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Remove separate RPO traversal

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This integrates the preorder and postorder traversals into one.
This commit is contained in:
Mark Rousskov 2021-05-08 19:50:50 -04:00
parent 7d12767dc5
commit 8991002644
1 changed files with 7 additions and 17 deletions
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24
compiler/rustc_data_structures/src/graph/dominators/mod.rs
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@ -4,7 +4,6 @@
//! "Linear-Time Algorithms for Dominators and Related Problems",
//! ftp://ftp.cs.princeton.edu/techreports/2005/737.pdf
use super::iterate::reverse_post_order;
use super::ControlFlowGraph;
use rustc_index::vec::{Idx, IndexVec};
use std::cmp::Ordering;
@ -12,38 +11,26 @@
#[cfg(test)]
mod tests;
pub fn dominators<G: ControlFlowGraph>(graph: G) -> Dominators<G::Node> {
let start_node = graph.start_node();
let rpo = reverse_post_order(&graph, start_node);
dominators_given_rpo(graph, &rpo)
}
struct PreOrderFrame<Node, Iter> {
node: Node,
iter: Iter,
}
fn dominators_given_rpo<G: ControlFlowGraph>(graph: G, rpo: &[G::Node]) -> Dominators<G::Node> {
let start_node = graph.start_node();
assert_eq!(rpo[0], start_node);
pub fn dominators<G: ControlFlowGraph>(graph: G) -> Dominators<G::Node> {
// compute the post order index (rank) for each node
let mut post_order_rank = IndexVec::from_elem_n(0, graph.num_nodes());
for (index, node) in rpo.iter().rev().cloned().enumerate() {
post_order_rank[node] = index;
}
let mut visited = BitSet::new_empty(graph.num_nodes());
let mut parent: IndexVec<usize, Option<usize>> = IndexVec::from_elem_n(None, rpo.len());
let mut parent: IndexVec<usize, Option<usize>> = IndexVec::from_elem_n(None, graph.num_nodes());
let mut stack = vec![PreOrderFrame { node: 0, iter: graph.successors(graph.start_node()) }];
visited.insert(graph.start_node());
let mut pre_order_to_real = Vec::with_capacity(rpo.len());
let mut pre_order_to_real = Vec::with_capacity(graph.num_nodes());
let mut real_to_pre_order: IndexVec<G::Node, Option<usize>> =
IndexVec::from_elem_n(None, graph.num_nodes());
pre_order_to_real.push(graph.start_node());
real_to_pre_order[graph.start_node()] = Some(0);
let mut idx = 1;
let mut post_order_idx = 0;
'recurse: while let Some(frame) = stack.last_mut() {
while let Some(successor) = frame.iter.next() {
@ -57,6 +44,9 @@ fn dominators_given_rpo<G: ControlFlowGraph>(graph: G, rpo: &[G::Node]) -> Domin
continue 'recurse;
}
}
post_order_rank[pre_order_to_real[frame.node]] = post_order_idx;
post_order_idx += 1;
stack.pop();
}