LI76282: INCORRECT OUTPUT WITH -O3 AND -QLIBANSI

XL C/C++ for Linux Fix Pack 9 (August 2013 Update) for 11.1
July 2011 Update for XL C/C++ for Linux, V11.1
October 2011 Update for XL C/C++ for Linux, V11.1
June 2012 Update for XL C/C++ for Linux, V11.1
October 2012 Update for XL C/C++ for Linux, V11.1
XL C/C++ for Linux Fix Pack 8 (June 2013 Update) for 11.1

APAR status

• Closed as program error.

Error description

• The following testcase produces incorrect output with "-O3
  -qlibansi":
  
  1. Testcase:
  
  /************ test.c ************/
  
  #include <stdio.h>
  
  void foo(void *ws) {
    *(int *)ws = 0;
  }
  
  int main()
  {
     int *            testInString;
     int *            testOutString;
     unsigned char    eq;
     testInString = (int *)malloc(6);
     testOutString = (int *)malloc(6);
     bzero(testInString,6);
     bzero(testOutString,6);
     memcpy(testInString,"HELLO",5);
     memcpy(testOutString,"HELLO",5);
     eq = (unsigned char)(!memcmp(testInString,testOutString,5));
     foo(testInString);
     if (!eq) printf("WRONG!!!! Should not print.\n");
     else printf("Correct!\n");
     return(1);
  
  }
  
  /******** end of test.c ***********/
  
  2. Compile with: xlc_r test.c -O3 -q64 -qlibansi
  
  3. Run:
  
  ./a.out
  
  
  Actual Output:
  
  WRONG!!!! Should not print.
  
  
  
  Expected output:
  
  Correct!
  

Local fix

• 1. Lower optimization level from -O3 to -O2
  2. Do not use option -qlibansi
  

Problem summary

• Incorrect code generation for memcmp operations with -O3 and
  -qlibansi
  

Problem conclusion

• Fixed a case where memcmp calls could be optimized incorrectly
  with -qlibansi.
  

Temporary fix

Comments

APAR Information

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

  IZ95269

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

Fix information

• Fixed component name

  XL C/C++ FOR LI

• Fixed component ID

  5724X1400

Applicable component levels

• RB10 PSN IZ95269

     UP06/09/13