ROOT 6.40.00 seems won't compile with Clang + GCC 16 standard library

[zhao-shihan]

Check duplicate issues.

• Checked for duplicates

Description

ROOT 6.40.00 cannot be built by clang or icpx with libstdc++ from GCC 16.1, but can be build with GCC 15.2 or 16.1.

Compiler	Can it build?
Intel icpx 2025.3.0	❌
Clang 21.1.8	❌
GCC 15.2	✅
GCC 16.1	✅

I think the issue raises from some kind of type mismatch with stdex::simd, but I haven't investigate it thoroughly yet.

[3896/5868] Building CXX object math/mathcore/CMakeFiles/MathCore.dir/src/FitUtil.cxx.o
FAILED: [code=1] math/mathcore/CMakeFiles/MathCore.dir/src/FitUtil.cxx.o 
/opt/intel/oneapi/2025.3.0/compiler/2025.3/bin/icpx -DROOT_CORE_THREAD_TBB -I/build/root/6.40.00/root-6.40.00/math/mathcore/inc -I/build/root/6.40.00/root-6.40.00/core/unix/../clib/res -I/build/root/6.40.00/root-6.40.00/core/unix/inc -I/build/root/6.40.00/root-6.40.00/core/zstd/inc -I/build/root/6.40.00/root-6.40.00/core/lz4/inc -I/build/root/6.40.00/root-6.40.00/core/lzma/inc -I/build/root/6.40.00/root-6.40.00/core/zip/inc -I/build/root/6.40.00/root-6.40.00/core/thread/inc -I/build/root/6.40.00/root-6.40.00/core/textinput/src -I/build/root/6.40.00/root-6.40.00/core/textinput/inc -I/build/root/6.40.00/root-6.40.00/core/rint/inc -I/build/root/6.40.00/root-6.40.00/core/meta/inc -I/build/root/6.40.00/root-6.40.00/core/gui/inc -I/build/root/6.40.00/root-6.40.00/core/foundation/res -I/build/root/6.40.00/root-6.40.00/core/foundation/inc -I/build/root/6.40.00/root-6.40.00/core/cont/inc -I/build/root/6.40.00/root-6.40.00/core/clingutils/res -I/build/root/6.40.00/root-6.40.00/core/clingutils/inc -I/build/root/6.40.00/root-6.40.00/core/clib/inc -I/build/root/6.40.00/root-6.40.00/core/base/inc -I/build/root/6.40.00/root-6.40.00/core/base/src -I/build/root/6.40.00/build/ginclude -I/build/root/6.40.00/root-6.40.00/core/imt/inc -I/build/root/6.40.00/root-6.40.00/core/multiproc/inc -I/build/root/6.40.00/root-6.40.00/net/net/inc -I/build/root/6.40.00/root-6.40.00/io/io/inc -xHost -pthread -O3 -DNDEBUG -std=c++20 -fPIC -MD -MT math/mathcore/CMakeFiles/MathCore.dir/src/FitUtil.cxx.o -MF math/mathcore/CMakeFiles/MathCore.dir/src/FitUtil.cxx.o.d -o math/mathcore/CMakeFiles/MathCore.dir/src/FitUtil.cxx.o -c /build/root/6.40.00/root-6.40.00/math/mathcore/src/FitUtil.cxx
In file included from /build/root/6.40.00/root-6.40.00/math/mathcore/src/FitUtil.cxx:13:
In file included from /build/root/6.40.00/root-6.40.00/math/mathcore/inc/Fit/FitUtil.h:17:
In file included from /build/root/6.40.00/root-6.40.00/math/mathcore/inc/Math/IParamFunction.h:23:
In file included from /build/root/6.40.00/root-6.40.00/math/mathcore/inc/Math/Util.h:29:
In file included from /build/root/6.40.00/root-6.40.00/math/mathcore/inc/Math/Types.h:10:
In file included from /usr/lib/gcc/x86_64-linux-gnu/16/../../../../include/c++/16/experimental/simd:80:
/usr/lib/gcc/x86_64-linux-gnu/16/../../../../include/c++/16/experimental/bits/simd_x86.h:4232:18: error: static assertion failed due to requirement 'is_same_v<long long, long>'
 4232 |           static_assert(is_same_v<_Tp, __int_for_sizeof_t<_Tp>>);
      |                         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/usr/lib/gcc/x86_64-linux-gnu/16/../../../../include/c++/16/experimental/bits/simd_x86.h:2392:26: note: in instantiation of function template specialization 'std::experimental::_MaskImplX86Mixin::_S_to_bits<long long, 8UL>' requested here
 2392 |               return _MaskImpl::_S_to_bits(
      |                                 ^
/usr/lib/gcc/x86_64-linux-gnu/16/../../../../include/c++/16/experimental/bits/simd.h:5648:40: note: in instantiation of function template specialization 'std::experimental::_SimdImplX86<std::experimental::simd_abi::_VecBltnBtmsk<64>>::_S_less<double, 8UL>' requested here
 5648 |     { return simd::_S_make_mask(_Impl::_S_less(__y._M_data, __x._M_data)); }
      |                                        ^
/build/root/6.40.00/root-6.40.00/math/mathcore/src/FitUtil.cxx:1966:18: note: in instantiation of member function 'std::experimental::operator>' requested here
 1966 |       where(chi2 > maxResValue, chi2) = maxResValue;
      |                  ^
1 error generated.
[3924/5868] Building CUDA object roofit/batchcompute/CMakeFiles/RooBatchCompute_CUDA.dir/src/ComputeFunctions.cu.o
ninja: build stopped: subcommand failed.

Reproducer

• See comments below.

