RFR: 8325083: jdk/incubator/vector/Double512VectorTests.java crashes in Assembler::vex_prefix_and_encode

[Vladimir Kozlov]

On Mon, 27 May 2024 06:06:47 GMT, Jatin Bhateja <jbhateja at openjdk.org> wrote:

> This bugfix patch limits the register class for operands of byte to double cast pattern to prevent reported assertion failure on Knights family CPUs.
> 
> Kindly review and share your feedback.
> 
> Best Regards,
> Jatin

@jatin-bhateja can you explain in more details what KNL is missing to trigger the assert? Can we predicate on missing feature here instead of KNL && DBL checks?
My concern is KNL check could be not enough if such feature is disabled in some container environment which does not match KNL settings.

Why we have `assert(UseAVX > 0` here? `Assembler::vpmov*()` instructions have corresponding asserts already. No need to fix it here but I think we need to cleanup `*.ad` files from such duplicated asserts as separate RFE.

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PR Review: https://git.openjdk.org/jdk/pull/19407#pullrequestreview-2081199278