RFR: 8315920: C2: "control input must dominate current control" assert failure

[Roland Westrelin]

The assert fires during range check eliminationin code that was added
recently. It catches a bug that's been going unnoticed. The `array[0]`
load of the test case ends up on the exit of the loop above it. After
pre/main/post loops are created for this loop (the inner loop is
optimized out), the load is at a region merging control from the just
created pre/main/post loops but its control (as returned by
`PhaseIdealLoop::get_ctrl()`) is not updated by pre/main/post loops
creation code so it's still the exit projection of one of the
loops. This causes the assert to fire (the load has bad control) when
RC runs next in the same loop opts pass.

The current logic for pre/main/post loops creation does update the
control of nodes on an exit projection but only if the node is
referenced from some other node in the loop body.

I think a similar bug with a node assigned control at the exit but not
pinned is likely to exist. So I doubt simply going over nodes pinned
at exits during pre/main/post and updating their control is good
enough. What I propose instead is to `lazy_replace()` the projection
by the region so that, for all nodes that are assigned the exit as
control, `get_ctrl()` will then return the region. It's not entirely
straightforward to implement because the `lazy_replace()` mechanism
assumes the control being replaced is dead which is not the case
here. That's why in the patch the exit projection is cloned so the
existing one is dead and can be used in `lazy_replace()`. This also
makes the calls to `sink_use()` redundant.

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Commit messages:
 - fix & test

Changes: https://git.openjdk.org/jdk/pull/15720/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=15720&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8315920
  Stats: 90 lines in 4 files changed: 69 ins; 17 del; 4 mod
  Patch: https://git.openjdk.org/jdk/pull/15720.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/15720/head:pull/15720

PR: https://git.openjdk.org/jdk/pull/15720