[Bug c++/65291] New: protected using constructor default arguments not recognized

[Bug c++/65291] New: protected using constructor default arguments not recognized

[webmatematika at hotmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65291

            Bug ID: 65291
           Summary: protected using constructor default arguments not
                    recognized
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: webmatematika at hotmail dot com

Created attachment 34931
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=34931&action=edit
Classes A and B, and main file c.cpp

using A::A in class B that inherits class A should allow us to construct B with
same number of arguments as class A.


run with gcc c.cpp -std=c++11
Tested with gcc 4.8.2, but I think it's active in 4.9 too.

[Bug c++/65291] protected using constructor default arguments not recognized

[webmatematika at hotmail dot com]

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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65291

--- Comment #1 from webmatematika at hotmail dot com ---
Here is compile error output:  

(I added in c.cpp line 4 "public:" in class C)





voja@vojaws:~/coding$ gcc c.cpp -std=c++11
c.cpp: In constructor ‘C::C()’:
c.cpp:5:11: error: no matching function for call to ‘B::B()’
   C() : B() {}
           ^
c.cpp:5:11: note: candidates are:
In file included from c.cpp:1:0:
b.h:7:12: note: B::B(int)
   using A::A;
            ^
b.h:7:12: note:   candidate expects 1 argument, 0 provided
b.h:5:3: note: B::B(int, int)
   B(int b1, int b2) : A(b1) {}
   ^
b.h:5:3: note:   candidate expects 2 arguments, 0 provided
b.h:3:7: note: constexpr B::B(const B&)
 class B : public A {
       ^
b.h:3:7: note:   candidate expects 1 argument, 0 provided
b.h:3:7: note: constexpr B::B(B&&)
b.h:3:7: note:   candidate expects 1 argument, 0 provided
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From: "raj.khem at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c++/65292] New: Template function not emitted
Date: Tue, 03 Mar 2015 05:48:00 -0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?ide292

            Bug ID: 65292
           Summary: Template function not emitted
           Product: gcc
           Version: 5.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: raj.khem at gmail dot com

Created attachment 34932
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id4932&actioníit
testcase

Attached code from webkit, shows that when compiling it for arm with gcc -O2, a
function goes missing in the object file

   case NonArrayWithInt32: case ArrayWithInt32: {
        putByIndexBeyondVectorLengthWithoutAttributes<Int32Shape>(exec, i,
value);
        break;
    }

    case NonArrayWithDouble: case ArrayWithDouble: {
        putByIndexBeyondVectorLengthWithoutAttributes<DoubleShape>(exec, i,
value);
        break;
    }

    case NonArrayWithContiguous: case ArrayWithContiguous: {
        putByIndexBeyondVectorLengthWithoutAttributes<ContiguousShape>(exec, i,
value);
        break;
    }

Out of those calls, putByIndexBeyondVectorLengthWithoutAttributes<Int32Shape>
is not emitted into .s file, when compiled with -O1 the function is emitted


This problem is not happening on 4.8.x or 4.9.x

gcc-5.0 - O2
=============
readelf -sW JSObject.o | c++filt | grep
putByIndexBeyondVectorLengthWithoutAttributes
   298: 00000000   284 FUNC    WEAK   HIDDEN    43 void
JSC::JSObject::putByIndexBeyondVectorLengthWithoutAttributes<(unsigned
char)22>(JSC::ExecState*, unsigned int, JSC::JSValue)
   300: 00000000   264 FUNC    WEAK   HIDDEN    45 void
JSC::JSObject::putByIndexBeyondVectorLengthWithoutAttributes<(unsigned
char)26>(JSC::ExecState*, unsigned int, JSC::JSValue)

