[Bug c++/54372] New: __attribute__((unused)) doesn't work with unused local typedef in template function.

[Bug c++/54372] New: __attribute__((unused)) doesn't work with unused local typedef in template function.

[flast at flast dot jp]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54372

             Bug #: 54372
           Summary: __attribute__((unused)) doesn't work with unused local
                    typedef in template function.
    Classification: Unclassified
           Product: gcc
           Version: 4.8.0
            Status: UNCONFIRMED
          Severity: minor
          Priority: P3
         Component: c++
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: flast@flast.jp


GCC 4.8 warns unused local typedefs and can suppres it with
__attribute__((unused)).
However, in member or non-member template function, it doesn't work with
dependent type.

I tested attached code.

[Bug c++/54372] __attribute__((unused)) doesn't work with unused local typedef in template function.

[flast at flast dot jp]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54372

--- Comment #1 from Kohei Takahashi <flast at flast dot jp> 2012-08-25 07:17:49 UTC ---
Created attachment 28082
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=28082
test code

[Bug c++/54372] __attribute__((unused)) doesn't work with unused local typedef in template function.

[paolo.carlini at oracle dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54372

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2012-09-18
                 CC|                            |paolo.carlini at oracle dot
                   |                            |com
     Ever Confirmed|0                           |1

--- Comment #2 from Paolo Carlini <paolo.carlini at oracle dot com> 2012-09-18 12:38:48 UTC ---
Now that the new warning is also in -Wall, it would be nice to fix this.

Note that local variables are already "more than Ok", that is at template
definition time we produce no -Wunused warnings at all even without the
attribute (we only warn at instantiation time): I suppose something similar
should be not too difficult to implement for the new warning too...

Dodji, what do you think?

[Bug c++/54372] __attribute__((unused)) doesn't work with unused local typedef in template function.

[dodji at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54372

Dodji Seketeli <dodji at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |ASSIGNED

--- Comment #3 from Dodji Seketeli <dodji at gcc dot gnu.org> 2012-09-20 11:27:19 UTC ---
The 'unused' attribute is applied to its appertaining entity only at
instantiation time.  As a result, TREE_USED is not set on the entity before
instantiation.

But then maybe_warn_unused_local_typedefs checks for TREE_USED at compile time,
and wrongly emits the warning.

I am testing this patch that tests for the syntactic presence of the unused
attribute:


diff --git a/gcc/c-family/c-common.c b/gcc/c-family/c-common.c
index 6de2f1c..36c4aa6 100644
--- a/gcc/c-family/c-common.c
+++ b/gcc/c-family/c-common.c
@@ -10899,7 +10899,8 @@ maybe_warn_unused_local_typedefs (void)
       && errorcount == unused_local_typedefs_warn_count)
     {
       FOR_EACH_VEC_ELT (tree, l->local_typedefs, i, decl)
-       if (!TREE_USED (decl))
+       if (!TREE_USED (decl)
+           && !lookup_attribute_spec (get_identifier ("unused")))
          warning_at (DECL_SOURCE_LOCATION (decl),
                      OPT_Wunused_local_typedefs,
                      "typedef %qD locally defined but not used", decl);

[Bug c++/54372] __attribute__((unused)) doesn't work with unused local typedef in template function.

[paolo.carlini at oracle dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54372

--- Comment #4 from Paolo Carlini <paolo.carlini at oracle dot com> 2012-09-20 11:59:11 UTC ---
Ah, ah, thanks, great that the issue seems easy to fix!

[Bug c++/54372] __attribute__((unused)) doesn't work with unused local typedef in template function.

[dodji at seketeli dot org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54372

--- Comment #5 from dodji at seketeli dot org <dodji at seketeli dot org> 2012-09-20 14:13:28 UTC ---
A candiate patch was sent to
http://gcc.gnu.org/ml/gcc-patches/2012-09/msg01456.html

[Bug c++/54372] __attribute__((unused)) doesn't work with unused local typedef in template function.

[flast at flast dot jp]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54372

--- Comment #6 from Kohei Takahashi <flast at flast dot jp> 2012-09-22 13:06:32 UTC ---
I tested on x86_64-linux-gnu and works fine.

[Bug c++/54372] __attribute__((unused)) doesn't work with unused local typedef in template function.

[dodji at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54372

--- Comment #7 from Dodji Seketeli <dodji at gcc dot gnu.org> 2012-09-28 13:32:52 UTC ---
Author: dodji
Date: Fri Sep 28 13:32:41 2012
New Revision: 191830

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=191830
Log:
PR c++/54372 - unused attribute inactive on dependant entities

In the example of this patch, gcc/g++ invoked with
-Wunused-local-typedefs warns on dependant entities even when those
are decorated with the 'unused' attribute.

This is because in cplus_decl_attributes, save_template_attributes
makes so that the 'unused' attribute is applied to its appertaining
entity only at instantiation time.  But then at parsing time
maybe_warn_unused_local_typedefs checks for TREE_USED before warning.

This patch applies the 'unused' attribute at compilation time.

Tested on x86_64-unknown-linux-gnu against trunk.

gcc/cp/

    * decl2.c (is_late_template_attribute): "unused" attribute is to
    be applied at compile time.

gcc/testsuite/

    * c-c++-common/Wunused-local-typedefs-2.c: New test.

Added:
    trunk/gcc/testsuite/c-c++-common/Wunused-local-typedefs-2.c
Modified:
    trunk/gcc/cp/ChangeLog
    trunk/gcc/cp/decl2.c
    trunk/gcc/testsuite/ChangeLog

[Bug c++/54372] __attribute__((unused)) doesn't work with unused local typedef in template function.

[dodji at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54372

Dodji Seketeli <dodji at gcc dot gnu.org> changed:

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

--- Comment #8 from Dodji Seketeli <dodji at gcc dot gnu.org> 2012-09-28 13:35:49 UTC ---
Fixed in trunk (4.8)