[Cbc] UndefinedBehaviorSanitizer error in OsiPresolvewhen casting Status

[Tobias Stengel]

Did you fix the errors upstream? If not: can you post a list of the errors you found so others can apply the fixes locally and/or John (or whoever else is allowed to do it) can fix them in trunk?

I ran GCC undefinedBehaviourSanitizer some time ago and found some issues which are partly fixed upstream, but missed the one with the Status enum.
I am interested how you fixed the integer overflow in the gomory cut generator as John’s fix in trunk just moved the problem a few lines down causing us to use „-gomory off“  all the time as we are using CBC as a libary and can not risk CBC killing or corrupting the process it runs in. This does not improve performance…

Tobias

Von: Cbc [mailto:cbc-bounces at coin-or.org] Im Auftrag von Petter Strandmark
Gesendet: Samstag, 21. Oktober 2017 17:09
An: cbc at list.coin-or.org
Betreff: [Cbc] UndefinedBehaviorSanitizer error in OsiPresolvewhen casting Status

I am compiling and running Cbc with Clang’s UndefinedBehaviorSanitizer. I have been able to fix several errors, but a more tricky one is the following. This line sometimes incorrecly casts an enum:

<https://github.com/coin-or/Osi/blob/master/Osi/src/Osi/OsiPresolve.cpp#L505>
https://github.com/coin-or/Osi/blob/master/Osi/src/Osi/OsiPresolve.cpp#L505

The original enum looks like:
  /*! \brief Enum for status of various sorts

    Matches CoinWarmStartBasis::Status and adds superBasic. Most code that
    converts between CoinPrePostsolveMatrix::Status and
    CoinWarmStartBasis::Status will break if this correspondence is broken.

    superBasic is an unresolved problem: there's no analogue in
    CoinWarmStartBasis::Status.
  */
  enum Status {
    isFree = 0x00,
    basic = 0x01,
    atUpperBound = 0x02,
    atLowerBound = 0x03,
    superBasic = 0x04
  };

and the target enum looks like:

  enum Status {
    isFree = 0x00,      ///< Nonbasic free variable
    basic = 0x01,       ///< Basic variable
    atUpperBound = 0x02, ///< Nonbasic at upper bound
    atLowerBound = 0x03      ///< Nonbasic at lower bound
  };

UndefinedBehaviorSanitizer stops the execution because the status is superBasic.

The question is, what is the correct course of action in that case?

Petter

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