RFR: 8364296: Set IntelJccErratumMitigation flag ergonomically

[Jatin Bhateja]

On Wed, 30 Jul 2025 16:27:42 GMT, Oli Gillespie <ogillespie at openjdk.org> wrote:

> We should update the flag if we are using a computed value. Nobody else reads IntelJccErratumMitigation specifically, but we want it to be correctly shown in PrintFlagsFinal and anywhere else these flags are inspected.
> 
> 
> Intel(R) Xeon(R) Platinum 8259CL
> java -XX:+UnlockDiagnosticVMOptions -XX:+PrintFlagsFinal -version | grep IntelJcc
> Before:
>      bool IntelJccErratumMitigation  = true   {ARCH diagnostic} {default}
> After:
>      bool IntelJccErratumMitigation  = true   {ARCH diagnostic} {ergonomic}
> 
> 
> Even worse when it's actually false, but shows as true:
> 
> 
> AMD EPYC 7R13
> java -XX:+UnlockDiagnosticVMOptions -XX:+PrintFlagsFinal -version | grep IntelJcc
> Before:
>      bool IntelJccErratumMitigation  = true   {ARCH diagnostic} {default}
> After:
>      bool IntelJccErratumMitigation  = false  {ARCH diagnostic} {ergonomic}

Marked as reviewed by jbhateja (Reviewer).

Hi @olivergillespie , This change looks good to me, what about other flags in vm_version_x86.cpp
https://github.com/openjdk/jdk/blob/master/src/hotspot/cpu/x86/vm_version_x86.cpp#L1198

JVM flag which is enabled through feature detection should have ERGONOMIC origin.

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PR Review: https://git.openjdk.org/jdk/pull/26560#pullrequestreview-3073968444
PR Comment: https://git.openjdk.org/jdk/pull/26560#issuecomment-3138552328