Index: include/llvm/Support/JSON.h
===================================================================
--- include/llvm/Support/JSON.h
+++ include/llvm/Support/JSON.h
@@ -452,7 +452,23 @@
     new (reinterpret_cast<T *>(Union.buffer)) T(std::forward<U>(V)...);
   }
   template <typename T> T &as() const {
+#if defined(__GNUC__) && !defined(__clang) && (__GNUC__ < 7)
+// Silence
+//
+//   warning: dereferencing type-punned pointer will break strict-aliasing rules
+//   [-Wstrict-aliasing]
+//
+// This private method is always called after type-checking, so the
+// reinterpret_cast<> just re-casts the char buffer to the type that was
+// placement-new-ed into it. Because AlignedCharArrayUnion guarantees correct
+// alignment for all contained types, this plays by the strict aliasing rules.
+#pragma GCC diagnostic push
+#pragma GCC diagnostic ignored "-Wstrict-aliasing"
+#endif
     return *reinterpret_cast<T *>(Union.buffer);
+#if defined(__GNUC__) && !defined(__clang) && (__GNUC__ < 7)
+#pragma GCC diagnostic pop
+#endif
   }
 
   template <typename Indenter>