RFR: 8350329: C2: Div looses dependency on condition that guarantees divisor not zero in counted loop after peeling [v2]

[Roland Westrelin]

> This is an issue similar to 8349139: the type of the iv phi of a
> counted loop is narrowed down so a `Div` node doesn't need a control
> input. The loop is then peeled. The `Div` in the loop body is
> guaranteed to be non zero only if it is actually executed so the `Div`
> is implicitly dependent on the zero trip guard. Then the loop looses
> its backedge and the `Div` freely floats. The `Div` instruction is
> scheduled above the zero trip guard and faults. Had the `Div` been
> control dependent on the zero trip guard, it wouldn't have
> executed. The fix, similar to 8349139 is to add a `CastII` on peeling
> to make the dependency between what's in the loop body and relies on
> the narrowed down type of the iv phi and the zero trip guard explicit.

Roland Westrelin has updated the pull request incrementally with one additional commit since the last revision:

  review

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/25262/files
  - new: https://git.openjdk.org/jdk/pull/25262/files/eb3a13b3..f5069b5e

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=25262&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=25262&range=00-01

  Stats: 4 lines in 1 file changed: 2 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/25262.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/25262/head:pull/25262

PR: https://git.openjdk.org/jdk/pull/25262