三地址指令和二地址指令的区别

先决条件 – 指令格式
1. 三地址指令：
三地址指令是机器指令的一种格式。它有一个操作码和三个地址字段。一个地址字段用于目的地，两个地址字段用于源。

例子 –

X = (A + B) x (C + D) 

解决方案：

ADD R1, A, B      R1 <- M[A] + M[B]
ADD R2, C, D      R2 <- M[C] + M[D]
MUL X, R1, R2     M[X] <- R1 x R2 

2. 二地址指令：
二地址指令是机器指令的一种格式。它有一个操作码和两个地址字段。一个地址字段是通用的，可用于目标或源，其他地址字段用于源。

例子 –

X = (A + B) x (C + D) 

解决方案：

MOV R1, A      R1 <- M[A]
ADD R1, B      R1 <- R1 + M[B]
MOV R2, C      R2 <- M[C]
ADD R2, D      R2 <- R2 + D
MUL R1, R2     R1 <- R1 x R2
MOV X, R1      M[X] <- R1 

三地址指令和双地址指令的区别：

THREE-ADDRESS INSTRUCTION	TWO-ADDRESS INSTRUCTION
It has four fields.	It has three fields.
It has one field for opcode and three fields for address.	It has one field for opcode and two fields for address.
It has long instruction length.	It has shorter instruction.
It is slower accessing location inside processor than memory.	It is faster accessing location inside processor than memory.
There is distinct address fields for destination and source.	There is one address field common for destination and source.
In 3-address format, destination address can not contain operand.	While in 2-address format, destination address can have operand.
In 3-address format, instructions are less.	While in 2-address format, instructions are more.
It generally requires three memory access.	It generally requires two memory access but in some cases it requires three memory access too.
In 3-address format, three memory access is required.	While in 2-address format, it eliminated three memory access but not completely.