unexpected Neon vector element type when building with Eigen3

[Marcus-Forte]

Describe the bug

I got an exception trying to build a program that simply includes Eigen3.

The following message was thrown:

unexpected Neon vector element type
UNREACHABLE executed at /tmp/llvm/clang/lib/AST/ItaniumMangle.cpp:4012!
PLEASE submit a bug report to https://github.com/intel/llvm/issues and include the crash backtrace, preprocessed source, and associated run script.
Stack dump:
0.      Program arguments: /opt/sycl/bin/clang-21 -cc1 -triple spir64-unknown-unknown -aux-triple aarch64-unknown-linux-gnu -fsycl-is-device -fdeclare-spirv-builtins -O2 -mllvm -sycl-opt -fenable-sycl-dae -Wno-sycl-strict -fsycl-int-header=/tmp/failed-header-9953d2.h -fsycl-int-footer=/tmp/failed-footer-ca97a3.h -sycl-std=2020 -ffine-grained-bitfield-accesses -fsycl-unique-prefix=uidc9772056fd4c0499 -D__SYCL_ANY_DEVICE_HAS_ANY_ASPECT__=1 -Wspir-compat -fno-offload-use-alloca-addrspace-for-srets -emit-llvm-bc -emit-llvm-uselists -disable-free -clear-ast-before-backend -main-file-name failed.cc -mrelocation-model static -mframe-pointer=all -fmath-errno -ffp-contract=on -fno-rounding-math -mconstructor-aliases -aux-target-cpu generic -aux-target-feature +v8a -aux-target-feature +fp-armv8 -aux-target-feature +neon -debug-info-kind=constructor -dwarf-version=5 -debugger-tuning=gdb -fdebug-compilation-dir=/workspaces/moptim/build -fcoverage-compilation-dir=/workspaces/moptim/build -resource-dir /opt/sycl/lib/clang/21 -dependency-file CMakeFiles/failed.dir/src/failed.cc.o.d -MT CMakeFiles/failed.dir/src/failed.cc.o -sys-header-deps -internal-isystem /opt/sycl/bin/../include/sycl/stl_wrappers -internal-isystem /opt/sycl/bin/../include -internal-isystem /opt/sycl/bin/../include/sycl/stl_wrappers -internal-isystem /opt/sycl/bin/../include -isystem /usr/include/eigen3 -internal-isystem /usr/lib/gcc/aarch64-linux-gnu/13/../../../../include/c++/13 -internal-isystem /usr/lib/gcc/aarch64-linux-gnu/13/../../../../include/aarch64-linux-gnu/c++/13 -internal-isystem /usr/lib/gcc/aarch64-linux-gnu/13/../../../../include/c++/13/backward -internal-isystem /usr/lib/gcc/aarch64-linux-gnu/13/../../../../include/c++/13 -internal-isystem /usr/lib/gcc/aarch64-linux-gnu/13/../../../../include/aarch64-linux-gnu/c++/13 -internal-isystem /usr/lib/gcc/aarch64-linux-gnu/13/../../../../include/c++/13/backward -internal-isystem /opt/sycl/lib/clang/21/include -internal-isystem /usr/local/include -internal-isystem /usr/lib/gcc/aarch64-linux-gnu/13/../../../../aarch64-linux-gnu/include -internal-externc-isystem /usr/include/aarch64-linux-gnu -internal-externc-isystem /include -internal-externc-isystem /usr/include -internal-isystem /opt/sycl/lib/clang/21/include -internal-isystem /usr/local/include -internal-isystem /usr/lib/gcc/aarch64-linux-gnu/13/../../../../aarch64-linux-gnu/include -internal-externc-isystem /usr/include/aarch64-linux-gnu -internal-externc-isystem /include -internal-externc-isystem /usr/include -std=gnu++20 -fdeprecated-macro -ferror-limit 19 -fmessage-length=165 -fgpu-rdc -fno-signed-char -fgnuc-version=4.2.1 -fno-implicit-modules -fskip-odr-check-in-gmf -fcxx-exceptions -fexceptions -fcolor-diagnostics -faddrsig -D__GCC_HAVE_DWARF2_CFI_ASM=1 -o /tmp/failed-e57e1e.bc -x c++ /workspaces/moptim/src/failed.cc
1.      /opt/sycl/lib/clang/21/include/arm_neon.h:5074:1 <Spelling=/opt/sycl/lib/clang/21/include/arm_neon.h:126:14>: current parser token 'static'
2.      /opt/sycl/lib/clang/21/include/arm_neon.h:5057:49: LLVM IR generation of declaration 'vaddq_u64'
