[Merged by Bors] - Reduce the use of atomics in the render phase

crates/bevy_ecs/src/system/function_system.rs

@@ -170,15 +170,17 @@ impl<Param: SystemParam> SystemState<Param> {
     where
         Param: ReadOnlySystemParam,
     {
-        self.validate_world_and_update_archetypes(world);
+        self.validate_world(world);
+        self.update_archetypes(world);
         // SAFETY: Param is read-only and doesn't allow mutable access to World. It also matches the World this SystemState was created with.
         unsafe { self.get_unchecked_manual(world) }
     }
 
     /// Retrieve the mutable [`SystemParam`] values.
     #[inline]
     pub fn get_mut<'w, 's>(&'s mut self, world: &'w mut World) -> SystemParamItem<'w, 's, Param> {
-        self.validate_world_and_update_archetypes(world);
+        self.validate_world(world);
+        self.update_archetypes(world);
         // SAFETY: World is uniquely borrowed and matches the World this SystemState was created with.
         unsafe { self.get_unchecked_manual(world) }
     }
@@ -196,8 +198,13 @@ impl<Param: SystemParam> SystemState<Param> {
         self.world_id == world.id()
     }
 
-    fn validate_world_and_update_archetypes(&mut self, world: &World) {
+    #[inline]
+    fn validate_world(&mut self, world: &World) {
         assert!(self.matches_world(world), "Encountered a mismatched World. A SystemState cannot be used with Worlds other than the one it was created with.");
+    }
+
+    #[inline]
+    pub fn update_archetypes(&mut self, world: &World) {
         let archetypes = world.archetypes();
         let new_generation = archetypes.generation();
         let old_generation = std::mem::replace(&mut self.archetype_generation, new_generation);
@@ -211,6 +218,42 @@ impl<Param: SystemParam> SystemState<Param> {
         }
     }
 
+    /// Retrieve the [`SystemParam`] values. This can only be called when all parameters are read-only.
+    /// This will not update archetypes automatically nor increment the world's change tick.
+    ///
+    /// For this to return accurate results, ensure [`SystemState::update_archetypes`] is called before this
+    /// function.
+    ///
+    /// Users should strongly prefer to use [`SystemState::get`] over this function.
+    #[inline]
+    pub fn get_manual<'w, 's>(&'s mut self, world: &'w World) -> SystemParamItem<'w, 's, Param>
+    where
+        Param: ReadOnlySystemParam,
+    {
+        self.validate_world(world);
+        let change_tick = world.read_change_tick();
+        // SAFETY: Param is read-only and doesn't allow mutable access to World. It also matches the World this SystemState was created with.
+        unsafe { self.fetch(world, change_tick) }
+    }
+
+    /// Retrieve the mutable [`SystemParam`] values.  This will not update archetypes automatically nor increment
+    /// the world's change tick.
+    ///
+    /// For this to return accurate results, ensure [`SystemState::update_archetypes`] is called before this
+    /// function.
+    ///
+    /// Users should strongly prefer to use [`SystemState::get_mut`] over this function.
+    #[inline]
+    pub fn get_manual_mut<'w, 's>(
+        &'s mut self,
+        world: &'w mut World,
+    ) -> SystemParamItem<'w, 's, Param> {
+        self.validate_world(world);
+        let change_tick = world.change_tick();
+        // SAFETY: World is uniquely borrowed and matches the World this SystemState was created with.
+        unsafe { self.fetch(world, change_tick) }
+    }
+
     /// Retrieve the [`SystemParam`] values. This will not update archetypes automatically.
     ///
     /// # Safety
@@ -223,6 +266,19 @@ impl<Param: SystemParam> SystemState<Param> {
         world: &'w World,
     ) -> SystemParamItem<'w, 's, Param> {
         let change_tick = world.increment_change_tick();
+        self.fetch(world, change_tick)
+    }
+
+    /// # Safety
+    /// This call might access any of the input parameters in a way that violates Rust's mutability rules. Make sure the data
+    /// access is safe in the context of global [`World`] access. The passed-in [`World`] _must_ be the [`World`] the [`SystemState`] was
+    /// created with.
+    #[inline]
+    unsafe fn fetch<'w, 's>(
+        &'s mut self,
+        world: &'w World,
+        change_tick: u32,
+    ) -> SystemParamItem<'w, 's, Param> {
         let param = <Param::State as SystemParamState>::get_param(
             &mut self.param_state,
             &self.meta,

crates/bevy_render/src/render_phase/draw.rs

@@ -325,6 +325,7 @@ where
     C::Param: ReadOnlySystemParam,
 {
     fn prepare(&mut self, world: &'_ World) {
+        self.state.update_archetypes(world);
         self.view.update_archetypes(world);
         self.entity.update_archetypes(world);
     }
@@ -337,7 +338,7 @@ where
         view: Entity,
         item: &P,
     ) {
-        let param = self.state.get(world);
+        let param = self.state.get_manual(world);
         let view = self.view.get_manual(world, view).unwrap();
         let entity = self.entity.get_manual(world, item.entity()).unwrap();
         C::render(item, view, entity, param, pass);