Compiler Construction Composed By, Muhammad Bilal Qureshi

2 Introduction  Book:Compilers Principles, Techniques, and Tools by Alfred V.Aho, Ravi Sethi, Jeffery D.Ullman  References: Introduction to computer theory Automata theory by Daniel I.A. Cohen  Pre Requisite: Theory of Automata Course Information

3 Introduction  Slides are only brief discussion about the topic. Consult book and lecture notes for complete details. Don’t depend on slides only.  No extension in assignments deadline will be allowed. Strictly follow timeline to get good marks.  Seniors (if any) and juniors are treated equally. No credit will be given on seniority basis.  Internal marks will be awarded as actual. No annoying query about marks will be entertained at the end of the course.  Ensure your presence during the lecture to avoid attendance shortage.  Golden Policy: No class miss – No course headache Class and Evaluation Policy

4 Introduction  Computer Program: A self-contained set of instructions used to operate a computer to produce a specific result.  Programming Language: A set of instructions that can be used to construct a program.  Low-Level Languages use instructions that are directly tied to one type of computer. Programs written in such language are fastest in execution. E.g., Assembly, Machine language,…  High Level Languages use instructions that resemble written languages (e.g., English language). Examples are C, C++, Fortran,…  Source Code/Source Program: Programs written in a computer language (high or low level).  Once a program is written in a high level language be translated in to machine language of that computer on which it will run. This translation can be accomplished in two ways: Interpretation or Compilation. Introduction

5  Interpreter: When each statement in a high level source program is translated individually and executed immediately upon translation, the program doing the translation is called as Interpreter.  Compiler: When all of the statements in a high level source program are translated as a complete unit before anyone statement is executed, the program doing this translation is called as compiler.  Source program may be converted into an executable file (executable program) by a compiler and later on executed by a CPU.  A compiler is a computer program (or set of programs) that transform source code written in a programming language (the source program) into another computer language (the target language having a binary form known as object code or machine code). Introduction

6 Simple taxonomy of compilation process: Source Code Object Code  The main role of compiler is to report any errors in the source program that it detects during the compilation process. (e.g. a missing semicolon at the end of a statement) Introduction Compilation Process Executable Code (extension is.exe) Linked with different libraries (.h,.lib, etc) Group of compilation phases (human readable) (extensions are.c,.cpp, etc) (Non-executable machine code) (extension is.obj)

7 Introduction  Compilation process operates as a sequence of phases each of which transforms one representation of the source program to another.  Two-Pass Compiler:  Front End: Recognizes legal and illegal programs presented to it. Consists of two modules: Scanner & Parser. Introduction Front EndBack End Source Code Intermediate Representation Machine Code Report errors if any

8 Introduction  Scanner: Maps the source code/source program character stream into words. It produces pairs (tokens) that consist of a word and its part of speech. Example: z = x – y It will be converted as; Tokens may be identifier, number, new, while, switch, if, +, -, / etc… Introduction ScannerParser Source Code Intermediate Representation Report errors if any Tokens Token Name Attribute Value

9 Introduction  Parser: Takes tokens as input, recognizes context-free syntax, report errors, and builds IR for the source program. It analysis the semantics like type checking. It builds a parse thus named parser. Parse can be represented by a tree called a parse tree.  Back End: Translates IR into target machine code. It selects instruction, allocate registers, and then schedule the instructions for execution. Introduction