[Bug c++/65706] New: [c++14] Pack expansion with variable template incorrectly marked as invalid

[Bug c++/65706] New: [c++14] Pack expansion with variable template incorrectly marked as invalid

[ldionne.2 at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65706

            Bug ID: 65706
           Summary: [c++14] Pack expansion with variable template
                    incorrectly marked as invalid
           Product: gcc
           Version: 5.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: ldionne.2 at gmail dot com

The following code produces an error on GCC trunk:

------------------------------------------------------------------------------
void allow_expansion(...);

template <int i>
int vtemplate = i;

template <int ...i>
void f() {
    allow_expansion(vtemplate<i>...);
}

template void f<>();
template void f<1>();
template void f<1, 2>();
------------------------------------------------------------------------------

Note that the three above statements trigger the same error. 
The exact output is 

› ~/code/gcc5/bin/g++ ~/code/hana/test/worksheet.cpp -std=c++1y
[...]: In function ‘void f()’:
[...]: error: expansion pattern ‘vtemplate<i>’ contains no argument packs
     allow_expansion(vtemplate<i>...);
                                 ^
>From gcc-bugs-return-483056-listarch-gcc-bugs=gcc.gnu.org@gcc.gnu.org Thu Apr 09 02:14:10 2015
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From: "ldionne.2 at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c++/65707] New: internal compiler error: in unify, at cp/pt.c:18577
Date: Thu, 09 Apr 2015 02:14:00 -0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65707

            Bug ID: 65707
           Summary: internal compiler error: in unify, at cp/pt.c:18577
           Product: gcc
           Version: 5.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: ldionne.2 at gmail dot com

The following code triggers an ICE on GCC trunk:

------------------------------------------------------------------------------
#include <type_traits>

template <bool>
struct when;

template <typename T>
struct always_true : std::true_type { };


template <typename T, typename = when<true>>
struct f;

template <typename T>
struct f<T, when<always_true<T>{}>> { };

template struct f<int>;
------------------------------------------------------------------------------

The exact command line is:

› ~/code/gcc5/bin/g++ ~/code/hana/test/worksheet.cpp -std=c++1y
[...]: internal compiler error: in unify, at cp/pt.c:18577
 template struct f<int>;
                 ^

Note that changing

    when<predicate<T>{}>

to

    when<predicate<T>{}()>

fixes the problem.
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From: "ldionne.2 at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c++/59766] c++1y: declaring friend function with 'auto' return type deduction is rejected with bogus reason
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=59766

Louis Dionne <ldionne.2 at gmail dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |ldionne.2 at gmail dot com

--- Comment #7 from Louis Dionne <ldionne.2 at gmail dot com> ---
The following still fails on GCC trunk:

    struct T {
        friend auto f() { }
    };


Sample command line:

› ~/code/gcc5/bin/g++ --version
g++ (GCC) 5.0.0 20150326 (experimental)
Copyright (C) 2015 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

› ~/code/gcc5/bin/g++ ~/code/hana/test/worksheet.cpp -std=c++1y
[...]: error: non-static data member declared ‘auto’
     friend auto f() { }
                   ^
>From gcc-bugs-return-483058-listarch-gcc-bugs=gcc.gnu.org@gcc.gnu.org Thu Apr 09 03:03:21 2015
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From: "ldionne.2 at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c++/65708] New: Non-type template argument not visible causes substitution failure
Date: Thu, 09 Apr 2015 03:03:00 -0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65708

            Bug ID: 65708
           Summary: Non-type template argument not visible causes
                    substitution failure
           Product: gcc
           Version: 5.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: ldionne.2 at gmail dot com

The following code produces an error on GCC trunk. The error says that there
is no matching `f` to call:

------------------------------------------------------------------------------
template <typename T, T v>
struct integral_constant { };

template <typename T, T v>
decltype(~v) f(integral_constant<T, v>);

int main() {
    f(integral_constant<int, 6>{});
}
------------------------------------------------------------------------------

Even more curious is that the problem goes away if I replace `decltype(~v)`
by `decltype(v)` or even `decltype(+v)`.


