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

[Francisco Ferrari Bihurriet]

On Wed, 13 Aug 2025 07:05:51 GMT, Christian Hagedorn <chagedorn at openjdk.org> wrote:

>> Francisco Ferrari Bihurriet has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   Apply code review suggestions and add JBS to test
>
> 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 already optimized in old code for _case 1b_.

I've found some possible candidates but haven't fully analyzed them yet:

* [Array construction of `new byte[FastAllocateSizeLimit & x]`](https://github.com/openjdk/jdk/blob/jdk-26+9/src/hotspot/share/opto/graphKit.cpp#L3820-L3821) with _case 1a_
* [Switch jump tables](https://github.com/openjdk/jdk/blob/jdk-26+9/src/hotspot/share/opto/parse2.cpp#L829-L830) with _case 1b_
* 8 more code searches ([A](https://github.com/openjdk/jdk/blob/jdk-26+9/src/hotspot/share/opto/graphKit.cpp#L3939-L3940), [B](https://github.com/openjdk/jdk/blob/jdk-26+9/src/hotspot/share/opto/library_call.cpp#L3449-L3450), [C](https://github.com/openjdk/jdk/blob/jdk-26+9/src/hotspot/share/opto/library_call.cpp#L3869-L3870), [D](https://github.com/openjdk/jdk/blob/jdk-26+9/src/hotspot/share/opto/parse2.cpp#L736-L737), [E](https://github.com/openjdk/jdk/blob/jdk-26+9/src/hotspot/share/opto/parse2.cpp#L829-L830), [F](https://github.com/openjdk/jdk/blob/jdk-26+9/src/hotspot/share/opto/subnode.cpp#L1650-L1651), [G](https://github.com/openjdk/jdk/blob/jdk-26+9/src/hotspot/share/opto/subnode.cpp#L1677-L1678), [H](https://github.com/openjdk/jdk/blob/jdk-26+9/src/hotspot/share/opto/subnode.cpp#L1680-L1681))
* 3 more possible indirect matches ([I](https://github.com/openjdk/jdk/blob/jdk-26+9/src/hotspot/share/opto/loopopts.cpp#L2944-L2947), [J](https://github.com/openjdk/jdk/blob/jdk-26+9/src/hotspot/share/opto/subnode.cpp#L1596-L1597), [K](https://github.com/openjdk/jdk/blob/jdk-26+9/src/hotspot/share/opto/subnode.cpp#L1601-L1602))

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PR Comment: https://git.openjdk.org/jdk/pull/26666#issuecomment-3183659818