#1932 Fixed SSE instability on mingw32

cmake/OpenCVCompilerOptions.cmake

-if (WIN32)
-  # mingw compiler is known to produce unstable SSE code with -O3 hence we are trying to use -O2 instead
-  if(CMAKE_COMPILER_IS_GNUCXX)
-    foreach(flags CMAKE_CXX_FLAGS CMAKE_CXX_FLAGS_RELEASE CMAKE_CXX_FLAGS_DEBUG)
-      string(REPLACE "-O3" "-O2" ${flags} "${${flags}}")
-    endforeach()
-  endif()
-
-  if(CMAKE_COMPILER_IS_GNUCC)
-    foreach(flags CMAKE_C_FLAGS CMAKE_C_FLAGS_RELEASE CMAKE_C_FLAGS_DEBUG)
-      string(REPLACE "-O3" "-O2" ${flags} "${${flags}}")
-    endforeach()
-  endif()
-endif()
-
 if(MSVC)
   if(CMAKE_CXX_FLAGS STREQUAL CMAKE_CXX_FLAGS_INIT)
     # override cmake default exception handling option
@@ -28,6 +13,21 @@ set(OPENCV_EXTRA_EXE_LINKER_FLAGS "")
 set(OPENCV_EXTRA_EXE_LINKER_FLAGS_RELEASE "")
 set(OPENCV_EXTRA_EXE_LINKER_FLAGS_DEBUG "")
 
+if(MINGW)
+  # mingw compiler is known to produce unstable SSE code
+  # here we are trying to workaround the problem
+  include(CheckCXXCompilerFlag)
+  CHECK_CXX_COMPILER_FLAG(-mstackrealign HAVE_STACKREALIGN_FLAG)
+  if(HAVE_STACKREALIGN_FLAG)
+    set(OPENCV_EXTRA_C_FLAGS "${OPENCV_EXTRA_C_FLAGS} -mstackrealign")
+  else()
+    CHECK_CXX_COMPILER_FLAG(-mpreferred-stack-boundary=2 HAVE_PREFERRED_STACKBOUNDARY_FLAG)
+    if(HAVE_PREFERRED_STACKBOUNDARY_FLAG)
+      set(OPENCV_EXTRA_C_FLAGS "${OPENCV_EXTRA_C_FLAGS} -mstackrealign")
+    endif()
+  endif()
+endif()
+
 if(CMAKE_COMPILER_IS_GNUCXX)
   # High level of warnings.
   set(OPENCV_EXTRA_C_FLAGS "${OPENCV_EXTRA_C_FLAGS} -Wall")