set default compiler flags to "-O2" in the case of MinGW

CMakeLists.txt

@@ -41,6 +41,10 @@ set(CMAKE_SHARED_LINKER_FLAGS_MINSIZEREL "" CACHE INTERNAL "" FORCE)
 set(CMAKE_SHARED_LINKER_FLAGS_RELWITHDEBINFO "" CACHE INTERNAL "" FORCE)
 set(CMAKE_VERBOSE OFF CACHE BOOL "Verbose mode")
 
+if (MINGW)
+    set(CMAKE_CXX_FLAGS_RELEASE "-O2 -DNDEBUG" CACHE STRING "")
+endif()
+
 if(CMAKE_VERBOSE)
     set(CMAKE_VERBOSE_MAKEFILE 1)
 endif()
@@ -307,13 +311,11 @@ if(CMAKE_COMPILER_IS_GNUCXX)
     endif()
 
     if(${CMAKE_SYSTEM_PROCESSOR} MATCHES powerpc*)
-        set(USE_O3 ON CACHE BOOL "Enable -O3 for GCC")
         set(ENABLE_POWERPC ON CACHE BOOL "Enable PowerPC for GCC")
     endif ()
 
     if(X86 OR X86_64)
         # enable everything, since the available set of instructions is checked at runtime
-        set(USE_O3 ON CACHE BOOL "Enable -O3")
         set(USE_FAST_MATH ON CACHE BOOL "Enable -ffast-math")
         set(ENABLE_SSE ON CACHE BOOL "Enable SSE instructions")
         set(ENABLE_SSE2 ON CACHE BOOL "Enable SSE2 instructions")
@@ -993,12 +995,6 @@ if(CMAKE_COMPILER_IS_GNUCXX)
     if(USE_OMIT_FRAME_POINTER)
         set(EXTRA_C_FLAGS_RELEASE "${EXTRA_C_FLAGS_RELEASE} -fomit-frame-pointer")
     endif()
-    if(USE_O2)
-        set(EXTRA_C_FLAGS_RELEASE "${EXTRA_C_FLAGS_RELEASE} -O2")
-    endif()
-    if(USE_O3)
-        set(EXTRA_C_FLAGS_RELEASE "${EXTRA_C_FLAGS_RELEASE} -O3")
-    endif()
     if(USE_FAST_MATH)
         set(EXTRA_C_FLAGS_RELEASE "${EXTRA_C_FLAGS_RELEASE} -ffast-math")
     endif()