Re: [PATCH, vec-tails 07/10] Support loop epilogue combining

[Ilya Enkovich <enkovich.gnu@gmail.com>]

2016-07-26 18:38 GMT+03:00 Ilya Enkovich <enkovich.gnu@gmail.com>:
> 2016-07-26 18:26 GMT+03:00 Jeff Law <law@redhat.com>:
>> On 07/26/2016 03:57 AM, Ilya Enkovich wrote:
>>>>
>>>>
>>>> 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.
>>
>> Right.  So what I think Richi wants you to try is to use the if-converted
>> loop to construct the if-converted epilogue.  It seems conceptually simple
>> and low cost -- the question is on the implementation side.  I have no clue
>> how painful that would be.
>
> Probably another part of if-conversion may be re-used to build required
> epilogue.  I'll have a look.

Hi,

Yuri will continue my work from this point.

Thanks,
Ilya

>
> Thanks,
> Ilya
>
>>
>> jeff
>>