RFR: 8315066: Add unsigned bounds and known bits to TypeInt/Long [v12]

[Dean Long]

On Thu, 5 Sep 2024 15:37:45 GMT, Quan Anh Mai <qamai at openjdk.org> wrote:

>> src/hotspot/share/opto/type.hpp line 564:
>> 
>>> 562:   // Dual sets are only used to compute the join of 2 sets, and not used
>>> 563:   // outside.
>>> 564:   const bool _is_dual;
>> 
>> Do you have a clear definition of what a dual is somewhere?
>
> Tbh I'm not entirely sure what does "dual" serve other than: it is to compute the join of 2 sets. Looking at the code suggests that a `Type` is somehow a symmetric space with all normal types on one side and the "dual" types on the other. This really confuses me and I cannot figure out what exactly a dual type represents.

My understanding is "join" means "union", "meet" means "intersection", and "dual" means "complement".

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PR Review Comment: https://git.openjdk.org/jdk/pull/17508#discussion_r1746317661