cmake: avoid amending of CMAKE_COMPILER_IS_[GNUCXX|CLANGCXX|CCACHE] vars

- Recommended compiler checks:
  - GCC: CV_GCC
  - Clang: CV_CLANG
- fixed problem with CMAKE_CXX_COMPILER_ID=Clang/AppleClang mess on MacOSX
  Details: cmake --help-policy CMP0025
- do not declare Clang as GCC compiler

3rdparty/carotene/hal/CMakeLists.txt

@@ -14,16 +14,16 @@ endif()
 
 set(TEGRA_COMPILER_FLAGS "")
 
-if(CMAKE_COMPILER_IS_GNUCXX)
+if(CV_GCC OR CV_CLANG)
   # Generate unwind information even for functions that can't throw/propagate exceptions.
   # This lets debuggers and such get non-broken backtraces for such functions, even without debugging symbols.
   list(APPEND TEGRA_COMPILER_FLAGS -funwind-tables)
 endif()
 
-if(CMAKE_COMPILER_IS_GNUCXX)
+if(CV_GCC OR CV_CLANG)
   if(X86 OR ARMEABI_V6 OR (MIPS AND ANDROID_COMPILER_VERSION VERSION_LESS "4.6"))
     list(APPEND TEGRA_COMPILER_FLAGS -fweb -fwrapv -frename-registers -fsched-stalled-insns-dep=100 -fsched-stalled-insns=2)
-  elseif(CMAKE_COMPILER_IS_CLANGCXX)
+  elseif(CV_CLANG)
     list(APPEND TEGRA_COMPILER_FLAGS -fwrapv)
   else()
     list(APPEND TEGRA_COMPILER_FLAGS -fweb -fwrapv -frename-registers -fsched2-use-superblocks -fsched2-use-traces
@@ -40,7 +40,7 @@ set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} ${TEGRA_COMPILER_FLAGS}")
 set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} ${TEGRA_COMPILER_FLAGS}")
 
 if(ARMEABI_V7A)
-  if (CMAKE_COMPILER_IS_GNUCXX)
+  if(CV_GCC OR CV_CLANG)
     set( CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -fno-tree-vectorize" )
     set( CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -fno-tree-vectorize" )
   endif()
@@ -83,7 +83,7 @@ include_directories("${CAROTENE_DIR}/include")
 get_target_property(carotene_defs carotene_objs INTERFACE_COMPILE_DEFINITIONS)
 set_property(DIRECTORY APPEND PROPERTY COMPILE_DEFINITIONS ${carotene_defs})
 
-  if (CMAKE_COMPILER_IS_GNUCXX)
+  if(CV_GCC)
     # allow more inlines - these parameters improve performance for:
     #   matchTemplate about 5-10%
     #   goodFeaturesToTrack 10-20%

3rdparty/ippicv/CMakeLists.txt

@@ -20,10 +20,10 @@ file(GLOB lib_hdrs ${IPP_IW_PATH}/include/*.h ${IPP_IW_PATH}/include/iw/*.h ${IP
 add_library(${IPP_IW_LIBRARY} STATIC ${lib_srcs} ${lib_hdrs})
 
 if(UNIX)
-  if(CMAKE_COMPILER_IS_GNUCXX OR CV_ICC)
+  if(CV_GCC OR CV_CLANG OR CV_ICC)
     set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -Wno-unused-function -Wno-missing-braces -Wno-missing-field-initializers")
   endif()
-  if (CMAKE_C_COMPILER_ID MATCHES "Clang")
+  if(CV_CLANG)
     set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -Wno-self-assign")
   endif()
 endif()

3rdparty/libjpeg/CMakeLists.txt

@@ -28,7 +28,7 @@ endif()
 
 add_library(${JPEG_LIBRARY} STATIC ${lib_srcs} ${lib_hdrs})
 
-if(CMAKE_COMPILER_IS_GNUCXX)
+if(CV_GCC OR CV_CLANG)
   set_source_files_properties(jcdctmgr.c PROPERTIES COMPILE_FLAGS "-O1")
 endif()
 

3rdparty/libtiff/CMakeLists.txt

@@ -244,7 +244,7 @@ mark_as_advanced(HAVE_IEEEFP)
 
 # Large file support
 if(UNIX OR MINGW)
-  if(ANDROID AND (ANDROID_NATIVE_API_LEVEL LESS 21) AND (NOT "${CMAKE_CXX_COMPILER_ID}" MATCHES Clang))
+  if(ANDROID AND (ANDROID_NATIVE_API_LEVEL LESS 21) AND CV_GCC)
     # Android NDK build problem: 'mmap' issue with GCC and API<21
   else()
     # This might not catch every possibility catered for by

3rdparty/tbb/CMakeLists.txt

@@ -73,7 +73,7 @@ if(HAVE_PTHREAD)
   add_definitions(-DUSE_PTHREAD) #required for Unix
 endif()
 
-if(CMAKE_COMPILER_IS_GNUCXX AND NOT CMAKE_COMPILER_IS_CLANGCXX)
+if(CV_GCC)
   add_definitions(-DTBB_USE_GCC_BUILTINS=1) #required for ARM GCC
   if(NOT CMAKE_CXX_COMPILER_VERSION LESS 6.0)
     set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -flifetime-dse=1") # workaround for GCC 6.x

