disable x86 auto recip optimization for potential precision loss (#5762)

CMakeLists.txt

@@ -517,6 +517,8 @@ else()
 
         unset(CMAKE_REQUIRED_FLAGS)
     elseif(CMAKE_CXX_COMPILER_ID MATCHES "Clang" AND CMAKE_CXX_SIMULATE_ID MATCHES "MSVC" AND CMAKE_CXX_COMPILER_FRONTEND_VARIANT MATCHES "MSVC")
+        check_cxx_compiler_flag("-mrecip=none" NCNN_COMPILER_SUPPORT_X86_RECIP_NONE)
+
         check_cxx_compiler_flag("/arch:AVX" NCNN_COMPILER_SUPPORT_X86_AVX)
 
         set(CMAKE_REQUIRED_FLAGS "/arch:AVX -mfma -mf16c")
@@ -543,6 +545,8 @@ else()
 
         unset(CMAKE_REQUIRED_FLAGS)
     else()
+        check_cxx_compiler_flag("-mrecip=none" NCNN_COMPILER_SUPPORT_X86_RECIP_NONE)
+
         check_cxx_compiler_flag("-mavx" NCNN_COMPILER_SUPPORT_X86_AVX)
 
         set(CMAKE_REQUIRED_FLAGS "-mfma -mf16c")

src/CMakeLists.txt

@@ -403,6 +403,11 @@ if(NCNN_TARGET_ARCH STREQUAL "x86")
                 target_compile_options(ncnn PRIVATE -msimd128)
             endif()
         endif()
+
+        if(NCNN_COMPILER_SUPPORT_X86_RECIP_NONE)
+            # recip optimization causes precision loss
+            target_compile_options(ncnn PRIVATE -mrecip=none)
+        endif()
     endif()
 
     if(NOT NCNN_RUNTIME_CPU AND NCNN_AVX512)