[committed] Fix -Wmissing-attributes warning in libstdc++ (PR libstdc++/89402)

[Martin Sebor]

On 2/21/19 6:10 PM, Jonathan Wakely wrote:
> On 20/02/19 09:07 +0100, Jakub Jelinek wrote:
>> Hi!
>>
>> The following patch fixes a warning when building on targets where long
>> double switched from being the same as double to something wider,
>> like e.g. powerpc*-linux, alpha*-linux, s390*-linux etc.
>>
>> Fixed thusly, bootstrapped/regtested on {x86_64,i686,s390x}-linux and
>> bootstrapped on powerpc64le-linux, on both s390x and powerpc64le it 
>> removed
>> all
>> ../../../../libstdc++-v3/src/c++98/compatibility-ldbl.cc:77:17: 
>> warning: 'void _ZNKSt4hashIeEclEe()' specifies less restrictive 
>> attribute than its target 'std::size_t 
>> std::tr1::hash<_Tp>::operator()(_Tp) const [with _Tp = long double]': 
>> 'pure' [-Wmissing-attributes]
>> warnings from the build log.  Preapproved by Jonathan in the PR, 
>> committed
>> to trunk.
> 
> Now I see:
> 
> /home/jwakely/src/gcc/libstdc++-v3/src/c++98/compatibility-ldbl.cc:78:65: warning: 
> ‘pure’ attribute on function returning ‘void’ [-Wattributes]
>  Â  78 |Â Â  _GLIBCXX_PURE __attribute__((alias ("_ZNKSt3tr14hashIeEclEe")));
>  Â Â Â Â  |Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â  ^

Are the attributes on this alias ever considered in calls to it?
If not (and assuming there's a way to tell, which I think there
should be but haven't verified it) the warning could be relaxed
to only trigger for those that are.  I think those would be
either aliases declared in headers, or those with the TREE_USED
bit set.

Martin

> 
> We can disable that with a diagnostic pragma.
> 
> 
> 
>> 2019-02-20  Jakub Jelinek  <jakub@redhat.com>
>>
>> Â Â Â Â PR libstdc++/89402
>> Â Â Â Â * src/c++98/compatibility-ldbl.cc (_ZNKSt4hashIeEclEe): Add
>> Â Â Â Â _GLIBCXX_PURE to the alias declaration.
>>
>> --- libstdc++-v3/src/c++98/compatibility-ldbl.cc.jj    2019-01-01 
>> 12:39:41.530606161 +0100
>> +++ libstdc++-v3/src/c++98/compatibility-ldbl.cc    2019-02-19 
>> 16:12:52.402123217 +0100
>> @@ -75,6 +75,6 @@ namespace std _GLIBCXX_VISIBILITY(defaul
>> // and std::hash<long double>::operator()
>> // are the same, no need to duplicate them.
>> extern "C" void _ZNKSt4hashIeEclEe (void)
>> -Â  __attribute__((alias ("_ZNKSt3tr14hashIeEclEe")));
>> +Â  _GLIBCXX_PURE __attribute__((alias ("_ZNKSt3tr14hashIeEclEe")));
>>
>> #endif
>>
>>
>> Â Â Â Â Jakub