core: fix F16C compilation check

modules/core/include/opencv2/core/cv_cpu_dispatch.h

@@ -216,6 +216,11 @@ struct VZeroUpperGuard {
 #  define CV_VSX 1
 #endif
 
+#ifdef __F16C__
+#  include <immintrin.h>
+#  define CV_FP16 1
+#endif
+
 #endif // !__OPENCV_BUILD && !__CUDACC (Compatibility code)
 
 

modules/core/include/opencv2/core/cvdef.h

@@ -765,7 +765,7 @@ protected:
     float16_t() {}
     explicit float16_t(float x)
     {
-    #if CV_AVX2
+    #if CV_FP16
         __m128 v = _mm_load_ss(&x);
         w = (ushort)_mm_cvtsi128_si32(_mm_cvtps_ph(v, 0));
     #else
@@ -796,7 +796,7 @@ protected:
 
     operator float() const
     {
-    #if CV_AVX2
+    #if CV_FP16
         float f;
         _mm_store_ss(&f, _mm_cvtph_ps(_mm_cvtsi32_si128(w)));
         return f;

modules/core/include/opencv2/core/hal/intrin_avx.hpp

@@ -3121,18 +3121,39 @@ OPENCV_HAL_IMPL_AVX_LOADSTORE_INTERLEAVE(v_float32x8, float, f32, v_uint32x8, un
 OPENCV_HAL_IMPL_AVX_LOADSTORE_INTERLEAVE(v_int64x4, int64, s64, v_uint64x4, uint64, u64)
 OPENCV_HAL_IMPL_AVX_LOADSTORE_INTERLEAVE(v_float64x4, double, f64, v_uint64x4, uint64, u64)
 
+//
 // FP16
+//
+
 inline v_float32x8 v256_load_expand(const float16_t* ptr)
 {
+#if CV_FP16
     return v_float32x8(_mm256_cvtph_ps(_mm_loadu_si128((const __m128i*)ptr)));
+#else
+    float CV_DECL_ALIGNED(32) buf[8];
+    for (int i = 0; i < 8; i++)
+        buf[i] = (float)ptr[i];
+    return v256_load_aligned(buf);
+#endif
 }
 
 inline void v_pack_store(float16_t* ptr, const v_float32x8& a)
 {
+#if CV_FP16
     __m128i ah = _mm256_cvtps_ph(a.val, 0);
     _mm_storeu_si128((__m128i*)ptr, ah);
+#else
+    float CV_DECL_ALIGNED(32) buf[8];
+    v_store_aligned(buf, a);
+    for (int i = 0; i < 8; i++)
+        ptr[i] = float16_t(buf[i]);
+#endif
 }
 
+//
+// end of FP16
+//
+
 inline void v256_cleanup() { _mm256_zeroall(); }
 
 CV_CPU_OPTIMIZATION_HAL_NAMESPACE_END

modules/core/src/convert.simd.hpp

@@ -5,6 +5,11 @@
 #include "precomp.hpp"
 #include "convert.hpp"
 
+#if !defined(OPENCV_SUPRESS_WARNING_AVX2_WITHOUT_FP16C) && \
+    (defined(__GNUC__) && defined(__AVX2__) && !defined(__F16C__))
+#warning "Non-optimal compiler flags: AVX2 without FP16. Generated code is very slow. Consider adding '-mf16c' compiler option."
+#endif
+
 namespace cv {
 CV_CPU_OPTIMIZATION_NAMESPACE_BEGIN
 

modules/core/test/test_intrin.cpp

@@ -126,9 +126,11 @@ DEFINE_SIMD_TESTS(256, AVX512_SKX)
 
 TEST(hal_intrin256, float16x16_FP16)
 {
+#if CV_TRY_FP16
     //CV_CPU_CALL_FP16_(test_hal_intrin_float16, ());
     CV_CPU_CALL_AVX2_(test_hal_intrin_float16, ());
-    throw SkipTestException("Unsupported hardware: FP16 is not available");
+#endif
+    throw SkipTestException("Unsupported: FP16 is not available");
 }
 
 
@@ -142,8 +144,10 @@ namespace intrin512 {
 
 TEST(hal_intrin512, float16x32_FP16)
 {
+#if CV_TRY_FP16
     CV_CPU_CALL_AVX512_SKX_(test_hal_intrin_float16, ());
-    throw SkipTestException("Unsupported hardware: FP16 is not available");
+#endif
+    throw SkipTestException("Unsupported: FP16 is not available");
 }
 
 

modules/core/test/test_intrin_utils.hpp

@@ -1902,21 +1902,21 @@ void test_hal_intrin_float64()
 #endif
 }
 
-#if CV_FP16
 void test_hal_intrin_float16()
 {
     DUMP_ENTRY(v_float16);
 #if CV_FP16
     TheTest<v_float32>()
         .test_loadstore_fp16_f32()
-#endif
 #if CV_SIMD_FP16
         .test_loadstore_fp16()
         .test_float_cvt_fp16()
 #endif
         ;
-}
+#else
+    std::cout << "SKIP: CV_FP16 is not available" << std::endl;
 #endif
+}
 
 /*#if defined(CV_CPU_DISPATCH_MODE_FP16) && CV_CPU_DISPATCH_MODE == FP16
 void test_hal_intrin_float16()