1
  2
  3
  4
  5
  6
  7
  8
  9
 10
 11
 12
 13
 14
 15
 16
 17
 18
 19
 20
 21
 22
 23
 24
 25
 26
 27
 28
 29
 30
 31
 32
 33
 34
 35
 36
 37
 38
 39
 40
 41
 42
 43
 44
 45
 46
 47
 48
 49
 50
 51
 52
 53
 54
 55
 56
 57
 58
 59
 60
 61
 62
 63
 64
 65
 66
 67
 68
 69
 70
 71
 72
 73
 74
 75
 76
 77
 78
 79
 80
 81
 82
 83
 84
 85
 86
 87
 88
 89
 90
 91
 92
 93
 94
 95
 96
 97
 98
 99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
//! A graph module for use in dataflow, region resolution, and elsewhere.
//!
//! # Interface details
//!
//! You customize the graph by specifying a "node data" type `N` and an
//! "edge data" type `E`. You can then later gain access (mutable or
//! immutable) to these "user-data" bits. Currently, you can only add
//! nodes or edges to the graph. You cannot remove or modify them once
//! added. This could be changed if we have a need.
//!
//! # Implementation details
//!
//! The main tricky thing about this code is the way that edges are
//! stored. The edges are stored in a central array, but they are also
//! threaded onto two linked lists for each node, one for incoming edges
//! and one for outgoing edges. Note that every edge is a member of some
//! incoming list and some outgoing list. Basically you can load the
//! first index of the linked list from the node data structures (the
//! field `first_edge`) and then, for each edge, load the next index from
//! the field `next_edge`). Each of those fields is an array that should
//! be indexed by the direction (see the type `Direction`).

use crate::snapshot_vec::{SnapshotVec, SnapshotVecDelegate};
use rustc_index::bit_set::BitSet;
use std::fmt::Debug;

#[cfg(test)]
mod tests;

pub struct Graph<N, E> {
    nodes: SnapshotVec<Node<N>>,
    edges: SnapshotVec<Edge<E>>,
}

pub struct Node<N> {
    first_edge: [EdgeIndex; 2], // see module comment
    pub data: N,
}

#[derive(Debug)]
pub struct Edge<E> {
    next_edge: [EdgeIndex; 2], // see module comment
    source: NodeIndex,
    target: NodeIndex,
    pub data: E,
}

impl<N> SnapshotVecDelegate for Node<N> {
    type Value = Node<N>;
    type Undo = ();

    fn reverse(_: &mut Vec<Node<N>>, _: ()) {}
}

impl<N> SnapshotVecDelegate for Edge<N> {
    type Value = Edge<N>;
    type Undo = ();

    fn reverse(_: &mut Vec<Edge<N>>, _: ()) {}
}

#[derive(Copy, Clone, PartialEq, Debug)]
pub struct NodeIndex(pub usize);

#[derive(Copy, Clone, PartialEq, Debug)]
pub struct EdgeIndex(pub usize);

pub const INVALID_EDGE_INDEX: EdgeIndex = EdgeIndex(usize::MAX);

// Use a private field here to guarantee no more instances are created:
#[derive(Copy, Clone, Debug, PartialEq)]
pub struct Direction {
    repr: usize,
}

pub const OUTGOING: Direction = Direction { repr: 0 };

pub const INCOMING: Direction = Direction { repr: 1 };

impl NodeIndex {
    /// Returns unique ID (unique with respect to the graph holding associated node).
    pub fn node_id(self) -> usize {
        self.0
    }
}

impl<N: Debug, E: Debug> Graph<N, E> {
    pub fn new() -> Graph<N, E> {
        Graph { nodes: SnapshotVec::new(), edges: SnapshotVec::new() }
    }

    pub fn with_capacity(nodes: usize, edges: usize) -> Graph<N, E> {
        Graph { nodes: SnapshotVec::with_capacity(nodes), edges: SnapshotVec::with_capacity(edges) }
    }

