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

[Jatin Bhateja]

On Fri, 27 Jun 2025 22:13:47 GMT, Srinivas Vamsi Parasa <sparasa 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/os_cpu/bsd_x86/os_bsd_x86.cpp line 432:

> 430:     }
> 431: 
> 432: #if defined(_LP64)

Is it still required after the removal of the 32-bit port of x86?

src/hotspot/os_cpu/linux_x86/os_linux_x86.cpp line 258:

> 256:     }
> 257: 
> 258: #if defined(_LP64)

Do we still need this after removal of 32-bit port of x86 ?

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PR Review Comment: https://git.openjdk.org/jdk/pull/26029#discussion_r2173167666
PR Review Comment: https://git.openjdk.org/jdk/pull/26029#discussion_r2173167885