[Bug tree-optimization/17252] [3.5 Regression] not marking char types as aliasing anything

["dnovillo at redhat dot com" <gcc-bugzilla at gcc dot gnu dot org>]

------- Additional Comments From dnovillo at redhat dot com  2004-08-31 23:26 -------
Subject: Re:  [3.5 Regression] not marking
	char types as aliasing anything

On Tue, 2004-08-31 at 19:21, pinskia at gcc dot gnu dot org wrote:
> ------- Additional Comments From pinskia at gcc dot gnu dot org  2004-08-31 23:21 -------
> Hmm, For the last example I think this patch caused it: <http://gcc.gnu.org/ml/gcc-patches/2003-12/
> msg01584.html>. but that code was removed in Feburary.
> 
> Diego also I should note that Phil's regression hunter also can reproduce this bug (the one related to 
> LIM).
>
<dnovillo> i think i know where the bug is.  We have the case a=&a, there's a shortcut in may_alias_p that says 'a pointer can't possibly have its own address'.  and we do check if the alias set of the variable is != 0, we don't check whether the alias set of *p is != 0. try this
<dnovillo> @@ -1532,7 +1531,8 @@ may_alias_p (tree ptr, HOST_WIDE_INT mem
<dnovillo>       for PTR's alias set here, not its pointed-to type.  We also can't
<dnovillo>       do this check with relaxed aliasing enabled.  */
<dnovillo>    if (POINTER_TYPE_P (TREE_TYPE (var))
<dnovillo> -      && var_alias_set != 0)
<dnovillo> +      && var_alias_set != 0
<dnovillo> +      && mem_alias_set != 0)
<dnovillo>      {
<dnovillo>        HOST_WIDE_INT ptr_alias_set = get_alias_set (ptr);
<dnovillo>        if (ptr_alias_set == var_alias_set)


Diego.



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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=17252