[16] RFR(S): 8248552: C2 crashes with SIGFPE due to division by zero

[Christian Hagedorn]

Thank you Vladimir for your review!

Best regards,
Christian

On 11.07.20 01:25, Vladimir Kozlov wrote:
> Looks good.
> 
> Thanks,
> Vladimir
> 
> On 7/10/20 12:37 AM, Christian Hagedorn wrote:
>> Hi
>>
>> Please review the following patch:
>> https://bugs.openjdk.java.net/browse/JDK-8248552
>> http://cr.openjdk.java.net/~chagedorn/8248552/webrev.00/
>>
>> In the failing testcase, C2 removes a zero check for a division/modulo 
>> node n based on the type information of the loop induction variable 
>> phi p (always between 1 and 50 and never 0). However, n is later split 
>> through p and ends up after the AddNode which updates the induction 
>> variable p. In the last iteration j equals 2 and is then updated to 0. 
>> The division/modulo node n is now executed before the loop limit check 
>> which results in a SIGFPE.
>>
>> The fix bails out of PhaseIdealLoop::split_thru_phi if a division or 
>> modulo node has its zero check removed (i.e. control in NULL) and is 
>> split through a phi which has an input that could be zero. This should 
>> only happen for an induction variable phi of a trip-counted (integer) 
>> loop.
>>
>> Best regards,
>> Christian