RFR: 8366455: Move VarHandles.GuardMethodGenerator to execute on build

[Chen Liang]

On Tue, 2 Sep 2025 15:24:07 GMT, Paul Sandoz <psandoz at openjdk.org> wrote:

>> @PaulSandoz Do you know if there was/is a particular reason for not generating the VarHandle guards as part of the build?
>
>> @PaulSandoz Do you know if there was/is a particular reason for not generating the VarHandle guards as part of the build?
> 
> At the time there were other priorities and we did not know what the frequency of updates might be, but we left gen code in place just in case (and did use it occasionally). I think this PR is good, addressing tech debt.

Can @PaulSandoz or @JornVernee re-review this patch?

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PR Comment: https://git.openjdk.org/jdk/pull/27009#issuecomment-3258882442