+#define SET_GCT(to) gct = (to)
+
+#if defined(sparc_HOST_ARCH) || defined(i386_HOST_ARCH)
+// Don't use REG_base or R1 for gct on SPARC because they're getting clobbered
+// by something else. Not sure what yet. -- BL 2009/01/03
+
+// Using __thread is better than stealing a register on x86, because
+// we have too few registers available. In my tests it was worth
+// about 5% in GC performance, but of course that might change as gcc
+// improves. -- SDM 2009/04/03
+
+extern __thread gc_thread* gct;
+#define DECLARE_GCT __thread gc_thread* gct;
+
+#elif defined(REG_Base) && !defined(i386_HOST_ARCH)
+// on i386, REG_Base is %ebx which is also used for PIC, so we don't
+// want to steal it