------- Comment #1 from pinskia at gmail dot com 2010-07-06 16:33 -------
Subject: Re: New: gcc should not issue warnings for code that will never be
executed
This is a dup of a much older bug which I cannot find right now.
On Jul 6, 2010, at 8:10 AM, "vincent at vinc17 dot org"
<gcc-bugzi...@gcc.gnu.org
> wrote:
> GCC issues warnings like "division by zero" or "right shift count >=
> width of
> type" even though the corresponding code will never be executed
> (under a
> condition that is always false); it shouldn't do this, at least by
> default. For
> instance:
>
> int tst (void)
> {
> int x;
> x = 0 ? 1 / 0 : 0;
> return x;
> if (0)
> {
> x = 1 / 0;
> x = 1 >> 128;
> }
> return x;
> }
>
> $ gcc-snapshot -std=c99 -O2 -c tst.c
> tst.c: In function 'tst':
> tst.c:8:13: warning: division by zero [-Wdiv-by-zero]
> tst.c:9:7: warning: right shift count >= width of type [enabled by
> default]
>
> One can see that GCC detects neither the first "return x;" nor the
> always-false
> condition, and issues spurious warnings for the lines:
>
> x = 1 / 0;
> x = 1 >> 128;
>
> On the other hand, GCC could successfully detect that the 1 / 0 in
>
> x = 0 ? 1 / 0 : 0;
>
> would never be executed.
>
> Note: always-false conditions occur in practice for platform-
> dependent code,
> e.g. by doing a test on integer types.
>
>
> --
> Summary: gcc should not issue warnings for code that will
> never
> be executed
> Product: gcc
> Version: unknown
> Status: UNCONFIRMED
> Severity: enhancement
> Priority: P3
> Component: c
> AssignedTo: unassigned at gcc dot gnu dot org
> ReportedBy: vincent at vinc17 dot org
>
>
> http://gcc.gnu.org/bugzilla/show_bug.cgi?id=44842
>
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=44842
