[Bug c++/65174] New: noexcept() returns true when operator delete with the object that has a throwing destructor

[Bug c++/65174] New: noexcept() returns true when operator delete with the object that has a throwing destructor

[redboltz at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65174

            Bug ID: 65174
           Summary: noexcept() returns true when operator delete with the
                    object that has a throwing destructor
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: redboltz at gmail dot com

==========================================================================
Summary:
noexcept() returns true unexpectedly when the following conditions are
satisfied:
  1. noexcept argument expression is 'delete'.
  2. The argument of delete is the pointer literal that type has throwing
     destructor.
  3. The value of the pointer literal is null.
--------------------------------------------------------------------------
Test code: test.cpp
--------------------------------------------------------------------------
#include <iostream>

struct foo {
    ~foo() throw(std::bad_alloc) {}
};

int main() {
    std::cout << std::boolalpha;
    std::cout << noexcept(delete static_cast<foo*>(nullptr)) << std::endl;
    std::cout << noexcept(delete reinterpret_cast<foo*>(0)) << std::endl;
    std::cout << noexcept(delete reinterpret_cast<foo*>(1)) << std::endl;
}
--------------------------------------------------------------------------
Compile command:
g++ -Wall -Wextra -std=c++11 noexcept.cpp
--------------------------------------------------------------------------
Expected output:
false
false
false
--------------------------------------------------------------------------
Actual output:
true
true
false
--------------------------------------------------------------------------
gcc -v                                                                          
Using built-in specs.
COLLECT_GCC=gcc
COLLECT_LTO_WRAPPER=/usr/lib/gcc/x86_64-unknown-linux-gnu/4.9.2/lto-wrapper
Target: x86_64-unknown-linux-gnu
Configured with: /build/gcc-multilib/src/gcc-4.9-20150204/configure
--prefix=/usr --libdir=/usr/lib --libexecdir=/usr/lib --mandir=/usr/share/man
--infodir=/usr/share/info --with-bugurl=https://bugs.archlinux.org/
--enable-languages=c,c++,ada,fortran,go,lto,objc,obj-c++ --enable-shared
--enable-threads=posix --with-system-zlib --enable-__cxa_atexit
--disable-libunwind-exceptions --enable-clocale=gnu --disable-libstdcxx-pch
--disable-libssp --enable-gnu-unique-object --enable-linker-build-id
--enable-cloog-backend=isl --enable-lto --enable-plugin
--enable-install-libiberty --with-linker-hash-style=gnu --enable-multilib
--disable-werror --enable-checking=release
Thread model: posix
gcc version 4.9.2 20150204 (prerelease) (GCC) 
==========================================================================

[Bug c++/65174] noexcept() returns true when operator delete with the object that has a throwing destructor

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65174

--- Comment #1 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Hmm, interesting. When the operand of the delete expression is null the
destructor is not invoked, so it can't throw. It's not obvious to me whether
GCC's result is allowed by the standard or not.

[Bug c++/65174] noexcept() returns true when operator delete with the object that has a throwing destructor

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65174

--- Comment #2 from Jonathan Wakely <redi at gcc dot gnu.org> ---
FWIW clang and EDG both fail the first two static assertions here, while GCC
passes all three:

struct foo {
    ~foo() throw(int) {}
};

int main() {
    static_assert( noexcept(delete static_cast<foo*>(nullptr)), "");
    static_assert( noexcept(delete static_cast<foo*>(0)), "");
    static_assert( !noexcept(delete (1+static_cast<foo*>(0))), "");
}

[Bug c++/65174] noexcept() returns true when operator delete with a NULL PTR that has a throwing destructor

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65174

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Last reconfirmed|2018-10-17 00:00:00         |2021-8-27
            Summary|noexcept() returns true     |noexcept() returns true
                   |when operator delete with   |when operator delete with a
                   |the object that has a       |NULL PTR that has a
                   |throwing destructor         |throwing destructor
           Keywords|                            |wrong-code

--- Comment #4 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Updated testcase to show that noexcept will also cause it to happen so it does
matter for C++17+ (where throw(std::bad_alloc) support has been removed):
#include <iostream>

struct foo1 {
    ~foo1() noexcept(false) {}
};

int main() {
    std::cout << std::boolalpha;
    std::cout << noexcept(delete static_cast<foo1*>(nullptr)) << std::endl;
    std::cout << noexcept(delete reinterpret_cast<foo1*>(0)) << std::endl;
    std::cout << noexcept(delete reinterpret_cast<foo1*>(1)) << std::endl;
    return 0;
}