[aarch64-port-dev ] RFR: 8191954: AArch64: disable UseCISCSpill in C2

[Ningsheng Jian]

Thanks for the review!

On 28 November 2017 at 17:35, Andrew Dinn <adinn at redhat.com> wrote:
> On 28/11/17 08:49, Andrew Haley wrote:
>> On 28/11/17 05:54, Ningsheng Jian wrote:
>>> JBS:
>>> https://bugs.openjdk.java.net/browse/JDK-8191954
>>>
>>> Webrev:
>>> http://cr.openjdk.java.net/~njian/8191954/webrev.00/
>>>
>>> This sets UseCISCSpill to false on AArch64, as we actually don't use
>>> that. jtreg tests passed with fastdebug build.
>>
>> That's too risky right now.  We'll look at it in the next cycle.
> I don't think it is actually /risky/ because UseCISCSpill would only
> take effect if aarch64.ad declared a cisc_spilling_operand_name in the
> frame section (it doesn't).
>
> That declaration drives adlc to generate an overriding version of a
> virtual method of class Node which is used by the chaitin allocator to
> determine how to spill a value. Without any override the method always
> returns -1, meaning that operands are never considered for CISC spilling.

Yes, that's why I think it's low risk but also trivial.

>
> So, leaving UseCISCSpill set to true causes a small amount of extra
> checking to be done but no action is ever taken. Of course that also
> means the change is not going to be /critical/ to performance i.e.
> rushing to squeeze it into jdk10 is not justified.
>
> regards,
>
>
> Andrew Dinn
> -----------
> Senior Principal Software Engineer
> Red Hat UK Ltd
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Thanks,
Ningsheng