5. A computer program product for USING range validation during assembly of an assembly language program, the computer program product comprising: a non-transitory computer readable storage medium comprising a storage device having computer readable program code embodied therewith, the computer readable program code comprising: computer readable program code for parsing assembler language source code loaded for assembly in an assembler executing in memory of a computer; computer readable program code for identifying a USING statement in the source code establishing a base address as the content of a register; and, computer readable program code for responding to additionally identifying a subsequent statement in the source code modifying the content of the register, by generating a warning of an invalid USING range, determining that the subsequent statement modifies the content of the register to a value consistent with an address but an address that differs from the base address identified by the USING statement and including in the warning text that the register had been the subject of a USING statement and has been directed to hold a value that is a different address than that specified by the USING statement.
5. A computer program product for USING range validation during assembly of an assembly language program, the computer program product comprising: a non-transitory computer readable storage medium comprising a storage device having computer readable program code embodied therewith, the computer readable program code comprising: computer readable program code for parsing assembler language source code loaded for assembly in an assembler executing in memory of a computer; computer readable program code for identifying a USING statement in the source code establishing a base address as the content of a register; and, computer readable program code for responding to additionally identifying a subsequent statement in the source code modifying the content of the register, by generating a warning of an invalid USING range, determining that the subsequent statement modifies the content of the register to a value consistent with an address but an address that differs from the base address identified by the USING statement and including in the warning text that the register had been the subject of a USING statement and has been directed to hold a value that is a different address than that specified by the USING statement. 6. The computer program product of claim 5 , further comprising: computer readable program code for identifying a different subsequent statement in the source code modifying the content of the register; computer readable program code for responding to the identification by generating a warning of an invalid USING range, determining that the different subsequent statement modifies the content of the register to a value not consistent with an address, computer readable program code for including in the warning text that the register had been the subject of a USING statement and has been directed to hold a value that is not an address.