[Bug c++/56762] New: too aggressive optimization or missing warnings

[Bug c++/56762] New: too aggressive optimization or missing warnings

[npl at chello dot at]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56762

             Bug #: 56762
           Summary: too aggressive optimization or missing warnings
    Classification: Unclassified
           Product: gcc
           Version: 4.7.2
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: npl@chello.at


Created attachment 29743
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=29743
code describing the issue

Alternatively this could be just me misunderstanding C++.
But the issue is that I have an object created on the stack and I would expect
it to survive until it goes out of scope.
Now I understand that I probably used it the wrong way by giving it a temporary
when it needed a reference to something more solid, but I would expect an error
message in this case.

Please look at the provided code, which compiles without error/warning. the
exchange function wont have any calls to lock/unlock.

tested with gcc 4.7.2 + 4.8.0

[Bug c++/56762] too aggressive optimization or missing warnings

[daniel.kruegler at googlemail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56762

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> 2013-03-28 12:15:30 UTC ---
This line does not what you expect it would do (Search for "most vexing
parse"):

CLockGuard<CIntLock> sGuard(CIntLock());

It does *not* construct an CIntLock object nor does it declare an sGuard
object, instead it does declare a function and has no further effects.
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From: "rguenth at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/56756] [4.9 Regression] ICE: verify_ssa failed (definition in block n follows the use !)
Date: Thu, 28 Mar 2013 12:34:00 -0000
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http://gcc.gnu.org/bugzilla/show_bug.cgi?idV756

--- Comment #8 from Richard Biener <rguenth at gcc dot gnu.org> 2013-03-28 12:34:24 UTC ---
Ok, so one reason is that we simply "ignore" dependencies when computing
what stmts to move (which happens in the same processing order):

static bool
add_dependency (tree def, struct lim_aux_data *data, struct loop *loop,
                bool add_cost)
{
...
  max_loop = outermost_invariant_loop (def, loop);
  if (!max_loop)
    return false;
...
  def_data = get_lim_data (def_stmt);
  if (!def_data)
    return true;

so, when we don't know anything about the stmt we depend on because we
didn't visit it yet outermost_invariant_loop returns garbage in this case.

But I got side-tracked by the above (which still should be fixed IMHO),
as also store-motion does not properly initialize dependence.

[Bug c++/56762] too aggressive optimization or missing warnings

[npl at chello dot at]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56762

--- Comment #2 from npl at chello dot at 2013-03-28 13:38:01 UTC ---
Oh how I hate this rule. Thanks for the info and sorry for the invalid report.

[Bug c++/56762] too aggressive optimization or missing warnings

[redi at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56762

Jonathan Wakely <redi at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
         Resolution|                            |DUPLICATE

--- Comment #3 from Jonathan Wakely <redi at gcc dot gnu.org> 2013-03-28 15:14:11 UTC ---
We should give a warning, see PR 15672

*** This bug has been marked as a duplicate of bug 15672 ***