add BUILD_NATIVE option to the makefiles. This will squeeze a bit more out of gcc when optimising for your machine. Only really useful for people doing their own builds but it does seem to make a difference on my machine at least

makefile

@@ -24,6 +24,9 @@ UNICODE = 1
 # Include x86 Assembly routines
 BUILD_X86_ASM = 1
 
+# Include GCC optmisations for your CPU e.g use -march=native. WARNING: This might mean that the generated binaries will not run on other peoples (older) machines!
+#BUILD_NATIVE = 1
+
 # Build for x64 targets (MinGW64 and MSVC only, this will undefine BUILD_A68K and BUILD_X86_ASM)
 #BUILD_X64_EXE = 1
 

makefile.mamemingw

@@ -270,6 +270,12 @@ ifdef BUILD_X86_ASM
 	CXXFLAGS += -mmmx
 endif
 
+ifdef BUILD_NATIVE
+	CFLAGS	 += -march=native -mtune=native
+	CXXFLAGS += -march=native -mtune=native 
+endif
+
+
 # For zlib
 DEF := $(DEF) -DNO_VIZ -D_LARGEFILE64_SOURCE=0 -D_FILE_OFFSET_BITS=32
 

makefile.mingw

@@ -379,6 +379,11 @@ ifdef BUILD_X86_ASM
 	CXXFLAGS += -mmmx
 endif
 
+ifdef BUILD_NATIVE
+	CFLAGS	 += -march=native -mtune=native
+	CXXFLAGS += -march=native -mtune=native
+endif
+
 # For zlib
 DEF := $(DEF) -DNO_VIZ -D_LARGEFILE64_SOURCE=0 -D_FILE_OFFSET_BITS=32
 

makefile.sdl

@@ -256,6 +256,11 @@ else
 	LDFLAGS	 += -s
 endif
 
+ifdef BUILD_NATIVE
+	CFLAGS	 += -march=native -mtune=native
+	CXXFLAGS += -march=native -mtune=native
+endif
+
 # For zlib
 DEF := $(DEF) -DNO_VIZ -D_LARGEFILE64_SOURCE=0 -D_FILE_OFFSET_BITS=32
 

makefile.sdl2

@@ -277,6 +277,11 @@ else
 	LDFLAGS	 += -s
 endif
 
+ifdef BUILD_NATIVE
+	CFLAGS	 += -march=native -mtune=native
+	CXXFLAGS += -march=native -mtune=native
+endif
+
 # For zlib
 DEF := $(DEF) -DNO_VIZ -D_LARGEFILE64_SOURCE=0 -D_FILE_OFFSET_BITS=32