RFR: 8264271: Avoid creating non_oop_word oops

[Stefan Karlsson]

On Mon, 29 Mar 2021 02:17:21 GMT, Kim Barrett <kbarrett at openjdk.org> wrote:

>> Some parts of the JVM puts an marker to show that a location does not contain a valid oop. The code that handles this typically look like this:
>> 
>> oop* p = ...
>> if (*p != Universe::non_oop_word())
>> 
>> This means that sometimes the *p will create an oop that contains the non_oop_word. This makes it problematic to add stricter oop verification. I propose that we add a new function that checks the value of locations without converting it to an oop. 
>> 
>> (Note: I'm testing the new dependent pull Skara feature with this PR. It builds depends on the pr/3214 branch)
>
> Looks good.

Thanks, Kim. Now lets see what happens now that #3214 has been updated ...

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PR: https://git.openjdk.java.net/jdk/pull/3215