GEP not implemented for type struct [_; 0]

[Firestar99]

Original issue: EmbarkStudios/rust-gpu#1075

Expected Behaviour

This compiles fine with rustc (I guess this bit is probably eliminated?).

Example & Steps To Reproduce

I was using const generic parameters to determine the length of some arrays. At some point, a base case ended up declaring a zero-length array, like so:

#![cfg_attr(target_arch = "spirv", no_std)]
use spirv_std::spirv;

fn example<const LENGTH: usize>() {
    let mut array = [0; LENGTH];
    for i in 0..array.len() {
        array[i] += i;
    }
}

#[spirv(compute(threads(1, 1, 1)))]
pub fn compute() {
    example::<0>();
}

Resulting in:

error: GEP not implemented for type struct [usize; 0] {  }
 --> examples/shaders/compute-shader/src/lib.rs:7:9
  |
7 |         array[i] += i;
  |         ^^^^^^^^^^^^^

System Info

* rustc: 1.71.0-nightly (1a5f8bce7 2023-05-26)

* rust-gpu: [b2e5eb7](https://github.com/EmbarkStudios/rust-gpu/commit/b2e5eb75951545782b121665c20f9f1c66fe5bdd)

[JulianKnodt]

Is it alright if I check this out?

[Firestar99]

Feel free to give it a try. This old patch won't be directly cherry-pickable due to some larger gep changes.

[JulianKnodt]

I'm a bit confused what should be emitted, since it doesn't make sense to have a GEP to an array with zero elements. Should it just emit a constant value?

For context I added the patch you linked here (which is very WIP), but it still fails with this:

Ah I realize we're hitting this because we're emitting a struct and not an array now