DIP 1006 - Preliminary Review Round 1

[Iain Buclaw]

On Monday, 5 March 2018 at 15:48:12 UTC, Timon Gehr wrote:
>
> - Using existing assertions as compiler hints is not necessary. 
> (Without having checked it, I'm sure that LDC/GDC have a more 
> suitable intrinsic for this already.)
>
> As far as I can discern, forcing disabled asserts to give 
> compiler hints has no upsides.
>


In the simple cases, or in anything that looks like a 
unittest/testsuite, probably not.

There are likely going to be more aggressive optimizations 
however if CFA can see that a variable will never be outside a 
given range, i.e:

---
int[5] arr;

if (len < 0 || len >= 5)
{
     unreachable();  // in non-release code, this would throw a 
RangeError.
}

return arr[len];
---

 From this, we aggressively assume that len is a valid index of 
arr.  Something that happens in optimized non-release builds, but 
in release builds we must accommodate for the possibility of a 
range error.