RFR: fix loop unswitching with -XX:-ShenandoahWriteBarrierMemBar

[Roman Kennke]

OK thanks a lot!!

Cheers, Roman


Am 2. Februar 2018 08:59:30 MEZ schrieb Roland Westrelin <rwestrel at redhat.com>:
>
>> But it may affect compiler optimizations? Or if something went wrong,
>> inhibit them?
>
>I checked that the optimizations that happen after the write barrier is
>expanded trigger ShenandoahWriteBarrierMemBar on/off correctly trigger
>with simple test cases.
>
>> True. But we have both observed a noticable regression. Better to
>> check it? No-membars will likely become the default/only path, so it
>> better be good ;-)
>
>I ran Compiler for longer (-f 10) a couple of times and results with
>ShenandoahWriteBarrierMemBar on/off are almost identical:
>
>-ShenandoahWriteBarrierMemBar: Compiler.compiler  thrpt  100  384.413 ±
>11.802  ops/min
>+ShenandoahWriteBarrierMemBar: Compiler.compiler  thrpt  100  384.253 ±
>10.919  ops/min
>-ShenandoahWriteBarrierMemBar: Compiler.compiler  thrpt  100  382.996 ±
>10.339  ops/min
>+ShenandoahWriteBarrierMemBar: Compiler.compiler  thrpt  100  385.405 ±
>10.961  ops/min
>
>Roland.

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