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From: "anlauf at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug fortran/109575] Implement runtime check for valid function
 result
Date: Fri, 21 Apr 2023 20:24:45 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D109575

--- Comment #2 from anlauf at gcc dot gnu.org ---
I have some idea how (and where) the runtime checks need to be implemented,
but I am confused by the following observations on the occurence of an
explicit RETURN statement and the use of a RESULT variable:

function f()
  integer :: f
end

function f1()
  integer :: f1
  f1 =3D 1
end

function q() result (f)
  integer :: f
end

function q2() result (f)
  integer :: f
  f =3D 2
end

function g()
  integer :: g
  return
end

function g3()
  integer :: g3
  g3 =3D 3
  return
end

function r() result (f)
  integer :: f
  return
end

function r4() result (f)
  integer :: f
  f =3D 4
  return
end

While the dump-fortran-original does not show any surprises, the tree-dump
looks somewhat irregular:

__attribute__((fn spec (". ")))
integer(kind=3D4) f ()
{
  (void) 0;
}


__attribute__((fn spec (". ")))
integer(kind=3D4) f1 ()
{
  integer(kind=3D4) __result_f1;

  __result_f1 =3D 1;
  return __result_f1;
}


__attribute__((fn spec (". ")))
integer(kind=3D4) q ()
{
  (void) 0;
}


__attribute__((fn spec (". ")))
integer(kind=3D4) q2 ()
{
  integer(kind=3D4) f;

  f =3D 2;
  return f;
}


__attribute__((fn spec (". ")))
integer(kind=3D4) g ()
{
  integer(kind=3D4) __result_g;

  return __result_g;
  return __result_g;
}


__attribute__((fn spec (". ")))
integer(kind=3D4) g3 ()
{
  integer(kind=3D4) __result_g3;

  __result_g3 =3D 3;
  return __result_g3;
  return __result_g3;
}


__attribute__((fn spec (". ")))
integer(kind=3D4) r ()
{
  return;
}


__attribute__((fn spec (". ")))
integer(kind=3D4) r4 ()
{
  integer(kind=3D4) f;

  f =3D 4;
  return f;
  return f;
}


This seems to correspond to two different paths to gfc_generate_return().=