CMakeLists.txt

@@ -313,23 +313,23 @@ OCV_OPTION(INSTALL_TESTS            "Install accuracy and performance test binar
 OCV_OPTION(ENABLE_CCACHE              "Use ccache"                                               (UNIX AND NOT IOS AND (CMAKE_GENERATOR MATCHES "Makefile" OR CMAKE_GENERATOR MATCHES "Ninja")) )
 OCV_OPTION(ENABLE_PRECOMPILED_HEADERS "Use precompiled headers"                                  ON IF (NOT IOS AND NOT CMAKE_CROSSCOMPILING) )
 OCV_OPTION(ENABLE_SOLUTION_FOLDERS    "Solution folder in Visual Studio or in other IDEs"        (MSVC_IDE OR CMAKE_GENERATOR MATCHES Xcode) )
-OCV_OPTION(ENABLE_PROFILING           "Enable profiling in the GCC compiler (Add flags: -g -pg)" OFF  IF CMAKE_COMPILER_IS_GNUCXX )
-OCV_OPTION(ENABLE_COVERAGE            "Enable coverage collection with  GCov"                    OFF  IF CMAKE_COMPILER_IS_GNUCXX )
-OCV_OPTION(ENABLE_OMIT_FRAME_POINTER  "Enable -fomit-frame-pointer for GCC"                      ON   IF CMAKE_COMPILER_IS_GNUCXX AND NOT (APPLE AND CMAKE_COMPILER_IS_CLANGCXX) )
-OCV_OPTION(ENABLE_POWERPC             "Enable PowerPC for GCC"                                   ON   IF (CMAKE_COMPILER_IS_GNUCXX AND CMAKE_SYSTEM_PROCESSOR MATCHES powerpc.*) )
-OCV_OPTION(ENABLE_VSX                 "Enable POWER8 and above VSX (64-bit little-endian)"       ON   IF (CMAKE_COMPILER_IS_GNUCXX AND PPC64LE) )
-OCV_OPTION(ENABLE_FAST_MATH           "Enable -ffast-math (not recommended for GCC 4.6.x)"       OFF  IF (CMAKE_COMPILER_IS_GNUCXX AND (X86 OR X86_64)) )
-OCV_OPTION(ENABLE_NEON                "Enable NEON instructions"                                 (NEON OR ANDROID_ARM_NEON OR AARCH64) IF CMAKE_COMPILER_IS_GNUCXX AND (ARM OR AARCH64 OR IOS) )
-OCV_OPTION(ENABLE_VFPV3               "Enable VFPv3-D32 instructions"                            OFF  IF CMAKE_COMPILER_IS_GNUCXX AND (ARM OR AARCH64 OR IOS) )
+OCV_OPTION(ENABLE_PROFILING           "Enable profiling in the GCC compiler (Add flags: -g -pg)" OFF  IF CV_GCC )
+OCV_OPTION(ENABLE_COVERAGE            "Enable coverage collection with  GCov"                    OFF  IF CV_GCC )
+OCV_OPTION(ENABLE_OMIT_FRAME_POINTER  "Enable -fomit-frame-pointer for GCC"                      ON   IF CV_GCC )
+OCV_OPTION(ENABLE_POWERPC             "Enable PowerPC for GCC"                                   ON   IF (CV_GCC AND CMAKE_SYSTEM_PROCESSOR MATCHES powerpc.*) )
+OCV_OPTION(ENABLE_VSX                 "Enable POWER8 and above VSX (64-bit little-endian)"       ON   IF (CV_GCC AND PPC64LE) )
+OCV_OPTION(ENABLE_FAST_MATH           "Enable -ffast-math (not recommended for GCC 4.6.x)"       OFF  IF (CV_GCC AND (X86 OR X86_64)) )
+OCV_OPTION(ENABLE_NEON                "Enable NEON instructions"                                 (NEON OR ANDROID_ARM_NEON OR AARCH64) IF (CV_GCC OR CV_CLANG) AND (ARM OR AARCH64 OR IOS) )
+OCV_OPTION(ENABLE_VFPV3               "Enable VFPv3-D32 instructions"                            OFF  IF (CV_GCC OR CV_CLANG) AND (ARM OR AARCH64 OR IOS) )
 OCV_OPTION(ENABLE_NOISY_WARNINGS      "Show all warnings even if they are too noisy"             OFF )
 OCV_OPTION(OPENCV_WARNINGS_ARE_ERRORS "Treat warnings as errors"                                 OFF )
 OCV_OPTION(ANDROID_EXAMPLES_WITH_LIBS "Build binaries of Android examples with native libraries" OFF  IF ANDROID )
 OCV_OPTION(ENABLE_IMPL_COLLECTION     "Collect implementation data on function call"             OFF )
 OCV_OPTION(ENABLE_INSTRUMENTATION     "Instrument functions to collect calls trace and performance" OFF )
-OCV_OPTION(ENABLE_GNU_STL_DEBUG       "Enable GNU STL Debug mode (defines _GLIBCXX_DEBUG)"       OFF IF ((NOT CMAKE_VERSION VERSION_LESS "2.8.11") AND CMAKE_COMPILER_IS_GNUCXX) )
+OCV_OPTION(ENABLE_GNU_STL_DEBUG       "Enable GNU STL Debug mode (defines _GLIBCXX_DEBUG)"       OFF IF ((NOT CMAKE_VERSION VERSION_LESS "2.8.11") AND CV_GCC) )
 OCV_OPTION(ENABLE_BUILD_HARDENING     "Enable hardening of the resulting binaries (against security attacks, detects memory corruption, etc)" OFF)
-OCV_OPTION(ENABLE_LTO                 "Enable Link Time Optimization" OFF IF CMAKE_COMPILER_IS_GNUCXX OR MSVC)
-OCV_OPTION(ENABLE_THIN_LTO            "Enable Thin LTO" OFF IF CMAKE_COMPILER_IS_CLANGCXX)
+OCV_OPTION(ENABLE_LTO                 "Enable Link Time Optimization" OFF IF CV_GCC OR MSVC)
+OCV_OPTION(ENABLE_THIN_LTO            "Enable Thin LTO" OFF IF CV_CLANG)
 OCV_OPTION(GENERATE_ABI_DESCRIPTOR    "Generate XML file for abi_compliance_checker tool" OFF IF UNIX)
 OCV_OPTION(CV_ENABLE_INTRINSICS       "Use intrinsic-based optimized code" ON )
 OCV_OPTION(CV_DISABLE_OPTIMIZATION    "Disable explicit optimized code (dispatched code/intrinsics/loop unrolling/etc)" OFF )
@@ -1037,7 +1037,7 @@ else()
   status("    Linker flags (Release):" ${CMAKE_SHARED_LINKER_FLAGS} ${CMAKE_SHARED_LINKER_FLAGS_RELEASE})
   status("    Linker flags (Debug):"   ${CMAKE_SHARED_LINKER_FLAGS} ${CMAKE_SHARED_LINKER_FLAGS_DEBUG})
 endif()
-status("    ccache:"                  CMAKE_COMPILER_IS_CCACHE THEN YES ELSE NO)
+status("    ccache:"                  OPENCV_COMPILER_IS_CCACHE THEN YES ELSE NO)
 status("    Precompiled headers:"     PCHSupport_FOUND AND ENABLE_PRECOMPILED_HEADERS THEN YES ELSE NO)
 
