1 // Copyright 2016 The Rust Project Developers. See the COPYRIGHT
2 // file at the top-level directory of this distribution and at
3 // http://rust-lang.org/COPYRIGHT.
5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
8 // option. This file may not be copied, modified, or distributed
9 // except according to those terms.
11 use rustc_data_structures::bitvec::BitVector;
15 /// Preorder traversal of a graph.
17 /// Preorder traversal is when each node is visited before an of it's
31 /// A preorder traversal of this graph is either `A B D C` or `A C D B`
33 pub struct Preorder<'a, 'tcx: 'a> {
35 visited: BitVector<BasicBlock>,
36 worklist: Vec<BasicBlock>,
39 impl<'a, 'tcx> Preorder<'a, 'tcx> {
40 pub fn new(mir: &'a Mir<'tcx>, root: BasicBlock) -> Preorder<'a, 'tcx> {
41 let worklist = vec![root];
45 visited: BitVector::new(mir.basic_blocks().len()),
51 pub fn preorder<'a, 'tcx>(mir: &'a Mir<'tcx>) -> Preorder<'a, 'tcx> {
52 Preorder::new(mir, START_BLOCK)
55 impl<'a, 'tcx> Iterator for Preorder<'a, 'tcx> {
56 type Item = (BasicBlock, &'a BasicBlockData<'tcx>);
58 fn next(&mut self) -> Option<(BasicBlock, &'a BasicBlockData<'tcx>)> {
59 while let Some(idx) = self.worklist.pop() {
60 if !self.visited.insert(idx) {
64 let data = &self.mir[idx];
66 if let Some(ref term) = data.terminator {
67 for &succ in term.successors() {
68 self.worklist.push(succ);
72 return Some((idx, data));
78 fn size_hint(&self) -> (usize, Option<usize>) {
79 // All the blocks, minus the number of blocks we've visited.
80 let remaining = self.mir.basic_blocks().len() - self.visited.count();
82 // We will visit all remaining blocks exactly once.
83 (remaining, Some(remaining))
87 impl<'a, 'tcx> ExactSizeIterator for Preorder<'a, 'tcx> {}
89 /// Postorder traversal of a graph.
91 /// Postorder traversal is when each node is visited after all of it's
92 /// successors, except when the successor is only reachable by a back-edge
106 /// A Postorder traversal of this graph is `D B C A` or `D C B A`
107 pub struct Postorder<'a, 'tcx: 'a> {
109 visited: BitVector<BasicBlock>,
110 visit_stack: Vec<(BasicBlock, Successors<'a>)>
113 impl<'a, 'tcx> Postorder<'a, 'tcx> {
114 pub fn new(mir: &'a Mir<'tcx>, root: BasicBlock) -> Postorder<'a, 'tcx> {
115 let mut po = Postorder {
117 visited: BitVector::new(mir.basic_blocks().len()),
118 visit_stack: Vec::new()
122 let data = &po.mir[root];
124 if let Some(ref term) = data.terminator {
125 po.visited.insert(root);
126 po.visit_stack.push((root, term.successors()));
127 po.traverse_successor();
133 fn traverse_successor(&mut self) {
134 // This is quite a complex loop due to 1. the borrow checker not liking it much
135 // and 2. what exactly is going on is not clear
137 // It does the actual traversal of the graph, while the `next` method on the iterator
138 // just pops off of the stack. `visit_stack` is a stack containing pairs of nodes and
139 // iterators over the sucessors of those nodes. Each iteration attempts to get the next
140 // node from the top of the stack, then pushes that node and an iterator over the
141 // successors to the top of the stack. This loop only grows `visit_stack`, stopping when
142 // we reach a child that has no children that we haven't already visited.
