IV56792: OPTIMIZATION CAUSES EXE TO HANG

XL C for AIX Fix Pack 8 (March 2014 PTF) for 12.1
XL C/C++ for AIX Fix Pack 8 (March 2014 PTF) for 12.1
XL C/C++ for AIX Fix Pack 11 (February 2015 PTF) for 12.1
XL C for AIX Fix Pack 12 (May 2015 PTF) for 12.1
XL C/C++ for AIX Fix Pack 12 (May 2015 PTF) for 12.1
XL C/C++ for AIX Fix Pack 13 (August 2015 Update) for 12.1
XL C/C++ for AIX Fix Pack 14 (December 2015 Update) for 12.1
XL C for AIX Fix Pack 15 (April 2016 Update) for 12.1
XL C/C++ for AIX Fix Pack 15 (April 2016 Update) for 12.1
XL C for AIX Fix Pack 16 (July 2016 Update) for 12.1
XL C/C++ for AIX Fix Pack 16 (July 2016 Update) for 12.1
XL C/C++ for AIX Fix Pack 17 (November 2016 Update) for 12.1
XL C for AIX Fix Pack 17 (November 2016 Update) for 12.1
XL C for AIX Fix Pack 18 (February 2017 Update) for 12.1
XL C/C++ for AIX Fix Pack 18 (February 2017 Update) for 12.1
XL C for AIX Fix Pack 19 (August 2017 Update) for 12.1
XL C/C++ for AIX Fix Pack 19 (August 2017 Update) for 12.1
XL C for AIX Fix Pack 20 (March 2018 Update) for 12.1
XL C/C++ for AIX Fix Pack 20 (March 2018 Update) for 12.1
XL C for AIX Fix Pack 9 (July 2014 PTF) for 12.1
XL C/C++ for AIX Fix Pack 9 (July 2014 PTF) for 12.1
XL C for AIX Fix Pack 10 (October 2014 PTF) for 12.1
XL C/C++ for AIX Fix Pack 10 (October 2014 PTF) for 12.1
XL C for AIX Fix Pack 11 (February 2015 PTF) for 12.1
XL C for AIX Fix Pack 13 (August 2015 Update) for 12.1
XL C for AIX Fix Pack 14 (December 2015 Update) for 12.1
XL C/C++ for AIX Fix Pack 21 (January 2019 Update) for 12.1
XL C for AIX Fix Pack 21 (January 2019 Update) for 12.1

APAR status

• Closed as program error.

Error description

• When compiling the following two test cases with -O2, the
  resulting binaries hang at runtime.
  
  ===== COMPILE COMMAND:
  xlc_r -q64 -O2 test1.c
  xlc_r -q64 -O2 test2.c
  
  ===== TESTCASE:
  $ cat test1.c
  int main (void)
  {
      long x, x64 = (long)0xFFFFFFFFFFFFFFFFuLL;
      long andval = 0;
      do { x = __ldarx(&x64); } while (!__stdcx(&x64, (x &
  andval)));
      return (x64 == 0);
  }
  $
  
  $ cat test2.c
  int main (void)
  {
      int x, x32 = (int)0xFFFFFFFFu;
      int andval = 0;
      do { x = __lwarx(&x32); } while (!__stwcx(&x32, (x &
  andval)));
      return (x32 == 0);
  }
  $
  
  
  
  ===== ACTUAL OUTPUT:
  The resulting binaries hang at runtime
  
  
  ===== EXPECTED OUTPUT:
  The resulting binaries should not hang at runtime.
  

Local fix

• N/A
  

Problem summary

• USERS AFFECTED:
  Clients who use high optimization(-O2 and above) with programs
  that use store conditional return value which depends on load
  and reserve that may be discarded may be affected by this
  issue.
  
  PROBLEM DESCRIPTION:
  The optimization that optimizes the load and reserve
  instruction away causes some exes to hang.
  

Problem conclusion

• The compiler has been fixed to prevent load and reserve from
  being discarded.
  

Temporary fix

Comments

APAR Information

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

  IV52591

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

Fix information

• Fixed component name

  XL C FOR AIX

• Fixed component ID

  5725C7100

Applicable component levels