[jdk19] RFR: 8287794: Reverse*VNode::Identity problem

[Dean Long]

On Fri, 22 Jul 2022 17:24:04 GMT, Jatin Bhateja <jbhateja at openjdk.org> wrote:

> Hi All,
> 
> - This bug fix patch fixes a missing case during reverse[bits|bytes] identity transformation.
> - Unlike AARCH64(SVE),  X86(AVX512) ISA has no direct instruction to reverse[bits|bytes] of a vector lane hence a predicated operation is supported through blend instruction.
> - New IR framework based tests have been added for transforms relevant to AVX2, AVX512 and SVE.
> 
> Kindly review and share your feedback.
> 
> Best Regards,
> Jatin

The "else if" clause still returns the same value as the "else" clause, so why is the "else if" part needed?  This change doesn't seem to address the question asked by the submitter of the bug:
>  Seems to me the first condition checks that MASKs are the same in both nodes. But if they are not, we are falling to "else" branch, where we do the same transformation anyway. So, there might be a bug lurking there when MASKs are different.

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Changes requested by dlong (Reviewer).

PR: https://git.openjdk.org/jdk19/pull/153