Fix -Wdeprecated-ofast warning in Clang

Author: kblaschke

cmake/FastMathOptimizations.cmake

@@ -4,22 +4,37 @@
 # visible artifacts, but may be undesirable in some uses. In this case, disable the ENABLE_FAST_MATH option
 # and specify the safe set of flags via the CMAKE_C_FLAGS and CMAKE_CXX_FLAGS variables.
 
-if(ENABLE_FAST_MATH)
+if (ENABLE_FAST_MATH)
     include(CheckCCompilerFlag)
-    if(MSVC)
+    if (CMAKE_C_COMPILER_ID STREQUAL "MSVC")
         check_c_compiler_flag("/fp:fast" FAST_MATH_OPTIMIZATION_SUPPORTED)
-        if(FAST_MATH_OPTIMIZATION_SUPPORTED)
+        if (FAST_MATH_OPTIMIZATION_SUPPORTED)
             add_compile_options($<$<CONFIG:Release,RelWithDebInfo>:/fp:fast>)
-        endif()
-    else()
+        endif ()
+    elseif (CMAKE_C_COMPILER_ID STREQUAL "Clang" OR CMAKE_C_COMPILER_ID STREQUAL "AppleClang")
+        check_c_compiler_flag("-O3" ALL_OPTIMIZATIONS_FLAG_SUPPORTED)
+        if (ALL_OPTIMIZATIONS_FLAG_SUPPORTED)
+            add_compile_options($<$<CONFIG:Release,RelWithDebInfo>:-O3>)
+        endif ()
+
+        # Clang has deprecated -Ofast, use -ffast-math instead.
+        check_c_compiler_flag("-ffast-math" FAST_MATH_OPTIMIZATION_SUPPORTED)
+        if (FAST_MATH_OPTIMIZATION_SUPPORTED)
+            add_compile_options($<$<CONFIG:Release,RelWithDebInfo>:-ffast-math>)
+        endif ()
+    elseif (CMAKE_C_COMPILER_ID STREQUAL "GNU")
         check_c_compiler_flag("-Ofast" FAST_MATH_OPTIMIZATION_SUPPORTED)
-        if(FAST_MATH_OPTIMIZATION_SUPPORTED)
+        if (FAST_MATH_OPTIMIZATION_SUPPORTED)
             add_compile_options($<$<CONFIG:Release,RelWithDebInfo>:-Ofast>)
-        else()
+        else ()
             check_c_compiler_flag("-O3" ALL_OPTIMIZATIONS_FLAG_SUPPORTED)
-            if(ALL_OPTIMIZATIONS_FLAG_SUPPORTED)
+            if (ALL_OPTIMIZATIONS_FLAG_SUPPORTED)
                 add_compile_options($<$<CONFIG:Release,RelWithDebInfo>:-O3>)
-            endif()
-        endif()
-    endif()
-endif()
+            endif ()
+        endif ()
+    else ()
+        message(AUTHOR_WARNING
+            "ENABLE_FAST_MATH was requested, but compiler is not supported: ${CMAKE_C_COMPILER_ID}. "
+            "Please use CMAKE_C_FLAGS to pass the correct optimization flags manually.")
+    endif ()
+endif ()