 # ========================== Dependencies ============================

cmake/OpenCVCompilerDefenses.cmake

@@ -44,7 +44,7 @@ if(MSVC)
   if(NOT X86_64)
     set(OPENCV_LINKER_DEFENSES_FLAGS_COMMON "${OPENCV_LINKER_DEFENSES_FLAGS_COMMON} /safeseh")
   endif()
-elseif(CMAKE_COMPILER_IS_GNUCXX)
+elseif(CV_GCC)
   if(CMAKE_CXX_COMPILER_VERSION VERSION_LESS "4.9")
     ocv_add_defense_compiler_flag("-fstack-protector")
   else()
@@ -71,7 +71,7 @@ else()
 endif()
 
 set(CMAKE_POSITION_INDEPENDENT_CODE TRUE)
-if(CMAKE_COMPILER_IS_GNUCXX)
+if(CV_GCC OR CV_CLANG)
     if(NOT CMAKE_CXX_FLAGS MATCHES "-fPIC")
       ocv_add_defense_compiler_flag("-fPIC")
     endif()
@@ -82,7 +82,7 @@ set( CMAKE_SHARED_LINKER_FLAGS "${CMAKE_SHARED_LINKER_FLAGS} ${OPENCV_LINKER_DEF
 set( CMAKE_MODULE_LINKER_FLAGS "${CMAKE_MODULE_LINKER_FLAGS} ${OPENCV_LINKER_DEFENSES_FLAGS_COMMON}" )
 set( CMAKE_EXE_LINKER_FLAGS "${CMAKE_EXE_LINKER_FLAGS} ${OPENCV_LINKER_DEFENSES_FLAGS_COMMON}" )
 
-if(CMAKE_COMPILER_IS_GNUCXX)
+if(CV_GCC OR CV_CLANG)
   foreach(flags
           CMAKE_CXX_FLAGS CMAKE_CXX_FLAGS_RELEASE CMAKE_CXX_FLAGS_DEBUG
           CMAKE_C_FLAGS CMAKE_C_FLAGS_RELEASE CMAKE_C_FLAGS_DEBUG)

