Hi Sandra,
the OMP_FOR documentation says that the loop index variable
must be signed and it does not list "!=" in the allowed conditional
expressions. But there is nothing that would automatically cast an 
unsigned variable
to signed or that converts the "!=" as you can see from the dump
for this program:

int main ()
{
#pragma omp for
for (unsigned i = 0; i != 10; i++) {}
}

The 005t.gimple dump is:

int __GIMPLE ()
{
   int D_2064;

   {
     {
       unsigned int i;

       #pragma omp for private(i)
       for (i = 0u; i != 10u; i = i + 1u)
     }
   }
   D_2064 = 0;
   return D_2064;
}

(Strictly speaking, the OMP_FOR is represented as a gomp_for at this point,
but this does not really matter.)

Can I commit the patch?

Best regards,
Frederik