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//! Topological order of blocks, according to the dominator tree.
use crate::dominator_tree::DominatorTree;
use crate::entity::EntitySet;
use crate::ir::{Block, Layout};
use alloc::vec::Vec;
/// Present blocks in a topological order such that all dominating blocks are guaranteed to be visited
/// before the current block.
///
/// There are many topological orders of the blocks in a function, so it is possible to provide a
/// preferred order, and the `TopoOrder` will present blocks in an order that is as close as possible
/// to the preferred order.
pub struct TopoOrder {
/// Preferred order of blocks to visit.
preferred: Vec<Block>,
/// Next entry to get from `preferred`.
next: usize,
/// Set of visited blocks.
visited: EntitySet<Block>,
/// Stack of blocks to be visited next, already in `visited`.
stack: Vec<Block>,
}
impl TopoOrder {
/// Create a new empty topological order.
pub fn new() -> Self {
Self {
preferred: Vec::new(),
next: 0,
visited: EntitySet::new(),
stack: Vec::new(),
}
}
/// Clear all data structures in this topological order.
pub fn clear(&mut self) {
self.preferred.clear();
self.next = 0;
self.visited.clear();
self.stack.clear();
}
/// Reset and initialize with a preferred sequence of blocks. The resulting topological order is
/// guaranteed to contain all of the blocks in `preferred` as well as any dominators.
pub fn reset<Blocks>(&mut self, preferred: Blocks)
where
Blocks: IntoIterator<Item = Block>,
{
self.preferred.clear();
self.preferred.extend(preferred);
self.next = 0;
self.visited.clear();
self.stack.clear();
}
/// Get the next block in the topological order.
///
/// Two things are guaranteed about the blocks returned by this function:
///
/// - All blocks in the `preferred` iterator given to `reset` will be returned.
/// - All dominators are visited before the block returned.
pub fn next(&mut self, layout: &Layout, domtree: &DominatorTree) -> Option<Block> {
self.visited.resize(layout.block_capacity());
// Any entries in `stack` should be returned immediately. They have already been added to
// `visited`.
while self.stack.is_empty() {
match self.preferred.get(self.next).cloned() {
None => return None,
Some(mut block) => {
// We have the next block in the preferred order.
self.next += 1;
// Push it along with any non-visited dominators.
while self.visited.insert(block) {
self.stack.push(block);
match domtree.idom(block) {
Some(idom) => {
block = layout.inst_block(idom).expect("idom not in layout")
}
None => break,
}
}
}
}
}
self.stack.pop()
}
}
#[cfg(test)]
mod tests {
use super::*;
use crate::cursor::{Cursor, FuncCursor};
use crate::dominator_tree::DominatorTree;
use crate::flowgraph::ControlFlowGraph;
use crate::ir::{Function, InstBuilder};
use core::iter;
#[test]
fn empty() {
let func = Function::new();
let cfg = ControlFlowGraph::with_function(&func);
let domtree = DominatorTree::with_function(&func, &cfg);
let mut topo = TopoOrder::new();
assert_eq!(topo.next(&func.layout, &domtree), None);
topo.reset(func.layout.blocks());
assert_eq!(topo.next(&func.layout, &domtree), None);
}
#[test]
fn simple() {
let mut func = Function::new();
let block0 = func.dfg.make_block();
let block1 = func.dfg.make_block();
{
let mut cur = FuncCursor::new(&mut func);
cur.insert_block(block0);
cur.ins().jump(block1, &[]);
cur.insert_block(block1);
cur.ins().jump(block1, &[]);
}
let cfg = ControlFlowGraph::with_function(&func);
let domtree = DominatorTree::with_function(&func, &cfg);
let mut topo = TopoOrder::new();
topo.reset(iter::once(block1));
assert_eq!(topo.next(&func.layout, &domtree), Some(block0));
assert_eq!(topo.next(&func.layout, &domtree), Some(block1));
assert_eq!(topo.next(&func.layout, &domtree), None);
}
}