3.      /opt/sycl/lib/clang/21/include/arm_neon.h:5057:49: Mangling declaration 'vaddq_u64'
 #0 0x0000aaaac90bc5f8 llvm::sys::PrintStackTrace(llvm::raw_ostream&, int) (/opt/sycl/bin/clang-21+0x22ec5f8)
 #1 0x0000aaaac90b9ad0 llvm::sys::RunSignalHandlers() (/opt/sycl/bin/clang-21+0x22e9ad0)
 #2 0x0000aaaac90b9c38 SignalHandler(int, siginfo_t*, void*) Signals.cpp:0:0
 #3 0x0000ffffbcb5f7a0 (linux-vdso.so.1+0x7a0)
 #4 0x0000ffffbc617628 (/lib/aarch64-linux-gnu/libc.so.6+0x87628)
 #5 0x0000ffffbc5ccb3c raise (/lib/aarch64-linux-gnu/libc.so.6+0x3cb3c)
 #6 0x0000ffffbc5b7e00 abort (/lib/aarch64-linux-gnu/libc.so.6+0x27e00)
 #7 0x0000aaaac9016a9c (/opt/sycl/bin/clang-21+0x2246a9c)
 #8 0x0000aaaacca4dc08 (anonymous namespace)::CXXNameMangler::mangleType(clang::VectorType const*) ItaniumMangle.cpp:0:0
 #9 0x0000aaaacca4b610 (anonymous namespace)::CXXNameMangler::mangleType(clang::QualType) ItaniumMangle.cpp:0:0
#10 0x0000aaaacca54bb4 (anonymous namespace)::CXXNameMangler::mangleFunctionEncoding(clang::GlobalDecl) ItaniumMangle.cpp:0:0
#11 0x0000aaaacca5e1d8 (anonymous namespace)::ItaniumMangleContextImpl::mangleCXXName(clang::GlobalDecl, llvm::raw_ostream&) ItaniumMangle.cpp:0:0
#12 0x0000aaaac95d37b8 getMangledNameImpl(clang::CodeGen::CodeGenModule&, clang::GlobalDecl, clang::NamedDecl const*, bool) CodeGenModule.cpp:0:0
#13 0x0000aaaac95e10a8 clang::CodeGen::CodeGenModule::getMangledName(clang::GlobalDecl) (/opt/sycl/bin/clang-21+0x28110a8)
#14 0x0000aaaac96056d4 clang::CodeGen::CodeGenModule::EmitGlobal(clang::GlobalDecl) (/opt/sycl/bin/clang-21+0x28356d4)
#15 0x0000aaaac960de48 clang::CodeGen::CodeGenModule::EmitTopLevelDecl(clang::Decl*) (.part.0) CodeGenModule.cpp:0:0
#16 0x0000aaaac99c378c (anonymous namespace)::CodeGeneratorImpl::HandleTopLevelDecl(clang::DeclGroupRef) ModuleBuilder.cpp:0:0
#17 0x0000aaaac99b3d10 clang::BackendConsumer::HandleTopLevelDecl(clang::DeclGroupRef) (/opt/sycl/bin/clang-21+0x2be3d10)
#18 0x0000aaaacb508150 clang::ParseAST(clang::Sema&, bool, bool) (/opt/sycl/bin/clang-21+0x4738150)
#19 0x0000aaaac99c06f0 clang::CodeGenAction::ExecuteAction() (/opt/sycl/bin/clang-21+0x2bf06f0)
#20 0x0000aaaac9cb137c clang::FrontendAction::Execute() (/opt/sycl/bin/clang-21+0x2ee137c)
#21 0x0000aaaac9c44bb4 clang::CompilerInstance::ExecuteAction(clang::FrontendAction&) (/opt/sycl/bin/clang-21+0x2e74bb4)
#22 0x0000aaaac9d86fec clang::ExecuteCompilerInvocation(clang::CompilerInstance*) (/opt/sycl/bin/clang-21+0x2fb6fec)
#23 0x0000aaaac7b01a34 cc1_main(llvm::ArrayRef<char const*>, char const*, void*) (/opt/sycl/bin/clang-21+0xd31a34)
#24 0x0000aaaac7af8c64 ExecuteCC1Tool(llvm::SmallVectorImpl<char const*>&, llvm::ToolContext const&) driver.cpp:0:0
#25 0x0000aaaac7afbe64 clang_main(int, char**, llvm::ToolContext const&) (/opt/sycl/bin/clang-21+0xd2be64)
#26 0x0000aaaac7a2f250 main (/opt/sycl/bin/clang-21+0xc5f250)
#27 0x0000ffffbc5b84c4 (/lib/aarch64-linux-gnu/libc.so.6+0x284c4)
#28 0x0000ffffbc5b8598 __libc_start_main (/lib/aarch64-linux-gnu/libc.so.6+0x28598)
#29 0x0000aaaac7af8270 _start (/opt/sycl/bin/clang-21+0xd28270)
clang++: error: unable to execute command: Aborted
clang++: error: clang frontend command failed due to signal (use -v to see invocation)
clang version 21.0.0git (https://github.com/intel/llvm c7ff66105a7b7dfa2c8a3544f0b132e39ace7594)
Target: aarch64-unknown-linux-gnu
Thread model: posix
InstalledDir: /opt/sycl/bin
Build config: +assertions
clang++: note: diagnostic msg: Error generating preprocessed source(s).

