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Re: food for optimizer developers


Most of the time is spent in this function...

void
dlasr(
  str_cref side,
  str_cref pivot,
  str_cref direct,
  int const& m,
  int const& n,
  arr_cref<double> c,
  arr_cref<double> s,
  arr_ref<double, 2> a,
  int const& lda)

in this loop:

        FEM_DOSTEP(j, n - 1, 1, -1) {
          ctemp = c(j);
          stemp = s(j);
          if ((ctemp != one) || (stemp != zero)) {
            FEM_DO(i, 1, m) {
              temp = a(i, j + 1);
              a(i, j + 1) = ctemp * temp - stemp * a(i, j);
              a(i, j) = stemp * temp + ctemp * a(i, j);
            }
          }
        }

a(i, j) is implemented as
    
  T* elems_; // member

    T const&
    operator()(
      ssize_t i1,
      ssize_t i2) const
    {
      return elems_[dims_.index_1d(i1, i2)];
    }

with
  
  ssize_t all[Ndims]; // member
  ssize_t origin[Ndims]; // member

    size_t
    index_1d(
      ssize_t i1,
      ssize_t i2) const
    {
      return
          (i2 - origin[1]) * all[0]
        + (i1 - origin[0]);
    }

The array pointer is buried as elems_ member in the arr_ref<> class template.
How can I apply __restrict in this case?

Ralf




----- Original Message ----
From: Andrew Pinski <pinskia@gmail.com>
To: Ralf W. Grosse-Kunstleve <rwgk@yahoo.com>
Cc: gcc@gcc.gnu.org
Sent: Tue, August 10, 2010 8:47:18 PM
Subject: Re: food for optimizer developers

On Tue, Aug 10, 2010 at 6:51 PM, Ralf W. Grosse-Kunstleve
<rwgk@yahoo.com> wrote:
> I wrote a Fortran to C++ conversion program that I used to convert selected
> LAPACK sources. Comparing runtimes with different compilers I get:
>
>                         absolute  relative
> ifort 11.1.072            1.790s    1.00
> gfortran 4.4.4            2.470s    1.38
> g++ 4.4.4                 2.922s    1.63

I wonder if adding __restrict to some of the arguments of the
functions will help.  Fortran aliasing is so different from C
aliasing.

-- Pinski


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