[Bug preprocessor/97498] New: #pragma GCC diagnostic ignored "-Wunused-function" inconsistent

[Bug preprocessor/97498] New: #pragma GCC diagnostic ignored "-Wunused-function" inconsistent

[matthewp515 at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97498

            Bug ID: 97498
           Summary: #pragma GCC diagnostic ignored "-Wunused-function"
                    inconsistent
           Product: gcc
           Version: 9.3.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: preprocessor
          Assignee: unassigned at gcc dot gnu.org
          Reporter: matthewp515 at gmail dot com
  Target Milestone: ---

Ubuntu Linux 20.04


#define STR(x) #x
#define WIGNORE(x, instrs) \
        _Pragma("GCC diagnostic push") \
        _Pragma(STR(GCC diagnostic ignored #x)) \
        instrs \
        _Pragma("GCC diagnostic pop")

// REPLACE

int main(void) {return 1;}


When REPLACE is replaced with:

WIGNORE(-Wunused-function,
static int f(int a) {return a + 1;}
)

The command:

gcc main.c -Wall -Werror -Wextra

fails (-Werror=unused-function). However, breaking up the command into separate
preprocessing and compilation stages:

gcc -E main.c -Wall -Werror -Wextra | gcc -x c -

passes.

When the macro is unwound by REPLACE being replaced with:

_Pragma("GCC diagnostic push");
_Pragma("GCC diagnostic ignored \"-Wunused-function\"");
static int f(int p) {return p + 1;}
_Pragma("GCC diagnostic pop");

The first command then passes. By adding a single backslash (\) right after the
implementation of f, as is required to keep the WIGNORE macro all as one, the
command fails. But how else can the macro be constructed?

[Bug preprocessor/97498] #pragma GCC diagnostic ignored "-Wunused-function" inconsistent

[lhyatt at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97498

Lewis Hyatt <lhyatt at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |lhyatt at gcc dot gnu.org
     Ever confirmed|0                           |1
   Last reconfirmed|                            |2022-07-07
             Status|UNCONFIRMED                 |NEW

--- Comment #1 from Lewis Hyatt <lhyatt at gcc dot gnu.org> ---
This is closely related to PR69543, but it's not quite the same. That PR is
about the use of input_location when processing a "#pragma GCC diagnostic
ignored"; this one is about the use of input_location when processing a pop
rather.

In c-pragma.cc line ~943 we call

      diagnostic_pop_diagnostics (global_dc, input_location);

When processing the line:

static int f(int p) {return p + 1;} _Pragma("GCC diagnostic pop");

In C++ mode, input_location points to the _Pragma and so it works fine. In
preprocess mode (gcc -E or gcc with -save-temps), it's fine also because the
_Pragma turns into a #pragma on the next line  before being actually processed.

In C mode though, input_location points to the start of the line and hence the
pop takes effect too early which leads to the issue.

It feels to me like we shouldn't use input_location anywhere in this function,
rather the location of the relevant tokens, but I am not sure all the details
of that, will see if anyone on PR69543 has ideas as well.

Here is a one-line test case that reveals the same problem with using
input_location while processing the GCC diagnostic pragma, i.e. exactly
PR69543's case:

======
static void f() {} _Pragma("GCC diagnostic error \"-Wunused-function\"")
======

Compiled without any other arguments, it works with gcc -x c++ and with gcc
-save-temps, but it fails with gcc -x c.

