Re: [BUGS] BUG #14722: Segfault in tuplesort_heap_siftup, 32 bitoverflow

On 07/06/2017 01:14 AM, Andres Freund wrote:
> On 2017-07-05 18:03:56 -0400, Tom Lane wrote:
>> I don't like s/int/int64/g as a fix for this.  That loop is probably
>> a hot spot, and this fix is going to be expensive on any machine where
>> int64 isn't the native word width.  How about something like this instead:
>>
>> -        int            j = 2 * i + 1;
>> +        int            j;
>>
>> +        if (unlikely(i > INT_MAX / 2))
>> +            break;        /* if j would overflow, we're done */
>> +        j = 2 * i + 1;
>>         if (j >= n)
>>             break;
>
> Isn't an added conditional likely going to be more costly than the
> s/32/64/ bit calculations on the majority of machines pg runs on? I'm
> quite doubtful that it's worth catering for the few cases where that's
> really slow.

Another option to use "unsigned int", on the assumption that UINT_MAX >= 
INT_MAX * 2 + 1. And to eliminate that assumption, we can use (UINT_MAX 
- 1) / 2 as the maximum size of the memtuples array, rather than INT_MAX.

- Heikki



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