Guile CSE elimination of record accessor?

[Simon Tournier <zimon.toutoune@gmail.com>]

Hi,

In Guile module (ice-9 vlist), one reads:

--8<---------------cut here---------------start------------->8---
;; Asserting that something is a vlist is actually a win if your next
;; step is to call record accessors, because that causes CSE to
;; eliminate the type checks in those accessors.
;;
(define-inlinable (assert-vlist val)
  (unless (vlist? val)
    (throw 'wrong-type-arg
           #f
           "Not a vlist: ~S"
           (list val)
           (list val))))

[...]

(define (vlist-head vlist)
  "Return the head of VLIST."
  (assert-vlist vlist)
  (let ((base   (vlist-base vlist))
        (offset (vlist-offset vlist)))
    (block-ref (block-content base) offset)))
--8<---------------cut here---------------end--------------->8---

Other said, the argument ’vlist’ is “type-checked” with ’assert-vlist’
and thus that is exploited by Guile compiler, if I understand correctly
the comment.

The first question is: is it still correct?  Because this module had
been implemented before many Guile compiler improvements.


The second question, if the comment above is still valid, is: could we
also “win” for some record inside Guix source code?

Concretely, one example about the record <package>, there is some
procedures such that:

--8<---------------cut here---------------start------------->8---
(define* (package->manifest-entry package #:optional (output "out")
                                  #:key (parent (delay #f))
                                  (properties (default-properties package)))
  "Return a manifest entry for the OUTPUT of package PACKAGE."
  ;; For each dependency, keep a promise pointing to its "parent" entry.
  (letrec* ((deps  (map (match-lambda
                          ((label package)
                           (package->manifest-entry package
                                                    #:parent (delay entry)))
                          ((label package output)
                           (package->manifest-entry package output
                                                    #:parent (delay entry))))
                        (package-propagated-inputs package)))
            (entry (manifest-entry
                     (name (package-name package))
                     (version (package-version package))
                     (output output)
                     (item package)
                     (dependencies (delete-duplicates deps))
                     (search-paths
                      (package-transitive-native-search-paths package))
                     (parent parent)
                     (properties properties))))
    entry))
--8<---------------cut here---------------end--------------->8---

which fits the comment above: a record as argument and record accessor
call.

And that could also be applied to other records, I guess.


Any answers, explanations or references are very welcome. :-)

Cheers,
simon

PS: Raining day and weird pastime… diving into Guile source code. ;-)