RFR: 8003310: Enable -Wunused when compiling with GCC

[David Holmes]

One final comment - please liaise with Joe Provino who is adding -Wundef 
so we can get a consistent approach as to where these -Wxxx flags get 
added. :)


(Don't know what I was looking at with the trace_locking stuff - it ends 
up as an empty method.)

David

On 22/02/2013 6:00 AM, Mikael Vidstedt wrote:
>
> On 2013-02-20 10:04, Coleen Phillimore wrote:
>> On 2/20/2013 12:33 PM, Mikael Vidstedt wrote:
>>>
>>> On 2/19/2013 12:01 PM, Christian Thalinger wrote:
>>>> On Feb 18, 2013, at 3:14 PM, Mikael Vidstedt
>>>> <mikael.vidstedt at oracle.com> wrote:
>>>>
>>>>> A really good control question, thanks a lot for asking!
>>>>>
>>>>> As a matter of fact these changes are basically just doing what the
>>>>> compiler already does for us, so it's more about cleaning up the
>>>>> source code than reducing the size of the binary. So in theory
>>>>> these changes should have no impact on the binary size at all, but
>>>>> it actually turns out they do. Very specifically, the fact that I
>>>>> moved the same_page() function from being duplicated in the three
>>>>> os_<os>.cpp files to having it be in globalDefinitions.cpp makes
>>>>> the binary grow a few bytes (54 bytes to be specific). The reason
>>>>> is a bit subtle:
>>>>>
>>>>> The same_page() function is (was) static in the respective os_*.cpp
>>>>> files. They are only ever used when the Verbose flag is true, and
>>>>> furthermore the Verbose option is a develop only flag, which means
>>>>> it is hardcoded to false in product. The compiler knows that's the
>>>>> case and eliminates the same_page() function completely.
>>>>>
>>>>> Since I moved it to globalDefinitions.cpp there's no way easy for
>>>>> the compiler to know that it is not being used, so it will actually
>>>>> keep the function.
>>>>>
>>>>> Unless there are strong opinions I'm not going to do anything about
>>>>> this.
>>>>>
>>>>> However, this made me question my earlier experiments with using
>>>>> the const bool = false construct in constantPool.cpp, because after
>>>>> all that is the exact same pattern. And it turns out that I must
>>>>> have done something wrong when I was performing the experiments,
>>>>> because when I do the same thing again now it turns out the
>>>>> compiler actually *does* deadcode eliminate the debug-only
>>>>> functions. So I take everything back and conclude that const bool =
>>>>> false is indeed a great way to make sure the debug code does not
>>>>> rot over time, and that the product binary will *not* contain the
>>>>> dead functions. Sorry for any confusion this may have caused.
>>>>>
>>>>> With all that in mind, here's another version of the webrev:
>>>>>
>>>>> http://cr.openjdk.java.net/~mikael/webrevs/8003310/webrev04/webrev/
>>>> src/share/vm/interpreter/interpreterRuntime.cpp:
>>>>
>>>> I suppose that #if 0 is to keep that code for...?  Could we add a
>>>> comment why we keep it?
>>>
>>> This was by "popular request" (from David Holmes) :)
>>>
>>> I personally don't know if and how this is being used. Note that
>>> ObjectSynchronizer::trace_locking is PRODUCT_RETURN and the
>>> non-product implementation in synchronizer.cpp is empty (modulo the
>>> comment saying "Don't know what to do here"), so one can question the
>>> value of keeping the any of the trace_locking functions, but they may
>>> be someone's favorite debugging tool. Until proven differently I will
>>> leave it in there for now. If somebody can help me provide a useful
>>> comment about how the code is actually being used then I will
>>> certainly add it, otherwise I'll keep this as it is.
>>
>> If I remember correctly, this trace_locking code was associated with a
>> flag that we removed a long time ago.   I don't think if we want to
>> implement TraceLocking we'd use this function.  My vote is that it and
>> the ObjectMonitor:: version should be removed.
>
> Thanks Coleen, that makes sense. I've prepared a final version of the
> webrev with the trace_locking methods removed too:
>
> http://cr.openjdk.java.net/~mikael/webrevs/8003310/webrev.06/webrev/
>
> Any final comments?
>
> Cheers,
> Mikael
>
>>
>> Coleen
>>>
>>>> src/share/vm/oops/constantPool.cpp:
>>>>
>>>> So we use:
>>>>
>>>> + const bool debug_cpool = false;
>>>>
>>>> but we still have the DBG macro.  Can't we have a static debug
>>>> method that takes all printf arguments and prints them?  The
>>>> debug_cpool should make that method empty and the compiler can
>>>> remove it.  I really start to hate all these macros...
>>>
>>> I share your macro hate and I actually played around with removing
>>> the macros just as you say. There is one small problem with doing it
>>> that way, and that's the fact that a few of the printf:s print
>>> symbols names, and as part of that they need to create utf8 strings
>>> using sym->as_utf8(). The compiler can unfortunately not know that
>>> that function is for all intents and purposes a no-op, so it will
>>> keep the call even in product meaning increased binary size and it
>>> will also add to the runtime since it actually performs the call and
>>> creates the utf8 string. So I'm going to keep the macros for now.
>>>
>>>
>>> I also moved the clamp_address_in_page to the globalDefinitions.hpp
>>> header file, meaning it will be inlined and dead code eliminated.
>>>
>>> New webrev here:
>>>
>>> http://cr.openjdk.java.net/~mikael/webrevs/8003310/webrev.05/webrev/
>>>
>>> Final comments?
>>>
>>> Cheers,
>>> Mikael
>>>
>>
>