LI77871: INCORRECT IF STATEMENT LOGIC WITH -O3

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
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

• ERROR DESCRIPTION:Ø
  In a larger program,  the following statement fails with -O3
  when the "if" statement is coded:
   if (memcmp(rr->getLastName().getData(),"Brown",5) != 0)
     allBrown = false;
  
  But it works with -O3 if the "if" statement is coded:
   if (memcmp(rr->getLastName().getData(),"Brown",5) != 0) {
     allBrown = false;
     CPPUNIT_ASSERT (allBrown == true);  // or anything else on
  this line, "cout << ..."for example.
   }
  
  Somehow the "allBrown = false;" statement is executed even when
  the "if" condition is false when only a single statement
  follows the "if" with -O3.
  

Local fix

• LOCAL FIX:Ø
  Change program source or use xlC 12.1.0.0.
  

Problem summary

• PROBLEM DESCRIPTION: Incorrect code generation for IF
  statements using results of memcmp library function.
  
  USERS AFFECTED: Any using XLC/C++ with inlining enabled and -O2
  and up, with the code pattern described in the problem
  description.
  

Problem conclusion

• Fixed an erroneous optimization of if statements using memcmp
  as the condition.
  

Temporary fix

Comments

APAR Information

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

  IV44027

• 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