On Thu, Jun 16, 2016 at 8:00 AM, Jeff Law <[email protected]> wrote:
> On 05/19/2016 01:39 PM, Ilya Enkovich wrote:
>>
>> Hi,
>>
>> This patch introduces changes required to run vectorizer on loop epilogue.
>> This also enables epilogue vectorization using a vector of smaller size.
>>
>> Thanks,
>> Ilya
>> --
>> gcc/
>>
>> 2016-05-19 Ilya Enkovich <[email protected]>
>>
>> * tree-if-conv.c (tree_if_conversion): Make public.
>> * tree-if-conv.h: New file.
>> * tree-vect-data-refs.c (vect_enhance_data_refs_alignment): Don't
>> try to enhance alignment for epilogues.
>> * tree-vect-loop-manip.c (vect_do_peeling_for_loop_bound): Return
>> created loop.
>> * tree-vect-loop.c: include tree-if-conv.h.
>> (destroy_loop_vec_info): Preserve LOOP_VINFO_ORIG_LOOP_INFO in
>> loop->aux.
>> (vect_analyze_loop_form): Init LOOP_VINFO_ORIG_LOOP_INFO and reset
>> loop->aux.
>> (vect_analyze_loop): Reset loop->aux.
>> (vect_transform_loop): Check if created epilogue should be
>> returned
>> for further vectorization. If-convert epilogue if required.
>> * tree-vectorizer.c (vectorize_loops): Add a queue of loops to
>> process and insert vectorized loop epilogues into this queue.
>> * tree-vectorizer.h (vect_do_peeling_for_loop_bound): Return
>> created
>> loop.
>> (vect_transform_loop): Return created loop.
>
> As Richi noted, the additional calls into the if-converter are unfortunate.
> I'm not sure how else to avoid them though. It looks like we can run
> if-conversion on just the epilogue, so maybe that's not too bad.
We could use the if-converted loop as source when doing the loop copy
for the epilogue... (and do it similar to if-conversion when it inserts a
__builtin_vectorized_loop () check, that is, create two versions for
the epilogue).
>> @@ -1212,8 +1213,8 @@ destroy_loop_vec_info (loop_vec_info loop_vinfo,
>> bool clean_stmts)
>> destroy_cost_data (LOOP_VINFO_TARGET_COST_DATA (loop_vinfo));
>> loop_vinfo->scalar_cost_vec.release ();
>>
>> + loop->aux = LOOP_VINFO_ORIG_LOOP_INFO (loop_vinfo);
>> free (loop_vinfo);
>> - loop->aux = NULL;
>> }
>
> Hmm, there seems to be a level of indirection I'm missing here. We're
> smuggling LOOP_VINFO_ORIG_LOOP_INFO around in loop->aux. Ewww. I thought
> the whole point of LOOP_VINFO_ORIG_LOOP_INFO was to smuggle the VINFO from
> the original loop to the vectorized epilogue. What am I missing? Rather
> than smuggling around in the aux field, is there some inherent reason why we
> can't just copy the info from the original loop directly into
> LOOP_VINFO_ORIG_LOOP_INFO for the vectorized epilogue?
>
>> + /* FORNOW: Currently alias checks are not inherited for epilogues.
>> + Don't try to vectorize epilogue because it will require
>> + additional alias checks. */
>
> Are the alias checks here redundant with the ones done for the original
> loop? If so won't DOM eliminate them?
They are too complex for this. But the epilogue could be annotated with ivdep
pragma / safelen in some way?
> And something just occurred to me -- is there some inherent reason why SLP
> doesn't vectorize the epilogue, particularly for the cases where we can
> vectorize the epilogue using smaller vectors? Sorry if you've already
> answered this somewhere or it's a dumb question.
It usually can but only if we unroll the epilogue later (and thus when the
number of iterations is known at compile-time).
>
>
>>
>> + /* Add new loop to a processing queue. To make it easier
>> + to match loop and its epilogue vectorization in dumps
>> + put new loop as the next loop to process. */
>> + if (new_loop)
>> + {
>> + loops.safe_insert (i + 1, new_loop->num);
>> + vect_loops_num = number_of_loops (cfun);
>> + }
>> +
>
> So just to be clear, the only reason to do this is for dumps -- other than
> processing the loop before it's epilogue, there's no other inherently
> necessary ordering of the loops, right?
>
>
> Jeff
