diff --git a/CMakeLists.txt b/CMakeLists.txt
index d95e5db16351..16df90c9aee8 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -91,6 +91,12 @@ ocv_cmake_hook(CMAKE_INIT)
 
 # must go before the project()/enable_language() commands
 ocv_update(CMAKE_CONFIGURATION_TYPES "Debug;Release" CACHE STRING "Configs" FORCE)
+if(NOT DEFINED CMAKE_BUILD_TYPE
+    AND NOT OPENCV_SKIP_DEFAULT_BUILD_TYPE
+)
+  message(STATUS "'Release' build type is used by default. Use CMAKE_BUILD_TYPE to specify build type (Release or Debug)")
+  set(CMAKE_BUILD_TYPE "Release" CACHE STRING "Choose the type of build")
+endif()
 if(DEFINED CMAKE_BUILD_TYPE)
   set_property(CACHE CMAKE_BUILD_TYPE PROPERTY STRINGS "${CMAKE_CONFIGURATION_TYPES}")
 endif()
@@ -610,10 +616,6 @@ endif()
 # ----------------------------------------------------------------------------
 # OpenCV compiler and linker options
 # ----------------------------------------------------------------------------
-# In case of Makefiles if the user does not setup CMAKE_BUILD_TYPE, assume it's Release:
-if(CMAKE_GENERATOR MATCHES "Makefiles|Ninja" AND "${CMAKE_BUILD_TYPE}" STREQUAL "")
-  set(CMAKE_BUILD_TYPE Release)
-endif()
 
 ocv_cmake_hook(POST_CMAKE_BUILD_OPTIONS)
 
diff --git a/cmake/OpenCVCompilerOptimizations.cmake b/cmake/OpenCVCompilerOptimizations.cmake
index 6fda0c84ebf9..1c40ee7a1b6a 100644
--- a/cmake/OpenCVCompilerOptimizations.cmake
+++ b/cmake/OpenCVCompilerOptimizations.cmake
@@ -241,7 +241,7 @@ if(X86 OR X86_64)
     ocv_intel_compiler_optimization_option(FP16 "-mavx" "/arch:AVX")
     ocv_intel_compiler_optimization_option(AVX "-mavx" "/arch:AVX")
     ocv_intel_compiler_optimization_option(FMA3 "" "")
-    ocv_intel_compiler_optimization_option(POPCNT "" "")
+    ocv_intel_compiler_optimization_option(POPCNT "-mpopcnt" "")  # -mpopcnt is available since ICC 19.0.0
     ocv_intel_compiler_optimization_option(SSE4_2 "-msse4.2" "/arch:SSE4.2")
     ocv_intel_compiler_optimization_option(SSE4_1 "-msse4.1" "/arch:SSE4.1")
     ocv_intel_compiler_optimization_option(SSE3 "-msse3" "/arch:SSE3")
diff --git a/modules/core/include/opencv2/core/cvdef.h b/modules/core/include/opencv2/core/cvdef.h
index ada460334c54..f785f32b6e2c 100644
--- a/modules/core/include/opencv2/core/cvdef.h
+++ b/modules/core/include/opencv2/core/cvdef.h
@@ -719,6 +719,8 @@ __CV_ENUM_FLAGS_BITWISE_XOR_EQ   (EnumType, EnumType)
 #  elif __cplusplus >= 201703L
 //   available when compiler is C++17 compliant
 #    define CV_NODISCARD_STD [[nodiscard]]
+#  elif defined(__INTEL_COMPILER)
+     // see above, available when C++17 is enabled
 #  elif defined(_MSC_VER) && _MSC_VER >= 1911 && _MSVC_LANG >= 201703L
 //   available with VS2017 v15.3+ with /std:c++17 or higher; works on functions and classes
 #    define CV_NODISCARD_STD [[nodiscard]]
diff --git a/modules/core/include/opencv2/core/hal/intrin_sse.hpp b/modules/core/include/opencv2/core/hal/intrin_sse.hpp
index 2244717e1986..443ee16097f3 100644
--- a/modules/core/include/opencv2/core/hal/intrin_sse.hpp
+++ b/modules/core/include/opencv2/core/hal/intrin_sse.hpp
@@ -244,7 +244,7 @@ struct v_uint64x2
     explicit v_uint64x2(__m128i v) : val(v) {}
     v_uint64x2(uint64 v0, uint64 v1)
     {
-#if defined(_MSC_VER) && _MSC_VER >= 1920/*MSVS 2019*/ && defined(_M_X64)
+#if defined(_MSC_VER) && _MSC_VER >= 1920/*MSVS 2019*/ && defined(_M_X64) && !defined(__clang__)
         val = _mm_setr_epi64x((int64_t)v0, (int64_t)v1);
 #elif defined(__GNUC__)
         val = _mm_setr_epi64((__m64)v0, (__m64)v1);
@@ -278,7 +278,7 @@ struct v_int64x2
     explicit v_int64x2(__m128i v) : val(v) {}
     v_int64x2(int64 v0, int64 v1)
     {
-#if defined(_MSC_VER) && _MSC_VER >= 1920/*MSVS 2019*/ && defined(_M_X64)
+#if defined(_MSC_VER) && _MSC_VER >= 1920/*MSVS 2019*/ && defined(_M_X64) && !defined(__clang__)
         val = _mm_setr_epi64x((int64_t)v0, (int64_t)v1);
 #elif defined(__GNUC__)
         val = _mm_setr_epi64((__m64)v0, (__m64)v1);
diff --git a/modules/core/src/hal_replacement.hpp b/modules/core/src/hal_replacement.hpp
index 1a558f253278..6ed795b5e1c0 100644
--- a/modules/core/src/hal_replacement.hpp
+++ b/modules/core/src/hal_replacement.hpp
@@ -47,12 +47,15 @@
 
