RFR (M): 8184334: Generalizing Atomic with templates

[Erik Österlund]

Hi Aleksey,

Thank you for checking this. Glad it turned out as I expected.

/Erik

On 2017-07-17 18:49, Aleksey Shipilev wrote:
> On 07/17/2017 05:56 PM, Aleksey Shipilev wrote:
>> On 07/17/2017 05:49 PM, Erik Österlund wrote:
>>>> Something like the Unsafe.{get|put|CAS} -Xint performance test would be nice to
>>>> have.
>>> Sorry, but I do not understand what you mean here.
>>>
>>> 1) The code only boils down to performing casts that do not change any bit
>>> pattern, and is by contract forced to be expanded and inlined at compile time,
>>> so I would be very surprised about any regressions.
>>> 2) This code executes when we are about to perform atomic operations, so any
>>> accidental code generated for the casting (which seems odd in the first place),
>>> I would be very surprised to see.
>>> 3) Even if there was some barely noticeable regression in fastdebug atomics for
>>> whatever reason, I do not know if I think it makes sense to pollute the code
>>> with ugly hacks to micro optimize fastdebug execution time.
>> I agree that fastdebug should not be our primary optimization target. I was
>> wondering if all the template magic actually works well in fastdebug builds.
>>
>> Or product builds, for that matter: because while templates are indeed done
>> during compile-time, say, the inliner that has to deal with new code shapes can
>> have opinions.
>>
>> There are some VarHandles perf tests I have lying around, I can check this
>> myself today.
> Checked, times are the same for baseline/patched builds with either fastdebug or
> release bits. Ditto the instruction counts, number of memory accesses, branches,
> etc. Seems good!
>
> Thanks,
> -Aleksey
>