post_initialize() is a virtual function of CollectedHeap. EpsilonGC doesn't have a particular reason to override it. Its implementation just calls the base's post_initialize().

```
void EpsilonHeap::post_initialize() {
  CollectedHeap::post_initialize();
}
```

In universe_post_init(), HotSpot invokes post_initialize() via vtable.

  // ("weak") refs processing infrastructure initialization
  Universe::heap()->post_initialize();

 1bf724e: 48 8b 3d 73 8a 82 00 mov 0x828a73(%rip),%rdi # 241fcc8 <_ZN8Universe14_collectedHeapE>
 1bf7255: 48 8b 07 mov (%rdi),%rax
 1bf7258: ff 50 40 callq *0x40(%rax)

By deleting it, HotSpot still needs a call via vtable, but the target is correct. It won't need to the second jump to CollectedHeap::post_initialize().