MSVC compile error for NEON (win/arm64)

[niyas-sait]

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.

[niyas-sait]

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

[niyas-sait]

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.

[niyas-sait]

Pull Request for approach (A)