[Bug c++/97420] New: error: no matching function for call to 'find_if'

[Bug c++/97420] New: error: no matching function for call to 'find_if'

[tangyixuan at mail dot dlut.edu.cn]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97420

            Bug ID: 97420
           Summary: error: no matching function for call to 'find_if'
           Product: gcc
           Version: 11.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: tangyixuan at mail dot dlut.edu.cn
  Target Milestone: ---

Hi, the following code maybe valid, since 'std::find_if' is allowed since
c++17.
https://en.cppreference.com/w/cpp/algorithm/find

$ cat s.cpp

# include <cctype>
# include <algorithm>

template<int (& F)(int)>
constexpr int A(unsigned char a) noexcept(noexcept(F(a)))
{ return F(a); }

int main()
{
    const char t[] = "a";

    std::find_if(t, t + 1, A<std::isspace>);
}

$ g++ -c -std=c++2a s.cpp
s.cpp: In function ‘int main()’:
s.cpp:12:43: error: no matching function for call to ‘find_if(const char [2],
const char*, <unresolved overloaded function type>)’
   12 |     std::find_if(t, t + 1, A<std::isspace>);
      |

[Bug c++/97420] error: no matching function for call to 'find_if'

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97420

--- Comment #1 from Jonathan Wakely <redi at gcc dot gnu.org> ---
std::find_if has existed since C++98.

[Bug c++/97420] error: no matching function for call to 'find_if'

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97420

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2020-10-14
           Keywords|                            |rejects-valid
     Ever confirmed|0                           |1

--- Comment #2 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Reduced:

int isspace (int) noexcept;
template<int (& F)(int)> void A() { }
auto p = A<isspace>;

The problem is that the NTTP reference cannot bind to a noexcept function.

It works with a reference to a noexcept function:

template<int (& F)(int) noexcept> void A() { }


It only fails for C++17 and later because the noexcept isn't part of the type
before that.

I think we can consider this a regression, since the same code compiles in
C++14 and with previous versions of GCC.

[Bug c++/97420] [8/9/10/11/12 Regression] NTTP function reference cannot bind to noexcept function

[ppalka at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97420

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
      Known to fail|                            |10.3.0, 11.0, 8.4.0, 9.3.0
   Target Milestone|---                         |8.5
                 CC|                            |ppalka at gcc dot gnu.org
      Known to work|                            |7.5.0
            Summary|NTTP function reference     |[8/9/10/11/12 Regression]
                   |cannot bind to noexcept     |NTTP function reference
                   |function                    |cannot bind to noexcept
                   |                            |function

--- Comment #3 from Patrick Palka <ppalka at gcc dot gnu.org> ---
We started to reject the testcase in comment #2 (with -std=c++17) after
r8-1259.

[Bug c++/97420] [8/9/10/11/12 Regression] NTTP function reference cannot bind to noexcept function

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97420

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Priority|P3                          |P2

[Bug c++/97420] [8/9/10/11/12 Regression] NTTP function reference cannot bind to noexcept function

[ppalka at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97420

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |frankhb1989 at gmail dot com

--- Comment #4 from Patrick Palka <ppalka at gcc dot gnu.org> ---
*** Bug 100472 has been marked as a duplicate of this bug. ***

[Bug c++/97420] [8/9/10/11/12 Regression] NTTP function reference cannot bind to noexcept function

[ppalka at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97420

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

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

[Bug c++/97420] [9/10/11/12 Regression] NTTP function reference cannot bind to noexcept function

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97420

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|8.5                         |9.4

--- Comment #5 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
GCC 8 branch is being closed.

[Bug c++/97420] [9/10/11/12 Regression] NTTP function reference cannot bind to noexcept function

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97420

--- Comment #6 from CVS 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:b4329e3dd6fb7c78948fcf9d2f5b9d873deec284

commit r12-1067-gb4329e3dd6fb7c78948fcf9d2f5b9d873deec284
Author: Patrick Palka <ppalka@redhat.com>
Date:   Wed May 26 08:35:31 2021 -0400

    c++: Fix reference NTTP binding to noexcept fn [PR97420]

    Here, in C++17 mode, convert_nontype_argument_function is rejecting
    binding a non-noexcept function reference template parameter to a
    noexcept function (encoded as the template argument '*(int (&) (int)) &f').

    The first roadblock to making this work is that the argument is wrapped
    an an implicit INDIRECT_REF, so we need to unwrap it before calling
    strip_fnptr_conv.

    The second roadblock is that the NOP_EXPR cast converts from a function
    pointer type to a reference type while simultaneously removing the
    noexcept qualification, and fnptr_conv_p doesn't consider this cast to
    be a function pointer conversion.  This patch fixes this by making
    fnptr_conv_p treat REFERENCE_TYPEs and POINTER_TYPEs interchangeably.

    Finally, in passing, this patch also simplifies noexcept_conv_p by
    removing a bunch of redundant checks already performed by its only
    caller fnptr_conv_p.

            PR c++/97420

    gcc/cp/ChangeLog:

            * cvt.c (noexcept_conv_p): Remove redundant checks and simplify.
            (fnptr_conv_p): Don't call non_reference.  Use INDIRECT_TYPE_P
            instead of TYPE_PTR_P.
            * pt.c (convert_nontype_argument_function): Look through
            implicit INDIRECT_REFs before calling strip_fnptr_conv.

    gcc/testsuite/ChangeLog:

            * g++.dg/cpp0x/noexcept68.C: New test.

[Bug c++/97420] [9/10/11/12 Regression] NTTP function reference cannot bind to noexcept function

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97420

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|9.4                         |9.5

--- Comment #7 from Richard Biener <rguenth at gcc dot gnu.org> ---
GCC 9.4 is being released, retargeting bugs to GCC 9.5.

