Small refactors related to bind group tracking for compute passes

* Don't remove resources from the usage scope, it is not necessary, and
  not useful, since we don't verify the scope is empty afterwards.
* Avoid some unnecessary `unsafe`.

Author: andyleiserson

wgpu-core/src/command/compute.rs

@@ -293,21 +293,14 @@ impl<'scope, 'snatch_guard, 'cmd_enc> State<'scope, 'snatch_guard, 'cmd_enc> {
         }
 
         for bind_group in self.pass.binder.list_active() {
-            unsafe {
-                self.intermediate_trackers
-                    .set_and_remove_from_usage_scope_sparse(&mut self.pass.scope, &bind_group.used)
-            }
+            self.intermediate_trackers
+                .set_from_bind_group(&mut self.pass.scope, &bind_group.used);
         }
 
         // Add the state of the indirect buffer if it hasn't been hit before.
-        unsafe {
-            self.intermediate_trackers
-                .buffers
-                .set_and_remove_from_usage_scope_sparse(
-                    &mut self.pass.scope.buffers,
-                    indirect_buffer,
-                );
-        }
+        self.intermediate_trackers
+            .buffers
+            .set_multiple(&mut self.pass.scope.buffers, indirect_buffer);
 
         CommandEncoder::drain_barriers(
             self.pass.base.raw_encoder,

wgpu-core/src/track/buffer.rs

@@ -442,12 +442,7 @@ impl BufferTracker {
     /// over all elements in the usage scope. We use each the
     /// a given iterator of ids as a source of which IDs to look at.
     /// All the IDs must have first been added to the usage scope.
-    ///
-    /// # Safety
-    ///
-    /// [`Self::set_size`] must be called with the maximum possible Buffer ID before this
-    /// method is called.
-    pub unsafe fn set_and_remove_from_usage_scope_sparse(
+    pub fn set_multiple(
         &mut self,
         scope: &mut BufferUsageScope,
         index_source: impl IntoIterator<Item = TrackerIndex>,
@@ -465,6 +460,9 @@ impl BufferTracker {
             if unsafe { !scope.metadata.contains_unchecked(index) } {
                 continue;
             }
+
+            // SAFETY: we checked that the index is in bounds for the scope, and
+            // called `set_size` to ensure it is valid for `self`.
             unsafe {
                 self.insert_or_barrier_update(
                     index,
@@ -477,8 +475,6 @@ impl BufferTracker {
                     },
                 )
             };
-
-            unsafe { scope.metadata.remove(index) };
         }
     }
 

wgpu-core/src/track/metadata.rs

@@ -130,14 +130,6 @@ impl<T: Clone> ResourceMetadata<T> {
         };
         iterate_bitvec_indices(&self.owned)
     }
-
-    /// Remove the resource with the given index from the set.
-    pub(super) unsafe fn remove(&mut self, index: usize) {
-        unsafe {
-            *self.resources.get_unchecked_mut(index) = None;
-        }
-        self.owned.set(index, false);
-    }
 }
 
 /// A source of resource metadata.

wgpu-core/src/track/mod.rs

@@ -641,41 +641,25 @@ impl Tracker {
     }
 
     /// Iterates through all resources in the given bind group and adopts
-    /// the state given for those resources in the UsageScope. It also
-    /// removes all touched resources from the usage scope.
+    /// the state given for those resources in the UsageScope.
     ///
     /// If a transition is needed to get the resources into the needed
     /// state, those transitions are stored within the tracker. A
     /// subsequent call to [`BufferTracker::drain_transitions`] or
     /// [`TextureTracker::drain_transitions`] is needed to get those transitions.
     ///
     /// This is a really funky method used by Compute Passes to generate
-    /// barriers after a call to dispatch without needing to iterate
-    /// over all elements in the usage scope. We use each the
-    /// bind group as a source of which IDs to look at. The bind groups
-    /// must have first been added to the usage scope.
+    /// barriers for each dispatch. We use the bind group as a source of which
+    /// IDs to look at.
     ///
     /// Only stateful things are merged in here, all other resources are owned
     /// indirectly by the bind group.
-    ///
-    /// # Safety
-    ///
-    /// The maximum ID given by each bind group resource must be less than the
-    /// value given to `set_size`
-    pub unsafe fn set_and_remove_from_usage_scope_sparse(
-        &mut self,
-        scope: &mut UsageScope,
-        bind_group: &BindGroupStates,
-    ) {
-        unsafe {
-            self.buffers.set_and_remove_from_usage_scope_sparse(
-                &mut scope.buffers,
-                bind_group.buffers.used_tracker_indices(),
-            )
-        };
-        unsafe {
-            self.textures
-                .set_and_remove_from_usage_scope_sparse(&mut scope.textures, &bind_group.views)
-        };
+    pub fn set_from_bind_group(&mut self, scope: &mut UsageScope, bind_group: &BindGroupStates) {
+        self.buffers.set_multiple(
+            &mut scope.buffers,
+            bind_group.buffers.used_tracker_indices(),
+        );
+        self.textures
+            .set_multiple(&mut scope.textures, &bind_group.views);
     }
 }

wgpu-core/src/track/texture.rs

@@ -611,12 +611,7 @@ impl TextureTracker {
     /// over all elements in the usage scope. We use each the
     /// bind group as a source of which IDs to look at. The bind groups
     /// must have first been added to the usage scope.
-    ///
-    /// # Safety
-    ///
-    /// [`Self::set_size`] must be called with the maximum possible Buffer ID before this
-    /// method is called.
-    pub unsafe fn set_and_remove_from_usage_scope_sparse(
+    pub fn set_multiple(
         &mut self,
         scope: &mut TextureUsageScope,
         bind_group_state: &TextureViewBindGroupState,
@@ -634,6 +629,8 @@ impl TextureTracker {
                 continue;
             }
             let texture_selector = &view.parent.full_range;
+            // SAFETY: we checked that the index is in bounds for the scope, and
+            // called `set_size` to ensure it is valid for `self`.
             unsafe {
                 insert_or_barrier_update(
                     texture_selector,
@@ -649,8 +646,6 @@ impl TextureTracker {
                     &mut self.temp,
                 )
             };
-
-            unsafe { scope.metadata.remove(index) };
         }
     }
 }