[Bug c/58101] New: Wrong out-of-bounds warning under -Os

[Bug c/58101] New: Wrong out-of-bounds warning under -Os

[llozano at google dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58101

            Bug ID: 58101
           Summary: Wrong out-of-bounds warning under -Os
           Product: gcc
           Version: 4.8.2
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: llozano at google dot com

The following test case generates a wrong "out-of-bounds" warning. 
This problem only happens under -Os

gcc test.i -c -Os -Werror -Wall

 In function ‘rcu_init_lal’:
/home/llozano/trash/min_rcutree.i:17:13: error: array subscript is above array
bounds [-Werror=array-bounds]
   rsp->level[i] = rsp->level[i - 1] + rsp->levelcnt[i - 1];

rcu_num_levels is never larger than 1. So the code inside the loop is never
executed. 

test.i:
---
extern int rcu_num_lvls;
int rcu_num_lvls = 1;

struct rcu_node {
};

struct rcu_state {
 struct rcu_node *level[1];
 int levelcnt[4 + 1];
};

void rcu_init_lal(struct rcu_state *rsp)
{
 int i;

 for (i = 1; i < rcu_num_lvls; i++)
  rsp->level[i] = rsp->level[i - 1] + rsp->levelcnt[i - 1];
}
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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=12081

Michael Meissner <meissner at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |meissner at gcc dot gnu.org

--- Comment #27 from Michael Meissner <meissner at gcc dot gnu.org> ---
The patch from Oleg Endo breaks the PowerPC build.

.../gcc/config/rs6000/rs6000.c: In function ‘void rs6000_emit_swdiv(rtx_def*,
rtx_def*, rtx_def*, bool)’:
.../gcc/config/rs6000/rs6000.c:28142: error: invalid cast from type ‘const
insn_gen_fn’ to type ‘rtx_def* (*)(rtx_def*, rtx_def*, rtx_def*)’
.../gcc/config/rs6000/rs6000.c: In function ‘void rs6000_emit_swrsqrt(rtx_def*,
rtx_def*)’:
.../gcc/config/rs6000/rs6000.c:28220: error: invalid cast from type ‘const
insn_gen_fn’ to type ‘rtx_def* (*)(rtx_def*, rtx_def*, rtx_def*)’
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Subject: [Bug other/12081] Gcc can't be compiled with -mregparm=3
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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=12081

--- Comment #28 from Uroš Bizjak <ubizjak at gmail dot com> ---
(In reply to Michael Meissner from comment #27)
> The patch from Oleg Endo breaks the PowerPC build.
> 
> .../gcc/config/rs6000/rs6000.c: In function ‘void
> rs6000_emit_swdiv(rtx_def*, rtx_def*, rtx_def*, bool)’:
> .../gcc/config/rs6000/rs6000.c:28142: error: invalid cast from type ‘const
> insn_gen_fn’ to type ‘rtx_def* (*)(rtx_def*, rtx_def*, rtx_def*)’
> .../gcc/config/rs6000/rs6000.c: In function ‘void
> rs6000_emit_swrsqrt(rtx_def*, rtx_def*)’:
> .../gcc/config/rs6000/rs6000.c:28220: error: invalid cast from type ‘const
> insn_gen_fn’ to type ‘rtx_def* (*)(rtx_def*, rtx_def*, rtx_def*)’

Patch at [1].

[1] http://gcc.gnu.org/ml/gcc-patches/2013-08/msg00323.html
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From: "olegendo at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug other/12081] Gcc can't be compiled with -mregparm=3
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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=12081

--- Comment #29 from Oleg Endo <olegendo at gcc dot gnu.org> ---
(In reply to Uroš Bizjak from comment #28)
> (In reply to Michael Meissner from comment #27)
> > The patch from Oleg Endo breaks the PowerPC build.
> > 
> > .../gcc/config/rs6000/rs6000.c: In function ‘void
> > rs6000_emit_swdiv(rtx_def*, rtx_def*, rtx_def*, bool)’:
> > .../gcc/config/rs6000/rs6000.c:28142: error: invalid cast from type ‘const
> > insn_gen_fn’ to type ‘rtx_def* (*)(rtx_def*, rtx_def*, rtx_def*)’
> > .../gcc/config/rs6000/rs6000.c: In function ‘void
> > rs6000_emit_swrsqrt(rtx_def*, rtx_def*)’:
> > .../gcc/config/rs6000/rs6000.c:28220: error: invalid cast from type ‘const
> > insn_gen_fn’ to type ‘rtx_def* (*)(rtx_def*, rtx_def*, rtx_def*)’
> 
> Patch at [1].
> 
> [1] http://gcc.gnu.org/ml/gcc-patches/2013-08/msg00323.html

Fixed on trunk.

http://gcc.gnu.org/viewcvs/gcc?view=revision&revision=201580

    PR other/12081
    config/rs6000/rs6000.c (gen_2arg_fn_t): Remove typedef.
    (rs6000_emit_swdiv, rs6000_emit_swrsqrt): Don't cast result of GEN_FCN
    to gen_2arg_fn_t.
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From: "meissner at linux dot vnet.ibm.com" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug other/12081] Gcc can't be compiled with -mregparm=3
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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=12081

