[LLVMdev] tot clang/llvm and tot gcc performance comparision

[Xinliang David Li]

Hi, I have looked at the LLVM code generation quality using small test cases
and in general it is better than I thought and in some cases better than
gcc. However, there are still some gap in SPEC performance. I have not
looked at the root cause of those gaps. Anyone who cares about LLVM
performance need to take this seriously.

For fair comparison, I used -fno-strict-aliasing in gcc to turn off type
based aliasing. I also used -fomit-frame-pointer for clang/llvm because this
is not the default.  The base option is -O2.  Measured on 2.4GHz core-2 box.

64bit:

                                             llvm                 gcc
gcc vs LLVM
            164.gzip                1268                1320      4.15%
             175.vpr                1605                1534     -4.42%
             176.gcc                2203                2315      5.08%
             181.mcf                1625                1737      6.85%
          186.crafty                2411                2307     -4.30%
          197.parser                1173                1166     -0.57%
             252.eon                2245                2464      9.72%
         253.perlbmk                2214                2444     10.37%
             254.gap                1987                1978     -0.47%
          255.vortex                2497                2422     -3.00%
           256.bzip2                1585                1740      9.80%
           300.twolf                2294                2281     -0.58%

As you can see, LLVM beats gcc in vpr, crafty and vortex by about 3%, but
falls behind gcc in gzip, gcc, mcf, eon, perfbmk, and bzip2 by a large
margin.


32bit:
                                           llvm                   gcc
 gcc vs llvm
            164.gzip                1210                1239      2.44%
             175.vpr                1662                1621     -2.42%
             181.mcf                2733                3109     13.75%
          186.crafty                1812                1721     -5.00%
          197.parser                1328                1289     -2.92%
         253.perlbmk                2086                2580     23.67%
             254.gap                1968                1912     -2.86%
          255.vortex                1842                1965      6.66%
           256.bzip2                1440                1553      7.82%
           300.twolf                2284                2213     -3.08%

It beats gcc in vpr, crafty, parser, gap, and twolf by ~3%, but falls behind
 gcc in gzip, mcf, perlbmk, vortex, and bzip2. Some of them have very large
performance gap.  eon and gcc mis-compile.

Thanks,

David
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