Handle vector, matrix and array OOB accesses for HLSL

[teoxoy]

The following WGSL causes FXC to error with: error X3504: array index out of bounds

@compute @workgroup_size(1)
fn main() {
    var idx = 9;
    var v = vec2<f32>();
    var m = mat2x2<f32>();
    var a = array<f32,1>();
    var vi = v[idx];
    var mi = m[idx];
    var ai = a[idx];
}

https://shader-playground.timjones.io/19d35c227236839667eb8830d12a4af0

Related:

• [hlsl-out] Avoid error X3504: array index out of bounds (for FXC) naga#1922
• error X3504: literal loop terminated early due to out of bounds array access #4381

[teoxoy]

According to the WGSL spec the same example from above but using let instead of var should also work but validation currently errors.

@jimblandy can you confirm this?

[jimblandy]

Yes, with let I get:

error: Index 9 is out of bounds for expression [2]

This is Naga's fault: it's reporting as a compile-time error a problem that WGSL requires us to handle at run-time.

Could you file a separate issue for this?

[nical]

See also: #4337