RFR: 8349479: C2: when a Type node becomes dead, make CFG path that uses it unreachable [v2]

[Roland Westrelin]

On Fri, 28 Mar 2025 12:37:34 GMT, Roland Westrelin <roland at openjdk.org> wrote:

>> src/hotspot/share/opto/node.cpp line 3100:
>> 
>>> 3098:     loop->register_new_node(frame, igvn->C->start());
>>> 3099:   }
>>> 3100:   Node* halt = new HaltNode(c, frame, "dead path discovered by TypeNode");
>> 
>> The more info we can attach to the `HaltNode`, the better. It would make debugging easier if it is ever hit.
>
> Is there anything in particular you think makes sense adding?

Maybe what phase (igvn or ccp) found the dead path might be useful for diagnosis. Not sure what else would be.

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PR Review Comment: https://git.openjdk.org/jdk/pull/23468#discussion_r2018593940