RFR: 8282874: Bad performance on gather/scatter API caused by different IntSpecies of indexMap

[Paul Sandoz]

On Wed, 9 Mar 2022 12:33:49 GMT, Joshua Zhu <jzhu at openjdk.org> wrote:

> I came across a performance issue when using scatter store VectorAPI for Integer and Long in the same application. The poor performance was caused by vector intrinsic inlining failure because of non-determined IntSpecies for a constant VectorShape of IndexMap in this scenario.
> As discussion at https://github.com/openjdk/jdk/pull/7721 , I change the code in VectorAPI.
> Please help review.

I think its OK, to follow up after this with some tests for "polluted" profiles of vectors (which may expose more issues).
Given the scope of the fix i would recommend adding a comment in each place as to why we don't switch over the enum constant itself (note we are very careful in other performance critical areas of the JDK to avoid this e.g. in VarHandle code).

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PR: https://git.openjdk.java.net/jdk/pull/7757