LI76649: OPTIMIZATION CAUSES INCORRECT OUTPUT

XL C/C++ for Linux Fix Pack 9 (August 2013 Update) for 11.1
June 2012 Update for XL C/C++ for Linux, V11.1
October 2012 Update for XL C/C++ for Linux, V11.1
XL C/C++ for Linux Fix Pack 8 (June 2013 Update) for 11.1

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 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

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