[Bug c++/95825] New: [7/8/9/10/11 Regression] boost::optional -Wuninitialized

[Bug c++/95825] New: [7/8/9/10/11 Regression] boost::optional -Wuninitialized

[nok.raven at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95825

            Bug ID: 95825
           Summary: [7/8/9/10/11 Regression] boost::optional
                    -Wuninitialized
           Product: gcc
           Version: 10.0
            Status: UNCONFIRMED
          Keywords: diagnostic
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: nok.raven at gmail dot com
  Target Milestone: ---

#include <boost/optional.hpp>

boost::optional<char> get()
{
  return {};
}

boost::optional<char> foo()
{
  return get();
}

// g++ -O3 -Wall -Wextra -fsanitize=address

<source>: In function 'boost::optional<char> foo()':
<source>:5:11: warning:
'<anonymous>.boost::optional<char>::<anonymous>.boost::optional_detail::tc_optional_base<char>::m_storage'
is used uninitialized in this function [-Wuninitialized]
    5 |   return {};
      |           ^

https://godbolt.org/z/PD_qan

Most likely related to bug 86465

[Bug c++/95825] [8/9/10/11 Regression] boost::optional -Wuninitialized

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95825

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
            Summary|[7/8/9/10/11 Regression]    |[8/9/10/11 Regression]
                   |boost::optional             |boost::optional
                   |-Wuninitialized             |-Wuninitialized
   Target Milestone|---                         |8.5

[Bug tree-optimization/95825] [8/9/10/11 Regression] boost::optional -Wuninitialized

[mpolacek at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95825

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Last reconfirmed|                            |2020-08-04
                 CC|                            |mpolacek at gcc dot gnu.org
     Ever confirmed|0                           |1
             Status|UNCONFIRMED                 |NEW
          Component|c++                         |tree-optimization

--- Comment #1 from Marek Polacek <mpolacek at gcc dot gnu.org> ---
Started with r245840, not a C++ issue.

[Bug tree-optimization/95825] [8/9/10/11 Regression] boost::optional -Wuninitialized

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95825

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

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

[Bug tree-optimization/95825] [9/10/11/12 Regression] boost::optional -Wuninitialized

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95825

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|8.5                         |9.4

--- Comment #2 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
GCC 8 branch is being closed.

[Bug tree-optimization/95825] [9/10/11/12 Regression] boost::optional -Wuninitialized

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95825

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|9.4                         |9.5

--- Comment #3 from Richard Biener <rguenth at gcc dot gnu.org> ---
GCC 9.4 is being released, retargeting bugs to GCC 9.5.

[Bug tree-optimization/95825] [10/11/12/13 Regression] boost::optional -Wuninitialized

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95825

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|9.5                         |10.4

--- Comment #4 from Richard Biener <rguenth at gcc dot gnu.org> ---
GCC 9 branch is being closed

[Bug tree-optimization/95825] [10/11/12/13 Regression] boost::optional -Wuninitialized

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95825

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|10.4                        |10.5

--- Comment #5 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
GCC 10.4 is being released, retargeting bugs to GCC 10.5.

[Bug tree-optimization/95825] [10/11/12/13 Regression] boost::optional -Wuninitialized with -fsanitize=address

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95825

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
            Summary|[10/11/12/13 Regression]    |[10/11/12/13 Regression]
                   |boost::optional             |boost::optional
                   |-Wuninitialized             |-Wuninitialized with
                   |                            |-fsanitize=address
   Last reconfirmed|2020-08-04 00:00:00         |2022-9-22

--- Comment #6 from Richard Biener <rguenth at gcc dot gnu.org> ---
requires -fsanitize=address

[Bug tree-optimization/95825] [10/11/12/13 Regression] boost::optional -Wuninitialized with -fsanitize=address

[daniel.klauer at gin dot de]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95825

daniel.klauer at gin dot de changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |daniel.klauer at gin dot de

--- Comment #7 from daniel.klauer at gin dot de ---
Reduced test case:


template<typename T>
struct tc_optional_base
{
        // default ctor leaves m_storage uninitialized
        tc_optional_base() : m_initialized(false) {}
        bool m_initialized;
        T m_storage;
};

template<typename T>
tc_optional_base<T> f()
{
        return {};
}

tc_optional_base<int> g()
{
        return f<int>();
}


$ g++ -Wall -O1 -fsanitize=address b.cxx -c
In function ‘tc_optional_base<T> f() [with T = int]’,
    inlined from ‘tc_optional_base<int> g()’ at b.cxx:18:15:
b.cxx:13:17: warning: ‘<anonymous>.tc_optional_base<int>::m_storage’ is used
uninitialized [-Wuninitialized]
   13 |         return {};
      |                 ^
b.cxx: In function ‘tc_optional_base<int> g()’:
b.cxx:13:17: note: ‘<anonymous>’ declared here
   13 |         return {};
      |

$ g++ --version
g++ (Ubuntu 11.3.0-1ubuntu1~22.04) 11.3.0


It looks like the m_storage field really is uninitialized, although I think in
practice boost::optional does not access it in that state in its implementation
thanks to m_initialized. Does gcc warn about the uninitialized data during
copying of the object here? It does seem to be correct...

In the above case with templates it happens at -O1 already, but without
templates it happens too, at -O2.

[Bug tree-optimization/95825] [10/11/12/13 Regression] boost::optional -Wuninitialized with -fsanitize=address

[daniel.kruegler at googlemail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95825

--- Comment #8 from Daniel Krügler <daniel.kruegler at googlemail dot com> ---
(In reply to daniel.klauer from comment #7)
> Reduced test case:
> 
> 
> template<typename T>
> struct tc_optional_base
> {
> 	// default ctor leaves m_storage uninitialized
> 	tc_optional_base() : m_initialized(false) {}
> 	bool m_initialized;
> 	T m_storage;
> };

This example seems unrelated to the issue, because you have here a struct, not
a union.

[Bug tree-optimization/95825] [10/11/12/13 Regression] boost::optional -Wuninitialized with -fsanitize=address

[daniel.klauer at gin dot de]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95825

--- Comment #9 from daniel.klauer at gin dot de ---
Unless I'm missing something, this is not about unions. boost::optional (at
least from boost 1.80.0) does not always use unions; instead it has two
possible implementations: optional_base, which uses unions, and
tc_optional_base, which does not. The original test case triggers the
tc_optional_base case too.

[Bug tree-optimization/95825] [11/12/13/14 Regression] boost::optional -Wuninitialized with -fsanitize=address

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95825

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|10.5                        |11.5

--- Comment #10 from Richard Biener <rguenth at gcc dot gnu.org> ---
GCC 10 branch is being closed.