[Bug libstdc++/109482] New: experimental/net/internet/endpoint/cons.cc FAILs

[Bug libstdc++/109482] New: experimental/net/internet/endpoint/cons.cc FAILs

[ro at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109482

            Bug ID: 109482
           Summary: experimental/net/internet/endpoint/cons.cc FAILs
           Product: gcc
           Version: 13.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: libstdc++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: ro at gcc dot gnu.org
  Target Milestone: ---
              Host: *-*-solaris2.11
            Target: *-*-solaris2.11
             Build: *-*-solaris2.11

Created attachment 54839
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=54839&action=edit
32-bit i386-pc-solaris2.11 cons-cons.ii

Between 20230329 (b2f327b9be81326c9e59fc6da98074c909ac7408) and 20230330
(a23b33a1bdeff7bc2289d9ebb7cb7b7ec0a605f5), the
experimental/net/internet/endpoint/cons.cc test began to FAIL on Solaris
(11.3 and 11.4, SPARC and x86):

+FAIL: experimental/net/internet/endpoint/cons.cc (test for excess errors)
+UNRESOLVED: experimental/net/internet/endpoint/cons.cc compilation failed to
produce executable

The log shows

Excess errors:
/vol/gcc/src/hg/master/local/libstdc++-v3/testsuite/experimental/net/internet/endpoint/cons.cc:78:
error: non-constant condition for static assertion
/vol/gcc/src/hg/master/local/libstdc++-v3/testsuite/experimental/net/internet/endpoint/cons.cc:78:
error: accessing 'in_addr::<unnamed union>::S_addr' member instead of
initialized 'in_addr::<unnamed union>::S_un_b' member in constant expression

The full message is

/vol/gcc/src/hg/master/local/libstdc++-v3/testsuite/experimental/net/internet/endpoint/cons.cc:
In function 'int main()':
/vol/gcc/src/hg/master/local/libstdc++-v3/testsuite/experimental/net/internet/endpoint/cons.cc:78:
error: non-constant condition for static assertion
/vol/gcc/src/hg/master/local/libstdc++-v3/testsuite/experimental/net/internet/endpoint/cons.cc:78:
  in 'constexpr' expansion of 'test_constexpr()'
/vol/gcc/src/hg/master/local/libstdc++-v3/testsuite/experimental/net/internet/endpoint/cons.cc:63:
  in 'constexpr' expansion of 'test_default()'
/vol/gcc/src/hg/master/local/libstdc++-v3/testsuite/experimental/net/internet/endpoint/cons.cc:15:
  in 'constexpr' expansion of
'std::experimental::net::v1::ip::basic_endpoint<_InternetProtocol>::address()
const [with _InternetProtocol = std::experimental::net::v1::ip::tcp]()'
/vol/gcc/src/hg/master/local/libstdc++-v3/testsuite/experimental/net/internet/endpoint/cons.cc:78:
error: accessing 'in_addr::<unnamed union>::S_addr' member instead of
initialized 'in_addr::<unnamed union>::S_un_b' member in constant expression

This is no doubt due to

commit e0d77144aaa56ee6e00fd0ba520b0a5c7e052423
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Wed Mar 22 17:00:11 2023 +0000

    libstdc++: Fix constexpr functions in <experimental/internet>

but I don't know what's going on.  I'm attaching the preprocessed testcase.

[Bug libstdc++/109482] experimental/net/internet/endpoint/cons.cc FAILs

[ro at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109482

Rainer Orth <ro at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|---                         |13.0

[Bug libstdc++/109482] experimental/net/internet/endpoint/cons.cc FAILs

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109482

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Last reconfirmed|                            |2023-04-12
           Assignee|unassigned at gcc dot gnu.org      |redi at gcc dot gnu.org
             Status|UNCONFIRMED                 |ASSIGNED
     Ever confirmed|0                           |1

--- Comment #1 from Jonathan Wakely <redi at gcc dot gnu.org> ---
I see the problem, but it's a pain.

