RFR: 8361699: C2: assert(can_reduce_phi(n->as_Phi())) failed: Sanity: previous reducible Phi is no longer reducible before SUT [v4]

[Cesar Soares Lucas]

> Please, review this patch to fix issue that may occur when reducing allocation merge.
> 
> As the assert message describe, the problem is a `Phi` considered reducible during one invocation of  `adjust_scalar_replaceable_state` turned out to be later non-reducible. This situation can happen if a subsequent invocation of the same method causes all inputs to the phi to be NSR; therefore there is no point in reducing the Phi. It can also happen during the propagation of NSR state done by `find_scalar_replaceable_allocs`. 
> 
> The change in `revisit_reducible_phi_status` is just a clean-up.
> The real fix is in `find_scalar_replaceable_allocs`.
> 
> Tested on Linux x64/Aarch64 release/fastdebug with JTREG tier1-3.

Cesar Soares Lucas has updated the pull request incrementally with two additional commits since the last revision:

 - Merge remote-tracking branch 'refs/remotes/origin/ram-non-reducible' into ram-non-reducible
 - Merge consecutive ifs

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/27063/files
  - new: https://git.openjdk.org/jdk/pull/27063/files/28d9432e..2236348b

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=27063&range=03
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=27063&range=02-03

  Stats: 7 lines in 1 file changed: 0 ins; 2 del; 5 mod
  Patch: https://git.openjdk.org/jdk/pull/27063.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/27063/head:pull/27063

PR: https://git.openjdk.org/jdk/pull/27063