+/* Define POINTERS_MIGHT_HIDE_IN_OBJECTS to 1 if marking via C pointers does
+ not suffice, which is the typical case. A host where a Lisp_Object is
+ wider than a pointer might allocate a Lisp_Object in non-adjacent halves.
+ If USE_LSB_TAG, the bottom half is not a valid pointer, but it should
+ suffice to widen it to to a Lisp_Object and check it that way. */
+#if defined USE_LSB_TAG || UINTPTR_MAX >> VALBITS != 0
+# if !defined USE_LSB_TAG && UINTPTR_MAX >> VALBITS >> GCTYPEBITS != 0
+ /* If tag bits straddle pointer-word boundaries, neither mark_maybe_pointer
+ nor mark_maybe_object can follow the pointers. This should not occur on
+ any practical porting target. */
+# error "MSB type bits straddle pointer-word boundaries"
+# endif
+ /* Marking via C pointers does not suffice, because Lisp_Objects contain
+ pointer words that hold pointers ORed with type bits. */
+# define POINTERS_MIGHT_HIDE_IN_OBJECTS 1
+#else
+ /* Marking via C pointers suffices, because Lisp_Objects contain pointer
+ words that hold unmodified pointers. */
+# define POINTERS_MIGHT_HIDE_IN_OBJECTS 0
+#endif
+