[Bug c++/57599] New: g++ accepts invalid dynamic_cast of a const type to a regular type

[Bug c++/57599] New: g++ accepts invalid dynamic_cast of a const type to a regular type

[abel at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=57599

            Bug ID: 57599
           Summary: g++ accepts invalid dynamic_cast of a const type to a
                    regular type
           Product: gcc
           Version: 4.7.2
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: abel at gcc dot gnu.org

The following code is accepted by g++ (versions 3.3, 4.6, 4.7 at least, I
didn't check trunk) but seems to be invalid c++ and is rejected by clang 3.2,
icc 13, msvc 12:

class A {
};

class B : public A {
};

int main() {
    A* a;
    B* b = new B();
    a = dynamic_cast<const A*>(b);
    return 0;
}

An expected error is along the lines of (icc):
error: a value of type "const A *" cannot be assigned to an entity of type "A
*"

[Bug c++/57599] g++ accepts invalid dynamic_cast of a const type to a regular type

[redi at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=57599

--- Comment #1 from Jonathan Wakely <redi at gcc dot gnu.org> ---
The summary is very misleading. You're not casting a const type to a non-const
type, you're casting a non-const type to a const type, then assigning that to a
non-const type.

What actually happens is that dynamic_cast<const A*>(b) returns A*

[Bug c++/57599] g++ accepts invalid assignment of a dynamic_cast<const A*> to A*

[abel at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=57599

Andrey Belevantsev <abel at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
            Summary|g++ accepts invalid         |g++ accepts invalid
                   |dynamic_cast of a const     |assignment of a
                   |type to a regular type      |dynamic_cast<const A*> to
                   |                            |A*

--- Comment #2 from Andrey Belevantsev <abel at gcc dot gnu.org> ---
Sorry, I tried to fix the summary.  Feel free to improve it more if needed :)

[Bug c++/57599] result of dynamic_cast<cv T> is just T

[paolo.carlini at oracle dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=57599

Paolo Carlini <paolo.carlini at oracle dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |ASSIGNED
   Last reconfirmed|                            |2013-06-12
           Assignee|unassigned at gcc dot gnu.org      |paolo.carlini at oracle dot com
     Ever confirmed|0                           |1

--- Comment #3 from Paolo Carlini <paolo.carlini at oracle dot com> ---
On it.

[Bug c++/57599] result of dynamic_cast<cv T> is just T

[daniel.kruegler at googlemail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=57599

Daniel Krügler <daniel.kruegler at googlemail dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |daniel.kruegler@googlemail.
                   |                            |com

--- Comment #4 from Daniel Krügler <daniel.kruegler at googlemail dot com> ---
I created a test case for all type conversion operators:

struct A {};
struct B : public A {};

template<class, class>
struct is_same { static constexpr bool value = false; };

template<class T>
struct is_same<T, T> { static constexpr bool value = true; };

template<class T>
T val();

static_assert(is_same<decltype(static_cast<const A*>(val<B*>())), const
A*>::value, "Ouch");
static_assert(is_same<decltype(static_cast<const A&>(val<B&>())), const
A&>::value, "Ouch");

static_assert(is_same<decltype(const_cast<const A*>(val<A*>())), const
A*>::value, "Ouch");
static_assert(is_same<decltype(const_cast<const A&>(val<A&>())), const
A&>::value, "Ouch");

static_assert(is_same<decltype(reinterpret_cast<const A*>(val<B*>())), const
A*>::value, "Ouch");
static_assert(is_same<decltype(reinterpret_cast<const A&>(val<B&>())), const
A&>::value, "Ouch");

static_assert(is_same<decltype(dynamic_cast<const A*>(val<B*>())), const
A*>::value, "Ouch"); // Error!
static_assert(is_same<decltype(dynamic_cast<const A&>(val<B&>())), const
A&>::value, "Ouch"); // Error!