For Solaris the in_addr struct looks roughly like:

struct in_addr {
  union {
    struct bytes { char b[4]; };
    in_addr_t s_addr;
  };
};

which means that a value-initialized in_addr does not have s_addr as the active
member of the union, and so we can't access it in constexpr contexts.

I think this means that the basic_endpoint default ctor cannot be constexpr
before C++20. Sigh.

[Bug libstdc++/109482] experimental/net/internet/endpoint/cons.cc FAILs

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109482

--- Comment #2 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:9f10b4957ca6058d1a801c5e4bfe11bf159da809

commit r13-7149-g9f10b4957ca6058d1a801c5e4bfe11bf159da809
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Wed Apr 12 11:55:24 2023 +0100

    libstdc++: Initialize all members of basic_endpoint union [PR109482]

    On Solaris the in_addr struct contains a union and value-initializing it
    does not make the s_addr member active. This means we can't access that
    member later during constant evaluation.

    Make the constructors explicitly set every member that we might want to
    read later in constexpr member functions. This means even the default
    constructor can only be constexpr for C++20, because we can't change the
    active member of a union in older standards.

    libstdc++-v3/ChangeLog:

            PR libstdc++/109482
            * include/experimental/internet (basic_endpoint::basic_endpoint()):
            Ensure that the required union members are active. Only define
            as constexpr for C++20 and later.
            (basic_endpoint::basic_endpoint(const protocol_type&, port_type)):
            Likewise.
            * testsuite/experimental/net/internet/endpoint/cons.cc: Only
            check constexpr default constructor for C++20 and later.
            * testsuite/experimental/net/internet/endpoint/extensible.cc:
            Likewise.

[Bug libstdc++/109482] experimental/net/internet/endpoint/cons.cc FAILs

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109482

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

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

--- Comment #3 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Fixed, by removing functionality :-(

[Bug libstdc++/109482] experimental/net/internet/endpoint/cons.cc FAILs

[m.cencora at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109482

m.cencora at gmail dot com changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |m.cencora at gmail dot com

--- Comment #4 from m.cencora at gmail dot com ---
Can't you use designated initializer?

https://godbolt.org/z/nWP7avK9x

struct in_addr_t
{
    void * dummy;
};

struct in_addr {
  union {
    struct { char b[4]; };
    in_addr_t s_addr;
  };
};


constexpr bool test()
{
    in_addr a = {.s_addr = {}};
    return a.s_addr.dummy == nullptr;
}

static_assert(test());

[Bug libstdc++/109482] experimental/net/internet/endpoint/cons.cc FAILs

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109482

--- Comment #5 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Not when s_addr is a macro for S_un.S_addr or something like that.

[Bug libstdc++/109482] experimental/net/internet/endpoint/cons.cc FAILs

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109482

--- Comment #6 from Jonathan Wakely <redi at gcc dot gnu.org> ---
I did try it.

It's also not valid in older standards, so would give pedantic warnings with
-Wsystem-headers

[Bug libstdc++/109482] experimental/net/internet/endpoint/cons.cc FAILs

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109482

--- Comment #7 from Jonathan Wakely <redi at gcc dot gnu.org> ---
(In reply to Jonathan Wakely from comment #5)
> Not when s_addr is a macro for S_un.S_addr or something like that.

The real definition on Solaris is more like:

struct in_addr {
  union {
    struct { char b[4]; };
    in_addr_t S_addr;
  } S_un;
#define s_addr S_un.S_addr
};

And this gives:

error: expected primary-expression before '.' token
     in_addr a = {.s_addr = {}};
                  ^

[Bug libstdc++/109482] experimental/net/internet/endpoint/cons.cc FAILs

[m.cencora at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109482

--- Comment #8 from m.cencora at gmail dot com ---
Ah, I see that gcc doesn't support nested designated initializer in C++ mode
(compared to C mode, or clang in both C and C++ modes).