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]

[Emanuel Peter]

On Wed, 22 Oct 2025 06:46:21 GMT, Emanuel Peter <epeter at openjdk.org> wrote:

>> Emanuel Peter has updated the pull request incrementally with two additional commits since the last revision:
>> 
>>  - Merge branch 'JDK-8370220-get-ctrl-documentation' of https://github.com/eme64/jdk into JDK-8370220-get-ctrl-documentation
>>  - fix shenandoah replace for phis
>
> 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?

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PR Review Comment: https://git.openjdk.org/jdk/pull/27892#discussion_r2450776790