this-pointer NULL-checks in hotspot codebase [-Wtautological-undefined-compare]

[Harold Seigel]

The functions that compare 'this' to NULL could be changed from instance 
to static functions where 'this' is explicitly passed as a parameter.  
Then you could keep the equivalent NULL checks.

Harold

On 7/12/2019 4:22 AM, Erik Österlund wrote:
> Hi Matthias,
>
> Removing such NULL checks seems like a good idea in general due to the 
> undefined behaviour.
> Worth mentioning though that there are some tricky ones, like in 
> markOopDesc* where this == NULL
> means that the mark word has the "inflating" value. So we explicitly 
> check if this == NULL and
> hope the compiler will not elide the check. Just gonna drop that one 
> here and run for it.
>
> Thanks,
> /Erik
>
> On 2019-07-12 09:48, Baesken, Matthias wrote:
>> Hello , when looking  into  the  recent xlc16 / xlclang   warnings I 
>> came  across  those  3 :
>>
>> /nightly/jdk/src/hotspot/share/adlc/formssel.cpp:1729:7: warning: 
>> 'this' pointer cannot be null in well-defined C++ code;
>> comparison may be assumed to always evaluate to true 
>> [-Wtautological-undefined-compare]
>>    if( this != NULL ) {
>>        ^~~~    ~~~~
>>
>> /nightly/jdk/src/hotspot/share/adlc/formssel.cpp:3416:7: warning: 
>> 'this' pointer cannot be null in well-defined C++ code;
>> comparison may be assumed to always evaluate to false 
>> [-Wtautological-undefined-compare]
>>    if( this == NULL ) return;
>>
>> /nightly/jdk/src/hotspot/share/libadt/set.cpp:46:7: warning: 'this' 
>> pointer cannot be null in well-defined C++ code;
>> comparison may be assumed to always evaluate to false 
>> [-Wtautological-undefined-compare]
>>    if( this == NULL ) return os::strdup("{no set}");
>>
>>
>> Do you think the  NULL-checks can be removed or is there still some 
>> value in doing them ?
>>
>> Best regards, Matthias
>