-/* These constants define how many stg registers are *actually* in
- * registers: the code generator uses this information to avoid
- * generating code to load/store registers which are really offsets
- * from BaseReg.
+#endif /* NO_REGS */
+
+/* -----------------------------------------------------------------------------
+ * These constants define how many stg registers will be used for
+ * passing arguments (and results, in the case of an unboxed-tuple
+ * return).
+ *
+ * We usually set MAX_REAL_VANILLA_REG and co. to be the number of the
+ * highest STG register to occupy a real machine register, otherwise
+ * the calling conventions will needlessly shuffle data between the
+ * stack and memory-resident STG registers. We might occasionally
+ * set these macros to other values for testing, though.