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Re: [PATCH] Fix unaligned access generated by IVOPTS


On Fri, Sep 13, 2013 at 4:56 PM, Eric Botcazou <ebotcazou@adacore.com> wrote:
> Hi,
>
> in Ada we can have misaligned array components in record types, that is to say
> object with BLKmode whose alignment is lower than that of their type.  In this
> case IVOPTS can generate misaligned TARGET_MEM_REFs, which will lead to an
> unaligned access on strict-alignment platforms.
>
> Tested on SPARC/Solaris, OK for the mainline?

I think that may_be_unaligned_p is just seriously out-dated ... shouldn't it be
sth like

  get_object_alignment_1 (ref, &align, &bitpos);
  if step * BITS_PER_UNIT + bitpos is misaligned
...

or rather all this may_be_unaligned_p stuff should be dropped and IVOPTs
should finally generate proper [TARGET_]MEM_REFs instead?  That is,
we already handle aliasing fine:

  ref = create_mem_ref (&bsi, TREE_TYPE (*use->op_p), &aff,
                        reference_alias_ptr_type (*use->op_p),
                        iv, base_hint, data->speed);

so just also handle alignment properly by passing down
get_object_alignment (*use->op_p) and in create_mem_ref_raw
do at the end do the

  if (TYPE_MODE (type) != BLKmode
      && GET_MODE_ALIGNMENT (TYPE_MODE (type)) > align)
    type = build_aligned_type (type, align);

for BLKmode we already look at TYPE_ALIGN and as we do not change
the access type(?) either the previous code was already wrong or it was
fine, so there is nothing to do.

So - if you want to give it a try...?

Thanks,
Richard.

> 2013-09-13  Eric Botcazou  <ebotcazou@adacore.com>
>
>         * tree-ssa-loop-ivopts.c (may_be_unaligned_p): Deal with BLKmode as
>         the access mode.
>
>
> 2013-09-13  Eric Botcazou  <ebotcazou@adacore.com>
>
>         * gnat.dg/loop_optimization17.adb: New test.
>         * gnat.dg/loop_optimization17_pkg.ad[sb]: New helper.
>
>
> --
> Eric Botcazou


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