IV36964: SUBOPTIMAL CODE FOR VECTOR LONG LONG ADD

Subscribe

You can track all active APARs for this component.

APAR status

  • Closed as program error.

Error description

  • For the simple test case below,
    extern "C" vector unsigned long long add64(vector unsigned long
    long a,
    vector unsigned long long b)
    {
      return a + b;
    }
    
    Output:
          | 000000           add64
        2|                   a,b,vs34,vs35
        4| 000000 vadduwm    vs32=vs34,vs35
        4| 000004 vaddcuw    vs33=vs34,vs35
        4| 000008 ld         gr3=.+CONSTANT_AREA(gr2,0)
        4| 00000C xxsldwi    vs0=vs33,vs33,1
        4| 000010 lxvdsx     vs1=+CONSTANT_AREA(gr3,0)
        4| 000014 xxland     vs33=vs0,vs1
        4| 000018 vadduwm    vs34=vs32,vs33
        5| 00001C bclr       lr
    
    Compiler could generate a code sequence that replaces xxsldwi +
    xxland with 1 vperm call.
    

Local fix

  • Use the vec_addc and vec_perm builtins.
    

Problem summary

  • USERS AFFECTED:
    Users using -qarch=pwr7 -qaltivec with vector long long types
    may be affected by this issue.
    
    PROBLEM DESCRIPTION:
    The compiler produces inefficient code for vector long long add
    routines.
    

Problem conclusion

  • Fixed vector long long add to generate fewer instructions for
    -qarch=pwr7.
    

Temporary fix

Comments

APAR Information

  • APAR number

    IV36964

  • Reported component name

    XL C/C++ FOR AI

  • Reported component ID

    5725C7200

  • Reported release

    C10

  • Status

    CLOSED PER

  • PE

    NoPE

  • HIPER

    NoHIPER

  • Special Attention

    NoSpecatt

  • Submitted date

    2013-02-19

  • Closed date

    2013-06-17

  • Last modified date

    2013-06-17

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

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

    LI77657

Fix information

  • Fixed component name

    XL C FOR AIX

  • Fixed component ID

    5725C7100

Applicable component levels

  • RC10 PSY U860046

       UP C



Rate this page:

(0 users)Average rating

Add comments

Document information


More support for:

XL C for AIX
Compiler

Software version:

12.1

Reference #:

IV36964

Modified date:

2013-06-17

Translate my page

Machine Translation

Content navigation