[Bug other/43949] New: bogus warning: array subscript is above array bounds

[Bug other/43949] New: bogus warning: array subscript is above array bounds

[joachim dot reichel at gmx dot de]

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$ cat test.cpp
void f();

int c[3];
int result;

struct Vector {
    static int get(int i) {
        if (i >= 3)
            f();
        return c[i];
    }
};

void g()
{
    for (int i = 0; i < 3; ++i) {
        const int index = i % 3;
        result = Vector::get(index) + Vector::get(index);
    }
}

$ g++ -Wall -c test.cpp
[no warnings]

$ g++ -Wall -c -O2 test.cpp
test.cpp: In function ‘void g()’:
test.cpp:10: error: array subscript is above array bounds

$ g++ -v
Using built-in specs.
Target: x86_64-linux-gnu
Configured with: ../src/configure -v --with-pkgversion='Debian 4.4.2-9'
--with-bugurl=file:///usr/share/doc/gcc-4.4/README.Bugs
--enable-languages=c,c++,fortran,objc,obj-c++ --prefix=/usr --enable-shared
--enable-multiarch --enable-linker-build-id --with-system-zlib
--libexecdir=/usr/lib --without-included-gettext --enable-threads=posix
--with-gxx-include-dir=/usr/include/c++/4.4 --program-suffix=-4.4 --enable-nls
--enable-clocale=gnu --enable-libstdcxx-debug --enable-objc-gc
--with-arch-32=i486 --with-tune=generic --enable-checking=release
--build=x86_64-linux-gnu --host=x86_64-linux-gnu --target=x86_64-linux-gnu
Thread model: posix
gcc version 4.4.3 20100108 (prerelease) (Debian 4.4.2-9)

The bogus warning disappears if
- (index) is replaced by (i)
- Vector::get(index) is assigned to result (no addition)
- the if statement is removed (call of f() in all cases)
- get() is a global function

The bogus warning does not appear in gcc 4.2.4 (Debian 4.2.4-6). It appears
also in 4.3.2 (Debian 4.3.2-1.1) and gcc 4.5.0 (GCC).


-- 
           Summary: bogus warning: array subscript is above array bounds
           Product: gcc
           Version: 4.4.3
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: other
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: joachim dot reichel at gmx dot de
 GCC build triplet: x86_64-linux-gnu
  GCC host triplet: x86_64-linux-gnu
GCC target triplet: x86_64-linux-gnu


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=43949

[Bug other/43949] bogus warning: array subscript is above array bounds

[rguenth at gcc dot gnu dot org]

------- Comment #1 from rguenth at gcc dot gnu dot org  2010-04-30 17:25 -------
Confirmed.  VRP is stupid and does

Visiting statement:
index_4 = i_21 % 3;

Found new range for index_4: VARYING

Yet another missed optimization.


-- 

rguenth at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         AssignedTo|unassigned at gcc dot gnu   |rguenth at gcc dot gnu dot
                   |dot org                     |org
             Status|UNCONFIRMED                 |ASSIGNED
     Ever Confirmed|0                           |1
   Last reconfirmed|0000-00-00 00:00:00         |2010-04-30 17:25:26
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=43949

[Bug other/43949] bogus warning: array subscript is above array bounds

[rguenth at gcc dot gnu dot org]

------- Comment #2 from rguenth at gcc dot gnu dot org  2010-05-01 21:30 -------
Subject: Bug 43949

Author: rguenth
Date: Sat May  1 21:30:26 2010
New Revision: 158965

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=158965
Log:
2010-05-01  Richard Guenther  <rguenther@suse.de>

        PR tree-optimization/43949
        * tree-vrp.c (ssa_name_nonnegative_p): Return true for unsigned
        types.
        (extract_range_from_binary_expr): Handle *_MOD_EXPR.

        * g++.dg/warn/Warray-bounds-5.C: New testcase.

Added:
    trunk/gcc/testsuite/g++.dg/warn/Warray-bounds-5.C
Modified:
    trunk/gcc/ChangeLog
    trunk/gcc/testsuite/ChangeLog
    trunk/gcc/tree-vrp.c


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=43949

[Bug tree-optimization/43949] [4.3/4.4/4.5 Regression] bogus warning: array subscript is above array bounds

[rguenth at gcc dot gnu dot org]

------- Comment #3 from rguenth at gcc dot gnu dot org  2010-05-01 21:31 -------
Fixed for trunk sofar.


