[jdk21u] RFR: 8316396: Endless loop in C2 compilation triggered by AddNode::IdealIL

[Aleksey Shipilev]

Clean backport to fix potential C2 problem. "Potential", because neither of fuzzer tests from the issue, nor the new regression test actually triggers the issue. I suppose that is because some other C2 optimization/bugfix is missing. However, it seems profitable to protect from this issue in 21u as well. @TobiHartmann, do you agree?

Additional testing:
 - [x] macos-aarch64-server-fastdebug, new regression test passes before and after the patch
 - [ ] linux-aarch64-server-fastdebug, `tier1 tier2 tier3`

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Commit messages:
 - Backport b0d6c8472f69fef0265b41a4caf9e564adf68f6e

Changes: https://git.openjdk.org/jdk21u/pull/259/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk21u&pr=259&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8316396
  Stats: 70 lines in 2 files changed: 68 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jdk21u/pull/259.diff
  Fetch: git fetch https://git.openjdk.org/jdk21u.git pull/259/head:pull/259

PR: https://git.openjdk.org/jdk21u/pull/259