As a follow up to

https://github.com/D-Programming-Language/dmd/pull/4293

would it be possible to also avoid range-checking in expressions such as

    x[0 .. $/n]

and

    x[$/n .. $]

where n is an integer compile-time constant >= 2.

I'm askingbecause this is a reoccurring pattern in D-style binary divide-and-conquer algorithms and would be a good show-case for D from a performance standpoint.

Is DMD prepared for (easily) adding this to e2ir.c and expression.c?

On Wednesday, 21 January 2015 at 23:50:44 UTC, Nordlöw wrote:
> As a follow up to
>
> https://github.com/D-Programming-Language/dmd/pull/4293
>
> would it be possible to also avoid range-checking in expressions such as
>
>     x[0 .. $/n]
>
> and
>
>     x[$/n .. $]
>
> where n is an integer compile-time constant >= 2.
>
> I'm askingbecause this is a reoccurring pattern in D-style binary divide-and-conquer algorithms and would be a good show-case for D from a performance standpoint.
>
> Is DMD prepared for (easily) adding this to e2ir.c and expression.c?

That is reasonable to expect a compiler to remove such a check with optimization enabled already. I'm not sure about DMD, but I'd be willing to bet that LDC and GDC already do it.

deadalnix:

> That is reasonable to expect a compiler to remove such a check with optimization enabled already. I'm not sure about DMD, but I'd be willing to bet that LDC and GDC already do it.

I think this thread is about an enhancement request for a guaranteed front-end optimization.

Bye,
bearophile