[Bug c++/110734] New: Attributes cannot be applied to asm statements

[Bug c++/110734] New: Attributes cannot be applied to asm statements

[tanksherman27 at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110734

            Bug ID: 110734
           Summary: Attributes cannot be applied to asm statements
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: tanksherman27 at gmail dot com
  Target Milestone: ---

Consider the following:

[[gnu::no_reorder]]
asm ("nop");

The correct gcc warning should be that "attributes in front of statements
are ignored", signifying that the asm was correctly processed as a
statement, and the attribute dropped during that processing, but instead:

error.cpp:51:5: error: expected primary-expression before 'asm'
   51 |     asm ("nop" "\n\t"
      |     ^~~
error.cpp:50:5: warning: attributes at the beginning of statement are
ignored [-Wattributes]
   50 |     [[gnu::no_reorder]]
      |     ^~~~~~~~~~~~~~~~~~~

The compiler errors out, with the parser strangely having expected an
expression after the attribute. Afterwards, it then confusingly parses the
asm statement and discards the attribute correctly, so I am fairly certain
this is a bug. The attribute above may not be a very good example, but
there are attributes like gnu::hot and gnu::cold which are supposed to work
with asm statements.

[Bug c++/110734] Attributes cannot be applied to asm statements

[tanksherman27 at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110734

Julian Waters <tanksherman27 at gmail dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
            Version|unknown                     |13.1.1

--- Comment #1 from Julian Waters <tanksherman27 at gmail dot com> ---
Set version to 13.1, but this problem is very likely in every version

[Bug c++/110734] Attributes cannot be applied to asm statements

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110734

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Severity|normal                      |enhancement

[Bug c++/110734] Attributes cannot be applied to asm statements

[tanksherman27 at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110734

--- Comment #2 from Julian Waters <tanksherman27 at gmail dot com> ---
Is this accurately described as an enhancement? This is erroneous behaviour
with something that is already meant to be a feature in gcc (applying
attributes to statements, as seen inside parser.cc), not a feature request for
new behaviour

[Bug c++/110734] Attributes cannot be applied to asm statements

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110734

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |diagnostic
                 CC|                            |hubicka at gcc dot gnu.org
     Ever confirmed|0                           |1
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2023-07-19

--- Comment #3 from Richard Biener <rguenth at gcc dot gnu.org> ---
But a toplevel asm isn't a "statement" in the sense of parsing.  Still
confirmed.  Note that I'm not sure we can handle no-reorder for toplevel
asms, IIRC they are not entities in the symtab.  I don't remember off head
where they are recorded either ...

Btw, I don't get

t.c:3:1: warning: attributes at the beginning of statement are ignored
[-Wattributes]
    3 | [[gnu::no_reorder]]
      | ^~~~~~~~~~~~~~~~~~~

unless I wrap your source inside a function.  Was your testcase complete?

[Bug c++/110734] Attributes cannot be applied to asm statements

[tanksherman27 at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110734

--- Comment #4 from Julian Waters <tanksherman27 at gmail dot com> ---
My mistake, I forgot to mention that it was indeed inside a function body. I
can't seem to figure out what in parser.cc is causing this bug, anything on
your end?

[Bug c++/110734] Attributes cannot be applied to asm statements

[tanksherman27 at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110734

--- Comment #5 from Julian Waters <tanksherman27 at gmail dot com> ---
Note: Trying this with a top level asm gives me:

$ g++ -O3 -flto=auto -std=c++14 -pedantic -Wpedantic -fno-omit-frame-pointer
exceptions.cpp
exceptions.cpp:8:1: error: expected unqualified-id before 'asm'
    8 | asm ("nop");
      | ^~~

So while it seems the errors are different, it fundamentally is the same issue

[Bug c++/110734] Attributes cannot be applied to asm statements

[tanksherman27 at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110734

Julian Waters <tanksherman27 at gmail dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |tanksherman27 at gmail dot com

--- Comment #6 from Julian Waters <tanksherman27 at gmail dot com> ---
Created attachment 56717
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=56717&action=edit
Attribute for asm declarations

[Bug c++/110734] Attributes cannot be applied to asm statements

[tanksherman27 at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110734

--- Comment #7 from Julian Waters <tanksherman27 at gmail dot com> ---
I have a new attribute proposed for asm declarations that fixes this issue, but
I need help from reviews to proceed with fixing up the patch properly

[Bug c++/110734] Attributes cannot be applied to asm declarations

[tanksherman27 at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110734

Julian Waters <tanksherman27 at gmail dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
  Attachment #56717|0                           |1
        is obsolete|                            |

--- Comment #8 from Julian Waters <tanksherman27 at gmail dot com> ---
Created attachment 56732
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=56732&action=edit
Attribute for asm declarations

[Bug c++/110734] Attributes cannot be applied to asm declarations

[xry111 at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110734

Xi Ruoyao <xry111 at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |xry111 at gcc dot gnu.org

--- Comment #9 from Xi Ruoyao <xry111 at gcc dot gnu.org> ---
(In reply to Julian Waters from comment #8)
> Created attachment 56732 [details]
> Attribute for asm declarations

Please just fix this issue (i.e. make [[gnu::no_reorder]] work) instead of
adding fancy new features.  Now we are in stage 3 of GCC 14 so any fancy new
feature should be deferred into stage 1 of GCC 15.

