8025728: Missing volatile specifier for field G1AllocRegion::_alloc_region Summary: The field G1AllocRegion::_alloc_region needs to be declared volatile as it is used with that intention. Otherwise the compiler may generate the code that reloads the value which might have changed in the meantime, leading to spurious crashes. Reviewed-by: iveresov, simonis, tschatzl Contributed-by: Axel Siebenborn <axel.siebenborn@sap.com>