[Carpet] potential integer overflow in Grid setup

[Thomas Radke]

Erik Schnetter wrote:
> Thanks.  With this command, and after a complete rebuild, this test  
> case passes when I run it manually.
> 
> I pushed some unrelated changes recently.  Maybe they were not really  
> unrelated.

Hmm, it doesn't pass for me yet. This is with a standard configuration 
compiled with DEBUG=yes and OPTIMISE=yes.

I have tried to isolate the problem and came to the conclusion that it 
must be compiler-related. This is the function in bbox.cc where the 
abort is triggered, added with a few debug output statements:

> template<class T, int D>
> void bbox<T,D>::assert_bbox_limits () const
> {
>   assert (all(_stride>T(0)));
>   assert (all((_upper-_lower)%_stride == T(0)));
>   if (numeric_limits<T>::is_integer) {
>     // prevent accidental wrap-around
>     if (any (_lower >= numeric_limits<T>::max() / 2) or
>         any (_lower <= numeric_limits<T>::min() / 2) or
>         any (_upper >= numeric_limits<T>::max() / 2) or
>         any (_upper <= numeric_limits<T>::min() / 2))
>     {
> std::cerr << "=== _lower: " << _lower << " _upper: " << _upper
>           << " min/2: " << (numeric_limits<T>::min() / 2)
>           << " max/2: " << (numeric_limits<T>::max() / 2)
>           << std::endl;
> std::cerr << "=== _lower >= max: "
>           << any (_lower >= numeric_limits<T>::max() / 2)
>           << " _lower <= min: "
>           << any (_lower <= numeric_limits<T>::min() / 2)
>           << std::endl
>           << "=== _upper >= max: "
>           << any (_upper >= numeric_limits<T>::max() / 2) 
>           << " _upper <= min: "
>           << any (_upper <= numeric_limits<T>::min() / 2) 
>           << std::endl;
>       CCTK_WARN (CCTK_WARN_ABORT, 
>                  "Tried to create a very large bbox -- it is likely that this would lead to an integer overflow");
>     }
>   }
> }

The runtime output looks like this:

> INFO (Carpet): Base grid specification for map 0:
>    number of grid points : [20,20,20]
>    number of ghost points: [[2,2,2],[2,2,2]]
> === _lower: [0,0,0] _upper: [38,38,38] min/2: -1073741824 max/2: 1073741823
> === _lower >= max: 0 _lower <= min: 1
> === _upper >= max: 0 _upper <= min: 1
> WARNING level 0 in thorn CarpetLib processor 0 host peg304.hpc.lsu.edu
>   (line 45 of /mnt/gpfs.work/tradke/cactus/configs/mpich-opt/build/CarpetLib/bbox.cc): 
>   -> Tried to create a very large bbox -- it is likely that this would lead to an integer overflow

Note that the comparisons against numeric_limits<int>::min()/2 are all 
true, hence the level 0 warning. When I emulate the inlined any() 
function and compare individual vector elements, everything works fine.

-- 
Cheers, Thomas.