WGSL backend limits
Miri's first GPU backend targets WebGPU (WGSL) through wgpu, the most portable GPU host driver.
A few features sit outside WGSL's core. Each is gated explicitly — refused before dispatch with a clear
message, never miscomputed:
| Feature | Behavior today |
|---|---|
Native i64 / u64 / f64 | Run on adapters that support them (checked before dispatch). Refused otherwise. Not available in browser bundles. |
| Warp / subgroup ops | Run on adapters with subgroup support. Refused otherwise. |
| 64-bit atomics | Unavailable — Atomic<T> is 32-bit only. |
| Cooperative matrix (tensor cores) | Unavailable until the native backends land. |
bf16 / fp8 / fp4 | Unavailable — f16 is the smallest float today. |
WGSL stays the browser and embedded path. The native primaries — SPIR-V, PTX, Metal — target these features directly once the surface stabilizes. WGSL-first is an implementation milestone, not a long-term ranking.