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10657 :: gensym redeclaration

• dlesnoff (orginal) [2023-11-19T22:49:45+01:00] view original

  I have a strange error with the following program:

  import sequtils
  
  proc luDecomposition(n: int) =
    # Créer des matrices L et U
    var lower, upper: seq[seq[float]] = newSeqWith(n, newSeq[float](n))
  
  # Exemple d'utilisation
  let n = 3
  luDecomposition(n)
  Run

  
  Hint: used config file '/home/kolmogorov/.choosenim/toolchains/nim-2.0.0/config/nim.cfg' [Conf]
  Hint: used config file '/home/kolmogorov/.choosenim/toolchains/nim-2.0.0/config/config.nims' [Conf]
  ............................................................................
  CC: lu_factorisation.nim
  /home/kolmogorov/.cache/nim/lu_factorisation_d/@mlu_factorisation.nim.c: In function ‘luDecomposition__lu95factorisation_u3’:
  /home/kolmogorov/.cache/nim/lu_factorisation_d/@mlu_factorisation.nim.c:176:45: error: redeclaration of ‘resultX60gensym0_’ with no linkage
    176 |         tySequence__Is9bsejK6Dzx0wAHnaSKL3Q resultX60gensym0_;
        |                                             ^~~~~~~~~~~~~~~~~
  /home/kolmogorov/.cache/nim/lu_factorisation_d/@mlu_factorisation.nim.c:174:45: note: previous declaration of ‘resultX60gensym0_’ with type ‘tySequence__Is9bsejK6Dzx0wAHnaSKL3Q’
    174 |         tySequence__Is9bsejK6Dzx0wAHnaSKL3Q resultX60gensym0_;
        |                                             ^~~~~~~~~~~~~~~~~
  /home/kolmogorov/.cache/nim/lu_factorisation_d/@mlu_factorisation.nim.c:180:12: error: redeclaration of ‘newLenX60gensym0_’ with no linkage
    180 |         NI newLenX60gensym0_;
        |            ^~~~~~~~~~~~~~~~~
  /home/kolmogorov/.cache/nim/lu_factorisation_d/@mlu_factorisation.nim.c:179:12: note: previous declaration of ‘newLenX60gensym0_’ with type ‘NI’ {aka ‘long int’}
    179 |         NI newLenX60gensym0_;
        |            ^~~~~~~~~~~~~~~~~
  Error: execution of an external compiler program 'gcc -c  -w -fmax-errors=3 -pthread   -I/home/kolmogorov/.choosenim/toolchains/nim-2.0.0/lib -I/home/kolmogorov -o /home/kolmogorov/.cache/nim/lu_factorisation_d/@mlu_factorisation.nim.c.o /home/kolmogorov/.cache/nim/lu_factorisation_d/@mlu_factorisation.nim.c' failed with exit code: 1
  Run

  Could you tell me what is the cause of the error (Is this a double reference issue?). What would be the correct way to initialize matrices here?

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• sky_khan (orginal) [2023-11-19T23:10:59+01:00] view original

  Your code is kinda ambiguous, not clear if you want to create two seperate sequences or two references to same sequence. Still, seems like a compiler bug to me. I mean, it should be caught at nim compilation phase.

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• dlesnoff (orginal) [2023-11-20T09:04:04+01:00] view original

  Thanks! I want to create two separate sequences. I guess this would be more clearer for the compiler:

  var (lower, upper) = (newSeqWith(n, newSeq[float](n)), newSeqWith(n, newSeq[float](n)))
  Run

  Before I raise an issue in the Nim repository, I would like to understand this inconsistent behavior. Why does the following code works when declared at the global level and not when declared inside a procedure?

  var lower, upper = newSeqWith(n, newSeq[float](n))
  Run

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• sky_khan (orginal) [2023-11-20T13:00:52+01:00] view original

  I dont know much about compiler internals but it may be related to optimization, I think. Global references are kept until exit so they're kinda const regarding to variable lifetime. Inside procedures compiler needs to keep track of assignments and refcounts and fails. Thats just a guess, I may be wrong.

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