In sbcl-0.6.11.41 (and in all earlier SBCL, and in CMU
CL), out-of-line structure slot setters are horribly inefficient
whenever the type of the slot is declared, because out-of-line
structure slot setters are implemented as closures to save space,
so the compiler doesn't compile the type test into code, but
instead just saves the type in a lexical closure and interprets it
at runtime.
To exercise the problem, compile and load
(cl:in-package :cl-user)
(defstruct foo
(bar (error "missing") :type bar))
(defvar *foo*)
(defun wastrel1 (x)
(loop (setf (foo-bar *foo*) x)))
(defstruct bar)
(defvar *bar* (make-bar))
(defvar *foo* (make-foo :bar *bar*))
(defvar *setf-foo-bar* #'(setf foo-bar))
(defun wastrel2 (x)
(loop (funcall *setf-foo-bar* x *foo*)))
then run (WASTREL1 *BAR*) or (WASTREL2 *BAR*), hit Ctrl-C, and
use BACKTRACE, to see it's spending all essentially all its time
in %TYPEP and VALUES-SPECIFIER-TYPE and so forth.
One possible solution would be simply to give up on
representing structure slot accessors as functions, and represent
them as macroexpansions instead. This can be inconvenient for users,
but it's not clear that it's worse than trying to help by expanding
into a horribly inefficient implementation.
As a workaround for the problem, #'(SETF FOO) expressions
can be replaced with (EFFICIENT-SETF-FUNCTION FOO), where
(defmacro efficient-setf-function (place-function-name)
(or #+sbcl (and (sb-int:info :function :accessor-for place-function-name)
;; a workaround for the problem, encouraging the
;; inline expansion of the structure accessor, so
;; that the compiler can optimize its type test
(let ((new-value (gensym "NEW-VALUE-"))
(structure-value (gensym "STRUCTURE-VALUE-")))
`(lambda (,new-value ,structure-value)
(setf (,place-function-name ,structure-value)
,new-value))))
;; no problem, can just use the ordinary expansion
`(function (setf ,place-function-name))))
In 02fa22e7c496fb6