[Bug fortran/57262] New: Optimize bound intrinsics with dim=var for rank one arrays

[Bug fortran/57262] New: Optimize bound intrinsics with dim=var for rank one arrays

[burnus at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=57262

            Bug ID: 57262
           Summary: Optimize bound intrinsics with dim=var for rank one
                    arrays
           Product: gcc
           Version: 4.9.0
            Status: UNCONFIRMED
          Keywords: missed-optimization
          Severity: minor
          Priority: P3
         Component: fortran
          Assignee: unassigned at gcc dot gnu.org
          Reporter: burnus at gcc dot gnu.org

I am not really sure whether this really occurs in real-world code, but I
realized that for rank=1 arrays, the following can be compile-time simplified.

! { dg-options "-fdump-tree-original" }

integer function foo(i)
  implicit none
  integer :: i, a(10)
  foo = lbound (a, dim=i) + 2*ubound(a,dim=i) + 3*size(a,dim=i)
end

! { dg-final { scan-tree-dump "__result_bar = 51;" "original" } }

!
! * * *
!
! For the tree version, one could also replace the dim=i by dim=1:

integer function bar(jjj,n)
  implicit none
  integer :: jjj, n, a(n:)
  bar = lbound (a, dim=jjj) + 2*ubound(a,dim=jjj) + 3*size(a,dim=jjj)
end
! { dg-final { scan-tree-dump-not "jjj" "original" } }

[Bug fortran/57262] Optimize bound intrinsics with dim=var for rank one arrays

[dominiq at lps dot ens.fr]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=57262

--- Comment #1 from Dominique d'Humieres <dominiq at lps dot ens.fr> ---
What is expected if i (jjj) /= 1?

[Bug fortran/57262] Optimize bound intrinsics with dim=var for rank one arrays

[burnus at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=57262

--- Comment #2 from Tobias Burnus <burnus at gcc dot gnu.org> ---
Created attachment 30105
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=30105&action=edit
Draft patch (trans-intrinsic.c only, ubound/lbound only, untested)

PATCH: Draft patch for the second case (i.e. after the bound check) - only
handles LBOUND/UBOUND. For SIZE, it only matters with inlining (which is done
on the Fortran-dev branch); thus, this part is left out.

TODO: Testing, test case and simplify.c handling.


(In reply to Dominique d'Humieres from comment #1)
> What is expected if i (jjj) /= 1?

Well, the whole bug is only for rank == 1 array!

Thus, using, e.g., jjj == 2 will be invalid (according to the Fortran standard)
and will access invalid memory. With my (untested!) attached patch, jjj=2
should still give a run-time error for -fcheck=all. (And without, it accesses
the bounds for dim=1 instead of invalid memory.)

For the first test case (patch to be written), you will loose the run-time
bounds check. Sorry!