[Bug c++/55446] New: array new with size zero vanishes from object code

[Bug c++/55446] New: array new with size zero vanishes from object code

[jens.maurer at gmx dot net]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55446

             Bug #: 55446
           Summary: array new with size zero vanishes from object code
    Classification: Unclassified
           Product: gcc
           Version: 4.7.2
            Status: UNCONFIRMED
          Severity: major
          Priority: P3
         Component: c++
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: jens.maurer@gmx.net
              Host: x86_64-unknown-linux-gnu
            Target: x86_64-unknown-linux-gnu


The following program compiles successfully and outputs nothing at all.  In
fact, the generated assembly has an empty "main".  This happens even when
compiling with -O0.

#include <iostream>

struct S {
  S() { }
};

int main()
{
  std::cout << new S[0] << " bla" << std::endl;
}

$  g++ new-opt.cc -Wall -Wextra 
$ ./a.out 
(no output)

The issue goes away when removing the default constructor of "S".  It seems gcc
believes array-new with zero size is undefined behavior and thus removes the
rest of the expression.  I can't follow the "undefined behavior" part;
array-new with zero size should yield a non-zero pointer (see 3.7.3.1p2
[basic.stc.dynamic.allocation] and 5.3.4p7 [expr.new]).

[Bug c++/55446] array new with size zero vanishes from object code

[daniel.kruegler at googlemail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55446

Daniel Krügler <daniel.kruegler at googlemail dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |daniel.kruegler at
                   |                            |googlemail dot com

--- Comment #1 from Daniel Krügler <daniel.kruegler at googlemail dot com> 2012-11-23 22:21:30 UTC ---
I observe the same thing with gcc 4.8.0 20121104 (experimental) on my
mingw-x86_64 system. Odd.

[Bug c++/55446] array new with size zero vanishes from object code

[paolo.carlini at oracle dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55446

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2012-11-23
     Ever Confirmed|0                           |1

--- Comment #2 from Paolo Carlini <paolo.carlini at oracle dot com> 2012-11-23 22:28:26 UTC ---
Yes, this is confirmed.

[Bug c++/55446] array new with size zero vanishes from object code

[paolo.carlini at oracle dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55446

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

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

[Bug c++/55446] array new with size zero vanishes from object code

[paolo.carlini at oracle dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55446

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |wrong-code

--- Comment #3 from Paolo Carlini <paolo.carlini at oracle dot com> 2012-11-24 00:30:40 UTC ---
build_new_1, called by build_new, returns error_mark_node.

This happens because something goes very badly wrong in the cp_build_binary_op
call around line 2712: essentially it computes 0 - 1!

[Bug c++/55446] [4.7/4.8 Regression] array new with size zero vanishes from object code

[paolo.carlini at oracle dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55446

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|---                         |4.7.3
            Summary|array new with size zero    |[4.7/4.8 Regression] array
                   |vanishes from object code   |new with size zero vanishes
                   |                            |from object code

--- Comment #4 from Paolo Carlini <paolo.carlini at oracle dot com> 2012-11-24 01:24:38 UTC ---
And it's a regression.

[Bug c++/55446] [4.7/4.8 Regression] array new with size zero vanishes from object code

[paolo.carlini at oracle dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55446

--- Comment #5 from Paolo Carlini <paolo.carlini at oracle dot com> 2012-11-24 01:52:49 UTC ---
And it's mine because I caused it with the fix for PR45385 :(

[Bug c++/55446] [4.7/4.8 Regression] array new with size zero vanishes from object code

[paolo.carlini at oracle dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55446

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |ASSIGNED
         AssignedTo|unassigned at gcc dot       |paolo.carlini at oracle dot
                   |gnu.org                     |com

[Bug c++/55446] [4.7/4.8 Regression] array new with size zero vanishes from object code

[harald at gigawatt dot nl]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55446

Harald van Dijk <harald at gigawatt dot nl> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |harald at gigawatt dot nl

--- Comment #6 from Harald van Dijk <harald at gigawatt dot nl> 2012-11-24 09:28:44 UTC ---
A compile-only test for this can be

struct S { S(); };
void f(S *);
void g() {
  S *s = new S[0];
  f(s);
}

which causes a bogus warning:

test.cc: In function 'void g()':
test.cc:5:7: warning: 's' is used uninitialized in this function
[-Wuninitialized]

[Bug c++/55446] [4.7/4.8 Regression] array new with size zero vanishes from object code

[paolo.carlini at oracle dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55446

--- Comment #7 from Paolo Carlini <paolo.carlini at oracle dot com> 2012-11-24 09:32:48 UTC ---
Thanks. Relying on a warning seems a bit brittle, maybe a scan in the original
dump would be good enough in terms of compile only testcases, but I sent to the
mailing list a run time test.

