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Compilers - COMP 3012
A compiler is a tool that maps one language into another language. It takes a program written in a source programming language and maps it to program written in a target programming language. A compiler is written in an implementation language.
Notation of semantics of program A: [\![A]\!]
An interpreter is a program that takes a source program and executes the program.
NOTE: Java uses both. A java source program is compiled into byte code (by a compiler) which is then executed by an interpreter (called java virtual machine - JVM). JVM will also compile fragments of code so that if there is a call back, it can execute the compiled code. This is called compilation on the fly.
Compilers will often use an intermediate representation (IR) to bridge the gap between the source language and the executable language. Converting source language to IR is called front end, where as converting IR to executable code is called back end.
- The front end focuses on understand the source-language program.
- The back end focuses on mapping programs to the target machine
- The front end, intermediate representation and the back end are all part of the compiler.
IR is stored as an Abstract Syntax Tree AST.
The syntactic details needed for parsing the source program are represented in the structure of the tree.
The IR could be broken down into many sub-steps i.e. a IR1 could be created which is then ran through an optimiser to create IR2 which is fed into the back end instead of IR1. This is called a three-phase compiler.
