[Bug tree-optimization/117888] New: cunrolli doesn't accurately remember what's "innermost"

[liuhongt at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=117888

            Bug ID: 117888
           Summary: cunrolli doesn't accurately remember what's
                    "innermost"
           Product: gcc
           Version: 15.0
            Status: UNCONFIRMED
          Keywords: missed-optimization
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: liuhongt at gcc dot gnu.org
  Target Milestone: ---

> 
> that's the r15-919-gef27b91b62c3aa change I think.  The heuristic, while
> careful, doesn't accurately remember what's "innermost" in this case
> though it's still correct that the body isn't simplified by 1/3 - in
I also notice another testcase which has similar issue, it takes innermost as
an  outerloop.

typedef struct {
    double real;
    double imag;
} complex;
typedef struct { complex e[3][3]; } su3_matrix;
void mult_su3_nn( su3_matrix *a, su3_matrix *b, su3_matrix *c )
{
  int i,j;
  double t,ar,ai,br,bi,cr,ci;
  for(i=0;i<3;i++)for(j=0;j<3;j++){

      ar=a->e[i][0].real; ai=a->e[i][0].imag;
      br=b->e[0][j].real; bi=b->e[0][j].imag; 
      cr=ar*br; t=ai*bi; cr -= t;
      ci=ar*bi; t=ai*br; ci += t;

      ar=a->e[i][1].real; ai=a->e[i][1].imag; 
      br=b->e[1][j].real; bi=b->e[1][j].imag;
      t=ar*br; cr += t; t=ai*bi; cr -= t; 
      t=ar*bi; ci += t; t=ai*br; ci += t;

      ar=a->e[i][2].real; ai=a->e[i][2].imag;
      br=b->e[2][j].real; bi=b->e[2][j].imag;
      t=ar*br; cr += t; t=ai*bi; cr -= t;
      t=ar*bi; ci += t; t=ai*br; ci += t;

      c->e[i][j].real=cr;
      c->e[i][j].imag=ci;
  }
}