CS335 IITK Compiler Project

Description

This project aims to develop a compiler for C language as a part of the course CS335 Compiler Design.

NOTE: To run the code for the respective Milestone, please checkout the tags. Future versions are not supposed to be backwards compatible.

Milestone 1

TAG: lexer

We develop a scanner using lex and yacc, which takes as input any C program and generates a table of tokens along with the corresponding lexeme, line no and column no of the token as output. We use the specifications for scanner and parser as mentioned in the problem statement.

We test it using the testcases present in the tests/ sub-directory. The procedure to build and run the program is as follows: ```bash $ mkdir bin $ cd src $ make $ cd .. $ ./bin/lexer tests/testlexer1.c -o out_file

Any of the files having name testlexer*.c can be used

-o flag redirects the output to the out_file

```

Milestone 2

TAG: parser

We implemented the parser for an (extended) ANSI C version which outputs a dot file which can then be visualized using any standing dot file viewer. We expect ply and graphviz to be installed (can be setup using pip install -r requirements.txt).

We test it using the testcases present in the tests/ sub-directory. The procedure to run the program is as follows: ```bash $ python src/parser/parser.py tests/testparser1.c --trim -o ast.dot

--trim produces a smaller AST meant for humans (though it preserves all the important information needed)

-o is used to redirect output to a file

Both are optional

```

How to visualize the AST: bash $ dot -Tps AST.dot -o AST.ps $ xdg-open AST.ps

Milestone 3

TAG: semantics

Continuing with our Python based implementation of the parser in Milestone 2, we have now added the functionality for symbol table and semantic checks. Now, our program generates ASTs that are consistent with semantic checking. We expect the requirements mentioned in the requirements.txt to be installed (can be setup using pip install -r requirements.txt).

We test it using the testcases present in the tests/ sub-directory. The procedure to run the program is as follows: ```bash $ python src/parser.py tests/testsemantics1.c -o ast.dot

-o is used to redirect output to a file (optional parameter)

How to visualize the AST: bash $ dot -Tps AST.dot -o AST.ps $ xdg-open AST.ps ```

Miscellaneous

How to move from C yacc -> Python PLY yacc in < 1 mins?

It is pretty simple actually :o. Use the helper src/parser/yacc_to_ply.py file, which converts the c_yacc.y file present in that directory to the corresponding ply format. Finally, if visual aesthetics is important for you, run black -l 79 ./src/parser/ply_file.py.

Design Details

• Column and Line Numbers start from 1

• Features supported by the lexer in addition to the standard C specifications:

  • Inheritance
    • public, protected, private have been added as keywords.
    • <- is used to define inheritance. class Car <- public Vehicle is equivalent to the C++ declaration of class Car : public Vehicle.
    • To declare variables as public, protected, private they need to be enclosed in {} instead of the traditional : notation in C++.

How to use the SymbolTable?

• Initialize with a parent. Global Table has no parent
• insert: Takes an entry (dict), refer to the code to see what fields are needed for each kind of identifier. All these fields are mandatory. Additionally a kind (int) variable must be passed to indicate what type of identifier is it (see the top of SymbolTable to find out the exact numbers).
• check_type: Whether typename (str) is a valid type.
• translate_type: For mental sanity we shall replace struct ___/union ___ with a typedef. Call this function to get this typedef"ed" type.
• lookup: Returns a list/dict if the symbol being searched is found in the current table / it's parents
• display: Pretty Printing