GNU bug report logs - #15533
optimizing away noticeable effects

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From: Mark H Weaver <mhw <at> netris.org>
To: Ian Price <ianprice90 <at> googlemail.com>
Cc: Andy Wingo <wingo <at> pobox.com>, 15533 <at> debbugs.gnu.org
Subject: bug#15533: optimizing away noticeable effects
Date: Sun, 06 Oct 2013 03:36:13 -0400

Ian Price <ianprice90 <at> googlemail.com> writes:

> scheme@(guile-user)> ,optimize (define (foo f arg)
>   (let* ((l '())
>          (m (if (pair? arg)
>                 (begin
>                   (set! l (cdr arg))
>                   (car arg))
>                 arg)))
>     (lambda () (apply f m l))))
> $14 = (define (foo f arg)
>   (let ((m (if (pair? arg)
>              (begin (begin (cdr arg) (if #f #f)) (car arg))
>              arg)))
>     (lambda () (f m))))

Using git bisect, I've determined that this bug was introduced in the
following commit:

commit d21537efb4a0edea30a7ab801909207d4bb69030
Author: Andy Wingo <wingo <at> pobox.com>
Date:   Fri Feb 15 12:11:29 2013 +0100

    better inlining of `apply' with rest arguments
    
    * module/language/tree-il/peval.scm (peval): Move up the find-definition
      helper.  Use it to speculatively destructure conses and lists into the
      tail position of an `apply' form.
    
    * test-suite/tests/peval.test ("partial evaluation"): Add tests.

Andy, would you be willing to investigate further?

     Mark

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