Subject: Re: bug#33036: Bug with the procedure nil? inside a specific code

From: Andy Wingo <[email-masked]>
Date: Thu, 18 Oct 2018 14:33:55 +0200

Hi!

Thank you, Mark!  That looks great.

I note also that this is fixed in master, unless I made another bug.
See type-fold.scm:66-87 and types.scm:574-617.

Cheers!

Andy

On Sun 14 Oct 2018 06:05, Mark H Weaver <[email-masked]> writes:

> Mark H Weaver <[email-masked]> writes:
>
>> calcium <[email-masked]> writes:
>>> Here is the bug that I found :
>>>
>>> ;;; -START- code with the bug -START- ;;;
>>>
>>> (define (strange lst)
>>>   (let loop ((lst lst)
>>>              (is-empty '()))
>>>     (cond ((nil? lst)
>>>            (if (nil? is-empty) 'works
>>>              (list 'should-not-occur is-empty)))
>>>           (else
>>>            (loop (cdr lst)
>>>                  is-empty)))))
>>>
>>> (strange '())
>>> => (should-not-occur ())
>>>
>>> (strange #nil)
>>> => (should-not-occur ())
>>
>> Indeed, this certainly indicates a bug.
>>
>> I believe the bug is in 'local-type-fold' in (language cps type-fold).
>> It contains a local procedure 'scalar-value' which, if I understand
>> correctly, seems to incorrectly assume that (nil? x) returns #t if and
>> only if X is 'eq?' to #nil.
>
> The bug actually wasn't in 'local-type-fold', but it's true that the
> type inferencer assumed in a few places that if (nil? X) returned #t
> that X must be #nil, and similarly for 'null?' and ().
>
> I've attached a proposed fix.
>
> Andy, does this fix look right to you?
>
>      Thanks,
>        Mark
>
>
> From d904d5233582e51a4be06d2c08ccdd15a66b8d77 Mon Sep 17 00:00:00 2001
> From: Mark H Weaver <[email-masked]>
> Date: Sat, 13 Oct 2018 23:02:05 -0400
> Subject: [PATCH] Fix type inferencing for 'nil?' and 'null?' predicates.
>
> Fixes <https://bugs.gnu.org/33036>.
> Reported by <[email-masked]>.
>
> * module/language/cps/types.scm (define-simple-type-inferrer):
> Apply (logand (&type val) <>) uniformly.  Previously, this was done only
> in the false branch.  Rename local variable to 'type*', to allow the
> macro operand 'type' to be an arbitrary expression.
> (*type-inferrers*)<null?>: Add &nil to the set of possible types.
> (*type-inferrers*)<nil?>: Add &false and &null to the set the possible
> types.
> * module/language/cps/type-fold.scm (*branch-folders*)<null?>: Add &nil
> to the set of possible types.
> (*branch-folders*)<nil?>: Add &false and &null to the set the possible
> types.
> * test-suite/tests/compiler.test: Add tests.
> ---
>  module/language/cps/type-fold.scm |  6 ++--
>  module/language/cps/types.scm     | 13 ++++----
>  test-suite/tests/compiler.test    | 51 ++++++++++++++++++++++++++++++-
>  3 files changed, 60 insertions(+), 10 deletions(-)
>
> diff --git a/module/language/cps/type-fold.scm b/module/language/cps/type-fold.scm
> index fc37fac50..163ef659d 100644
> --- a/module/language/cps/type-fold.scm
> +++ b/module/language/cps/type-fold.scm
> @@ -1,5 +1,5 @@
>  ;;; Abstract constant folding on CPS
> -;;; Copyright (C) 2014, 2015 Free Software Foundation, Inc.
> +;;; Copyright (C) 2014, 2015, 2018 Free Software Foundation, Inc.
>  ;;;
>  ;;; This library is free software: you can redistribute it and/or modify
>  ;;; it under the terms of the GNU Lesser General Public License as
> @@ -69,8 +69,8 @@
>  
>  ;; All the cases that are in compile-bytecode.
>  (define-unary-type-predicate-folder pair? &pair)
> -(define-unary-type-predicate-folder null? &null)
> -(define-unary-type-predicate-folder nil? &nil)
> +(define-unary-type-predicate-folder null? (logior &nil &null))
> +(define-unary-type-predicate-folder nil? (logior &false &nil &null))
