RFR: 8360776: Disable Intel APX by default and enable it only if requested by the user using -XX:+UnlockExperimentalVMOptions -XX:+UseAPX

[Sandhya Viswanathan]

On Mon, 30 Jun 2025 06:54:42 GMT, David Holmes <dholmes at openjdk.org> wrote:

>> Currently, APX is not enabled consistently between product and debug builds.
>> 
>> If the hardware supports Intel APX:
>> 
>> 1) In product builds, APX is disabled by default, even if the user explicitly enables it using `-XX:+UnlockExperimentalVMOptions -XX:+UseAPX`.
>> 
>> 2) In debug builds, APX is enabled by default regardless of whether the user explicitly enables it or not.
>> 
>> **The goal of this PR is to enable APX for both product and debug builds if and only if the user explicitly enables it using `-XX:+UnlockExperimentalVMOptions -XX:+UseAPX`.**
>
> src/hotspot/cpu/x86/vm_version_x86.cpp line 3155:
> 
>> 3153:   }
>> 3154:   // Enable APX support for product builds after
>> 3155:   // completion of planned features listed in JDK-8329030.
> 
> So you have decided not to follow the original plan ( as JDK-8329030 is not complete) and instead go ahead and enable APX in product mode now. Why? Was this discussed anywhere?

@dholmes-ora  The remaining items in JDK-8329030 are nice to have. I will update JDK-8329030 accordingly to reflect this.

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PR Review Comment: https://git.openjdk.org/jdk/pull/26029#discussion_r2175521518