RFR: 8254793: [JVMCI] improve speculation encoding [v5]

[Vladimir Kozlov]

On Sun, 18 Oct 2020 21:51:23 GMT, Doug Simon <dnsimon at openjdk.org> wrote:

>> This PR changes the encoding of a `jdk.vm.ci.hotspot.HotSpotSpeculationLog.HotSpotSpeculation` from a long to an int.
>> The `Thread::_pending_failed_speculation` field remains as a `jlong` since it is already exposed to JVMCI Java code
>> already via VMStructs and this PR does not update its usage in Graal.
>
> Doug Simon has updated the pull request incrementally with two additional commits since the last revision:
> 
>  - require SHA1 algorithm to be present
>  - simplified changes such that only the length component of an encode speculation is reduced (to 5 bits)

Still good.

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Marked as reviewed by kvn (Reviewer).

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