RFR: 8325495: C2: implement optimization for series of Add of unique value [v2]

[Kangcheng Xu]

On Mon, 23 Sep 2024 11:37:38 GMT, Roland Westrelin <roland at openjdk.org> wrote:

>> I disagree: `integercon()` internally uses `checked_cast<jint>(l)` to make prevent information loss during type conversion and asserts at runtime if the value is larger what a `jint` can hold. However, such an information loss is intended for integer arithmetic overflows. (e.g., `Integer.MAX_VALUE * a + a` is extracted to `((jlong) Integer.MAX_VALUE + (jlong) 1) * a`. Here we want `Integer.MAX_VALUE + 1` to overflow to `(int) Integer.MIN_VALUE`).
>> 
>> If I were to use `integercon()`, the best I could do is `intgercon(bt == T_INT ? (jint) factor : factor)` which is rather pointless.
>
> Good catch.
> It makes sense to add a comment about that in the source code.
> Do you have a test case for that corner case?

Added comments.

> Do you have a test case for that corner case?

Yes: `TestSerialAdditions::mulAndAddToOverflow`

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PR Review Comment: https://git.openjdk.org/jdk/pull/20754#discussion_r1771808870