Request for review (S): C2 should recognize "obj.getClass() == A.class" code pattern

[John Rose]

On Apr 25, 2012, at 7:37 PM, John Rose wrote:

> On Apr 25, 2012, at 6:32 PM, Krystal Mok wrote:
> 
>> Oops. I'm getting native NPE in CmpPNode::Ideal() with SPECjvm2008.
>> Will investigate and post an updated patch later.
> 
> In the long run, those asserts will fire also.  (At least, such asserts usually do.  Compilers eventually explore all dark corners in the IR schema.)
> 
> I am mulling over some more comments along that line.  Basically, pattern-matching code has to "expect the unexpected".

One other quick comment:  LoadKlass nodes are not just for oopDesc::_klass.  They load klasses from other places too.  The way you tell the difference is by looking at the base object and offset.  Grep for LoadKlassNode::make to see various constructions.  Also look at uses of Ideal_base_and_offset; the offset is never disregarded.

— John