[Bug libstdc++/112467] New: [14 Regression] libstdc++ fails to build on clang: bits/stl_bvector.h:189:23: error: '__assume__' attribute cannot be applied to a statement

[Bug libstdc++/112467] New: [14 Regression] libstdc++ fails to build on clang: bits/stl_bvector.h:189:23: error: '__assume__' attribute cannot be applied to a statement

[slyfox at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112467

            Bug ID: 112467
           Summary: [14 Regression] libstdc++ fails to build on clang:
                    bits/stl_bvector.h:189:23: error: '__assume__'
                    attribute cannot be applied to a statement
           Product: gcc
           Version: 14.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: libstdc++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: slyfox at gcc dot gnu.org
  Target Milestone: ---

Build failure is probably introduced by r14-5260-ge39b3e02c27bd7 and fails on
clang-16 as:

    // $ cat a.cc
    #include <vector>

$ clang++ -c a.cc
In file included from a.cc:1:
In file included from /<<NIX>>/gcc-14.0.0/include/c++/14.0.0/vector:67:
/<<NIX>>/gcc-14.0.0/include/c++/14.0.0/bits/stl_bvector.h:189:23: error:
'__assume__' attribute cannot be applied to a statement
      __attribute__ ((__assume__ (__ofst < unsigned(_S_word_bit))));
                      ^                                            ~
1 error generated.

I think it happens because `clang` implements different `assume` attribute
compared to `gcc`: https://clang.llvm.org/docs/AttributeReference.html#assume

[Bug libstdc++/112467] [14 Regression] libstdc++ fails to build on clang: bits/stl_bvector.h:189:23: error: '__assume__' attribute cannot be applied to a statement

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112467

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
GCC/GNUC's assume is the same as the way C++23 attribute is defined ...

Looks like clang decided to implement an attribute assume which is totally
different ...

[Bug libstdc++/112467] [14 Regression] libstdc++ fails to build on clang: bits/stl_bvector.h:189:23: error: '__assume__' attribute cannot be applied to a statement

[slyfox at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112467

--- Comment #2 from Sergei Trofimovich <slyfox at gcc dot gnu.org> ---
Filed a feature request on `clang` side to consider implementing it:
https://github.com/llvm/llvm-project/issues/71858

Meanwhile would it be reasonable to enable the attribute only for `gcc`?

[Bug libstdc++/112467] [14 Regression] libstdc++ fails to build on clang: bits/stl_bvector.h:189:23: error: '__assume__' attribute cannot be applied to a statement

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112467

--- Comment #3 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
(In reply to Sergei Trofimovich from comment #2)
> Meanwhile would it be reasonable to enable the attribute only for `gcc`?

Or rather for !__CLANG__  :).

[Bug libstdc++/112467] [14 Regression] libstdc++ fails to build on clang: bits/stl_bvector.h:189:23: error: '__assume__' attribute cannot be applied to a statement

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112467

Jonathan Wakely <redi at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
     Ever confirmed|0                           |1
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2023-11-09

--- Comment #4 from Jonathan Wakely <redi at gcc dot gnu.org> ---
No, for __has_attribute(__assume__)

[Bug libstdc++/112467] [14 Regression] libstdc++ fails to build on clang: bits/stl_bvector.h:189:23: error: '__assume__' attribute cannot be applied to a statement

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112467

--- Comment #5 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Oh, but that's presumably true for clang, just not in this context. Ugh.

[Bug libstdc++/112467] [14 Regression] libstdc++ fails to build on clang: bits/stl_bvector.h:189:23: error: '__assume__' attribute cannot be applied to a statement

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112467

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|---                         |14.0

[Bug libstdc++/112467] [14 Regression] libstdc++ fails to build on clang: bits/stl_bvector.h:189:23: error: '__assume__' attribute cannot be applied to a statement

[sjames at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112467

Sam James <sjames at gcc dot gnu.org> changed:

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

--- Comment #6 from Sam James <sjames at gcc dot gnu.org> ---
I hit the same when building Firefox with Clang which figures.

[Bug libstdc++/112467] [14 Regression] libstdc++ fails to build on clang: bits/stl_bvector.h:189:23: error: '__assume__' attribute cannot be applied to a statement

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112467

Jonathan Wakely <redi at gcc dot gnu.org> changed:

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

--- Comment #7 from Jonathan Wakely <redi at gcc dot gnu.org> ---
This seems to work:

--- a/libstdc++-v3/include/bits/stl_bvector.h
+++ b/libstdc++-v3/include/bits/stl_bvector.h
@@ -185,8 +185,10 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
     void
     _M_assume_normalized() const
     {
+#if __has_attribute(__assume__) && !defined(__clang__)
       unsigned int __ofst = _M_offset;
       __attribute__ ((__assume__ (__ofst < unsigned(_S_word_bit))));
+#endif
     }

     _GLIBCXX20_CONSTEXPR

[Bug libstdc++/112467] [14 Regression] libstdc++ fails to build on clang: bits/stl_bvector.h:189:23: error: '__assume__' attribute cannot be applied to a statement

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112467

--- Comment #8 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Jonathan Wakely <redi@gcc.gnu.org>:

https://gcc.gnu.org/g:807f47497f17ed50be91f0f879308cb6fa063966

commit r14-5350-g807f47497f17ed50be91f0f879308cb6fa063966
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Fri Nov 10 21:06:15 2023 +0000

    libstdc++: Do not use assume attribute for Clang [PR112467]

    Clang has an 'assume' attribute, but it's a function attribute not a
    statement attribute. The recently-added use of the statement form causes
    an error with Clang.

    libstdc++-v3/ChangeLog:

            PR libstdc++/112467
            * include/bits/stl_bvector.h (_M_assume_normalized): Do not use
            statement form of assume attribute for Clang.

[Bug libstdc++/112467] [14 Regression] libstdc++ fails to build on clang: bits/stl_bvector.h:189:23: error: '__assume__' attribute cannot be applied to a statement

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112467

Jonathan Wakely <redi at gcc dot gnu.org> changed:

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

--- Comment #9 from Jonathan Wakely <redi at gcc dot gnu.org> ---
done

[Bug libstdc++/112467] [14 Regression] libstdc++ fails to build on clang: bits/stl_bvector.h:189:23: error: '__assume__' attribute cannot be applied to a statement

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112467

--- Comment #10 from GCC Commits <cvs-commit at gcc dot gnu.org> ---
The releases/gcc-13 branch has been updated by Torbjorn Svensson
<azoff@gcc.gnu.org>:

https://gcc.gnu.org/g:adef1e0ebeb5055ed4e8776fd3f73c9d84821eaa

commit r13-8310-gadef1e0ebeb5055ed4e8776fd3f73c9d84821eaa
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Fri Nov 10 21:06:15 2023 +0000

    libstdc++: Do not use assume attribute for Clang [PR112467]

    Clang has an 'assume' attribute, but it's a function attribute not a
    statement attribute. The recently-added use of the statement form causes
    an error with Clang.

    libstdc++-v3/ChangeLog:

            PR libstdc++/112467
            * include/bits/stl_bvector.h (_M_assume_normalized): Do not use
            statement form of assume attribute for Clang.

    (cherry picked from commit 807f47497f17ed50be91f0f879308cb6fa063966)