Optimization of slot access in default argument expressions

[lgm@iexist.att.com]

I've noticed that Symbolics CLOS does not optimize slot access in
expressions given as default argument values.  For example, consider the
following definitions:

(defclass 1class-a 0() (slot-a))

(defmethod 1method-a 0((self class-a)
		     &aux (var (slot-value self 'slot-a)))
  var
  )

(defmethod 1method-b 0((self class-a))
  (let ((var (slot-value self 'slot-a)))
    var
    )
  )

A disassembly of (METHOD METHOD-A (CLASS-A)) gives:

  0  ENTRY: 3 REQUIRED, 0 OPTIONAL
  1  PUSH-LOCAL FP|0            ;SELF
  2  PUSH-CONSTANT 'SLOT-A
  3  CALL-2-STACK #'SLOT-VALUE  ;creating VAR(FP|3)
  4  RETURN-STACK 

A disassembly of (METHOD METHOD-B (CLASS-A)) gives:

  0  ENTRY: 3 REQUIRED, 0 OPTIONAL
  1  BUILTIN PUSH-INSTANCE-VARIABLE STACK 3     ;SLOT SELF SLOT-A       creating VAR(FP|3)
  2  RETURN-STACK 

Notice that when SLOT-A is accessed in the default value expression for
VAR, the Symbolics compiler generates an actual call to the SLOT-VALUE
function; whereas when SLOT-A is accessed within the method body, the
compiler generates a single PUSH-INSTANCE-VARIABLE instruction.

Is this difference somehow required by the ANSI Common Lisp spec, or is
this simply a minor case that Symbolics has not yet gotten around to
optimizing?


	Lawrence G. Mayka
	AT&T Bell Laboratories
	lgm@iexist.att.com

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