Fix barrier unrolling to preserve multi-qubit barrier statements#295
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TheGupta2012 merged 5 commits intomainfrom Mar 11, 2026
Merged
Fix barrier unrolling to preserve multi-qubit barrier statements#295TheGupta2012 merged 5 commits intomainfrom
TheGupta2012 merged 5 commits intomainfrom
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Support barrier merge/split operations in transformer, fix visitor handling of physical qubits, and add corresponding tests. Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
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WalkthroughBarrier unrolling now preserves multi‑qubit barrier directives as single statements. The visitor expands barrier ranges into explicit qubit indices; the transformer maps each qubit to device indices and rewrites qubit references. Tests and CHANGELOG updated to expect consolidated, comma‑separated barrier statements. Changes
Sequence DiagramsequenceDiagram
participant Parser as Visitor / Parser
participant Barrier as Barrier Statement
participant Transformer as Transformer
participant Emitter as Emitter / Output
Parser->>Barrier: parse barrier (identifiers, ranges, indexed ids)
Barrier-->>Parser: expanded qubit list (ranges -> explicit indices)
Parser->>Transformer: pass single expanded_barrier
Transformer->>Transformer: iterate qubits -> map to device indices
Transformer->>Transformer: rewrite qubit refs to __PYQASM_QUBITS__[…]
Transformer-->>Emitter: emit single consolidated barrier statement
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Actionable comments posted: 2
🤖 Prompt for all review comments with AI agents
Verify each finding against the current code and only fix it if needed.
Inline comments:
In `@src/pyqasm/transformer.py`:
- Line 508: The long call that passes _qubit_str.name, ind.value,
qubit_register_offsets, global_qreg_size_map exceeds the line-length limit;
split the arguments across multiple lines (or assign a temporary
tuple/list/kwargs) so each line stays under the formatter max length, e.g.,
break the argument list into one-per-line inside the enclosing parentheses where
this call occurs (look for the call site involving _qubit_str.name and ind.value
in transformer.py) and ensure you keep proper commas and indentation to satisfy
the linter.
- Around line 495-499: The current code mutates Identifier.name to embed slice
syntax (the block setting _qubit_id.name to "__PYQASM_QUBITS__[...]" when
handling barrier ranges), which breaks downstream consumers; instead, replace
that mutation by constructing an IndexedIdentifier whose index is a
RangeDefinition built from IntegerLiteral nodes (use IndexedIdentifier,
RangeDefinition, IntegerLiteral) so the AST retains a proper range node; modify
the branch that handles consolidate_qubits=True and unroll_barriers=False (the
branches that set _qubit_id.name for the three cases: full slice, open-ended
slice, and start:end slice) to create and assign an IndexedIdentifier containing
a RangeDefinition with appropriate IntegerLiteral start/end (or omitted for
open-ended), rather than changing Identifier.name.
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CHANGELOG.mdsrc/pyqasm/transformer.pysrc/pyqasm/visitor.pytests/qasm2/test_operations.pytests/qasm3/test_barrier.pytests/qasm3/test_device_qubits.py
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Building circuit composer on account. This update is needed from pyqasm to support the backend. So linking that issue here. This PR will close the issue because the bulk of the issue is being actively worked on elsewhere, and this is the only pyqasm related change needed (as far as I can tell) |
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Actionable comments posted: 1
🤖 Prompt for all review comments with AI agents
Verify each finding against the current code and only fix it if needed.
Inline comments:
In `@src/pyqasm/transformer.py`:
- Around line 503-511: The loop that remaps indices (iterating _qubit_ind and
then ind) assumes each ind is an IntegerLiteral and accesses ind.value, which
fails for RangeDefinition nodes (e.g., q[0:2]); update the logic in
consolidate_qubit_registers (used when consolidate_qubits=True and
unroll_barriers=False) to guard against non-literal nodes: before accessing
ind.value, check the node type (e.g., isinstance(ind, IntegerLiteral)); if it's
an IntegerLiteral, call _get_pyqasm_device_qubit_index(_qubit_str.name,
ind.value, qubit_register_offsets, global_qreg_size_map) and assign back to
ind.value; if it's a RangeDefinition (or other range node), explicitly handle it
by remapping its bounds/contained indices to device indices (iterate its
start..end or child indices and replace those elements with remapped
IntegerLiteral nodes or update the range representation accordingly) instead of
directly accessing .value; apply the same guarded handling to the equivalent
loops used for measurement and reset remapping that call
_get_pyqasm_device_qubit_index.
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src/pyqasm/transformer.pysrc/pyqasm/visitor.py
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Actionable comments posted: 2
🤖 Prompt for all review comments with AI agents
Verify each finding against the current code and only fix it if needed.
