⚡️ Improve Performance of getNqubits

[ystade]

Description

This PR improves the performance of getNqubits by avoiding to constructing a set of qubits via getUsedQubits in most cases (except for compound operations).

This improvement was suggested here in PR 624 of QMAP.

Checklist:

• The pull request only contains commits that are focused and relevant to this change.
• I have added appropriate tests that cover the new/changed functionality.
• I have updated the documentation to reflect these changes.
• I have added entries to the changelog for any noteworthy additions, changes, fixes or removals.
• I have added migration instructions to the upgrade guide (if needed).
• The changes follow the project's style guidelines and introduce no new warnings.
• The changes are fully tested and pass the CI checks.
• I have reviewed my own code changes.

[ystade]

The CI will throw an error in this test.

This is actually a bug not related to this change and must be treated in the parsing. It should not be possible to construct a gate where control and target qubits overlap.

[burgholzer]

This is actually a bug not related to this change and must be treated in the parsing. It should not be possible to construct a gate where control and target qubits overlap.

This is definitely a bug. Or at least a badly written test that has not been detected due to the lack of sanity checks. Would you mind submitting a PR that adds such checks and corrects the test?

Changes are probably necessary in the following places:

• core/src/ir/operations/StandardOperation.cpp

  Lines 212 to 238 in 3e39a9a

  	StandardOperation::StandardOperation(const Control control, const Qubit target,
  	const OpType g,
  	const std::vector<fp>& params)
  	: StandardOperation(target, g, params) {
  	controls.insert(control);
  	}
  	StandardOperation::StandardOperation(const Control control, const Targets& targ,
  	const OpType g,
  	const std::vector<fp>& params)
  	: StandardOperation(targ, g, params) {
  	controls.insert(control);
  	}
  	StandardOperation::StandardOperation(const Controls& c, const Qubit target,
  	const OpType g,
  	const std::vector<fp>& params)
  	: StandardOperation(target, g, params) {
  	controls = c;
  	}
  	StandardOperation::StandardOperation(const Controls& c, const Targets& targ,
  	const OpType g,
  	const std::vector<fp>& params)
  	: StandardOperation(targ, g, params) {
  	controls = c;
  	}

• core/src/ir/operations/SymbolicOperation.cpp

  Lines 286 to 312 in 3e39a9a

  	SymbolicOperation::SymbolicOperation(const Control control, const Qubit target,
  	const OpType g,
  	const std::vector<SymbolOrNumber>& params)
  	: SymbolicOperation(target, g, params) {
  	controls.insert(control);
  	}
  	SymbolicOperation::SymbolicOperation(const Control control, const Targets& targ,
  	const OpType g,
  	const std::vector<SymbolOrNumber>& params)
  	: SymbolicOperation(targ, g, params) {
  	controls.insert(control);
  	}
  	SymbolicOperation::SymbolicOperation(const Controls& c, const Qubit target,
  	const OpType g,
  	const std::vector<SymbolOrNumber>& params)
  	: SymbolicOperation(target, g, params) {
  	controls = c;
  	}
  	SymbolicOperation::SymbolicOperation(const Controls& c, const Targets& targ,
  	const OpType g,
  	const std::vector<SymbolOrNumber>& params)
  	: SymbolicOperation(targ, g, params) {
  	controls = c;
  	}

The addControl methods already check for duplicates, so it should not be an issue there.

[codecov]

Codecov Report

Attention: Patch coverage is 50.00000% with 2 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
src/ir/operations/CompoundOperation.cpp	0.0%	2 Missing ⚠️

📢 Thoughts on this report? Let us know!

[burgholzer]

@ystade I think this might need one additional test for the ci to be green