[LLVMdev] AESOP autoparallelizing compiler

[Timothy Mattausch Creech]

Hi Rahul,
  Thanks for your interest!

  Our work does not attempt to make any significant contributions to alias analysis, and acts as a client to existing LLVM AA. Furthermore, the options passed to the AESOP frontend scripts are obeyed at compile time, but at link time certain transformations occur unconditionally.

Here, AESOP has actually thwarted your experiment by performing inlining just before link-time. You can disable this in ~/aesop/blank/Makefile. It does this unconditionally as a standard set of pre passes to help the analysis as much as possible. As a result, AESOP knows that A and B do not alias and is correctly parallelizing here.

Best,
Tim
 
On Mar 11, 2013, at 8:59 AM, Rahul wrote:

> Hi Timothy,
> 
> Today I happened to download the code and do some experiments.
> I actually wanted to see how you handle inter-procedure alias analysis. 
> So, I set inline threshold to zero and tried out following example
> ===============================================
> #define N 1024
> void func(double *A, double *B) 
> {
>   int i;
>   for (i=1; i<N-2; i++) {
>     B[i] = A[i] + i*3;
>   }
> }
> 
> void func1(double *A, double *B)
> {
>   func(A,B);
> }
> 
> int main(void)
> {
>   double data[N];
>   double data1[N];
>   double result=0;
>   int i;
>   
>   for (i=0; i<N; i++) {
>     result += i*3;
>     data[i] = result;
>   }
>   func1(data, data1);
>   
>   printf(" Data[10] = %lf\n", data[10]);
>   printf("Data1[10] = %lf\n", data1[10]);
>   
>   return 0;
> }
> ===============================================
> I got following parallalization info after compiling:
> 
>     Loop main:for.body has a loop carried scalar dependence, hence will not be parallelized 
>     Loop func:for.body carries no dependence, hence is being parallelized 
> 
> Since A and B to function "func" are aliases it shouldn't have parallelized.
> 
> Can you please let me know how you compute dependence ??
> 
> 
> Thanks,
> Rahul
> 
> 
> 
> On Sun, Mar 10, 2013 at 7:28 AM, Timothy Mattausch Creech <tcreech at umd.edu> wrote:
> On Mon, Mar 04, 2013 at 03:01:15PM +0800, 陳韋任 (Wei-Ren Chen) wrote:
> > Hi Timothy,
> >
> > >  We would like to inform the community that we're releasing a version of our research compiler, "AESOP", developed at UMD using LLVM. AESOP is a distance-vector-based autoparallelizing compiler for shared-memory machines. The source code and some further information is available at
> > >
> > >  http://aesop.ece.umd.edu
> > >
> > > The main components of the released implementation are loop memory dependence analysis and parallel code generation using calls to POSIX threads. Since we currently have only a 2-person development team, we are still on LLVM 3.0, and some of the code could use some cleanup. Still, we hope that the work will be of interest to some.
> >
> >   Do you have data show us that how much parallelization the AESOP can
> > extract from those benchmarks? :)
> >
> > Regards,
> > chenwj
> >
> > --
> > Wei-Ren Chen (陳韋任)
> > Computer Systems Lab, Institute of Information Science,
> > Academia Sinica, Taiwan (R.O.C.)
> > Tel:886-2-2788-3799 #1667
> > Homepage: http://people.cs.nctu.edu.tw/~chenwj
> 
> Hi Wei-Ren,
>   Sorry for the slow response. We're working on a short tech report which will be up on the website in April. This will contain a "results" section, including results from the SPEC benchmarks which we can't include in the source distribution.
> 
> Briefly, I can say that we get good speedups on some of the NAS and SPEC benchmarks, such as a 3.6x+ speedup on 4 cores on the serial version of NAS "CG" (Fortran), and "lbm" (C) from CPU2006. (These are of course among our best results.)
> 
> -Tim
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> 
> 
> 
> -- 
> Regards,
> Rahul Patil.