RFR: 8315066: Add unsigned bounds and known bits to TypeInt/Long [v9]

[Quan Anh Mai]

On Wed, 4 Sep 2024 09:40:10 GMT, Emanuel Peter <epeter at openjdk.org> wrote:

>> I think you could generally add `static_asserts` everywhere you use `U` or `S` types.
>
> Yes, I definately need some explanation about what `present`, `progress`, `data` mean in these classes. It is not directly clear from the use-site to me, and I don't want to reverse-engineer to much as a reader ;)

Done that, hope it is more clear now.

>> `one_violation`: bit that could be one, but is zero
>> `zero_violation`: bit that could be zero, but is one
>> Hmm. Do we assume that `KnownBits` is "sane", i.e. that we never have `zeros[i] = 0 = ones[i]`?
>> Because then we are basically asserting that `ones = ~zeros = 0`, right? And so the bits only allow a single bit pattern.
>> 
>> I'm probably just very confused and need some more comments here.
>
> I won't read more down before I understand this first part.

Yes it seems you have misunderstood `zeros` and `ones`. This suggests me grouping them into `KnownBits` and I have added explanation regarding their semantics. In short, for each position such that the corresponding bit in `zeros` is set, the corresponding bit in the value must be unset, similar with `ones`. As a result, a sane bit constraints would require `(zeros & ones) == 0`

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PR Review Comment: https://git.openjdk.org/jdk/pull/17508#discussion_r1744293432
PR Review Comment: https://git.openjdk.org/jdk/pull/17508#discussion_r1744295301