RFR: 8220411: Remove ScavengeRootsInCode=0 code

[Stefan Karlsson]

Updated webrev after some offline feedback from ErikÖ:

  http://cr.openjdk.java.net/~stefank/8220411/webrev.02.delta
  http://cr.openjdk.java.net/~stefank/8220411/webrev.02

- I've removed can_be_constant and updated the code where it was used.
- Removed and replaced check_oop with oopDesc::is_oop_or_null checks.

Thanks,
StefanK

On 2019-03-11 09:57, Stefan Karlsson wrote:
> Hi all,
> 
> Please review this patch to remove code that checks and acts upon 
> ScavengeRootsInCode=0.
> 
> http://cr.openjdk.java.net/~stefank/8220411/webrev.01/
> https://bugs.openjdk.java.net/browse/JDK-8220411
> 
> Since a while now, we have not supported -XX:ScavengeRootsInCode=0, and 
> the code actively sets it to 1 if the user passes in 0. This patch 
> removes the actual code, there's another RFE to deal with changing the 
> argument handling to explicitly not support that the flag is set to 0. 
> See: JDK-8144954.
> 
> My main motivation for this patch is to get rid of some of the usages of 
> CollectedHeap::is_scavengable. The intention is that later patches will 
> completely remove that function.
> 
> Thanks,
> StefanK