[riscv-port-jdk17u:riscv-port] RFR: 8307446: RISC-V: Improve performance of floating point to integer conversion

[Feilong Jiang]

Hi,
please review this clean backport of [JDK-8307446](https://bugs.openjdk.org/browse/JDK-8307446).

JHM shows the same improvement on Unmatched board:


Benchmark                     (size)   Mode  Cnt   Score   Error   Units
--- baseline -----------------------------------------------------------
FloatConversion.doubleToInt     2048  thrpt   15  30.270 ? 0.144  ops/ms
FloatConversion.doubleToLong    2048  thrpt   15  29.831 ? 0.128  ops/ms
FloatConversion.floatToInt      2048  thrpt   15  30.530 ? 0.031  ops/ms
FloatConversion.floatToLong     2048  thrpt   15  30.189 ? 0.100  ops/ms
--- optimized ----------------------------------------------------------
FloatConversion.doubleToInt     2048  thrpt   15  66.051 ? 0.064  ops/ms
FloatConversion.doubleToLong    2048  thrpt   15  66.095 ? 0.460  ops/ms
FloatConversion.floatToInt      2048  thrpt   15  68.114 ? 0.072  ops/ms
FloatConversion.floatToLong     2048  thrpt   15  68.482 ? 0.193  ops/ms

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

Commit messages:
 - 8307446: RISC-V: Improve performance of floating point to integer conversion

Changes: https://git.openjdk.org/riscv-port-jdk17u/pull/57/files
 Webrev: https://webrevs.openjdk.org/?repo=riscv-port-jdk17u&pr=57&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8307446
  Stats: 18 lines in 1 file changed: 0 ins; 1 del; 17 mod
  Patch: https://git.openjdk.org/riscv-port-jdk17u/pull/57.diff
  Fetch: git fetch https://git.openjdk.org/riscv-port-jdk17u.git pull/57/head:pull/57

PR: https://git.openjdk.org/riscv-port-jdk17u/pull/57