To reproduce

1. Include a code snippet that is as short as possible:
   Source:

#include <Eigen/Dense>

int main() {}

3. Specify the command which should be used to compile the program:

/opt/sycl/bin/clang++ -isystem /usr/include/eigen3 -g -std=gnu++20 -fsycl -fsycl-targets=native_cpu -MD -MT CMakeFiles/failed.dir/src/failed.cc.o -MF CMakeFiles/failed.dir/src/failed.cc.o.d -o CMakeFiles/failed.dir/src/failed.cc.o -c /workspaces/moptim/src/failed.cc

4. Specify the command which should be used to launch the program: failed before
5. Indicate what is wrong and what was expected: failed before

Environment

• OS: Linux/Docker from MacOS
• Target device and vendor: native_cpu
• DPC++ version: clang version 21.0.0git (https://github.com/intel/llvm c7ff661) (How I built: https://github.com/Marcus-Forte/learning-sycl/blob/main/.devcontainer/Dockerfile)
• Dependencies version:

Platform [#1]:
    Version  : 0.1
    Name     : SYCL_NATIVE_CPU
    Vendor   : tbd
    Devices  : 1
        Device [#0]:
        Type              : cpu
        Version           : 0.1
        Name              : SYCL Native CPU
        Vendor            : Intel(R) Corporation
        Driver            : 0.0.0
        DeviceID          : UNKNOWN
        Num SubDevices    : 0
        Num SubSubDevices : 0
        Aspects           : cpu fp64 online_compiler online_linker queue_profiling usm_device_allocations usm_host_allocations usm_shared_allocations usm_system_allocations usm_atomic_host_allocations usm_atomic_shared_allocations atomic64
        info::device::sub_group_sizes: 1
        Architecture: unknown
default_selector()      : cpu, SYCL_NATIVE_CPU, SYCL Native CPU 0.1 [0.0.0]
accelerator_selector()  : No device of requested type available.
cpu_selector()          : cpu, SYCL_NATIVE_CPU, SYCL Native CPU 0.1 [0.0.0]
gpu_selector()          : No device of requested type available.
custom_selector(gpu)    : No device of requested type available.
custom_selector(cpu)    : cpu, SYCL_NATIVE_CPU, SYCL Native CPU 0.1 [0.0.0]
custom_selector(acc)    : No device of requested type available.

Additional context

No response

[Marcus-Forte]

Hi, I'd like to add that I get the same problem if specifying-fsycl_targets=nvptx64-nvidia-cuda, so doesn't look specific to native_cpu?

