[Bug fortran/67531] FAIL: gfortran.dg/ieee/large_2.f90 -O0 execution test

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67531

--- Comment #3 from Francois-Xavier Coudert <fxcoudert at gcc dot gnu.org> ---
(In reply to Pat Haugen from comment #2)
> pthaugen@genoa:~$ ~/install/gcc/trunk/bin/gcc z.c -lm && ./a.out
> 0.3333333333333333333333333333333353876586
> 0.3333333333333333333333333333333292246827

How about with this? I'm trying to come as close as possible to the exact
sequence of fe.etround() calls as the Fortran front-end and runtime library
would end up performing…


#include <fenv.h>
#include <stdio.h>

int main (void)
{
  int r;
  long double x1, x2, x;

  x1 = 1;
  x = 3;
  r = fegetround ();
  fesetround (FE_UPWARD);
  x1 = x1 / x;
  fesetround (r);

  x2 = 1;
  x = 3;
  r = fegetround ();
  fesetround (FE_DOWNWARD);
  x2 = x2 / x;
  fesetround (r);

  printf ("%.40Lg\n", x1);
  printf ("%.40Lg\n", x2);
}
>From gcc-bugs-return-496923-listarch-gcc-bugs=gcc.gnu.org@gcc.gnu.org Thu Sep 10 21:52:57 2015
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From: "pangbw at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/59124] [4.9/5/6 Regression] Wrong warnings "array subscript is above array bounds"
Date: Thu, 10 Sep 2015 21:52:00 -0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?idY124

--- Comment #19 from baoshan <pangbw at gmail dot com> ---
I did a little investigation to the code:

The warning occurs because tree_int_cst_lt (up_bound, up_sub) is true here:
  else if (TREE_CODE (up_sub) == INTEGER_CST
           && (ignore_off_by_one
               ? (tree_int_cst_lt (up_bound, up_sub)
                  && !tree_int_cst_equal (up_bound_p1, up_sub))
               : (tree_int_cst_lt (up_bound, up_sub)
                  || tree_int_cst_equal (up_bound_p1, up_sub))))
    {
      if (dump_file && (dump_flags & TDF_DETAILS))
        {
          fprintf (dump_file, "Array bound warning for ");
          dump_generic_expr (MSG_NOTE, TDF_SLIM, ref);
          fprintf (dump_file, "\n");
        }
      warning_at (location, OPT_Warray_bounds,
=>                "array subscript is above array bounds");
      TREE_NO_WARNING (ref) = 1;
    }

I dumped the tree up_bound and up_sub:
(gdb) p debug_tree(up_bound)
 <integer_cst 0x7ffff6acd3a8 type <integer_type 0x7ffff6c3d0a8 sizetype>
constant 5>
 p debug_tree(up_sub)
 <integer_cst 0x7ffff6ae92d0 type <integer_type 0x7ffff6c3d738 unsigned int>
constant 4294967291>

We can see the value of up_sub is represented as unsigned int value 4294967291
which is really weird to me, it suppose to be a int value -5 here.