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RE: More of a Loop distribution.
- From: Richard Biener <richard dot guenther at gmail dot com>
- To: Ajit Kumar Agarwal <ajit dot kumar dot agarwal at xilinx dot com>
- Cc: Jeff Law <law at redhat dot com>,"gcc at gcc dot gnu dot org" <gcc at gcc dot gnu dot org>,Vinod Kathail <vinodk at xilinx dot com>,Shail Aditya Gupta <shailadi at xilinx dot com>,Vidhumouli Hunsigida <vidhum at xilinx dot com>,Nagaraju Mekala <nmekala at xilinx dot com>
- Date: Fri, 14 Aug 2015 08:00:15 +0200
- Subject: RE: More of a Loop distribution.
- Authentication-results: sourceware.org; auth=none
- References: <37378DC5BCD0EE48BA4B082E0B55DFAA42959F07 at XAP-PVEXMBX02 dot xlnx dot xilinx dot com> <CAFiYyc3o7zKrbu4UVsmqoh5Lw+uBfaASA_vP8YaqzQm8sT_5Rg at mail dot gmail dot com> <37378DC5BCD0EE48BA4B082E0B55DFAA4295A47A at XAP-PVEXMBX02 dot xlnx dot xilinx dot com>
On August 14, 2015 4:59:07 AM GMT+02:00, Ajit Kumar Agarwal <firstname.lastname@example.org> wrote:
>From: Richard Biener [mailto:email@example.com]
>Sent: Thursday, August 13, 2015 3:23 PM
>To: Ajit Kumar Agarwal
>Cc: Jeff Law; firstname.lastname@example.org; Vinod Kathail; Shail Aditya Gupta;
>Vidhumouli Hunsigida; Nagaraju Mekala
>Subject: Re: More of a Loop distribution.
>On Thu, Aug 13, 2015 at 9:37 AM, Ajit Kumar Agarwal
>> Loop distribution considers DDG to decide on distributing the Loops.
>> The Loops with control statements like IF-THEN-ELSE can also be
>> Distributed. Instead of Data Dependency Graph, the Control Dependence
>Graph should be considered in order to distribute the loops In presence
>of control Statements.
>> Also the presence of multiple exits in the Loop can also be
>considered for Loop distribution transformation.
>> Thus the above transformation helps in the Libquantum benchmarks for
>> There are following articles that looks interesting to me.
>> "Loop Distribution in presence of arbitrarily control flow Ken
>> "Loop Distribution in presence of Multiple Exits Bor-Ming Hsieh
>> I don't think the loop distribution in presence of control flow is
>implemented in GCC/LLVM.
>> I think it is feasible to consider the above for the implementation
>>>It's true that loop distribution does not try to distribute based on
>any control structure heuristics but it only considers data locality.
>It does however already >>compute the control dependence graph (and
>uses it to add control edges to the DDG to properly add data dependence
>edges to uses of control statements >>necessary in partitions).
>>>So it should be a matter of specifying the proper set of starting
>statements it tries separating.
>>>Not sure which kind of distribution you are after, can you give an
>I would like to have a distribution of the loop having control flow.
>For (I = 2 ; I < N; i++)
> If (condition)
> S1: A[i] = ...
> S2: D[i] = A[i-1]...
>The above loop can be distributed with two loops having one loop with
>S1 inside IF and another loop with S2 with the IF.
>The two scenario can be true.
>1. The condition inside IF have a check on A[i] and is dependent on S1.
>In this case the distribution is difficult. And the above article
>From Ken Kennedy et.al does store the partial results of comparison in
>an temporary array and that array is compared inside the IF
>Condition. This makes the loop distributed. This is what I was looking
>for which I found in the above article.
>2. The condition inside the IF in the above loop is not dependent on
>the S1 and S2 , and this case the loop can be distributed.
>In the above two scenario the GCC can't distribute the loop, as the
>control dependency graph ( control structure ) is not used.
The above loop can be distributed by gcc just fine.
>The above loop distribution makes the loop vectorizable which otherwise
>not possible due to presence of multiple statements inside the IF and
>Also may not be IF-converted due to presence of multiple statements. If
>we distribute the loop for the above two scenarios the individual loops
>in the distributed loop can be vectorized which is otherwise not
>Thanks & Regards
>> Thanks & Regards