IV91651: INLINING CAUSING INCORRECT ARRAY POINTER CALCULATION

XL C/C++ for AIX, V13.1.3.3 Fix Pack (December 2016)
XL C/C++ for AIX, V13.1.3.4 Fix Pack (April 2017)
XL C/C++ for AIX, V13.1.3.5 Fix Pack (July 2018)
XL C/C++ for AIX, V13.1.3.6 Fix Pack (May 2019)

APAR status

• Closed as program error.

Error description

• When inlining is enabled, a simple array memory address
  calculation is done incorrectly, giving an incorrect array
  element position.
  
  The issue is related to calculating an element position of an
  initialized array inside a struct using synatx:
  
      &array[0] + elem    (GOOD)
  
      versus
  
      array + elem        (BAD)
  
  Arrays outside of a struct work OK.
  
  
  
     === TEST CASE ===
  
  #include <stdio.h>
  
  struct X { int a[7]; } x = { {1, 4, 9, 16, 25, 36, 49} };
  
  int *safe(int (&array)[7], int elem)
  {
      return &array[0] + elem;
  }
  
  int *unsafe(int (&array)[7], int elem)
  {
      return array + elem;
  }
  
  int main() {
      printf("safe=%d, unsafe=%d\n",
      *safe(x.a,4),
      *unsafe(x.a,4));
  
      return (safe(x.a,4) - unsafe(x.a,4));
  }
  
  
  
  $ xlC -qinline test.cpp
  $ ./a.out
  safe=25, unsafe=4
  $
  

Local fix

• Do not use inlining.
  

Problem summary

• USERS AFFECTED:
  Users with array pointer arithmetic using function inlining.
  PROBLEM DESCRIPTION:
  Problem with inlining function with array pointer arithmetic on
  return expression (e.x.  'return array + elem').
  
  USERS AFFECTED:
  Users with array pointer arithmetic using function inlining.
  

Problem conclusion

• The problem has been fixed.
  

Temporary fix

Comments

APAR Information

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

  IV90070

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

Fix information

• Fixed component name

  XL C/C++ FOR AI

• Fixed component ID

  5725C7200

Applicable component levels