RFR: 8356647: C2: Excessively strict assert in PhaseIdealLoop::do_unroll [v5]

[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 incrementally with two additional commits since the last revision:

 - +message in assert
 - Move asserts around

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/25295/files
  - new: https://git.openjdk.org/jdk/pull/25295/files/a5552ffd..fa4dd336

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=25295&range=04
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=25295&range=03-04

  Stats: 21 lines in 2 files changed: 5 ins; 14 del; 2 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