Inline comments:
In `@src/pyqasm/visitor.py`:
- Around line 782-799: The consolidation logic incorrectly expands barrier
operands by comparing register names in barrier_qubits (using eq.name.name and
_global_qreg_size_map) which collapses aliases and over-consumes adjacent
operands; instead, for each original operand (op_qubit) call the expansion
routine (_get_op_bits or equivalent used upstream) and append that operand's
concrete list of qubit bits to consolidated_qubits, advancing expanded_idx by
the number of bits produced for that operand rather than scanning by name;
update the loop around expanded_idx/op_qubit to use the per-operand expanded
list and remove name-based comparisons (eq.name.name and qubit_name) so
constructs like "let a = q; barrier a;" and mixed slices "barrier q[0:2], q[3]"
expand correctly.
In `@tests/visualization/test_mpl_draw.py`:
- Around line 132-134: The test uses _check_fig(circ, fig) which only inspects
ax.texts and therefore misses barrier rendering (barriers are drawn as
collections/patches in src/pyqasm/printer.py); update the test to assert
directly on the Matplotlib artists created by mpl_draw by checking
fig.axes[0].collections and fig.axes[0].patches for the expected barrier artists
(or modify _check_fig to include those checks), or alternatively convert this
test into an mpl_image_compare style test to verify the rendered barrier
visually.
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src/pyqasm/visitor.pytests/qasm3/test_device_qubits.pytests/visualization/test_mpl_draw.py
Replace name-based comparisons in _expand_barrier_ranges with per-operand expansion counting via _get_op_bits, fixing incorrect behavior for aliases and mixed same-register slices. Add barrier-specific artist assertions to test_draw_barriers. Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
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| if not self._unroll_barriers: | ||
| if self._consolidate_qubits: | ||
| consolidated_qubits = self._expand_barrier_ranges(barrier, barrier_qubits) |
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There seems to be an edge case here -
from pyqasm import loads
qasm3_string = """OPENQASM 3.0;
include "stdgates.inc";
qubit[2] q;
qreg q2[3];
barrier q2;
barrier q, q2;
"""
mod = loads(qasm3_string)
mod.unroll(unroll_barriers = False, consolidate_qubits = True)
mod.unroll(unroll_barriers = True, consolidate_qubits = True)raises -
ERROR:pyqasm: Error at line 5, column 4 in QASM file
>>>>>> barrier __PYQASM_QUBITS__[2:];
...
File ~/Desktop/qBraid/repos/pyqasm/src/pyqasm/visitor.py:849, in QasmVisitor._visit_barrier(self, barrier)
839 for transform_map, size_map in zip(
840 reversed(self._function_qreg_transform_map), reversed(self._function_qreg_size_map)
841 ):
842 barrier.qubits = (
843 Qasm3Transformer.transform_function_qubits( # type: ignore [assignment]
844 barrier,
(...) 847 )
848 )
--> 849 barrier_qubits = self._get_op_bits(barrier, qubits=True)
850 unrolled_barriers = []
851 max_involved_depth = 0
File ~/Desktop/qBraid/repos/pyqasm/src/pyqasm/visitor.py:340, in QasmVisitor._get_op_bits(self, operation, qubits, function_qubit_sizes)
335 if function_qubit_sizes is None:
336 err_msg = (
337 f"Missing {'qubit' if qubits else 'clbit'} register declaration "
338 f"for '{reg_name}' in {type(operation).__name__}"
339 )
--> 340 raise_qasm3_error(
341 err_msg,
342 error_node=operation,
343 span=operation.span,
344 )
345 # we are trying to replace the qubits inside a nested function
346 assert function_qubit_sizes is not None
File ~/Desktop/qBraid/repos/pyqasm/src/pyqasm/exceptions.py:137, in raise_qasm3_error(message, err_type, error_node, span, raised_from)
135 if raised_from:
136 raise err_type(message) from raised_from
--> 137 raise err_type(message)
ValidationError: Missing qubit register declaration for '__PYQASM_QUBITS__[2:]' in QuantumBarrierSome weird behaviour where the commands work individually , and with switched order -
# works individually and in this order
mod.unroll(unroll_barriers = True, consolidate_qubits = True)
mod.unroll(unroll_barriers = False, consolidate_qubits = True)but fail with -
# fails
mod.unroll(unroll_barriers = False, consolidate_qubits = True)
mod.unroll(unroll_barriers = True, consolidate_qubits = True)
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Edit : seems like this is a consolidate_qubits error , not particularly related to the barriers. Invoking unroll twice raises it
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Summary
barrier q[0], q[1], q[2]) instead of splitting into individual per-qubit barriersSummary by CodeRabbit