RFR (sh/jdk11): Relax Shenandoah/C2 verifier against JDK11 shortcomings

[Roman Kennke]

We determined (on IRC) that the check for null-inputs doesn't do
anything useful in post-LRB-world: there are no barriers directly
feeding into intrinsics, and therefore doesn't make a difference whether
or not the input comes as not-null-type or not. Let's remove the test in
sh/jdk11 to make nightlies happy, and also in -dev:

updated webrev:
http://cr.openjdk.java.net/~rkennke/jdk11-c2-verifier-fixes/webrev.01/

Bug for -dev:
https://bugs.openjdk.java.net/browse/JDK-8228775

or we can fix it in jdk/jdk real quick first, then cherry-pick it to
sh/11. What do you think?

Roman

> On 7/30/19 12:28 AM, Roman Kennke wrote:
>> - A couple of intrinsics are a bit careless and don't check+cast their
>> inputs to not-null. Our verifier doesn't like. Let's special-case them
>> and silence the verifier. (We might want to fix the cases via jdk11u
>> properly.)
> 
> I understand this is missing in 11u?
>  https://bugs.openjdk.java.net/browse/JDK-8209684
> 
>> http://cr.openjdk.java.net/~rkennke/jdk11-c2-verifier-fixes/webrev.00/
> 
> Please put "TODO:" in the comments, and maybe reference the bug above?
>