[LLVMdev] Why is CLANG++ so freaking slow -- with example.
nkwmailinglists at gmail.com
Fri Dec 30 13:47:08 PST 2011
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:
>> 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
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>> LLVMdev at cs.uiuc.edu http://llvm.cs.uiuc.edu
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