IZ95594: PERFORMANCE DROP WITH -O2 -Q64

March 2011 PTF for XL C/C++ Enterprise Edition for AIX, V9.0
March 2011 PTF for XL C Enterprise Edition for AIX, V9.0
July 2011 PTF for XL C/C++ Enterprise Edition for AIX, V9.0
December 2011 PTF for XL C/C++ Enterprise Edition for AIX, V9.0
March 2012 PTF for XL C Enterprise Edition for AIX, V9.0
March 2012 PTF for XL C/C++ Enterprise Edition for AIX, V9.0
July 2011 PTF for XL C Enterprise Edition for AIX, V9.0
December 2011 PTF for XL C Enterprise Edition for AIX, V9.0

APAR status

• Closed as program error.

Error description

• A preformance drop is observed when compiling programs with -q64
  and -O2 (or higher) that contain loops with integer
  counters.
  

Local fix

• Compile with -q32 instead of -q64.
  

Problem summary

• PROBLEM DESCRIPTION:
  Poor performance for loops with 32-bit int control variables
  with -q64 at -O2 and up.
  
  USERS AFFECTED:
  Users with programs with for/do loops controlled by 32-bit
  integer variables concerned with performance.
  

Problem conclusion

• Fixed bug inhibiting loop optimization for loops with 32-bit
  integer control variables with -q64.
  

Temporary fix

Comments

APAR Information

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

  IZ87268

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

Fix information

• Fixed component name

  XL C AIX

• Fixed component ID

  5724S7000

Applicable component levels