Re: changing "configure" to default to "gcc -g -O2 -fwrapv ..."

[Diego Novillo]

Mark Mitchell wrote on 01/01/07 14:46:

> What a thread this has turned out to be.
Indeed.

In general, I'm not too thrilled with the idea of disabling
transformations for the sake of non-conforming code.  However, I would
not mind a -fconforming flag similar to -fstrict-aliasing.


> I haven't yet seen that anyone has actually tried the obvious: run SPEC
> with and without -fwrapv.  Would someone please do that?  Or, pick your
> favorite high-performance application and do the same.  But, let's get
> some concrete data as to how much this optimization helps.
On x86_64:

        SPEC2000int is almost identical.
        SPEC2000fp shows a -6% drop when using -fwrapv.


-----------------------------------------------------------------------------
                                  HARDWARE
                                  --------
                CPU: Intel(R) Core(TM)2 CPU          6400  @ 2.13GHz
            CPU MHz: 2128.001
                FPU: Integrated
     CPU(s) enabled: 2
    Secondary Cache: 2048 KB
             Memory: 2053792 kB


                                  SOFTWARE
                                  --------
   Operating System: Linux 2.6.18-1.2868.fc6
           Compiler: GNU C version 4.3.0 20070101 (experimental) (x86_64-unknow
n-linux-gnu)

                                   NOTES
                                   -----
    Base is -O2 -march=nocona -mtune=generic -fwrapv
    Peak is -O2 -march=nocona -mtune=generic


                           SPEC CINT2000 Summary

                                    Estimated                     Estimated
                  Base      Base      Base      Peak      Peak      Peak
  Benchmarks    Ref Time  Run Time   Ratio    Ref Time  Run Time   Ratio
  ------------  --------  --------  --------  --------  --------  --------
  164.gzip          1400  127            1099*     1400  127            1106*
  175.vpr           1400  114            1227*     1400  116            1209*
  176.gcc                                   X                             X
  181.mcf           1800  195             921*     1800  194             927*
  186.crafty        1000  48.7          2054*     1000  48.2          2076*
  197.parser        1800  197             915*     1800  195             923*
  252.eon           1300  64.7          2011*     1300  64.8          2005*
  253.perlbmk                               X                             X
  254.gap           1100  64.9          1696*     1100  65.3          1685*
  255.vortex                                X                             X
  256.bzip2         1500  108            1384*     1500  108            1395*
  300.twolf         3000  169            1771*     3000  169            1775*
  Est. SPECint_base2000                 1391
  Est. SPECint2000                                                    1394



                           SPEC CFP2000 Summary

                                    Estimated                     Estimated
                  Base      Base      Base      Peak      Peak      Peak
  Benchmarks    Ref Time  Run Time   Ratio    Ref Time  Run Time   Ratio
  ------------  --------  --------  --------  --------  --------  --------
  168.wupwise       1600     103        1547*     1600      88.3      1812*
  171.swim          3100     152        2033*     3100     145        2131*
  172.mgrid         1800     193         935*     1800     131        1376*
  173.applu         2100     195        1076*     2100     188        1116*
  177.mesa          1400      71.1      1968*     1400      71.3      1964*
  178.galgel        2900     107        2699*     2900      99.1      2927*
  179.art           2600      96.7      2689*     2600      94.6      2749*
  183.equake        1300      69.0      1884*     1300      67.1      1939*
  187.facerec       1900     149        1273*     1900     146        1302*
  188.ammp          2200     170        1292*     2200     168        1312*
  189.lucas         2000     102        1965*     2000      98.7      2025*
  191.fma3d         2100     195        1079*     2100     192        1092*
  200.sixtrack      1100     199         553*     1100     198         556*
  301.apsi          2600     208        1248*     2600     196        1329*
  Est. SPECfp_base2000                  1463
  Est. SPECfp2000                                                     1560

-----------------------------------------------------------------------------