[Bug target/63679] [5/6 Regression][AArch64] Failure to constant fold.

[rguenther at suse dot de]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63679

--- Comment #38 from rguenther at suse dot de <rguenther at suse dot de> ---
On Mon, 3 Aug 2015, alalaw01 at gcc dot gnu.org wrote:

> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63679
> 
> --- Comment #37 from alalaw01 at gcc dot gnu.org ---
> Hmmm, no it's not the hashing - that pretty much ignores all types. It's the
> comparison in hashable_expr_equal_p, which just uses operand_equal_p,
> specifically this part (in fold-const.c):
> 
>     case MEM_REF:
>           /* Require equal access sizes, and similar pointer types.
>              We can have incomplete types for array references of
>              variable-sized arrays from the Fortran frontend
>              though.  Also verify the types are compatible.  */
>           if (!((TYPE_SIZE (TREE_TYPE (arg0)) == TYPE_SIZE (TREE_TYPE (arg1))
>                    || (TYPE_SIZE (TREE_TYPE (arg0))
>                        && TYPE_SIZE (TREE_TYPE (arg1))
>                        && operand_equal_p (TYPE_SIZE (TREE_TYPE (arg0)),
>                                            TYPE_SIZE (TREE_TYPE (arg1)),
> flags)))
>                   && types_compatible_p (TREE_TYPE (arg0), TREE_TYPE (arg1))
>                   && ((flags & OEP_ADDRESS_OF)
>                       || (alias_ptr_types_compatible_p
>                             (TREE_TYPE (TREE_OPERAND (arg0, 1)),
>                              TREE_TYPE (TREE_OPERAND (arg1, 1)))
>                           && (MR_DEPENDENCE_CLIQUE (arg0)
>                               == MR_DEPENDENCE_CLIQUE (arg1))
>                           && (MR_DEPENDENCE_BASE (arg0)
>                               == MR_DEPENDENCE_BASE (arg1))
>                           && (TYPE_ALIGN (TREE_TYPE (arg0))
>                             == TYPE_ALIGN (TREE_TYPE (arg1)))))))
> 
> specifically, a pointer to int, and a pointer to an array of int, are not
> alias_ptr_types_compatible_p. (I'm not clear that they should be, either!?)

As said neither the hashing nor operand_equal_p are perfect fits for
the constraints on equality DOM needs to put on memory references.