Home | | Compiler Design | | Compiler Design | Target Machine

Target Machine - | Study Material, Lecturing Notes, Assignment, Reference, Wiki description explanation, brief detail |

Chapter: Principles of Compiler Design - Code Generation

Target Machine

Familiarity with the target machine and its instruction set is a prerequisite for designing a good code generator.

TARGET MACHINE

 

 Familiarity with the target machine and its instruction set is a prerequisite for designing a good code generator.

 The target computer is a byte-addressable machine with 4 bytes to a word.

 It has ngeneral-purpose registers, R0, R1, . . . , Rn-1.

 It has two-address instructions of the form:

 

o op source, destination

o       where, opis an op-code, and sourceanddestinationaredatafields.

 

·                                                     It has the following op-codes :

o       MOV (move sourcetodstination)


 

For example : MOV R0, M stores contents of Register R0 into memory location M.

 

Instruction costs :

 

  Instruction cost = 1+cost for source and destination address modes. This cost corresponds to the length of the instruction.

Address modes involving registers have cost zero.

 

Address modes involving memory location or literal have cost one.

 

  Instruction length should be minimized if space is important. Doing so also minimizes the time taken to fetch and perform the instruction.

 

For example : MOV R0, R1 copies the contents of register R0 into R1. It has cost one, since

 

occupies only one word of memory.

• The three-address statement a : = b + c can be implemented by many different instruction sequences :

 

i) MOV b, R0

 

ADD c, R0 cost = 6 MOV R0, a

 

ii) MOV b, a

ADD c, a cost = 6

 

iii) Assuming R0, R1 and R2 contain the addresses of a, b, and c : MOV *R1, *R0

ADD *R2, *R0 cost = 2

 

• In order to generate good code for target machine, we must utilize its addressing capabilities efficiently.

 

Study Material, Lecturing Notes, Assignment, Reference, Wiki description explanation, brief detail


Copyright © 2018-2021 BrainKart.com; All Rights Reserved. (BS) Developed by Therithal info, Chennai.