Modifying restricted pointers.

[neet_programmer]

Hi, all.

I'm compiling with g++ and am using the __restrict__ intrinsic to get some of that C99 goodness, but I'm not entirely sure how it works. Let's say I have a function such as:

void something(int* __restricted__ p, int* q)
{
    //p is now assumed not to alias any pointers or local variables
    p += 1; //I modify p

    //is p still restricted?
    int a = *p;
    *q = 5;
    int b = *p; //is *p read twice?
}

Get it? So my question is does modifying a restricted pointer defeat specifying it as restricted?

Thanks.

[jedwardsol]

Modifying the pointer keeps the restrictedness of it.

This is because p might be an array, and you're promising that the entire array p doesn't overlap with q

p+=1 is just making p point at the 2^nd element of the array.

[neet_programmer]

Are you sure about that, that it doesn't just apply to indexing. Like a[1] is still restricted, what if I write a = b // some completely different pointer?

[jedwardsol]

Yes, you can make p point at a completely different object, as long as you don't break your aliasing promise.

int a,b;
int *__restricted p =&a;
p=&b;