Qiskit / qiskit / 17325698704

88%

Build Type

push

github

Committed by web-flow

Commit Message

Add custom `DAGCircuit.__deepcopy__` implementation (#14965)

Previously we were relying on the pickling behaviour.  This was
desperately slow, and gets slower over time as more of our data is Rust
native and need to be serialised to and from Python in order to interact
with pickle.

Instead, we can use the `Clone` implementation of `StableGraph`, which
preserves node and edge ids (including holes), then only thread through
the deepcopy nature to the few parts of the data model where we still
store Python objects.  In casual testing, this sped up a microbenchmark:

```python
import copy
from qiskit.converters import circuit_to_dag
from qiskit.circuit.library import quantum_volume

qv = quantum_volume(100, 100, seed=1).decompose()
dag = circuit_to_dag(qv)
%timeit copy.deepcopy(dag)
```

from about 1.05s to 6ms on my machine.

This is directly relevant for the performance of `optimization_level=3`,
which needs to deepcopy as part of its `MinimumPoint` check in the
optimisation loop.

Run Details

47 of 51 new or added lines in 3 files covered. (92.16%)

61 existing lines in 6 files now uncovered.

91061 of 103009 relevant lines covered (88.4%)

481688.38 hits per line