bounds checking and optimization

[Bruce Carneal]

On Tuesday, 29 June 2021 at 11:20:19 UTC, Johan wrote:
> On Sunday, 27 June 2021 at 17:49:22 UTC, Bruce Carneal wrote:
>> [snip]
> [snip]
>
> This means that we can solve it by reordering/optimizing our 
> optimization pipeline in LDC. It is non-trivial work and I 
> would suggest not to undertake it before we have switched to 
> LLVM's new PassManager (because I think that also tweaks the 
> order of optimization passes)
>
> -Johan

Thanks for the update Johan.  I'll keep working with the "manual" 
version, @trusted and .ptr, and watch for any updates.  You guys 
seem pretty busy already so I hope it fits in with your other 
work.

A related question: is there anything preventing the compiler 
from lifting range checks out of loops and throwing early?  For 
example, on something like:

     foreach(i, ref dst; c[])
         dst = a[i] + b[i];

could c.length be extracted and asserted as being leq a.length 
and b.length before we drop in to the loop?

Finally, it seems like bounds checking optimizations of this sort 
belong in the front end or am I mistaken?