    // # Simple accessors

    #[inline]
    pub fn all_nodes(&self) -> &[Node<N>] {
        &self.nodes
    }

    #[inline]
    pub fn len_nodes(&self) -> usize {
        self.nodes.len()
    }

    #[inline]
    pub fn all_edges(&self) -> &[Edge<E>] {
        &self.edges
    }

    #[inline]
    pub fn len_edges(&self) -> usize {
        self.edges.len()
    }

    // # Node construction

    pub fn next_node_index(&self) -> NodeIndex {
        NodeIndex(self.nodes.len())
    }

    pub fn add_node(&mut self, data: N) -> NodeIndex {
        let idx = self.next_node_index();
        self.nodes.push(Node { first_edge: [INVALID_EDGE_INDEX, INVALID_EDGE_INDEX], data });
        idx
    }

    pub fn mut_node_data(&mut self, idx: NodeIndex) -> &mut N {
        &mut self.nodes[idx.0].data
    }

    pub fn node_data(&self, idx: NodeIndex) -> &N {
        &self.nodes[idx.0].data
    }

    pub fn node(&self, idx: NodeIndex) -> &Node<N> {
        &self.nodes[idx.0]
    }

    // # Edge construction and queries

    pub fn next_edge_index(&self) -> EdgeIndex {
        EdgeIndex(self.edges.len())
    }

    pub fn add_edge(&mut self, source: NodeIndex, target: NodeIndex, data: E) -> EdgeIndex {
        debug!("graph: add_edge({:?}, {:?}, {:?})", source, target, data);

        let idx = self.next_edge_index();

        // read current first of the list of edges from each node
        let source_first = self.nodes[source.0].first_edge[OUTGOING.repr];
        let target_first = self.nodes[target.0].first_edge[INCOMING.repr];

        // create the new edge, with the previous firsts from each node
        // as the next pointers
        self.edges.push(Edge { next_edge: [source_first, target_first], source, target, data });

        // adjust the firsts for each node target be the next object.
        self.nodes[source.0].first_edge[OUTGOING.repr] = idx;
        self.nodes[target.0].first_edge[INCOMING.repr] = idx;

        idx
    }

    pub fn edge(&self, idx: EdgeIndex) -> &Edge<E> {
        &self.edges[idx.0]
    }

    // # Iterating over nodes, edges

    pub fn enumerated_nodes(&self) -> impl Iterator<Item = (NodeIndex, &Node<N>)> {
        self.nodes.iter().enumerate().map(|(idx, n)| (NodeIndex(idx), n))
    }

    pub fn enumerated_edges(&self) -> impl Iterator<Item = (EdgeIndex, &Edge<E>)> {
        self.edges.iter().enumerate().map(|(idx, e)| (EdgeIndex(idx), e))
    }

    pub fn each_node<'a>(&'a self, mut f: impl FnMut(NodeIndex, &'a Node<N>) -> bool) -> bool {
        //! Iterates over all edges defined in the graph.
        self.enumerated_nodes().all(|(node_idx, node)| f(node_idx, node))
    }

    pub fn each_edge<'a>(&'a self, mut f: impl FnMut(EdgeIndex, &'a Edge<E>) -> bool) -> bool {
        //! Iterates over all edges defined in the graph
        self.enumerated_edges().all(|(edge_idx, edge)| f(edge_idx, edge))
    }

    pub fn outgoing_edges(&self, source: NodeIndex) -> AdjacentEdges<'_, N, E> {
        self.adjacent_edges(source, OUTGOING)
    }

    pub fn incoming_edges(&self, source: NodeIndex) -> AdjacentEdges<'_, N, E> {
        self.adjacent_edges(source, INCOMING)
    }

    pub fn adjacent_edges(
        &self,
        source: NodeIndex,
        direction: Direction,
    ) -> AdjacentEdges<'_, N, E> {
        let first_edge = self.node(source).first_edge[direction.repr];
        AdjacentEdges { graph: self, direction, next: first_edge }
    }

    pub fn successor_nodes<'a>(
        &'a self,
        source: NodeIndex,
    ) -> impl Iterator<Item = NodeIndex> + 'a {
        self.outgoing_edges(source).targets()
    }

    pub fn predecessor_nodes<'a>(
        &'a self,
        target: NodeIndex,
    ) -> impl Iterator<Item = NodeIndex> + 'a {
        self.incoming_edges(target).sources()
    }

    pub fn depth_traverse(
        &self,
        start: NodeIndex,
        direction: Direction,
    ) -> DepthFirstTraversal<'_, N, E> {
        DepthFirstTraversal::with_start_node(self, start, direction)
    }

