6601321: Assert(j == 1 || b->_nodes[j-1]->is_Phi(),"CreateEx must be first instruction in block")
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CreateEx nodes represents the incoming exception at an exception
handler and as such must be the first node in the block so that
register lifetimes are handled correctly. The lcm select logic always
places certain nodes as soon as it sees them, incuding the CreateEx,
but this only works correctly if the CreateEx is seen before other
high priority nodes. There is no explicit logic guaranteeing this
order though it almost always works out that way. The fix is to make
this explicit in the ordering of the worklist so that CreateEx is
always processed first if it exists.