Re: BUG #14722: Segfault in tuplesort_heap_siftup, 32 bit overflow

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