[Bug libstdc++/69769] arithmetic operation on pointer to a function

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=69769

Jonathan Wakely  changed:

   What|Removed |Added

 Status|ASSIGNED|RESOLVED
 Resolution|--- |FIXED
   Target Milestone|--- |9.0

--- Comment #8 from Jonathan Wakely  ---
The C++17 standard says that arithmetic on atomic pointer types is ill-formed,
so libstdc++ now enforces that for C++17 and later.

[Bug libstdc++/69769] arithmetic operation on pointer to a function

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=69769

--- Comment #7 from Jonathan Wakely  ---
Author: redi
Date: Thu May 24 15:28:26 2018
New Revision: 260676

URL: https://gcc.gnu.org/viewcvs?rev=260676=gcc=rev
Log:
Implement P0558R2 changes to std::atomic

The restrictions forbidding arithmetic on atomic pointer types are only
enabled for C++17 and later, retaining the GNU extension for older
standards. The new nested typedefs and changes to prevent scalar
parameters participating in template argument deduction are enabled
unconditionally.

PR libstdc++/69769
PR libstdc++/85886
* include/bits/atomic_base.h (__atomic_base::value_type)
(__atomic_base::difference_type): Add new typedefs.
* include/std/atomic (atomic::value_type, atomic::value_type)
(atomic::value_type, atomic::difference_type): Likewise.
(atomic::operator++, atomic::operator--)
(atomic::operator+=, atomic::operator-=)
(atomic::fetch_add, atomic::fetch_sub): Add static assertion
to enforce C++17 requirement on pointer arithmetic.
(__atomic_val_t, __atomic_diff_t): New alias templates.
(atomic_init, atomic_store_explicit, atomic_exchange_explicit)
(atomic_compare_exchange_weak_explicit)
(atomic_compare_exchange_strong_explicit, atomic_store)
(atomic_exchange, atomic_compare_exchange_weak)
(atomic_compare_exchange_strong): Use __atomic_val_t to make
scalar parameters be non-deduced contexts.
(atomic_fetch_add_explicit, atomic_fetch_sub_explicit)
(atomic_fetch_add, atomic_fetch_sub): Change first parameter to be
atomic instead of __atomic_base, and use __atomic_diff_t for scalar
parameters.
(atomic_fetch_and_explicit, atomic_fetch_or_explicit)
(atomic_fetch_xor_explicit, atomic_fetch_and, atomic_fetch_or)
(atomic_fetch_xor): Use __atomic_val_t for scalar parameters.
(atomic_fetch_add_explicit, atomic_fetch_sub_explicit)
(atomic_fetch_add, atomic_fetch_sub): Remove overloads for atomic
address types.
* testsuite/29_atomics/atomic/60695.cc: Adjust dg-error lineno.
* testsuite/29_atomics/atomic/69769.cc: New test.
* testsuite/29_atomics/atomic/nonmembers.cc: New test.
* testsuite/29_atomics/atomic/operators/pointer_partial_void.cc:
Disable test for C++17 and later.
* testsuite/29_atomics/atomic/requirements/typedefs.cc: New test.
* testsuite/29_atomics/atomic_integral/nonmembers.cc: New test.
* testsuite/29_atomics/atomic_integral/requirements/typedefs.cc: New
test.

Added:
trunk/libstdc++-v3/testsuite/29_atomics/atomic/69769.cc
trunk/libstdc++-v3/testsuite/29_atomics/atomic/nonmembers.cc
trunk/libstdc++-v3/testsuite/29_atomics/atomic/requirements/typedefs.cc
  - copied, changed from r260635,
trunk/libstdc++-v3/testsuite/29_atomics/atomic/60695.cc
trunk/libstdc++-v3/testsuite/29_atomics/atomic_integral/nonmembers.cc
   
trunk/libstdc++-v3/testsuite/29_atomics/atomic_integral/requirements/typedefs.cc
  - copied, changed from r260635,
trunk/libstdc++-v3/testsuite/29_atomics/atomic/60695.cc
Modified:
trunk/libstdc++-v3/ChangeLog
trunk/libstdc++-v3/include/bits/atomic_base.h
trunk/libstdc++-v3/include/std/atomic
trunk/libstdc++-v3/testsuite/29_atomics/atomic/60695.cc
   
trunk/libstdc++-v3/testsuite/29_atomics/atomic/operators/pointer_partial_void.cc

[Bug libstdc++/69769] arithmetic operation on pointer to a function

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=69769

Jonathan Wakely  changed:

   What|Removed |Added

 Status|NEW |ASSIGNED
   Assignee|unassigned at gcc dot gnu.org  |redi at gcc dot gnu.org

[Bug libstdc++/69769] arithmetic operation on pointer to a function

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=69769

--- Comment #6 from Jonathan Wakely  ---
(In reply to Wolfgang Roehrl from comment #0)
> The compiler accepts this programm despite of performing an arithmetic
> operation on pointer to a function.

Arithmetic on (non-atomic) function pointers is supported by GCC:
https://gcc.gnu.org/onlinedocs/gcc/Pointer-Arith.html

So this is consistent with the built-in types.

[Bug libstdc++/69769] arithmetic operation on pointer to a function

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=69769

Jonathan Wakely  changed:

   What|Removed |Added

 Status|UNCONFIRMED |NEW
   Last reconfirmed||2017-04-18
 Ever confirmed|0   |1

--- Comment #5 from Jonathan Wakely  ---
P0558R1 added the following to the atomic specialization:

Requires: T shall be an object type, otherwise the program is ill-formed.
[Note: Pointer arithmetic on void* or function pointers is ill-formed. — end
note ]

[Bug libstdc++/69769] arithmetic operation on pointer to a function

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=69769

--- Comment #4 from Jonathan Wakely  ---
For atomic Clang rejects use of its builtin with a void*:

/usr/local/libcxx-head/include/c++/v1/atomic:1081:40: error: incomplete type
'void' where a complete type is required

But it allows the function pointer case.

Arguably it makes sense for __atomic_fetch_add etc. to do the checking,
although the fact that GCC does allow arithmetic on void* complicates that.

[Bug libstdc++/69769] arithmetic operation on pointer to a function

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=69769

--- Comment #3 from Jonathan Wakely  ---
The same problem exists for std::atomic

[Bug libstdc++/69769] arithmetic operation on pointer to a function

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=69769

--- Comment #2 from Jonathan Wakely  ---
No, I'm not aware of one.

[Bug libstdc++/69769] arithmetic operation on pointer to a function

[msebor at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=69769

Martin Sebor  changed:

   What|Removed |Added

 CC||jwakely.gcc at gmail dot com,
   ||msebor at gcc dot gnu.org
  Component|c++ |libstdc++

--- Comment #1 from Martin Sebor  ---
The  header is part of libstdc++ so setting Component to it.  I agree
that this should be rejected but I'm not sure that this isn't actually a defect
in the standard.  AFAICS, the partial specializations of atomic for pointers
don't say that function pointers should be treated differently than object
pointers.  Jonathan, is there an issue on this (I may have overlooked int)?