[Bug c++/55446] [4.7/4.8 Regression] array new with size zero vanishes from object code

[paolo.carlini at oracle dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55446

--- Comment #8 from Paolo Carlini <paolo.carlini at oracle dot com> 2012-11-24 10:04:27 UTC ---
Patch here:

  http://gcc.gnu.org/ml/gcc-patches/2012-11/msg01991.html

[Bug c++/55446] [4.7/4.8 Regression] array new with size zero vanishes from object code

[harald at gigawatt dot nl]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55446

--- Comment #9 from Harald van Dijk <harald at gigawatt dot nl> 2012-11-24 11:27:25 UTC ---
Ah, okay, an alternative compile-only testcase that does not rely on particular
warnings would be

struct S { S(); };
__typeof__(new S[0]) s;

test.cc:2:23: error: invalid type in declaration before ';' token

but if you've already got a good testcase, sure, go with that :)

[Bug c++/55446] [4.7/4.8 Regression] array new with size zero vanishes from object code

[paolo at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55446

--- Comment #10 from paolo at gcc dot gnu.org <paolo at gcc dot gnu.org> 2012-11-24 23:45:49 UTC ---
Author: paolo
Date: Sat Nov 24 23:45:45 2012
New Revision: 193785

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=193785
Log:
/cp
2012-11-24  Paolo Carlini  <paolo.carlini@oracle.com>

    PR c++/55446
    * init.c (build_vec_init): Do not early return error_mark_mode
    when integer_all_onesp (maxindex).

/testsuite
2012-11-24  Paolo Carlini  <paolo.carlini@oracle.com>

    PR c++/55446
    * g++.dg/init/new41.C: New.

Added:
    trunk/gcc/testsuite/g++.dg/init/new41.C
Modified:
    trunk/gcc/cp/ChangeLog
    trunk/gcc/cp/init.c
    trunk/gcc/testsuite/ChangeLog

[Bug c++/55446] [4.7/4.8 Regression] array new with size zero vanishes from object code

[paolo at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55446

--- Comment #11 from paolo at gcc dot gnu.org <paolo at gcc dot gnu.org> 2012-11-24 23:55:26 UTC ---
Author: paolo
Date: Sat Nov 24 23:55:22 2012
New Revision: 193786

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=193786
Log:
/cp
2012-11-24  Paolo Carlini  <paolo.carlini@oracle.com>

    PR c++/55446
    * init.c (build_vec_init): Do not early return error_mark_mode
    when integer_all_onesp (maxindex).

/testsuite
2012-11-24  Paolo Carlini  <paolo.carlini@oracle.com>

    PR c++/55446
    * g++.dg/init/new41.C: New.

Added:
    branches/gcc-4_7-branch/gcc/testsuite/g++.dg/init/new41.C
Modified:
    branches/gcc-4_7-branch/gcc/cp/ChangeLog
    branches/gcc-4_7-branch/gcc/cp/init.c
    branches/gcc-4_7-branch/gcc/testsuite/ChangeLog

[Bug c++/55446] [4.7/4.8 Regression] array new with size zero vanishes from object code

[paolo.carlini at oracle dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55446

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|ASSIGNED                    |RESOLVED
         Resolution|                            |FIXED

--- Comment #12 from Paolo Carlini <paolo.carlini at oracle dot com> 2012-11-24 23:56:20 UTC ---
Fixed.

[Bug c++/55446] [4.7/4.8 Regression] array new with size zero vanishes from object code

[paolo.carlini at oracle dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55446

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |2013.bugzilla.gcc.gnu.org
                   |                            |at ingomueller dot net

--- Comment #13 from Paolo Carlini <paolo.carlini at oracle dot com> 2013-01-30 10:19:05 UTC ---
*** Bug 56146 has been marked as a duplicate of this bug. ***