Index: include/llvm/ADT/DenseMapInfo.h
===================================================================
--- include/llvm/ADT/DenseMapInfo.h
+++ include/llvm/ADT/DenseMapInfo.h
@@ -30,14 +30,21 @@
 // Provide DenseMapInfo for all pointers.
 template<typename T>
 struct DenseMapInfo<T*> {
+  // Objects of types T may require large alignment, which we might not know (if
+  // T is forward-declared). Generate empty/tombstone keys to account for that.
+  enum { MaxAlignmentLog = 5 };
   static inline T* getEmptyKey() {
     uintptr_t Val = static_cast<uintptr_t>(-1);
-    Val <<= PointerLikeTypeTraits<T*>::NumLowBitsAvailable;
+    Val <<= PointerLikeTypeTraits<T *>::NumLowBitsAvailable < MaxAlignmentLog
+                ? MaxAlignmentLog
+                : PointerLikeTypeTraits<T *>::NumLowBitsAvailable;
     return reinterpret_cast<T*>(Val);
   }
   static inline T* getTombstoneKey() {
     uintptr_t Val = static_cast<uintptr_t>(-2);
-    Val <<= PointerLikeTypeTraits<T*>::NumLowBitsAvailable;
+    Val <<= PointerLikeTypeTraits<T *>::NumLowBitsAvailable < MaxAlignmentLog
+                ? MaxAlignmentLog
+                : PointerLikeTypeTraits<T *>::NumLowBitsAvailable;
     return reinterpret_cast<T*>(Val);
   }
   static unsigned getHashValue(const T *PtrVal) {