[Bug c++/55203] No unused warning for variables of non-trivial types

[l.lunak at suse dot cz]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55203

--- Comment #5 from Lubos Lunak l.lunak at suse dot cz ---
Gcc patch is in, r200941.

Keeping open for libstdc++ to use the attribute for its relevant classes. I can
try to submit a patch when I find the time, but I doubt I'll get past the most
obvious classes, so anyone more knowledgeable about libstdc++ can feel free.

[Bug c++/55203] No unused warning for variables of non-trivial types

[l.lunak at suse dot cz]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55203

--- Comment #8 from Lubos Lunak l.lunak at suse dot cz ---
(In reply to Jonathan Wakely from comment #6)
 Which are the relevant classes?  It seems to me that we want to tag almost
 everything except a few RAII types such as std::lock_guard and
 std::unique_lock, which would be quite tedious.  It's certainly applicable
 on all containers, and most streams except fstreams (which have constructors
 with side-effects.)

 Correct. And I do not see a better way than tagging everything where it
applies.

 I think your extend.texi change is wrong, a std::mutex that is unused is
 useless, its constructor and destructor don't do anything useful. A
 std::lock_guard that is unused is *not* useless.

 Correct as well. But that doesn't come from my patch, that section was altered
by Jason Merrill before committing, and I overlooked that. Can you fix that
easily or should I submit a patch?

[Bug c++/55203] New: No unused warning for variables of non-trivial types

[l.lunak at suse dot cz]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55203

 Bug #: 55203
   Summary: No unused warning for variables of non-trivial types
Classification: Unclassified
   Product: gcc
   Version: 4.8.0
Status: UNCONFIRMED
  Severity: normal
  Priority: P3
 Component: c++
AssignedTo: unassig...@gcc.gnu.org
ReportedBy: l.lu...@suse.cz


GCC warns about unused variables e.g. of type 'int', but not 'std::string' :

$ cat a.cpp
#include string

void foo()
{
int i;
std::string s;
}
$ g++ -Wall -Wunused -c a.cpp
a.cpp: In function ‘void foo()’:
a.cpp:5:9: warning: unused variable ‘i’ [-Wunused-variable]
 int i;
 ^

In the function 's' is apparently unused too, but the compiler cannot tell it.

[Bug c++/55203] No unused warning for variables of non-trivial types

[l.lunak at suse dot cz]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55203



Lubos Lunak l.lunak at suse dot cz changed:



   What|Removed |Added



   Severity|normal  |enhancement



--- Comment #1 from Lubos Lunak l.lunak at suse dot cz 2012-11-04 11:04:01 
UTC ---

As the compiler cannot tell for sure in some cases, such as the ctor calling an

external function, the only reasonable way of handling this I see is explicit

tagging of types for which there should be an unused warning if only ctor/dtor

are called for a variable. Here's my attempt at attribute warn_unused.

[Bug c++/55203] No unused warning for variables of non-trivial types

[l.lunak at suse dot cz]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55203



--- Comment #2 from Lubos Lunak l.lunak at suse dot cz 2012-11-04 11:04:52 
UTC ---

Created attachment 28609

  -- http://gcc.gnu.org/bugzilla/attachment.cgi?id=28609

gcc patch