RFR: 8287425: Remove unnecessary register push for MacroAssembler::check_klass_subtype_slow_path

[Xiaolin Zheng]

Hi team,

![AE98A8E7-9F6F-4722-B310-299A9A96A957](https://user-images.githubusercontent.com/38156692/170670906-2ce37a13-af21-4cf8-acbd-ca24528bc3a9.png)

Some perf results show necessary pushes in `MacroAssembler::check_klass_subtype_slow_path()` under `UseCompressedOops`. History logs show the original code is like [1], and it gets refactored in [JDK-6813212](https://bugs.openjdk.java.net/browse/JDK-6813212), and the counterparts of the `UseCompressedOops` in the diff are at [2] and [3], and we could see the push of rax is just because `encode_heap_oop_not_null()` would kill it, so here needs a push and restore. After that, [JDK-6964458](https://bugs.openjdk.java.net/browse/JDK-6964458) (removal of perm gen) at [4] removed [3] so that there is no need to do UseCompressedOops work in `MacroAssembler::check_klass_subtype_slow_path()`; but in that patch [2] didn't get removed, so we finally come here. As a result, [2] could also be safely removed.

I was wondering if this minor change could be sponsored?

This enhancement is raised on behalf of Wei Kuai <kuaiwei.kw at alibaba-inc.com>.

Tested x86_64 hotspot tier1~tier4 twice, aarch64 hotspot tier1~tier4 once with another jdk tier1 once, and riscv64 hotspot tier1~tier4 once.

Thanks,
Xiaolin

[1] https://github.com/openjdk/jdk/blob/de67e5294982ce197f2abd051cbb1c8aa6c29499/hotspot/src/cpu/x86/vm/interp_masm_x86_64.cpp#L273-L284
[2] https://github.com/openjdk/jdk/commit/b8dbe8d8f650124b61a4ce8b70286b5b444a3316#diff-beb6684583b0a552a99bbe4b5a21828489a6d689b32a05e1a9af8c3be9f463c3R7441-R7444
[3] https://github.com/openjdk/jdk/commit/b8dbe8d8f650124b61a4ce8b70286b5b444a3316#diff-beb6684583b0a552a99bbe4b5a21828489a6d689b32a05e1a9af8c3be9f463c3R7466-R7477
[4] https://github.com/openjdk/jdk/commit/5c58d27aac7b291b879a7a3ff6f39fca25619103#diff-beb6684583b0a552a99bbe4b5a21828489a6d689b32a05e1a9af8c3be9f463c3L9347-L9361

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Commit messages:
 - Enhancement

Changes: https://git.openjdk.java.net/jdk/pull/8915/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=8915&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8287425
  Stats: 3 lines in 3 files changed: 0 ins; 0 del; 3 mod
  Patch: https://git.openjdk.java.net/jdk/pull/8915.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/8915/head:pull/8915

PR: https://git.openjdk.java.net/jdk/pull/8915