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Re: [PATCH GCC][12/13]Workaround reduction statements for distribution
On Tue, Jun 20, 2017 at 11:20 AM, Bin.Cheng <email@example.com> wrote:
> On Fri, Jun 16, 2017 at 6:15 PM, Bin.Cheng <firstname.lastname@example.org> wrote:
>> On Fri, Jun 16, 2017 at 11:21 AM, Richard Biener
>> <email@example.com> wrote:
>>> On Mon, Jun 12, 2017 at 7:03 PM, Bin Cheng <Bin.Cheng@arm.com> wrote:
>>>> For now, loop distribution handles variables used outside of loop as reduction.
>>>> This is inaccurate because all partitions contain statement defining induction
>>> But final induction values are usually not used outside of the loop...
>> This is in actuality for induction variable which is used outside of the loop.
>>> What is missing is loop distribution trying to change partition order. In fact
>>> we somehow assume we can move a reduction across a detected builtin
>>> (I don't remember if we ever check for validity of that...).
>> Hmm, I am not sure when we can't. If there is any dependence between
>> builtin/reduction partitions, it should be captured by RDG or PG,
>> otherwise the partitions are independent and can be freely ordered as
>> long as reduction partition is scheduled last?
>>>> Ideally we should factor out scev-propagation as a standalone interface
>>>> which can be called when necessary. Before that, this patch simply workarounds
>>>> reduction issue by checking if the statement belongs to all partitions. If yes,
>>>> the reduction must be computed in the last partition no matter how the loop is
>>>> Bootstrap and test on x86_64 and AArch64. Is it OK?
>>> stmt_in_all_partitions is not kept up-to-date during partition merging and if
>>> merging makes the reduction partition(s) pass the stmt_in_all_partitions
>>> test your simple workaround doesn't work ...
>> I think it doesn't matter because:
>> A) it's really workaround for induction variables. In general,
>> induction variables are included by all partition.
>> B) After classify partition, we immediately fuses all reduction
>> partitions. More stmt_in_all_partitions means we are fusing
>> non-reduction partition with reduction partition, so the newly
>> generated (stmt_in_all_partitions) are actually not reduction
>> statements. The workaround won't work anyway even the bitmap is
>>> As written it's a valid optimization but can you please note it's limitation in
>>> some comment please?
>> Yeah, I will add comment explaining it.
> Comment added in new version patch. It also computes bitmap outside
> now, is it OK?
Ok. Can you add a testcase for this as well please? I think the
series up to this
is now fully reviewed, I defered 1/n (the new IFN) to the last one
runtime versioning. Can you re-post that (you can merge with the IFN patch)
to apply after the series has been applied up to this?
> 2017-06-07 Bin Cheng <firstname.lastname@example.org>
> * tree-loop-distribution.c (classify_partition): New parameter and
> better handle reduction statement.
> (rdg_build_partitions): Revise comment.
> (distribute_loop): Compute statements in all partitions and pass it
> to classify_partition.