[jdk21u-dev] RFR: 8323154: C2: assert(cmp != nullptr && cmp->Opcode() == Op_Cmp(bt)) failed: no exit test

[Aleksey Shipilev]

Clean backport to fix another C2 corner case; introduced by https://bugs.openjdk.org/browse/JDK-8316719, which is in 21.0.2.

Additional testing:
 - [x] New test fails without the fix, passes with it
 - [ ] Linux x86_64 fastdebug `tier{1,2,3,4}`

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

Commit messages:
 - Backport 6997bfc68def7f80fbf6a7486a4b9f61225fc471

Changes: https://git.openjdk.org/jdk21u-dev/pull/201/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk21u-dev&pr=201&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8323154
  Stats: 50 lines in 2 files changed: 49 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk21u-dev/pull/201.diff
  Fetch: git fetch https://git.openjdk.org/jdk21u-dev.git pull/201/head:pull/201

PR: https://git.openjdk.org/jdk21u-dev/pull/201