ROOT version

6.40.00

Installation method

Build from source

Operating system

Debian Testing

Additional context

C++ standard library: libstdc++ from GCC 16.1

[zhao-shihan]

I attach the CMake configuration here:

cmake -G Ninja ../root-6.40.00/ \
  -DCMAKE_INSTALL_PREFIX=/opt/root/6.40.00/cxx20 \
  -DCMAKE_CXX_COMPILER=icpx \
  -DCMAKE_C_COMPILER=icx \
  -DCMAKE_BUILD_TYPE=Release \
  -DCMAKE_C_STANDARD=17 \
  -DCMAKE_CXX_STANDARD=20 \
  -DCMAKE_C_FLAGS='-xHost' \
  -DCMAKE_CXX_FLAGS='-xHost' \
  -Dfftw3=ON \
  -Dgviz=ON \
  -Dmathmore=ON \
  -Dmpi=ON \
  -Dqt6web=ON \
  -Dshadowpw=ON \
  -Dunfold=ON \
  -Dunuran=ON \
  -During=ON \
  -Duse_gsl_cblas=OFF \
  -DCMAKE_CUDA_STANDARD=20 \
  -DCMAKE_CUDA_ARCHITECTURES=all \
  -Dcuda=ON \
  -Dtmva-cudnn=ON \
  -Dtmva-gpu=ON

[zhao-shihan]

I confirmed Clang 21.1.8 also fails with the same issue:

CMake options:

cmake -G Ninja ../root-6.40.00/ \
  -DCMAKE_INSTALL_PREFIX=/opt/root/6.40.00/cxx20 \
  -DCMAKE_CXX_COMPILER=clang++ \
  -DCMAKE_C_COMPILER=clang \
  -DCMAKE_BUILD_TYPE=Release \
  -DCMAKE_C_STANDARD=17 \
  -DCMAKE_CXX_STANDARD=20 \
  -DCMAKE_C_FLAGS='-march=native' \
  -DCMAKE_CXX_FLAGS='-march=native' \
  -Dfftw3=ON \
  -Dgviz=ON \
  -Dmathmore=ON \
  -Dmpi=ON \
  -Dqt6web=ON \
  -Dshadowpw=ON \
  -Dunfold=ON \
  -Dunuran=ON \
  -During=ON \
  -Duse_gsl_cblas=OFF \
  -DCMAKE_CUDA_STANDARD=20 \
  -DCMAKE_CUDA_ARCHITECTURES=all \
  -Dcuda=ON \
  -Dtmva-cudnn=ON \
  -Dtmva-gpu=ON

Error log:

[3925/5880] Building CXX object math/mathcore/CMakeFiles/MathCore.dir/src/FitUtil.cxx.o
FAILED: [code=1] math/mathcore/CMakeFiles/MathCore.dir/src/FitUtil.cxx.o 
/usr/bin/clang++ -DROOT_CORE_THREAD_TBB -I/root-6.40.00/math/mathcore/inc -I/root-6.40.00/core/unix/../clib/res -I/root-6.40.00/core/unix/inc -I/root-6.40.00/core/zstd/inc -I/root-6.40.00/core/lz4/inc -I/root-6.40.00/core/lzma/inc -I/root-6.40.00/core/zip/inc -I/root-6.40.00/core/thread/inc -I/root-6.40.00/core/textinput/src -I/root-6.40.00/core/textinput/inc -I/root-6.40.00/core/rint/inc -I/root-6.40.00/core/meta/inc -I/root-6.40.00/core/gui/inc -I/root-6.40.00/core/foundation/res -I/root-6.40.00/core/foundation/inc -I/root-6.40.00/core/cont/inc -I/root-6.40.00/core/clingutils/res -I/root-6.40.00/core/clingutils/inc -I/root-6.40.00/core/clib/inc -I/root-6.40.00/core/base/inc -I/root-6.40.00/core/base/src -I/build-clang/ginclude -I/root-6.40.00/core/imt/inc -I/root-6.40.00/core/multiproc/inc -I/root-6.40.00/net/net/inc -I/root-6.40.00/io/io/inc -march=native -Wc++11-narrowing -Wsign-compare -Wsometimes-uninitialized -Wconditional-uninitialized -Wheader-guard -Warray-bounds -Wcomment -Wtautological-compare -Wstrncat-size -Wloop-analysis -Wbool-conversion -pipe  -Wall -W -Woverloaded-virtual -fsigned-char -fsized-deallocation -pthread -O3 -DNDEBUG -std=c++20 -fPIC -fcolor-diagnostics -MD -MT math/mathcore/CMakeFiles/MathCore.dir/src/FitUtil.cxx.o -MF math/mathcore/CMakeFiles/MathCore.dir/src/FitUtil.cxx.o.d -o math/mathcore/CMakeFiles/MathCore.dir/src/FitUtil.cxx.o -c /root-6.40.00/math/mathcore/src/FitUtil.cxx
In file included from /root-6.40.00/math/mathcore/src/FitUtil.cxx:13:
In file included from /root-6.40.00/math/mathcore/inc/Fit/FitUtil.h:17:
In file included from /root-6.40.00/math/mathcore/inc/Math/IParamFunction.h:23:
In file included from /root-6.40.00/math/mathcore/inc/Math/Util.h:29:
In file included from /root-6.40.00/math/mathcore/inc/Math/Types.h:10:
In file included from /usr/lib/gcc/x86_64-linux-gnu/16/../../../../include/c++/16/experimental/simd:80:
/usr/lib/gcc/x86_64-linux-gnu/16/../../../../include/c++/16/experimental/bits/simd_x86.h:4232:18: error: static assertion failed due to requirement 'is_same_v<long long, long>'
 4232 |           static_assert(is_same_v<_Tp, __int_for_sizeof_t<_Tp>>);
      |                         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/usr/lib/gcc/x86_64-linux-gnu/16/../../../../include/c++/16/experimental/bits/simd_x86.h:2392:26: note: in instantiation of function template specialization 'std::experimental::_MaskImplX86Mixin::_S_to_bits<long long, 8UL>' requested here
 2392 |               return _MaskImpl::_S_to_bits(
      |                                 ^
/usr/lib/gcc/x86_64-linux-gnu/16/../../../../include/c++/16/experimental/bits/simd.h:5648:40: note: in instantiation of function template specialization 'std::experimental::_SimdImplX86<std::experimental::simd_abi::_VecBltnBtmsk<64>>::_S_less<double, 8UL>' requested here
 5648 |     { return simd::_S_make_mask(_Impl::_S_less(__y._M_data, __x._M_data)); }
      |                                        ^
/root-6.40.00/math/mathcore/src/FitUtil.cxx:1966:18: note: in instantiation of member function 'std::experimental::operator>' requested here
 1966 |       where(chi2 > maxResValue, chi2) = maxResValue;
      |                  ^
1 error generated.
[3936/5880] Building CUDA object roofit/batchcompute/CMakeFiles/RooBatchCompute_CUDA.dir/src/ComputeFunctions.cu.o
ninja: build stopped: subcommand failed.

