Port the count_ops method in QuantumCircuit to Rust

crates/circuit/src/circuit_data.rs

@@ -31,6 +31,7 @@ use pyo3::types::{IntoPyDict, PyDict, PyList, PySet, PyTuple, PyType};
 use pyo3::{import_exception, intern, PyTraverseError, PyVisit};
 
 use hashbrown::{HashMap, HashSet};
+use indexmap::IndexMap;
 use smallvec::SmallVec;
 
 import_exception!(qiskit.circuit.exceptions, CircuitError);
@@ -983,6 +984,22 @@ impl CircuitData {
         self.param_table.clear();
     }
 
+    /// Counts the number of times each operation is used in the circuit.
+    ///
+    /// # Parameters
+    /// - `self` - A mutable reference to the CircuitData struct.
+    ///
+    /// # Returns
+    /// An IndexMap containing the operation names as keys and their respective counts as values.
+    pub fn count_ops(&self) -> IndexMap<&str, usize, ::ahash::RandomState> {
+        let mut ops_count: IndexMap<&str, usize, ::ahash::RandomState> = IndexMap::default();
+        for instruction in &self.data {
+            *ops_count.entry(instruction.op.name()).or_insert(0) += 1;
+        }
+        ops_count.par_sort_by(|_k1, v1, _k2, v2| v2.cmp(v1));
+        ops_count
+    }
+
     // Marks this pyclass as NOT hashable.
     #[classattr]
     const __hash__: Option<Py<PyAny>> = None;

qiskit/circuit/quantumcircuit.py

@@ -3516,10 +3516,8 @@ def count_ops(self) -> "OrderedDict[Instruction, int]":
         Returns:
             OrderedDict: a breakdown of how many operations of each kind, sorted by amount.
         """
-        count_ops: dict[Instruction, int] = {}
-        for instruction in self._data:
-            count_ops[instruction.operation.name] = count_ops.get(instruction.operation.name, 0) + 1
-        return OrderedDict(sorted(count_ops.items(), key=lambda kv: kv[1], reverse=True))
+        ops_dict = self._data.count_ops()
+        return OrderedDict(ops_dict)
 
     def num_nonlocal_gates(self) -> int:
         """Return number of non-local gates (i.e. involving 2+ qubits).

releasenotes/notes/port-countops-method-3ad362c20b13182c.yaml

@@ -0,0 +1,5 @@
+---
+features_circuits:
+  - |
+    The :meth:`~.QuantumCircuit.count_ops` method in :class:`.QuantumCircuit` 
+    has been re-written in Rust. It now runs between 3 and 9 times faster.