Compiler Design Phases

Lexical Analysis: * Stream of characters in the source program is grouped into meaningful sequences called lexemes. Tokens are produced for each lexeme. A token is an abstract symbol generated during lexical analysis. * Generally, a token has an attribute value attached to it. It denotes the position of the variable in a symbol table. A symbol table is a table which stores information about an identifier and is referred at various stages of compilation. Syntax Analysis: * The syntax analyzer checks each line of the code and spots every tiny mistake that the programmer has committed while typing the code. The compiler follows a detailed procedure using the tokens creates by the lexical analyzer and creates a tree-like structure called the syntax tree. * The syntax analyzer checks whether the order of tokens conform to the rules of the programming language. Unmatched parenthesis, missing semicolons are some of the errors detected in this phase. * If there are no errors in the code, the syntax analyser successfully constructs a syntax tree which is later used by the semantic analyser. Semantic Analysis: * “Semantic” by definition is concerned with meanings.
A semantic analyser is mainly concerned with what the program means and how it executes. * Type checking is an important aspect of semantic analysis where each operator should be compatible with its operands. Intermediate Code Generation * A compiler may construct intermediate representations while converting a source program to a target program. * The representation should be easy to convert into a target language. It is then passed onto the second phase of compiler design: the synthesis phase. This phase involves the actual construction of target program and includes code optimisation and code generation.
Code Optimization * As the name suggests, this phase aims at optimising the target code. * The code can be optimised in terms of time taken to execute, length of the code, memory utilised or any other criteria. Code Generation * Target code is generated at this phase using the intermediate representation of the source program. * The machine instructions perform the same tasks as the intermediate code. Registers are allocated to variables in the program. * This has to be done carefully so as to avoid any clashes or repeated assignments. Various algorithms have been formulated to generate the most efficient machine code.