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

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]> 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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