improve parfor get/setitem replacement
improve parfor get/setitem replacement

propagate setitem values from first block if loop body
to other blocks if the array is not changed later.

IntelLabs/numba,seibert/numba,cpcloud/numba,sklam/numba,numba/numba,stonebig/numba,seibert/numba,stuartarchibald/numba,gmarkall/numba,stonebig/numba,sklam/numba,IntelLabs/numba,stuartarchibald/numba,gmarkall/numba,stuartarchibald/numba,numba/numba,jriehl/numba,IntelLabs/numba,IntelLabs/numba,gmarkall/numba,stonebig/numba,stuartarchibald/numba,gmarkall/numba,stuartarchibald/numba,seibert/numba,numba/numba,numba/numba,jriehl/numba,stonebig/numba,gmarkall/numba,jriehl/numba,cpcloud/numba,sklam/numba,cpcloud/numba,jriehl/numba,numba/numba,jriehl/numba,cpcloud/numba,sklam/numba,seibert/numba,stonebig/numba,IntelLabs/numba,cpcloud/numba,seibert/numba,sklam/numba