Fix basis_count checking in ConsolidateBlocks (#13463)

The ConsolidateBlocks pass was ported to rust in #13368 and as part of
that implementation a small behavior difference between the rust and
python interfaces was causing the pass to not work correctly with non-CX
gates. The internal 2q decomposer interface stores a sentinel string for
the kak gate which is used to tell the python space constructor use the
python defined gate object. However in the pass code we weren't
factoring this difference in, and for non-CX gates we were evaluating
the basis count as the number of gates with that sentinel value name
(which is almost always zero) and this was preventing the pass from
consolidating many blocks that should have been. This commit fixes this
issue by taking the name from python space and passing it through to the
rust portion of the code and using that for the comparison.

Fixes #13459

crates/accelerate/src/consolidate_blocks.rs

@@ -54,11 +54,12 @@ const MAX_2Q_DEPTH: usize = 20;
 
 #[allow(clippy::too_many_arguments)]
 #[pyfunction]
-#[pyo3(signature = (dag, decomposer, force_consolidate, target=None, basis_gates=None, blocks=None, runs=None))]
+#[pyo3(signature = (dag, decomposer, basis_gate_name, force_consolidate, target=None, basis_gates=None, blocks=None, runs=None))]
 pub(crate) fn consolidate_blocks(
     py: Python,
     dag: &mut DAGCircuit,
     decomposer: &TwoQubitBasisDecomposer,
+    basis_gate_name: &str,
     force_consolidate: bool,
     target: Option<&Target>,
     basis_gates: Option<HashSet<String>>,
@@ -125,7 +126,7 @@ pub(crate) fn consolidate_blocks(
             let inst = dag.dag()[*node].unwrap_operation();
             block_qargs.extend(dag.get_qargs(inst.qubits));
             all_block_gates.insert(*node);
-            if inst.op.name() == decomposer.gate_name() {
+            if inst.op.name() == basis_gate_name {
                 basis_count += 1;
             }
             if !is_supported(

qiskit/transpiler/passes/optimization/consolidate_blocks.py

@@ -109,6 +109,7 @@ def run(self, dag):
         consolidate_blocks(
             dag,
             self.decomposer._inner_decomposer,
+            self.decomposer.gate.name,
             self.force_consolidate,
             target=self.target,
             basis_gates=self.basis_gates,

test/python/transpiler/test_consolidate_blocks.py

@@ -18,8 +18,17 @@
 import numpy as np
 from ddt import ddt, data
 
-from qiskit.circuit import QuantumCircuit, QuantumRegister, IfElseOp, Gate
-from qiskit.circuit.library import U2Gate, SwapGate, CXGate, CZGate, UnitaryGate
+from qiskit.circuit import QuantumCircuit, QuantumRegister, IfElseOp, Gate, Parameter
+from qiskit.circuit.library import (
+    U2Gate,
+    SwapGate,
+    CXGate,
+    CZGate,
+    UnitaryGate,
+    SXGate,
+    XGate,
+    RZGate,
+)
 from qiskit.converters import circuit_to_dag
 from qiskit.quantum_info.operators import Operator
 from qiskit.quantum_info.operators.measures import process_fidelity
@@ -590,6 +599,73 @@ def test_no_kak_gates_in_preset_pm(self, opt_level):
         tqc = pm.run(qc)
         self.assertEqual(ref_tqc, tqc)
 
+    def test_non_cx_basis_gate(self):
+        """Test a non-cx kak gate is consolidated correctly."""
+        qc = QuantumCircuit(2)
+        qc.cz(0, 1)
+        qc.x(0)
+        qc.h(1)
+        qc.z(1)
+        qc.t(1)
+        qc.h(0)
+        qc.t(0)
+        qc.cz(1, 0)
+        qc.sx(0)
+        qc.sx(1)
+        qc.cz(0, 1)
+        qc.sx(0)
+        qc.sx(1)
+        qc.cz(1, 0)
+        qc.x(0)
+        qc.h(1)
+        qc.z(1)
+        qc.t(1)
+        qc.h(0)
+        qc.t(0)
+        qc.cz(0, 1)
+
+        consolidate_pass = ConsolidateBlocks(basis_gates=["sx", "x", "rz", "cz"])
+        res = consolidate_pass(qc)
+        self.assertEqual({"unitary": 1}, res.count_ops())
+        self.assertEqual(Operator.from_circuit(qc), Operator(res.data[0].operation.params[0]))
+
+    def test_non_cx_target(self):
+        """Test a non-cx kak gate is consolidated correctly."""
+        qc = QuantumCircuit(2)
+        qc.cz(0, 1)
+        qc.x(0)
+        qc.h(1)
+        qc.z(1)
+        qc.t(1)
+        qc.h(0)
+        qc.t(0)
+        qc.cz(1, 0)
+        qc.sx(0)
+        qc.sx(1)
+        qc.cz(0, 1)
+        qc.sx(0)
+        qc.sx(1)
+        qc.cz(1, 0)
+        qc.x(0)
+        qc.h(1)
+        qc.z(1)
+        qc.t(1)
+        qc.h(0)
+        qc.t(0)
+        qc.cz(0, 1)
+
+        phi = Parameter("phi")
+        target = Target(num_qubits=2)
+        target.add_instruction(SXGate(), {(0,): None, (1,): None})
+        target.add_instruction(XGate(), {(0,): None, (1,): None})
+        target.add_instruction(RZGate(phi), {(0,): None, (1,): None})
+        target.add_instruction(CZGate(), {(0, 1): None, (1, 0): None})
+
+        consolidate_pass = ConsolidateBlocks(target=target)
+        res = consolidate_pass(qc)
+        self.assertEqual({"unitary": 1}, res.count_ops())
+        self.assertEqual(Operator.from_circuit(qc), Operator(res.data[0].operation.params[0]))
+
 
 if __name__ == "__main__":
     unittest.main()