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Rollup merge of #136082 - Zalathar:iter-nodes, r=oli-obk

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Incorporate `iter_nodes` into `graph::DirectedGraph`

This helper method iterates over all node IDs in the dense range `0..num_nodes`.

In practice, we have a lot of graph-algorithm code that already assumes that nodes are densely numbered, by using `num_nodes` to allocate per-node indexed data structures. So I don't think this is actually a substantial change to the de-facto semantics of `graph::DirectedGraph`.

---

Resolves a FIXME from #135481.
This commit is contained in:
Guillaume Gomez 2025-01-27 15:38:28 +01:00 • committed by GitHub
commit f29979aebe
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6 changed files with 18 additions and 23 deletions
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2
compiler/rustc_mir_transform/src/coverage/counters.rs
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@ -10,14 +10,12 @@ use rustc_index::bit_set::DenseBitSet;
use rustc_middle::mir::coverage::{CounterId, CovTerm, Expression, ExpressionId, Op};
use crate::coverage::counters::balanced_flow::BalancedFlowGraph;
use crate::coverage::counters::iter_nodes::IterNodes;
use crate::coverage::counters::node_flow::{
CounterTerm, NodeCounters, make_node_counters, node_flow_data_for_balanced_graph,
};
use crate::coverage::graph::{BasicCoverageBlock, CoverageGraph};
mod balanced_flow;
mod iter_nodes;
mod node_flow;
mod union_find;

2
compiler/rustc_mir_transform/src/coverage/counters/balanced_flow.rs
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@ -20,8 +20,6 @@ use rustc_data_structures::graph::reversed::ReversedGraph;
use rustc_index::Idx;
use rustc_index::bit_set::DenseBitSet;
use crate::coverage::counters::iter_nodes::IterNodes;
/// A view of an underlying graph that has been augmented to have “balanced flow”.
/// This means that the flow (execution count) of each node is equal to the
/// sum of its in-edge flows, and also equal to the sum of its out-edge flows.

16
compiler/rustc_mir_transform/src/coverage/counters/iter_nodes.rs
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@ -1,16 +0,0 @@
use rustc_data_structures::graph;
use rustc_index::Idx;
pub(crate) trait IterNodes: graph::DirectedGraph {
/// Iterates over all nodes of a graph in ascending numeric order.
/// Assumes that nodes are densely numbered, i.e. every index in
/// `0..num_nodes` is a valid node.
///
/// FIXME: Can this just be part of [`graph::DirectedGraph`]?
fn iter_nodes(
&self,
) -> impl Iterator<Item = Self::Node> + DoubleEndedIterator + ExactSizeIterator {
(0..self.num_nodes()).map(<Self::Node as Idx>::new)
}
}
impl<G: graph::DirectedGraph> IterNodes for G {}

1
compiler/rustc_mir_transform/src/coverage/counters/node_flow.rs
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@ -11,7 +11,6 @@ use rustc_index::bit_set::DenseBitSet;
use rustc_index::{Idx, IndexSlice, IndexVec};
use rustc_middle::mir::coverage::Op;
use crate::coverage::counters::iter_nodes::IterNodes;
use crate::coverage::counters::union_find::UnionFind;
#[cfg(test)]