RFR: 8255670: Improve C2's detection of modified nodes [v2]

[Emanuel Peter]

> Added `record_modified_node` to:
> 
> Node::clone
> Node::add_req
> Node::add_req_batch
> Node::ins_req
> Node::add_prec
> Node::rm_prec
> Node::set_prec
> 
> 
> Added `igvn->_worklist.push(node)` in various places that modified a `node` but did not add it to the igvn worklist.
> 
> 7 times I had to push `Root`, 5 of these it was because of the creation of a `HaltNode`, which means we have a `root->add_req(halt)`. 
> 
> In one case we have a MergeMemStream node, which gets two MergeMem nodes as input, and streams over them.
> Unfortunately, it modifies one of the two, which then can trigger our assertion code. I now push this node to the igvn worklist, but a better fix would be to make MergeMemStream leave the MergeMem nodes unmodified. I think that should be possible, filed an RFE [JDK-8293358](https://bugs.openjdk.org/browse/JDK-8293358)
> 
> FYI:
> What I am NOT doing here, and leave to a future RFE/independent change: investigate / implement these assertions for late/incremental inlining [JDK-8293362](https://bugs.openjdk.org/browse/JDK-8293362).
> 
> Ran larger regression tests, and 7-9h of fuzzing on 3 platforms.

Emanuel Peter has updated the pull request incrementally with three additional commits since the last revision:

 - cleanup of refactoring, one more small case refactored
 - expand refactoring a bit
 - refactoring: where I already had to add igvn.worklist.push

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/9439/files
  - new: https://git.openjdk.org/jdk/pull/9439/files/94132ae1..84091bd8

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=9439&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=9439&range=00-01

  Stats: 73 lines in 9 files changed: 14 ins; 40 del; 19 mod
  Patch: https://git.openjdk.org/jdk/pull/9439.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/9439/head:pull/9439

PR: https://git.openjdk.org/jdk/pull/9439