RFR: 8336830: C2: assert(get_loop(lca)->_nest < n_loop->_nest || lca->in(0)->is_NeverBranch()) failed: must not be moved into inner loop

[Roland Westrelin]

A store is sunk from a counted loop into an enclosing infinite
loop. The assert fires because:


get_loop(lca)->_nest < n_loop->_nest


is false. That happens because the outer loop was found to be infinite
in the current loop opts pass. When that happens, it's not properly
attached to the loop tree. The second part of the assert was added to
cover a similar case:


lca->in(0)->is_NeverBranch()


but it doesn't work in this case bcause lca is not a projection of the
`NeverBranch`. It's the exit projection of the counted loop. The fix I
propose changes that part of the assert to test that lca is, indeed,
in an infinite loop in a way that's robust.

I also removed some code that I believe to be useless following
8335709.

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Commit messages:
 - fix & test

Changes: https://git.openjdk.org/jdk/pull/20334/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=20334&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8336830
  Stats: 61 lines in 2 files changed: 57 ins; 2 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/20334.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/20334/head:pull/20334

PR: https://git.openjdk.org/jdk/pull/20334