LI78230: -O OPTIMIZES AWAY AN IF CLAUSE

XL C/C++ for Linux Fix Pack 2 (February 2015 Update) for 13.1
XL C/C++ for Linux Fix Pack 1 (October 2014 Update) for 13.1

APAR status

• Closed as program error.

Error description

• When compiling the following test case with -O2, the resulting
  binary leads to an incorrect output:
  
  ===== COMPILE COMMAND:
  xlC_r -qmakedep=gcc -D_AIX51 -D_LARGE_FILES
  -D__NO_XLC_BUILTIN_VA -DOS_LEVEL=710 -D_Packed= -qnotempinc
  -U__unix -q64 -qtbtable=full -qhalt=e -qalias=noansi -qutf -+ -O
  -qfdpr -qstrict -qlibansi -qinlglue -qmaxmem=-1 -DNDEBUG
  -qarch=pwr4 -qtune=balanced -qspill=2560 -qlonglong
  -qalign=natural -qldbl128  -qdebug=RNSSMALL -c -o test.o test.c
  
  xlC_r -o a.out -bcdtors:mbr::s -bweaklocal -q64 -brtl  -bbigtoc
  -lc -lc128 test.o  -lperfstat  -lrt -lwlm -lpthread -lm
  
  ===== TESTCASE:
  $ cat test.c
  #include <stdio.h>
  #include <stdlib.h>
  #include <unistd.h>
  
  typedef unsigned short P_CHAR;
  
  static bool isStandardChar(P_CHAR &c)
  {
          printf ("-->isStandardChar (%d: %c) a: %d z: %d
  \n",(P_CHAR) c, (P_CHAR) c, (P_CHAR)u'a', (P_CHAR)u'z');
      if ( (c >= (P_CHAR) u'a') && (c <= (P_CHAR) u'z') )
      {
          return true;
      }
      else if ( (c >= (P_CHAR) u'A') && (c <= (P_CHAR) u'Z') )
      {
          return true;
      }
      else if ( (c >= (P_CHAR) u'0') && (c <= (P_CHAR) u'9') )
      {
          return true;
      }
      else if ( ( c == u'_') || ( c == u':') ||
                ( c == u'/') || ( c == u'-') ||
                ( c == u';') )
      {
          return true;
      }
  
      return false;
  }
  
  int main(int argc, char** argv)
  {
      P_CHAR c = 117;
      if ( isStandardChar(c) )
          printf ("%c is a StandardChar\n", (P_CHAR) c);
          else
          printf ("%c is NOT a StandardChar\n", (P_CHAR) c);
  
      return 0;
  }
  $
  
  
  ===== ACTUAL OUTPUT:
  $ ./restKrn
  -->isStandardChar (117: u) a: 97 z: 122
  u is NOT a StandardChar
  $
  
  ===== EXPECTED OUTPUT:
  $ ./restKm
  -->isStandardChar (117: u) a: 97 z: 122
  u is a StandardChar
  

Local fix

• Change
  
  typedef unsigned short P_CHAR;
  
  to
  
  typedef unsigned int P_CHAR;
  
  as a workaround.
  

Problem summary

• USERS AFFECTED:
  Users who perform a range check of alphabetical ASCII
  characters (a-z,A-Z) in their code may be affected by this
  issue.
  
  PROBLEM DESCRIPTION:
  The compiler optimizes out an IF clause under specific
  circumstances whenever a char is checked for the range of
  alphabetical ASCII characters (a-z,A-Z).
  This occured because a parameter passed was mangled without
  restoring to next parameter.
  

Problem conclusion

• The compiler has been fixed to properly check the range of
  alphabetical ASCII characters (a-z,A-Z).
  

Temporary fix

Comments

APAR Information

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

  IV62591

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

Fix information

• Fixed component name

  XL C/C++ FOR LI

• Fixed component ID

  5725C7300

Applicable component levels

• RD10 PSN IV62591

     UP06/09/13