bug#46843: 28.0.50; [native-comp] (lambda (x) (if (equal x b) (eq x b) (error ""))) miscompiled

bug#46843: 28.0.50; [native-comp] (lambda (x) (if (equal x b) (eq x b) (error ""))) miscompiled

[Pip Cet]

In *scratch*, evaluate

(funcall
 (let* ((lexical-binding t)
        (a (list 'a))
        (b (cons a a)))
   (native-compile
    `(lambda (x) (if (equal x ',b) (eq x ',b) (error "")))))
 '((a) a))

Expected result:

nil

Actual result:

t

bug#46843: 28.0.50; [native-comp] (lambda (x) (if (equal x b) (eq x b) (error ""))) miscompiled

[Pip Cet]

On Mon, Mar 1, 2021 at 6:53 AM Pip Cet <pipcet@gmail.com> wrote:
>
> In *scratch*, evaluate
>
> (funcall
>  (let* ((lexical-binding t)
>         (a (list 'a))
>         (b (cons a a)))
>    (native-compile
>     `(lambda (x) (if (equal x ',b) (eq x ',b) (error "")))))
>  '((a) a))

The same issue applies to eql. However, I had to convince myself first
that there is valid and useful code that keeps track of the eq-uality
of eql floats. There is, because there might be an eq-based hash table
that uses them.

(funcall
 (let* ((canonical-one 1.0)
        (hash (make-hash-table :test 'eq)))
   (puthash canonical-one t hash)
   (let* ((is-canonical-one
           `(lambda (x) (if (eql x ,canonical-one) (eq x
,canonical-one) (error "")))))
     (setq is-canonical-one (native-compile is-canonical-one))
     `(lambda (x) (if (funcall ',is-canonical-one x) (cl-assert
(gethash x ',hash))))))
 1.0)

is miscompiled to code that causes an assertion violation when it
actually is correct code that verifies, in two different ways, that x
is eq to a canonical float representing 1.0.
Pip

bug#46843: 28.0.50; [native-comp] (lambda (x) (if (equal x b) (eq x b) (error ""))) miscompiled

[Andrea Corallo via Bug reports for GNU Emacs, the Swiss army knife of text editors]

Pip Cet <pipcet@gmail.com> writes:

> In *scratch*, evaluate
>
> (funcall
>  (let* ((lexical-binding t)
>         (a (list 'a))
>         (b (cons a a)))
>    (native-compile
>     `(lambda (x) (if (equal x ',b) (eq x ',b) (error "")))))
>  '((a) a))
>
> Expected result:
>
> nil
>
> Actual result:
>
> t

Thanks for reporting this, will come-up with a fix.

  Andrea

bug#46843: 28.0.50; [native-comp] (lambda (x) (if (equal x b) (eq x b) (error ""))) miscompiled

[Andrea Corallo via Bug reports for GNU Emacs, the Swiss army knife of text editors]

Andrea Corallo via "Bug reports for GNU Emacs, the Swiss army knife of
text editors" <bug-gnu-emacs@gnu.org> writes:

> Pip Cet <pipcet@gmail.com> writes:
>
>> In *scratch*, evaluate
>>
>> (funcall
>>  (let* ((lexical-binding t)
>>         (a (list 'a))
>>         (b (cons a a)))
>>    (native-compile
>>     `(lambda (x) (if (equal x ',b) (eq x ',b) (error "")))))
>>  '((a) a))
>>
>> Expected result:
>>
>> nil
>>
>> Actual result:
>>
>> t
>
> Thanks for reporting this, will come-up with a fix.

Right 3d014e1bf4 is fixing the wrong assumtion that `equal' `eql' can be
treated as `eq' in propagation as every immediate in the compilation
unit is hash consed.  Indeed this assumtion is wrong for more than one
reason.

Now under `equal' `eql' we propagate only fixnums and symbols values,
all the other kind of values are promoted to their respective types and
propagated as such.

The patch adds some tests for that too.

As the two reproducer are working here I'm closing this.

Thanks for reporting.

  Andrea