RFR: 8254793: [JVMCI] improve speculation encoding [v4]

[Doug Simon]

On Fri, 16 Oct 2020 16:56:01 GMT, Tom Rodriguez <never at openjdk.org> wrote:

>> Doug Simon has refreshed the contents of this pull request, and previous commits have been removed. The incremental
>> views will show differences compared to the previous content of the PR.
>
> src/hotspot/share/jvmci/jvmciRuntime.hpp line 55:
> 
>> 53:   FailedSpeculation** _failed_speculations;
>> 54:
>> 55:   // A speculation id is an index (high 26 bits) and a length (low 5 bits).
> 
> We don't really have to enforce that it fits in an int any more.  I think it would be more natural to allow to use all
> the remaining bits even though we'll never actually use that space in practice.  Doing so makes the code look a little
> odd I think since there's no obvious reason for limit.  We just want an encoding that's int friendly for the normal
> case.

All good points. Please confirm that 2 most recent commits to this PR align with your suggestions.

-------------

PR: https://git.openjdk.java.net/jdk/pull/667