[Bug preprocessor/97498] #pragma GCC diagnostic ignored "-Wunused-function" inconsistent

[lhyatt at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97498

--- Comment #2 from Lewis Hyatt <lhyatt at gcc dot gnu.org> ---
Patch submitted for review here:
https://gcc.gnu.org/pipermail/gcc-patches/2022-July/598116.html

[Bug preprocessor/97498] #pragma GCC diagnostic ignored "-Wunused-function" inconsistent

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97498

--- Comment #3 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Lewis Hyatt <lhyatt@gcc.gnu.org>:

https://gcc.gnu.org/g:0587cef3d7962a8b0f44779589ba2920dd3d71e5

commit r13-1596-g0587cef3d7962a8b0f44779589ba2920dd3d71e5
Author: Lewis Hyatt <lhyatt@gmail.com>
Date:   Sat Jul 9 16:12:21 2022 -0400

    c: Fix location for _Pragma tokens [PR97498]

    The handling of #pragma GCC diagnostic uses input_location, which is not
always
    as precise as needed; in particular the relative location of some tokens
and a
    _Pragma directive will crucially determine whether a given diagnostic is
enabled
    or suppressed in the desired way. PR97498 shows how the C frontend ends up
with
    input_location pointing to the beginning of the line containing a _Pragma()
    directive, resulting in the wrong behavior if the diagnostic to be modified
    pertains to some tokens found earlier on the same line. This patch fixes
that by
    addressing two issues:

        a) libcpp was not assigning a valid location to the CPP_PRAGMA token
        generated by the _Pragma directive.
        b) C frontend was not setting input_location to something reasonable.

    With this change, the C frontend is able to change input_location to point
to
    the _Pragma token as needed.

    This is just a two-line fix (one for each of a) and b)), the testsuite
changes
    were needed only because the location on the tested warnings has been
somewhat
    improved, so the tests need to look for the new locations.

    gcc/c/ChangeLog:

            PR preprocessor/97498
            * c-parser.cc (c_parser_pragma): Set input_location to the
            location of the pragma, rather than the start of the line.

    libcpp/ChangeLog:

            PR preprocessor/97498
            * directives.cc (destringize_and_run): Override the location of
            the CPP_PRAGMA token from a _Pragma directive to the location of
            the expansion point, as is done for the tokens lexed from it.

    gcc/testsuite/ChangeLog:

            PR preprocessor/97498
            * c-c++-common/pr97498.c: New test.
            * c-c++-common/gomp/pragma-3.c: Adapt for improved warning
locations.
            * c-c++-common/gomp/pragma-5.c: Likewise.
            * gcc.dg/pragma-message.c: Likewise.

    libgomp/ChangeLog:

            * testsuite/libgomp.oacc-c-c++-common/reduction-5.c: Adapt for
            improved warning locations.
            * testsuite/libgomp.oacc-c-c++-common/vred2d-128.c: Likewise.

[Bug preprocessor/97498] #pragma GCC diagnostic ignored "-Wunused-function" inconsistent

[lhyatt at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97498

Lewis Hyatt <lhyatt at gcc dot gnu.org> changed:

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

--- Comment #4 from Lewis Hyatt <lhyatt at gcc dot gnu.org> ---
Fixed for GCC 13.

[Bug preprocessor/97498] #pragma GCC diagnostic ignored "-Wunused-function" inconsistent

[marxin at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97498

Martin Liška <marxin at gcc dot gnu.org> changed:

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

--- Comment #5 from Martin Liška <marxin at gcc dot gnu.org> ---
*** Bug 106267 has been marked as a duplicate of this bug. ***

[Bug preprocessor/97498] #pragma GCC diagnostic ignored "-Wunused-function" inconsistent

[marxin at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97498

--- Comment #6 from Martin Liška <marxin at gcc dot gnu.org> ---
Am I correct that it's not something for backport to GCC 12 or any older
version?

[Bug preprocessor/97498] #pragma GCC diagnostic ignored "-Wunused-function" inconsistent

[marxin at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97498

--- Comment #7 from Martin Liška <marxin at gcc dot gnu.org> ---
(In reply to Martin Liška from comment #6)
> Am I correct that it's not something for backport to GCC 12 or any older
> version?

We actually speak about 2 modified lines, so can we backport it, please?

[Bug preprocessor/97498] #pragma GCC diagnostic ignored "-Wunused-function" inconsistent

[lhyatt at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97498

Lewis Hyatt <lhyatt at gmail dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |lhyatt at gmail dot com

--- Comment #8 from Lewis Hyatt <lhyatt at gmail dot com> ---
(In reply to Martin Liška from comment #7)

> We actually speak about 2 modified lines, so can we backport it, please?

