RFR: 8356647: C2: Excessively strict assert in PhaseIdealLoop::do_unroll [v2]

[Marc Chevalier]

> This assert seems a bit too tight. See the JBS issue to check the math: the bound of `trip_count` should be `<= 2^31`, while the current bound is ` < (julong)max_juint/2` = floor((2^32-1)/2) = (2^32-2) / 2 = 2^31-1.

Marc Chevalier 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:

 - A test
 - Merge branch 'master' into fix/do_unroll-assert
 - Relax the assert

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/25295/files
  - new: https://git.openjdk.org/jdk/pull/25295/files/f4084179..9c44f068

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=25295&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=25295&range=00-01

  Stats: 60447 lines in 903 files changed: 35531 ins; 20408 del; 4508 mod
  Patch: https://git.openjdk.org/jdk/pull/25295.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/25295/head:pull/25295

PR: https://git.openjdk.org/jdk/pull/25295