RFR: 8370220: C2: rename methods and improve documentation around get_ctrl and idom lazy updating/forwarding of ctrl and idom via dead ctrl nodes [v9]

[Roland Westrelin]

On Wed, 22 Oct 2025 07:56:12 GMT, Emanuel Peter <epeter at openjdk.org> wrote:

>> src/hotspot/share/gc/shenandoah/c2/shenandoahSupport.cpp line 1780:
>> 
>>> 1778:             fix_memory_uses(u, n, n, c);
>>> 1779:           } else if (_phase->C->get_alias_index(u->adr_type()) == _alias) {
>>> 1780:             _phase->igvn().replace_node(u, n);
>> 
>> As far as I can see, the `lazy_replace` only did `igvn.replace_node` for non-ctrl nodes anyway. Since we are dealing with `PhiNode`s here, we might as well only use `igvn.replace_node`.
>> 
>> I discovered this, because it hit my `!old_node->is_CFG()` check.
>
> @rwestrel Do you have an opinion on this?

That change looks good to me.

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PR Review Comment: https://git.openjdk.org/jdk/pull/27892#discussion_r2464914445