As comments said, for negative value, the arithmetic  over-shift-right should return -1. So here it should be signed-extended, when bitwidth larger than 64.
As comments said, for negative value, the arithmetic 
over-shift-right should return -1. So here it should be signed-extended,
when bitwidth larger than 64.

test case: llvm/test/ExecutionEngine/2008-06-05-APInt-OverAShr.ll


git-svn-id: 0ff597fd157e6f4fc38580e8d64ab130330d2411@51999 91177308-0d34-0410-b5e6-96231b3b80d8

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