LI77578: IMPROVEMENTS TO MEMSET GENERATED CODE

XL C/C++ for Blue Gene/Q Fix Pack 12 (May 2015 Update) for 12.1
XL C/C++ for Blue Gene/Q Fix Pack 14 (May 2016 Update) for 12.1
XL C/C++ for Blue Gene/Q Fix Pack 15 (October 2017 Update) for 12.1
XL C/C++ for Blue Gene/Q Fix Pack 5 (August 2013 Update) for 12.1
XL C/C++ for Blue Gene/Q Fix Pack 6 (November 2013 Update) for 12.1
XL C/C++ for Blue Gene/Q Fix Pack 7 (February 2014 Update) for 12.1
XL C/C++ for Blue Gene/Q Fix Pack 8 (May 2014 Update) for 12.1
XL C/C++ for Blue Gene/Q Fix Pack 9 (August 2014 Update) for 12.1
XL C/C++ for Blue Gene/Q Fix Pack 10 (November 2014 Update) for 12.1
XL C/C++ for Blue Gene/Q Fix Pack 11 (February 2015 Update) for 12.1
XL C/C++ for Blue Gene/Q Fix Pack 13 (August 2015 Update) for 12.1

APAR status

• Closed as program error.

Error description

• Compiler adds improvements to memset generated code.
  

Local fix

• N/A
  

Problem summary

• inefficient code being generated for memset.  There are several
  issues 1) The constant area is used to hold the splatted value
  of the character 2) we don't always widen the stores to 8 bytes
  3) there are unnecessary multiply instructions generated by
  widening
  

Problem conclusion

• The test in macro expansion to decide whether to use 4 byte or
  8 byte stores was incorrect.   Having macro expansion generate
  8 byte stores means that widening is no longer involved.  Also,
  instead of putting the constant into the constant area, let the
  normal macro expansion code decide how to manifest the
  constant.
  

Temporary fix

Comments

APAR Information

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

  IV48060

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

Fix information

• Fixed component name

  XL C/C++ FOR BG

• Fixed component ID

  5799AG100

Applicable component levels