RFR: 8373613: PEXT/PDEP intrinsics cause performance regression on AMD pre-Zen 3 CPUs [v3]

[Alessandro Autiero]

> The `Integer/Long.compress()` and `Integer/Long.expand()` intrinsics (added in JDK 19 by JDK-8283893) unconditionally use BMI2 PEXT/PDEP instructions on all BMI2-capable x86 CPUs. However, AMD processors before Zen 3 (Family < 0x19) and Zhaoxin CPUs implement PEXT/PDEP via microcode with ~18-cycle  latency, making the intrinsified path 1.4-2.4x slower than the Java software fallback.
> 
> This patch introduces a `CPU_FAST_BMI2` feature flag that distinguishes CPUs with native hardware PEXT/PDEP support (Intel Haswell+, AMD Zen 3+) from those with slow microcoded implementations. The `Op_CompressBits`/`Op_ExpandBits` match rules in `x86.ad` are gated on this new flag instead of the general `supports_bmi2()`, so CPUs without fast hardware support fall back to the Java implementation. C2 IR tests are updated to use the new `fast_bmi2` CPU feature predicate.

Alessandro Autiero has updated the pull request incrementally with one additional commit since the last revision:

  added FAST_BMI2 CPU feature to CI for AMD64 arch

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/29809/files
  - new: https://git.openjdk.org/jdk/pull/29809/files/a077caab..64748dc1

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=29809&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=29809&range=01-02

  Stats: 3 lines in 1 file changed: 1 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/29809.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/29809/head:pull/29809

PR: https://git.openjdk.org/jdk/pull/29809