-fno-type-redefinition-check

don't catch redefinition for local vars. With this option on
    tcc accepts the following code:
    int main()
    {
        int a = 0;
        long a = 0;
    }
    But if you shure there is no problem with your local variables,
    then a compilation speed can be improved if you have a lots of
    the local variables (50000+)

libtcc.c

@@ -1764,6 +1764,7 @@ static const FlagDef flag_defs[] = {
     { offsetof(TCCState, old_struct_init_code), 0, "old-struct-init-code" },
     { offsetof(TCCState, dollars_in_identifiers), 0, "dollars-in-identifiers" },
     { offsetof(TCCState, normalize_inc_dirs), 0, "normalize-inc-dirs" },
+    { offsetof(TCCState, no_type_redef_check), FD_INVERT, "type-redefinition-check" },
 };
 
 /* set/reset a flag */