cmake/OpenCVCompilerOptimizations.cmake

@@ -211,7 +211,7 @@ if(X86 OR X86_64)
     endif()
     ocv_intel_compiler_optimization_option(AVX_512F "-march=common-avx512" "/arch:COMMON-AVX512")
     ocv_intel_compiler_optimization_option(AVX512_SKX "-march=core-avx512" "/arch:CORE-AVX512")
-  elseif(CMAKE_COMPILER_IS_GNUCXX)
+  elseif(CV_GCC OR CV_CLANG)
     ocv_update(CPU_AVX2_FLAGS_ON "-mavx2")
     ocv_update(CPU_FP16_FLAGS_ON "-mf16c")
     ocv_update(CPU_AVX_FLAGS_ON "-mavx")
@@ -223,7 +223,7 @@ if(X86 OR X86_64)
     ocv_update(CPU_SSSE3_FLAGS_ON "-mssse3")
     ocv_update(CPU_SSE2_FLAGS_ON "-msse2")
     ocv_update(CPU_SSE_FLAGS_ON "-msse")
-    if(NOT (CMAKE_CXX_COMPILER_ID STREQUAL "GNU" AND CMAKE_CXX_COMPILER_VERSION VERSION_LESS "5.0"))  # GCC >= 5.0
+    if(NOT (CV_GCC AND CMAKE_CXX_COMPILER_VERSION VERSION_LESS "5.0"))  # GCC >= 5.0
       # -mavx512f -mavx512pf -mavx512er -mavx512cd -mavx512vl -mavx512bw -mavx512dq -mavx512ifma -mavx512vbmi
       ocv_update(CPU_AVX_512F_FLAGS_ON "-mavx512f")
       ocv_update(CPU_AVX512_SKX_FLAGS_ON "-mavx512f -mavx512cd -mavx512vl -mavx512bw -mavx512dq")
@@ -288,7 +288,7 @@ elseif(PPC64LE)
   ocv_update(CPU_KNOWN_OPTIMIZATIONS "VSX")
   ocv_update(CPU_VSX_TEST_FILE "${OpenCV_SOURCE_DIR}/cmake/checks/cpu_vsx.cpp")
 
-  if(CMAKE_COMPILER_IS_CLANGCXX AND (NOT ${CMAKE_CXX_COMPILER} MATCHES "xlc"))
+  if(CV_CLANG AND (NOT ${CMAKE_CXX_COMPILER} MATCHES "xlc"))
     ocv_update(CPU_VSX_FLAGS_ON "-mvsx -maltivec")
   else()
     ocv_update(CPU_VSX_FLAGS_ON "-mcpu=power8")
@@ -545,7 +545,7 @@ macro(ocv_compiler_optimization_options)
 endmacro()
 
 macro(ocv_compiler_optimization_options_finalize)
-  if(CMAKE_COMPILER_IS_GNUCXX AND (X86 OR X86_64))
+  if((CV_GCC OR CV_CLANG) AND (X86 OR X86_64))
     if(NOT APPLE AND CMAKE_SIZEOF_VOID_P EQUAL 4)
       if(OPENCV_EXTRA_CXX_FLAGS MATCHES "-m(sse2|avx)")
         add_extra_compiler_option(-mfpmath=sse) # !! important - be on the same wave with x64 compilers

cmake/OpenCVCompilerOptions.cmake

-if(ENABLE_CCACHE AND NOT CMAKE_COMPILER_IS_CCACHE)
+if("${CMAKE_CXX_COMPILER};${CMAKE_C_COMPILER};${CMAKE_CXX_COMPILER_LAUNCHER}" MATCHES "ccache")
+  set(CMAKE_COMPILER_IS_CCACHE 1)  # FIXIT Avoid setting of CMAKE_ variables
+  set(OPENCV_COMPILER_IS_CCACHE 1)
+endif()
+function(access_CMAKE_COMPILER_IS_CCACHE)
+  if(NOT OPENCV_SUPPRESS_DEPRECATIONS)
+    message(WARNING "DEPRECATED: CMAKE_COMPILER_IS_CCACHE is replaced to OPENCV_COMPILER_IS_CCACHE.")
+  endif()
+endfunction()
+variable_watch(CMAKE_COMPILER_IS_CCACHE access_CMAKE_COMPILER_IS_CCACHE)
+if(ENABLE_CCACHE AND NOT OPENCV_COMPILER_IS_CCACHE AND NOT CMAKE_GENERATOR MATCHES "Xcode")
   # This works fine with Unix Makefiles and Ninja generators
   find_host_program(CCACHE_PROGRAM ccache)
   if(CCACHE_PROGRAM)
@@ -13,7 +23,7 @@ if(ENABLE_CCACHE AND NOT CMAKE_COMPILER_IS_CCACHE)
       # ocv_check_compiler_flag(CXX "" IS_CCACHE_WORKS)
       set(IS_CCACHE_WORKS 1)
       if(IS_CCACHE_WORKS)
-        set(CMAKE_COMPILER_IS_CCACHE 1)
+        set(OPENCV_COMPILER_IS_CCACHE 1)
       else()
         message(STATUS "Unable to compile program with enabled ccache, reverting...")
         set_property(GLOBAL PROPERTY RULE_LAUNCH_COMPILE "${__OLD_RULE_LAUNCH_COMPILE}")
@@ -24,7 +34,9 @@ if(ENABLE_CCACHE AND NOT CMAKE_COMPILER_IS_CCACHE)
   endif()
 endif()
 
-if((CMAKE_COMPILER_IS_CLANGCXX OR CMAKE_COMPILER_IS_CLANGCC OR CMAKE_COMPILER_IS_CCACHE) AND NOT CMAKE_GENERATOR MATCHES "Xcode")
+if((CV_CLANG AND NOT CMAKE_GENERATOR MATCHES "Xcode")  # PCH has no support for Clang
+    OR OPENCV_COMPILER_IS_CCACHE
+)
   set(ENABLE_PRECOMPILED_HEADERS OFF CACHE BOOL "" FORCE)
 endif()
 
@@ -71,7 +83,7 @@ if(CV_ICC AND NOT ENABLE_FAST_MATH)
   endif()
 endif()
 
