VM doesn't generate implicit null check if there are empty blocks
between null test and uncommon_trap call.
Also VM specifies the holder of a tested oop in uncommon_trap's debug info
instead of passing NULL. This increase registers pressure.
Skip over empty blocks when looking for uncommon_trap
and add the missing offset check for compressed oops when
looking for an implicit null check opportunities.
Use NULL as value for a tested oop in uncommon_trap's debug info.