[Bug fortran/48636] Enable more inlining with -O2 and higher

["tkoenig at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48636

--- Comment #4 from Thomas Koenig <tkoenig at gcc dot gnu.org> 2011-04-17 13:32:11 UTC ---
(In reply to comment #3)

> The second item is interesting - it would be cool if backend was able to work
> out that the code is supposed to simplify after inlining. Either by itself or
> by frontend hint.
> Can you provide me very simple testcase for that I can look into how it looks
> like in backend?  Perhaps some kind of frontend hinting would work well here.

Here is some sample code (extreme, I admit) which profits a lot from
inlining:

- Strides are known to be one when inlining (a common case, but you can
  never be sure if the user doesn't call a(1:5:2))

- Expensive setting up of, and reading from the array descriptor

- Loops can be completely unrolled

module foo
  implicit none
contains
  subroutine bar(a,x)
    real, dimension(:,:), intent(in) :: a
    real, intent(out) :: x
    integer :: i,j

    x = 0
    do j=1,ubound(a,2)
       do i=1,ubound(a,1)
          x = x + a(i,j)**2
       end do
    end do
  end subroutine bar
end module foo

program main
  use foo
  implicit none
  real, dimension(2,3) :: a
  real :: x

  data a /1.0, 2.0, 3.0, -1.0, -2.0, -3.0/

  call bar(a,x)
  print *,x
end program main