RFR: 8332163: C2 SuperWord: refactor PacksetGraph and SuperWord::output into VTransformGraph [v11]

[Emanuel Peter]

On Thu, 4 Jul 2024 10:09:05 GMT, Emanuel Peter <epeter at openjdk.org> wrote:

>> src/hotspot/share/opto/vtransform.hpp line 266:
>> 
>>> 264:     _req(req),
>>> 265:     _in(vtransform.arena(),  req, req, nullptr),
>>> 266:     _out(vtransform.arena(), 4, 0, nullptr)
>> 
>> Just noticed this here and totally unrelated, but there are a lot of places where we create a `GrowableArray` without a filler. So, we just pass `nullptr` or 0 (latter should probably be replaced by `nullptr`). Maybe `GrowableArray` should provide a constructor without a filler. Might be worth to do in an RFE at some point.
>
> Feel free to take this up with the Runtime team ;)

There are advantages and disadvantages to having an explicit `filler`. Because the way `GrowableArray` is implemented there needs to be a `fillter`. I guess one could have a `default` filler - but then that would only work for some pre-defined types I think... complicated.

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PR Review Comment: https://git.openjdk.org/jdk/pull/19719#discussion_r1665481673