unexpected Neon vector element type
UNREACHABLE executed at /tmp/llvm/clang/lib/AST/ItaniumMangle.cpp:4012!
PLEASE submit a bug report to https://github.com/intel/llvm/issues and include the crash backtrace, preprocessed source, and associated run script.
Stack dump:
0.      Program arguments: /opt/sycl/bin/clang-21 -cc1 -triple nvptx64-nvidia-cuda -O3 -aux-triple aarch64-unknown-linux-gnu -fsycl-is-device -fdeclare-spirv-builtins -fenable-sycl-dae -Wno-sycl-strict -fsycl-int-header=/tmp/failed-header-b413e1.h -fsycl-int-footer=/tmp/failed-footer-b8566d.h -D__SYCL_TARGET_NVIDIA_GPU_SM_50__ -sycl-std=2020 -fsycl-unique-prefix=uidb798d9276cb066f2 -D__SYCL_ANY_DEVICE_HAS_ANY_ASPECT__=1 -D__SYCL_ALL_DEVICES_HAVE_ext_intel_device_id__=1 -D__SYCL_ALL_DEVICES_HAVE_ext_intel_device_info_uuid__=1 -D__SYCL_ALL_DEVICES_HAVE_ext_intel_free_memory__=1 -D__SYCL_ALL_DEVICES_HAVE_ext_intel_memory_bus_width__=1 -D__SYCL_ALL_DEVICES_HAVE_ext_intel_memory_clock_rate__=1 -D__SYCL_ALL_DEVICES_HAVE_ext_intel_pci_address__=1 -D__SYCL_ALL_DEVICES_HAVE_ext_oneapi_bindless_images__=1 -D__SYCL_ALL_DEVICES_HAVE_ext_oneapi_bindless_images_1d_usm__=1 -D__SYCL_ALL_DEVICES_HAVE_ext_oneapi_bindless_images_2d_usm__=1 -D__SYCL_ALL_DEVICES_HAVE_ext_oneapi_bindless_images_shared_usm__=1 -D__SYCL_ALL_DEVICES_HAVE_ext_oneapi_chunk__=1 -D__SYCL_ALL_DEVICES_HAVE_ext_oneapi_cubemap__=1 -D__SYCL_ALL_DEVICES_HAVE_ext_oneapi_cubemap_seamless_filtering__=1 -D__SYCL_ALL_DEVICES_HAVE_ext_oneapi_external_memory_import__=1 -D__SYCL_ALL_DEVICES_HAVE_ext_oneapi_external_semaphore_import__=1 -D__SYCL_ALL_DEVICES_HAVE_ext_oneapi_fragment__=1 -D__SYCL_ALL_DEVICES_HAVE_ext_oneapi_graph__=1 -D__SYCL_ALL_DEVICES_HAVE_ext_oneapi_image_array__=1 -D__SYCL_ALL_DEVICES_HAVE_ext_oneapi_limited_graph__=1 -D__SYCL_ALL_DEVICES_HAVE_ext_oneapi_mipmap__=1 -D__SYCL_ALL_DEVICES_HAVE_ext_oneapi_mipmap_anisotropy__=1 -D__SYCL_ALL_DEVICES_HAVE_ext_oneapi_mipmap_level_reference__=1 -D__SYCL_ALL_DEVICES_HAVE_ext_oneapi_native_assert__=1 -D__SYCL_ALL_DEVICES_HAVE_ext_oneapi_unique_addressing_per_dim__=1 -D__SYCL_ALL_DEVICES_HAVE_fp64__=1 -D__SYCL_ALL_DEVICES_HAVE_gpu__=1 -D__SYCL_ALL_DEVICES_HAVE_online_compiler__=1 -D__SYCL_ALL_DEVICES_HAVE_online_linker__=1 -D__SYCL_ALL_DEVICES_HAVE_queue_profiling__=1 -D__SYCL_ALL_DEVICES_HAVE_usm_device_allocations__=1 -D__SYCL_ALL_DEVICES_HAVE_usm_host_allocations__=1 -D__SYCL_ALL_DEVICES_HAVE_usm_shared_allocations__=1 -emit-llvm-bc -emit-llvm-uselists -disable-free -clear-ast-before-backend -main-file-name test_powell.cc -mrelocation-model static -mframe-pointer=all -ffp-contract=on -fno-rounding-math -no-integrated-as -aux-target-cpu generic -aux-target-feature +v8a -aux-target-feature +fp-armv8 -aux-target-feature +neon -internal-isystem /opt/sycl/bin/../include/sycl/stl_wrappers -internal-isystem /opt/sycl/bin/../include -mllvm -enable-memcpyopt-without-libcalls -mlink-builtin-bitcode /opt/sycl/bin/../lib/clc/remangled-l64-signed_char.libspirv-nvptx64-nvidia-cuda.bc -mlink-builtin-bitcode /usr/local/cuda-12.6/nvvm/libdevice/libdevice.10.bc -target-sdk-version=12.6 -target-cpu sm_50 -target-feature +ptx85 -debugger-tuning=gdb -fno-dwarf-directory-asm -fdebug-compilation-dir=/workspaces/moptim/build -resource-dir /opt/sycl/lib/clang/21 -dependency-file test/CMakeFiles/moptim_tests.dir/test_powell.cc.o.d -MT test/CMakeFiles/moptim_tests.dir/test_powell.cc.o -sys-header-deps -isystem /usr/include/eigen3 -D TEST_PATH=\"/workspaces/moptim/test/data\" -I /workspaces/moptim/include -I /workspaces/moptim/utils -D NDEBUG -internal-isystem /usr/lib/gcc/aarch64-linux-gnu/13/../../../../include/c++/13 -internal-isystem /usr/lib/gcc/aarch64-linux-gnu/13/../../../../include/aarch64-linux-gnu/c++/13 -internal-isystem /usr/lib/gcc/aarch64-linux-gnu/13/../../../../include/c++/13/backward -internal-isystem /usr/lib/gcc/aarch64-linux-gnu/13/../../../../include/c++/13 -internal-isystem /usr/lib/gcc/aarch64-linux-gnu/13/../../../../include/aarch64-linux-gnu/c++/13 -internal-isystem /usr/lib/gcc/aarch64-linux-gnu/13/../../../../include/c++/13/backward -internal-isystem /opt/sycl/lib/clang/21/include -internal-isystem /usr/local/include -internal-isystem /usr/lib/gcc/aarch64-linux-gnu/13/../../../../aarch64-linux-gnu/include -internal-externc-isystem /usr/include/aarch64-linux-gnu -internal-externc-isystem /include -internal-externc-isystem /usr/include -internal-isystem /usr/local/cuda-12.6/include -internal-isystem /opt/sycl/lib/clang/21/include -internal-isystem /usr/local/include -internal-isystem /usr/lib/gcc/aarch64-linux-gnu/13/../../../../aarch64-linux-gnu/include -internal-externc-isystem /usr/include/aarch64-linux-gnu -internal-externc-isystem /include -internal-externc-isystem /usr/include -std=gnu++20 -fdeprecated-macro -ferror-limit 19 -fgpu-rdc -fno-signed-char -fgnuc-version=4.2.1 -fno-implicit-modules -fskip-odr-check-in-gmf -fcxx-exceptions -fexceptions -vectorize-loops -vectorize-slp -D__GCC_HAVE_DWARF2_CFI_ASM=1 -o /tmp/test_powell-sm_50-41ea3f.bc -x c++ /workspaces/moptim/src/failed.cc
1.      /opt/sycl/lib/clang/21/include/arm_neon.h:5074:1 <Spelling=/opt/sycl/lib/clang/21/include/arm_neon.h:126:14>: current parser token 'static'
2.      /opt/sycl/lib/clang/21/include/arm_neon.h:5057:49: LLVM IR generation of declaration 'vaddq_u64'
3.      /opt/sycl/lib/clang/21/include/arm_neon.h:5057:49: Mangling declaration 'vaddq_u64'
 #0 0x0000aaaab636c5f8 llvm::sys::PrintStackTrace(llvm::raw_ostream&, int) (/opt/sycl/bin/clang-21+0x22ec5f8)
 #1 0x0000aaaab6369ad0 llvm::sys::RunSignalHandlers() (/opt/sycl/bin/clang-21+0x22e9ad0)
 #2 0x0000aaaab6369c38 SignalHandler(int, siginfo_t*, void*) Signals.cpp:0:0
 #3 0x0000ffffa38f17a0 (linux-vdso.so.1+0x7a0)
 #4 0x0000ffffa33d7628 (/lib/aarch64-linux-gnu/libc.so.6+0x87628)
 #5 0x0000ffffa338cb3c raise (/lib/aarch64-linux-gnu/libc.so.6+0x3cb3c)
 #6 0x0000ffffa3377e00 abort (/lib/aarch64-linux-gnu/libc.so.6+0x27e00)
 #7 0x0000aaaab62c6a9c (/opt/sycl/bin/clang-21+0x2246a9c)
 #8 0x0000aaaab9cfdc08 (anonymous namespace)::CXXNameMangler::mangleType(clang::VectorType const*) ItaniumMangle.cpp:0:0
