Integrated: 8255670: Improve C2's detection of modified nodes

[Emanuel Peter]

On Sat, 9 Jul 2022 08:37:24 GMT, Emanuel Peter <epeter at openjdk.org> wrote:

> 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)
> 
> Other small refactorings (review suggestions):
> - Refactored a few cases of `igvn.worklist.push` and `set_req` with `set_req_X`.
> - Removed unecessary `igvn.worklist.push` before `replace_input_of`.
> - Refactored some code with `delete_precedence_of`, `add_input_to` and `replace_input_of`.
> 
> 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.

This pull request has now been integrated.

Changeset: 83abfa5d
Author:    Emanuel Peter <epeter at openjdk.org>
URL:       https://git.openjdk.org/jdk/commit/83abfa5d8231d5bfa383989159758cbe3530ee51
Stats:     78 lines in 11 files changed: 24 ins; 33 del; 21 mod

8255670: Improve C2's detection of modified nodes

Reviewed-by: kvn, thartmann, roland

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