[PATCH] D100464: [DSE] Remove stores in the same loop iteration

[Changpeng Fang via Phabricator via llvm-commits]

cfang added a comment.

We see a big performance regression caused by this patch due to register pressure increase.
We found that remove stores in the same iteration could increase
the register pressure dramatically.  In the following piece of code,   group 1 and group 2 stores 
are eliminated and the register usage increased from 70 to 171.  This is from our 
critical application, I am not sure whether this DSE could estimate RP?

  // group 1 stores
  sw[0][j][i] = r0 * du0;
  sw[1][j][i] = r0 * du1;
  sw[2][j][i] = r0 * du2;
  
  .....
             

#pragma unroll 8

  for (int m = 0; m < 8; m++) {
    const double vs =sv[m][j];
    du0 += vs * sq[0][m][i];
    du1 += vs * sq[1][m][i];
    du2 += vs * sq[2][m][i];
  }
  // group 2 stores
  sw[0][j][i] += r1 * du0;
  sw[1][j][i] += r1 * du1;
  sw[2][j][i] += r1 * du2;
  
  ......

#pragma unroll 8

  for (int m = 0; m < 8; m++) {
    const double xt = st[m][k];
    dx0 += xt * ru[0][m];
    dx1 += xt * ru[1][m];
    dx2 += xt * ru[2][m];
  }
  // group 3 stores
  sw[0][j][i] += r2 * dx0;
  sw[1][j][i] += r2 * dx1;
  sw[2][j][i] += r2 * dx2;
     

Any suggestions are welcome to resolve this issue. Thanks.


CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D100464/new/

https://reviews.llvm.org/D100464