This is the mail archive of the
gcc-patches@gcc.gnu.org
mailing list for the GCC project.
Re: PR 58958: wrong aliasing info
- From: Richard Biener <richard dot guenther at gmail dot com>
- To: Marc Glisse <marc dot glisse at inria dot fr>
- Cc: GCC Patches <gcc-patches at gcc dot gnu dot org>
- Date: Mon, 4 Nov 2013 12:59:20 +0100
- Subject: Re: PR 58958: wrong aliasing info
- Authentication-results: sourceware.org; auth=none
- References: <alpine dot DEB dot 2 dot 02 dot 1311012323530 dot 24250 at stedding dot saclay dot inria dot fr> <CAFiYyc0i9pNC=Jpz-1LpUx673fffJY0tDKAqD1AfYm_gbvmKcg at mail dot gmail dot com> <CAFiYyc0v-TwQACBDJ_0LORV4o7O6QBa3aFcDGD+1moZM4fYtYA at mail dot gmail dot com> <alpine dot DEB dot 2 dot 10 dot 1311041215080 dot 4556 at stedding dot saclay dot inria dot fr>
On Mon, Nov 4, 2013 at 12:18 PM, Marc Glisse <marc.glisse@inria.fr> wrote:
> On Mon, 4 Nov 2013, Richard Biener wrote:
>
>> On Mon, Nov 4, 2013 at 11:55 AM, Richard Biener
>> <richard.guenther@gmail.com> wrote:
>>>
>>> On Fri, Nov 1, 2013 at 11:39 PM, Marc Glisse <marc.glisse@inria.fr>
>>> wrote:
>>>>
>>>> Hello,
>>>>
>>>> the issue was described in the PR and the message linked from there.
>>>> ao_ref_init_from_ptr_and_size calls get_ref_base_and_extent, which may
>>>> detect an array_ref of variable index, but ao_ref_init_from_ptr_and_size
>>>> never learns of it and uses the offset+size as if they were meaningful.
>>>
>>>
>>> Well... it certainly learns of it, but it chooses to ignore...
>>>
>>> if (TREE_CODE (ptr) == ADDR_EXPR)
>>> - ref->base = get_ref_base_and_extent (TREE_OPERAND (ptr, 0),
>>> - &ref->offset, &t1, &t2);
>>> + {
>>> + ref->base = get_addr_base_and_unit_offset_1 (TREE_OPERAND (ptr,
>>> 0),
>>> + &t, 0, &safe);
>>> + ref->offset = BITS_PER_UNIT * t;
>>> + }
>>>
>>> safe == (t1 != -1 && t1 == t2)
>>>
>>> note that ao_ref_init_from_ptr_and_size gets the size fed in as argument
>>> so I fail to see why it matters at all ...? That is, if you feed in a
>>> wrong
>>> size then it's the callers error.
>>
>>
>> I think one issue is that the above code uses get_ref_base_and_extent
>> on an address. It should have used get_addr_base_and_unit_offset.
>
>
> Isn't that what my patch does? Except that get_addr_base_and_unit_offset
> often gives up and returns NULL_TREE, whereas I believe we still want a base
> even if we have trouble determining a constant offset, so I modified
> get_addr_base_and_unit_offset_1 a bit.
>
> (not saying the result is pretty...)
I don't think we want get_addr_base_and_unit_offset to return non-NULL
for a non-constant offset. But yes, inside your patch is the correct fix,
so if you drop changing get_addr_base_and_unit_offset ...
Richard.
> --
> Marc Glisse