JDK-8253113 added an optimization in C1 to reduce the number of heap allocations and copies when reading nested values in flattened fields. This optimization had several unforeseen interactions with existing C1 optimizations (JDK-8262128, JDK-8266086). At this point, it makes sense to have a VM flag to control the optimization added in JDK-8253113 in order to more easily future potential issues that could be related to this change.