On August 14, 2015 4:59:07 AM GMT+02:00, Ajit Kumar Agarwal <ajit.kumar.agar...@xilinx.com> wrote: > > >-----Original Message----- >From: Richard Biener [mailto:richard.guent...@gmail.com] >Sent: Thursday, August 13, 2015 3:23 PM >To: Ajit Kumar Agarwal >Cc: Jeff Law; gcc@gcc.gnu.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 ><ajit.kumar.agar...@xilinx.com> wrote: >> All: >> >> 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 >SPEC 2006. >> >> There are following articles that looks interesting to me. >> >> "Loop Distribution in presence of arbitrarily control flow Ken >Kennedy et.al." >> "Loop Distribution in presence of Multiple Exits Bor-Ming Hsieh >etal." >> >> >> 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 >in GCC. > >>>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. > >Thanks. > >>>Not sure which kind of distribution you are after, can you give an >example? > >I would like to have a distribution of the loop having control flow. >For example > >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. Richard. The >advantage of >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 >possible. > >Thanks & Regards >Ajit > > >Richard. > >> Thanks & Regards >> Ajit
