[RFR] Remove MemBarRelease when final field's allocation is NoEscape or ArgEscape

[Hui Shi]

Thanks Aleksey!  Could someone help sponsor and review?

Regards
Hui

On 8 September 2015 at 22:48, Aleksey Shipilev <aleksey.shipilev at oracle.com>
wrote:

> Hi,
>
> On 09/08/2015 03:41 PM, Hui Shi wrote:
> > There might be better use of escape analysis result when optimizing
> > MemBarRelease node for final field stores. Could anyone help review and
> > comments?
> >
> > Patch
> > in
> http://people.linaro.org/~hui.shi/MemBarRelease_Escape/MemBarEscape.patch
> > <
> http://people.linaro.org/%7Ehui.shi/MemBarRelease_Escape/MemBarEscape.patch
> >
> >
> >  __
> >
> > In hotspot, there are two different escape information recorded on a
> node.
> >
> > 1. AlllocateNode._is_non_escaping, true means allocation node’s escape
> > state is noEscape.____
> >
> > 2. InitializeNode._does_not_escape, true means its allocation node’s
> > escape state is noEscape or ArgEscape.____
> >
> > NoEscape has literal meaning. ArgEscape means allocation node is passed
> > to callee but will not escape current thread. So ArgEscape is safe to
> > remove MemBarRelase node for final field store in initialization
> method.____
>
> Yes, the explanation looks reasonable to me. (Didn't know our escape
> analyzer looks into static callees to figure out ArgEscape). I think
> this is what EA intended its users to look for, when marking
> InitializeNode-s:
>
>     if (n->is_Allocate()) {
>       // The object allocated by this Allocate node will never be
>       // seen by an other thread. Mark it so that when it is
>       // expanded no MemBarStoreStore is added.
>       InitializeNode* ini = n->as_Allocate()->initialization();
>       if (ini != NULL)
>         ini->set_does_not_escape();
>     }
>
> Thanks,
> -Aleksey
>
>
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