spirv: instantiate the backend in mod.rs, not gpu.rs

crates/coremem/src/sim/spirv/gpu.rs

@@ -2,7 +2,6 @@ use futures::FutureExt as _;
 use log::{info, warn};
 use std::borrow::Cow;
 use std::num::NonZeroU64;
-use std::sync::Arc;
 use wgpu;
 use wgpu::util::DeviceExt as _;
 
@@ -73,9 +72,6 @@ where
 
         let sim_meta = [self.meta.clone()];
 
-        self.wgpu.get_or_insert_with(
-            || Arc::new(WgpuData::new::<M>(size.volume()))
-        );
         let wgpu = &**self.wgpu.as_ref().unwrap();
         let device = &wgpu.device;
         let queue = &wgpu.queue;

crates/coremem/src/sim/spirv/mod.rs

@@ -93,6 +93,10 @@ where
     M: Send + Sync + Material<f32> + 'static
 {
     fn step_multiple<S: AbstractStimulus>(&mut self, num_steps: u32, s: &S) {
+        let vol = self.size().volume();
+        self.wgpu.get_or_insert_with(
+            || Arc::new(WgpuData::new::<M>(vol))
+        );
         self.step_spirv(num_steps, s);
         self.step_no += num_steps as u64;
     }