This aim of this project is to construct a compiler for Extended MiniJava language. The compiler is being constructed in various logical phases. The phases are defined as follows:
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Lexical Analysis: Separate a stream of characters into different tokens of the language which are described by using regular expressions. I constructed regular expressions to describe token types of eMiniJava and used it as input for JFlex to generate a Lexer.
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Syntax Analysis: We define a class hierarchy to represent nodes in the Abstract Syntax Tree (AST) for eMiniJava programs. This is used to create LL(1) version of context free grammar for eMiniJava. A recursive-descent Parser can parse LL(1) gramar in linear time to create an Abstract Syntax Tree.
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Name Analysis: In this phase, we map (multiple) occurrences of class, method and variable names in a program, to their (unique) definition.
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Type checking: In this phase, we enforce all the constraints not enforced already by the previous phases.
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Byte Code Generation: In this phase, the AST is convertde to intermediate code, which is utiliszed by Jasmin assembler to generate class files. The generated class files should be executable on the Java Virtual Machine.
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Optimization: We have implemented the following optimisations in our compiler:
a. Constant folding : Every expression which is made up of only constants can be evaluated at compile time. Further if a condition of an if or while statement can be folded to a bool literal, we can directly skip the if or else clause in an if statement and the whole body in a while statement. It can be done for any expression which has only constants as operands and for if and while loops. The correctness of the program is not affected as the value of the expression remains the same.
b. Using a branch construct: By using a branch construct for conditional expressions of control structures we are saving few byte code instructions. It can be used for all control structures which have a conditional expression. The
Command-line is the primary interface for users to interact with this compiler. The format of command-line interface is as follows:
emjc [options]
As of now, there are six possible options.
- ––help: Prints a synopsis of options
- ––pp: Pretty-prints the input file to the standard output
- ––lex: Generates output from lexical analysis as described in Assignment 2.
- ––ast: Generates output from syntactic analysis as described in Assignment 3.
- ––name: Generates output from name analysis as described in Assignment 4
- ––type: Generates output from type analysis
After executing the compiler with the option ––type for the source file filename.emj the compiler either accepts the program as a good eMiniJava program with printing out the following line:
Valid eMiniJava Program
Or, it prints out a set of errors (such as unknown identifier). Like the previous phases the format of an error message is the following:
: error: where and indicate the beginning position of the error, and details the error.