[PATCH, PR52252] Alternative way of vectorization for load groups of size 2 and 3.

[Ramana Radhakrishnan]

On 06/05/14 12:43, Evgeny Stupachenko wrote:
> New hook is related to vector instructions only. Vector instructions
> could be sequential in pipeline, but scalar - parallel. For x86
> architectures TARGET_SCHED_REASSOC_WIDTH does not give required
> differentiation.
> General hooks could be potentially reused in other algorithms/by other
> architectures.

It already takes a "mode" argument. Couldn't you use a vector mode to 
work this out ?

If it is not enough then please be more specific about the documentation 
of this hook about where it is useful so that it's easy for people 
reading the documentation to understand at a glance what purpose it serves.


Ramana

>
> Thanks,
> Evgeny
>
> On Thu, Jun 5, 2014 at 2:04 PM, Ramana Radhakrishnan
> <ramana.gcc@googlemail.com> wrote:
>> On Wed, May 28, 2014 at 2:09 PM, Evgeny Stupachenko <evstupac@gmail.com> wrote:
>>> Hi,
>>>
>>> The patch introduces alternative way of permutations for load groups
>>> of size 2 and 3 which should be faster on architectures with low
>>> parallelism.
>>> The patch gives 2 times gain on Silvermont to the test from PR52252
>>> (in addition to already committed 3 times gain).
>>>
>>> Patch passes bootstrap on x86. Make check is in progress.
>>
>> Why do we need a new hook ? Can't you derive this information from
>> something which is equally badly named TARGET_SCHED_REASSOC_WIDTH
>> though used in the reassociation logic but also serves a similar
>> purpose ?
>>
>> Also the documentation of this hook is incomplete at best and wrong at
>> worst as this is not applied everywhere in the vectorizer but just for
>> this special case for load store permuting. Implying this is useful
>> everywhere in the vectorizer does not appear to be correct.
>>
>> regards
>> Ramana
>>
>>
>>
>>
>>>
>>> ChangeLog:
>>>
>>> 2014-05-28  Evgeny Stupachenko  <evstupac@gmail.com>
>>>
>>>          * config/i386/i386.c (ix86_have_vector_parallel_execution): New.
>>>          (TARGET_VECTORIZE_HAVE_VECTOR_PARALLEL_EXECUTION): New.
>>>          * config/i386/i386.h (TARGET_VECTOR_PARALLEL_EXECUTION): New.
>>>          * config/i386/x86-tune.def (X86_TUNE_VECTOR_PARALLEL_EXECUTION): New.
>>>          * target.def (have_vector_parallel_execution): New.
>>>          * doc/tm.texi.in (have_vector_parallel_execution)): New.
>>>          * doc/tm.texi: Regenerate.
>>>          * targhooks.c (default_have_vector_parallel_execution): New.
>>>          * tree-vect-data-refs.c (vect_shift_permute_load_chain): New.
>>>          Introduces alternative way of loads group permutaions.
>>>          (vect_transform_grouped_load): Try alternative way of permutaions.
>>>
>>> Evgeny
>