It will work fine for any of 10, 11, 12. I'll ask for approval for that on
gcc-patches then.

[Bug preprocessor/97498] #pragma GCC diagnostic ignored "-Wunused-function" inconsistent

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97498

--- Comment #9 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The releases/gcc-12 branch has been updated by Lewis Hyatt
<lhyatt@gcc.gnu.org>:

https://gcc.gnu.org/g:98e2676558f6f50cfb90610e5a160642a24d1596

commit r12-8648-g98e2676558f6f50cfb90610e5a160642a24d1596
Author: Lewis Hyatt <lhyatt@gmail.com>
Date:   Sat Jul 9 16:12:21 2022 -0400

    c: Fix location for _Pragma tokens [PR97498]

    The handling of #pragma GCC diagnostic uses input_location, which is not
always
    as precise as needed; in particular the relative location of some tokens
and a
    _Pragma directive will crucially determine whether a given diagnostic is
enabled
    or suppressed in the desired way. PR97498 shows how the C frontend ends up
with
    input_location pointing to the beginning of the line containing a _Pragma()
    directive, resulting in the wrong behavior if the diagnostic to be modified
    pertains to some tokens found earlier on the same line. This patch fixes
that by
    addressing two issues:

        a) libcpp was not assigning a valid location to the CPP_PRAGMA token
        generated by the _Pragma directive.
        b) C frontend was not setting input_location to something reasonable.

    With this change, the C frontend is able to change input_location to point
to
    the _Pragma token as needed.

    This is just a two-line fix (one for each of a) and b)), the testsuite
changes
    were needed only because the location on the tested warnings has been
somewhat
    improved, so the tests need to look for the new locations.

    gcc/c/ChangeLog:

            PR preprocessor/97498
            * c-parser.cc (c_parser_pragma): Set input_location to the
            location of the pragma, rather than the start of the line.

    libcpp/ChangeLog:

            PR preprocessor/97498
            * directives.cc (destringize_and_run): Override the location of
            the CPP_PRAGMA token from a _Pragma directive to the location of
            the expansion point, as is done for the tokens lexed from it.

    gcc/testsuite/ChangeLog:

            PR preprocessor/97498
            * c-c++-common/pr97498.c: New test.
            * c-c++-common/gomp/pragma-3.c: Adapt for improved warning
locations.
            * c-c++-common/gomp/pragma-5.c: Likewise.
            * gcc.dg/pragma-message.c: Likewise.

    libgomp/ChangeLog:

            * testsuite/libgomp.oacc-c-c++-common/reduction-5.c: Adapt for
            improved warning locations.
            * testsuite/libgomp.oacc-c-c++-common/vred2d-128.c: Likewise.

    (cherry picked from commit 0587cef3d7962a8b0f44779589ba2920dd3d71e5)

[Bug preprocessor/97498] #pragma GCC diagnostic ignored "-Wunused-function" inconsistent

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97498

--- Comment #10 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The releases/gcc-10 branch has been updated by Lewis Hyatt
<lhyatt@gcc.gnu.org>:

https://gcc.gnu.org/g:8d783f0f6955e6aa7af218490b068004669b09e0

commit r10-10926-g8d783f0f6955e6aa7af218490b068004669b09e0
Author: Lewis Hyatt <lhyatt@gmail.com>
Date:   Sat Jul 9 16:12:21 2022 -0400

    c: Fix location for _Pragma tokens [PR97498]

    The handling of #pragma GCC diagnostic uses input_location, which is not
always
    as precise as needed; in particular the relative location of some tokens
and a
    _Pragma directive will crucially determine whether a given diagnostic is
enabled
    or suppressed in the desired way. PR97498 shows how the C frontend ends up
with
    input_location pointing to the beginning of the line containing a _Pragma()
    directive, resulting in the wrong behavior if the diagnostic to be modified
    pertains to some tokens found earlier on the same line. This patch fixes
that by
    addressing two issues:

        a) libcpp was not assigning a valid location to the CPP_PRAGMA token
        generated by the _Pragma directive.
        b) C frontend was not setting input_location to something reasonable.

