RFR: 8254264: Remove redundant cross_modify_fence()

[David Holmes]

On Wed, 14 Oct 2020 14:25:14 GMT, Patricio Chilano Mateo <pchilanomate at openjdk.org> wrote:

> Hi all,
> 
> Please review the following patch that removes some uneeded uses of cross_modify_fence() in common code, in particular
> from ~ThreadBlockInVM(), ~ThreadBlockInVMWithDeadlockCheck() and java_suspend_self_with_safepoint_check(). These fences
> were added before each JavaThread had to disarm itself (8230594). After a safepoint/handshake each JavaThread will
> always call SafepointMechanism::process_if_requested_slow() when transitioning out of the safe state and will execute a
> cross_modify_fence(). Tested with mach5 tiers1-7.  Thanks, Patricio

Marked as reviewed by dholmes (Reviewer).

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PR: https://git.openjdk.java.net/jdk/pull/655