RFR: 8303511: C2: assert(get_ctrl(n) == cle_out) during unrolling

[Roland Westrelin]

In the same round of loop optimizations:

- `PhaseIdealLoop::remix_address_expressions()` creates a new `AddP`
  out of loop. It sets it control to
  `n_loop->_head->in(LoopNode::EntryControl)` which, because the loop is
  strip mined, is an `OuterStripMinedLoop`.
  
- The `LoadI` for that `AddP` is found to only have uses outside the
  loop and is cloned out of the loop. It's referenced by the outer
  loop's safepoint.
  
- The loop is unrolled. Unrolling follows the safepoint's inputs and
  find the new `AddP` with control set to the `OuterStripMinedLoop`
  and the assert fires.
  
No control should be set to an `OuterStripMinedLoop`. The fix is
straightforward and sets the control to the `OuterStripMinedLoop`
entry control.

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

Commit messages:
 - test
 - fix

Changes: https://git.openjdk.org/jdk/pull/12824/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=12824&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8303511
  Stats: 84 lines in 2 files changed: 82 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/12824.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/12824/head:pull/12824

PR: https://git.openjdk.org/jdk/pull/12824