The exact error is:
› ~/code/gcc5/bin/g++ ~/code/hana/test/worksheet.cpp -std=c++11
[...]: In function ‘int main()’:
[...]: error: no matching function for call to ‘f(integral_constant<int, 6>)’
     f(integral_constant<int, 6>{});
                                  ^
[...]: note: candidate: template<class T, T v> decltype (~ v)
f(integral_constant<T, v>)
 decltype(~v) f(integral_constant<T, v>);
              ^
[...]: note:   template argument deduction/substitution failed:
[...]: In substitution of ‘template<class T, T v> decltype (~ v)
f(integral_constant<T, v>) [with T = int; T v = 6]’:
[...]:   required from here
[...]: error: ‘v’ was not declared in this scope


My GCC version:
› ~/code/gcc5/bin/g++ --version
g++ (GCC) 5.0.0 20150326 (experimental)
Copyright (C) 2015 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
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Subject: [Bug tree-optimization/42172] inefficient bit fields assignments
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https://gcc.gnu.org/bugzilla/show_bug.cgi?idB172

--- Comment #10 from amker at gcc dot gnu.org ---
The optimal code is generated on pre-armv7 processors.  The difference starts
from expand.  On armv7-processors, zero_extract operator is generated, rather
than logic operation.  Seem combiner can't handle bit-field in the form of
zero_extract as well as logic forms.

I uploaded ud_dce&combine dumps for both cortex-m0 and cortex-m3.  Apparently,
code for m0 is what we want.

[Bug c++/65706] [c++14] Pack expansion with variable template incorrectly marked as invalid

[mpolacek at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65706

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2015-04-09
                 CC|                            |mpolacek at gcc dot gnu.org
     Ever confirmed|0                           |1

--- Comment #1 from Marek Polacek <mpolacek at gcc dot gnu.org> ---
Confirmed.

[Bug c++/65706] [c++14] Pack expansion with variable template incorrectly marked as invalid

[andreash87 at gmx dot ch]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65706

Andreas Herrmann <andreash87 at gmx dot ch> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |andreash87 at gmx dot ch

--- Comment #2 from Andreas Herrmann <andreash87 at gmx dot ch> ---
I just stumbled up this problem in GCC 5.2.0. And it seems that Bug 66336 is a
duplicate of this one.

$ g++ --version
g++ (GCC) 5.2.0
Copyright (C) 2015 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

$ cat bug.cc
template <class T, T value_>
struct constant {
    using type = T;
    static constexpr T value = value_;
};

template <class Constant>
constexpr typename Constant::type get = Constant::value;

template <class... Args>
void callme(Args...) {}

template <class... Args>
void works(Args...) {
    callme(Args::value...);
}

template <class... Args>
void fails(Args...) {
    callme(get<Args>...);  // !!! Parameter pack is not expanded.
}

int main() {
    int x = get<constant<int, 1>>;  // The variable template works on its own.
    works(constant<int, 0>{}, constant<int, 1>{});
    fails(constant<int, 0>{}, constant<int, 1>{});
}

$ g++ -std=c++14 bug.cc
bug.cc: In function ‘void fails(Args ...)’:
bug.cc:20:21: error: expansion pattern ‘get<Args>’ contains no argument packs
     callme(get<Args>...);  // !!! Parameter pack is not expanded.
>From gcc-bugs-return-493732-listarch-gcc-bugs=gcc.gnu.org@gcc.gnu.org Thu Jul 30 08:01:05 2015
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Subject: [Bug target/63679] [5/6 Regression][AArch64] Failure to constant fold.
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https://gcc.gnu.org/bugzilla/show_bug.cgi?idc679

--- Comment #36 from rguenther at suse dot de <rguenther at suse dot de> ---
On Wed, 29 Jul 2015, alalaw01 at gcc dot gnu.org wrote:

> but also feel that those two statements hashing differently is not really
> helpful!

Well, it still uses hash_tree_expr (now 'add_expr') which has to
be compatible with operand_equal_p, not just with finding
redundancies.

[Bug c++/65706] [c++14] Pack expansion with variable template incorrectly marked as invalid

[jason at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65706

Jason Merrill <jason at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
                 CC|                            |jason at gcc dot gnu.org
         Resolution|---                         |DUPLICATE

--- Comment #3 from Jason Merrill <jason at gcc dot gnu.org> ---
Fixed on the trunk by r225692.

*** This bug has been marked as a duplicate of bug 66336 ***