DROP instruction
- Frees base registers previously assigned by the USING instruction for other programming purposes
- Ensures that the assembler uses the base register you want in a particular coding situation, for example, when two USING ranges overlap or coincide
- sequence_symbol
- Is a sequence symbol.
- base_register
- Is an absolute expression whose value represents one of the general registers 0 through 15. The expression in base_register indicates a general register, previously specified in the operand of an ordinary USING statement, that is no longer to be used for base addressing.
- label
- Is one of the following:
- An ordinary symbol
- A variable symbol that has been assigned a character string with a value that is valid for an ordinary symbol
The ordinary symbol denoted by label must be a symbol previously used in the name field of a labeled USING statement or a labeled dependent USING statement.
- address
-
Is a simply relocatable expression that represents an implicit address within the range of an active USING instruction. The range of an active USING is considered to be that which is valid for generating 12 bit displacements, or signed 20 bit displacements if the specified OPTABLE level includes support for instructions with displacements in this form.
This form ends the domain of the USING instruction used to resolve that address. If that instruction was an ordinary USING or a labeled (non-dependent) USING then any dependent USING based directly or indirectly on that USING instruction is also dropped. Any base registers from a dropped USING instruction which have already been dropped are ignored.
If no operand is specified for a DROP instruction, all active base registers assigned by USING instructions are dropped including ordinary, labeled, dependent and labeled dependent USING instructions.
- The assembler does not use the register or registers specified in the DROP instruction as base registers. A register made unavailable as a base register by a DROP instruction can be reassigned as a base register by a subsequent USING instruction.
- The label or labels specified in the DROP instruction are no longer available as symbol qualifiers. A label made unavailable as a symbol qualifier by a DROP instruction can be reassigned as a symbol qualifier by a subsequent labeled USING instruction.
FIRST
as
a symbol qualifier: DROP 7,11
DROP FIRST