Register Variables
==================

   Register variables have their own stab type, `N_RSYM' (`C_RSYM' for
XCOFF), and their own symbol descriptor, `r'.  The stab's value is the
number of the register where the variable data will be stored.

   AIX defines a separate symbol descriptor `d' for floating point
registers.  This seems unnecessary; why not just just give floating
point registers different register numbers?  I have not verified whether
the compiler actually uses `d'.

   If the register is explicitly allocated to a global variable, but not
initialized, as in:

     register int g_bar asm ("%g5");

then the stab may be emitted at the end of the object file, with the
other bss symbols.