This is a wgpu reproduction of the Metal bug described in https://github.com/armansito/metal-workgroup-memory-bug.

Results on native

On macOS using Metal on Apple M1 GPUs, this program results in 10 while the expected result is 640.

On Linux using Vulkan on a NVIDIA RTX 4090, this program results in 640, which is correct.

Result in Chrome (WASM) on macOS

On WebGPU with Chrome (using Dawn's implementation) this results in 640, which is correct.

However, a modified version of the program using a matrix type in workgroup shared memory results in 10 (see shader-broken-on-dawn.wgsl).

Running the test

To run the test natively:

$ cargo run

For WASM, run the following commands to build and host a page that you can run in a browser that supports WebGPU). Navigate your browser to http://localhost:8000 to view the page.

$ RUSTFLAGS=--cfg=web_sys_unstable_apis wasm-pack build --target web --release
$ python -m http.server