.second, "Metadata attachment may not be null!", &I);
+  }
+
   if (MDNode *MD = I.getMetadata(LLVMContext::MD_fpmath)) {
     Assert(I.getType()->isFPOrFPVectorTy(),
            "fpmath requires a floating point result!", &I);