From: Jeff Law <law@redhat.com>
To: Richard Biener <richard.guenther@gmail.com>
Cc: gcc-patches <gcc-patches@gcc.gnu.org>
Subject: Re: [RFA] [tree-optimization/80576] Handle non-constant sizes in DSE
Date: Tue, 03 Sep 2019 21:24:00 -0000 [thread overview]
Message-ID: <fafa77c7-1fd0-5f4b-ddcd-bcf2772bb864@redhat.com> (raw)
In-Reply-To: <CAFiYyc0UhXffAHhWvvi1geCnHTmAjvEdfPokc-6ERaLVH36Rvg@mail.gmail.com>
On 8/26/19 3:00 AM, Richard Biener wrote:
> On Fri, Aug 23, 2019 at 9:19 PM Jeff Law <law@redhat.com> wrote:
>>
>> On 8/22/19 4:46 AM, Richard Biener wrote:
>>>>> Also you seem to use this info to constrain optimization when you
>>>>> might remember that types of addresses do not carry such information...
>>>>> Thus it should be "trivially" possible to write a testcase that is miscompiled
>>>>> after your patch. I also don't see this really exercised in the
>>>>> testcases you add?
>>>> Arggh. You're absolutely correct. I must be blocking out that entire
>>>> discussion from last summer due to the trama :-)
>>>>
>>>> If the destination is the address of a _DECL node, can we use the size
>>>> of the _DECL?
>>>
>>> Yes, but this should already happen for both invariant ones like &a.b.c
>>> and variant ones like &a.b[i].c in ao_ref_init_from_ptr_and_size.
>> I don't see that in ao_ref_init_from_ptr_and_size. AFAICT if you don't
>> know the size when you call that routine (size == NULL), then you end up
>> with the ref->size and ref->max_size set to -1.
>>
>> Am I missing something here?
>
> Ah, of course. ao_ref_from_ptr_and_size would need to be extended
> to constrain max_size. So what I was
> saying is that ao_ref_init_from_ptr_and_size should get you
> a DECL ao_ref_base () from which you could constrain max_size with.
> Or rather ao_ref_from_ptr_and_size should be extended do that,
> mimicing what get_ref_base_and_extent does at the end in the
> if (DECL_P (exp)) case (mind flag_unconstrained_commons!).
Not a bad idea to constrain ao_ref's max_size this way. Not offhand
sure if other passes would be able to exploit having that max_size set,
but DSE certainly could.
I'll see if I can add that and drop the equivalent DSE bits.
Jeff
next prev parent reply other threads:[~2019-09-03 21:24 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-08-16 18:10 Jeff Law
2019-08-16 19:55 ` Marc Glisse
2019-08-16 20:41 ` Jeff Law
2019-08-16 22:49 ` Martin Sebor
2019-08-22 0:30 ` Jeff Law
2019-08-22 18:50 ` Martin Sebor
2019-08-23 16:50 ` Jeff Law
2019-08-19 14:23 ` Richard Biener
2019-08-22 2:12 ` Jeff Law
2019-08-22 11:14 ` Richard Biener
2019-08-23 20:27 ` Jeff Law
2019-08-26 10:07 ` Richard Biener
2019-09-03 21:24 ` Jeff Law [this message]
2019-09-09 20:10 ` Jeff Law
2019-09-16 9:12 ` Richard Biener
2019-09-16 9:18 ` Richard Biener
2019-08-22 15:53 ` Martin Sebor
2019-08-23 16:50 ` Jeff Law
2019-08-16 21:50 ` Jeff Law
2019-08-16 22:19 ` Marc Glisse
2019-08-16 22:43 ` Jeff Law
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