RFR: 8201318: Introduce GCThreadLocalData to abstract GC-specific data belonging to a thread

[Robbin Ehn]

On 2018-04-10 17:47, Aleksey Shipilev wrote:
> On 04/10/2018 05:25 PM, Robbin Ehn wrote:
>> Had quick look, what I saw looked good. (not a full review)
>> Is there a reason for moving the gc data to 'zero offset' in Thread?
> 
> Oh! I missed that, and I fully agree with this move. At least one reason I see, smaller offsets
> against TLS open up opportunities for denser code-generation when e.g. GC barriers poll thread-local
> data. Right now SATB barrier generates something like "cmpb $0x0, 0x3d8(%r15)", while it could
> generate just "cmpb $0x0, 0x0(%r15)" now :)

Yes, but it pushes down e.g.:
333   volatile void* _polling_page;                 // Thread local polling page
Which may not matter, as long as it's on the first page I suppose.

/Robbin

> 
> Thanks,
> -Aleksey
>