RFR: 8144072: G1ParScanThreadState::update_rs does not need to call is_in_reserved

[Thomas Schatzl]

Hi,

On Wed, 2015-11-25 at 19:17 +0100, Erik Helin wrote:
> Hi all,
> 
> based on the patch "8144067: Pass obj directly to
> G1ParScanThreadState::update_rs", here is another small optimization
> that can utilize that G1ParScanThreadState::update_rs now has access to
> both the field and the obj. Instead of calling from->is_in_reserved(o),
> which is defined as
> 
>   bool is_in_reserved(const void* p) {
>     return _bottom <= p && p < _end;
>   }
> 
> we can do the same things as the write barrier for G1:
> 
>   bool is_in_same_region(T* p, oop o) {
>     return ((p ^ o) >> Log2HeapRegionSize) == 0;
>   }

I think the function should assert that both p and o are non-NULL. In
the current uses this is true. I would not need to re-review for this
change.

> 
> which requires no loads at all.

Well, Log2HeapRegionSize.

> This patch adds the new static function HeapRegion::is_in_same_region
> and patches G1ParScanThreadState::update_rs to make use of it.
> 
> Thanks to Thomas for pointing this optimization out.
> 
> Bug:
> https://bugs.openjdk.java.net/browse/JDK-8144072
> 
> Webrev:
> http://cr.openjdk.java.net/~ehelin/8144072/webrev.00/
> 
> Please note this patch is based upon the patch for 8144067.
> 
> Testing:
> - GC test suite with full verification.
> 

Good.

Thanks,
  Thomas