RFR: 8323116: [REDO] Computational test more than 2x slower when AVX instructions are used [v6]

[Srinivas Vamsi Parasa]

> The goal of this small PR is improve the performance of convert instructions and address the slowdown when AVX>0 is used.
> 
> The performance data using the ComputePI.java benchmark (part of this PR) is as follows:
> 
> 
> Benchmark   (ns/op) | Stock JDK | This PR (AVX=3) | Speedup
> -- | -- | -- | --
> ComputePI.compute_pi_dbl_flt | 511.34 | 510.989 | 1.0
> ComputePI.compute_pi_flt_dbl | 2024.06 | 518.695 | 3.9
> ComputePI.compute_pi_int_dbl | 695.482 | 453.054 | 1.5
> ComputePI.compute_pi_int_flt | 799.268 | 449.83 | 1.8
> ComputePI.compute_pi_long_dbl | 802.992 | 454.891 | 1.8
> ComputePI.compute_pi_long_flt | 628.62 | 463.617 | 1.4
> 
> 
> 
> Benchmark (ns/op) | Stock JDK | This PR (AVX=0) | Speedup
> -- | -- | -- | --
> ComputePI.compute_pi_dbl_flt | 473.778 | 472.529 | 1.0
> ComputePI.compute_pi_flt_dbl | 536.004 | 538.418 | 1.0
> ComputePI.compute_pi_int_dbl | 458.08 | 460.245 | 1.0
> ComputePI.compute_pi_int_flt | 477.305 | 476.975 | 1.0
> ComputePI.compute_pi_long_dbl | 455.132 | 455.064 | 1.0
> ComputePI.compute_pi_long_flt | 474.734 | 476.571 | 1.0

Srinivas Vamsi Parasa has updated the pull request incrementally with one additional commit since the last revision:

  change reg to vlReg to fix KNL failure

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/18503/files
  - new: https://git.openjdk.org/jdk/pull/18503/files/b4a11ba8..8c34df80

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=18503&range=05
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=18503&range=04-05

  Stats: 5 lines in 2 files changed: 0 ins; 0 del; 5 mod
  Patch: https://git.openjdk.org/jdk/pull/18503.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/18503/head:pull/18503

PR: https://git.openjdk.org/jdk/pull/18503