change interferrence graph impl

crates/renderer_rendergraph/src/graph.rs

@@ -1,6 +1,6 @@
 use std::{
     cmp::Reverse,
-    collections::{BTreeMap, BTreeSet, BinaryHeap, HashMap, VecDeque},
+    collections::{BTreeSet, BinaryHeap, HashMap, VecDeque},
     sync::Arc,
 };
 
@@ -64,41 +64,60 @@ impl ResourceLifetime {
 /// An edge means the two resources are live at the same command index.
 #[derive(Debug, Clone, Default)]
 pub struct ResourceInterference {
-    adj: BTreeMap<ResourceId, BTreeSet<ResourceId>>,
+    edges: Vec<BTreeSet<ResourceId>>,
 }
 
 impl ResourceInterference {
     /// Build a symmetric interference graph from inclusive resource lifetimes.
     pub fn from_lifetimes(lifetimes: &HashMap<ResourceId, ResourceLifetime>) -> Self {
-        let mut graph = Self::default();
-
-        let resources: Vec<_> = lifetimes
+        let mut max_id = ResourceId(0);
+        let mut resources: Vec<_> = lifetimes
             .iter()
+            .inspect(|(id, _)| {
+                if **id > max_id {
+                    max_id = **id;
+                }
+            })
             .map(|(&id, lifetime)| (id, *lifetime))
             .collect();
 
-        for (index, &(id, lifetime)) in resources.iter().enumerate() {
-            graph.adj.entry(id).or_default();
-            for &(other_id, other) in &resources[index + 1..] {
-                if lifetime.overlaps(&other) {
-                    graph.adj.entry(id).or_default().insert(other_id);
-                    graph.adj.entry(other_id).or_default().insert(id);
+        let mut edges = vec![BTreeSet::new(); max_id.index() + 1];
+
+        resources.sort_unstable_by_key(|&(_, lifetime)| lifetime.first_command);
+        let mut resources = VecDeque::from(resources);
+
+        let mut index = 0;
+        while index < resources.len() {
+            let (id, lifetime) = resources[index];
+
+            let mut j = 0;
+            while j < index {
+                if resources[j].1.last_command < lifetime.first_command {
+                    resources.swap_remove_front(j);
+                    index -= 1;
+                } else {
+                    j += 1;
                 }
             }
+
+            index += 1;
+
+            // resources is no longer sorted in the interval ..index, but because of the invariant `last_command >= first_command`, it is still partitioned by `a.last_command <= b.first_command`.
+            let active = resources
+                .partition_point(|&(_, other)| other.first_command <= lifetime.last_command);
+
+            for &(other_id, _) in resources.range(..active) {
+                edges[id.index()].insert(other_id);
+                edges[other_id.index()].insert(id);
             }
-        graph
+        }
+
+        Self { edges }
     }
 
     /// Returns whether both resources are live at any common command index.
     pub fn interferes(&self, a: ResourceId, b: ResourceId) -> bool {
-        self.adj
-            .get(&a)
-            .is_some_and(|neighbors| neighbors.contains(&b))
-    }
-
-    /// Returns the resources that overlap `id`'s inclusive lifetime interval.
-    pub fn neighbors(&self, id: ResourceId) -> Option<&BTreeSet<ResourceId>> {
-        self.adj.get(&id)
+        self.edges[a.index()].contains(&b)
     }
 }