extract kahn algo and build interference graph

crates/renderer_rendergraph/src/graph.rs

@@ -53,6 +53,100 @@ pub struct ResourceLifetime {
     pub memory_offset: u64,
 }
 
+impl ResourceLifetime {
+    fn overlaps(&self, other: &Self) -> bool {
+        self.first_command <= other.last_command && other.first_command <= self.last_command
+    }
+}
+
+/// The resource-level interference graph used by transient-resource aliasing.
+/// 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>>,
+}
+
+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
+            .iter()
+            .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);
+                }
+            }
+        }
+        graph
+    }
+
+    /// 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)
+    }
+}
+
+/// Deterministic Kahn topological-sort state for command dependencies.
+struct Kahn {
+    edges: Vec<BTreeSet<usize>>,
+    indegree: Vec<usize>,
+    ready: BTreeSet<usize>,
+    emitted: usize,
+    total: usize,
+}
+
+impl Kahn {
+    fn new(node_count: usize) -> Self {
+        Self {
+            edges: vec![BTreeSet::new(); node_count],
+            indegree: vec![0; node_count],
+            ready: (0..node_count).collect(),
+            emitted: 0,
+            total: node_count,
+        }
+    }
+
+    fn add_edge(&mut self, from: usize, to: usize) {
+        if self.edges[from].insert(to) {
+            self.indegree[to] += 1;
+            self.ready.remove(&to);
+        }
+    }
+
+    fn pop_ready(&mut self) -> Option<usize> {
+        self.ready.pop_first()
+    }
+
+    fn complete(&mut self, node: usize) {
+        self.emitted += 1;
+        for &dependent in &self.edges[node] {
+            self.indegree[dependent] -= 1;
+            if self.indegree[dependent] == 0 {
+                self.ready.insert(dependent);
+            }
+        }
+    }
+
+    fn is_complete(&self) -> bool {
+        self.emitted == self.total
+    }
+}
+
 pub struct RenderGraph {
     next_id: u64,
     resources: BTreeMap<ResourceId, ResourceDesc>,
@@ -116,7 +210,7 @@ impl RenderGraph {
         let order = compiler.topo_sort()?;
         compiler.validate_resources()?;
         let barriers = compiler.build_barriers(&order);
-        let lifetimes = compiler.bind_lifetimes();
+        let (lifetimes, interference) = compiler.bind_lifetimes();
 
         Ok(CompiledGraph {
             resources: self.resources,
@@ -125,6 +219,7 @@ impl RenderGraph {
             order,
             barriers,
             lifetimes,
+            interference,
         })
     }
 }
@@ -148,9 +243,8 @@ impl<'a> GraphCompiler<'a> {
         }
     }
 
-    fn dependencies(&self) -> (Vec<BTreeSet<usize>>, Vec<usize>) {
+    fn dependencies(&self) -> Kahn {
-        let mut edges = vec![BTreeSet::new(); self.command_count];
+        let mut kahn = Kahn::new(self.command_count);
-        let mut indegree = vec![0usize; self.command_count];
 
         for current in 0..self.command_count {
             for prior in 0..current {
@@ -159,32 +253,22 @@ impl<'a> GraphCompiler<'a> {
                         earlier.resource == later.resource && earlier.scope.conflicts(&later.scope)
                     })
                 });
-                if dependency && edges[prior].insert(current) {
+                if dependency {
-                    indegree[current] += 1;
+                    kahn.add_edge(prior, current);
                 }
             }
         }
-        (edges, indegree)
+        kahn
     }
 
     fn topo_sort(&self) -> Result<Vec<CommandIndex>, GraphError> {
-        let (edges, mut indegree) = self.dependencies();
+        let mut kahn = self.dependencies();
-        let mut ready: BTreeSet<_> = indegree
-            .iter()
-            .enumerate()
-            .filter_map(|(index, &degree)| (degree == 0).then_some(index))
-            .collect();
         let mut order = Vec::with_capacity(self.command_count);
-        while let Some(index) = ready.pop_first() {
+        while let Some(index) = kahn.pop_ready() {
             order.push(index.into());
-            for &dependent in &edges[index] {
+            kahn.complete(index);
-                indegree[dependent] -= 1;
-                if indegree[dependent] == 0 {
-                    ready.insert(dependent);
-                }
-            }
         }
-        if order.len() != self.command_count {
+        if !kahn.is_complete() {
             return Err(GraphError::DependencyCycle);
         }
         Ok(order)
@@ -284,7 +368,7 @@ impl<'a> GraphCompiler<'a> {
         (initial.layout, current_layout)
     }
 
