Disallow null references in safe code?

[deadalnix]

On Sunday, 2 February 2014 at 07:54:26 UTC, Jonathan M Davis 
wrote:
> On Saturday, February 01, 2014 19:44:44 Andrei Alexandrescu 
> wrote:
>> On 2/1/14, 7:35 PM, deadalnix wrote:
>> > http://blog.llvm.org/2011/05/what-every-c-programmer-should-know_14.html
>> 
>> Whoa, thanks. So the compiler figures null pointer dereference 
>> in C is
>> undefined behavior, which means the entire program could do 
>> whatever if
>> that does happen.
>
> I think that article clearly illustrates that some of Walter's 
> decisions in D
> with regards to fully defining some stuff that C didn't define 
> were indeed
> correct. Undefined behavior is your enemy, and clearly, it gets 
> even worse
> when the optimizer gets involved. *shudder*
>
> - Jonathan M Davis

What you don't seem to understand is the associated cost.

Defining integer overflow to wrap around is easy and do not cost 
much. But in our case, it imply that the optimizer won't be able 
to optimize away load that it can't prove won't trap. That mean 
the compiler won"t be able to optimize most load.