1.2.2 (e. Stages of compilation (lexical analysis, syntax analysis, code generation and optimisation))

What stages does a compiler go through to convert source code to object code?

Lexical analysis​

Symbol table​

Syntax analysis​

Semantic analysis​

Code generation

What happens during lexical analysis?

- All unnecessary spaces and comments ​are removed​

- Keywords (e.g. print), constants and identifiers are replaced with tokens representing their function in the program

What is a lexer?

builds up a symbol table for every keyword and identifier in a program​

What is the symbol table?

helps to keep track of the run-time memory address for each identifier

What are the token classes?

Identifier​:Any function or variable name​

Keyword​:As If Else EndIf Function EndFunction Return​

Separator​:( ) &​

Operator​:+ - * / % ^ DIV MOD < <= > >=​

Literal​:Hello world​

Number​: -4 0 3.4​

Quote​: " "​

Bool​: True False​

Datatype​: Integer Decimal String Boolean

What is syntax analysis?

The process of splitting the stream of tokens into phrases, parsing them and recording the error if they are invalid

-If the phrase is not valid, an error will be recorded

What is semantic analysis?

Checks if syntactically correct statements are logically correct and can actually work in the program

What is code generation?

- Once the program has been checked, the compiler generates the machine code​

- It may do this in several 'passes' over the code because code optimisation will also take place

What is code optimisation?

Tweaking the code so it will run as efficiently as possible.

This might mean optimising the speed of execution or optimising for using as little memory as possible.

What are disadvantages of code optimisation?

- It will increase compilation time, sometimes quite

considerably

- it may sometimes produce unexpected results.