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

[Milian Wolff]

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 could reproduce this locally with clang 3.5.1 from the ArchLinux packages. I 
ran it through my heaptrack [1] tool until ~630MB peak memory where consumed, 
which should give enough of an insight already. The full report can be found 
at [2]. Here is an excerpt:

7137759 calls with 475.81MB peak consumption from:
    0x7f83d81ff4ef
      in /usr/bin/../lib/libLLVM-3.5.so
    llvm::LazyValueInfo::getConstant(llvm::Value*, llvm::BasicBlock*)
      in /usr/bin/../lib/libLLVM-3.5.so
    0x7f83d80ba72f
      in /usr/bin/../lib/libLLVM-3.5.so
    llvm::FPPassManager::runOnFunction(llvm::Function&)
      in /usr/bin/../lib/libLLVM-3.5.so
    0x7f83d78df9c3
      in /usr/bin/../lib/libLLVM-3.5.so
    llvm::legacy::PassManagerImpl::run(llvm::Module&)
      in /usr/bin/../lib/libLLVM-3.5.so
    clang::EmitBackendOutput(clang::DiagnosticsEngine&, clang::CodeGenOptions 
const&, clang::TargetOptions const&, clang::LangOptions const&, 
llvm::StringRef, llvm::Module*, clang::BackendAction, llvm::raw_ostream*)
      in /usr/bin/clang
    0x8735a1
      in /usr/bin/clang
    clang::ParseAST(clang::Sema&, bool, bool)
      in /usr/bin/clang
    clang::CodeGenAction::ExecuteAction()
      in /usr/bin/clang
    clang::FrontendAction::Execute()
      in /usr/bin/clang
    clang::CompilerInstance::ExecuteAction(clang::FrontendAction&)
      in /usr/bin/clang
    clang::ExecuteCompilerInvocation(clang::CompilerInstance*)
      in /usr/bin/clang
    cc1_main(char const**, char const**, char const*, void*)
      in /usr/bin/clang
    main
      in /usr/bin/clang

HTH

[1]: http://milianw.de/blog/heaptrack-a-heap-memory-profiler-for-linux
[2]: https://userpage.physik.fu-berlin.de/~milianw/heaptrack.clang.report.txt.gz


-- 
Milian Wolff
mail at milianw.de
http://milianw.de