-if(CMAKE_COMPILER_IS_GNUCXX)
+if(CV_GCC OR CV_CLANG)
   # High level of warnings.
   add_extra_compiler_option(-W)
   add_extra_compiler_option(-Wall)
@@ -101,7 +113,7 @@ if(CMAKE_COMPILER_IS_GNUCXX)
     add_extra_compiler_option(-Wno-unnamed-type-template-args)
     add_extra_compiler_option(-Wno-comment)
     add_extra_compiler_option(-Wno-implicit-fallthrough)
-    if(CMAKE_COMPILER_IS_GNUCXX AND CMAKE_CXX_COMPILER_VERSION VERSION_EQUAL 7.2.0)
+    if(CV_GCC AND CMAKE_CXX_COMPILER_VERSION VERSION_EQUAL 7.2.0)
       add_extra_compiler_option(-Wno-strict-overflow) # Issue is fixed in GCC 7.2.1
     endif()
   endif()
@@ -113,11 +125,11 @@ if(CMAKE_COMPILER_IS_GNUCXX)
   endif()
 
   # We need pthread's
-  if(UNIX AND NOT ANDROID AND NOT (APPLE AND CMAKE_COMPILER_IS_CLANGCXX)) # TODO
+  if(UNIX AND NOT ANDROID AND NOT (APPLE AND CV_CLANG)) # TODO
     add_extra_compiler_option(-pthread)
   endif()
 
-  if(CMAKE_COMPILER_IS_CLANGCXX)
+  if(CV_CLANG)
     add_extra_compiler_option(-Qunused-arguments)
   endif()
 
@@ -241,7 +253,7 @@ if(COMMAND ocv_compiler_optimization_options_finalize)
 endif()
 
 # set default visibility to hidden
-if((CMAKE_CXX_COMPILER_ID STREQUAL "GNU" OR CMAKE_CXX_COMPILER_ID STREQUAL "Clang")
+if((CV_GCC OR CV_CLANG)
     AND NOT OPENCV_SKIP_VISIBILITY_HIDDEN
     AND NOT " ${CMAKE_CXX_FLAGS} ${OPENCV_EXTRA_FLAGS} ${OPENCV_EXTRA_CXX_FLAGS}" MATCHES " -fvisibility")
   add_extra_compiler_option(-fvisibility=hidden)

cmake/OpenCVDetectCUDA.cmake

@@ -3,7 +3,7 @@ if(WIN32 AND NOT MSVC)
   return()
 endif()
 
-if(CMAKE_COMPILER_IS_GNUCXX AND NOT APPLE AND CMAKE_CXX_COMPILER_ID STREQUAL "Clang")
+if(NOT APPLE AND CV_CLANG)
   message(STATUS "CUDA compilation is disabled (due to Clang unsupported on your platform).")
   return()
 endif()
@@ -222,7 +222,7 @@ if(CUDA_FOUND)
     endif()
 
     # disabled because of multiple warnings during building nvcc auto generated files
-    if(CMAKE_COMPILER_IS_GNUCXX AND CMAKE_CXX_COMPILER_VERSION VERSION_GREATER "4.6.0")
+    if(CV_GCC AND CMAKE_CXX_COMPILER_VERSION VERSION_GREATER "4.6.0")
       ocv_warnings_disable(CMAKE_CXX_FLAGS -Wunused-but-set-variable)
     endif()
 

cmake/OpenCVDetectCXXCompiler.cmake

+# Compilers:
+# - CV_GCC - GNU compiler (CMAKE_CXX_COMPILER_ID STREQUAL "GNU")
+# - CV_CLANG - Clang-compatible compiler (CMAKE_CXX_COMPILER_ID MATCHES "Clang" - Clang or AppleClang, see CMP0025)
+# - CV_ICC - Intel compiler
+# - MSVC - Microsoft Visual Compiler (CMake variable)
+# - MSVC64 - additional flag, 64-bit
+# - MINGW / CYGWIN / CMAKE_COMPILER_IS_MINGW / CMAKE_COMPILER_IS_CYGWIN (CMake original variables)
+# - MINGW64 - 64-bit
+#
+# CPU Platforms:
+# - X86 / X86_64
+# - ARM - ARM CPU, not defined for AArch64
+# - AARCH64 - ARMv8+ (64-bit)
+# - PPC64 / PPC64LE - PowerPC
+#
+# OS:
+# - WIN32 - Windows | MINGW
+# - UNIX - Linux | MacOSX | ANDROID
+# - ANDROID
+# - IOS
+# - APPLE - MacOSX | iOS
 # ----------------------------------------------------------------------------
-# Detect Microsoft compiler:
-# ----------------------------------------------------------------------------
+
 if(CMAKE_CL_64)
     set(MSVC64 1)
 endif()
 
