Re: SBCL tells me it is deleting unreachable code that is almost surely reachable

Thanks -- ((member sgn '($neg $zero $pos)) sgn) eliminates the message.

--Barton

________________________________
From: Stavros Macrakis <[email protected]>
Sent: Wednesday, April 15, 2026 12:12 PM
To: Raymond Toy <[email protected]>
Cc: [email protected] <[email protected]>
Subject: Re: [Maxima-discuss] SBCL tells me it is deleting unreachable code that is almost surely reachable

Caution: Non-NU Email

Of course, this:
  ((memq sgn '($neg '$zero '$pos)) sgn)
should be
  ((memq sgn '($neg $zero $pos)) sgn)
and might as well be
((member sgn '($neg $zero $pos)) sgn)
If the compiler is so incompetent that it doesn't recognize it can't use eq for a list of symbols, the compiler should be fixed!
And, as Ray suggests, it will almost certainly inline member/eq for a length-3 list: that is both faster and smaller than calling member on most (all?) Lisp systems.
And memq is already declaimed inline in clmacs.lisp, line 232.

Looking at the generated code, I see that with optimize speed:0 space:3, SBCL calls member-eq, even though that takes more space. Apparently it uses an inaccurate heuristic to estimate space usage.

           -s

On Wed, Apr 15, 2026 at 12:10 PM Raymond Toy <[email protected]<mailto:[email protected]>> wrote:

On 4/15/26 8:25 AM, Barton Willis via Maxima-discuss wrote:

Here is a revision of a function in hayat. The revision eliminates or helps to eliminate two testsuite failures.

The SBCL (2.4.7)  compiler tells me that

; file: C:/Users/barton/maxima-code-pure/maxima-code/src/./hayat.lisp
; in: DEFUN COEF-SIGN
;     (EQ MAXIMA::SGN 'MAXIMA::$POS)
;
; note: deleting unreachable code

I think that is rubbish—likely, I'll commit the (commented out) memq version.

Check to see what $csign returns? Or rather what csign-impl returns. For me, I see the return type is * (anything).

memq should do exactly the same as testing (or (eq sgn '$neg) (eq sgn '$zero) (eq sgn '$pos)). Well, it would if it were declared inline, but it’s not.

Seems to me that it would be easy to test if that code were actually deleted by calling coef-sign with an arg that is known to be $pos.

(defun coef-sign (coef)

  (let ((sgn ($csign coef)))
    (cond ((or (eq sgn '$complex) (eq sgn '$imaginary)) '$im)
          ;((memq sgn '($neg '$zero '$pos)) sgn)
          ((or (eq sgn '$neg) (eq sgn '$zero) (eq sgn '$pos)) sgn)
          (t
             (let ((asgn ($asksign coef)))
                ;; When sgn is zero and limit is active, record this fact as a noun equality
                ;; in *limit-assumptions*.
             (when (and *limit-assumptions* (eq asgn '$zero))
               (push (ftake '$equal coef 0) *limit-assumptions*))
            asgn)))))





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