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From: "rguenth at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug other/52609] -Wstrict-aliasing / missed diagnostics
Date: Mon, 19 Mar 2012 10:57:00 -0000
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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52609

--- Comment #3 from Richard Guenther <rguenth at gcc dot gnu.org> 2012-03-19 10:54:24 UTC ---
(In reply to comment #2)
> (In reply to comment #1)
> > >accessing unsigned* via float* looks buggy
> > 
> > It does not have to be if the original argument was originally of type float.
> > Aliasing is not about type of pointers but the type which is used to access and
> > such.
> 
> ok, here's an updated testcase:
> 
> $ cat alias-bug.c
> unsigned buffer[1];
> 
> float bug1( unsigned u )
> {
>         buffer[0]=u;
>         return *(float*)(&buffer[0]); // warning.
> }
> 
> float bug2( unsigned u )
> {
>         buffer[0]=u;
>         float* ptr=(float*)&buffer[0];
>         return *ptr; // missed strict aliasing warning.
> }
> 
> gcc repots warning only for bug1() and misses warning for bug2():

There is a duplicate bug for this somewhere.  The warning machinery
only looks at a single stmt.