    pub fn nodes_in_postorder(
        &self,
        direction: Direction,
        entry_node: NodeIndex,
    ) -> Vec<NodeIndex> {
        let mut visited = BitSet::new_empty(self.len_nodes());
        let mut stack = vec![];
        let mut result = Vec::with_capacity(self.len_nodes());
        let mut push_node = |stack: &mut Vec<_>, node: NodeIndex| {
            if visited.insert(node.0) {
                stack.push((node, self.adjacent_edges(node, direction)));
            }
        };

        for node in
            Some(entry_node).into_iter().chain(self.enumerated_nodes().map(|(node, _)| node))
        {
            push_node(&mut stack, node);
            while let Some((node, mut iter)) = stack.pop() {
                if let Some((_, child)) = iter.next() {
                    let target = child.source_or_target(direction);
                    // the current node needs more processing, so
                    // add it back to the stack
                    stack.push((node, iter));
                    // and then push the new node
                    push_node(&mut stack, target);
                } else {
                    result.push(node);
                }
            }
        }

        assert_eq!(result.len(), self.len_nodes());
        result
    }
}

// # Iterators

pub struct AdjacentEdges<'g, N, E> {
    graph: &'g Graph<N, E>,
    direction: Direction,
    next: EdgeIndex,
}

impl<'g, N: Debug, E: Debug> AdjacentEdges<'g, N, E> {
    fn targets(self) -> impl Iterator<Item = NodeIndex> + 'g {
        self.map(|(_, edge)| edge.target)
    }

    fn sources(self) -> impl Iterator<Item = NodeIndex> + 'g {
        self.map(|(_, edge)| edge.source)
    }
}

impl<'g, N: Debug, E: Debug> Iterator for AdjacentEdges<'g, N, E> {
    type Item = (EdgeIndex, &'g Edge<E>);

    fn next(&mut self) -> Option<(EdgeIndex, &'g Edge<E>)> {
        let edge_index = self.next;
        if edge_index == INVALID_EDGE_INDEX {
            return None;
        }

        let edge = self.graph.edge(edge_index);
        self.next = edge.next_edge[self.direction.repr];
        Some((edge_index, edge))
    }

    fn size_hint(&self) -> (usize, Option<usize>) {
        // At most, all the edges in the graph.
        (0, Some(self.graph.len_edges()))
    }
}

pub struct DepthFirstTraversal<'g, N, E> {
    graph: &'g Graph<N, E>,
    stack: Vec<NodeIndex>,
    visited: BitSet<usize>,
    direction: Direction,
}

impl<'g, N: Debug, E: Debug> DepthFirstTraversal<'g, N, E> {
    pub fn with_start_node(
        graph: &'g Graph<N, E>,
        start_node: NodeIndex,
        direction: Direction,
    ) -> Self {
        let mut visited = BitSet::new_empty(graph.len_nodes());
        visited.insert(start_node.node_id());
        DepthFirstTraversal { graph, stack: vec![start_node], visited, direction }
    }

    fn visit(&mut self, node: NodeIndex) {
        if self.visited.insert(node.node_id()) {
            self.stack.push(node);
        }
    }
}

impl<'g, N: Debug, E: Debug> Iterator for DepthFirstTraversal<'g, N, E> {
    type Item = NodeIndex;

    fn next(&mut self) -> Option<NodeIndex> {
        let next = self.stack.pop();
        if let Some(idx) = next {
            for (_, edge) in self.graph.adjacent_edges(idx, self.direction) {
                let target = edge.source_or_target(self.direction);
                self.visit(target);
            }
        }
        next
    }

    fn size_hint(&self) -> (usize, Option<usize>) {
        // We will visit every node in the graph exactly once.
        let remaining = self.graph.len_nodes() - self.visited.count();
        (remaining, Some(remaining))
    }
}

impl<'g, N: Debug, E: Debug> ExactSizeIterator for DepthFirstTraversal<'g, N, E> {}

impl<E> Edge<E> {
    pub fn source(&self) -> NodeIndex {
        self.source
    }

    pub fn target(&self) -> NodeIndex {
        self.target
    }

    pub fn source_or_target(&self, direction: Direction) -> NodeIndex {
        if direction == OUTGOING { self.target } else { self.source }
    }
}