dmd optimizer now converted to D!

[Seb]

On Thursday, 5 July 2018 at 12:50:18 UTC, Ivan Kazmenko wrote:
> With D, I used mixins, and they were cumbersome.  Now that we 
> have static foreach, it's just this:
>
>     for (int i = 0; i < 4 * n; i += 4)
>         static foreach (k; 0..4)
>             a[i + k] += i + k;
>
> This looks very nice to me, but still not ideal: a 
> static-foreach argument cannot encapsulate a runtime variable, 
> so we have to repeat "i + k" twice.  This can get cumbersome 
> for a more complex example.  Is there any better way?  To 
> prevent introducing bugs when micro-optimizing, I'd like the 
> loop body to remain as unchanged as it can be.
>
> Ivan Kazmenko.

FYI: you can introduce scopes with static foreach to declare new 
variables:

for (int i = 0; i < 4 * n; i += 4)
{
     static foreach (k; 0..4)
     {{
        auto idx = i + k
        a[idx] += idx;
     }}
}

However, LDC is pretty good at loop unrolling out of the box:

https://godbolt.org/g/4nSWzQ

(even though gdc is written there, it's "ldc" - known typo: 
https://github.com/mattgodbolt/compiler-explorer/pull/988)