[Bug tree-optimization/52904] -Wstrict-overflow false alarm with bounded loop

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

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52904

--- Comment #8 from eggert at gnu dot org ---
On 12/12/2013 10:19 AM, Laurent.Rineau__gcc at normalesup dot org wrote:
> The developer has two solutions:
>   - remove that test,
>   - or compile with -fno-strict-overflow.

Sure, and because of this problem, GNU Emacs has chosen #2, that
is, Emacs doesn't use -Wstrict-overflow any more.  (Removing
the test would unnecessarily complicate Emacs, since the
test is needed on some platforms that are conditionally
compiled away in this stripped-down example.)

A goal of -Wstrict-overflow, at least at the 1 level, is to
not generate false alarms, so that it's generally useful in
real programs.  This bug report gives one example where the
goal is not being met.  Emacs currently has a half dozen or
so such examples of this (please see below for what the
current Emacs bzr trunk would output, if we enabled this
warning) and I thought that the GCC developers would find it
useful to see one of them.  If you're not interested, that's
OK too; Emacs will continue to not use -Wstrict-overflow.

In file included from dispnew.c:26:0:
dispnew.c: In function ‘update_window’:
lisp.h:749:30: warning: assuming signed overflow does not occur when
simplifying conditional to constant [-Wstrict-overflow]
   return num < lower ? lower : num <= upper ? num : upper;

dispnew.c: In function ‘update_frame_1’:
dispnew.c:4490:19: warning: assuming signed overflow does not occur when
simplifying conditional to constant [-Wstrict-overflow]
   pause_p = 0 < i && i < FRAME_LINES (f) - 1;
fileio.c: In function ‘Finsert_file_contents’:
fileio.c:3630:11: warning: assuming signed overflow does not occur when
simplifying conditional to constant [-Wstrict-overflow]
        if (nread < 0)
           ^
fileio.c:3632:16: warning: assuming signed overflow does not occur when
simplifying conditional to constant [-Wstrict-overflow]
        else if (nread > 0)
                ^
eval.c: In function ‘backtrace_eval_unrewind’:
eval.c:3496:3: warning: assuming signed overflow does not occur when
simplifying conditional to constant [-Wstrict-overflow]
   for (; distance > 0; distance--)
   ^
intervals.c: In function ‘offset_intervals’:
intervals.c:1364:6: warning: assuming signed overflow does not occur when
simplifying conditional to constant [-Wstrict-overflow]
   if (length == TOTAL_LENGTH (tree))
      ^
intervals.c:1379:9: warning: assuming signed overflow does not occur when
simplifying conditional to constant [-Wstrict-overflow]
   while (left_to_delete > 0)
         ^
>From gcc-bugs-return-437439-listarch-gcc-bugs=gcc.gnu.org@gcc.gnu.org Thu Dec 12 19:41:17 2013
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To: gcc-bugs@gcc.gnu.org
Subject: [Bug fortran/59440] [4.9 Regression] ICE in force_decl_die, at dwarf2out.c:20111 with -g
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http://gcc.gnu.org/bugzilla/show_bug.cgi?idY440

--- Comment #4 from Tobias Burnus <burnus at gcc dot gnu.org> ---
Author: burnus
Date: Thu Dec 12 19:41:11 2013
New Revision: 205939

URL: http://gcc.gnu.org/viewcvs?rev 5939&root=gcc&view=rev
Log:
2013-12-12  Tobias Burnus  <burnus@net-b.de>

        PR fortran/59440
        * trans-decl.c (generate_namelist_decl): Ensure debug DIE
        is created by setting DECL_IGNORED_P to 0.

2013-12-12  Tobias Burnus  <burnus@net-b.de>

        PR fortran/59440
        * gfortran.dg/namelist_83.f90: New.
        * gfortran.dg/namelist_83_2.f90: New.


Added:
    trunk/gcc/testsuite/gfortran.dg/namelist_83.f90
    trunk/gcc/testsuite/gfortran.dg/namelist_83_2.f90
Modified:
    trunk/gcc/fortran/ChangeLog
    trunk/gcc/fortran/trans-decl.c
    trunk/gcc/testsuite/ChangeLog