[Bug fortran/35685] UBOUND incorrect for run-time zero-sized section

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

------- Comment #1 from fxcoudert at gcc dot gnu dot org  2008-03-25 12:35 -------
Versions <= 4.2.3 fail also for SHAPE:

$ /opt/gcc-4.0.?/bin/gfortran a.f90 -static && ./a.out
 UBOUND ZDA1=           0          -5          -1
 SHAPE =           0          -5          -1
$ /opt/gcc-4.1.?/bin/gfortran a.f90 -static && ./a.out
 UBOUND ZDA1=           0          -5          -1
 SHAPE =           0          -5          -1
$ /opt/gcc-4.2.?/bin/gfortran a.f90 -static && ./a.out
 UBOUND ZDA1=           0          -5          -1
 SHAPE =           0          -5          -1


What's happening is that we simply forget to check for zero-sized sections. The
following code:

  call s(1)
contains
  subroutine s(n)
    real x(10)
    print *, ubound(x(5:n))
  end subroutine
end program

is translated into:

            parm.2.dim[0].lbound = 1;
            parm.2.dim[0].ubound = *n + -4;
            parm.2.dim[0].stride = 1;
            parm.2.data = (void *) &x[4];
            parm.2.offset = -5;
            D.886 = (parm.2.dim[S.1].ubound - parm.2.dim[S.1].lbound) + 1;
            _gfortran_transfer_integer (&dt_parm.0, &D.886, 4);

We're missing something like D.886 = MAX_EXPR (D.886, 0). I remembered taking
care of these problems in the past, in trans-intrinsic.c
(gfc_conv_intrinsic_bound), but apparently I forgot the block of code in the
second arm of the "if (as)" condition. I think the following patch does what is
required (but have not time for testing right now):

Index: trans-intrinsic.c
===================================================================
--- trans-intrinsic.c   (revision 132747)
+++ trans-intrinsic.c   (working copy)
@@ -930,6 +930,8 @@
          size = fold_build2 (MINUS_EXPR, gfc_array_index_type, ubound,
lbound);
          se->expr = fold_build2 (PLUS_EXPR, gfc_array_index_type, size,
                                  gfc_index_one_node);
+         se->expr = fold_build2 (MAX_EXPR, gfc_array_index_type, se->expr,
+                                 gfc_index_zero_node);
        }
       else
        se->expr = gfc_index_one_node;


-- 

fxcoudert at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |fxcoudert at gcc dot gnu dot
                   |                            |org
      Known to fail|                            |4.0.4 4.1.2 4.2.3 4.3.0
                   |                            |4.4.0


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35685