Qiskit / qiskit / 8909651178

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Commit Message

Add representation of `expr.Var` to `DAGCircuit` (#12204)

* Add representation of `expr.Var` to `DAGCircuit`

This adds basic support for `Var`s to `DAGCircuit`, enabling the base
representation using the same wire structure used for clbits.  This is
known to be an inefficient representation of the dataflow for clbits,
which can be read multiple times without implying an order between those
operations (unlike qubits for which reads and writes are more naturally
linked).  We're using this simpler representation to make a better
initial MVP; optimising the data-flow representation would come as part
of a larger effort within the `DAGCircuit`.

This commit adds support in `DAGCircuit` for:

- representation of `Var` nodes
- appending all operations that might contain `Var` nodes to the DAG and
  updating the wire structure (including control-flow ops and stores)
- equality checking of DAGs with `Var`s (and so enables
  `QuantumCircuit.__eq__` as well)
- `DAGCircuit.copy_empty_like` with `Var`s
- the DAG/circuit converters

The other methods in `DAGCircuit` that might need to be aware of `Var`
nodes will be handled separately.

* Expand test coverage

* Fix copy/paste error

Run Details

127 of 129 new or added lines in 4 files covered. (98.45%)

4 existing lines in 1 file now uncovered.

61492 of 68676 relevant lines covered (89.54%)

217858.21 hits per line