Object.getClass() is called often in reflection code, and some customers (e.g. Nortel) use the class object for hash table lookup of class specific data:

  Object obj = ...
  ClassInfo info = lookup_class_info(obj.getClass());

  ClassInfo lookup_class_info(Class cls) {
    int hash = cls.hashCode();
    // do hash table lookup
    ...
  }

Calling Object.hashCode() is already fast, but getClass() is not. Storing a pointer to the class (or class info) in each instance will have footprint impact.



Inlining it is trivial. Object.getClass() is already "final native", and the implementation would be:


const int klass_offset = oopDesc::klass_offset_in_bytes();
const int mirror_offset = klassOopDesc::klass_part_offset_in_bytes() + Klass::java_mirror_offset_in_bytes();

// receiver in eax
__ movl(eax, Address(eax, oopDesc::klass_offset_in_bytes()));
__ movl(eax, Address(eax, mirror_offset));


There has to be a null check on the receiver somewhere (throwing a NullPointerException).

This should be done in both compiler1 and compiler2.
steffen.grarup@eng 1999-11-10