-    fn bind_lifetimes(&self) -> HashMap<ResourceId, ResourceLifetime> {
+    fn bind_lifetimes(&self) -> (HashMap<ResourceId, ResourceLifetime>, ResourceInterference) {
         let mut lifetimes = HashMap::new();
         for (command, command_accesses) in self.accesses.iter().enumerate() {
             for access in command_accesses {
@@ -301,9 +385,13 @@ impl<'a> GraphCompiler<'a> {
             }
         }
 
+        let interference = ResourceInterference::from_lifetimes(&lifetimes);
+
         // Skeleton aliasing policy: resources with non-overlapping lifetimes may
-        // share a heap offset. Actual size/alignment-aware Vulkan allocation is TODO.
+        // share a heap offset. The graph test is equivalent to the previous
-        let mut slots: Vec<(u64, CommandIndex, u64)> = Vec::new(); // (offset, last use, capacity)
+        // strict `last_use < first_command` check (intervals are inclusive).
+        // Actual size/alignment-aware Vulkan allocation is TODO.
+        let mut slots: Vec<(u64, ResourceId, u64)> = Vec::new(); // (offset, last occupant, capacity)
         let mut next_offset = 0;
         let mut ids: Vec<_> = lifetimes.keys().copied().collect();
         ids.sort_by_key(|id| lifetimes[id].first_command);
@@ -317,20 +405,20 @@ impl<'a> GraphCompiler<'a> {
             if self.resources[&id].is_created()
                 && let Some((offset, last_use, capacity)) = slots
                     .iter_mut()
-                    .find(|(_, last, cap)| *last < lifetime.first_command && *cap >= size)
+                    .find(|(_, last, cap)| !interference.interferes(*last, id) && *cap >= size)
             {
                 lifetime.memory_offset = *offset;
-                *last_use = lifetime.last_command;
+                *last_use = id;
                 let _ = capacity;
             } else {
                 lifetime.memory_offset = next_offset;
                 if self.resources[&id].is_created() {
-                    slots.push((next_offset, lifetime.last_command, size));
+                    slots.push((next_offset, id, size));
                     next_offset = next_offset.saturating_add(size);
                 }
             }
         }
-        lifetimes
+        (lifetimes, interference)
     }
 }
 
@@ -347,6 +435,7 @@ pub struct CompiledGraph {
     order: Vec<CommandIndex>,
     barriers: Vec<PipelineBarrier>,
     lifetimes: HashMap<ResourceId, ResourceLifetime>,
+    interference: ResourceInterference,
 }
 
 enum ResolvedResource {
@@ -367,6 +456,10 @@ impl CompiledGraph {
         &self.lifetimes
     }
 
+    pub fn interference(&self) -> &ResourceInterference {
+        &self.interference
+    }
+
     /// Create the graph's transient resources. Compilation remains independent
     /// of a Vulkan device, while command recording requires this resolution step
     /// for any created resources used by commands.
@@ -701,9 +794,124 @@ mod tests {
     use super::*;
     use crate::{
         commands::{ClearTexture, CopyBuffer},
-        resources::{BufferRange, GraphBufferDesc, GraphTextureDesc},
+        resources::{BufferRange, GraphBufferDesc, GraphTextureDesc, ResourceDesc},
     };
 
