LI75853: QIPA LEVEL 2 AND QHOT LEVEL 1 LEAD TO HANG

June 2011 Update for XL C/C++ for Linux, V10.1
XL C/C++ for Linux Fix Pack 8 (January 2014 Update) for 10.1
January 2011 Update for XL C/C++ for Linux, V10.1
January 2012 Update for XL C/C++ for Linux, V10.1
July 2012 Update for XL C/C++ for Linux, V10.1

APAR status

• Closed as program error.

Error description

• When trying to compile a small test case using -qhot and/or
  -qipa, compilation hangs. It appears that during
  compilation, the compiler becomes trapped within an infinite
  loop.
  
  Test case hangs in the same location when the following
  options are used:
   1) -qhot=level=1
   2) -qhot=level=0 -qipa=level=2
  
  
  ========== Test Case:
  void
  rounds(unsigned short *a,unsigned short *b,unsigned int r)
  {
    unsigned short ai, bi, aandb, axorb, carry, z;
    int i;
  
    while (r > 0) {
      /* add x[0....] into x[1....]: */
      carry = 0;
      for (i = 0;i < 32;++i) {
        ai = a[i];
        bi = b[i];
        aandb = ai & bi;
        axorb = ai ^ bi;
        b[i] = axorb ^ carry;
        carry &= axorb;
        carry |= aandb;
      }
  
      /*rotate x[0....] upwards by 11 bits, and swap 0.0.. with
  0.1..:*/
      i = 0;
      ai = a[i];
      do {
        z = ((ai >> 4) & 0x0f0f) | ((ai & 0x0f0f) << 4);
        i = (i + 11) & 31;
        ai = a[i];
        a[i] = z;
      } while (i != 0);
  
      /*xor x[1....] into x[0....], and swap 1...0 with 1...1:*/
      for (i = 0;i < 32;++i) {
        bi = b[i];
        a[i] ^= bi;
        b[i] = ((bi >> 1) & 0x5555) | ((bi & 0x5555) << 1);
      }
  
      --r;
    }
  }
  =====================
  

Local fix

• Compile with:
  "-qhot=level=0" or
  "-qhot=level=0 -qipa=level=0" or
  "-qhot=level=0 -qipa=level=1"
  
  
  Another workaround is to either increase or decrease the limit
  on the second 'for' loop. Ensure that the limit is not 32.
  

Problem summary

• PROBLEM DESCRIPTION:
  There is an infinite loop in the compiler when attempting to
  build the Acyclic DDG, used by loop fusion.
  
  USERS AFFECTED:
  Any users using -qhot.
  

Problem conclusion

• Problem should be fixed.
  

Temporary fix

Comments

APAR Information

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

  IZ86837

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

Fix information

• Fixed component name

  XL C/C++ SLES10

• Fixed component ID

  5724U8300

Applicable component levels

• RA10 PSN IZ86837

     UP06/09/13