[zhao-shihan]

Interestingly, GCC 15.2.0 passes compilation.

Here's the CMake config:

cmake -G Ninja ../root-6.40.00/ \
  -DCMAKE_INSTALL_PREFIX=/opt/root/6.40.00/cxx20 \
  -DCMAKE_CXX_COMPILER=g++ \
  -DCMAKE_C_COMPILER=gcc \
  -DCMAKE_BUILD_TYPE=Release \
  -DCMAKE_C_STANDARD=17 \
  -DCMAKE_CXX_STANDARD=20 \
  -DCMAKE_C_FLAGS='-march=native' \
  -DCMAKE_CXX_FLAGS='-march=native' \
  -Dfftw3=ON \
  -Dgviz=ON \
  -Dmathmore=ON \
  -Dmpi=ON \
  -Dqt6web=ON \
  -Dshadowpw=ON \
  -Dunfold=ON \
  -Dunuran=ON \
  -During=ON \
  -Duse_gsl_cblas=OFF \
  -DCMAKE_CUDA_STANDARD=20 \
  -DCMAKE_CUDA_ARCHITECTURES=all \
  -Dcuda=ON \
  -Dtmva-cudnn=ON \
  -Dtmva-gpu=ON

Note that gcc is gcc 15.2.0, not gcc 16.1.

[zhao-shihan]

So do GCC 16.1.0.

cmake -G Ninja ../root-6.40.00/ \
  -DCMAKE_INSTALL_PREFIX=/opt/root/6.40.00/cxx20 \
  -DCMAKE_CXX_COMPILER=g++-16 \
  -DCMAKE_C_COMPILER=gcc-16 \
  -DCMAKE_BUILD_TYPE=Release \
  -DCMAKE_C_STANDARD=17 \
  -DCMAKE_CXX_STANDARD=20 \
  -DCMAKE_C_FLAGS='-march=native' \
  -DCMAKE_CXX_FLAGS='-march=native' \
  -Dfftw3=ON \
  -Dgviz=ON \
  -Dmathmore=ON \
  -Dmpi=ON \
  -Dqt6web=ON \
  -Dshadowpw=ON \
  -Dunfold=ON \
  -Dunuran=ON \
  -During=ON \
  -Duse_gsl_cblas=OFF \
  -DCMAKE_CUDA_STANDARD=20 \
  -DCMAKE_CUDA_ARCHITECTURES=all \
  -Dcuda=ON \
  -Dtmva-cudnn=ON \
  -Dtmva-gpu=ON

However, it generates a lot of -Warray-bound warnings from RooFit component, but it's another issue. For example,

