Compiler is a computer program that has the capacity to translate high-level language into a machine language/ low-level language that is readable to the computer. The high-level language is know as source while the low-level language is known as machine code.
Computers usually read instructions in machine language format written in binary. A binary is string of numbers made up of 0s and 1s. Computers can’t understand human readable languages and humans many not also understand computer language (machine). Therefore programmers work with the programming language the have understanding of, which can then be translated to the machine language which the computer can understand. Compilers do the job of translating high-level (human-readable) language machine (computer-readable) language.
Program Sources Code Analysis
Source code can be analyzed in three main steps. They are:
Linear analysis, hierarchical analysis and semantic analysis
Linear Analysis
In linear analysis, the source code characters are read from
left to right. The characters are therefore grouped according to their
collective meanings, and the groups are called tokens.
Hierarchical Analysis
Having grouped the source codes according to collective meaning
known as tokens, the tokens are further divided in order of hierarchy in a
nested manner.
Semantic Analysis
Semantic analysis involves checking if the source code
components are appropriate in meaning.
Compiler Structures
The steps in the analysis of source code are further taken
in phases, which determine the structure of the program language code. In the compilation
process, output of each step becomes the input for the next step. The following
are the phases or structures of the compilation process: lexical analyzer,
syntax analyzer, semantic analyzer, intermediate code generator (ICG), code optimizer,
target code generator
Lexical Analyzer
Also known as scanner, Lexical Analyzer takes the high-level
language sources code as the input, scans the source code characters from left
to right, groups them into lexemes (groups of characters with same meaning)
forming tokens. It removes white spaces and comments, and check deletes the
lexical errors.
Syntax Analyzer
The output of lexical analyzer is the input of syntax
analyzer, also known as Parser. The syntax analyzer checks for syntax errors in
the source code. It does this by constructing a parse tree of all the tokens. The
parse tree must be according to the rules of th source code grammar for the
syntax to be correct. The grammar for the codes is also context-free grammar.
Semantic Analyzer
The output of parse tree of the syntax analyzer acts as the
input in semantic analyzer. It does the following to the parse tree output:
- verifies the parse tree,
- checks for validity of the programming language source code such as compatibility of data types, declaration and initialization of variable, and so on.
- creates a verified parse tree called annotated parse tree, and
- finally performs flow checking , type checking etc.
Intermediate Code Generator (ICG)
This generates an intermediate code. The intermediate code
is a code that is neither high-level language nor machine language. All compilers
have same intermediate code. The intermediate code is converted to the machine
language according to the platform.
Code Optimizer
This coverts and optimizes the intermediate code such that
it is executed faster using less resources such as CPU, memory. It deletes any
meaningless lines of code and rearranges the code, but the meaning of the
source code remains unchanged.
Target Code Generator
This is the finally phase of compiler structuring and
compilation.
It generates a machine code of the optimized intermediate
code. This machine code is relocatabe. Relocatabe machine code can be loaded and run at any time.
Sections of Compiler
The phases of compilation process is divided into two
sections:
1 Frond End
The frond end section of compiler comprises of lexical
analysis, syntax analysis, and intermediate code generation.
2 Back End
The back end is made up of
the code optimization, and target code generation.
Features of a Compiler
- A compiler has the following features:
- Independence
- Error detection
- Optimization
- Data security
- Speed
Types of Compiler
There are four types of compiler
Bootstrap Compilers
The bootstrap compilers are written in a programming
language they have to compile
Cross Compilers
These compilers generate executable machine language code
for a platform. This platform is different from the platform on which the
compiler is running.
Source to Source or Trancompilers
These types of compilers convert the source code of one
programming language to source code of another programming language.
Decompiler
As the name implies, this is the reverse of compiler. It convert machine code into high-level language
Applications/ Uses of Compilers
Compilers have the following uses:
They generate executable code files
Translate code from one language to another.
Make the code independent of the platform
Debug the code of syntax and semantic errors.
Read also: Advantages and Disadvantages of Compiler