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Clean up dominators_given_rpo #81338

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Jan 25, 2021
Merged

Clean up dominators_given_rpo #81338

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16 changes: 5 additions & 11 deletions compiler/rustc_data_structures/src/graph/dominators/mod.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -8,7 +8,6 @@
use super::iterate::reverse_post_order;
use super::ControlFlowGraph;
use rustc_index::vec::{Idx, IndexVec};
use std::borrow::BorrowMut;
use std::cmp::Ordering;

#[cfg(test)]
Expand All @@ -20,22 +19,17 @@ pub fn dominators<G: ControlFlowGraph>(graph: G) -> Dominators<G::Node> {
dominators_given_rpo(graph, &rpo)
}

fn dominators_given_rpo<G: ControlFlowGraph + BorrowMut<G>>(
mut graph: G,
rpo: &[G::Node],
) -> Dominators<G::Node> {
let start_node = graph.borrow().start_node();
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);

// compute the post order index (rank) for each node
let mut post_order_rank: IndexVec<G::Node, usize> =
(0..graph.borrow().num_nodes()).map(|_| 0).collect();
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 immediate_dominators: IndexVec<G::Node, Option<G::Node>> =
(0..graph.borrow().num_nodes()).map(|_| None).collect();
let mut immediate_dominators = IndexVec::from_elem_n(None, graph.num_nodes());
immediate_dominators[start_node] = Some(start_node);

let mut changed = true;
Expand All @@ -44,7 +38,7 @@ fn dominators_given_rpo<G: ControlFlowGraph + BorrowMut<G>>(

for &node in &rpo[1..] {
let mut new_idom = None;
for pred in graph.borrow_mut().predecessors(node) {
for pred in graph.predecessors(node) {
if immediate_dominators[pred].is_some() {
// (*) dominators for `pred` have been calculated
new_idom = Some(if let Some(new_idom) = new_idom {
Expand Down