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LI76649: OPTIMIZATION CAUSES INCORRECT OUTPUT

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You can track all active APARs for this component.

APAR status

  • Closed as program error.

Error description

  • Consider the following testcase:
    
    //////////////// test.cpp ///////////////////
    extern "C" int printf(const char *, ...);
    
    struct Date {
      Date(int i) : i_(i) { }
      friend inline Date foo(Date date, int secs);
      Date& operator +=(int secs);
      int i_;
    };
    
    inline Date foo(Date date, int secs) { return date += secs; }
    
    Date& Date::operator+=(int secs) {
      i_ += secs;
      return *this;
    }
    
    int main() {
      Date now = Date(42);
      foo(now, 56);
      printf("%d\n", now.i_);
    }
    /////////////////////////////////////////////
    
    Compile with optimization turned OFF:
    
    $xlC test.cpp
    $./a.out
    42  // correct
    
    Compile with optimization turned ON:
    $xlC -O test.cpp
    $./a.out
    98  // incorrect
    

Local fix

  • Do not turn on optimization
    

Problem summary

  • Front-end failed to create a temporary to latch an argument
    when inlining.
    

Problem conclusion

  • The fix is safe and the correct means of resolving the problem.
    

Temporary fix

Comments

APAR Information

  • APAR number

    LI76649

  • Reported component name

    XL C/C++ FOR LI

  • Reported component ID

    5724X1400

  • Reported release

    B10

  • Status

    CLOSED PER

  • PE

    NoPE

  • HIPER

    NoHIPER

  • Special Attention

    NoSpecatt / Xsystem

  • Submitted date

    2012-02-06

  • Closed date

    2012-02-06

  • Last modified date

    2012-02-06

  • APAR is sysrouted FROM one or more of the following:

    IV10507

  • APAR is sysrouted TO one or more of the following:

Fix information

  • Fixed component name

    XL C/C++ FOR LI

  • Fixed component ID

    5724X1400

Applicable component levels

  • RB10 PSY

       UP



Document information

More support for: XL C/C++ for Linux

Software version: B10

Reference #: LI76649

Modified date: 06 February 2012