[jdk21u-dev] RFR: 8323101: C2: assert(n->in(0) == nullptr) failed: divisions with zero check should already have bailed out earlier in split-if

[Aleksey Shipilev]

Clean backport to fix a C2 corner case.

Additional testing:
 - [x] MacOS AArch64 server fastdebug: new tests fail without the patch, pass with the patch
 - [ ] Linux AArch64 server fastdebug, `tier{1,2,3,4}`

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Commit messages:
 - Backport 7e0a4ed6292586772c23292dbdd67ed1db5c12f7

Changes: https://git.openjdk.org/jdk21u-dev/pull/179/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk21u-dev&pr=179&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8323101
  Stats: 215 lines in 2 files changed: 214 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk21u-dev/pull/179.diff
  Fetch: git fetch https://git.openjdk.org/jdk21u-dev.git pull/179/head:pull/179

PR: https://git.openjdk.org/jdk21u-dev/pull/179