RFR: 8332163: C2 SuperWord: refactor PacksetGraph and SuperWord::output into VTransformGraph [v9]

[Emanuel Peter]

On Tue, 2 Jul 2024 14:43:43 GMT, Emanuel Peter <epeter at openjdk.org> wrote:

>> src/hotspot/share/opto/superword.cpp line 3143:
>> 
>>> 3141: 
>>> 3142:   if (p0->is_Load()) {
>>> 3143:     vtn = new (_graph.arena()) VTransformLoadVectorNode(_graph, pack_size);
>> 
>> You use `_graph.arena()` quite often. Maybe you want to create a new `_arena` field for easier access.
>
> I'll see if I can do this directly with the `new` operator...

I think having a `_arena` field in the `SuperWordVTransformBuilder` would be confusing and not a good idea. People might think that this is an arena that is used during the life-cycle of the builder. But this `_graph.arena()`, now `_vtransform.arena()` is used for the life-cycle of the `vtransform`, which outlives the builder. We could have a `_vtransform_arena` field, but this is not really better than `_vtransform.arena()` IMHO.

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PR Review Comment: https://git.openjdk.org/jdk/pull/19719#discussion_r1664203248