In agreement with that bug report I see failures for the last two even for gcc
4.9.0 20130609 (experimental)
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From: "valeryweber at hotmail dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug fortran/57596] select type bug with optional variables?
Date: Thu, 13 Jun 2013 07:00:00 -0000
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http://gcc.gnu.org/bugzilla/show_bug.cgi?idW596

--- Comment #2 from Valery Weber <valeryweber at hotmail dot com> ---
But the selector is not optional. The problem even remains if I
move the optional variables outside the SELECT TYPE (see bellow).
Those 2 codes run just fine with other compilers like ifort or xlf.
Thanks
Valery


MODULE base_types
  TYPE :: base_integer_type
     INTEGER :: i
  END TYPE base_integer_type
  TYPE :: base_character_type
     CHARACTER( 10 ) :: c
  END TYPE base_character_type
END MODULE base_types

PROGRAM main
  USE base_types
  IMPLICIT NONE
  INTEGER::i_val
  call get (  i_val=i_val )
  write(*,*) 'i_val',i_val
contains

  SUBROUTINE get (i_val, c_val)
    INTEGER, INTENT( OUT ), OPTIONAL :: i_val
    CHARACTER( : ), INTENT( OUT ), ALLOCATABLE, OPTIONAL :: c_val
    CLASS( * ), POINTER :: p
    TYPE( base_integer_type ),target :: i_base
    INTEGER :: i_val_tmp
    CHARACTER( 10 ) :: c_val_tmp
    i_base%i=-12
    p=>i_base
    SELECT TYPE( p )
    TYPE IS( base_integer_type )
       i_val_tmp = p%i
    TYPE IS( base_character_type )
       c_val_tmp = p%c
    CLASS DEFAULT
       stop
    END SELECT
    IF(present(i_val)) i_val = i_val_tmp
    if(present(c_val)) c_val = c_val_tmp
  END SUBROUTINE get
END PROGRAM main

[Bug c++/57599] result of dynamic_cast<cv T> is just T

[abel at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=57599

--- Comment #5 from Andrey Belevantsev <abel at gcc dot gnu.org> ---
(In reply to Daniel Krügler from comment #4)
> I created a test case for all type conversion operators:

Paolo has already submitted a patch with the expanded test case at
http://gcc.gnu.org/ml/gcc-patches/2013-06/msg00760.html/
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Subject: [Bug tree-optimization/57601] New: Vector lowering could use larger modes
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http://gcc.gnu.org/bugzilla/show_bug.cgi?idW601

            Bug ID: 57601
           Summary: Vector lowering could use larger modes
           Product: gcc
           Version: 4.9.0
            Status: UNCONFIRMED
          Keywords: missed-optimization
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: glisse at gcc dot gnu.org
            Target: x86_64-linux-gnu

typedef int vec __attribute__((vector_size(2*sizeof(int))));
vec f(vec a, vec b){
  return a-b;
}

    vmovq    %xmm0, %rcx
    vmovq    %xmm1, %rdx
    movl    %ecx, %eax
    shrq    $32, %rcx
    subl    %edx, %eax
    shrq    $32, %rdx
    subl    %edx, %ecx
    vmovd    %eax, %xmm2
    vpinsrd    $1, %ecx, %xmm2, %xmm0

(with -Ofast -mavx2) whereas if I change the size to 4, I get:

    vpsubd    %xmm1, %xmm0, %xmm0

which seems valid to me even for size 2. It is not clear to me how to model
that at tree level, maybe it would be easier to just implement V2SI operations
in the backend?

[Bug c++/57599] result of dynamic_cast<cv T> is just T

[paolo.carlini at oracle dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=57599

Paolo Carlini <paolo.carlini at oracle dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|ASSIGNED                    |RESOLVED
         Resolution|---                         |FIXED
   Target Milestone|---                         |4.9.0

--- Comment #6 from Paolo Carlini <paolo.carlini at oracle dot com> ---
Fixed for 4.9.0.

[Bug c++/57599] result of dynamic_cast<cv T> is just T

[abel at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=57599

--- Comment #7 from Andrey Belevantsev <abel at gcc dot gnu.org> ---
(In reply to Paolo Carlini from comment #6)
> Fixed for 4.9.0.

Do you plan to backport this to 4.7 and 4.8?

[Bug c++/57599] result of dynamic_cast<cv T> is just T

[paolo.carlini at oracle dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=57599

--- Comment #8 from Paolo Carlini <paolo.carlini at oracle dot com> ---
No, because isn't a regression. If you care a lot about that, just ask on the
mailing list.