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

[zhao-shihan]

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• Checked for duplicates

Description

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

• Build ROOT 6.40.00 using intel compiler (icpx) with libstdc++ from GCC 16.
• Clang should also face this issue.
• I didn't test it with GCC yet.

ROOT version

6.40.00

Installation method

Build from source

Operating system

Debian Testing

Additional context

No response