RFR (S) 8140685: Fix backtrace building to not rely on constant pool merging

[Coleen Phillimore]

On 1/24/17 10:09 AM, Lois Foltan wrote:
> Looks good Coleen.

Thank you!
Coleen

> Lois
>
> On 1/23/2017 6:00 PM, Coleen Phillimore wrote:
>> Summary: Store Symbol* for the name in the backtrace
>>
>> There was some thought that storing a u2 for cpref would be more 
>> memory efficient than storing Symbol* in the backtraces, but recent 
>> runs of Jetty show that this doesn't cause footprint increases or 
>> performance decreases.   Storing the Symbol* for the method name 
>> guarantees it is there when creating the StackTraceElement, whereas 
>> cpref relies on constant pool merging for redefinition and is 
>> dependent on being an index in the right constant pool, which has 
>> been a source of bugs in the past.
>>
>> dev-submit performance testing was run with no regressions. Also, all 
>> hotspot jtreg tests were run.
>>
>> This is a change for JDK10 whenever that opens.
>>
>> open webrev at http://cr.openjdk.java.net/~coleenp/8140685.01/webrev
>> bug link https://bugs.openjdk.java.net/browse/JDK-8140685
>>
>> Thanks,
>> Coleen
>