Re: [Bug middle-end/39460] New: strange aliasing warnings compiling pymol under gcc 4.4

[Andrew Thomas Pinski <pinskia at gmail dot com>]

Sent from my iPhone

On Mar 13, 2009, at 9:11 PM, "howarth at nitro dot med dot uc dot edu"  
<gcc-bugzilla@gcc.gnu.org> wrote:

> There are a number of aliasing warnings coming out of tree-ssa- 
> structalias.c
> when compiling code in pymol which uses their endianswap.h header at  
> -O3 -Wall.
> The warnings are of the form...
>
> In file included from gromacsplugin.cpp:34:
> endianswap.h: In function âint put_trx_real(md_file*, float)â:
> endianswap.h:117: warning: dereferencing pointer âNâ does break  
> strict-aliasing
> rules
> endianswap.h:115: note: initialized from here
> endianswap.h: In function âint trx_real(md_file*, float*)â:
> endianswap.h:143: warning: dereferencing pointer âNâ does break  
> strict-aliasing
> rules
> endianswap.h:135: warning: dereferencing pointer âNâ does break  
> strict-aliasing
> rules
> endianswap.h:128: note: initialized from here
> endianswap.h:144: warning: dereferencing pointer â<anonymous>â  
> does break
> strict-aliasing rules
> endianswap.h:139: warning: dereferencing pointer â<anonymous>â  
> does break
> strict-aliasing rules
> endianswap.h:139: note: initialized from here
> endianswap.h: In function âint write_trr_timestep(void*, const
> molfile_timestep_t*)â:
> endianswap.h:117: warning: dereferencing pointer âNâ does break  
> strict-aliasing
> rules
> endianswap.h:115: note: initialized from here
> endianswap.h:117: warning: dereferencing pointer âNâ does break  
> strict-aliasing
> rules
> endianswap.h:115: note: initialized from here
>
> and don't occur under gcc 4.3. I am wondering if these are valid  
> warnings or a
> bug in gcc 4.4? I am attaching the preprocessed source for  
> gromacsplugin.ii.
> The weird part is that just compiling the contents of endianswap.h  
> doesn't
> trigger the warnings. Also many files in pymol use this header and  
> the errors
> appear rather randomly among them. Also I have never seen the 'does  
> break'
> warning from tree-ssa-structalias.c, but only the 'will break'  
> warning from
> c-common.c.

Inling causes warning to show up. The warning is correct though as the  
access is via a short but the original type is float.

> --
>           Summary: strange aliasing warnings compiling pymol under  
> gcc 4.4
>           Product: gcc
>           Version: 4.4.0
>            Status: UNCONFIRMED
>          Severity: normal
>          Priority: P3
>         Component: middle-end
>        AssignedTo: unassigned at gcc dot gnu dot org
>        ReportedBy: howarth at nitro dot med dot uc dot edu
> GCC build triplet: i686-apple-darwin9
>  GCC host triplet: i686-apple-darwin9
> GCC target triplet: i686-apple-darwin9
>
>
> http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39460