+    #[test]
+    fn kahn_emits_dag_in_deterministic_order() {
+        let mut kahn = Kahn::new(4);
+        kahn.add_edge(0, 2);
+        kahn.add_edge(1, 2);
+        kahn.add_edge(2, 3);
+
+        let mut order = Vec::new();
+        while let Some(node) = kahn.pop_ready() {
+            order.push(node);
+            kahn.complete(node);
+        }
+
+        assert_eq!(order, [0, 1, 2, 3]);
+        assert!(kahn.is_complete());
+    }
+
+    #[test]
+    fn kahn_detects_cycles() {
+        let mut kahn = Kahn::new(3);
+        kahn.add_edge(0, 1);
+        kahn.add_edge(1, 2);
+        kahn.add_edge(2, 1);
+
+        while let Some(node) = kahn.pop_ready() {
+            kahn.complete(node);
+        }
+
+        assert_eq!(kahn.emitted, 1);
+        assert!(!kahn.is_complete());
+    }
+
+    #[test]
+    fn interference_tracks_overlapping_inclusive_lifetimes() {
+        let lifetimes = HashMap::from([
+            (
+                ResourceId(0),
+                ResourceLifetime {
+                    first_command: CommandIndex(0),
+                    last_command: CommandIndex(2),
+                    memory_offset: 0,
+                },
+            ),
+            (
+                ResourceId(1),
+                ResourceLifetime {
+                    first_command: CommandIndex(2),
+                    last_command: CommandIndex(3),
+                    memory_offset: 0,
+                },
+            ),
+            (
+                ResourceId(2),
+                ResourceLifetime {
+                    first_command: CommandIndex(4),
+                    last_command: CommandIndex(5),
+                    memory_offset: 0,
+                },
+            ),
+        ]);
+        let interference = ResourceInterference::from_lifetimes(&lifetimes);
+
+        assert!(interference.interferes(ResourceId(0), ResourceId(1)));
+        assert!(interference.interferes(ResourceId(1), ResourceId(0)));
+        assert!(!interference.interferes(ResourceId(0), ResourceId(2)));
+        assert!(!interference.interferes(ResourceId(1), ResourceId(2)));
+    }
+
+    #[test]
+    fn aliasing_reuses_non_interfering_slot_and_separates_interfering_resources() {
+        let resources = BTreeMap::from([
+            (
+                ResourceId(0),
+                ResourceDesc::CreatedBuffer(GraphBufferDesc {
+                    size: 8,
+                    ..Default::default()
+                }),
+            ),
+            (
+                ResourceId(1),
+                ResourceDesc::CreatedBuffer(GraphBufferDesc {
+                    size: 8,
+                    ..Default::default()
+                }),
+            ),
+            (
+                ResourceId(2),
+                ResourceDesc::CreatedBuffer(GraphBufferDesc {
+                    size: 8,
+                    ..Default::default()
+                }),
+            ),
+        ]);
+        let accesses = vec![
+            vec![resource_access_for(ResourceId(0))],
+            vec![
+                resource_access_for(ResourceId(0)),
+                resource_access_for(ResourceId(1)),
+            ],
+            vec![resource_access_for(ResourceId(0))],
+            vec![resource_access_for(ResourceId(2))],
+        ];
+        let compiler = GraphCompiler::new(&resources, &accesses, accesses.len());
+        let (lifetimes, interference) = compiler.bind_lifetimes();
+
+        let long_lived_offset = lifetimes[&ResourceId(0)].memory_offset;
+        let overlapping_offset = lifetimes[&ResourceId(1)].memory_offset;
+        let later_offset = lifetimes[&ResourceId(2)].memory_offset;
+        assert!(interference.interferes(ResourceId(0), ResourceId(1)));
+        assert_ne!(long_lived_offset, overlapping_offset);
+        assert!(!interference.interferes(ResourceId(0), ResourceId(2)));
+        assert!(!interference.interferes(ResourceId(1), ResourceId(2)));
+        assert!(later_offset == long_lived_offset || later_offset == overlapping_offset);
+    }
+
     #[test]
     fn copy_buffer_compiles_with_dependency_and_barrier() {
         let mut graph = RenderGraph::new();
@@ -732,6 +940,7 @@ mod tests {
         assert_eq!(compiled.command_order(), &[CommandIndex(0)]);
         assert!(compiled.barriers().is_empty());
         assert_eq!(compiled.resource_lifetimes().len(), 2);
+        assert!(compiled.interference().interferes(src.id(), dst.id()));
     }
 
     #[test]
@@ -977,4 +1186,15 @@ mod tests {
             },
         }
     }
+
+    fn resource_access_for(resource: ResourceId) -> crate::recorder::ResourceAccess {
+        crate::recorder::ResourceAccess {
+            resource,
+            scope: SubresourceScope {
+                stage: vk::PipelineStageFlags2::COPY,
+                access: vk::AccessFlags2::TRANSFER_WRITE,
+                subresource: SubresourceScopeInner::Buffer(BufferRange::full()),
+            },
+        }
+    }
 }

crates/renderer_rendergraph/src/lib.rs

@@ -6,6 +6,6 @@ pub mod graph;
 pub mod recorder;
 pub mod resources;
 
-pub use graph::{CompiledGraph, GraphError, RenderGraph};
+pub use graph::{CompiledGraph, GraphError, RenderGraph, ResourceInterference};
 pub use recorder::{CommandIndex, CommandList, CommandRecorder, SideEffectMap};
 pub use resources::{Buffer, GraphBufferDesc, GraphTextureDesc, ResourceId, Texture};