RFR: 8303511: C2: assert(get_ctrl(n) == cle_out) during unrolling [v2]

[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.

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

  Update test/hotspot/jtreg/compiler/loopstripmining/TestAddPAtOuterLoopHead.java
  
  Co-authored-by: Andrey Turbanov <turbanoff at gmail.com>

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/12824/files
  - new: https://git.openjdk.org/jdk/pull/12824/files/c2787438..f20e29b6

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=12824&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=12824&range=00-01

  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 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