[5857/5872] Building CXX object roofit/hs3/CMakeFiles/RooFitHS3.dir/src/JSONFactories_RooFitCore.cxx.o
In file included from /root-6.40.00/roofit/roofitcore/inc/RooSetProxy.h:5,
                 from /root-6.40.00/roofit/roofitcore/inc/RooHistPdf.h:21,
                 from /root-6.40.00/roofit/roofitcore/inc/RooAbsCachedPdf.h:18,
                 from /root-6.40.00/roofit/hs3/src/JSONFactories_RooFitCore.cxx:15:
In member function ‘bool RooCollectionProxy<RooCollection_t>::add(const RooAbsArg&, bool) [with RooCollection_t = RooArgList]’,
    inlined from ‘bool RooAbsCollection::add(Iterator_t, Iterator_t, bool) [with Iterator_t = __gnu_cxx::__normal_iterator<RooAbsArg* const*, std::vector<RooAbsArg*, std::allocator<RooAbsArg*> > >; value_type = std::remove_pointer<RooAbsArg*>; <template-parameter-1-3> = std::enable_if<false, void>]’ at /root-6.40.00/roofit/roofitcore/inc/RooAbsCollection.h:144:20,
    inlined from ‘bool RooAbsCollection::add(const RooAbsCollection&, bool)’ at /root-6.40.00/roofit/roofitcore/inc/RooAbsCollection.h:152:15,
    inlined from ‘RooArgSet RooRealIntegral::intVars() const’ at /root-6.40.00/roofit/roofitcore/inc/RooRealIntegral.h:51:104,
    inlined from ‘virtual bool {anonymous}::RooRealIntegralStreamer::exportObject(RooJSONFactoryWSTool*, const RooAbsArg*, RooFit::Detail::JSONNode&) const’ at /root-6.40.00/roofit/hs3/src/JSONFactories_RooFitCore.cxx:1034:73:
/root-6.40.00/roofit/roofitcore/inc/RooCollectionProxy.h:135:17: warning: array subscript ‘RooCollectionProxy<RooArgList>[0]’ is partly outside array bounds of ‘RooArgSet [1]’ [-Warray-bounds=]
  135 |       return add(var, _defValueServer, _defShapeServer, silent);
      |              ~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/root-6.40.00/roofit/hs3/src/JSONFactories_RooFitCore.cxx: In member function ‘virtual bool {anonymous}::RooRealIntegralStreamer::exportObject(RooJSONFactoryWSTool*, const RooAbsArg*, RooFit::Detail::JSONNode&) const’:
/root-6.40.00/roofit/hs3/src/JSONFactories_RooFitCore.cxx:1034:73: note: object ‘<anonymous>’ of size 128
 1034 |       RooJSONFactoryWSTool::fillSeq(elem["variables"], integral->intVars());
      |                                                        ~~~~~~~~~~~~~~~~~^~
In member function ‘bool RooCollectionProxy<RooCollection_t>::add(const RooAbsArg&, bool) [with RooCollection_t = RooArgList]’,
    inlined from ‘bool RooAbsCollection::add(Iterator_t, Iterator_t, bool) [with Iterator_t = __gnu_cxx::__normal_iterator<RooAbsArg* const*, std::vector<RooAbsArg*, std::allocator<RooAbsArg*> > >; value_type = std::remove_pointer<RooAbsArg*>; <template-parameter-1-3> = std::enable_if<false, void>]’ at /root-6.40.00/roofit/roofitcore/inc/RooAbsCollection.h:144:20,
    inlined from ‘bool RooAbsCollection::add(const RooAbsCollection&, bool)’ at /root-6.40.00/roofit/roofitcore/inc/RooAbsCollection.h:152:15,
    inlined from ‘RooArgSet RooRealIntegral::intVars() const’ at /root-6.40.00/roofit/roofitcore/inc/RooRealIntegral.h:51:104,
    inlined from ‘virtual bool {anonymous}::RooRealIntegralStreamer::exportObject(RooJSONFactoryWSTool*, const RooAbsArg*, RooFit::Detail::JSONNode&) const’ at /root-6.40.00/roofit/hs3/src/JSONFactories_RooFitCore.cxx:1034:73:
/root-6.40.00/roofit/roofitcore/inc/RooCollectionProxy.h:135:17: warning: array subscript ‘RooCollectionProxy<RooArgList>[0]’ is partly outside array bounds of ‘RooArgSet [1]’ [-Warray-bounds=]
  135 |       return add(var, _defValueServer, _defShapeServer, silent);
      |              ~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/root-6.40.00/roofit/hs3/src/JSONFactories_RooFitCore.cxx: In member function ‘virtual bool {anonymous}::RooRealIntegralStreamer::exportObject(RooJSONFactoryWSTool*, const RooAbsArg*, RooFit::Detail::JSONNode&) const’:
/root-6.40.00/roofit/hs3/src/JSONFactories_RooFitCore.cxx:1034:73: note: object ‘<anonymous>’ of size 128
 1034 |       RooJSONFactoryWSTool::fillSeq(elem["variables"], integral->intVars());
      |                                                        ~~~~~~~~~~~~~~~~~^~
In member function ‘bool RooCollectionProxy<RooCollection_t>::add(const RooAbsArg&, bool, bool, bool) [with RooCollection_t = RooArgList]’,
    inlined from ‘bool RooCollectionProxy<RooCollection_t>::add(const RooAbsArg&, bool) [with RooCollection_t = RooArgList]’ at /root-6.40.00/roofit/roofitcore/inc/RooCollectionProxy.h:135:17,
    inlined from ‘bool RooAbsCollection::add(Iterator_t, Iterator_t, bool) [with Iterator_t = __gnu_cxx::__normal_iterator<RooAbsArg* const*, std::vector<RooAbsArg*, std::allocator<RooAbsArg*> > >; value_type = std::remove_pointer<RooAbsArg*>; <template-parameter-1-3> = std::enable_if<false, void>]’ at /root-6.40.00/roofit/roofitcore/inc/RooAbsCollection.h:144:20,
    inlined from ‘bool RooAbsCollection::add(const RooAbsCollection&, bool)’ at /root-6.40.00/roofit/roofitcore/inc/RooAbsCollection.h:152:15,
    inlined from ‘RooArgSet RooRealIntegral::intVars() const’ at /root-6.40.00/roofit/roofitcore/inc/RooRealIntegral.h:51:104,
    inlined from ‘virtual bool {anonymous}::RooRealIntegralStreamer::exportObject(RooJSONFactoryWSTool*, const RooAbsArg*, RooFit::Detail::JSONNode&) const’ at /root-6.40.00/roofit/hs3/src/JSONFactories_RooFitCore.cxx:1034:73:
/root-6.40.00/roofit/roofitcore/inc/RooCollectionProxy.h:215:7: warning: array subscript ‘RooCollectionProxy<RooArgList>[0]’ is partly outside array bounds of ‘RooArgSet [1]’ [-Warray-bounds=]
  215 |       _owner->addServer((RooAbsArg &)var, valueServer, shapeServer);
      |       ^~~~~~
/root-6.40.00/roofit/hs3/src/JSONFactories_RooFitCore.cxx: In member function ‘virtual bool {anonymous}::RooRealIntegralStreamer::exportObject(RooJSONFactoryWSTool*, const RooAbsArg*, RooFit::Detail::JSONNode&) const’:
/root-6.40.00/roofit/hs3/src/JSONFactories_RooFitCore.cxx:1034:73: note: object ‘<anonymous>’ of size 128
 1034 |       RooJSONFactoryWSTool::fillSeq(elem["variables"], integral->intVars());
      |                                                        ~~~~~~~~~~~~~~~~~^~
In member function ‘bool RooCollectionProxy<RooCollection_t>::add(const RooAbsArg&, bool) [with RooCollection_t = RooArgSet]’,
    inlined from ‘bool RooAbsCollection::add(Iterator_t, Iterator_t, bool) [with Iterator_t = __gnu_cxx::__normal_iterator<RooAbsArg* const*, std::vector<RooAbsArg*, std::allocator<RooAbsArg*> > >; value_type = std::remove_pointer<RooAbsArg*>; <template-parameter-1-3> = std::enable_if<false, void>]’ at /root-6.40.00/roofit/roofitcore/inc/RooAbsCollection.h:144:20,
    inlined from ‘bool RooAbsCollection::add(const RooAbsCollection&, bool)’ at /root-6.40.00/roofit/roofitcore/inc/RooAbsCollection.h:152:15,
    inlined from ‘RooArgSet RooRealIntegral::intVars() const’ at /root-6.40.00/roofit/roofitcore/inc/RooRealIntegral.h:51:104,
    inlined from ‘virtual bool {anonymous}::RooRealIntegralStreamer::exportObject(RooJSONFactoryWSTool*, const RooAbsArg*, RooFit::Detail::JSONNode&) const’ at /root-6.40.00/roofit/hs3/src/JSONFactories_RooFitCore.cxx:1034:73:
/root-6.40.00/roofit/roofitcore/inc/RooCollectionProxy.h:135:17: warning: array subscript ‘RooCollectionProxy<RooArgSet>[0]’ is partly outside array bounds of ‘RooArgSet [1]’ [-Warray-bounds=]
  135 |       return add(var, _defValueServer, _defShapeServer, silent);
      |              ~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/root-6.40.00/roofit/hs3/src/JSONFactories_RooFitCore.cxx: In member function ‘virtual bool {anonymous}::RooRealIntegralStreamer::exportObject(RooJSONFactoryWSTool*, const RooAbsArg*, RooFit::Detail::JSONNode&) const’:
/root-6.40.00/roofit/hs3/src/JSONFactories_RooFitCore.cxx:1034:73: note: object ‘<anonymous>’ of size 128
 1034 |       RooJSONFactoryWSTool::fillSeq(elem["variables"], integral->intVars());
      |                                                        ~~~~~~~~~~~~~~~~~^~
In member function ‘bool RooCollectionProxy<RooCollection_t>::add(const RooAbsArg&, bool) [with RooCollection_t = RooArgSet]’,
    inlined from ‘bool RooAbsCollection::add(Iterator_t, Iterator_t, bool) [with Iterator_t = __gnu_cxx::__normal_iterator<RooAbsArg* const*, std::vector<RooAbsArg*, std::allocator<RooAbsArg*> > >; value_type = std::remove_pointer<RooAbsArg*>; <template-parameter-1-3> = std::enable_if<false, void>]’ at /root-6.40.00/roofit/roofitcore/inc/RooAbsCollection.h:144:20,
    inlined from ‘bool RooAbsCollection::add(const RooAbsCollection&, bool)’ at /root-6.40.00/roofit/roofitcore/inc/RooAbsCollection.h:152:15,
    inlined from ‘RooArgSet RooRealIntegral::intVars() const’ at /root-6.40.00/roofit/roofitcore/inc/RooRealIntegral.h:51:104,
    inlined from ‘virtual bool {anonymous}::RooRealIntegralStreamer::exportObject(RooJSONFactoryWSTool*, const RooAbsArg*, RooFit::Detail::JSONNode&) const’ at /root-6.40.00/roofit/hs3/src/JSONFactories_RooFitCore.cxx:1034:73:
/root-6.40.00/roofit/roofitcore/inc/RooCollectionProxy.h:135:17: warning: array subscript ‘RooCollectionProxy<RooArgSet>[0]’ is partly outside array bounds of ‘RooArgSet [1]’ [-Warray-bounds=]
  135 |       return add(var, _defValueServer, _defShapeServer, silent);
      |              ~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/root-6.40.00/roofit/hs3/src/JSONFactories_RooFitCore.cxx: In member function ‘virtual bool {anonymous}::RooRealIntegralStreamer::exportObject(RooJSONFactoryWSTool*, const RooAbsArg*, RooFit::Detail::JSONNode&) const’:
/root-6.40.00/roofit/hs3/src/JSONFactories_RooFitCore.cxx:1034:73: note: object ‘<anonymous>’ of size 128
 1034 |       RooJSONFactoryWSTool::fillSeq(elem["variables"], integral->intVars());
      |                                                        ~~~~~~~~~~~~~~~~~^~
In member function ‘bool RooCollectionProxy<RooCollection_t>::add(const RooAbsArg&, bool, bool, bool) [with RooCollection_t = RooArgSet]’,
    inlined from ‘bool RooCollectionProxy<RooCollection_t>::add(const RooAbsArg&, bool) [with RooCollection_t = RooArgSet]’ at /root-6.40.00/roofit/roofitcore/inc/RooCollectionProxy.h:135:17,
    inlined from ‘bool RooAbsCollection::add(Iterator_t, Iterator_t, bool) [with Iterator_t = __gnu_cxx::__normal_iterator<RooAbsArg* const*, std::vector<RooAbsArg*, std::allocator<RooAbsArg*> > >; value_type = std::remove_pointer<RooAbsArg*>; <template-parameter-1-3> = std::enable_if<false, void>]’ at /root-6.40.00/roofit/roofitcore/inc/RooAbsCollection.h:144:20,
    inlined from ‘bool RooAbsCollection::add(const RooAbsCollection&, bool)’ at /root-6.40.00/roofit/roofitcore/inc/RooAbsCollection.h:152:15,
    inlined from ‘RooArgSet RooRealIntegral::intVars() const’ at /root-6.40.00/roofit/roofitcore/inc/RooRealIntegral.h:51:104,
    inlined from ‘virtual bool {anonymous}::RooRealIntegralStreamer::exportObject(RooJSONFactoryWSTool*, const RooAbsArg*, RooFit::Detail::JSONNode&) const’ at /root-6.40.00/roofit/hs3/src/JSONFactories_RooFitCore.cxx:1034:73:
/root-6.40.00/roofit/roofitcore/inc/RooCollectionProxy.h:215:7: warning: array subscript ‘RooCollectionProxy<RooArgSet>[0]’ is partly outside array bounds of ‘RooArgSet [1]’ [-Warray-bounds=]
  215 |       _owner->addServer((RooAbsArg &)var, valueServer, shapeServer);
      |       ^~~~~~
/root-6.40.00/roofit/hs3/src/JSONFactories_RooFitCore.cxx: In member function ‘virtual bool {anonymous}::RooRealIntegralStreamer::exportObject(RooJSONFactoryWSTool*, const RooAbsArg*, RooFit::Detail::JSONNode&) const’:
/root-6.40.00/roofit/hs3/src/JSONFactories_RooFitCore.cxx:1034:73: note: object ‘<anonymous>’ of size 128
 1034 |       RooJSONFactoryWSTool::fillSeq(elem["variables"], integral->intVars());
      |                                                        ~~~~~~~~~~~~~~~~~^~
In member function ‘bool RooCollectionProxy<RooCollection_t>::add(const RooAbsArg&, bool) [with RooCollection_t = RooArgList]’,
    inlined from ‘bool RooAbsCollection::add(Iterator_t, Iterator_t, bool) [with Iterator_t = __gnu_cxx::__normal_iterator<RooAbsArg* const*, std::vector<RooAbsArg*, std::allocator<RooAbsArg*> > >; value_type = std::remove_pointer<RooAbsArg*>; <template-parameter-1-3> = std::enable_if<false, void>]’ at /root-6.40.00/roofit/roofitcore/inc/RooAbsCollection.h:144:20,
    inlined from ‘bool RooAbsCollection::add(const RooAbsCollection&, bool)’ at /root-6.40.00/roofit/roofitcore/inc/RooAbsCollection.h:152:15,
    inlined from ‘RooArgSet RooRealIntegral::intVars() const’ at /root-6.40.00/roofit/roofitcore/inc/RooRealIntegral.h:51:84,
    inlined from ‘virtual bool {anonymous}::RooRealIntegralStreamer::exportObject(RooJSONFactoryWSTool*, const RooAbsArg*, RooFit::Detail::JSONNode&) const’ at /root-6.40.00/roofit/hs3/src/JSONFactories_RooFitCore.cxx:1034:73:
/root-6.40.00/roofit/roofitcore/inc/RooCollectionProxy.h:135:17: warning: array subscript ‘RooCollectionProxy<RooArgList>[0]’ is partly outside array bounds of ‘RooArgSet [1]’ [-Warray-bounds=]
  135 |       return add(var, _defValueServer, _defShapeServer, silent);
      |              ~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/root-6.40.00/roofit/hs3/src/JSONFactories_RooFitCore.cxx: In member function ‘virtual bool {anonymous}::RooRealIntegralStreamer::exportObject(RooJSONFactoryWSTool*, const RooAbsArg*, RooFit::Detail::JSONNode&) const’:
/root-6.40.00/roofit/hs3/src/JSONFactories_RooFitCore.cxx:1034:73: note: object ‘<anonymous>’ of size 128
 1034 |       RooJSONFactoryWSTool::fillSeq(elem["variables"], integral->intVars());
      |                                                        ~~~~~~~~~~~~~~~~~^~
In member function ‘bool RooCollectionProxy<RooCollection_t>::add(const RooAbsArg&, bool) [with RooCollection_t = RooArgList]’,
    inlined from ‘bool RooAbsCollection::add(Iterator_t, Iterator_t, bool) [with Iterator_t = __gnu_cxx::__normal_iterator<RooAbsArg* const*, std::vector<RooAbsArg*, std::allocator<RooAbsArg*> > >; value_type = std::remove_pointer<RooAbsArg*>; <template-parameter-1-3> = std::enable_if<false, void>]’ at /root-6.40.00/roofit/roofitcore/inc/RooAbsCollection.h:144:20,
    inlined from ‘bool RooAbsCollection::add(const RooAbsCollection&, bool)’ at /root-6.40.00/roofit/roofitcore/inc/RooAbsCollection.h:152:15,
    inlined from ‘RooArgSet RooRealIntegral::intVars() const’ at /root-6.40.00/roofit/roofitcore/inc/RooRealIntegral.h:51:84,
    inlined from ‘virtual bool {anonymous}::RooRealIntegralStreamer::exportObject(RooJSONFactoryWSTool*, const RooAbsArg*, RooFit::Detail::JSONNode&) const’ at /root-6.40.00/roofit/hs3/src/JSONFactories_RooFitCore.cxx:1034:73:
/root-6.40.00/roofit/roofitcore/inc/RooCollectionProxy.h:135:17: warning: array subscript ‘RooCollectionProxy<RooArgList>[0]’ is partly outside array bounds of ‘RooArgSet [1]’ [-Warray-bounds=]
  135 |       return add(var, _defValueServer, _defShapeServer, silent);
      |              ~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/root-6.40.00/roofit/hs3/src/JSONFactories_RooFitCore.cxx: In member function ‘virtual bool {anonymous}::RooRealIntegralStreamer::exportObject(RooJSONFactoryWSTool*, const RooAbsArg*, RooFit::Detail::JSONNode&) const’:
/root-6.40.00/roofit/hs3/src/JSONFactories_RooFitCore.cxx:1034:73: note: object ‘<anonymous>’ of size 128
 1034 |       RooJSONFactoryWSTool::fillSeq(elem["variables"], integral->intVars());
      |                                                        ~~~~~~~~~~~~~~~~~^~
In member function ‘bool RooCollectionProxy<RooCollection_t>::add(const RooAbsArg&, bool, bool, bool) [with RooCollection_t = RooArgList]’,
    inlined from ‘bool RooCollectionProxy<RooCollection_t>::add(const RooAbsArg&, bool) [with RooCollection_t = RooArgList]’ at /root-6.40.00/roofit/roofitcore/inc/RooCollectionProxy.h:135:17,
    inlined from ‘bool RooAbsCollection::add(Iterator_t, Iterator_t, bool) [with Iterator_t = __gnu_cxx::__normal_iterator<RooAbsArg* const*, std::vector<RooAbsArg*, std::allocator<RooAbsArg*> > >; value_type = std::remove_pointer<RooAbsArg*>; <template-parameter-1-3> = std::enable_if<false, void>]’ at /root-6.40.00/roofit/roofitcore/inc/RooAbsCollection.h:144:20,
    inlined from ‘bool RooAbsCollection::add(const RooAbsCollection&, bool)’ at /root-6.40.00/roofit/roofitcore/inc/RooAbsCollection.h:152:15,
    inlined from ‘RooArgSet RooRealIntegral::intVars() const’ at /root-6.40.00/roofit/roofitcore/inc/RooRealIntegral.h:51:84,
    inlined from ‘virtual bool {anonymous}::RooRealIntegralStreamer::exportObject(RooJSONFactoryWSTool*, const RooAbsArg*, RooFit::Detail::JSONNode&) const’ at /root-6.40.00/roofit/hs3/src/JSONFactories_RooFitCore.cxx:1034:73:
/root-6.40.00/roofit/roofitcore/inc/RooCollectionProxy.h:215:7: warning: array subscript ‘RooCollectionProxy<RooArgList>[0]’ is partly outside array bounds of ‘RooArgSet [1]’ [-Warray-bounds=]
  215 |       _owner->addServer((RooAbsArg &)var, valueServer, shapeServer);
      |       ^~~~~~
/root-6.40.00/roofit/hs3/src/JSONFactories_RooFitCore.cxx: In member function ‘virtual bool {anonymous}::RooRealIntegralStreamer::exportObject(RooJSONFactoryWSTool*, const RooAbsArg*, RooFit::Detail::JSONNode&) const’:
/root-6.40.00/roofit/hs3/src/JSONFactories_RooFitCore.cxx:1034:73: note: object ‘<anonymous>’ of size 128
