Dependent USINGs

The format of the assembler USING instruction now lets you specify a relocatable expression instead of a base register in the instruction operand. When you specify a relocatable expression, it is known as the supporting base address, and the USING is known as a dependent USING. If a valid ordinary symbol, or a variable symbol that has been assigned a valid ordinary symbol, is specified in the name entry of a dependent USING instruction, the USING is known as a labeled dependent USING.

A dependent USING depends on the presence of one or more corresponding ordinary or labeled USINGs to resolve the symbolic expressions in the dependent USING range.

Dependent USINGs provide you with further control over the resolution of symbolic expressions into base-displacement form. With dependent USINGs you can reduce the number of base registers you need for addressing by using an existing base register to provide addressability to the symbolic address.