AMD x86 manual Execution Unit Resources, Terminology, Operands, Results, Examples

AMD Athlon™ Processor x86 Code Optimization

Execution Unit Resources

22007E/0 — November 1999

Terminology

	The execution units operate with two types of register values—
	operands and results. There are three operand types and two
	result types, which are described in this section.
Operands	The three types of operands are as follows:
	■ Address register operands—Used for address calculations of
	load and store instructions
	■ Data register operands—Used for register instructions
	■ Store data register operands—Used for memory stores
Results	The two types of results are as follows:
	■ Data register results—Produced by load or register
	instructions
	■ Address register results—Produced by LEA or PUSH
	instructions
Examples	The following examples illustrate the operand and result
	definitions:
	ADD	EAX, EBX
	The ADD instruction has two data register operands (EAX
	and EBX) and one data register result (EAX).
	MOV	EBX, [ESP+4*ECX+8]	;Load
	The Load instruction has two address register operands
	(ESP and ECX as base and index registers, respectively)
	and a data register result (EBX).
	MOV	[ESP+4*ECX+8], EAX	;Store

The Store instruction has a data register operand (EAX) and two address register operands (ESP and ECX as base and index registers, respectively).

LEA ESI, [ESP+4*ECX+8]

The LEA instruction has address register operands (ESP and ECX as base and index registers, respectively), and an address register result (ESI).

148 Execution Unit Resources