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fix: add runtime check for AVX512-FP16 support instead of relying on compiler version #28236

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fix: add runtime check for AVX512-FP16 support instead of relying on compiler version #28236

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fbb7edf
[fix] solve avx516 bug
PriscillaJCorn Apr 27, 2026
6a61fe8
Update cmake/onnxruntime_mlas.cmake
PriscillaJCorn Apr 28, 2026
d8cb7ed
Update cmake/onnxruntime_mlas.cmake
PriscillaJCorn Apr 28, 2026
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22 changes: 20 additions & 2 deletions cmake/onnxruntime_mlas.cmake
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Original file line number Diff line number Diff line change
Expand Up @@ -774,11 +774,29 @@ else()
${MLAS_SRC_DIR}/rotary_embedding_kernel_avx2.cpp
${MLAS_SRC_DIR}/rotary_embedding_kernel_avx2.cpp
)
if(CMAKE_CXX_COMPILER_VERSION GREATER_EQUAL 13.1 AND NOT(APPLE))

include(CheckCSourceCompiles)
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Copilot AI Apr 29, 2026

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This feature is consumed by C++ sources (platform.cpp), but the probe uses CheckCSourceCompiles. Using CheckCXXSourceCompiles (and the corresponding include) makes the probe match the actual compilation environment (C++ compiler, flags, and frontend), and avoids coupling this logic to the presence/configuration of the C language in the build.

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set(MLAS_OLD_CMAKE_REQUIRED_FLAGS "${CMAKE_REQUIRED_FLAGS}")
if(CMAKE_REQUIRED_FLAGS)
set(CMAKE_REQUIRED_FLAGS "${CMAKE_REQUIRED_FLAGS} -mavx512fp16")
else()
set(CMAKE_REQUIRED_FLAGS "-mavx512fp16")
endif()
check_c_source_compiles("
int main() {
__asm__ volatile(\"vcvtneeph2ps %ymm0, %ymm1\");
return 0;
}
" COMPILER_SUPPORTS_AVX512FP16)
set(CMAKE_REQUIRED_FLAGS "${MLAS_OLD_CMAKE_REQUIRED_FLAGS}")

if(COMPILER_SUPPORTS_AVX512FP16 AND NOT APPLE)
set(mlas_platform_srcs_avx2
${mlas_platform_srcs_avx2}
${MLAS_SRC_DIR}/x86_64/cvtfp16Avx.S
)
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list(APPEND mlas_private_compile_definitions MLAS_SUPPORTS_AVX512FP16)
endif()
Comment on lines +799 to 800
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Copilot AI Apr 29, 2026

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The probe is hardwired to GCC/Clang-style flags (-mavx512fp16) and GNU inline asm syntax, which will fail under MSVC (and some clang-cl configurations). This can silently disable the FP16 path on Windows even when the toolchain supports it, changing behavior vs the prior _MSC_VER branch. Consider branching on CMAKE_CXX_COMPILER_ID and using a C++-based probe with compiler-appropriate flags (e.g., MSVC /arch: equivalent or a clang-cl compatible approach), so the macro is correctly set across supported toolchains.

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message(STATUS "CMAKE_CXX_COMPILER_ID: ${CMAKE_CXX_COMPILER_ID}")
Expand Down Expand Up @@ -997,4 +1015,4 @@ if (NOT onnxruntime_ORT_MINIMAL_BUILD)
endif()
endif()

endif()
endif()
6 changes: 3 additions & 3 deletions onnxruntime/core/mlas/lib/platform.cpp
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Expand Up @@ -527,14 +527,14 @@ Return Value:
}

#ifndef __APPLE__
#if (defined(_MSC_VER) && (_MSC_VER >= 1933)) || (defined(__GNUC__) && (__GNUC__ >= 13))
#if defined(MLAS_SUPPORTS_AVX512FP16)
//
// Check if the processor supports AVX NE CONVERT.
//
if ((Cpuid7_1[3] & (0b1 << 5)) != 0) {
this->CastF16ToF32Kernel = &MlasCastF16ToF32KernelAvx;
}
#endif // (defined(_MSC_VER) && (_MSC_VER >= 1933)) || (defined(__GNUC__) && (__GNUC__ >= 13))
#endif // MLAS_SUPPORTS_AVX512FP16
Comment on lines 529 to +537
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Copilot AI Apr 27, 2026

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MLAS_SUPPORTS_AVX512FP16 now gates enabling CastF16ToF32Kernel, but that macro is only defined in the non-MSVC CMake path. On Windows/MSVC, setup_mlas_source_for_windows() can still add amd64/cvtfp16Avx.asm (MSVC_VERSION>=1933), yet this block will never run, so AVX512-FP16 support may be silently disabled at runtime even when the kernel is built. Consider defining MLAS_SUPPORTS_AVX512FP16 in the MSVC path when cvtfp16Avx.asm is enabled (or reintroduce an MSVC-specific compile-time guard).

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@PriscillaJCorn PriscillaJCorn Apr 28, 2026

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@copilot apply changes based on this feedback Yes, in func setup_mlas_source_for_windows() , we should define MLAS_SUPPORTS_AVX512FP16 in the MSVC path when cvtfp16Avx.asm is enabled.

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@hariharans29 hariharans29 Apr 29, 2026

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Is this comment addressed ?

Comment on lines +530 to +537
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Copilot AI Apr 29, 2026

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The compile-time guard name MLAS_SUPPORTS_AVX512FP16 doesn’t match the runtime check/comment (“AVX NE CONVERT”) and the instruction used in the CMake probe (vcvtneeph2ps). Please align terminology so it’s clear what’s actually being required (e.g., rename the macro/probe variable to reflect AVX-NE-CONVERT, or update the comment/probe to match AVX512-FP16 if that’s the intended feature).

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//
Expand Down Expand Up @@ -671,7 +671,7 @@ Return Value:
}
else{
this->ErfFP16KernelRoutine = MlasNeonErfFP16Kernel;
this->GeluFP16KernelRoutine = MlasNeonGeluFP16Kernel;
this->GeluFP16KernelRoutine = MlasNeonGeluFP16Kernel;
}
#else
this->ErfFP16KernelRoutine = MlasNeonErfFP16Kernel;
Expand Down
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