RFR: 8364970: Redo JDK-8327381 by updating the CmpU type instead of the Bool type [v2]

[Kangcheng Xu]

On Wed, 13 Aug 2025 12:22:00 GMT, Francisco Ferrari Bihurriet <fferrari at openjdk.org> wrote:

>> Update looks good, thanks! I'll run some testing and report back again.
>> 
>>> Could you already find some examples, where this change gives us an improved IR? If so, you could also add it as IR test.
>> 
>> Just double-checking, were you able to find such a test which now improves the IR with the better type info and `CmpU` while we could not with the old code? Otherwise, you could also file a follow-up RFE.
>
> @chhagedorn
>> > Could you already find some examples, where this change gives us an improved IR? If so, you could also add it as IR test.
>>
>> Just double-checking, were you able to find such a test which now improves the IR with the better type info and `CmpU` while we could not with the old code? Otherwise, you could also file a follow-up RFE.
> 
> Sorry for not replying that, I'm working on it.
> 
> We were explicitly matching the `BoolNode` tests, so let's explore the tests we were previously discarding.
> 
> For **case 1a**, we were explicitly matching `BoolTest::le`, but now `CmpUNode` has `TypeInt::CC_LE` reflecting the fact that `m & x ≤u m` is always true, so:
> 
> |        Test        | Symbolic representation |  Result  |        Improved IR        |
> |:------------------:|:-----------------------:|:--------:|:-------------------------:|
> |   `BoolTest::eq`   |      `m & x =u m`       | unknown  |            no             |
> |   `BoolTest::ne`   |      `m & x ≠u m`       | unknown  |            no             |
> | **`BoolTest::le`** |    **`m & x ≤u m`**     | **true** | **no (old optimization)** |
> |   `BoolTest::ge`   |      `m & x ≥u m`       | unknown  |            no             |
> |   `BoolTest::lt`   |      `m & x <u m`       | unknown  |            no             |
> |   `BoolTest::gt`   |      `m & x >u m`       |  false   |            yes            |
> 
> For **case 1b**, we were explicitly matching `BoolTest::lt`, but now `CmpUNode` has `TypeInt::CC_LT` reflecting the fact that `m & x <u m + 1` is always true (if `m ≠ -1`), so:
> 
> |        Test        | Symbolic representation | Result if `m ≠ -1` |        Improved IR        |
> |:------------------:|:-----------------------:|:------------------:|:-------------------------:|
> |   `BoolTest::eq`   |    `m & x =u m + 1`     |       false        |            yes            |
> |   `BoolTest::ne`   |    `m & x ≠u m + 1`     |        true        |            yes            |
> |   `BoolTest::le`   |    `m & x ≤u m + 1`     |        true        |            yes            |
> |   `BoolTest::ge`   |    `m & x ≥u m + 1`     |       false        |            yes            |
> | **`BoolTest::lt`** |  **`m & x <u m + 1`**   |      **true**      | **no (old optimization)** |
> |   `BoolTest::gt`   |    `m & x >u m + 1`     |       false        |            yes            |
> 
> I will work on adding IR tests for these cases.
> 
> Regarding real-world use cases, we need to rule out `BoolTest::lt`, as it didn't improve for _case 1a_ and was alread...

Thank you @franferrax for catching and addressing the inconsistent state. I neglected that in my original PR. I think it would be beneficial to include [your tables](https://github.com/openjdk/jdk/pull/26666#issuecomment-3183659818) of the two cases in the comments too. Thank you for the hard work.

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PR Comment: https://git.openjdk.org/jdk/pull/26666#issuecomment-3185308088