Should we warn if we detect null derefernces or void value uses ?

[Walter Bright via Digitalmars-d]

On 12/7/2016 3:52 AM, Stefan Koch wrote:
> That is why I said unambiguously.

Ok.

> We will neither warn or error in the above case, because p could have been
> assigned to.
> Only if we directly read from something uninitialized will we error.

The dmd optimizer does global data flow analysis:

int fn(int y)
{
   int x = void;
   ++x;
   return x+y;
}

----

dmd -c test7 -O
test7.d(4): Error: variable x used before set

----

https://github.com/dlang/dmd/blob/master/src/backend/gother.c#L418

dmd's back end has done global data flow analysis since about 1985, even though 
popular opinion holds that clang invented it :-)