LI71622: INCORRECT OUTPUT FOR POST DECREMENT/INCREMENT OPTIMIZATION

Latest updates for XL C/C++ Advanced Edition V7 for Linux

APAR status

• Closed as program error.

Error description

• Compiler generates incorrect operand value for post
  decrement/increment operations in while/for/if statements.
  
  ___________________
  Test Case for while statement:
  int main()
  {
  
  int id=6;
  int sum=0;
  
  while(id--)
  {
  for (int i=0; i<id; i++)
  sum+=i;
  printf("sum=%d, id=%d\n", sum, id);
  }
  }
  
  Expected output:
  sum=10, id=5
  sum=16, id=4
  sum=19, id=3
  sum=20, id=2
  sum=20, id=1
  sum=20, id=0
  
  Actual output:
  sum=15, id=5
  sum=25, id=4
  sum=31, id=3
  sum=34, id=2
  sum=35, id=1
  sum=35, id=0
  
  
  __________________________
  
  
  
  
  
  
  Testcase for if statement.
  int main()
  {
  
  int id=6;
  int sum=0;
  
  if(id--)
  {
  for (int i=0; i<id; i++)
  sum+=i;
  printf("sum=%d, id=%d\n", sum, id);
  }
  }
  
  Expected output:
  sum=10, id=5
  
  Actual output:
  sum=15, id=5
  ___________________________________________
  

Local fix

• Avoid using whie(id--) or if (id--) statements.
  Or printf id's value before comparison statement in the for
  loop.
  

Problem summary

• Compiler incorrectly treats postfix increment/decrement
  operations in while and for loop's conditional statement as
  compiler generated statement and generates incorrect operand
  value.
  

Problem conclusion

• Fixed the optimizatin process for postfix increment/decrement
  operations in while and for loop's conditional statement by
  creating a querry function to check if a statement is truely a
  compiler generated statement. Also fix a similar problem in the
  if-else statement.
  

Temporary fix

Comments

APAR Information

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

  IY81172

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

Fix information

• Fixed component name

  XL C/C++ RHEL4

• Fixed component ID

  5724K7720

Applicable component levels

• R701 PSN IY81172

     UP06/09/13