RFR: 8324833: Signed integer overflows in ABS [v5]

[Dean Long]

On Thu, 22 Feb 2024 08:53:24 GMT, Aleksey Shipilev <shade at openjdk.org> wrote:

>> See the details in the bug. I think current `ABS` implementation is beyond repair, and we should just switch to `uabs`.
>> 
>> Additional testing:
>>  - [x] Linux x86_64 fastdebug, `all` with `-ftrapv` (now fully passes!)
>>  - [x] Linux x86_64 fastdebug, `all`
>
> Aleksey Shipilev has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Fix a place where we cast to jlong after uabs

src/hotspot/share/opto/loopnode.cpp line 805:

> 803:   // overflow: max_jint - stride_con max. -1 so there's no need for a
> 804:   // loop limit check if the exit test is <= or >=.
> 805:   int iters_limit = max_jint - uabs(stride_con) - 1;

It appears iters_limit can become -1 or -2 here, depending on the value of stride_con.  See below for the problem.

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PR Review Comment: https://git.openjdk.org/jdk/pull/17617#discussion_r1500178001