Merge pull request #10700 from alalek:cpu_dispatch_axv512

* cmake: enable CPU dispatching for AVX512 (SKX)

* cmake: update handling of unsupported flags/modes

cmake/OpenCVCompilerOptimizations.cmake

@@ -227,6 +227,9 @@ if(X86 OR X86_64)
       # -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")
+    else()
+      ocv_update(CPU_AVX_512F_SUPPORTED OFF)
+      ocv_update(CPU_AVX512_SKX_SUPPORTED OFF)
     endif()
   elseif(MSVC)
     ocv_update(CPU_AVX2_FLAGS_ON "/arch:AVX2")
@@ -247,7 +250,11 @@ if(X86 OR X86_64)
   endif()
 
   if(NOT DEFINED CPU_DISPATCH)
-    set(CPU_DISPATCH "SSE4_1;SSE4_2;AVX;FP16;AVX2" CACHE STRING "${HELP_CPU_DISPATCH}")
+    if(X86_64)
+      set(CPU_DISPATCH "SSE4_1;SSE4_2;AVX;FP16;AVX2;AVX512_SKX" CACHE STRING "${HELP_CPU_DISPATCH}")
+    else()
+      set(CPU_DISPATCH "SSE4_1;SSE4_2;AVX;FP16" CACHE STRING "${HELP_CPU_DISPATCH}")
+    endif()
   endif()
 
   if(NOT DEFINED CPU_BASELINE)
@@ -354,16 +361,27 @@ endmacro()
 
 foreach(OPT ${CPU_KNOWN_OPTIMIZATIONS})
   set(CPU_${OPT}_USAGE_COUNT 0 CACHE INTERNAL "")
-  if(DEFINED CPU_${OPT}_GROUP)
+  if("${CPU_${OPT}_FLAGS_ON}" STREQUAL "disabled")
+    set(CPU_${OPT}_SUPPORTED OFF)
+  elseif(DEFINED CPU_${OPT}_GROUP)
     if(NOT DEFINED CPU_${OPT}_IMPLIES)
       set(CPU_${OPT}_IMPLIES "${CPU_${OPT}_GROUP}")
     endif()
-    if(NOT DEFINED CPU_${OPT}_FLAGS_ON)
-      set(__flags "")
-      foreach(OPT2 ${CPU_${OPT}_GROUP})
-        set(__flags "${__flags} ${CPU_${OPT2}_FLAGS_ON}")
-      endforeach()
-      set(CPU_${OPT}_FLAGS_ON "${__flags}")
+    set(__disabled 0)
+    set(__flags "")
+    foreach(OPT2 ${CPU_${OPT}_GROUP})
+      if("${CPU_${OPT2}_FLAGS_ON}" STREQUAL "disabled" OR (DEFINED CPU_${OPT2}_SUPPORTED AND NOT CPU_${OPT}_SUPPORTED))
+        set(__disabled 1)
+      endif()
+      set(__flags "${__flags} ${CPU_${OPT2}_FLAGS_ON}")
+      string(STRIP "${__flags}" __flags)
+    endforeach()
+    if(__disabled)
+      set(CPU_${OPT}_SUPPORTED OFF)
+    else()
+      if(NOT DEFINED CPU_${OPT}_FLAGS_ON)
+        set(CPU_${OPT}_FLAGS_ON "${__flags}")
+      endif()
     endif()
   endif()
   if(NOT DEFINED CPU_${OPT}_FORCE)