 #9 0x0000aaaab9cfb610 (anonymous namespace)::CXXNameMangler::mangleType(clang::QualType) ItaniumMangle.cpp:0:0
#10 0x0000aaaab9d04bb4 (anonymous namespace)::CXXNameMangler::mangleFunctionEncoding(clang::GlobalDecl) ItaniumMangle.cpp:0:0
#11 0x0000aaaab9d0e1d8 (anonymous namespace)::ItaniumMangleContextImpl::mangleCXXName(clang::GlobalDecl, llvm::raw_ostream&) ItaniumMangle.cpp:0:0
#12 0x0000aaaab68837b8 getMangledNameImpl(clang::CodeGen::CodeGenModule&, clang::GlobalDecl, clang::NamedDecl const*, bool) CodeGenModule.cpp:0:0
#13 0x0000aaaab68910a8 clang::CodeGen::CodeGenModule::getMangledName(clang::GlobalDecl) (/opt/sycl/bin/clang-21+0x28110a8)
#14 0x0000aaaab68b56d4 clang::CodeGen::CodeGenModule::EmitGlobal(clang::GlobalDecl) (/opt/sycl/bin/clang-21+0x28356d4)
#15 0x0000aaaab68bde48 clang::CodeGen::CodeGenModule::EmitTopLevelDecl(clang::Decl*) (.part.0) CodeGenModule.cpp:0:0
#16 0x0000aaaab6c7378c (anonymous namespace)::CodeGeneratorImpl::HandleTopLevelDecl(clang::DeclGroupRef) ModuleBuilder.cpp:0:0
#17 0x0000aaaab6c63d10 clang::BackendConsumer::HandleTopLevelDecl(clang::DeclGroupRef) (/opt/sycl/bin/clang-21+0x2be3d10)
#18 0x0000aaaab87b8150 clang::ParseAST(clang::Sema&, bool, bool) (/opt/sycl/bin/clang-21+0x4738150)
#19 0x0000aaaab6c706f0 clang::CodeGenAction::ExecuteAction() (/opt/sycl/bin/clang-21+0x2bf06f0)
#20 0x0000aaaab6f6137c clang::FrontendAction::Execute() (/opt/sycl/bin/clang-21+0x2ee137c)
#21 0x0000aaaab6ef4bb4 clang::CompilerInstance::ExecuteAction(clang::FrontendAction&) (/opt/sycl/bin/clang-21+0x2e74bb4)
#22 0x0000aaaab7036fec clang::ExecuteCompilerInvocation(clang::CompilerInstance*) (/opt/sycl/bin/clang-21+0x2fb6fec)
#23 0x0000aaaab4db1a34 cc1_main(llvm::ArrayRef<char const*>, char const*, void*) (/opt/sycl/bin/clang-21+0xd31a34)
#24 0x0000aaaab4da8c64 ExecuteCC1Tool(llvm::SmallVectorImpl<char const*>&, llvm::ToolContext const&) driver.cpp:0:0
#25 0x0000aaaab4dabe64 clang_main(int, char**, llvm::ToolContext const&) (/opt/sycl/bin/clang-21+0xd2be64)
#26 0x0000aaaab4cdf250 main (/opt/sycl/bin/clang-21+0xc5f250)
#27 0x0000ffffa33784c4 (/lib/aarch64-linux-gnu/libc.so.6+0x284c4)
#28 0x0000ffffa3378598 __libc_start_main (/lib/aarch64-linux-gnu/libc.so.6+0x28598)
#29 0x0000aaaab4da8270 _start (/opt/sycl/bin/clang-21+0xd28270)
clang++: error: unable to execute command: Aborted
clang++: error: clang frontend command failed due to signal (use -v to see invocation)
clang version 21.0.0git (https://github.com/intel/llvm c7ff66105a7b7dfa2c8a3544f0b132e39ace7594)
Target: aarch64-unknown-linux-gnu
Thread model: posix
InstalledDir: /opt/sycl/bin
Build config: +assertions
clang++: note: diagnostic msg: Error generating preprocessed source(s).

[Marcus-Forte]

Thanks to this post I was able to proceed by passing EIGEN_ARM64_USE_SVE to instruct Eigen NOT to include arm_neon.h.

I'm not sure what would be the best way to indicate to people that is an issue - the "Mangling declaration 'vaddq_u64'" from the compilation error seems cryptic.