RFR: JDK-8290822: C2: assert in PhaseIdealLoop::do_unroll() is subject to undefined behavior

[Tobias Holenstein]

On Thu, 16 Feb 2023 18:11:00 GMT, Vladimir Kozlov <kvn at openjdk.org> wrote:

>> The following assert had undefined behavior (UB) because of _signed_ integer underflow/overflow: 
>> 
>>     assert(stride_con > 0 && ((limit_type->_hi - stride_con) < limit_type->_hi) || 
>>            stride_con < 0 && ((limit_type->_lo - stride_con) > limit_type->_lo), 
>>            "sanity"); 
>> 
>> 
>> # Solution 
>> The fix is to check for underflow/overflow (the purpose of the assert) without actually underflowing/overflowing.
>
> Looks good.

thanks @vnkozlov and @TobiHartmann !

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PR: https://git.openjdk.org/jdk/pull/12576