RFR: 8357267: ZGC: Handle APX EGPRs spilling in ZRuntimeCallSpill

[Jatin Bhateja]

Patch spills APX EGPRs across runtime calls to slow-path barriers using PUSH2P/POP2 instructions with PPX hints.
These instructions operate over a pair of registers resulting into an smaller save/restoration JIT code, on the hind side they have hard alignment and balancing constraints, as they operate at 16-byte aligned stack address.
ZRuntimeCallSpill is agnostic to live register, thus resulting SPILL sequence should not modify the contents of the register.

Patch has been verified using Intel SDE all test under test/hotspot/jtreg/compiler/gcbarriers are green.

Kindly review and share your feedback.

Best Regards,
Jatin

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Commit messages:
 - 8357267: ZGC: Handle APX EGPRs spilling in ZRuntimeCallSpill

Changes: https://git.openjdk.org/jdk/pull/25351/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=25351&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8357267
  Stats: 63 lines in 1 file changed: 46 ins; 0 del; 17 mod
  Patch: https://git.openjdk.org/jdk/pull/25351.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/25351/head:pull/25351

PR: https://git.openjdk.org/jdk/pull/25351