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use std::ops::Index;
use petgraph::{Direction, Graph, visit::EdgeRef};
use rustc_hash::{FxHashMap, FxHashSet};
use turbo_tasks::FxIndexSet;
use crate::tree_shake::graph::{Dependency, ItemId};
pub(super) struct GraphOptimizer<'a> {
pub graph_ix: &'a FxIndexSet<ItemId>,
}
impl Index<u32> for GraphOptimizer<'_> {
type Output = ItemId;
fn index(&self, index: u32) -> &Self::Output {
&self.graph_ix[index as usize]
}
}
impl GraphOptimizer<'_> {
pub(super) fn should_not_merge<N>(&self, item: &N) -> bool
where
N: Copy,
Self: Index<N, Output = ItemId>,
{
let item_id = &self[*item];
// Currently we don't merge import bindings because those node are phantom nodes.
item_id.is_phantom()
}
fn should_not_merge_iter<N>(&self, items: &[N]) -> bool
where
N: Copy,
Self: Index<N, Output = ItemId>,
{
items.iter().any(|item| self.should_not_merge(item))
}
/// Optimizes a condensed graph by merging nodes with only one incoming edge.
///
/// Returns true if any nodes were merged.
pub(super) fn merge_single_incoming_nodes<N>(&self, g: &mut Graph<Vec<N>, Dependency>) -> bool
where
N: Copy,
Self: Index<N, Output = ItemId>,
{
let mut queue = vec![];
let mut removed_nodes = vec![];
for node in g.node_indices() {
// ImportBinding nodes should not be merged
let node_data = g.node_weight(node).expect("Node should exist");
if self.should_not_merge_iter(node_data) {
continue;
}
// If the node has only one incoming edge, we enqueue it
if g.edges_directed(node, Direction::Incoming).count() == 1 {
let dependant = g
.edges_directed(node, Direction::Incoming)
.next()
.unwrap()
.source();
if self.should_not_merge_iter(&g[dependant]) {
continue;
}
let dependencies = g
.edges_directed(node, Direction::Outgoing)
.map(|e| (e.target(), *e.weight()))
.collect::<Vec<_>>();
queue.push((node, dependant, dependencies));
removed_nodes.push(node);
}
}
for (original, dependant, dependencies) in queue {
// Move all edges from node to dependant
for (dependency, weight) in dependencies {
let edge = g
.find_edge(dependant, dependency)
.and_then(|e| g.edge_weight_mut(e));
match edge {
Some(v) => {
if matches!(v, Dependency::Weak) {
*v = weight;
}
}
None => {
g.add_edge(dependant, dependency, weight);
}
}
}
// Move items from original to dependant
let items = g.node_weight(original).expect("Node should exist").clone();
g.node_weight_mut(dependant).unwrap().extend(items);
}
let mut did_work = false;
// Remove all edges from source
for node in removed_nodes.into_iter().rev() {
g.remove_node(node).expect("Node should exist");
did_work = true;
}
did_work
}
/// This function merges nodes that can only be reached from a single starting point.
/// Example:
/// If we have a graph with edges: A->B, B->C, A->C, B->E, D->E
/// Then B and C can only be reached from A, so they will be merged into A.
/// The resulting graph would have edges like: (A,B,C)->E, D->E
pub(super) fn merge_nodes_with_same_starting_point<N>(
&self,
g: &mut Graph<Vec<N>, Dependency>,
) -> bool
where
N: Copy,
Self: Index<N, Output = ItemId>,
{
let mut did_work = false;
let mut reachability: FxHashMap<_, FxHashSet<_>> = FxHashMap::default();
// Step 1: Build a reverse reachability map (which starting nodes can reach each node)
// We consider a "starting node" as one with no incoming edges
let starting_nodes: Vec<_> = g
.node_indices()
.filter(|&node| g.edges_directed(node, Direction::Incoming).count() == 0)
.collect();
// For each starting node, find all nodes reachable from it
for &start in &starting_nodes {
let mut visited = FxHashSet::default();
let mut queue = vec![start];
while let Some(node) = queue.pop() {
if !visited.insert(node) {
continue;
}
// For each outgoing edge, add the target to queue
for edge in g.edges_directed(node, Direction::Outgoing) {
let target = edge.target();
queue.push(target);
// Add this starting node to the set of starting nodes that can reach target
reachability.entry(target).or_default().insert(start);
}
}
}
// Step 2: Find nodes that are reachable from exactly one starting node
// and group them by that starting node
let mut merge_groups: FxHashMap<_, Vec<_>> = FxHashMap::default();
for node in g.node_indices() {
// Skip starting nodes
if starting_nodes.contains(&node) {
continue;
}
// Skip nodes that should not be merged
if self.should_not_merge_iter(g.node_weight(node).expect("Node should exist")) {
continue;
}
// If this node is reachable from exactly one starting node, add it to that group
if let Some(reachable_from) = reachability.get(&node)
&& reachable_from.len() == 1
{
let start = *reachable_from.iter().next().unwrap();
// Don't merge if the starting node should not be merged
if self.should_not_merge_iter(g.node_weight(start).expect("Node should exist")) {
continue;
}
merge_groups.entry(start).or_default().push(node);
}
}
// Step 3: Merge nodes into their starting points
for (start, nodes_to_merge) in merge_groups {
if nodes_to_merge.is_empty() {
continue;
}
let mut nodes_to_remove = Vec::new();
for node in nodes_to_merge {
// Skip if a node no longer exists in the graph. This may happen if `nodes_to_merge`
// contains a duplicate.
if g.node_weight(node).is_none() {
continue;
}
// Move outgoing edges from node to start
let outgoing_edges: Vec<_> = g
.edges_directed(node, Direction::Outgoing)
.map(|e| (e.target(), *e.weight()))
.collect();
for (target, weight) in outgoing_edges {
// If there's already an edge from start to target, only update if necessary
let existing_edge = g.find_edge(start, target);
match existing_edge {
Some(e) => {
let edge_weight = g.edge_weight_mut(e).unwrap();
// Only upgrade from weak to strong dependency
if matches!(edge_weight, Dependency::Weak)
&& !matches!(weight, Dependency::Weak)
{
*edge_weight = weight;
}
}
None => {
// Add a new edge
g.add_edge(start, target, weight);
}
}
}
// Move items from this node to the starting node
let items = g.node_weight(node).expect("Node should exist").clone();
g.node_weight_mut(start).unwrap().extend(items);
nodes_to_remove.push(node);
}
// Remove merged nodes (in reverse order to preserve indices)
nodes_to_remove.sort();
for node in nodes_to_remove.into_iter().rev() {
g.remove_node(node).expect("Node should exist");
did_work = true;
}
}
did_work
}
}
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