[clang][bytecode] Report mutable reads when copying unions (llvm#149320)

Author: tbaederr

clang/lib/AST/ByteCode/InterpBuiltin.cpp

@@ -2905,6 +2905,8 @@ static bool copyRecord(InterpState &S, CodePtr OpPC, const Pointer &Src,
         if (!copyField(F, /*Activate=*/true))
           return false;
       } else {
+        if (!CheckMutable(S, OpPC, Src.atField(F.Offset)))
+          return false;
         Pointer DestField = Dest.atField(F.Offset);
         zeroAll(DestField);
       }

clang/lib/AST/ByteCode/InterpFrame.cpp

@@ -128,6 +128,11 @@ static bool shouldSkipInBacktrace(const Function *F) {
   if (FD->getDeclName().getCXXOverloadedOperator() == OO_New ||
       FD->getDeclName().getCXXOverloadedOperator() == OO_Array_New)
     return true;
+
+  if (const auto *MD = dyn_cast<CXXMethodDecl>(FD);
+      MD && MD->getParent()->isAnonymousStructOrUnion())
+    return true;
+
   return false;
 }
 

clang/test/AST/ByteCode/unions.cpp

@@ -847,6 +847,20 @@ namespace Activation2 {
   }
   static_assert(change_member_indirectly() == 4);
 }
+
+namespace CopyCtorMutable {
+  struct E {
+    union { // expected-note {{read of mutable member 'b'}}
+      int a;
+      mutable int b; // both-note {{here}}
+    };
+  };
+  constexpr E e1 = {{1}};
+  constexpr E e2 = e1; // both-error {{constant}} \
+                       // ref-note {{read of mutable member 'b'}} \
+                       // both-note {{in call}}
+}
+
 #endif
 
 namespace AddressComparison {