[cfe-users] Clang 3.9 running 50% slower than 3.7

[jpsota@gmail.com via cfe-users]

Got it -- thanks!

On Wednesday, March 16, 2016, David Blaikie <dblaikie at gmail.com> wrote:

>
>
> On Wed, Mar 16, 2016 at 7:25 AM, jpsota at gmail.com
> <javascript:_e(%7B%7D,'cvml','jpsota at gmail.com');> via cfe-users <
> cfe-users at lists.llvm.org
> <javascript:_e(%7B%7D,'cvml','cfe-users at lists.llvm.org');>> wrote:
>
>> Hi, I recently installed "Release" clang (svn r263305) from source on my
>> OSX machine, and it's compiling a 20 file C++ program about 50% slower than
>> the natively installed clang 3.7 (that came with xcode, I believe, although
>> I don't use xcode). I currently have both sets of tools installed and am
>> able to switch back and forth and verify using time that clang 3.7 takes
>> about 30 seconds and clang 3.9 takes about 45 seconds, on average (all
>> flags, settings, etc. are the same for both). I did build with "Release" as
>> the build type, although I also did set DLLVM_ENABLE_ASSERTIONS=ON (could
>> this be the problem?).
>>
>
> Yes, the build system should print a warning telling you that an
> assertions enabled build can be up to ten times slower. Performance
> comparisons/measurements of an assertions enabled compiler aren't something
> we really do/tune for.
>
>
>> More details below. Please let me know if you have any ideas about why
>> this newer clang would be noticable slower.
>>
>> Generally, I'm just trying to use clang as a user, not a clang developer,
>> so if you have general recommendations for how to configure this, please
>> let me know.
>>
>> Thank you,
>> Jim
>>
>> How I configured and installed:
>>
>> cmake -G "Unix Makefiles" -DCMAKE_BUILD_TYPE=Release
>> -DLLVM_ENABLE_ASSERTIONS=ON ../llvm
>> make
>> cmake -DCMAKE_INSTALL_PREFIX=$CLANG_PREFIX -P cmake_install.cmake
>>
>>
>> Here are some specifics:
>>
>> $ uname -a
>> Darwin localhost 15.0.0 Darwin Kernel Version 15.0.0: Wed Aug 26 16:57:32
>> PDT 2015; root:xnu-3247.1.106~1/RELEASE_X86_64 x86_64
>>
>> $ clang --version
>> clang version 3.9.0 (trunk 263305)
>> Target: x86_64-apple-darwin15.0.0
>> Thread model: posix
>> InstalledDir: /Users/jim/toolchains/llvm/bin
>>
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>>
>
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