RFR: 8282590: C2: assert(addp->is_AddP() && addp->outcnt() > 0) failed: Don't process dead nodes

[Emanuel Peter]

Problem:
Sometimes nodes are generated, and then not properly added to any other node, nor added to the worklist, so that it could be deleted. In some cases, a node can thus survive after IGVN and enter into `ConnectionGraph::compute_escape`, where no dead nodes are expected (except constants).

In `ArrayCopyNode::prepare_array_copy`:
In one, I now add the new ConvI2LNode to the worklist if we are aborting.
In the other case, I could safely reorder the code, such new ConvI2LNode would only be generated once we know we are not going to abort.

In `SubTypeCheckNode::Ideal`:
Replaced `set_req` with `set_req_X`, such that the input-node that is replaced (which is now potentially a dead node) is put on the worklist.

Running running...

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Commit messages:
 - removing zombie catcher
 - Revert "another assert, probably want to fix it or remove it eventually"
 - Revert "adding another sanity check"
 - adding another sanity check
 - another assert, probably want to fix it or remove it eventually
 - fix another case where we may have left dead nodes behind
 - 8282590: C2: assert(addp->is_AddP() && addp->outcnt() > 0) failed: Don't process dead nodes

Changes: https://git.openjdk.java.net/jdk/pull/7728/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=7728&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8282590
  Stats: 20 lines in 2 files changed: 15 ins; 3 del; 2 mod
  Patch: https://git.openjdk.java.net/jdk/pull/7728.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/7728/head:pull/7728

PR: https://git.openjdk.java.net/jdk/pull/7728