RFR: 8291118: [vectorapi] Optimize the implementation of lanewise FIRST_NONZERO

[Eric Liu]

On Fri, 29 Jul 2022 03:55:54 GMT, Xiaohong Gong <xgong at openjdk.org> wrote:

> Vector API binary op "`FIRST_NONZERO`" represents the vector operation of "`a != 0 ? a : b`", which can be implemented with existing APIs like "`compare + blend`". The current implementation is more complex especially for the floating point type vectors. The main idea is:
> 
> 
> 1) mask = a.compare(0, ne);
> 2) b = b.blend(0, mask);
> 3) result = a | b;
> 
> 
> And for the floating point types, it needs the vector reinterpretation between the floating point type and the relative integral type, since the final "`OR`" operation is only valid for bitwise integral types.
> 
> A simpler implementation is:
> 
> 
> 1) mask = a.compare(0, eq);
> 2) result = a.blend(b, mask);
> 
> 
> This could save the final "`OR`" operation and the related reinterpretation between FP and integral types.
> 
> Here are the performance data of the "`FIRST_NONZERO`" benchmarks (please see the benchmark details for byte vector from [1]) on ARM NEON system:
> 
> Benchmark                          (size) Mode  Cnt  Before    After    Units
> ByteMaxVector.FIRST_NONZERO         1024  thrpt  15 12107.422 18385.157 ops/ms
> ByteMaxVector.FIRST_NONZEROMasked   1024  thrpt  15  9765.282 14739.775 ops/ms
> DoubleMaxVector.FIRST_NONZERO       1024  thrpt  15  1798.545  2331.214 ops/ms
> DoubleMaxVector.FIRST_NONZEROMasked 1024  thrpt  15  1211.838  1810.644 ops/ms
> FloatMaxVector.FIRST_NONZERO        1024  thrpt  15  3491.924  4377.167 ops/ms
> FloatMaxVector.FIRST_NONZEROMasked  1024  thrpt  15  2307.085  3606.576 ops/ms
> IntMaxVector.FIRST_NONZERO          1024  thrpt  15  3602.727  5610.258 ops/ms
> IntMaxVector.FIRST_NONZEROMasked    1024  thrpt  15  2726.843  4210.741 ops/ms
> LongMaxVector.FIRST_NONZERO         1024  thrpt  15  1819.886  2974.655 ops/ms
> LongMaxVector.FIRST_NONZEROMasked   1024  thrpt  15  1337.737  2315.094 ops/ms
> ShortMaxVector.FIRST_NONZERO        1024  thrpt  15  6603.642  9586.320 ops/ms
> ShortMaxVector.FIRST_NONZEROMasked  1024  thrpt  15  5222.006  7991.443 ops/ms
> 
> We can also observe the similar improvement on x86 system.
> 
> [1] https://github.com/openjdk/panama-vector/blob/vectorIntrinsics/test/micro/org/openjdk/bench/jdk/incubator/vector/operation/ByteMaxVector.java#L266

LGTM.

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Marked as reviewed by eliu (Author).

PR: https://git.openjdk.org/jdk/pull/9683