Transpiler eliminates classical condition for optimization_level 3 #6016
Description
Information
- Qiskit Terra version:
- 0.17.0.dev0+83eb665
- Python version:
- 3.9.1 (default, Dec 11 2020, 06:28:49) [Clang 10.0.0 ]
- Operating system:
- Darwin
What is the current behavior?
Circuits with feed-forward logic are incorrectly transpiled for optimization levels >0
Steps to reproduce the problem
from qiskit import execute, QuantumCircuit, QuantumRegister, ClassicalRegister
from qiskit import transpile
from qiskit.transpiler import CouplingMap
from qiskit.converters import dag_to_circuit
circ = QuantumCircuit()
registers = [
QuantumRegister(1,name='qr_data'),
QuantumRegister(1,name='qr_anci'),
ClassicalRegister(1,name='cr_data'),
ClassicalRegister(1,name='cr_anci'),
]
for regs in registers:
circ.add_register(regs)
circ.h(0)
circ.cx(0,1)
circ.measure(1,1)
circ.h(0).c_if(registers[3],1)
# make coupling maps
CMap = CouplingMap().from_ring(12)
CMap.add_physical_qubit(12)
CMap.add_edge(11,12)
CMap.add_edge(12,5)
CMap.make_symmetric()
def callback(**kwargs):
print(kwargs['pass_'])
print(dag_to_circuit(kwargs['dag']))
transpile_opts = {
'optimization_level': 3,
'callback': callback,
'coupling_map': CMap,
'basis_gates': ['cx', 'id', 'u1', 'u2', 'u3']
}
circ_transpiled = transpile(circ,**transpile_opts)
circ_transpiled.draw()What is the expected behavior?
The condition on the last h gate is preserved when transpiler optimization level 3 is run. Looking through the output of the callback function it is dropped by the consolidate blocks pass
Suggested solutions
Examine consolidate blocks section of transpiler (identified by @mtreinish )