RFR: 8349563: Improve AbsNode::Value() for integer types [v4]

[Quan Anh Mai]

On Thu, 3 Jul 2025 03:27:32 GMT, Jasmine Karthikeyan <jkarthikeyan at openjdk.org> wrote:

>> Hi all,
>> This is a small patch that improves the implementation of Value() for `AbsINode` and `AbsLNode` by returning the absolute value of the input range. Most of the logic is trivial except for the special case where `_lo == jint_min/jlong_min` which must return the entire type range when encountered, for which I've added a small proof in the comments. I've also added some unit tests and updated the file to limit IR check platforms with more granularity.
>> 
>> Thoughts and reviews would be appreciated!
>
> Jasmine Karthikeyan has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains six commits:
> 
>  - Code review and constant folding test
>  - Merge
>  - Replace uabs usage with ABS
>  - Merge branch 'master' into abs-value
>  - Merge
>  - Improve AbsNode::Value

With unsigned bounds, you can simply do:

    juint umin = MIN2<juint>(uabs(t->_ulo), uabs(t->_uhi));
    juint umax = MAX2<juint>(uabs(t->_lo), uabs(t->_hi));
    return TypeInt::make_unsigned(umin, umax, t->_widen);

The proof can be inferred trivially from the property of `TypeInt` (you can find this in the doc of `TypeInt`). Since the set of values of a `TypeInt` looks like this:

    smin ---------- lo ===== uhi ------ 0 -----ulo ========= hi --------- smax

or (in this case `lo == ulo`, `hi == uhi`)

    smin ----------- lo ======= hi --- 0 ------------------------------------- smax

or (in this case `lo == ulo`, `hi == uhi`)

    smin --------------------------------- 0 ------- lo ========= hi -------- smax

You can see that in all 3 cases, the minimum of the uabs of a value is either `uabs(ulo)` or `uabs(uhi)` and the maximum is either `uabs(lo)` or `uabs(hi)`.

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PR Comment: https://git.openjdk.org/jdk/pull/23685#issuecomment-3162975167