LI77421: INEFFICIENT CODE FOR TRIVIAL VECTOR CONSTANTS

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
May 2013 Update for XL C/C++ for Blue Gene/Q, V12.1
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

• The compiler generates in-efficient code for trivial vector
  contants.
  
  eg:
  $ cat test.cpp
  const vector signed int zeros = { 0,0,0,0 };
  
  extern "C" vector signed int vec_zeros()
  {
      return zeros;
  }
  
  $ cat test.lst
  VR's set/used:   --s- ---- ---- ----  ---- ---- ---- ----
      | 000000                           PDEF     vec_zeros
     3|                                  PROC
     5| 000000 ld       E8620008   1     L8
  gr3=.+CONSTANT_AREA(gr2,0)
     5| 000004 lxvd2x   7C401E99   1     VLQD
  vs34=zeros(gr3,0)
     6| 000008 bclr     4E800020   1     BA        lr
  
  $
  
  
  It should be generating code such as:
     21| 000040 xxlxor   F04004D7   1     VXOR      vs34=vs32,vs32
     22| 000044 bclr     4E800020   1     BA        lr
  

Local fix

• N/A
  

Problem summary

• USERS AFFECTED:
  Users who have test cases with trivial vectors of zeros.
  
  PROBLEM DESCRIPTION:
  The compiler generates inefficient code for trivial vector of
  zeros, when this vector is defined as a global variable.
  

Problem conclusion

• The compiler has been fixed so that once the zero vector is
  determined to be stored in the constant area, code is added to
  retrieve the zero vector.
  

Temporary fix

Comments

APAR Information

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

  IV36987

• 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