Consider removing `pyqir_0_6_compatibility` code

[Kartik Singhal]

We explicitly require pyqir 0.8.2 at

pytket-qir/setup.py

Line 49 in 6b500b8

 "pyqir == 0.8.2", 

So the bit below and other pyqir_0_6_compatibility code is unneeded.

pytket-qir/pytket/qir/conversion/api.py

Lines 88 to 129 in 6b500b8

     if pyqir_0_6_compatibility: 
         if len(circ.c_registers) > 1: 
             raise ValueError( 
                 """The qir optimised for pyqir 0.6 can only contain 
 one classical register""" 
             ) 
  
         initial_result = str(populated_module.module.ir())  # type: ignore 
  
         initial_result = ( 
             initial_result.replace("entry_point", "EntryPoint") 
             .replace("num_required_qubits", "requiredQubits") 
             .replace("num_required_results", "requiredResults") 
         ) 
  
         def keep_line(line: str) -> bool: 
             return ( 
                 ("@__quantum__qis__read_result__body" not in line) 
                 and ("@set_one_bit_in_reg" not in line) 
                 and ("@reg2var" not in line) 
                 and ("@read_bit_from_reg" not in line) 
                 and ("@set_all_bits_in_reg" not in line) 
             ) 
  
         result = "\n".join(filter(keep_line, initial_result.split("\n"))) 
  
         # replace the use of the removed register variable with i64 0 
         result = result.replace("i64 %0", "i64 0") 
  
         for _ in range(10): 
             result = result.replace("\n\n\n\n", "\n\n") 
  
         bitcode = pyqir.Module.from_ir(pyqir.Context(), result).bitcode  # type: ignore 
  
         if qir_format == QIRFormat.BINARY: 
             return bitcode  # type: ignore 
         elif qir_format == QIRFormat.STRING: 
             return result  # type: ignore 
         else: 
             assert not "unsupported return type"  # type: ignore 
  
     else: 

[Kartik Singhal]

@cqc-melf any objections? I can go ahead and remove this dead code if you agree.

[cqc-melf]

We have added this in the past because we wanted to be compatible with older versions used on your side, if you don't need this it can be removed. Are you using now 0.8.x as well?

[Kartik Singhal]

Yes, we are. There is no support for PyQIR below 0.8.2 in the backend compiler, AFAIK.

Just to confirm, @peter-campora do you think old versions are still in use and may require compatibility with pytket-qir?

Update (2023-08-15): We agreed that it can be removed.

[cqc-melf]

solved by #66