RFR: 8318650: Optimized subword gather for x86 targets. [v3]

[Sandhya Viswanathan]

On Mon, 6 Nov 2023 18:37:41 GMT, Sandhya Viswanathan <sviswanathan at openjdk.org> wrote:

>> match_rule_supported_vector  called in the beginning will enforce these checks.
>
> This method is match_rule_support_vector and it is not enforcing this check now. It was doing so before through fall through.

I will be more comfortable if either we add the size_in_bits == 64 check in LoadVectorGatherMasked for non subword types or document it properly via comment on why it is covered.

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PR Review Comment: https://git.openjdk.org/jdk/pull/16354#discussion_r1395080418