Unreachable code notes do not fire sometimes.

[Charles]

Consider

(lambda ()
  (block nil (let () (funcall #'+ (eval 'nil) (eval '1) (return :good)))))

We should expect an unreachable code note here, and also a note that the fourth argument of FUNCALL does not return. This used to work in the past, but now it doesn't.

[Stas Boukarev (stassats)]

This is because + is source transformed and loses its source location. This has always been the case. At least now
(block nil
  (return)
  (+ 1 2 3))
signals a note by attaching the source location to the starting ctran, but in the (+ 1 2 (return)) case the initial ctran gets executed and there's no good place to attach a source path.

[Charles (karlosz)]

(lambda ()
  (block nil
    (let ()
      (cons
        (eval 'nil)
        (return
         :good)))))

doesn't work either, and this is a regression since 2018. I identified the change that caused this and I will push soon. The other case cited worked pre-2003 (and CMU CL).

[Charles (karlosz)]

In CMU CL it even knows about the source transform:
(compile nil '(lambda () (block nil
                           (+ 1 2 (return :good)))))

; In: LAMBDA NIL

; (+ 1 2 (RETURN :GOOD))
; ==>
; (+ (+ 1 2) (RETURN :GOOD))
; Note: The second argument never returns a value.
;

[Charles (karlosz)]

And, while we're here, CMU CL doesn't need to attach stuff to ctrans to get

(block nil
  (return)
  (+ 1 2 3))

to report the correct source location for the deleted code either, so there must be some existing mechanism in SBCL that can handle this correctly already that it just being hidden.

[Stas Boukarev (stassats)]

Note: The second argument never returns a value. is not a code deletion note. Obscure the non-returning in something like (when t (return)) and it won't produce any notes.

My version of cmucl, nor sbcl from 2013, don't produce any notes for
(block nil
  (return)
  (+ 1 2 3))

[Charles (karlosz)]

Hm, interesting. This is what I see:

CMU Common Lisp 2022-05-02 21:52:41 (21D Unicode), running on skybluecherry
With core: /usr/lib/cmucl/lib/lisp-sse2.core
Dumped on: Mon, 2022-05-02 23:52:42+02:00 on arojas
See <http://www.cmucl.org/> for support information.
Loaded subsystems:
    Unicode 1.29 with Unicode version 6.2.0
    Python 1.1, target Intel x86/sse2
    CLOS based on Gerd's PCL 2010/03/19 15:19:03
* (block nil
    (return)
    (+ 1 2 3))

; In: BLOCK NIL

; (+ 1 2 3)
; Note: Deleting unreachable code.
;
NIL

So clearly the machinery is there *somewhere*.

[Stas Boukarev (stassats)]

That way, yes, but I'm using compile-file. Or compile.