Compiler Design

Question

Consider the following instruction:

a= b +c * d + e - f * 25;

Now convert this high-level code snippet to low level (assembly language) code snippet by using

all the phases of a compiler.

Answer 1

I do not know what is expected of you, but this is what I did and did not do below.

I am not showing the lexical phase, as that would be too tedious.

I am assume the input stream is already tokenized.

I am showing the syntactic phase by the keyword "Scan" which gives the token scanned.

I am showing parsing by indicating what the compiler would "Push" on its stack

and what it would "Pop".

I am showing code generation using "Emit", which emits an instruction for a

hypothetical computer.

I am assuming the computer to have

- at least two registers R1 and R2,

- Instruction for "Load" and "Store" between memory and registers.

- Arithmetic instructions between a register and memory, overwriting the register.

I am not showing anything involving the symbol table; instead I am using the

variable names from the high level code in the generated instructions.

Scan 'a'

Push 'a' on the stack

Scan '='

Push '=' on the stack

Scan 'b'

Push 'b' on the stack

Scan '+'

Push '+' on the stack

Scan 'c'

Push 'c' on the stack

Scan '*'

Push '*' on the stack

Scan 'd'

Push 'd' on the stack

Scan '+'

Emit 'Load d into R1'

Pop 'd' from the stack

Pop '*' from the stack

Pop 'c' from the stack

Emit 'Mult R1,c into R1'

Pop '+' from the stack

Pop 'b' from the stack

Emit 'Add R1,b into R1'

Push 'R1' on the stack

Push '+' on the stack

Scan 'e'

Push 'e' on the stack

Scan '-'

Push '-' on the stack

Scan 'f'

Push 'f' on the stack

Scan '*'

Push '*' on the stack

Scan '25'

Push '25' on the stack

Scan ';'

Pop '25' from the stack

Emit 'Load 25 into R2'

Pop '*' from the stack

Pop 'f' from the stack

Emit 'Mult R2,f into R2'

Pop '-' from the stack

Pop 'e' from the stack

Emit 'Sub e,R2 into R2'

Pop '+' from the stack

Pop 'R1' from the stack

Emit 'Add R1,R2 into R1'

Pop '=' from the stack

Pop 'a' from the stack

Emit 'Store R1 into a'