Index: include/llvm/ADT/Optional.h
===================================================================
--- include/llvm/ADT/Optional.h
+++ include/llvm/ADT/Optional.h
@@ -108,7 +108,6 @@
   }
 };
 
-#if !defined(__GNUC__) || defined(__clang__) // GCC up to GCC7 miscompiles this.
 /// Storage for trivially copyable types only.
 template <typename T> struct OptionalStorage<T, true> {
   AlignedCharArrayUnion<T> storage;
@@ -118,14 +117,20 @@
 
   OptionalStorage(const T &y) : hasVal(true) { new (storage.buffer) T(y); }
   OptionalStorage &operator=(const T &y) {
-    *reinterpret_cast<T *>(storage.buffer) = y;
-    hasVal = true;
+    if (hasVal) {
+      // Use std::addressof to silence strict-aliasing warnings from gcc.
+      *reinterpret_cast<T *>(std::addressof(storage.buffer)) = y;
+    } else {
+      // Copy assignment to uninitialized storage is undefined behavior so copy
+      // construct with placement new when no value is held.
+      new (storage.buffer) T(y);
+      hasVal = true;
+    }
     return *this;
   }
 
   void reset() { hasVal = false; }
 };
-#endif
 } // namespace optional_detail
 
 template <typename T> class Optional {