Compiler Construction CS 606 Sohail Aslam Lecture 1

2 Course Organization  General course information  Homework and project information

3 General Information InstructorSohail Aslam Lectures45 TextCompilers – Principles, Techniques and Tools by Aho, Sethi and Ullman

4 Work Distribution  Theory homeworks = 20% exams = 40%  Practice build a compiler = 40%

5 ProjectProject Implementation  language: subset of java  Generated code: Intel x86 assembly  Implementation language: C++  Six programming assignments

6 Why Take this Course Reason #1: understand compilers and languages  understand the code structure  understand language semantics  understand relation between source code and generated machine code  become a better programmer

7 Why Take this Course Reason #2: nice balance of theory and practice  Theory mathematical models: regular expressions, automata, grammars, graphs algorithms that use these models

8 Why Take this Course Reason #2: nice balance of theory and practice  Practice Apply theoretical notions to build a real compiler

9 Why Take this Course Reason #3: programming experience  write a large program which manipulates complex data structures  learn more about C++ and Intel x86

10 What are Compilers  Translate information from one representation to another  Usually information = program

11 ExamplesExamples  Typical Compilers: VC, VC++, GCC, JavaC FORTRAN, Pascal, VB(?)  Translators Word to PDF PDF to Postscript

12 In This Course We will study typical compilation:  from programs written in high- level languages to low-level object code and machine code

13 Typical Compilation High-level source code Compiler Low-level machine code

14 Source Code int expr( int n ) { int d; d = 4*n*n*(n+1)*(n+1); return d; }

15 Source Code  Optimized for human readability  Matches human notions of grammar  Uses named constructs such as variables and procedures

16 Assembly Code. globl _expr _expr: pushl %ebp movl %esp,%ebp subl $24,%esp movl 8(%ebp),%eax movl %eax,%edx leal 0(,%edx,4),%eax movl %eax,%edx imull 8(%ebp),%edx movl 8(%ebp),%eax incl %eax imull %eax,%edx movl 8(%ebp),%eax incl %eax imull %eax,%edx movl %edx,-4(%ebp) movl -4(%ebp),%edx movl %edx,%eax jmp L2.align 4 L2: leave ret

17 Assembly Code Optimized for hardware  Consists of machine instructions  Uses registers and unnamed memory locations  Much harder to understand by humans

18 How to Translate Correctness: the generated machine code must execute precisely the same computation as the source code

19 How to Translate  Is there a unique translation? No!  Is there an algorithm for an “ideal translation”? No!

20 How to Translate  Translation is a complex process  source language and generated code are very different  Need to structure the translation