RFR[S]: 8239014 -XX:-UseEmptySlotsInSupers sometime fails to reproduce the layout of the old code

[David Holmes]

Hi Fred,

Sorry for the delay getting back to this.

On 15/02/2020 4:34 am, Frederic Parain wrote:
> Hi David,
> 
> Here’s a new webrev with a test case:
> http://cr.openjdk.java.net/~fparain/8239014/webrev.01/
> 
> When -XX:-UseEmptySlotsInSupers is used, the field layout code
> emulates the behavior of the old code by appending fields after
> the rounded up end of the super class, adding primitive fields
> by decreasing size, then oops.
> 
> The issue was that this strategy doesn’t fill the gap after the
> header when the class pointer is 4 bytes and the first field is
> either a long or a double. There was a special case in the old
> code to handle this situation, but it was missing in the
> emulation mode of the new code.

Thanks for clarifying.

Changes look good.

David

> Thank you,
> 
> Fred
> 
> 
>> On Feb 13, 2020, at 17:53, David Holmes <david.holmes at oracle.com> wrote:
>>
>> Hi Fred,
>>
>> Can you add a testcase for this? I can't really evaluate the change just by looking at the code.
>>
>> Thanks,
>> David
>>
>> On 14/02/2020 6:28 am, Frederic Parain wrote:
>>> Please review this small change that fix the behavior of-XX: -UseEmptySlotsInSupers.
>>> CR: https://bugs.openjdk.java.net/browse/JDK-8239014
>>> Webrev: http://cr.openjdk.java.net/~fparain/8239014/webrev.00/index.html
>>> Thank you,
>>> Fred
>