-if(CMAKE_CXX_COMPILER_ID STREQUAL "Clang")
-  set(CMAKE_COMPILER_IS_GNUCXX 1)
-  set(CMAKE_COMPILER_IS_CLANGCXX 1)
+if(NOT DEFINED CV_GCC AND CMAKE_CXX_COMPILER_ID MATCHES "GNU")
+  set(CV_GCC 1)
 endif()
-if(CMAKE_C_COMPILER_ID STREQUAL "Clang")
-  set(CMAKE_COMPILER_IS_GNUCC 1)
-  set(CMAKE_COMPILER_IS_CLANGCC 1)
-endif()
-if("${CMAKE_CXX_COMPILER};${CMAKE_C_COMPILER};${CMAKE_CXX_COMPILER_LAUNCHER}" MATCHES "ccache")
-  set(CMAKE_COMPILER_IS_CCACHE 1)
+if(NOT DEFINED CV_CLANG AND CMAKE_CXX_COMPILER_ID MATCHES "Clang")  # Clang or AppleClang (see CMP0025)
+  set(CV_CLANG 1)
+  set(CMAKE_COMPILER_IS_CLANGCXX 1)  # TODO next release: remove this
+  set(CMAKE_COMPILER_IS_CLANGCC 1)   # TODO next release: remove this
 endif()
 
+function(access_CMAKE_COMPILER_IS_CLANGCXX)
+  if(NOT OPENCV_SUPPRESS_DEPRECATIONS)
+    message(WARNING "DEPRECATED: CMAKE_COMPILER_IS_CLANGCXX support is deprecated in OpenCV.
+    Consider using:
+    - CV_GCC    # GCC
+    - CV_CLANG  # Clang or AppleClang (see CMP0025)
+")
+  endif()
+endfunction()
+variable_watch(CMAKE_COMPILER_IS_CLANGCXX access_CMAKE_COMPILER_IS_CLANGCXX)
+variable_watch(CMAKE_COMPILER_IS_CLANGCC access_CMAKE_COMPILER_IS_CLANGCXX)
+
+
 # ----------------------------------------------------------------------------
-# Detect Intel ICC compiler -- for -fPIC in 3rdparty ( UNIX ONLY ):
-#  see  include/opencv/cxtypes.h file for related   ICC & CV_ICC defines.
-# NOTE: The system needs to determine if the '-fPIC' option needs to be added
-#  for the 3rdparty static libs being compiled.  The CMakeLists.txt files
-#  in 3rdparty use the CV_ICC definition being set here to determine if
-#  the -fPIC flag should be used.
+# Detect Intel ICC compiler
 # ----------------------------------------------------------------------------
 if(UNIX)
   if  (__ICL)
@@ -49,14 +74,12 @@ if(NOT DEFINED CMAKE_CXX_COMPILER_VERSION)
   message(WARNING "Compiler version is not available: CMAKE_CXX_COMPILER_VERSION is not set")
 endif()
 
-if(CMAKE_COMPILER_IS_GNUCXX)
-  if(WIN32)
-    execute_process(COMMAND ${CMAKE_CXX_COMPILER} -dumpmachine
-              OUTPUT_VARIABLE OPENCV_GCC_TARGET_MACHINE
-              OUTPUT_STRIP_TRAILING_WHITESPACE)
-    if(OPENCV_GCC_TARGET_MACHINE MATCHES "amd64|x86_64|AMD64")
-      set(MINGW64 1)
-    endif()
+if(WIN32 AND CV_GCC)
+  execute_process(COMMAND ${CMAKE_CXX_COMPILER} -dumpmachine
+                  OUTPUT_VARIABLE OPENCV_GCC_TARGET_MACHINE
+                  OUTPUT_STRIP_TRAILING_WHITESPACE)
+  if(OPENCV_GCC_TARGET_MACHINE MATCHES "amd64|x86_64|AMD64")
+    set(MINGW64 1)
   endif()
 endif()
 

cmake/OpenCVDetectTBB.cmake

@@ -72,7 +72,7 @@ function(ocv_tbb_env_guess _found)
       INTERFACE_INCLUDE_DIRECTORIES "${TBB_ENV_INCLUDE}"
     )
     # workaround: system TBB library is used for linking instead of provided
-    if(CMAKE_COMPILER_IS_GNUCXX)
+    if(CV_GCC)
       get_filename_component(_dir "${TBB_ENV_LIB}" DIRECTORY)
       set_target_properties(tbb PROPERTIES INTERFACE_LINK_LIBRARIES "-L${_dir}")
     endif()

cmake/OpenCVFindLibsGUI.cmake

@@ -84,7 +84,7 @@ endif(WITH_OPENGL)
 if(APPLE)
   if(WITH_CARBON)
     set(HAVE_CARBON YES)
-  elseif(NOT IOS AND CMAKE_COMPILER_IS_CLANGCXX)
+  elseif(NOT IOS AND CV_CLANG)
     set(HAVE_COCOA YES)
   endif()
 endif()

cmake/OpenCVPCHSupport.cmake

@@ -12,7 +12,7 @@
 #   ADD_NATIVE_PRECOMPILED_HEADER _targetName _input _dowarn
 #   GET_NATIVE_PRECOMPILED_HEADER _targetName _input
 
-IF(CMAKE_COMPILER_IS_GNUCXX)
+IF(CV_GCC)
 
     IF(NOT CMAKE_CXX_COMPILER_VERSION VERSION_LESS "4.2.0")
         SET(PCHSupport_FOUND TRUE)
@@ -36,7 +36,7 @@ MACRO(_PCH_GET_COMPILE_FLAGS _out_compile_flags)
     STRING(TOUPPER "CMAKE_CXX_FLAGS_${CMAKE_BUILD_TYPE}" _flags_var_name)
     SET(${_out_compile_flags} ${${_flags_var_name}} )
 
