RFR: 8361211: C2: Final graph reshaping generates unencodeable klass constants [v2]

[Aleksey Shipilev]

> See the bug for more investigation. I have tried to come up with an isolated test, but failed. So I am doing this change somewhat blindly, without a clear regression test. The investigation on the CTW points directly to this code, and I believe we should be more conservative in final graph reshaping. [JDK-8343206](https://bugs.openjdk.org/browse/JDK-8343206) added the assert for `ConNKlass`, which somehow does not trigger. I think it is safe to bail out of this transformation.
> 
> Also, this only plugs this particular leak. I think we should really be disabling the abstract/interface encoding optimization until C2 does not expose itself to this issue on more paths. There is [JDK-8343218](https://bugs.openjdk.org/browse/JDK-8343218) that we can re-open.
> 
> Additional testing:
>  - [x] Linux x86_64 server fastdebug, a rare CTW failure does not reproduce anymore
>  - [x] Linux x86_64 server fastdebug, `tier1`
>  - [x] Linux x86_64 server fastdebug, `all`
>  - [x] Linux AArch64 server fastdebug, `all`

Aleksey Shipilev has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains three additional commits since the last revision:

 - Assert and bailout for ConP -> EncodeP path
 - Merge branch 'master' into JDK-8361211-c2-encodeable
 - Fix

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/26559/files
  - new: https://git.openjdk.org/jdk/pull/26559/files/a309eb59..d5dd4d8d

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=26559&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=26559&range=00-01

  Stats: 13253 lines in 302 files changed: 9051 ins; 3517 del; 685 mod
  Patch: https://git.openjdk.org/jdk/pull/26559.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/26559/head:pull/26559

PR: https://git.openjdk.org/jdk/pull/26559