 1034 |       RooJSONFactoryWSTool::fillSeq(elem["variables"], integral->intVars());
      |                                                        ~~~~~~~~~~~~~~~~~^~
In member function ‘bool RooCollectionProxy<RooCollection_t>::add(const RooAbsArg&, bool) [with RooCollection_t = RooArgSet]’,
    inlined from ‘bool RooAbsCollection::add(Iterator_t, Iterator_t, bool) [with Iterator_t = __gnu_cxx::__normal_iterator<RooAbsArg* const*, std::vector<RooAbsArg*, std::allocator<RooAbsArg*> > >; value_type = std::remove_pointer<RooAbsArg*>; <template-parameter-1-3> = std::enable_if<false, void>]’ at /root-6.40.00/roofit/roofitcore/inc/RooAbsCollection.h:144:20,
    inlined from ‘bool RooAbsCollection::add(const RooAbsCollection&, bool)’ at /root-6.40.00/roofit/roofitcore/inc/RooAbsCollection.h:152:15,
    inlined from ‘RooArgSet RooRealIntegral::intVars() const’ at /root-6.40.00/roofit/roofitcore/inc/RooRealIntegral.h:51:84,
    inlined from ‘virtual bool {anonymous}::RooRealIntegralStreamer::exportObject(RooJSONFactoryWSTool*, const RooAbsArg*, RooFit::Detail::JSONNode&) const’ at /root-6.40.00/roofit/hs3/src/JSONFactories_RooFitCore.cxx:1034:73:
/root-6.40.00/roofit/roofitcore/inc/RooCollectionProxy.h:135:17: warning: array subscript ‘RooCollectionProxy<RooArgSet>[0]’ is partly outside array bounds of ‘RooArgSet [1]’ [-Warray-bounds=]
  135 |       return add(var, _defValueServer, _defShapeServer, silent);
      |              ~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/root-6.40.00/roofit/hs3/src/JSONFactories_RooFitCore.cxx: In member function ‘virtual bool {anonymous}::RooRealIntegralStreamer::exportObject(RooJSONFactoryWSTool*, const RooAbsArg*, RooFit::Detail::JSONNode&) const’:
/root-6.40.00/roofit/hs3/src/JSONFactories_RooFitCore.cxx:1034:73: note: object ‘<anonymous>’ of size 128
 1034 |       RooJSONFactoryWSTool::fillSeq(elem["variables"], integral->intVars());
      |                                                        ~~~~~~~~~~~~~~~~~^~
In member function ‘bool RooCollectionProxy<RooCollection_t>::add(const RooAbsArg&, bool) [with RooCollection_t = RooArgSet]’,
    inlined from ‘bool RooAbsCollection::add(Iterator_t, Iterator_t, bool) [with Iterator_t = __gnu_cxx::__normal_iterator<RooAbsArg* const*, std::vector<RooAbsArg*, std::allocator<RooAbsArg*> > >; value_type = std::remove_pointer<RooAbsArg*>; <template-parameter-1-3> = std::enable_if<false, void>]’ at /root-6.40.00/roofit/roofitcore/inc/RooAbsCollection.h:144:20,
    inlined from ‘bool RooAbsCollection::add(const RooAbsCollection&, bool)’ at /root-6.40.00/roofit/roofitcore/inc/RooAbsCollection.h:152:15,
    inlined from ‘RooArgSet RooRealIntegral::intVars() const’ at /root-6.40.00/roofit/roofitcore/inc/RooRealIntegral.h:51:84,
    inlined from ‘virtual bool {anonymous}::RooRealIntegralStreamer::exportObject(RooJSONFactoryWSTool*, const RooAbsArg*, RooFit::Detail::JSONNode&) const’ at /root-6.40.00/roofit/hs3/src/JSONFactories_RooFitCore.cxx:1034:73:
/root-6.40.00/roofit/roofitcore/inc/RooCollectionProxy.h:135:17: warning: array subscript ‘RooCollectionProxy<RooArgSet>[0]’ is partly outside array bounds of ‘RooArgSet [1]’ [-Warray-bounds=]
  135 |       return add(var, _defValueServer, _defShapeServer, silent);
      |              ~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/root-6.40.00/roofit/hs3/src/JSONFactories_RooFitCore.cxx: In member function ‘virtual bool {anonymous}::RooRealIntegralStreamer::exportObject(RooJSONFactoryWSTool*, const RooAbsArg*, RooFit::Detail::JSONNode&) const’:
/root-6.40.00/roofit/hs3/src/JSONFactories_RooFitCore.cxx:1034:73: note: object ‘<anonymous>’ of size 128
 1034 |       RooJSONFactoryWSTool::fillSeq(elem["variables"], integral->intVars());
      |                                                        ~~~~~~~~~~~~~~~~~^~
In member function ‘bool RooCollectionProxy<RooCollection_t>::add(const RooAbsArg&, bool, bool, bool) [with RooCollection_t = RooArgSet]’,
    inlined from ‘bool RooCollectionProxy<RooCollection_t>::add(const RooAbsArg&, bool) [with RooCollection_t = RooArgSet]’ at /root-6.40.00/roofit/roofitcore/inc/RooCollectionProxy.h:135:17,
    inlined from ‘bool RooAbsCollection::add(Iterator_t, Iterator_t, bool) [with Iterator_t = __gnu_cxx::__normal_iterator<RooAbsArg* const*, std::vector<RooAbsArg*, std::allocator<RooAbsArg*> > >; value_type = std::remove_pointer<RooAbsArg*>; <template-parameter-1-3> = std::enable_if<false, void>]’ at /root-6.40.00/roofit/roofitcore/inc/RooAbsCollection.h:144:20,
    inlined from ‘bool RooAbsCollection::add(const RooAbsCollection&, bool)’ at /root-6.40.00/roofit/roofitcore/inc/RooAbsCollection.h:152:15,
    inlined from ‘RooArgSet RooRealIntegral::intVars() const’ at /root-6.40.00/roofit/roofitcore/inc/RooRealIntegral.h:51:84,
    inlined from ‘virtual bool {anonymous}::RooRealIntegralStreamer::exportObject(RooJSONFactoryWSTool*, const RooAbsArg*, RooFit::Detail::JSONNode&) const’ at /root-6.40.00/roofit/hs3/src/JSONFactories_RooFitCore.cxx:1034:73:
/root-6.40.00/roofit/roofitcore/inc/RooCollectionProxy.h:215:7: warning: array subscript ‘RooCollectionProxy<RooArgSet>[0]’ is partly outside array bounds of ‘RooArgSet [1]’ [-Warray-bounds=]
  215 |       _owner->addServer((RooAbsArg &)var, valueServer, shapeServer);
      |       ^~~~~~
/root-6.40.00/roofit/hs3/src/JSONFactories_RooFitCore.cxx: In member function ‘virtual bool {anonymous}::RooRealIntegralStreamer::exportObject(RooJSONFactoryWSTool*, const RooAbsArg*, RooFit::Detail::JSONNode&) const’:
/root-6.40.00/roofit/hs3/src/JSONFactories_RooFitCore.cxx:1034:73: note: object ‘<anonymous>’ of size 128
 1034 |       RooJSONFactoryWSTool::fillSeq(elem["variables"], integral->intVars());
      |