-    IF(CMAKE_COMPILER_IS_GNUCXX)
+    IF(CV_GCC)
 
         GET_TARGET_PROPERTY(_targetType ${_PCH_current_target} TYPE)
         IF(${_targetType} STREQUAL SHARED_LIBRARY AND NOT WIN32)
@@ -74,7 +74,7 @@ MACRO(_PCH_GET_COMPILE_FLAGS _out_compile_flags)
         ocv_is_opencv_directory(__result ${item})
         if(__result)
           LIST(APPEND ${_out_compile_flags} "${_PCH_include_prefix}\"${item}\"")
-        elseif(CMAKE_COMPILER_IS_GNUCXX AND NOT CMAKE_CXX_COMPILER_VERSION VERSION_LESS "6.0" AND
+        elseif(CV_GCC AND NOT CMAKE_CXX_COMPILER_VERSION VERSION_LESS "6.0" AND
                item MATCHES "/usr/include$")
           # workaround for GCC 6.x bug
         else()
@@ -87,7 +87,7 @@ MACRO(_PCH_GET_COMPILE_FLAGS _out_compile_flags)
         ocv_is_opencv_directory(__result ${item})
         if(__result)
           LIST(APPEND ${_out_compile_flags} "${_PCH_include_prefix}\"${item}\"")
-        elseif(CMAKE_COMPILER_IS_GNUCXX AND NOT CMAKE_CXX_COMPILER_VERSION VERSION_LESS "6.0" AND
+        elseif(CV_GCC AND NOT CMAKE_CXX_COMPILER_VERSION VERSION_LESS "6.0" AND
                item MATCHES "/usr/include$")
           # workaround for GCC 6.x bug
         else()
@@ -128,7 +128,7 @@ MACRO(_PCH_GET_COMPILE_COMMAND out_command _input _output)
     FILE(TO_NATIVE_PATH ${_input} _native_input)
     FILE(TO_NATIVE_PATH ${_output} _native_output)
 
-    IF(CMAKE_COMPILER_IS_GNUCXX)
+    if(CV_GCC)
         IF(CMAKE_CXX_COMPILER_ARG1)
             # remove leading space in compiler argument
             STRING(REGEX REPLACE "^ +" "" pchsupport_compiler_cxx_arg1 ${CMAKE_CXX_COMPILER_ARG1})
@@ -141,7 +141,7 @@ MACRO(_PCH_GET_COMPILE_COMMAND out_command _input _output)
               ${CMAKE_CXX_COMPILER}  ${_compile_FLAGS} -x c++-header -o ${_output} ${_input}
               )
         ENDIF(CMAKE_CXX_COMPILER_ARG1)
-    ELSE(CMAKE_COMPILER_IS_GNUCXX)
+    ELSE()
 
         SET(_dummy_str "#include <${_input}>")
         FILE(WRITE ${CMAKE_CURRENT_BINARY_DIR}/pch_dummy.cpp ${_dummy_str})
@@ -151,7 +151,7 @@ MACRO(_PCH_GET_COMPILE_COMMAND out_command _input _output)
           )
         #/out:${_output}
 
-    ENDIF(CMAKE_COMPILER_IS_GNUCXX)
+    ENDIF()
 
 ENDMACRO(_PCH_GET_COMPILE_COMMAND )
 
@@ -160,7 +160,7 @@ MACRO(_PCH_GET_TARGET_COMPILE_FLAGS _cflags  _header_name _pch_path _dowarn )
 
     FILE(TO_NATIVE_PATH ${_pch_path} _native_pch_path)
 
-    IF(CMAKE_COMPILER_IS_GNUCXX)
+    IF(CV_GCC)
         # for use with distcc and gcc >4.0.1 if preprocessed files are accessible
         # on all remote machines set
         # PCH_ADDITIONAL_COMPILER_FLAGS to -fpch-preprocess
@@ -173,11 +173,11 @@ MACRO(_PCH_GET_TARGET_COMPILE_FLAGS _cflags  _header_name _pch_path _dowarn )
             SET(${_cflags} "${PCH_ADDITIONAL_COMPILER_FLAGS} " )
         ENDIF (_dowarn)
 
-    ELSE(CMAKE_COMPILER_IS_GNUCXX)
+    ELSE()
 
         set(${_cflags} "/Fp${_native_pch_path} /Yu${_header_name}" )
 
-    ENDIF(CMAKE_COMPILER_IS_GNUCXX)
+    ENDIF()
 
 ENDMACRO(_PCH_GET_TARGET_COMPILE_FLAGS )
 
@@ -205,7 +205,7 @@ MACRO(ADD_PRECOMPILED_HEADER_TO_TARGET _targetName _input _pch_output_to_use )
 
     _PCH_GET_TARGET_COMPILE_FLAGS(_target_cflags ${_name} ${_pch_output_to_use} ${_dowarn})
     #MESSAGE("Add flags ${_target_cflags} to ${_targetName} " )
-    if(CMAKE_COMPILER_IS_GNUCXX)
+    if(CV_GCC)
       set(_target_cflags "${_target_cflags} -include \"${CMAKE_CURRENT_BINARY_DIR}/${_name}\"")
     endif()
 
