Exercise 5.31.  In evaluating a procedure application, the 
explicit-control evaluator always saves and restores the env register 
around the evaluation of the operator, saves and restores env around the 
evaluation of each operand (except the final one), saves and restores 
argl around the evaluation of each operand, and saves and restores proc 
around the evaluation of the operand sequence. For each of the following 
combinations, say which of these save and restore operations are 
superfluous and thus could be eliminated by the compiler's preserving 
mechanism:

(f 'x 'y)

((f) 'x 'y)

(f (g 'x) y)

(f (g 'x) 'y)

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(f 'x 'y)
all of them are superfluous.

((f) 'x 'y)
env needs to be saved around the evaluation of (f), but not of the 
arguments.
argl and proc do not need to be saved.

(f (g 'x) y)
env, proc, and argl need to be saved when the first argument is 
evaluated.  The rest are superfluous.

(f (g 'x) 'y)
In this case the env will not be used by the last argument, so it 
does not need to be saved before (g 'x) is evaluated.
proc and argl still need to be saved before (g 'x) is evaluated.