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.