RFR(XXS): 8135179: Fix conversion warning after 8067341

[Volker Simonis]

On Thu, Sep 10, 2015 at 11:17 AM, Thomas Schatzl
<thomas.schatzl at oracle.com> wrote:
> Hi,
>
> On Tue, 2015-09-08 at 18:56 +0200, Volker Simonis wrote:
>> Hi,
>>
>> can somebody please review and sponsor the following trivial fix:
>>
>> http://cr.openjdk.java.net/~simonis/webrevs/2015/8135179/
>> https://bugs.openjdk.java.net/browse/JDK-8135179
>>
>> Change "8067341: Modify PLAB sizing algorithm to waste less"
>> introduced the following code:
>>
>> size_t const cur_plab_sz = (double)total_waste_allowed /
>> G1LastPLABAverageOccupancy;
>>
>> which triggers a conversion warning with older versions of GCC and
>> potentially other compilers as well:
>>
>> hotspot-rt/src/share/vm/gc/g1/g1EvacStats.cpp: In member function
>> 'virtual void G1EvacStats::adjust_desired_plab_sz()':
>> hotspot-rt/src/share/vm/gc/g1/g1EvacStats.cpp:96: warning: converting
>> to 'size_t' from 'double'
>> make[4]: *** [g1EvacStats.o] Error 1
>>
>> The warning can be easily fixed as follows:
>>
>> size_t const cur_plab_sz = (sizte_t)((double)total_waste_allowed /
>> G1LastPLABAverageOccupancy);
>
>   looks good. Thanks for the fix. I can push the change.
>

Hi Thomas,

thanks a lot for your help.

Regards,
Volker

>> Thank you and best regards,
>> Volker
>>
>>
>> PS: as a side note I want to mention that we are currently disabling
>> '-Wconversion' for GCC 4.3 and later because it produces too many
>> warnings which are by default treated as errors. All the warnings
>> produced by '-Wconversion' are about narrowing conversions which may
>> result in a potential data loss.
>>
>> It may be a good idea to fix all these implicit narrowing conversions
>> and re-enable -Wconversion warning by default.
>>
>> But unfortunately there's quite some code which has to be changed in
>> order to meet the requirements of '-Wconversion'. A quick research
>> showed that there are currently 137 different implicit narrowing
>> conversions spread over 1785 different code locations.
>>
>> For more details see "8135181: Re-enable '-Wconversion' for GCC 4.3
>> and later" (https://bugs.openjdk.java.net/browse/JDK-8135181) which
>> I've opened to track the issue.
>>
>> What's the general opinion? Would it be worth wile to fix all these
>> conversion warnings by inserting implicit casts?
>
> I would think so that the goal is to gradually enable more warnings. I
> guess it has been turned off because nobody stepped up fixing these
> issues. :)
>
> Thanks,
>   Thomas
>
>