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

[Evan Cheng]

Thanks David. Unfortunately many of us cannot use GPL v3 gcc so it's hard for us to investigate this. One question, can you tell if gcc is inlining significantly more than llvm? We have reports that this is one of the issue plaguing eon performance.

There are also some relatively well known spec optimizations that we haven't implemented. e.g. http://gcc.gnu.org/wiki/summit2010?action=AttachFile&do=get&target=meissner2.pdf Are there more?

Evan

On Nov 13, 2010, at 12:56 PM, Xinliang David Li wrote:

> 
> 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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