[DMD] Loop index incorrectly optimised out for -release -O

[Imperatorn]

On Sunday, 10 October 2021 at 02:41:55 UTC, Basile.B wrote:
> On Saturday, 9 October 2021 at 21:09:19 UTC, Teodor Dutu wrote:
>>[...]
>
> It is about optimization, it's about loop so a good candidate 
> to check is dmd.backend.gloop.d.
>
> [...]

Yup, I was also dissecting gloop last night