144 // For a graph that looks like this:
157 // The state of the stack starts out with just the root node (`A` in this case);
160 // When the first call to `traverse_sucessor` happens, the following happens:
162 // [(B, [D]), // `B` taken from the successors of `A`, pushed to the
163 // // top of the stack along with the successors of `B`
166 // [(D, [E]), // `D` taken from successors of `B`, pushed to stack
170 // [(E, []), // `E` taken from successors of `D`, pushed to stack
175 // Now that the top of the stack has no successors we can traverse, each item will
176 // be popped off during iteration until we get back to `A`. This yeilds [E, D, B].
178 // When we yield `B` and call `traverse_successor`, we push `C` to the stack, but
179 // since we've already visited `E`, that child isn't added to the stack. The last
180 // two iterations yield `C` and finally `A` for a final traversal of [E, D, B, C, A]
182 let bb = if let Some(&mut (_, ref mut iter)) = self.visit_stack.last_mut() {
183 if let Some(&bb) = iter.next() {
192 if self.visited.insert(bb) {
193 if let Some(term) = &self.mir[bb].terminator {
194 self.visit_stack.push((bb, term.successors()));
201 pub fn postorder<'a, 'tcx>(mir: &'a Mir<'tcx>) -> Postorder<'a, 'tcx> {
202 Postorder::new(mir, START_BLOCK)
205 impl<'a, 'tcx> Iterator for Postorder<'a, 'tcx> {
206 type Item = (BasicBlock, &'a BasicBlockData<'tcx>);
208 fn next(&mut self) -> Option<(BasicBlock, &'a BasicBlockData<'tcx>)> {
209 let next = self.visit_stack.pop();
211 self.traverse_successor();
214 next.map(|(bb, _)| (bb, &self.mir[bb]))
217 fn size_hint(&self) -> (usize, Option<usize>) {
218 // All the blocks, minus the number of blocks we've visited.
219 let remaining = self.mir.basic_blocks().len() - self.visited.count();
221 // We will visit all remaining blocks exactly once.
222 (remaining, Some(remaining))
226 impl<'a, 'tcx> ExactSizeIterator for Postorder<'a, 'tcx> {}
228 /// Reverse postorder traversal of a graph
230 /// Reverse postorder is the reverse order of a postorder traversal.
231 /// This is different to a preorder traversal and represents a natural
232 /// linearization of control-flow.
245 /// A reverse postorder traversal of this graph is either `A B C D` or `A C B D`
246 /// Note that for a graph containing no loops (i.e. A DAG), this is equivalent to
247 /// a topological sort.
249 /// Construction of a `ReversePostorder` traversal requires doing a full
250 /// postorder traversal of the graph, therefore this traversal should be
251 /// constructed as few times as possible. Use the `reset` method to be able
252 /// to re-use the traversal
254 pub struct ReversePostorder<'a, 'tcx: 'a> {
256 blocks: Vec<BasicBlock>,
260 impl<'a, 'tcx> ReversePostorder<'a, 'tcx> {
261 pub fn new(mir: &'a Mir<'tcx>, root: BasicBlock) -> ReversePostorder<'a, 'tcx> {
262 let blocks : Vec<_> = Postorder::new(mir, root).map(|(bb, _)| bb).collect();
264 let len = blocks.len();
273 pub fn reset(&mut self) {
274 self.idx = self.blocks.len();
279 pub fn reverse_postorder<'a, 'tcx>(mir: &'a Mir<'tcx>) -> ReversePostorder<'a, 'tcx> {
280 ReversePostorder::new(mir, START_BLOCK)
283 impl<'a, 'tcx> Iterator for ReversePostorder<'a, 'tcx> {
284 type Item = (BasicBlock, &'a BasicBlockData<'tcx>);
286 fn next(&mut self) -> Option<(BasicBlock, &'a BasicBlockData<'tcx>)> {
287 if self.idx == 0 { return None; }
290 self.blocks.get(self.idx).map(|&bb| (bb, &self.mir[bb]))
293 fn size_hint(&self) -> (usize, Option<usize>) {
294 (self.idx, Some(self.idx))
298 impl<'a, 'tcx> ExactSizeIterator for ReversePostorder<'a, 'tcx> {}