[clang][bytecode] Diagnose heap-allocated array elem pointers... (llvm#137523)

...  as "pointer to subobject".

Author: tbaederr

clang/lib/AST/ByteCode/EvaluationResult.cpp

@@ -230,8 +230,9 @@ bool EvaluationResult::checkReturnValue(InterpState &S, const Context &Ctx,
       assert(B->getDescriptor());
       assert(B->getDescriptor()->asExpr());
 
+      bool IsSubobj = !Ptr.isRoot() || Ptr.isArrayElement();
       S.FFDiag(Info, diag::note_constexpr_dynamic_alloc)
-          << Ptr.getType()->isReferenceType() << !Ptr.isRoot();
+          << Ptr.getType()->isReferenceType() << IsSubobj;
       S.Note(B->getDescriptor()->asExpr()->getExprLoc(),
              diag::note_constexpr_dynamic_alloc_here);
       return false;

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

@@ -620,6 +620,10 @@ namespace std {
   }
 }
 
+constexpr int *escape = std::allocator<int>().allocate(3); // both-error {{constant expression}} \
+                                                           // both-note {{pointer to subobject of heap-allocated}} \
+                                                           // both-note {{heap allocation performed here}}
+
 /// Specialization for float, using operator new/delete.
 namespace std {
   using size_t = decltype(sizeof(0));