+extern bool alias_set_subset_of (HOST_WIDE_INT, HOST_WIDE_INT);
+
+/* This alias set can be used to force a memory to conflict with all
+ other memories, creating a barrier across which no memory reference
+ can move. Note that there are other legacy ways to create such
+ memory barriers, including an address of SCRATCH. */
+#define ALIAS_SET_MEMORY_BARRIER ((HOST_WIDE_INT) -1)