[Bug c++/88061] section attributes of variable templates are ignored

[Bug c++/88061] section attributes of variable templates are ignored

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=88061

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

           What    |Removed                     |Added
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             Status|WAITING                     |NEW

[Bug c++/88061] section attributes of variable templates are ignored

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=88061

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

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

--- Comment #4 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
*** Bug 97771 has been marked as a duplicate of this bug. ***

[Bug c++/88061] section attributes of variable templates are ignored

[barry.revzin at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=88061

Barry Revzin <barry.revzin at gmail dot com> changed:

           What    |Removed                     |Added
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                 CC|                            |barry.revzin at gmail dot com

--- Comment #5 from Barry Revzin <barry.revzin at gmail dot com> ---
(In reply to Richard Biener from comment #1)
> Some things do not make very much sense for C++...

I disagree. This definitely makes sense for C++ and it is disappointing that it
doesn't work. 

For instance, this works:

[[gnu::used, gnu::section(".my_data")]] inline int data_int;
[[gnu::used, gnu::section(".my_data")]] inline double data_double;

int& get() {
    return data_int;
}

The C++ analogue, necessary for contexts where I may not be able to spell the
type in advance, would be this (or a static data member of a class template,
same thing):

template <typename T>
[[gnu::used, gnu::section(".my_data")]] inline T data{};

int& get() {
    return data<int>;
}

Except the latter puts data<int> into .bss.data<int>, while the former puts it
into .my_data. clang respects the section attribute
(https://godbolt.org/z/7137EbxsW), gcc does not
(https://godbolt.org/z/548YKjhzn).

[Bug c++/88061] section attributes of variable templates are ignored

[barry.revzin at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=88061

--- Comment #6 from Barry Revzin <barry.revzin at gmail dot com> ---
Any action on this one?

A workaround right now is to change code that would ideally look like (which is
pretty clean in my opinion):

template <typename T>
void foo() {
    [[gnu::section(".meow")]] static int value = 0;
}

to code that looks like:

template <typename T>
void foo() {
    static int PUT_IN_MEOW_value = 0;
}

and add a linker script that moves these variables over:

.meow : {
KEEP(*(SORT(.*PUT_IN_MEOW_*)))
}

But this is, to put it mildly, less than ideal.

[Bug c++/88061] section attributes of variable templates are ignored

[milan.svoboda at centrum dot cz]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=88061

Milan Svoboda <milan.svoboda at centrum dot cz> changed:

           What    |Removed                     |Added
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                 CC|                            |milan.svoboda at centrum dot cz

--- Comment #7 from Milan Svoboda <milan.svoboda at centrum dot cz> ---
template <typename T>
static void foo() {
    static int PUT_IN_MEOW_value = 0;
}


When the template function is static, this workaround with linker doesn't work.

[Bug c++/88061] section attributes of variable templates are ignored

[milan.svoboda at centrum dot cz]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=88061

--- Comment #8 from Milan Svoboda <milan.svoboda at centrum dot cz> ---
Well, additional workaround is to use -fdata-sections. Then the workaround with
the linker script works also for the templated static functions and for
functions (templated, static) in anonymous namespace (which is another
occurrence of this bug).

[Bug c++/88061] section attributes of variable templates are ignored

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=88061

--- Comment #9 from GCC Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Patrick Palka <ppalka@gcc.gnu.org>:

https://gcc.gnu.org/g:ea7bebff7cc5a5eb780a6ca646cb77cad1b625d6

commit r14-6595-gea7bebff7cc5a5eb780a6ca646cb77cad1b625d6
Author: Patrick Palka <ppalka@redhat.com>
Date:   Fri Dec 15 10:03:31 2023 -0500

    c++: section attribute on templates [PR70435, PR88061]

    The section attribute currently has no effect on templates because the
    call to set_decl_section_name only happens at parse time (on the
    dependent decl) and not also at instantiation time.  This patch fixes
    this by propagating the section name from the template to the
    instantiation.

            PR c++/70435
            PR c++/88061

    gcc/cp/ChangeLog:

            * pt.cc (tsubst_function_decl): Propagate DECL_SECTION_NAME
            via set_decl_section_name.
            (tsubst_decl) <case VAR_DECL>: Likewise.

    gcc/testsuite/ChangeLog:

            * g++.dg/ext/attr-section1.C: New test.
            * g++.dg/ext/attr-section1a.C: New test.
            * g++.dg/ext/attr-section2.C: New test.
            * g++.dg/ext/attr-section2a.C: New test.
            * g++.dg/ext/attr-section2b.C: New test.

[Bug c++/88061] section attributes of variable templates are ignored

[ppalka at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=88061

Patrick Palka <ppalka at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|---                         |14.0
         Resolution|---                         |FIXED
             Status|NEW                         |RESOLVED
                 CC|                            |ppalka at gcc dot gnu.org
           Assignee|unassigned at gcc dot gnu.org      |ppalka at gcc dot gnu.org

--- Comment #10 from Patrick Palka <ppalka at gcc dot gnu.org> ---
Fixed for GCC 14

[Bug c++/88061] section attributes of variable templates are ignored

[ppalka at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=88061

--- Comment #11 from Patrick Palka <ppalka at gcc dot gnu.org> ---
N.B. that commit just naively fixes the attribute propagation issue which seems
to make at least simple examples work as expected.  The question of section +
comdat handling could IIUC be demonstrated using non-template inline
functions/variables as well and so is really an orthogonal issue I think?