[Bug c/108079] New: -Wunused-variable gives misleading duplicate warning for unused static local variable

[Bug c/108079] New: -Wunused-variable gives misleading duplicate warning for unused static local variable

[stephenheumann at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108079

            Bug ID: 108079
           Summary: -Wunused-variable gives misleading duplicate warning
                    for unused static local variable
           Product: gcc
           Version: 13.0
            Status: UNCONFIRMED
          Keywords: diagnostic
          Severity: normal
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: stephenheumann at gmail dot com
  Target Milestone: ---

For this program:

int main(void) {
        static int x;
}

gcc -Wunused-variable reports:

<source>: In function 'main':
<source>:2:20: warning: unused variable 'x' [-Wunused-variable]
    2 |         static int x;
      |                    ^
<source>: At top level:
<source>:2:20: warning: 'x' defined but not used [-Wunused-variable]

These two warnings are about the same thing, except the second one is
incorrectly labeled "At top level." There should just be one warning, without
"At top level."

C++ does the same thing, except it says "At global scope" instead of "At top
level."

This seems to be a regression that occurred in GCC 6: 5.4 just gives one
warning, but 6.1 also gives the extra one with "At top level."

[Bug c/108079] [10/11/12/13 Regression] -Wunused-variable gives misleading duplicate warning for unused static local variable

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108079

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
            Summary|-Wunused-variable gives     |[10/11/12/13 Regression]
                   |misleading duplicate        |-Wunused-variable gives
                   |warning for unused static   |misleading duplicate
                   |local variable              |warning for unused static
                   |                            |local variable
             Status|UNCONFIRMED                 |NEW
     Ever confirmed|0                           |1
   Last reconfirmed|                            |2022-12-13
      Known to work|                            |5.5.0
   Target Milestone|---                         |10.5
           Priority|P3                          |P2
      Known to fail|                            |6.1.0

--- Comment #1 from Richard Biener <rguenth at gcc dot gnu.org> ---
Confirmed.

[Bug c/108079] [10/11/12/13 Regression] -Wunused-variable gives misleading duplicate warning for unused static local variable

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108079

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |jakub at gcc dot gnu.org

--- Comment #2 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Seems to have started with r6-1401-gd7438551ff5ffa0afeca2aa3efd13035b26bee34
One of the warnings is diagnosed by the FE (from pop_scope/poplevel),
the other by cgraphunit (check_global_declaration).

[Bug c/108079] [10/11/12/13 Regression] -Wunused-variable gives misleading duplicate warning for unused static local variable

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108079

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |ASSIGNED
           Assignee|unassigned at gcc dot gnu.org      |jakub at gcc dot gnu.org

--- Comment #3 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Created attachment 54143
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=54143&action=edit
gcc13-pr108079.patch

Untested fix.

[Bug c/108079] [10/11/12/13 Regression] -Wunused-variable gives misleading duplicate warning for unused static local variable

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108079

--- Comment #4 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Jakub Jelinek <jakub@gcc.gnu.org>:

https://gcc.gnu.org/g:2c63cc7268fd5615997989f153e9405d0f5aaa50

commit r13-6575-g2c63cc7268fd5615997989f153e9405d0f5aaa50
Author: Jakub Jelinek <jakub@redhat.com>
Date:   Fri Mar 10 10:10:24 2023 +0100

    c, c++, cgraphunit: Prevent duplicated -Wunused-value warnings [PR108079]

    On the following testcase, we warn with -Wunused-value twice, once
    in the FEs and later on cgraphunit again with slightly different
    wording.

    The following patch fixes that by registering a warning suppression in the
    FEs when we warn and not warning in cgraphunit anymore if that happened.

    2023-03-10  Jakub Jelinek  <jakub@redhat.com>

            PR c/108079
    gcc/
            * cgraphunit.cc (check_global_declaration): Don't warn for unused
            variables which have OPT_Wunused_variable warning suppressed.
    gcc/c/
            * c-decl.cc (pop_scope): Suppress OPT_Wunused_variable warning
            after diagnosing it.
    gcc/cp/
            * decl.cc (poplevel): Suppress OPT_Wunused_variable warning
            after diagnosing it.
    gcc/testsuite/
            * c-c++-common/Wunused-var-18.c: New test.

[Bug c/108079] [10/11/12 Regression] -Wunused-variable gives misleading duplicate warning for unused static local variable

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108079

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
            Summary|[10/11/12/13 Regression]    |[10/11/12 Regression]
                   |-Wunused-variable gives     |-Wunused-variable gives
                   |misleading duplicate        |misleading duplicate
                   |warning for unused static   |warning for unused static
                   |local variable              |local variable

--- Comment #5 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Fixed on the trunk so far.

[Bug c/108079] [10/11/12 Regression] -Wunused-variable gives misleading duplicate warning for unused static local variable

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108079

--- Comment #6 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The releases/gcc-12 branch has been updated by Jakub Jelinek
<jakub@gcc.gnu.org>:

https://gcc.gnu.org/g:e4984838f6af868399ef9d885377199c38907ee1

commit r12-9287-ge4984838f6af868399ef9d885377199c38907ee1
Author: Jakub Jelinek <jakub@redhat.com>
Date:   Fri Mar 10 10:10:24 2023 +0100

    c, c++, cgraphunit: Prevent duplicated -Wunused-value warnings [PR108079]

    On the following testcase, we warn with -Wunused-value twice, once
    in the FEs and later on cgraphunit again with slightly different
    wording.

    The following patch fixes that by registering a warning suppression in the
    FEs when we warn and not warning in cgraphunit anymore if that happened.

    2023-03-10  Jakub Jelinek  <jakub@redhat.com>

            PR c/108079
    gcc/
            * cgraphunit.cc (check_global_declaration): Don't warn for unused
            variables which have OPT_Wunused_variable warning suppressed.
    gcc/c/
            * c-decl.cc (pop_scope): Suppress OPT_Wunused_variable warning
            after diagnosing it.
    gcc/cp/
            * decl.cc (poplevel): Suppress OPT_Wunused_variable warning
            after diagnosing it.
    gcc/testsuite/
            * c-c++-common/Wunused-var-18.c: New test.

    (cherry picked from commit 2c63cc7268fd5615997989f153e9405d0f5aaa50)

[Bug c/108079] [10/11 Regression] -Wunused-variable gives misleading duplicate warning for unused static local variable

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108079

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
            Summary|[10/11/12 Regression]       |[10/11 Regression]
                   |-Wunused-variable gives     |-Wunused-variable gives
                   |misleading duplicate        |misleading duplicate
                   |warning for unused static   |warning for unused static
                   |local variable              |local variable

--- Comment #7 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Fixed for 12.3 too.

[Bug c/108079] [11 Regression] -Wunused-variable gives misleading duplicate warning for unused static local variable

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108079

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

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

--- Comment #8 from Richard Biener <rguenth at gcc dot gnu.org> ---
GCC 10 branch is being closed.