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From: "tkoenig at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug middle-end/97656] New: Specify that there is no address
 arithmetic on a pointer
Date: Sat, 31 Oct 2020 16:40:45 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D97656

            Bug ID: 97656
           Summary: Specify that there is no address arithmetic on a
                    pointer
           Product: gcc
           Version: 11.0
            Status: UNCONFIRMED
          Severity: enhancement
          Priority: P3
         Component: middle-end
          Assignee: unassigned at gcc dot gnu.org
          Reporter: tkoenig at gcc dot gnu.org
  Target Milestone: ---

This involves Fortran, but possibly also other languages.

Consider

$ cat alias.f90
program main
  interface
     subroutine foo(a)
       integer, intent(inout) :: a
     end subroutine foo
  end interface
  integer, dimension(2) :: x
  x(1) =3D 42
  x(2) =3D 42
  call foo(x(1))
  if (x(2) /=3D 42) stop "Error!"
end program main

This program specifies that foo has a scalar argument, passed by reference.
It is forbidden by Fortran's rules foo could access the element x(2),
therefore the call to stop could be optimized away, but it isn't:

$ gfortran -O3 -S alias.f90=20
$ grep _gfortran_stop alias.s=20
        call    _gfortran_stop_string
$=20

It would be good if there was a TREE_NO_POINTER_ARITHMETC (or simlar) flag
that could be set by the Fortran front end.=