 #include "opencv2/core/hal/interface.h"
 
-#if defined __GNUC__
-#  pragma GCC diagnostic push
-#  pragma GCC diagnostic ignored "-Wunused-parameter"
-#elif defined _MSC_VER
-#  pragma warning( push )
-#  pragma warning( disable: 4100 )
+#if defined(__clang__)  // clang or MSVC clang
+#pragma clang diagnostic push
+#pragma clang diagnostic ignored "-Wunused-parameter"
+#elif defined(_MSC_VER)
+#pragma warning(push)
+#pragma warning(disable : 4100)
+#elif defined(__GNUC__)
+#pragma GCC diagnostic push
+#pragma GCC diagnostic ignored "-Wunused-parameter"
 #endif
 
 //! @addtogroup core_hal_interface
@@ -731,10 +734,12 @@ inline int hal_ni_minMaxIdx(const uchar* src_data, size_t src_step, int width, i
 //! @}
 
 
-#if defined __GNUC__
-#  pragma GCC diagnostic pop
-#elif defined _MSC_VER
-#  pragma warning( pop )
+#if defined(__clang__)
+#pragma clang diagnostic pop
+#elif defined(_MSC_VER)
+#pragma warning(pop)
+#elif defined(__GNUC__)
+#pragma GCC diagnostic pop
 #endif
 
 #include "hal_internal.hpp"
diff --git a/modules/features2d/src/hal_replacement.hpp b/modules/features2d/src/hal_replacement.hpp
index 951b7b62ec85..f9fbf96daacd 100644
--- a/modules/features2d/src/hal_replacement.hpp
+++ b/modules/features2d/src/hal_replacement.hpp
@@ -44,12 +44,15 @@
 
 #include "opencv2/core/hal/interface.h"
 
-#if defined __GNUC__
-#  pragma GCC diagnostic push
-#  pragma GCC diagnostic ignored "-Wunused-parameter"
-#elif defined _MSC_VER
-#  pragma warning( push )
-#  pragma warning( disable: 4100 )
+#if defined(__clang__)  // clang or MSVC clang
+#pragma clang diagnostic push
+#pragma clang diagnostic ignored "-Wunused-parameter"
+#elif defined(_MSC_VER)
+#pragma warning(push)
+#pragma warning(disable : 4100)
+#elif defined(__GNUC__)
+#pragma GCC diagnostic push
+#pragma GCC diagnostic ignored "-Wunused-parameter"
 #endif
 
 //! @addtogroup features2d_hal_interface
@@ -103,10 +106,12 @@ inline int hal_ni_FAST(const uchar* src_data, size_t src_step, int width, int he
 //! @}
 
 
-#if defined __GNUC__
-#  pragma GCC diagnostic pop
-#elif defined _MSC_VER
-#  pragma warning( pop )
+#if defined(__clang__)
+#pragma clang diagnostic pop
+#elif defined(_MSC_VER)
+#pragma warning(pop)
+#elif defined(__GNUC__)
+#pragma GCC diagnostic pop
 #endif
 
 #include "custom_hal.hpp"
diff --git a/modules/imgproc/src/hal_replacement.hpp b/modules/imgproc/src/hal_replacement.hpp
index ff4a41923dc5..6eb956bfeeda 100644
--- a/modules/imgproc/src/hal_replacement.hpp
+++ b/modules/imgproc/src/hal_replacement.hpp
@@ -48,12 +48,15 @@
 #include "opencv2/core/hal/interface.h"
 #include "opencv2/imgproc/hal/interface.h"
 
-#if defined __GNUC__
-#  pragma GCC diagnostic push
-#  pragma GCC diagnostic ignored "-Wunused-parameter"
-#elif defined _MSC_VER
-#  pragma warning( push )
-#  pragma warning( disable: 4100 )
+#if defined(__clang__)  // clang or MSVC clang
+#pragma clang diagnostic push
+#pragma clang diagnostic ignored "-Wunused-parameter"
+#elif defined(_MSC_VER)
+#pragma warning(push)
+#pragma warning(disable : 4100)
+#elif defined(__GNUC__)
+#pragma GCC diagnostic push
+#pragma GCC diagnostic ignored "-Wunused-parameter"
 #endif
 
 //! @addtogroup imgproc_hal_interface
@@ -809,10 +812,12 @@ inline int hal_ni_canny(const uchar* src_data, size_t src_step, uchar* dst_data,
 
 //! @}
 
-#if defined __GNUC__
-#  pragma GCC diagnostic pop
-#elif defined _MSC_VER
-#  pragma warning( pop )
+#if defined(__clang__)
+#pragma clang diagnostic pop
+#elif defined(_MSC_VER)
+#pragma warning(pop)
+#elif defined(__GNUC__)
+#pragma GCC diagnostic pop
 #endif
 
 #include "custom_hal.hpp"