[aarch64-port-dev ] RFR: 8189596: AArch64: implementation for Thread-local handshakes

[Andrew Haley]

It was quite tricky to get this one right.

Sime notes:

I deleted LIR_Assembler::poll_for_safepoint because it's dead code.

I set ThreadLocalHandshakes to true.  This follows x86-64 and is
probably the right thing to do, but it does have the disadvantage that
it considerably extends the time to safepoint for interpreted code
because we only poll at branches.  I think this is probably a bad
idea, but again it's the same as x86-64.  OTOH, checking the safepoint
bit at every bytecode would seriously bloat the interpreter.  Oh dear.

-- 
Andrew Haley
Java Platform Lead Engineer
Red Hat UK Ltd. <https://www.redhat.com>
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