register variables

[shekita at crystal.UUCP]

I have some questions about register variables:

1) When is it appropriate to declare a variable as a
   register? I have been told that declaring a variable 
   as a register can actually result in slower code. Is
   there a rule of thumb dictating when and when not to
   declare a variable as a register?

2) How many variables can be declared as registers on a Vax 780?
   In general, is there some way to tell how many register variables
   can be declared?

								 Eugene Shekita
								 Univ of Wisconsin