[zhao-shihan]

So I'd like to summarize:

Compiler	Can it build?
Intel icpx 2025.3.0	❌
Clang 21.1.8	❌
GCC 15.2	✅
GCC 16.1	✅

C++ standard lib is libstdc++ from GCC 16.1.

[guitargeek]

Hi! Thanks for the report. This seems to be a general problem when using experimental/simd from GCC 16 on platforms with AVX-512. You can check if AVX-512 is available like this (for g++ or clang++):

clang++ -march=native -dM -E - </dev/null | grep -i avx512

If it prints out something, you have it. The problem is very easy to reproduce without ROOT then:

// repro.cxx
#include <experimental/simd>

using namespace std::experimental;

int main()
{
    native_simd<double> a(1.0), b(2.0);
    where(a > b, a) = b;   // triggers _S_to_bits<long long, 8> on AVX-512
}

Then you compile with Clang and the GCC standard library:

clang++ -std=c++20 -march=native repro.cxx -o repro

You'll get the same error that you also got when compiling ROOT, even with older GCC versions (in my case GCC 15):

In file included from repro.cxx:1:
In file included from /nix/store/qxaq7jz61a6zkr2mq49i0zvqip2m2jj8-gcc-15.2.0/include/c++/15.2.0/experimental/simd:80:
/nix/store/qxaq7jz61a6zkr2mq49i0zvqip2m2jj8-gcc-15.2.0/include/c++/15.2.0/experimental/bits/simd_x86.h:4232:18: error:
      static assertion failed due to requirement 'is_same_v<long long, long>'
 4232 |           static_assert(is_same_v<_Tp, __int_for_sizeof_t<_Tp>>);
      |                         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/nix/store/qxaq7jz61a6zkr2mq49i0zvqip2m2jj8-gcc-15.2.0/include/c++/15.2.0/experimental/bits/simd_x86.h:2392:26: note:
      in instantiation of function template specialization
      'std::experimental::_MaskImplX86Mixin::_S_to_bits<long long, 8UL>'
      requested here
 2392 |               return _MaskImpl::_S_to_bits(
      |                                 ^
/nix/store/qxaq7jz61a6zkr2mq49i0zvqip2m2jj8-gcc-15.2.0/include/c++/15.2.0/experimental/bits/simd.h:5646:40: note:
      in instantiation of function template specialization
      'std::experimental::_SimdImplX86<std::experimental::simd_abi::_VecBltnBtmsk<64>>::_S_less<double,
      8UL>' requested here
 5646 |     { return simd::_S_make_mask(_Impl::_S_less(__y._M_data, __x._M_data)); }
      |                                        ^
repro.cxx:8:13: note: in instantiation of member function
      'std::experimental::operator>' requested here
    8 |     where(a > b, a) = b;   // triggers _S_to_bits<long long, 8> on AVX-512
      |             ^
1 error generated.

So this is a libstdc++ issue in experimental/simd, not a ROOT issue. Please report it upstream to GCC's libstdc++.

In the meantime, the workaround to get ROOT to build is very easy. You add -mno-avx512f to your DCMAKE_CXX_FLAGS to avoid using AVX-512. Can you please confirm that this works? If you confirm that this works for both Intel icpx and Clang, we can also consider adding this workaround to the ROOT build system for the translation units that use experimental/simd, whenever ROOT is built with a compiler different than GCC but using libstdc++ from GCC. Other workaround are also possible, for example conditionally disabling the ROOT features that use experimental/simd, as these features are quite niche.

[zhao-shihan]

Thanks. I'm building on Intel Skylake server CPU and there's AVX512 for sure. So I believe that's the issue you said, since I was using -march=native.

I'll try building without avx512 and I'll get back to you soon.

[wdconinc]

You may(!) also be able to use clang's own libc++ instead of using gcc's libstdc++ in which case you may retain the avx512 vectorization.

[guitargeek]

I have suggested a workaround in ROOT that allows your build to compile by falling back to AVX-256 for experimental/simd, while keeping AVX-512 in all other contexts:

• [mathcore] Work around libstdc++ <experimental/simd> AVX-512 bug #22437