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

[David Abdurachmanov]

We also looked into it.

This seems to be coming from LLVM, not Clang code. We did a heap profile
with IgProf [1] in a middle of compilation.

In our case seems that all allocations are from here:

https://github.com/llvm-mirror/llvm/blob/f04ce0e65747b16e6f321c0fdd38b6e1dc3271a3/lib/Analysis/LazyValueInfo.cpp#L519

lookup(Val)[BB] is constantly allocating std::map<AssertingVH<BasicBlock>, 
LVILatticeVal> (104 bytes), that slowly eats the memory.

Current impression is that cache is exploding.

[1] http://igprof.org/

On Jan 28, 2015, at 11:11 AM, Kevin Funk wrote:

> 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

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