dip1000 + pure is a DEADLY COMBO

[Per Nordlöw]

On Friday, 14 May 2021 at 09:02:35 UTC, Per Nordlöw wrote:
> I fail to see the general issue here.

Nevermind this comment. I see the problem now, thanks. I was 
given the code example

```d
int bad_global = 1;

@safe pure void purefunc(int* x)
{
     *x = 2;
}

void main()
{
     assert(bad_global == 1);
     purefunc(&bad_global);
     assert(bad_global == 2);
}
```

that incorrectly succeeds to compile [1].

[1] 
https://run.dlang.io/?compiler=dmd&source=int%20bad_global%20%3D%201;%0Apure%20void%20purefunc(int*%20x)%0A%7B%0A%20%20%20%20*x%20%3D%202;%0A%7D%0Avoid%20main()%0A%7B%0A%20%20%20%20assert(bad_global%20%3D%3D%201);%0A%20%20%20%20purefunc(%26bad_global);%0A%20%20%20%20assert(bad_global%20%3D%3D%202);%0A%7D