Building NumPy from source for Windows on ARM using Clang-cl compiler

[Mugundanmcw]

Hello Developers,

• I am facing an issue while trying to build NumPy for Windows on ARM (WoA) using the Clang-cl compiler. Building NumPy from source requires C and C++ compilers with proper intrinsic support.
• Previously, I was able to successfully compile NumPy for WoA using the MSVC-optimized C/C++ CL compiler, enabling CPU baseline features that support ARM.
• However, I encountered limitations with the MSVC C/C++ CL compiler, as it does not support certain CPU dispatcher features like ASIMDHP, ASIMDFHM, and SVE. Is there any specific reason why these CPU dispatch features are not supported for WoA in MSVC?
• Meanwhile, I attempted to compile NumPy for WoA using the clang-cl compiler (both from MSVC and LLVM toolchains) to check if the CPU dispatcher features would be enabled. While I found that, apart from SVE, all other test features—including baseline features—were supported, I ran into compilation errors due to unidentified instructions.

Steps to Reproduce

1. Clone the Source code of NumPy and checkout to latest branch
2. Install LLVM toolchain/MSVC clang toolset
3. Remove the clang and clang++ from the bin directory to avoid conflicts
4. Add the bin path at the top of environment path variable

Compilers used for compilation:

Error and Workaround:

1. While building meson_cpu target, got an error with respect to invalid operand "fstcw" in multiarray_tests_c source file. Upon going through source code, the fstcw is floating-point control instructions for x86 assembly. So I made workaround to make one more condition to check whether it is a ARM64 arch build. Then the build proceeded:
   
   Workaround:
   before:
   
   After:
   

Issue:

1. Currently the build fails at 240+ targets while compiling meson_cpu due to unidentified assembly instructions:
   

Can anyone give some suggestions to overcome this issue? I need enable CPU dispatch support for NumPy on WoA to get better optimised version of NumPy.

Thanks!

[seberg]

Ping @Mousius, might be interesting to you (or you have a quick idea).

[Mugundanmcw]

@Mousius Any suggestions on this issue?

[DavidSpickett]

These look like MSVC intrinsics - https://learn.microsoft.com/en-us/cpp/intrinsics/arm64-intrinsics?view=msvc-170. We do not have support for all of these in clang-cl at the moment.

Just 2 days ago someone asked about this in fact - llvm/llvm-project#121689.

Without knwoing the numpy source code I can't suggest how to work around this, but the table on the Microsoft page tells you what each one does and for example, one of them produces the https://developer.arm.com/documentation/100069/0606/Data-Transfer-Instructions/LDARB instruction. So in theory you could use alternative APIs to do the same thing.

If anyone needs help figuring out the details of what the instructions do, I can help with that.

As for adding these intrinsics to clang-cl, I'll expand on that in the LLVM issue.

[seberg]

Ah, sorry, I misdiagnosed thinking it was related to SIMD (the second screenshot is so small... text would be easier).

This seems to be related to the atomics definitions, ping @ngoldbaum, I thought these are borrowed from Python, so it seems a bit surprising.

[DavidSpickett]

As a temporary workaround, it might work to edit the source so that the #ifdef STDC_ATOMICS branch is used instead (

numpy/numpy/_core/src/common/npy_atomic.h

Line 37 in 1d77082

#ifdef STDC_ATOMICS

).

I thought these are borrowed from Python

I recall Linaro doing work for Windows on Arm Python but it may not have been using clang-cl.

Edit: It was all done with msvc/Visual Studio not clang-cl.

[Mugundanmcw]

Is there any other workarounds I could perform for compiling NumPy on WoA?

[seberg]

Unless you want to dig into it yourself, please be patient for at least a few days. This will be fixed, but don't expect it to be fixed within hours.

[ngoldbaum]

I can install Windows in a VM on my ARM Macbook and hopefully reproduce this. Sorry for the trouble...

By the way, what command are you using to build NumPy? IIRC you need to go a little out of your way to build with clang-cl properly.

[ngoldbaum]

As a temporary workaround, it might work to edit the source so that the #ifdef STDC_ATOMICS branch is used instead

Is there a reason why STDC_ATOMICS isn't defined on the reporter's system?

[ngoldbaum]

I just successfully built NumPy after making the patch to _multiarray_tests.c.src suggested by OP. I do not see the same error about missing intrinsics as it seems clang-cl on my system is going into the STDC_ATOMICS branch as I expected it to do originally.

I suspect that there is something subtly wrong about the OP's compilation environment. Here's how I built NumPy, doing all this in a checkout of the NumPy repo:

"[binaries]","c = 'clang-cl'","cpp = 'clang-cl'","ar = 'llvm-lib'","c_ld = 'lld-link'","cpp_ld = 'lld-link'" | Out-File $PWD/clang-cl-build.ini -Encoding ascii
pip install -r requirements/build_requirements.txt
spin build -- --vsenv --native-file=$PWD/clang-cl-build.ini

Or alternatively via pip to actually install the numpy build:

python -m pip install -v . --no-build-isolation -C'setup-args=--vsenv' -C'setup-args=--native-file='$PWD'\clang-cl-build.ini'

I did this following our CI setup on github actions for clang-cl.

[ngoldbaum]

OP is short for original post, I was referring to the patch you found for the multiarray tests file.

You should be able to build NumPy using one of the commands I shared in my last comment after applying the patch you suggested for the tests file.

At least right now with clang-cl it is not sufficient to build just use spin build, you need to do something a little more involved to insure the clang toolchain is being used.

Please feel free to send in a pull request for the fix you found for the multiarray tests file.