[Bug c++/110734] Attributes cannot be applied to asm declarations

[xry111 at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110734

--- Comment #10 from Xi Ruoyao <xry111 at gcc dot gnu.org> ---
(In reply to Xi Ruoyao from comment #9)
> (In reply to Julian Waters from comment #8)
> > Created attachment 56732 [details]
> > Attribute for asm declarations
> 
> Please just fix this issue (i.e. make [[gnu::no_reorder]] work) instead of
> adding fancy new features.  Now we are in stage 3 of GCC 14 so any fancy new
> feature should be deferred into stage 1 of GCC 15.

Ok, I see you are only using no_reorder as an example.  Then try to make the
existing attributes work instead of adding a new one.

[Bug c++/110734] Attributes cannot be applied to asm declarations

[mpolacek at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110734

Marek Polacek <mpolacek at gcc dot gnu.org> changed:

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

--- Comment #11 from Marek Polacek <mpolacek at gcc dot gnu.org> ---
(In reply to Xi Ruoyao from comment #10)
> (In reply to Xi Ruoyao from comment #9)
> > (In reply to Julian Waters from comment #8)
> > > Created attachment 56732 [details]
> > > Attribute for asm declarations
> > 
> > Please just fix this issue (i.e. make [[gnu::no_reorder]] work) instead of
> > adding fancy new features.  Now we are in stage 3 of GCC 14 so any fancy new
> > feature should be deferred into stage 1 of GCC 15.
> 
> Ok, I see you are only using no_reorder as an example.  Then try to make the
> existing attributes work instead of adding a new one.

I agree.  I can hardly see the need for a new and a very complicated attribute.

[Bug c++/110734] Attributes cannot be applied to asm declarations

[tanksherman27 at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110734

--- Comment #12 from Julian Waters <tanksherman27 at gmail dot com> ---
Will do, will save the new attribute for gcc 15 and just fix the attribute
specifier sequence here

[Bug c++/110734] Attributes cannot be applied to asm statements

[xry111 at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110734

Xi Ruoyao <xry111 at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
            Summary|Attributes cannot be        |Attributes cannot be
                   |applied to asm declarations |applied to asm statements

--- Comment #13 from Xi Ruoyao <xry111 at gcc dot gnu.org> ---
Re-titling as there is no such a concept "asm declarations".

[Bug c++/110734] Attributes cannot be applied to asm statements

[xry111 at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110734

Xi Ruoyao <xry111 at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |WAITING

--- Comment #14 from Xi Ruoyao <xry111 at gcc dot gnu.org> ---
Wait a minute.  [[gnu::no_reorder]] is a function or variable attribute, so
it's just not intended to be used for an asm statement.  Actually it won't work
for any statement:

int x;
int main()
{
        [[gnu::no_reorder]]
        x += 1;
}

gives:

t.c: In function 'main':
t.c:5:9: warning: 'no_reorder' attribute ignored [-Wattributes]
    5 |         x += 1;
      |         ^

We have "statement attributes" (fallthrough and assume) but the doc is clear
that they can only be set on null statements, while asm statements are not null
statements.

Now to me this is just an invalid PR.  Or am I missing something?

[Bug c++/110734] Attributes cannot be applied to asm declaration

[xry111 at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110734

Xi Ruoyao <xry111 at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
            Summary|Attributes cannot be        |Attributes cannot be
                   |applied to asm statements   |applied to asm declaration
             Status|WAITING                     |NEW

--- Comment #15 from Xi Ruoyao <xry111 at gcc dot gnu.org> ---
Alright, this is a C++ issue and I mistakenly assumed it was C.

[Bug c++/110734] Attributes cannot be applied to asm declaration

[xry111 at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110734

--- Comment #16 from Xi Ruoyao <xry111 at gcc dot gnu.org> ---
(In reply to Xi Ruoyao from comment #15)
> Alright, this is a C++ issue and I mistakenly assumed it was C.

Note that in C++ we have some inconsistency with the standard.  In the standard
asm(...) are "declarations" but in GNU C++ asm(...) are always "statements".