@@ -403,7 +403,7 @@ macro(ocv_add_precompiled_header_to_target the_target pch_header)
   if(PCHSupport_FOUND AND ENABLE_PRECOMPILED_HEADERS AND EXISTS "${pch_header}")
     if(CMAKE_GENERATOR MATCHES "^Visual" OR CMAKE_GENERATOR MATCHES Xcode)
       add_native_precompiled_header(${the_target} ${pch_header})
-    elseif(CMAKE_COMPILER_IS_GNUCXX AND CMAKE_GENERATOR MATCHES "Makefiles|Ninja")
+    elseif(CV_GCC AND CMAKE_GENERATOR MATCHES "Makefiles|Ninja")
       add_precompiled_header(${the_target} ${pch_header})
     endif()
   endif()

cmake/OpenCVUtils.cmake

@@ -2,6 +2,7 @@ include(CMakeParseArguments)
 
 # Debugging function
 function(ocv_cmake_dump_vars)
+  set(OPENCV_SUPPRESS_DEPRECATIONS 1)  # suppress deprecation warnings from variable_watch() guards
   get_cmake_property(__variableNames VARIABLES)
   cmake_parse_arguments(DUMP "" "TOFILE" "" ${ARGN})
   set(regex "${DUMP_UNPARSED_ARGUMENTS}")
@@ -203,7 +204,7 @@ function(ocv_include_directories)
     ocv_is_opencv_directory(__is_opencv_dir "${dir}")
     if(__is_opencv_dir)
       list(APPEND __add_before "${dir}")
-    elseif(CMAKE_COMPILER_IS_GNUCXX AND NOT CMAKE_CXX_COMPILER_VERSION VERSION_LESS "6.0" AND
+    elseif(CV_GCC AND NOT CMAKE_CXX_COMPILER_VERSION VERSION_LESS "6.0" AND
            dir MATCHES "/usr/include$")
       # workaround for GCC 6.x bug
     else()
@@ -234,7 +235,7 @@ function(ocv_target_include_directories target)
   #ocv_debug_message("ocv_target_include_directories(${target} ${ARGN})")
   _ocv_fix_target(target)
   set(__params "")
-  if(CMAKE_COMPILER_IS_GNUCXX AND NOT CMAKE_CXX_COMPILER_VERSION VERSION_LESS "6.0" AND
+  if(CV_GCC AND NOT CMAKE_CXX_COMPILER_VERSION VERSION_LESS "6.0" AND
       ";${ARGN};" MATCHES "/usr/include;")
     return() # workaround for GCC 6.x bug
   endif()
@@ -444,7 +445,7 @@ macro(ocv_warnings_disable)
           set(${var} "${${var}} ${warning}")
         endforeach()
       endforeach()
-    elseif((CMAKE_COMPILER_IS_GNUCXX OR (UNIX AND CV_ICC)) AND _gxx_warnings AND _flag_vars)
+    elseif(((CV_GCC OR CV_CLANG) OR (UNIX AND CV_ICC)) AND _gxx_warnings AND _flag_vars)
       foreach(var ${_flag_vars})
         foreach(warning ${_gxx_warnings})
           if(NOT warning MATCHES "^-Wno-")

modules/java/jni/CMakeLists.txt

@@ -46,7 +46,7 @@ if(BUILD_FAT_JAVA_LIB)
     foreach(_dep ${__deps})
       ocv_target_link_libraries(${the_module} LINK_PRIVATE -Wl,-force_load "${_dep}")
     endforeach()
-  elseif(((CMAKE_COMPILER_IS_GNUCXX OR UNIX) OR (OPENCV_FORCE_FAT_JAVA_LIB_LD_RULES)) AND (NOT OPENCV_SKIP_FAT_JAVA_LIB_LD_RULES))
+  elseif(((CV_GCC OR CV_CLANG OR UNIX) OR (OPENCV_FORCE_FAT_JAVA_LIB_LD_RULES)) AND (NOT OPENCV_SKIP_FAT_JAVA_LIB_LD_RULES))
     ocv_target_link_libraries(${the_module} LINK_PRIVATE -Wl,-whole-archive ${__deps} -Wl,-no-whole-archive)
   else()
     ocv_target_link_libraries(${the_module} LINK_PRIVATE ${__deps})

modules/python/common.cmake

@@ -64,7 +64,7 @@ if(MSVC)
   add_definitions(-DCVAPI_EXPORTS)
 endif()
 
-if(CMAKE_COMPILER_IS_GNUCXX AND NOT ENABLE_NOISY_WARNINGS)
+if((CV_GCC OR CV_CLANG) AND NOT ENABLE_NOISY_WARNINGS)
   set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Wno-unused-function")
 endif()
 

samples/gpu/CMakeLists.txt

@@ -40,7 +40,7 @@ endif()
 if(HAVE_CUDA)
   ocv_include_directories(${CUDA_INCLUDE_DIRS})
 endif()
-if(CMAKE_COMPILER_IS_GNUCXX AND NOT ENABLE_NOISY_WARNINGS)
+if((CV_GCC OR CV_CLANG) AND NOT ENABLE_NOISY_WARNINGS)
   set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -Wno-unused-function")
 endif()
 file(GLOB all_samples RELATIVE ${CMAKE_CURRENT_SOURCE_DIR} *.cpp)