src/hotspot/share/classfile/fieldLayoutBuilder.cpp

*** 559,570 ****
              SystemDictionary::resolve_flattenable_field_or_fail(&fs,
                  Handle(THREAD, _cfp->_loader_data->class_loader()),
                  _cfp->_protection_domain, true, CHECK);
          assert(klass != NULL, "Sanity check");
          ValueKlass* vk = ValueKlass::cast(klass);
!         bool flattened = (ValueFieldMaxFlatSize < 0)
                           || (vk->size_helper() * HeapWordSize) <= ValueFieldMaxFlatSize;
          if (flattened) {
            group->add_flattened_field(fs, vk);
            _nonstatic_oopmap_count += vk->nonstatic_oop_map_count();
            fs.set_flattened(true);
          } else {
--- 559,572 ----
              SystemDictionary::resolve_flattenable_field_or_fail(&fs,
                  Handle(THREAD, _cfp->_loader_data->class_loader()),
                  _cfp->_protection_domain, true, CHECK);
          assert(klass != NULL, "Sanity check");
          ValueKlass* vk = ValueKlass::cast(klass);
!         bool has_flattenable_size = (ValueFieldMaxFlatSize < 0)
                           || (vk->size_helper() * HeapWordSize) <= ValueFieldMaxFlatSize;
+         // volatile fields are currently never flattened, this could change in the future
+         bool flattened = !fs.access_flags().is_volatile() && has_flattenable_size;
          if (flattened) {
            group->add_flattened_field(fs, vk);
            _nonstatic_oopmap_count += vk->nonstatic_oop_map_count();
            fs.set_flattened(true);
          } else {