checkedint call removal

[Andrei Alexandrescu via Digitalmars-d]

On 7/30/14, 12:54 AM, David Bregman wrote:
> On Wednesday, 30 July 2014 at 03:32:50 UTC, Walter Bright wrote:
>> I don't either. I still have no idea what the difference between
>> assume(i<6) and assert(i<6) is supposed to be.
>
> assert:
> is a runtime check of the condition.
> is a debugging/correctness checking feature.
> is used when the expression is believed true, but is not proven so.
> (if it was proven, then there is no purpose in asserting it with a
> redundant runtime check that is guaranteed to never activate.)
>
> assume:
> passes a hint to the optimizer to allow better code generation.
> is used when the expression is proven to be true (by the programmer,
> like @trusted).

Thanks for the summary! It seems to me indeed there's little assume does 
that can't be done with assert today.

> The only relation between the two is that if a runtime check for (x) is
> inserted at some point, it is safe to insert an assume(x) statement
> afterwards, because x is known true at that point.

So then one might redefine assert to always insert an assume right 
afterwards.

> If assert degenerates to assume in release mode, any bugs in the program
> could potentially cause a lot more brittleness and unexpected/undefined
> behavior than they otherwise would have. In particular, code generation
> based on invalid assumptions could be memory unsafe.

I think gcc does that.

Also, it's unclear to me what the optimizer would be supposed to do if 
an assumption turns out to be false.


Andrei