[clang][bytecode] Activate pointers in Init{,Pop} (#112832)

Author: tbaederr

clang/lib/AST/ByteCode/Interp.h

@@ -1841,6 +1841,7 @@ bool Init(InterpState &S, CodePtr OpPC) {
     assert(false);
     return false;
   }
+  Ptr.activate();
   Ptr.initialize();
   new (&Ptr.deref<T>()) T(Value);
   return true;
@@ -1852,6 +1853,7 @@ bool InitPop(InterpState &S, CodePtr OpPC) {
   const Pointer &Ptr = S.Stk.pop<Pointer>();
   if (!CheckInit(S, OpPC, Ptr))
     return false;
+  Ptr.activate();
   Ptr.initialize();
   new (&Ptr.deref<T>()) T(Value);
   return true;

clang/test/AST/ByteCode/placement-new.cpp

@@ -300,3 +300,14 @@ namespace UsedToCrash {
   }
   int alloc1 = (alloc(), 0);
 }
+
+constexpr bool change_union_member() {
+  union U {
+    int a;
+    int b;
+  };
+  U u = {.a = 1};
+  std::construct_at<int>(&u.b, 2);
+  return u.b == 2;
+}
+static_assert(change_union_member());