[8u20] [9] RFR (S): 8043546: C1 optimizes @Stable instance fields with default values

[Vladimir Kozlov]

Okay

Vladimir

On 7/10/14 3:05 AM, Vladimir Ivanov wrote:
> VladimirK, John, thanks for review.
>
> Fair enough. Updated version:
> http://cr.openjdk.java.net/~vlivanov/8043546/webrev.01/
>
> Also, I filed RFE [1] to refactor @Stable support for instance fields.
>
> Best regards,
> Vladimir Ivanov
>
> [1] https://bugs.openjdk.java.net/browse/JDK-8049837
>
> On 7/10/14 6:28 AM, John Rose wrote:
>> On Jul 9, 2014, at 7:16 PM, John Rose <john.r.rose at oracle.com
>> <mailto:john.r.rose at oracle.com>> wrote:
>>
>>>> C1 already optimizes stable static fields and after this change it
>>>> also optimizes stable instance fields. C1 doesn't support stable
>>>> array, so tests are changed to distiguish 3 outcomes: no @Stable
>>>> support, C1 & C2. I'll try to extend C1 support to arrays in the future.
>>>
>>> The same "non default value" check is needed for getstatic as well as
>>> getfield.  I don't see how the existing getstatic is already correct.
>>>
>>> — John
>>
>> Sorry; now I see it.  The required check, for statics, comes from the
>> setting at the bottom of ciField::initialize_from.  The corresponding
>> non-static case gets a cut-out near the top, before the default-check.
>>   This is why the *.hpp file says:
>>
>>    // For non-static fields, the null/zero check must be
>>    // arranged by the user, as constant_value().is_null_or_zero().
>>
>> I suppose an extra comment in c1_GB.cpp, near the processing of
>> getstatic, might reassure forgetful and/or nervous readers.
>>
>> — John