--- a/Makefile
+++ b/Makefile
@@ -508,6 +508,9 @@ CFLAGS += $(call cc-option, -fn
NOSTDINC_FLAGS += -nostdinc -isystem $(shell $(CC) -print-file-name=include)
CHECKFLAGS += $(NOSTDINC_FLAGS)
+# improve gcc optimization
+CFLAGS += $(call cc-option,-funit-at-a-time,)
+
# warn about C99 declaration after statement
CFLAGS += $(call cc-option,-Wdeclaration-after-statement,)