[Bug c++/97420] [9/10/11/12 Regression] NTTP function reference cannot bind to noexcept function

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97420

--- Comment #8 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The releases/gcc-11 branch has been updated by Patrick Palka
<ppalka@gcc.gnu.org>:

https://gcc.gnu.org/g:bbad9d7cfdb8dd8e28589160120546a61adeeedf

commit r11-8726-gbbad9d7cfdb8dd8e28589160120546a61adeeedf
Author: Patrick Palka <ppalka@redhat.com>
Date:   Wed May 26 08:35:31 2021 -0400

    c++: Fix reference NTTP binding to noexcept fn [PR97420]

    Here, in C++17 mode, convert_nontype_argument_function is rejecting
    binding a non-noexcept function reference template parameter to a
    noexcept function (encoded as the template argument '*(int (&) (int)) &f').

    The first roadblock to making this work is that the argument is wrapped
    an an implicit INDIRECT_REF, so we need to unwrap it before calling
    strip_fnptr_conv.

    The second roadblock is that the NOP_EXPR cast converts from a function
    pointer type to a reference type while simultaneously removing the
    noexcept qualification, and fnptr_conv_p doesn't consider this cast to
    be a function pointer conversion.  This patch fixes this by making
    fnptr_conv_p treat REFERENCE_TYPEs and POINTER_TYPEs interchangeably.

    Finally, in passing, this patch also simplifies noexcept_conv_p by
    removing a bunch of redundant checks already performed by its only
    caller fnptr_conv_p.

            PR c++/97420

    gcc/cp/ChangeLog:

            * cvt.c (noexcept_conv_p): Remove redundant checks and simplify.
            (fnptr_conv_p): Don't call non_reference.  Use INDIRECT_TYPE_P
            instead of TYPE_PTR_P.
            * pt.c (convert_nontype_argument_function): Look through
            implicit INDIRECT_REFs before calling strip_fnptr_conv.

    gcc/testsuite/ChangeLog:

            * g++.dg/cpp0x/noexcept68.C: New test.

    (cherry picked from commit b4329e3dd6fb7c78948fcf9d2f5b9d873deec284)

[Bug c++/97420] [9/10 Regression] NTTP function reference cannot bind to noexcept function

[ppalka at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97420

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
            Summary|[9/10/11/12 Regression]     |[9/10 Regression] NTTP
                   |NTTP function reference     |function reference cannot
                   |cannot bind to noexcept     |bind to noexcept function
                   |function                    |

--- Comment #9 from Patrick Palka <ppalka at gcc dot gnu.org> ---
Fixed for 11.2/12 so far

[Bug c++/97420] [10 Regression] NTTP function reference cannot bind to noexcept function

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97420

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|9.5                         |10.4

--- Comment #10 from Richard Biener <rguenth at gcc dot gnu.org> ---
GCC 9 branch is being closed

[Bug c++/97420] [10 Regression] NTTP function reference cannot bind to noexcept function

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97420

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|10.4                        |10.5

--- Comment #11 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
GCC 10.4 is being released, retargeting bugs to GCC 10.5.

[Bug c++/97420] [10 Regression] NTTP function reference cannot bind to noexcept function

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97420

--- Comment #12 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The releases/gcc-10 branch has been updated by Patrick Palka
<ppalka@gcc.gnu.org>:

https://gcc.gnu.org/g:ad42219766d0e67bede2c9bd94c98082cde42518

commit r10-11482-gad42219766d0e67bede2c9bd94c98082cde42518
Author: Patrick Palka <ppalka@redhat.com>
Date:   Wed May 26 08:35:31 2021 -0400

    c++: Fix reference NTTP binding to noexcept fn [PR97420]

    Here, in C++17 mode, convert_nontype_argument_function is rejecting
    binding a non-noexcept function reference template parameter to a
    noexcept function (encoded as the template argument '*(int (&) (int)) &f').

    The first roadblock to making this work is that the argument is wrapped
    an an implicit INDIRECT_REF, so we need to unwrap it before calling
    strip_fnptr_conv.

    The second roadblock is that the NOP_EXPR cast converts from a function
    pointer type to a reference type while simultaneously removing the
    noexcept qualification, and fnptr_conv_p doesn't consider this cast to
    be a function pointer conversion.  This patch fixes this by making
    fnptr_conv_p treat REFERENCE_TYPEs and POINTER_TYPEs interchangeably.

    Finally, in passing, this patch also simplifies noexcept_conv_p by
    removing a bunch of redundant checks already performed by its only
    caller fnptr_conv_p.

            PR c++/97420

    gcc/cp/ChangeLog:

            * cvt.c (noexcept_conv_p): Remove redundant checks and simplify.
            (fnptr_conv_p): Don't call non_reference.  Use INDIRECT_TYPE_P
            instead of TYPE_PTR_P.
            * pt.c (convert_nontype_argument_function): Look through
            implicit INDIRECT_REFs before calling strip_fnptr_conv.

    gcc/testsuite/ChangeLog:

            * g++.dg/cpp0x/noexcept68.C: New test.

    (cherry picked from commit b4329e3dd6fb7c78948fcf9d2f5b9d873deec284)

[Bug c++/97420] [10 Regression] NTTP function reference cannot bind to noexcept function

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97420

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
      Known to fail|                            |10.4.0, 11.1.0
      Known to work|                            |10.5.0, 11.2.0
             Status|ASSIGNED                    |RESOLVED
         Resolution|---                         |FIXED

--- Comment #13 from Richard Biener <rguenth at gcc dot gnu.org> ---
Fixed.