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

[Mikael Gerdin]

Hi Erik,

On 2015-11-25 19:17, 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;
>    }
>
> which requires no loads at all.
>
> 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/

Looks good.
/Mikael

>
> Please note this patch is based upon the patch for 8144067.
>
> Testing:
> - GC test suite with full verification.
>
> Thanks,
> Erik
>