Re: [PATCH] declare std::array members attribute const [PR101831]

[Martin Sebor <msebor@gmail.com>]

On 2/1/22 17:15, Jonathan Wakely wrote:
> On Wed, 2 Feb 2022 at 00:13, Martin Sebor <msebor@gmail.com> wrote:
>>
>> On 2/1/22 12:48, Jonathan Wakely wrote:
>>> On Tue, 1 Feb 2022 at 18:54, Martin Sebor via Libstdc++
>>> <libstdc++@gcc.gnu.org> wrote:
>>>>
>>>> Passing an uninitialized object to a function that takes its argument
>>>> by const reference is diagnosed by -Wmaybe-uninitialized because most
>>>> such functions read the argument.  The exceptions are functions that
>>>> don't access the object but instead use its address to compute
>>>> a result.  This includes a number of std::array member functions such
>>>> as std::array<N>::size() which returns the template argument N.  Such
>>>> functions may be candidates for attribute const which also avoids
>>>> the warning.  The attribute typically only benefits extern functions
>>>> that IPA cannot infer the property from, but in this case it helps
>>>> avoid the warning which runs very early on, even without optimization
>>>> or inlining.  The attached patch adds the attribute to a subset of
>>>> those member functions of std::array.  (It doesn't add it to const
>>>> member functions like cbegin() or front() that return a const_iterator
>>>> or const reference to the internal data.)
>>>>
>>>> It might be possible to infer this property from inline functions
>>>> earlier on than during IPA and avoid having to annotate them explicitly.
>>>> That seems like an enhancement worth considering in the future.
>>>>
>>>> Tested on x86_64-linux.
>>>>
>>>> Martin
>>>
>>> new file mode 100644
>>> index 00000000000..b7743adf3c9
>>> --- /dev/null
>>> +++ b/libstdc++-v3/testsuite/23_containers/array/iterators/begin_end.cc
>>> @@ -0,0 +1,56 @@
>>> +// { dg-do compile { target c++11 } }
>>> +//
>>> +// Copyright (C) 2011-2022 Free Software Foundation, Inc.
>>>
>>> Those dates look wrong. I no longer bother putting a license text and
>>> copyright notice on simple tests like this. It's meaningless to assert
>>> copyright on something so trivial that doesn't do anything.
>>>
>>
>> Should I take to mean that you're okay with the rest of the change
>> (i.e., with the notice removed)?
> 
> Yes, OK for trunk either with the notice entirely removed, or just fix
> the dates (I don't think it is copied from an existing test dating
> from 2011, right?)

I copied it from 23_containers/array/iterators/end_is_one_past.cc
without even looking at the dates.

> 
> Whichever you prefer.
> 

Okay, pushed in r12-6992.

Martin