C++ and Java CNI: Check Java references

Wed Apr 25 10:24:00 GMT 2001

Mark Mitchell writes:
 > 
 > JavaPointer<Foo> f;
 > 
 > f->bar();
 > 
 > You don't need to check `this' in `Foo::bar'; you'll have checked at
 > the call-site.
Okay, I guess that's true as long as we enforce this same rule in the
Java compiler: that is, whenever we call a method, even if that method
can be resolved without going via a vtable, we check that the object
is non-NULL. Problem solved.
 > I think this shows that there will be a huge efficiency win over the
 > patch as posted: you'll not check all the references through `this'
 > because `this' is always known to be non-NULL.
Hmm. I'm skeptical about huge: even though the initial tree code
contains checks for `this' every an instance variable is accessed, the
optimizer should be able to determine that it is non-NULL after the
start. I've had a look at the code for a few examples and I haven't
seen any spurious multiple checks.
Andrew.