>  (define-unary-type-predicate-folder symbol? &symbol)
>  (define-unary-type-predicate-folder variable? &box)
>  (define-unary-type-predicate-folder vector? &vector)
> diff --git a/module/language/cps/types.scm b/module/language/cps/types.scm
> index 5c1d71299..61de971fe 100644
> --- a/module/language/cps/types.scm
> +++ b/module/language/cps/types.scm
> @@ -529,13 +529,14 @@ minimum, and maximum."
>  
>  (define-syntax-rule (define-simple-predicate-inferrer predicate type)
>    (define-predicate-inferrer (predicate val true?)
> -    (let ((type (if true?
> -                    type
> -                    (logand (&type val) (lognot type)))))
> -      (restrict! val type -inf.0 +inf.0))))
> +    (let ((type* (logand (&type val)
> +                         (if true?
> +                             type
> +                             (lognot type)))))
> +      (restrict! val type* -inf.0 +inf.0))))
>  (define-simple-predicate-inferrer pair? &pair)
> -(define-simple-predicate-inferrer null? &null)
> -(define-simple-predicate-inferrer nil? &nil)
> +(define-simple-predicate-inferrer null? (logior &nil &null))
> +(define-simple-predicate-inferrer nil? (logior &false &nil &null))
>  (define-simple-predicate-inferrer symbol? &symbol)
>  (define-simple-predicate-inferrer variable? &box)
>  (define-simple-predicate-inferrer vector? &vector)
> diff --git a/test-suite/tests/compiler.test b/test-suite/tests/compiler.test
> index 4f644f339..64bb976fa 100644
> --- a/test-suite/tests/compiler.test
> +++ b/test-suite/tests/compiler.test
> @@ -1,5 +1,5 @@
>  ;;;; compiler.test --- tests for the compiler      -*- scheme -*-
> -;;;; Copyright (C) 2008, 2009, 2010, 2011, 2012, 2013, 2014 Free Software Foundation, Inc.
> +;;;; Copyright (C) 2008-2014, 2018 Free Software Foundation, Inc.
>  ;;;; 
>  ;;;; This library is free software; you can redistribute it and/or
>  ;;;; modify it under the terms of the GNU Lesser General Public
> @@ -251,3 +251,52 @@
>  
>    (pass-if-equal "test flonum" 0.0 (test-proc #t))
>    (pass-if-equal "test complex" 0.0+0.0i (test-proc #f)))
> +
> +(with-test-prefix "null? and nil? inference"
> +  (pass-if-equal "nil? after null?"
> +      '((f . f)  ; 3
> +        (f . f)  ; #t
> +        (f . t)  ; #f
> +        (t . t)  ; #nil
> +        (t . t)) ; ()
> +    (map (compile '(lambda (x)
> +                     (if (null? x)
> +                         (cons 't (if (nil? x) 't 'f))
> +                         (cons 'f (if (nil? x) 't 'f)))))
> +         '(3 #t #f #nil ())))
> +
> +  (pass-if-equal "nil? after truth test"
> +      '((t . f)  ; 3
> +        (t . f)  ; #t
> +        (f . t)  ; #f
> +        (f . t)  ; #nil
> +        (t . t)) ; ()
> +    (map (compile '(lambda (x)
> +                     (if x
> +                         (cons 't (if (nil? x) 't 'f))
> +                         (cons 'f (if (nil? x) 't 'f)))))
> +         '(3 #t #f #nil ())))
> +
> +  (pass-if-equal "null? after nil?"
> +      '((f . f)  ; 3
> +        (f . f)  ; #t
> +        (t . f)  ; #f
> +        (t . t)  ; #nil
> +        (t . t)) ; ()
> +    (map (compile '(lambda (x)
> +                     (if (nil? x)
> +                         (cons 't (if (null? x) 't 'f))
> +                         (cons 'f (if (null? x) 't 'f)))))
> +         '(3 #t #f #nil ())))
> +
> +  (pass-if-equal "truth test after nil?"
> +      '((f . t)  ; 3
> +        (f . t)  ; #t
> +        (t . f)  ; #f
> +        (t . f)  ; #nil
> +        (t . t)) ; ()
> +    (map (compile '(lambda (x)
> +                     (if (nil? x)
> +                         (cons 't (if x 't 'f))
> +                         (cons 'f (if x 't 'f)))))
> +         '(3 #t #f #nil ()))))