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LI76656: __D128_TEST_SIGNIFICANCE PERFORMANCE PROBLEM

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You can track all active APARs for this component.

APAR status

  • Closed as program error.

Error description

  • Consider the following testcase:
    
    $cat testsig.C:
    /////////////////////////////////////////////////
    #include <builtins.h>
    
    bool testSig(_Decimal128 dfp)
    {
       bool res = false;
       if (__d128_test_significance(dfp, 31ULL) > 0)
            res = true;
       return res;
    }
    
    /////////////////////////////////////////////////
    
    Compile using the following command:
    
    $ xlC -O2 -qarch=pwr6 -qdfp -qlist -q64 -c testsig.C
    
    
    Resulting listing points to inefficiency in
    __d128_test_significance implementation.
    
      | 000000                         PDEF testSig(_Decimal128)
      | 000000                         AKA  testSig__FDr
     0|                                PROC dfp,fp2,fp3
     7| 000000 addi  3800001F   1    LI   gr0=31
     7| 000004 std   F801FFF0   1    ST8  MX_CONVF1_0(gr1,-16)gr0
     7| 000008 lfd   C801FFF0   1    LDFL p0=#MX_CONVF1_0(gr1,16)
     7| 00000C dtstexq  FC001544   1     CDFSE r0=fp2,fp3,fp0
     7| 000010 bc    40800018   1     BFL.9,cr0,0x20/flt,
    taken=50%(0,0)
     7| 000014 addi  38000001   1     LI        gr0=1
     7| 000018 addi  3860FFFF   1     LI        gr3=-1
     7| 00001C andc  7C600078   1     ANDC      gr0=gr3,gr0
     7| 000020 rldicl   78030FE0   1     SRL8   gr3=gr0,63
     0| 000024 bclr     4E800020   1     BA     lr
     0|                              CL.9:
     7| 000028 bc       41820024   1     BT     CL.12,cr0,0x80/feq,
    taken=40%(40,60)
     7| 00002C bc       40810018   1     BF     CL.11,cr0,0x40/fgt,
    taken=30%(30,70)
     7| 000030 addi     3800FFFF   1     LI        gr0=-1
     7| 000034 addi     38600001   1     LI        gr3=1
     7| 000038 andc     7C600078   1     ANDC      gr0=gr3,gr0
     7| 00003C rldicl   78030FE0   1     SRL8      gr3=gr0,63
     0| 000040 bclr     4E800020   1     BA        lr
     0|                              CL.11:
     7| 000044 addi     38600000   1     LI        gr3=0
     11| 000048 bclr    4E800020   1     BA        lr
     0|                              CL.12:
     7| 00004C addi     38000000   1     LI        gr0=0
     7| 000050 addi     38600000   1     LI        gr3=0
     7| 000054 andc     7C600078   1     ANDC      gr0=gr3,gr0
     7| 000058 rldicl   78030FE0   1     SRL8      gr3=gr0,63
     0| 00005C bclr     4E800020   1     BA        lr
    
    4 branches are generated, but potentially it could be
    implemented with only 1 branch.
    

Local fix

  • N/A
    

Problem summary

  • DFP optimization opportunity with test significance compare
    greater than zero
    

Problem conclusion

  • Fix is provided
    

Temporary fix

Comments

APAR Information

  • APAR number

    LI76656

  • Reported component name

    XL C/C++ FOR LI

  • Reported component ID

    5724X1400

  • Reported release

    B10

  • Status

    CLOSED PER

  • PE

    NoPE

  • HIPER

    NoHIPER

  • Special Attention

    NoSpecatt / Xsystem

  • Submitted date

    2012-02-06

  • Closed date

    2012-02-06

  • Last modified date

    2012-02-06

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

    IV10810

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

Fix information

  • Fixed component name

    XL C/C++ FOR LI

  • Fixed component ID

    5724X1400

Applicable component levels



Document information

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

Software version: B10

Reference #: LI76656

Modified date: 06 February 2012