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Fix Windows ARM64 (MSVC) build broken by NEON SIMD templatization (#5274)

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Summary:
Pull Request resolved: https://github.com/facebookresearch/faiss/pull/5274

D95392150 (templatize simdlib types on SIMDLevel) added an unconditional CMake block that compiles `${FAISS_SIMD_NEON_SRC}` and defines `COMPILE_SIMD_ARM_NEON` for any ARM64 build target. Those TUs include `simdlib_neon.h`, which uses GCC/Clang-style patterns that MSVC's `<arm_neon.h>` cannot compile — most notably taking the address of NEON intrinsics as non-type template parameters (e.g. `.call<&vmulq_u16>()`, `.call<&detail::simdlib::vdupq_n_u16>()`). MSVC implements many of those intrinsics as macros/compiler builtins, so their addresses are not usable. AArch64-only intrinsics like `vmovn_high_u16` and `vsraq_n_*` further widen the gap.

Before D95392150, `simdlib.h` dispatched via `#elif defined(__aarch64__)`. MSVC on Windows ARM64 defines `_M_ARM64` (not `__aarch64__`), so the ARM64/MSVC build silently fell through to `simdlib_emulated.h` and worked. This diff restores that behavior for the new CMake gate.

Fixes the OSS Windows ARM64 build break reported on facebookresearch/faiss issue 4993.

Reviewed By: junjieqi

Differential Revision: D107447785

fbshipit-source-id: e4ebea7f2b22e4a9b4dc7d3ae1633c14738af7f7
This commit is contained in:
Michael Norris
2026-06-04 20:28:01 -07:00
committed by meta-codesync[bot]
parent fe46c3c804
commit eb4c1eafe2
1 changed files with 5 additions and 1 deletions
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faiss/CMakeLists.txt
+5 -1
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@@ -591,7 +591,11 @@ endif()
# NEON is mandatory on ARM64 — ensure COMPILE_SIMD_ARM_NEON is always defined
# and NEON source files are always compiled into the main faiss target.
# (On x86, AVX2/AVX512 are optional and only compiled per opt_level above.)
if(CMAKE_SYSTEM_PROCESSOR MATCHES "(aarch64|arm64|ARM64)")
# MSVC on Windows ARM64 is excluded: simdlib_neon.h takes the address of NEON
# intrinsics as non-type template parameters, but MSVC implements many of them
# as macros/compiler builtins, so &vmulq_u16 et al. are not usable. MSVC ARM64
# falls back to simdlib_emulated.h, matching the pre-D95392150 behavior.
if(CMAKE_SYSTEM_PROCESSOR MATCHES "(aarch64|arm64|ARM64)" AND NOT MSVC)
target_compile_definitions(faiss PRIVATE COMPILE_SIMD_ARM_NEON)
target_sources(faiss PRIVATE ${FAISS_SIMD_NEON_SRC})
endif()