[Bug tree-optimization/57303] [4.7/4.8 Regression] struct miscompiled at -O1 and above

[glisse at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=57303

--- Comment #9 from Marc Glisse <glisse at gcc dot gnu.org> ---
(In reply to rguenther@suse.de from comment #7)
> On Mon, 20 May 2013, glisse at gcc dot gnu.org wrote:
> > +    /* Remove *p = *p.  */
> > +    if (!inplace && TREE_CODE_CLASS (subcode) == tcc_reference
> > +        && operand_equal_p (lhs, gimple_assign_rhs1 (stmt), 0))
> > +      {
> > +        gsi_remove (gsi, true);
> > +        return true;
> > +      }
> 
> The obvious place would be dead store elimination.  But beware that
> the above, if not _literally_ being *p = *p can be changing the
> effective type of the memory location and thus might be not dead
> in terms of type-based aliasing rules (which basically means that
> we need to do sth more clever than just removing the store).

So operand_equal_p on a tcc_reference is not enough? Aliasing is complicated, I
guess I'll open a PR about this optimization.