RFR: JDK-8318228: RISC-V: C2 ConvF2HF [v2]

[Hamlin Li]

> Hi,
> Can you review the patch to add ConvF2HF intrinsic to JDK for riscv？
> Thanks!
> 
> ## Test
> ### Functionality
> #### hotspot tests
> test/hotspot/jtreg/compiler/intrinsics/ 
> test/hotspot/jtreg/compiler/c2/irTests
> 
> #### jdk tests
> test/jdk/java/lang/Float/Binary16Conversion*.java
> 
> ### Performance
> tested on licheepi.
> 
> #### with UseZfh enabled
> 
> Benchmark                                     (size)  Mode  Cnt     Score   Error  Units
> Fp16ConversionBenchmark.floatToFloat16          2048  avgt    2  4170.549          ns/op
> Fp16ConversionBenchmark.floatToFloat16Memory    2048  avgt    2    21.492          ns/op
> 
> 
> #### with UseZfh disabled
> (i.e. disable the intrinsic)
> 
> Benchmark                                     (size)  Mode  Cnt      Score   Error  Units
> Fp16ConversionBenchmark.floatToFloat16          2048  avgt    2  25036.647          ns/op
> Fp16ConversionBenchmark.floatToFloat16Memory    2048  avgt    2     27.326          ns/op

Hamlin Li has updated the pull request incrementally with one additional commit since the last revision:

  replace fclass with feq as performance optimization.

-------------

Changes:
  - all: https://git.openjdk.org/jdk/pull/17450/files
  - new: https://git.openjdk.org/jdk/pull/17450/files/c732a3ff..01ec31c2

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=17450&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=17450&range=00-01

  Stats: 3 lines in 1 file changed: 0 ins; 0 del; 3 mod
  Patch: https://git.openjdk.org/jdk/pull/17450.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/17450/head:pull/17450

PR: https://git.openjdk.org/jdk/pull/17450