[Bug c++/110734] Attributes cannot be applied to asm declaration

[tanksherman27 at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110734

--- Comment #17 from Julian Waters <tanksherman27 at gmail dot com> ---
Looking at the source of the C++ parser it doesn't seem like asm (""); is
considered a statement but rather is correctly parsed as a declaration, see
cp_parser_block_declaration and cp_parser_declaration_statement. The no_reorder
attribute is just a demonstration, I am aware it is not meant for asm
declarations, rather the error is in how the error message is formed, eg error:
expected primary-expression before 'asm' instead of error: expected
primary-expression before 'asm'

[Bug c++/110734] Attributes cannot be applied to asm declaration

[tanksherman27 at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110734

--- Comment #18 from Julian Waters <tanksherman27 at gmail dot com> ---
Oops, I meant warning: 'no_reorder' attribute ignored [-Wattributes] in my
above comment

[Bug c++/110734] Attributes cannot be applied to asm declaration

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110734

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

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

--- Comment #19 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Attributes have been allowed on asm in C++ only since 2017's
https://cplusplus.github.io/CWG/issues/2262.html
which we apparently don't implement.  See
https://gcc.gnu.org/projects/cxx-dr-status.html
It is not clear whether that change has been effectively applied as a DR and
thus whether it should apply to earlier standards as well (guess starting with
C++11) or not.

[Bug c++/110734] Attributes cannot be applied to asm declaration

[tanksherman27 at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110734

--- Comment #20 from Julian Waters <tanksherman27 at gmail dot com> ---
cppreference at least seems to indicate it retroactively applies to C++11
https://en.cppreference.com/w/cpp/language/asm

[Bug c++/110734] Attributes cannot be applied to asm declaration

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110734

--- Comment #21 from GCC 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:e5153e7d63b4cd9a3df490809c4f3fe1e94d3d37

commit r14-6187-ge5153e7d63b4cd9a3df490809c4f3fe1e94d3d37
Author: Jakub Jelinek <jakub@redhat.com>
Date:   Tue Dec 5 17:38:46 2023 +0100

    c++: Implement C++ DR 2262 - Attributes for asm-definition [PR110734]

    Seems in 2017 attribute-specifier-seq[opt] was added to asm-declaration
    and the change was voted in as a DR.

    The following patch implements it by parsing the attributes and warning
    about them.

    I found one attribute parsing bug I'll send a fix for momentarily.

    And there is another thing I wonder about: with -Wno-attributes= we are
    supposed to ignore the attributes altogether, but we are actually still
    warning about them when we emit these generic warnings about ignoring
    all attributes which appertain to this and that (perhaps with some
    exceptions we first remove from the attribute chain), like:
    void foo () { [[foo::bar]]; }
    with -Wattributes -Wno-attributes=foo::bar
    Shouldn't we call some helper function in cases like this and warn
    not when std_attrs (or how the attribute chain var is called) is non-NULL,
    but if it is non-NULL and contains at least one non-attribute_ignored_p
    attribute?  cp_parser_declaration at least tries:
          if (std_attrs != NULL_TREE && !attribute_ignored_p (std_attrs))
            warning_at (make_location (attrs_loc, attrs_loc, parser->lexer),
                        OPT_Wattributes, "attribute ignored");
    but attribute_ignored_p here checks the first attribute rather than the
    whole chain.  So it will incorrectly not warn if there is an ignored
    attribute followed by non-ignored.

    2023-12-05  Jakub Jelinek  <jakub@redhat.com>

            PR c++/110734
            * parser.cc (cp_parser_block_declaration): Implement C++ DR 2262
            - Attributes for asm-definition.  Call cp_parser_asm_definition
            even if RID_ASM token is only seen after sequence of standard
            attributes.
            (cp_parser_asm_definition): Parse standard attributes before
            RID_ASM token and warn for them with -Wattributes.

            * g++.dg/DRs/dr2262.C: New test.
            * g++.dg/cpp0x/gen-attrs-76.C (foo, bar): Don't expect errors
            on attributes on asm definitions.
            * g++.dg/gomp/attrs-11.C: Remove 2 expected errors.

[Bug c++/110734] Attributes cannot be applied to asm declaration

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110734

--- Comment #22 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
DR now implemented for GCC 12 (but gnu::no_reorder support for namespace scope
asms would be more work; I think we don't reorder toplevel asms anyway).

[Bug c++/110734] Attributes cannot be applied to asm declaration

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110734

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
         Resolution|---                         |FIXED
             Status|NEW                         |RESOLVED
   Target Milestone|---                         |14.0

--- Comment #23 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
.