LI77230: ?: METHOD PARAMETER OPTIMIZING AWAY VALID CODE

XL C/C++ for Blue Gene/Q Fix Pack 12 (May 2015 Update) for 12.1
XL C/C++ for Blue Gene/Q Fix Pack 14 (May 2016 Update) for 12.1
XL C/C++ for Blue Gene/Q Fix Pack 15 (October 2017 Update) for 12.1
February 2013 Update for XL C/C++ for Blue Gene/Q, V12.1
May 2013 Update for XL C/C++ for Blue Gene/Q, V12.1
XL C/C++ for Blue Gene/Q Fix Pack 5 (August 2013 Update) for 12.1
XL C/C++ for Blue Gene/Q Fix Pack 6 (November 2013 Update) for 12.1
XL C/C++ for Blue Gene/Q Fix Pack 7 (February 2014 Update) for 12.1
XL C/C++ for Blue Gene/Q Fix Pack 8 (May 2014 Update) for 12.1
XL C/C++ for Blue Gene/Q Fix Pack 9 (August 2014 Update) for 12.1
XL C/C++ for Blue Gene/Q Fix Pack 10 (November 2014 Update) for 12.1
XL C/C++ for Blue Gene/Q Fix Pack 11 (February 2015 Update) for 12.1
XL C/C++ for Blue Gene/Q Fix Pack 13 (August 2015 Update) for 12.1

APAR status

• Closed as program error.

Error description

• Compiling with -O2 and inlining enabled, with a ?: conditional
  as a template function parameter, is causing valid code to be
  optimized away, resulting in invalid code behaviour.  In the
  example below, invalid stack data is accessed, and output is
  incorrect:
  
  
      ====  TEST CASE  ====
  
  #include <iostream>
  
  struct MyStruct
  {
      template <typename T>
      static void print( T const & x )
      {
          std::cout << x;
      }
  };
  
  int main(int argc, char *argv[])
  {
    MyStruct::print(argc == 1?"test1":"test2");
  }
  
  
  $ xlC -q64 -O2 apar.cpp
  $ ./a.out | od -c
  0000000  º Ü 017 þ à Ý ð \r º Ü 017 þ à   Ý ð  \r
  0000020
  $
  $ ./a.out | od -x
  0000000  badc 0ffe e0dd f00d badc 0ffe e0dd f00d
  0000020
  $
  

Local fix

• - Disable inlining
  - Convert ?: conditional into an IF statement
  

Problem summary

• PROBLEM DESCRIPTION:
  Processing of the ?: ternary operator is ignoring the memory
  location of the result, leading to incorrect code and
  behaviour.
  
  USERS AFFECTED:
  Users of the ?: ternary operator, the << operator, and
  optimization.
  

Problem conclusion

• The issue has been corrected.
  

Temporary fix

Comments

APAR Information

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

  IV31404

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

Fix information

• Fixed component name

  XL C/C++ FOR BG

• Fixed component ID

  5799AG100

Applicable component levels