LI77191: INCORRECT EVALUATION OF SIZEOF IN TEMPLATES

February 2013 Update for XL C/C++ for Blue Gene/Q, V12.1

APAR status

• Closed as program error.

Error description

• When compiling the test case below, the compiler issues an
  incorrect error message.
  
  The diagnostic refers to this line:
  typedef char staticassert_type[sizeof(Type) == 2 ? 2 : 0]; //
  But this is NOT !!
  indicating that sizeof(Type) is not 2.
  
  The line just above it
  /// char staticassert_var[sizeof(Type) == 2 ? 2 : 0];
  
  is accepted, when uncommented.  If you uncommend line 4,
  and comment line 5 instead, the program compiles and links.
  When you
  run it, the value it returns is 2 (sizeof(Resolver<int>::Type)).
  
  
  ===== COMPILE COMMAND:
  xlC test.cpp
  
  
  ===== TESTCASE:
  $ cat test.cpp
  template <typename T>
  struct Resolver {
      typedef struct { char a[2]; } Type;
  //    char staticassert_var[sizeof(Type) == 2 ? 2 : 0];      //
  This is accepted
      typedef char staticassert_type[sizeof(Type) == 2 ? 2 : 0];
  // But this is NOT !!!
  };
  
  int main()
  {
      return sizeof(Resolver<int>::Type);
  }
  $
  
  
  ===== ACTUAL OUTPUT:
  $ xlC test.cpp
  "test.cpp", line 5.54: 1540-0135 (S) The array bound cannot be
  zero.
  $
  
  ===== EXPECTED OUTPUT:
  Clean compile
  

Local fix

• n/a
  

Problem summary

• USERS AFFECTED:
  The problem can be seen when a sizeof expression is used to
  compute an array bound inside a template definition.
  
  PROBLEM DESCRIPTION:
  The compiler was incorrectly evaluating a sizeof expression
  inside a template definition and reporting an error.
  

Problem conclusion

• The compiler has been fixed to resolve the above issue.
  

Temporary fix

Comments

APAR Information

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

  IV33977

• 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

• RC10 PSN IV33977

     UP06/09/13