RFR: 8214377: ZGC: Don't use memset to initialize array of ZForwardingTableEntry

[Per Liden]

Thanks for reviewing, Roman!

/Per

On 11/29/18 2:17 PM, Roman Kennke wrote:
> Looks good to me! It'll make my compiler happy(ier) :-)
> 
> Thanks, Roman
> 
>> Use placement new instead of memset() to avoid compiler warning/error
>> when using GCC 8 with -Werror=class-memaccess (memset to initialize
>> non-trivial object).
>>
>> To avoid any undefined behavior I also added a loop to destruct the
>> objects properly, but this loop will be compiled down to nothing.
>>
>> I ran SPECjbb2015 to see if the execution time for "Prepare Relocation
>> Set" was noticeably affected by this change (assuming memset does a
>> batter job than then loop), but I can't see any real difference. I'll
>> run a few more iterations over night just to make sure.
>>
>> Bug: https://bugs.openjdk.java.net/browse/JDK-8214377
>> Webrev: http://cr.openjdk.java.net/~pliden/8214377/webrev.0
>>
>> /Per
>