RFR: 8295276: AArch64: Add backend support for half float conversion intrinsics

[Ningsheng Jian]

On Thu, 20 Oct 2022 14:33:33 GMT, Bhavana Kilambi <bkilambi at openjdk.org> wrote:

> This patch adds aarch64 backend support for library intrinsics that implement conversions between half-precision and single-precision floats.
> 
> Ran the following benchmarks to assess the performance with this patch -
> 
> org.openjdk.bench.java.math.Fp16ConversionBenchmark.floatToFloat16 org.openjdk.bench.java.math.Fp16ConversionBenchmark.float16ToFloat
> 
> The performance (ops/ms) gain with the patch on an ARM NEON machine is shown below -
> 
> 
>   Benchmark                                      Gain
>   Fp16ConversionBenchmark.float16ToFloat         3.42
>   Fp16ConversionBenchmark.floatToFloat16         5.85

Looks good to me.

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Marked as reviewed by njian (Committer).

PR: https://git.openjdk.org/jdk/pull/10796