From: Ilya Enkovich <enkovich.gnu@gmail.com>
To: Richard Biener <richard.guenther@gmail.com>
Cc: Jeff Law <law@redhat.com>, gcc-patches <gcc-patches@gcc.gnu.org>
Subject: Re: [PATCH, vec-tails 07/10] Support loop epilogue combining
Date: Tue, 26 Jul 2016 13:03:00 -0000 [thread overview]
Message-ID: <CAMbmDYaNOA3T6iGOSNaWLBDEzktB4hBHnAmbtBpEamd4yfrryw@mail.gmail.com> (raw)
In-Reply-To: <CAFiYyc1fSoDW=3_unbTyZrjMosMfXEbn67vDLq6J3Lvjzr4B=Q@mail.gmail.com>
2016-07-26 14:51 GMT+03:00 Richard Biener <richard.guenther@gmail.com>:
> On Tue, Jul 26, 2016 at 11:57 AM, Ilya Enkovich <enkovich.gnu@gmail.com> wrote:
>> 2016-07-26 0:08 GMT+03:00 Jeff Law <law@redhat.com>:
>>> On 07/25/2016 12:32 PM, Richard Biener wrote:
>>>>
>>>> On July 25, 2016 8:01:17 PM GMT+02:00, Jeff Law <law@redhat.com> wrote:
>>>>>
>>>>> On 07/22/2016 05:36 AM, Richard Biener wrote:
>>>>>>
>>>>>> The thing that needs work I think is re-running of if-conversion.
>>>>>
>>>>> I wonder if we could revamp if-conversion to work on a subset of the
>>>>> CFG? I can see that potentially being useful in other contexts.
>>>>> Would
>>>>> that work for you Richi?
>>>>
>>>>
>>>> Well, you need to make it not need post-dominators or preserve them (or
>>>> compute "post-dominators" on SESE regions).
>>>
>>> Oh, but it'd be so nice to have DOMs and/or PDOMs on regions. But that's
>>> probably out of scope for gcc-7.
>>>
>>>
>>>>
>>>> What doesn't work with the idea to clone the epilogue using
>>>> __built-in_vectorized()
>>>> For the if- vs. Not if-converted loop?
>>>
>>> I must be missing something. I don't see how builtin_vectorized_function
>>> helps, but maybe I've got the wrong built-in or don't understand what you're
>>> suggesting.
>>>
>>> It sounds like this is the biggest impediment to moving forward. So let's
>>> reset and make sure we're all on the same page here.
>>>
>>> Ilya, what's the fundamental reason why we need to run if-conversion again?
>>> Yes, I know you want to if-convert the epilogue, but why?
>>>
>>> What are the consequences of not doing if-conversion on the epilogue?
>>> Presumably we miss a vectorization opportunity on the tail. But that may be
>>> a reasonable limitation to allow the existing work to move forward while you
>>> go back and revamp things a little.
>>
>> If we have some control-flow in a loop then we have to if-convert it
>> for vectorizer.
>> We need to preserve both versions: if-converted one for vectorizer and
>> the original
>> one to be used if vectorization fails. For epilogues we have similar
>> situation and
>> need two versions. I do it by running if-conversion on a copy of original loop.
>> Note that it doesn't run full if-conversion pass. If-conversion is
>> called for epilogue
>> loop only.
>
> But it will still compute post-dominators for the full function for example.
>
> You have the if-converted loop available already - it's the loop we are going
> to vectorize. If if-conversion generated if (__builtin_vectorized_p ()) style
> loop copies then you can simply create the epilogue in the same way.
> If it didn't then the loop is already if-converted anyway.
>
Agree. Calling if-conversion is just much simpler in implementation.
Thanks,
Ilya
> I see no need to re-run if-conversion here.
>
> Richard.
>
>> Thanks,
>> Ilya
>>
>>>
>>> Jeff
next prev parent reply other threads:[~2016-07-26 13:03 UTC|newest]
Thread overview: 29+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-05-19 19:46 Ilya Enkovich
2016-06-15 11:44 ` Richard Biener
2016-06-16 15:41 ` Ilya Enkovich
2016-06-16 15:51 ` Jeff Law
2016-06-16 16:03 ` Ilya Enkovich
2016-06-16 16:54 ` Jeff Law
2016-06-28 13:37 ` Ilya Enkovich
2016-06-28 14:16 ` Ilya Enkovich
2016-07-11 13:39 ` Ilya Enkovich
2016-07-14 22:04 ` Jeff Law
2016-07-20 14:40 ` Ilya Enkovich
2016-07-20 16:24 ` Jeff Law
2016-07-21 9:15 ` Ilya Enkovich
2016-07-21 16:34 ` Jeff Law
2016-07-22 11:36 ` Richard Biener
2016-07-25 18:01 ` Jeff Law
2016-07-25 18:33 ` Richard Biener
2016-07-25 21:08 ` Jeff Law
2016-07-26 9:57 ` Ilya Enkovich
2016-07-26 11:51 ` Richard Biener
2016-07-26 13:03 ` Ilya Enkovich [this message]
2016-07-26 13:05 ` Richard Biener
2016-07-26 15:26 ` Jeff Law
2016-07-26 15:38 ` Ilya Enkovich
2016-08-01 9:09 ` Ilya Enkovich
2016-08-01 16:10 ` Jeff Law
2016-09-02 14:46 ` Yuri Rumyantsev
2016-09-02 16:33 ` Bin.Cheng
2016-09-05 7:39 ` Richard Biener
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