🐛 Index out of range error when checking for overlapping qubit indices in operands of expression

[TooMuchDakka]

Environment information

• OS: Windows 10 x64
• C++ Compiler: clang 17.0.3
• MQT-Core: 3.0.3
• MQT-Syrec: Commit #3475265

Description

When attempting to synthesize the SyReC program:

module main(out output(2), out a(2), out b(2), out c(2))
  output ^= (a ^ (b ^ c))

an index-out-of-range exception is thrown in SyrecSynthesis::checkRepeats() when checking for overlapping qubit indices in the operands of the right-hand side expression of the assignment.

Expected behavior

The SyReC program should be synthesizable without errors.

How to Reproduce

1. Perform a build from source of mqt.syrec
2. Launch the syrec-editor python application and copy the SyReC circuit from the bug description into the code editor
3. Select either the cost or line aware synthesis radio button and then press the 'Build' button

[TooMuchDakka]

Another index-out-of-range error is thrown when trying to perform a line-aware synthesis of the assignment:

module main(out output(4), in a(4), in b(4), in c(4), in foldLeft(1))
  if foldLeft then
	output ^= (((b ^ c) ^ a) ^ c)
  else
	output ^= (c ^ (a ^ (b ^ c)))
  fi foldLeft

While the issue identified with the SyReC program in the description of this bug was an out of range index access in SyrecSynthesis::checkRepeats, the issue with the program above is an out of range index access when trying to generate the intermediate assignments.

[TooMuchDakka]

Another index-out-of-range error is thrown when trying to perform a line-aware synthesis of the assignment:

module main(out output(4), in a(4), in b(4), in c(4), in foldLeft(1))
  if foldLeft then
	output ^= (((b ^ c) ^ a) ^ c)
  else
	output ^= (c ^ (a ^ (b ^ c)))
  fi foldLeft

While the issue identified with the SyReC program in the description of this bug was an out of range index access in SyrecSynthesis::checkRepeats, the issue with the program above is an out of range index access when trying to generate the intermediate assignments.

PR #281 only partially fixes this issue since the another out of range index access is triggered in the `LineAwareSynthesis::processStatement(const Statement::ptr& statement) when trying to synthesis the provided the SyReC program of the thus this issue is reopened.