toy windowing auto-vec miss

[Bruce Carneal]

On Monday, 7 November 2022 at 16:49:24 UTC, Johan wrote:
> On Monday, 7 November 2022 at 01:59:03 UTC, Bruce Carneal wrote:
>> Here's a simple godbolt example of one of the areas in which 
>> gdc solidly outperforms ldc wrt auto-vectorization: simple but 
>> not trivial operand gather
>> https://godbolt.org/z/ox1vvxd8s
>
> Don't have time to dive deeper but I found that:
> Removing `@restrict` results in vectorized instructions with 
> LDC (don't know if it is faster, just that they appear in ASM).
>
> -Johan

That's very interesting.

This is the first time I've heard of @restrict making things 
worse wrt auto vectorization. From what I've seen in other 
experiments, @restrict provides a minor benefit (code size 
reduction) frequently while occasionally enabling vectorization 
of otherwise complex dependency graphs.

Thanks for the heads up.