xtensor-stack
MSVC compile error for NEON (win/arm64)
XSIMD library cannot be built using MSVC compiler on a windows/arm64 target.
Steps to reproduce
Visual Studio 2019 or higher is required for compilation.
Compilation can be done natively on a win/arm64 machine or can be cross-compiled from an x86/x64 machine.
From a command terminal
C:\Program Files (x86)\Microsoft Visual Studio\2019\Community\VC\Auxiliary\Build\vcvarsx86_arm64.bat
cmake -G "NMake Makefiles" -D DOWNLOAD_GTEST=1 -D CMAKE_BUILD_TYPE=Debug .
nmake test_xsimd
The issue has been noticed while building the apache arrow library and would be required to build an apache arrow for win/arm64 using MSVC.
The main issue seems to be due to MSVC arm/neon intrinsic vector type using the same underlying type for the neon vectors.
e.g: int8x16_t and uint8x16_t maps to __n128 type
This causes a couple of issues
- Function overloading issues as functions with same functions redefined in xsimd
- Neon dispatcher doesn't pick the right function as all of the functions might be using the same underlying type.
And other issues are
- reinterpret_cast doesn't work on neon vector types
- intrinsic functions defined using macro which might overwrite functions with the same name even defined under a namespace (e.g: wrap::vadd_f32)
- NEON identification require different flag checks
- Initializer_list constructor missing for neon vector types
Few approaches I can think of
- A) Replace the dispatcher to not use target vector type and use the scalar vector type to find the functions to use.
- B) Define a wrapper class for msvc neon vector types so that they are distinguishable and can be used with the current dispatcher mechanism.