gcc-5.0 - O1
===========
readelf -sW a.o | c++filt | grep putByIndexBeyondVectorLengthWithoutAttributes
   505: 00000000   224 FUNC    WEAK   DEFAULT  128 void
JSC::JSObject::putByIndexBeyondVectorLengthWithoutAttributes<(unsigned
char)20>(JSC::ExecState*, unsigned int, JSC::JSValue)
   507: 00000000   252 FUNC    WEAK   DEFAULT  138 void
JSC::JSObject::putByIndexBeyondVectorLengthWithoutAttributes<(unsigned
char)22>(JSC::ExecState*, unsigned int, JSC::JSValue)
   510: 00000000   224 FUNC    WEAK   DEFAULT  147 void
JSC::JSObject::putByIndexBeyondVectorLengthWithoutAttributes<(unsigned
char)26>(JSC::ExecState*, unsigned int, JSC::JSValue)


version I am at is gcc version 5.0.0 20150301 (experimental) (GCC)

[Bug c++/65291] mention that default arguments of constructors are not inherited

[manu at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65291

Manuel López-Ibáñez <manu at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|RESOLVED                    |REOPENED
   Last reconfirmed|                            |2015-03-03
                 CC|                            |manu at gcc dot gnu.org
         Resolution|INVALID                     |---
            Summary|protected using constructor |mention that default
                   |default arguments not       |arguments of constructors
                   |recognized                  |are not inherited
     Ever confirmed|0                           |1

--- Comment #3 from Manuel López-Ibáñez <manu at gcc dot gnu.org> ---
(In reply to Jonathan Wakely from comment #2)
> The C++ standard says that B inherits a constructor taking a single int, the
> default argument is not inherited, so B has no default constructor, and G++
> is correct to reject the program.

This is the key information. Couldn't g++ say something like?

b.h:7:12: note: B::B(int)
   using A::A;
            ^
b.h:7:12: note:   candidate expects 1 argument, 0 provided (default arguments
are not inherited)

BTW, clang rejects the 'using':

10 : error: using declaration cannot refer to a constructor
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Subject: [Bug target/65297] [5 Regression] ICE (in get_untransformed_body, at cgraph.c:3113) on arm-linux-gnueabihf
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https://gcc.gnu.org/bugzilla/show_bug.cgi?ide297

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

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

--- Comment #1 from Marek Polacek <mpolacek at gcc dot gnu.org> ---
This might be already fixed in r221134.

[Bug c++/65291] mention that default arguments of constructors are not inherited

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65291

--- Comment #4 from Jonathan Wakely <redi at gcc dot gnu.org> ---
(In reply to Manuel López-Ibáñez from comment #3)
> BTW, clang rejects the 'using':
> 
> 10 : error: using declaration cannot refer to a constructor

You need to compile as C++11.
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Subject: [Bug c++/65291] mention that default arguments of constructors are not inherited
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https://gcc.gnu.org/bugzilla/show_bug.cgi?ide291

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |diagnostic

--- Comment #5 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Reduced:

struct A {
  A(int a = 0) { }
};

struct B : A {
  using A::A;
  B(int, int);
};

B b;


FWIW the relevant output from Clang trunk is:

c.cc:10:3: error: no matching constructor for initialization of 'B'
B b;
  ^
c.cc:6:12: note: candidate constructor (inherited) not viable: requires 1
argument, but 0 were provided
  using A::A;
           ^
c.cc:2:3: note: inherited from here
  A(int a = 0) { }
  ^


EDG says simply:

"c.cc", line 10: error: no default constructor exists for class "B"
  B b;
    ^

[Bug c++/65291] mention that default arguments of constructors are not inherited

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65291

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|REOPENED                    |RESOLVED
         Resolution|---                         |INVALID

--- Comment #6 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Actually, I got the reason wrong. Default args are inherited, but the presence
of this constructor suppresses the default ctor B():

  B(int b1, int b2) : A(b1) {}

So we don't want to add a diagnostic about inheriting default arguments.

[Bug c++/65291] mention that default arguments of constructors are not inherited

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65291

--- Comment #7 from Jonathan Wakely <redi at gcc dot gnu.org> ---
We could potentially add a note saying that the default constructor is
suppressed by the presence of another user-declared constructor, but that's
unrelated to inheriting constructors, and should be a separate bug to avoid the
confusing history here (which is my fault).