llvm dev - Dec 2011 - [LLVMdev] Why is CLANG++ so freaking slow -- with example.

http://cornwarning.com/xfer/test.cxx.gz

This is a preprocessed version of a file from from the VV image viewer
package.  I stripped out all the lines beginning in '#' and multiple
empty lines.

It's about 75k lines of code.

On a Mac Pro, the unix 'time' command says it's using 249 seconds of
user time.  Wall time on my machine somewhere around 5 minutes?

249.035u 1.883s 4:12.44 99.3%	0+0k 0+2io 0pf+0w

CLang version:

clang version 3.1 (trunk 146659)
Target: x86_64-apple-darwin10.8.0
Thread model: posix

I built this CLang myself from the svn source a few weeks back -- I
compiled it with gcc, and then re-compiled it with itself.

This is just one example. GCC compiles all of ITK and VTK in around an
hour. CLang++ takes 4 or 5 hours.

Does LLVM's speed advantage go away when it has to deal with heavily
templated C++ code?

On 30.12.2011, at 22:12, kent williams wrote:
> http://cornwarning.com/xfer/test.cxx.gz
> 
> This is a preprocessed version of a file from from the VV image viewer
> package.  I stripped out all the lines beginning in '#' and
multiple
> empty lines.
> 
> It's about 75k lines of code.
> 
> On a Mac Pro, the unix 'time' command says it's using 249
seconds of
> user time.  Wall time on my machine somewhere around 5 minutes?
> 
> 249.035u 1.883s 4:12.44 99.3%	0+0k 0+2io 0pf+0w
> 
> CLang version:
> 
> clang version 3.1 (trunk 146659)
> Target: x86_64-apple-darwin10.8.0
> Thread model: posix
> 
> I built this CLang myself from the svn source a few weeks back -- I
> compiled it with gcc, and then re-compiled it with itself.
> 
> This is just one example. GCC compiles all of ITK and VTK in around an
> hour. CLang++ takes 4 or 5 hours.
> 
> Does LLVM's speed advantage go away when it has to deal with heavily
> templated C++ code?
Hi Kent,

are you using a Debug or Release build of clang? Debug builds are MUCH slower.
Your file takes less than a minute on my mac book pro (Release build).

- Ben
> _______________________________________________
> LLVM Developers mailing list
> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev

It is a release build.

On Fri, Dec 30, 2011 at 3:34 PM, Benjamin Kramer
<benny.kra at googlemail.com> wrote:
>
> On 30.12.2011, at 22:12, kent williams wrote:
>
>> http://cornwarning.com/xfer/test.cxx.gz
>>
>> This is a preprocessed version of a file from from the VV image viewer
>> package.  I stripped out all the lines beginning in '#' and
multiple
>> empty lines.
>>
>> It's about 75k lines of code.
>>
>> On a Mac Pro, the unix 'time' command says it's using 249
seconds of
>> user time.  Wall time on my machine somewhere around 5 minutes?
>>
>> 249.035u 1.883s 4:12.44 99.3% 0+0k 0+2io 0pf+0w
>>
>> CLang version:
>>
>> clang version 3.1 (trunk 146659)
>> Target: x86_64-apple-darwin10.8.0
>> Thread model: posix
>>
>> I built this CLang myself from the svn source a few weeks back -- I
>> compiled it with gcc, and then re-compiled it with itself.
>>
>> This is just one example. GCC compiles all of ITK and VTK in around an
>> hour. CLang++ takes 4 or 5 hours.
>>
>> Does LLVM's speed advantage go away when it has to deal with
heavily
>> templated C++ code?
>
> Hi Kent,
>
> are you using a Debug or Release build of clang? Debug builds are MUCH
slower.
> Your file takes less than a minute on my mac book pro (Release build).
>
> - Ben
>
>> _______________________________________________
>> LLVM Developers mailing list
>> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
>> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
>

On 12/30/2011 01:34 PM, Benjamin Kramer wrote:
>
> On 30.12.2011, at 22:12, kent williams wrote:
>
>> http://cornwarning.com/xfer/test.cxx.gz
>>
>> This is a preprocessed version of a file from from the VV image viewer
>> package.  I stripped out all the lines beginning in '#' and
multiple
>> empty lines.
>>
>> It's about 75k lines of code.
>>
>> On a Mac Pro, the unix 'time' command says it's using 249
seconds of
>> user time.  Wall time on my machine somewhere around 5 minutes?
>>
>> 249.035u 1.883s 4:12.44 99.3%	0+0k 0+2io 0pf+0w
>>
>> CLang version:
>>
>> clang version 3.1 (trunk 146659)
>> Target: x86_64-apple-darwin10.8.0
>> Thread model: posix
>>
>> I built this CLang myself from the svn source a few weeks back -- I
>> compiled it with gcc, and then re-compiled it with itself.
>>
>> This is just one example. GCC compiles all of ITK and VTK in around an
>> hour. CLang++ takes 4 or 5 hours.
>>
>> Does LLVM's speed advantage go away when it has to deal with
heavily
>> templated C++ code?
>
> Hi Kent,
>
> are you using a Debug or Release build of clang? Debug builds are MUCH
slower.
> Your file takes less than a minute on my mac book pro (Release build).
It takes 1 minute 12 seconds with my Debug+Asserts build. A profile 
would still be interesting though.

In general Clang's speed advantage increases with heavily templated C++ 
code. It'd be great to understand what's going on in this case. Perhaps 
there was a nasty regression at the svn revision you picked?

Nick
>
> - Ben
>
>> _______________________________________________
>> LLVM Developers mailing list
>> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
>> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
>
>
> _______________________________________________
> LLVM Developers mailing list
> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
>