-/* define NO_REGS to omit register declarations - used in RTS C code
- * that needs all the STG definitions but not the global register
- * settings.
+/*
+ * Defining NO_REGS causes no global registers to be used. NO_REGS is
+ * typically defined by GHC, via a command-line option passed to gcc,
+ * when the -funregisterised flag is given.
+ *
+ * NB. When NO_REGS is on, calling & return conventions may be
+ * different. For example, all function arguments will be passed on
+ * the stack, and components of an unboxed tuple will be returned on
+ * the stack rather than in registers.