RFR: 8347901: C2 should remove unused leaf / pure runtime calls [v3]

[Marc Chevalier]

On Wed, 2 Jul 2025 14:35:26 GMT, Benoît Maillard <bmaillard at openjdk.org> wrote:

>> Marc Chevalier has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   mostly comments
>
> src/hotspot/share/opto/parse2.cpp line 1100:
> 
>> 1098: Node* Parse::floating_point_mod(Node* a, Node* b, BasicType type) {
>> 1099:   assert(type == BasicType::T_FLOAT || type == BasicType::T_DOUBLE, "only float and double are floating points");
>> 1100:   CallLeafPureNode* mod = type == BasicType::T_DOUBLE ? static_cast<CallLeafPureNode*>(new ModDNode(C, a, b)) : new ModFNode(C, a, b);
> 
> May I ask why we only need the `static_cast` for the `ModDNode` here?

It's C/C++ being annoying here: both branches of the ternary must have the same type, or something compatible. If I remove the cast:

error: conditional expression between distinct pointer types 'ModDNode*' and 'ModFNode*' lacks a cast

With the case, C++ can converrt the `ModFNode*` into a `CallLeafPureNode*` just fine.

I didn't invent the cast, it was here before, but good to question it.

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PR Review Comment: https://git.openjdk.org/jdk/pull/25760#discussion_r2182166387