Please review fix for 6716785: implicit null checks not triggering with CompressedOops

[Vladimir Kozlov]

Coleen,

Why you added os::is_implicit_NPE() method?

All MacroAssembler::needs_explicit_null_check() methods
have  the code for compressed oops implicit NPE.

Also you removed _heap_base setting in universe.cpp.
Where it is set now?

Thanks,
Vladimir

Coleen Phillimore - Sun Microsystems wrote:
> 
> 6716785: implicit null checks not triggering with CompressedOops
> Summary: allocate alignment-sized page(s) below java heap so that memory 
> accesses at heap_base+1page give signal and cause an implicit null check
> Reviewed-by:
> 
> Webrev:
> http://webrev.invokedynamic.info/coleenp/6716785/
> 
> Note in this webrev, the change in arguments.cpp to enable 
> UseCompressedOops by default will be reverted for checking into HS13 
> (it's still off by default) for 6u6p.  Should I enable it in our HS14 
> source base?
> 
> Thanks!
> Coleen