[cfe-dev] [llvmdev] Clang 3.6 and trunk, high RSS usage compared to GCC (12.5GB vs. 0.5GB)

[Kevin Funk]

On Tuesday 27 January 2015 15:19:33 David Abdurachmanov wrote:
> Hi,
> 
> I found that after moving to Clang pre-3.6 (git
> 65d8b4c4998b3a0c20934ea72ede72ef4838a004) and trunk (git
> 718825a8666acd9ceaab70fc7868332f20e2758f) our internal build machines
> started going offline in Jenkins. Clang after 3.5 release is consuming
> extreme amounts of memory in some cases.
> 
> I have uploaded [1] one of affected files.
> 
> $ g++ -std=c++11 -c -O1 -fPIC vpp_generated.ii -o vpp_generated.o
> 
> vmpeak: 582432 KB
> rspeak: 504500 KB = ~ 0.5GB
> 
> $ clang++ -std=c++11 -c -O1 -fPIC vpp_generated.ii -o vpp_generated.o
> 
> vmpeak: 12992076 KB
> rspeak: 12820184 KB = ~12.5GB
> 
> Disabling optimzer (-O0) resolves the issue, and RSS usage drops to ~300MB.
> 
> I decided to write here directly instead of creating yet another bug report,
> which usually don't get any feedback/comments.
> 
> clang version 3.7.0 (git 718825a8666acd9ceaab70fc7868332f20e2758f)
> Target: x86_64-unknown-linux-gnu
> Thread model: posix
> 
> Compiled:
> 
> ../configure --prefix=<..> --enable-optimized --with-binutils-include=<..>
> --disable-terminfo --enable-bindings=none CC=gcc CXX=g++ 'CPP=gcc -E'
> 'CXXCPP=g++ -E'
> 
> Cheers,
> david
> - - -
> [1] http://davidlt.web.cern.ch/davidlt/vault/vpp_generated.ii.xz

I'd like to add that I was having similar issues with Clang 3.5, while 
compiling test-code inside the QtCreator code base, with optimizer enabled.

I'm not sure if it's known or if I should file a bug report for that.

Relevant issue: Attempting to compile the tst_dumpers.cpp [1] target, with 
optimizing flags enabled (-O2, iirc). => Clang runs OOM (with more than 5 GB 
allocated)
Fix: Don't pass -On -- https://codereview.qt-project.org/#/c/103556/

Note: tst_Dumpers::dumper() is a 5 KLOC function, which *might* be an issue :)

[1] https://qt.gitorious.org/qt-creator/qt-creator/source/487b05dba8b6e8f548ec3cd451965fdb6df71e4d:tests/auto/debugger/tst_dumpers.cpp

-- 
Kevin Funk | kfunk at kde.org | http://kfunk.org