-- 

rguenth at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
          Component|other                       |tree-optimization
           Keywords|                            |diagnostic, missed-
                   |                            |optimization
      Known to work|                            |4.2.4 4.6.0
            Summary|bogus warning: array        |[4.3/4.4/4.5 Regression]
                   |subscript is above array    |bogus warning: array
                   |bounds                      |subscript is above array
                   |                            |bounds
   Target Milestone|---                         |4.3.5


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=43949

[Bug tree-optimization/43949] [4.3/4.4/4.5 Regression] bogus warning: array subscript is above array bounds

[rguenth at gcc dot gnu dot org]

------- Comment #4 from rguenth at gcc dot gnu dot org  2010-05-04 09:53 -------
Subject: Bug 43949

Author: rguenth
Date: Tue May  4 09:53:28 2010
New Revision: 159020

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=159020
Log:
2010-05-04  Richard Guenther  <rguenther@suse.de>

        PR tree-optimization/43949
        * tree-vrp.c (extract_range_from_binary_expr): Only handle
        TRUNC_MOD_EXPR.

Modified:
    trunk/gcc/ChangeLog
    trunk/gcc/tree-vrp.c


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=43949

[Bug tree-optimization/43949] [4.3/4.4/4.5 Regression] bogus warning: array subscript is above array bounds

[rguenth at gcc dot gnu dot org]

-- 

rguenth at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Priority|P3                          |P2


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=43949

[Bug tree-optimization/43949] [4.3/4.4/4.5 Regression] bogus warning: array subscript is above array bounds

[joachim dot reichel at gmx dot de]

------- Comment #5 from joachim dot reichel at gmx dot de  2010-05-21 09:12 -------
Will this problem get fixed on the 4.5 branch too?


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=43949

[Bug tree-optimization/43949] [4.3/4.4/4.5 Regression] bogus warning: array subscript is above array bounds

[rguenther at suse dot de]

------- Comment #6 from rguenther at suse dot de  2010-05-21 09:15 -------
Subject: Re:  [4.3/4.4/4.5 Regression] bogus
 warning: array subscript is above array bounds

On Fri, 21 May 2010, joachim dot reichel at gmx dot de wrote:

> ------- Comment #5 from joachim dot reichel at gmx dot de  2010-05-21 09:12 -------
> Will this problem get fixed on the 4.5 branch too?

Yes.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=43949

[Bug tree-optimization/43949] [4.3/4.4/4.5 Regression] bogus warning: array subscript is above array bounds

[rguenth at gcc dot gnu dot org]

------- Comment #7 from rguenth at gcc dot gnu dot org  2010-05-21 11:17 -------
Subject: Bug 43949

Author: rguenth
Date: Fri May 21 11:16:46 2010
New Revision: 159656

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=159656
Log:
2010-05-21  Richard Guenther  <rguenther@suse.de>

        PR tree-optimization/43949
        * tree-vrp.c (ssa_name_nonnegative_p): Return true for unsigend
        types.
        (extract_range_from_binary_expr): Handle TRUNC_MOD_EXPR.

        * g++.dg/warn/Warray-bounds-5.C: New testcase.

Added:
    branches/gcc-4_5-branch/gcc/testsuite/g++.dg/warn/Warray-bounds-5.C
Modified:
    branches/gcc-4_5-branch/gcc/ChangeLog
    branches/gcc-4_5-branch/gcc/testsuite/ChangeLog
    branches/gcc-4_5-branch/gcc/tree-vrp.c


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=43949

[Bug tree-optimization/43949] [4.3/4.4 Regression] bogus warning: array subscript is above array bounds

[rguenth at gcc dot gnu dot org]

------- Comment #8 from rguenth at gcc dot gnu dot org  2010-05-22 18:14 -------
GCC 4.3.5 is being released, adjusting target milestone.


-- 

rguenth at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|4.3.5                       |4.3.6


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=43949

[Bug tree-optimization/43949] [4.3/4.4 Regression] bogus warning: array subscript is above array bounds

[rguenth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=43949

Richard Guenther <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|4.3.6                       |4.4.7

--- Comment #9 from Richard Guenther <rguenth at gcc dot gnu.org> 2011-06-27 12:13:49 UTC ---
4.3 branch is being closed, moving to 4.4.7 target.