Windows ARM64 link failure with the pinned cpuinfo revision

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Summary

A native Windows ARM64 build using Ruy's default cpuinfo integration fails at link time because Ruy pins a cpuinfo revision from before Windows ARM64 support was implemented.

The current workaround in #377 disables cpuinfo entirely on Windows ARM64. Although this allows the build to link, it also disables runtime CPU feature detection and makes CpuInfo::NeonDotprod() always return false. Updating the pinned cpuinfo dependency would be preferable.

Environment

• Windows 11 ARM64, running natively
• Visual Studio 2022 17.14
• MSVC 19.44
• Windows SDK 10.0.26100.0
• CMake 3.31.6
• Ruy commit: 363f252289fb7a1fba1703d99196524698cb884d
• Pinned cpuinfo commit: 082deffc80ce517f81dc2f3aebe6ba671fcd09c9

The pinned cpuinfo commit is dated June 17, 2022.

Failure

When Ruy is linked into a native Windows ARM64 CMake build, the final link fails with:

ruy_cpuinfo.lib(cpuinfo.obj) : error LNK2019:
unresolved external symbol cpuinfo_isa referenced in
ruy::CpuInfo::NeonDotprod()

The failure was reproduced while building CTranslate2 with:

cmake -A ARM64 \
  -DCMAKE_BUILD_TYPE=Release \
  -DBUILD_CLI=OFF \
  -DWITH_MKL=OFF \
  -DWITH_DNNL=OFF \
  -DWITH_RUY=ON \
  -DWITH_CUDA=OFF \
  -DOPENMP_RUNTIME=COMP \
  ..

Root cause

The pinned cpuinfo revision declares the ARM cpuinfo_isa symbol in include/cpuinfo.h, but only defines it in the Linux and Mach ARM implementations.

Its CMake configuration recognizes Windows and arm64 independently, but does not add an ARM Windows initialization implementation. The resulting cpuinfo library therefore does not define cpuinfo_isa.

Windows ARM64 support was added to cpuinfo after the revision currently pinned by Ruy. Relevant upstream changes include:

• Fix ISA detection on ARM64 Windows pytorch/cpuinfo#166 — Fix ISA detection on ARM64 Windows
• Include support for Windows on Arm on BUILD.bazel along with proper Volterra detection pytorch/cpuinfo#220 — Add Windows on Arm build support and detection tests

Current workaround

#377 disables RUY_HAVE_CPUINFO and removes the cpuinfo link dependency specifically on Windows ARM64.

This makes the build and native ARM64 inference tests pass, but it also causes Ruy to:

• use conservative hard-coded cache sizes;
• report NeonDotprod() as unavailable;
• potentially skip the optimized ARM64 dot-product path.

For this reason, the workaround does not appear suitable as the preferred long-term fix.

Requested resolution

Would it be possible to:

1. update Ruy's cpuinfo submodule to a revision that supports Windows ARM64;
2. validate both the CMake and Bazel integrations on Windows ARM64;
3. add a native Windows ARM64 CI build or link test;
4. keep RUY_HAVE_CPUINFO enabled so runtime cache and ISA detection remain available?

If updating cpuinfo is currently blocked by compatibility requirements, an explicit build option for disabling cpuinfo would still be preferable to a hard-coded Windows ARM64 platform exception.

Validation already completed

With cpuinfo disabled as in #377:

• Ruy links successfully in a native Windows ARM64 CTranslate2 build;
• multithreaded INT8 inference returns the expected result;
• the generated DLL and Python extension are native ARM64 (AA64);
• the installed-wheel test suite reports 82 passed and 89 skipped.

Related downstream PR: OpenNMT/CTranslate2#2086
Related workaround PR: #377