+#if !defined(LISP_FEATURE_X86) && !defined(LISP_FEATURE_X86_64)
+/* This is unused on X86 and X86_64, but is used as the global
+ * allocation pointer by the cheney GC, and, in some instances, as
+ * the global allocation pointer on PPC/GENCGC. This should probably
+ * be cleaned up such that it only needs to exist on cheney. At the
+ * moment, it is also used by the GENCGC, to hold the pseudo_atomic
+ * bits, and is tightly coupled to reg_ALLOC by the assembly
+ * routines. */