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

[Aleksey Shipilev]

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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