RFR: 8003310: Enable -Wunused when compiling with GCC

David Holmes david.holmes at oracle.com
Wed Apr 3 00:30:23 PDT 2013

Sorry for the delay.

Ship it! (As seems to be the new catch-cry ;-) )


On 29/03/2013 2:40 AM, Mikael Vidstedt wrote:
> I've been waiting for Joe's changes to bubble up so as to not add a
> conflict unnecessarily, and since they're now in hotspot-rt I have
> uploaded a webrev for what I hope is a final time *knocking on wood*. I
> would appreciate a quick check to see that everything still looks fine:
> http://cr.openjdk.java.net/~mikael/webrevs/8003310/webrev.08/webrev/
> The only relevant changes from the last webrev should be:
> make/linux/makefiles/gcc.make:
> * Eliminate the ADDITIONAL_WARNINGS variable and just use WARNING_FLAGS
> directly
> * Clean up the -Wconversion logic
> src/share/vm/runtime/arguments.cpp:
> * Updated after the recent changes to SERIAL/INCLUDE_ALL_GCS (8005915)
> Thanks,
> Mikael
> On 2/21/2013 7:16 PM, David Holmes wrote:
>> 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

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