[Bug middle-end/60092] posix_memalign not recognized to derive alias and alignment info

[jakub at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=60092

--- Comment #13 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
(In reply to Richard Biener from comment #12)
> (In reply to Andreas Schwab from comment #11)
> > If a function is not allowed to change errno this must be explicitly
> > documented.
> 
> That means
> 
> Index: gcc/tree-ssa-alias.c
> ===================================================================
> --- gcc/tree-ssa-alias.c.orig   2014-02-06 15:43:42.138266256 +0100
> +++ gcc/tree-ssa-alias.c        2014-02-06 15:43:33.046266882 +0100
> @@ -1847,7 +1847,9 @@ call_may_clobber_ref_p_1 (gimple call, a
>             ao_ref dref;
>             ao_ref_init_from_ptr_and_size (&dref, ptrptr,
>                                            TYPE_SIZE_UNIT (ptr_type_node));
> -           return refs_may_alias_p_1 (&dref, ref, false);
> +           return (refs_may_alias_p_1 (&dref, ref, false)
> +                   || (flag_errno_math
> +                       && targetm.ref_may_alias_errno (ref)));
>           }
>         /* Freeing memory kills the pointed-to memory.  More importantly
>            the call has to serve as a barrier for moving loads and stores
> 
> is necessary.

For posix_memalign?  I think errno can contain any value, except that library
is not allowed to clear errno.
So, IMHO *p = 1; posix_memalign (...); return *p; can be still optimized into
return 1;, because if p = &errno; then *p after the call has undefined value
(just known not to be zero).