coverage: Prefer to visit nodes whose predecessors have been visited

compiler/rustc_mir_transform/src/coverage/counters.rs

@@ -9,7 +9,7 @@ use rustc_index::bit_set::BitSet;
 use rustc_middle::mir::coverage::{CounterId, CovTerm, Expression, ExpressionId, Op};
 use tracing::{debug, debug_span, instrument};
 
-use crate::coverage::graph::{BasicCoverageBlock, CoverageGraph, TraverseCoverageGraphWithLoops};
+use crate::coverage::graph::{BasicCoverageBlock, CoverageGraph, ReadyFirstTraversal};
 
 #[cfg(test)]
 mod tests;
@@ -236,23 +236,12 @@ impl<'a> CountersBuilder<'a> {
 
         // Traverse the coverage graph, ensuring that every node that needs a
         // coverage counter has one.
-        //
-        // The traversal tries to ensure that, when a loop is encountered, all
-        // nodes within the loop are visited before visiting any nodes outside
-        // the loop.
-        let mut traversal = TraverseCoverageGraphWithLoops::new(self.graph);
-        while let Some(bcb) = traversal.next() {
+        for bcb in ReadyFirstTraversal::new(self.graph) {
             let _span = debug_span!("traversal", ?bcb).entered();
             if self.bcb_needs_counter.contains(bcb) {
                 self.make_node_counter_and_out_edge_counters(bcb);
             }
         }
-
-        assert!(
-            traversal.is_complete(),
-            "`TraverseCoverageGraphWithLoops` missed some `BasicCoverageBlock`s: {:?}",
-            traversal.unvisited(),
-        );
     }
 
     /// Make sure the given node has a node counter, and then make sure each of