[aarch64-port-dev ] RFR(S): 8087341: C2 doesn't optimize redundant memory operations with G1
Roland Westrelin
roland.westrelin at oracle.com
Fri Feb 19 07:54:26 UTC 2016
Thanks for the review, Vladimir.
Roland.
> On Feb 15, 2016, at 6:33 PM, Vladimir Kozlov <vladimir.kozlov at oracle.com> wrote:
>
> Good. Thank you.
>
> Vladimir
>
> On 2/15/16 1:21 AM, Roland Westrelin wrote:
>>
>>> Can you create new webrev which includes everything (aarch64)?
>>
>> Here it is:
>> http://cr.openjdk.java.net/~roland/8087341/webrev.01/
>>
>> Roland.
>>
>>> And I am satisfied with your answers to my objections.
>>>
>>> Thanks,
>>> Vladimir
>>>
>>> On 2/12/16 4:36 AM, Roland Westrelin wrote:
>>>> Hi Andrew,
>>>>
>>>>> A patch for the AArch64 C2 volatile/CAS generation code which deals with
>>>>> the effects of your proposed C2 patch is available as a webrev
>>>>>
>>>>> http://cr.openjdk.java.net/~adinn/8087341-aarch64/webrev.00/
>>>>
>>>> Thanks for putting that together. I didn’t expect that simple change to cause so much trouble.
>>>>
>>>>> n.b. I have /not/ created a separate issue for the AArch64 part of this
>>>>> fix. I am not sure whether you want to combine it with your patch or
>>>>> push it as a separate stage.
>>>>
>>>> I can push everything together and list you as a contributor (in the contributed-by field) if that works for you.
>>>>
>>>> Vladimir, can you take another look at this? Your two objections were:
>>>>
>>>>> Also we have specialized insert_mem_bar_volatile() if we don't want wide memory affect. Why not use it?
>>>>
>>>> The membar in the change takes the entire memory state as input but only changes raw memory. I don’t think that can be achieved with insert_mem_bar_volatile(). As explained by Mikael, the membar is here to force ordering between the oop store and the card table load. That’s why I think the membar’s inputs and outputs should be set up that way.
>>>>
>>>>> And we need to keep precedent edge link to oop store in case EA eliminates related allocation.
>>>>
>>>> Mikael said it’s not ok to eliminate the memory barrier if we leave the gc barrier.
>>>>
>>>> Roland.
>>>>
>>
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