--- Comment #30 from Michael Meissner <meissner at linux dot vnet.ibm.com> ---
On Wed, Aug 07, 2013 at 07:22:32PM +0000, olegendo at gcc dot gnu.org wrote:
> http://gcc.gnu.org/bugzilla/show_bug.cgi?id=12081
> 
> --- Comment #29 from Oleg Endo <olegendo at gcc dot gnu.org> ---
> (In reply to Uroš Bizjak from comment #28)
> > (In reply to Michael Meissner from comment #27)
> > > The patch from Oleg Endo breaks the PowerPC build.
> > > 
> > > .../gcc/config/rs6000/rs6000.c: In function ‘void
> > > rs6000_emit_swdiv(rtx_def*, rtx_def*, rtx_def*, bool)’:
> > > .../gcc/config/rs6000/rs6000.c:28142: error: invalid cast from type ‘const
> > > insn_gen_fn’ to type ‘rtx_def* (*)(rtx_def*, rtx_def*, rtx_def*)’
> > > .../gcc/config/rs6000/rs6000.c: In function ‘void
> > > rs6000_emit_swrsqrt(rtx_def*, rtx_def*)’:
> > > .../gcc/config/rs6000/rs6000.c:28220: error: invalid cast from type ‘const
> > > insn_gen_fn’ to type ‘rtx_def* (*)(rtx_def*, rtx_def*, rtx_def*)’
> > 
> > Patch at [1].
> > 
> > [1] http://gcc.gnu.org/ml/gcc-patches/2013-08/msg00323.html
> 
> Fixed on trunk.
> 
> http://gcc.gnu.org/viewcvs/gcc?view=revision&revision=201580
> 
>     PR other/12081
>     config/rs6000/rs6000.c (gen_2arg_fn_t): Remove typedef.
>     (rs6000_emit_swdiv, rs6000_emit_swrsqrt): Don't cast result of GEN_FCN
>     to gen_2arg_fn_t.

Great, thanks.  I was just starting the build process to verify it.
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Subject: [Bug c++/58102] New: rejects valid initialization of constexpr object with mutable member
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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58102

            Bug ID: 58102
           Summary: rejects valid initialization of constexpr object with
                    mutable member
           Product: gcc
           Version: 4.9.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: richard-gccbugzilla at metafoo dot co.uk

Given

  struct S {
    mutable int n;
    constexpr S() : n() {}
  };

GCC correctly accepts:

  constexpr S s {};

but incorrectly rejects:

  constexpr S s = {};

saying:

<stdin>: At global scope:
<stdin>:5:20: error: ‘const S’ cannot be the type of a complete constant
expression because it has mutable sub-objects

Per core issue 1405, both the above cases are valid.
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Subject: [Bug c++/54864] Decltype in nested class
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http://gcc.gnu.org/bugzilla/show_bug.cgi?idT864

Paolo Carlini <paolo.carlini at oracle dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|---                         |INVALID

--- Comment #2 from Paolo Carlini <paolo.carlini at oracle dot com> ---
Closing as invalid: http://gcc.gnu.org/ml/gcc-patches/2013-08/msg00398.html

[Bug middle-end/58101] Wrong out-of-bounds warning under -Os

[llozano at google dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58101

Luis A Lozano <llozano at google dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Severity|normal                      |major

--- Comment #1 from Luis A Lozano <llozano at google dot com> ---
Raising priority of this issue. 
This problem was found while build the ChromOS linux kernel. 
Most probably this will be found by other platfroms using the linux kernel.

[Bug middle-end/58101] Wrong out-of-bounds warning under -Os

[mpolacek at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58101

Marek Polacek <mpolacek at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |mpolacek at gcc dot gnu.org

--- Comment #2 from Marek Polacek <mpolacek at gcc dot gnu.org> ---
Perhaps a dup of PR41847.  Fails even with -O2, -O3, -Ofast, no only -Os. 
-fno-tree-vrp makes it go away...

[Bug middle-end/58101] Wrong out-of-bounds warning under -Os

[llozano at google dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58101

--- Comment #3 from Luis A Lozano <llozano at google dot com> ---
(In reply to Marek Polacek from comment #2)
> Perhaps a dup of PR41847.  Fails even with -O2, -O3, -Ofast, no only -Os. 
> -fno-tree-vrp makes it go away...

I dont think it is a duplicate of this issue. 
This problem does not happen with GCC 4.7.2

[Bug middle-end/58101] Wrong out-of-bounds warning under -Os

[dichlofos-mv at yandex dot ru]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58101

Mikhail Veltishchev <dichlofos-mv at yandex dot ru> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |dichlofos-mv at yandex dot ru

--- Comment #4 from Mikhail Veltishchev <dichlofos-mv at yandex dot ru> ---
Luis, why do you state that "rcu_num_levels is never larger than 1", this
cannot be proved as this variable is not const and can change its value (e.g.
in another thread).

[Bug middle-end/58101] Wrong out-of-bounds warning under -Os

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=58101

--- Comment #6 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Further reduced:
int a [1];

void foo (int n)
{
   if (n <= 1) return;
   int i = 1;
   a [i] = a [i - 1];
}

This is one of these false positives warning where we should maybe not warn but
instead just change the code to be a trap.

Note in the original testcase, GCC is able to remove the loop and just change
it to one statement. That is part of the reason for the warning even.

clang does not warn about the above because they only warn for the literal a[1]
case.