RFR: 8350840: C2: x64 Assembler::vpcmpeqq assert: failed: XMM register should be 0-15

[Jatin Bhateja]

On Wed, 12 Mar 2025 18:37:54 GMT, Vladimir Kozlov <kvn at openjdk.org> wrote:

>> This bug fix patch addressed an assertion failure due to unexpected register operand encoding.
>> AVX2 flavour of instruction "vpcmpeqq" expects to operate over XMM registers from lower register bank (0-15), in this case, the register mask associated with the destination vector operand of the matcher pattern also includes registers from the higher bank.
>> 
>> The issue can be reliably reproduced if we modify the static allocation order of XMM register through AD file change.
>> Existing bug [JDK-8343294](https://bugs.openjdk.org/browse/JDK-8343294) already tracks the requirement to randomize the allocation ordering.
>> 
>> Kindly review and share your feedback.
>> 
>> Best Regards,
>> Jatin
>
> My testing passed.

Thanks @vnkozlov, @sviswa7

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PR Comment: https://git.openjdk.org/jdk/pull/23979#issuecomment-2719749727