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LI78467: INEFFICIENT VEC_SPLATS WHEN LOADING FROM MEMORY

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APAR status

  • Closed as program error.

Error description

  • vec_splats for float, int/unsigned int and short/unsigned short
    are inefficient when loading from memory.
    
    Consider the following testcase:
    
    vector float splatFloat(float *in)
    {
       return vec_splats(*in);
    }
    
    xlC generates:
    
         | 000000                           PDEF
    splatFloat(float *)
         | 000000                           AKA
    splatFloat__FPf
        9|                                  PROC      in,gr3
       11| 000020 lfs      C0030000   1     LFS
    vs0=(float)(gr3,0)
       11| 000024 xscvdpsp F0000424   1     XCVDPSP   vs0=vs0
       11| 000028 xxspltw  F0400291   1     VSPLTW    vs34=vs0,0
       12| 00002C bclr     4E800020   1     BA        lr
    
    
    Optimal output can be generated with:
    vector float splatFloat_opt(float *in)
    {
       double d;
       vector float v;
       asm("lfiwzx %0,0,%1":"=f"(d):"r"(in));
       asm("xxspltw %x0,%1,2":"=v"(v):"f"(d));
       return v;
    }
    
         | 000000                           PDEF
    splatFloat_opt(float *)
         | 000000                           AKA
    splatFloat_opt__FPf
       14|                                  PROC      in,gr3
       18| 000040 lfiwzx   7C001EEE   1     ASMFPLS   vs0='lfiwzx
    %0,0,%1,'f r:,1,(float)",gr3
       19| 000044 xxspltw  F0420291   1     ASMFP     vs34='xxspltw
    %x0,%1,2,'v f:,2,vs0
       21| 000048 bclr     4E800020   1     BA        lr
    
    xlC -O2 -q64 -qarch=pwr7 -qaltivec -qlist -c splats.C
    -qtune=pwr7
    

Local fix

  • N/A
    

Problem summary

  • INEFFICIENT VEC_SPLATS WHEN LOADING FROM MEMORY
    

Problem conclusion

  • The problem had been addressed.
    

Temporary fix

Comments

APAR Information

  • APAR number

    LI78467

  • Reported component name

    XL C/C++ FOR LI

  • Reported component ID

    5725C7300

  • Reported release

    D10

  • Status

    CLOSED PER

  • PE

    NoPE

  • HIPER

    NoHIPER

  • Special Attention

    NoSpecatt

  • Submitted date

    2015-02-25

  • Closed date

    2015-02-25

  • Last modified date

    2015-02-25

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

    IV69753

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

Fix information

  • Fixed component name

    XL C/C++ FOR LI

  • Fixed component ID

    5725C7300

Applicable component levels

  • RD10 PSY

       UP



Document information

More support for: XL C/C++ for Linux
Compiler

Software version: 13.1

Reference #: LI78467

Modified date: 25 February 2015