    With this change, the C frontend is able to change input_location to point
to
    the _Pragma token as needed.

    This is just a two-line fix (one for each of a) and b)), the testsuite
changes
    were needed only because the location on the tested warnings has been
somewhat
    improved, so the tests need to look for the new locations.

    gcc/c/ChangeLog:

            PR preprocessor/97498
            * c-parser.c (c_parser_pragma): Set input_location to the
            location of the pragma, rather than the start of the line.

    libcpp/ChangeLog:

            PR preprocessor/97498
            * directives.c (destringize_and_run): Override the location of
            the CPP_PRAGMA token from a _Pragma directive to the location of
            the expansion point, as is done for the tokens lexed from it.

    gcc/testsuite/ChangeLog:

            PR preprocessor/97498
            * c-c++-common/pr97498.c: New test.
            * gcc.dg/pragma-message.c: Adapt for improved warning locations.

    (cherry picked from commit 0587cef3d7962a8b0f44779589ba2920dd3d71e5)

[Bug preprocessor/97498] #pragma GCC diagnostic ignored "-Wunused-function" inconsistent

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97498

--- Comment #11 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The releases/gcc-11 branch has been updated by Lewis Hyatt
<lhyatt@gcc.gnu.org>:

https://gcc.gnu.org/g:d431d48c4e503c3ff17ccd51e504877f3fc9ce0e

commit r11-10188-gd431d48c4e503c3ff17ccd51e504877f3fc9ce0e
Author: Lewis Hyatt <lhyatt@gmail.com>
Date:   Sat Jul 9 16:12:21 2022 -0400

    c: Fix location for _Pragma tokens [PR97498]

    The handling of #pragma GCC diagnostic uses input_location, which is not
always
    as precise as needed; in particular the relative location of some tokens
and a
    _Pragma directive will crucially determine whether a given diagnostic is
enabled
    or suppressed in the desired way. PR97498 shows how the C frontend ends up
with
    input_location pointing to the beginning of the line containing a _Pragma()
    directive, resulting in the wrong behavior if the diagnostic to be modified
    pertains to some tokens found earlier on the same line. This patch fixes
that by
    addressing two issues:

        a) libcpp was not assigning a valid location to the CPP_PRAGMA token
        generated by the _Pragma directive.
        b) C frontend was not setting input_location to something reasonable.

    With this change, the C frontend is able to change input_location to point
to
    the _Pragma token as needed.

    This is just a two-line fix (one for each of a) and b)), the testsuite
changes
    were needed only because the location on the tested warnings has been
somewhat
    improved, so the tests need to look for the new locations.

    gcc/c/ChangeLog:

            PR preprocessor/97498
            * c-parser.c (c_parser_pragma): Set input_location to the
            location of the pragma, rather than the start of the line.

    libcpp/ChangeLog:

            PR preprocessor/97498
            * directives.c (destringize_and_run): Override the location of
            the CPP_PRAGMA token from a _Pragma directive to the location of
            the expansion point, as is done for the tokens lexed from it.

    gcc/testsuite/ChangeLog:

            PR preprocessor/97498
            * c-c++-common/pr97498.c: New test.
            * gcc.dg/pragma-message.c: Adapt for improved warning locations.

    (cherry picked from commit 0587cef3d7962a8b0f44779589ba2920dd3d71e5)

[Bug preprocessor/97498] #pragma GCC diagnostic ignored "-Wunused-function" inconsistent

[lhyatt at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97498

Lewis Hyatt <lhyatt at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |evan@coeus-group.com

--- Comment #12 from Lewis Hyatt <lhyatt at gcc dot gnu.org> ---
*** Bug 95239 has been marked as a duplicate of this bug. ***