From: Andreas Schwab <schwab@suse.de>
Cc: emacs-devel@gnu.org
Subject: Re: Problem report #5
Date: Tue, 11 Apr 2006 20:07:05 +0200 [thread overview]
Message-ID: <jehd50j8ae.fsf@sykes.suse.de> (raw)
In-Reply-To: <39840.128.165.123.132.1144776171.squirrel@webmail.lanl.gov> (Stuart D. Herring's message of "Tue, 11 Apr 2006 10:22:51 -0700 (PDT)")
"Stuart D. Herring" <herring@lanl.gov> writes:
>> 3140 prev = NULL;
>> 3141 for (tail = buf->overlays_before; tail; prev = tail, tail = next)
>> 3142 {
>> 3143 next = tail->next;
>> 3144 XSETMISC (overlay, tail);
>> 3145
>> 3146 /* If the overlay is not valid, get rid of it. */
>> 3147 if (!OVERLAY_VALID (overlay))
>> [...]
>> 3161
>> 3162 beg = OVERLAY_START (overlay);
>> 3163 end = OVERLAY_END (overlay);
>> 3164
>> 3165 if (OVERLAY_POSITION (end) > pos)
>> 3166 {
>> 3167 /* OVERLAY needs to be moved. */
>> 3168 int where = OVERLAY_POSITION (beg);
>> 3169 struct Lisp_Overlay *other, *other_prev;
>> 3170
>> 3171 /* Splice the cons cell TAIL out of overlays_before. */
>>
>> Event dead_error_condition: On this path, the condition "prev != 0" could
>> not be true
>> Also see events: [dead_error_line][assignment][const][const][assignment]
>>
>> 3172 if (prev)
>
> It's true that tail is never 0 within the loop (loop test), and that on
> every iteration but the first prev has been assigned tail, which wasn't 0
> at the time of assignment. But on the first iteration, this test is
> guaranteed to pass! No bug.
The point is that prev can never get non-NULL because later prev (while
still being NULL) is assigned to tail, or else the loop is exited right
away in the false arm of the conditional in line 3165. But the comment
before the loop explains why it is written this way:
/* We don't strictly need prev in this loop; it should always be nil.
But we use it for symmetry and in case that should cease to be true
with some future change. */
So this is on purpose.
Andreas.
--
Andreas Schwab, SuSE Labs, schwab@suse.de
SuSE Linux Products GmbH, Maxfeldstraße 5, 90409 Nürnberg, Germany
PGP key fingerprint = 58CA 54C7 6D53 942B 1756 01D3 44D5 214B 8276 4ED5
"And now for something completely different."
next prev parent reply other threads:[~2006-04-11 18:07 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2006-04-11 15:49 Problem report #5 Dan Nicolaescu
2006-04-11 17:22 ` Stuart D. Herring
2006-04-11 18:07 ` Andreas Schwab [this message]
-- strict thread matches above, loose matches on Subject: below --
2006-04-09 6:59 Dan Nicolaescu
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