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From: "tkoenig at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug fortran/96018] [9/10/11 Regression] Optimization issue with
 external HDF5 library
Date: Mon, 06 Jul 2020 15:01:25 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D96018

--- Comment #12 from Thomas Koenig <tkoenig at gcc dot gnu.org> ---
I don't have a debuggable source here at the moment, but I think there
may be a problem with implicit_pure, which was either introduced by
a patch in the range that Dominique provided (maybe for PR 85599?), or
exposed by something in the middle end.

The problem can be seen with -fdump-tree-original (in my case, with 9.3.0):

Namespace: A-Z: (UNKNOWN 0)
procedure name =3D wrapper
  symtree: 'call_side_effect'|| symbol: 'call_side_effect'
    type spec : (INTEGER 4)
    attributes: (PROCEDURE MODULE-PROC  FUNCTION)
    result: ierr
  symtree: 'inner_3d'    || symbol: 'inner_3d'
    type spec : (INTEGER 4)
    attributes: (PROCEDURE MODULE-PROC  FUNCTION)
    result: ierr
    Formal arglist: array
  symtree: 'inner_4d'    || symbol: 'inner_4d'
    type spec : (INTEGER 4)
    attributes: (PROCEDURE MODULE-PROC  FUNCTION IMPLICIT_PURE)
    result: ierr
    Formal arglist: array

IMPLICIT_PURE should not be set on inner_4d, because it evaluates the
function call_side_effect (and marking is as PURE is correctly rejected
because of that).

It is also strange that inner_3d is not also wrongly marked as
IMPLICIT_PURE, I do not really see a significant difference between

   integer function inner_3d(array) result(ierr)
      real, intent(in) :: array(:,:,:)
      integer dimensions(3)
      dimensions =3D shape(array)
      ierr =3D call_side_effect()
   end function inner_3d

and

   integer function inner_4d(array) result(ierr)
      real, intent(in) :: array(:,:,:,:)
      integer dimensions(4)
      dimensions =3D shape(array)
      ierr =3D call_side_effect()
   end function inner_4d=