[hsa-branch 0/5] Gridification support for tiling algorithms

[Martin Jambor <mjambor@suse.cz>]

Hi,

this patch series, currently intended just for the branch but
eventually also for trunk in time for gcc 7, enables gridification,
that is the expansion of OpenMP loops for HSA GPUs, to work with
separate distribute and loop construct, provided that the step size of
the distribute loop is equal to the iteration size of iteration space
of the  "normal" loops in it.

It also allows the HSA back-end to emit group-segment variables and
expands any variables private to a distribute construct as such.

Apart from increased flexibility, one of the main motivations is to
enable tiling.  The patches enable the compiler to grok the matrix
multiplication code example and and emit it to HSA, which than runs
2.5 times faster (in my very non-scientific settings) than a naive
implementation (compiled for HSA).

Thanks,

Martin


#define BLOCK_SIZE 16

void tiled_sgemm_tt(const int M, const int N, const int K, const float alpha, const float*A, const int LDA,
   const float*B, const int LDB, const float beta, float*C, const int LDC){

#pragma omp target teams map(to:A[M*K],B[K*N]) map(from:C[M*N])
#pragma omp distribute collapse(2)
   for (int C_row_start=0 ; C_row_start < M ; C_row_start+=BLOCK_SIZE)
      for (int C_col_start=0 ; C_col_start < N ; C_col_start+=BLOCK_SIZE)
	{
         /* Each team has a local copy of these mini matrices */
         float As[BLOCK_SIZE][BLOCK_SIZE];
         float Bs[BLOCK_SIZE][BLOCK_SIZE];
#pragma omp parallel
	 {
         int C_row, C_col;
         float Cval = 0.0;

         for (int kblock = 0; kblock  < K ; kblock += BLOCK_SIZE )
	   {
#pragma omp for collapse(2)
	     for (int row=0 ; row < BLOCK_SIZE ; row++)
               for (int col=0 ; col < BLOCK_SIZE ; col++)
		 {
		   C_row = C_row_start + row;
		   C_col = C_col_start + col;
		   if ((C_row < M) && (kblock + col < K))
		     As[row][col] = A[(C_row*LDA)+ kblock + col];
		   else
		     As[row][col] = 0;
		   if ((kblock + row < K) && C_col < N)
		     Bs[row][col] = B[((kblock+row)*LDB)+ C_col];
		   else
		     Bs[row][col] = 0;
		 }

#pragma omp for collapse(2)
	     for (int row=0 ; row < BLOCK_SIZE ; row++)
	       for (int col=0 ; col < BLOCK_SIZE ; col++)
		 {
		   for (int e = 0; e < BLOCK_SIZE; ++e)
                     Cval += As[row][e] * Bs[e][col];
		 }
	   }  /* End for kblock .. */


#pragma omp for collapse(2)
         for (int row=0 ; row < BLOCK_SIZE ; row++)
	   for (int col=0 ; col < BLOCK_SIZE ; col++)
	     {
               C_row = C_row_start + row;
               C_col = C_col_start + col;
	       if ((C_row < M) && (C_col < N))
		 C[(C_row*LDC)+C_col] = alpha*Cval + beta*C[(C_row*LDC)+C_col];

	     }
         } /* end parallel */
      }	   /* end target teams distribute */
}