1. 410/510 1 of 20 Week 1 – Lecture 1 Introduction The Textbook Assessment Programming & Tools A v. small compiler Compiler Construction

2. 410/510 2 of 20 The Big Picture In this course we will be constructing a compiler! Moving from a High Level Language to a Low Level Language Compilers are complex programs –> 10,000 lines of code Integrate aspects from many different areas of CS –Formal language theory, algorithms, data structures, HLL & LLL (obviously), user interaction (error reporting)

3. 410/510 3 of 20 What is a compiler? A specialization of a language translator Usually in CS: – the Source is a high level programming language –the Target is a machine code for a micro-processor L1L2 SourceTarget Cx86 processor

4. 410/510 4 of 20 Applications of Compiler Techniques Potential Source languages include: –Natural languages (English, French,….) –Circuit layout languages –Mark-up languages (HTML, XML, …) –Command line languages (SQL interface) Potential Target languages include: –Natural languages –Printer drivers –Markup languages e.g. HTML to RTF converter –Could involve many of the aspects we will cover in compiler construction

5. 410/510 5 of 20 Compilers for Programming Languages If we had 1 compiler for each {Source,Target} pair then we would have a lot of compilers! Source LanguagesTarget Languages Compilers C Prolog Java Lisp Haskell C++ C# Fortran Pascal Sather x86 (MMX) JVM PowerPC 750 (G3) ARM SPARC AMD K6

6. 410/510 6 of 20 Modularity for Code Generation Compilers x86 ARM G4 Source Intermediate Representation  Compiler portability (man gcc – lists different target machines)

7. 410/510 7 of 20 Modularity for Source Languages? Compilers Intermediate Representation Sources Targets C Java Prolog Typically compilers only compile one source language – but the techniques used are very similar and are shared across different compilers

8. 410/510 8 of 20 Typical Compiler Intermediate Representation SourceTarget Front-endBack-end Independent of Source and Target languages AnalysisSynthesis For a new Source language – we can add a new front-end to an existing back-end For a new Target language – we can add a new back-end to an existing front-end course nowweek12  Ideally:

9. 410/510 9 of 20 Front End Knowledge about the source language –Lexical structure (tokens) –Syntax Programming constructs –Conditionals, iteration etc –Semantics Type checking Error-reporting –UI component Often basic (and unhelpful!) May vary if part of an IDE or standalone Source program Lexical analyser Syntax analyser Semantic analyser Symbol table Error Handler

10. 410/510 10 of 20 Back-end Knowledge about target processor / virtual machine –Instruction set ‘costs’ of different: –op-codes –instructions –Registers –Memory Semantic analyser Intermediate code generator Code optimiser Code generator Symbol table manager Error handler

11. 410/510 11 of 20 Putting it together Source program Lexical analyser Syntax analyser Semantic analyser Symbol table Error Handler Intermediate code generator Code optimiser Code generator Compiler Skeletal source program preprocessor compiler assembler Loader link-editor Target asse mbly program Relocatable machine code Absolute machine code Source program A language-processing system

12. 410/510 12 of 20 The Textbook Compilers: principles, techniques & tools Aho, Sethi & Ullman Addison-Wesley {‘The Dragon Book’}

13. 410/510 13 of 20 Assessment Building a compiler for a new language Front-end –Lexical analysis –Parsing Back end –Generating assembler code Some formal and some practical –Formal more at the front-end

14. 410/510 14 of 20 Programming & Tools Lexical analysis generator – lex / flex Parser generator – yacc / bison C / C++ –To implement the remainder of the compiler Unix environment –make files will be useful for coordinating lex and yacc

15. 410/510 15 of 20 History of Compilers Grace Hopper –A-0 1952 –B-0 (Flow-Matic) 1956 Fortran compiler – 1957 –(in the top 10 algorithms of 20 th century) –(also, quicksort, fast fourier transforms, simplex LP,..) BC (before compilers) –Low-level programming –Assemblers were a major advance Q: can an automatic translation to low-level languages be as efficient as writing it directly? The only way to show this was to do it - and the Fortran compiler provided a clear ‘yes’ answer

16. 410/510 16 of 20 Instant Compilation Consider the program: main() { int a = 3; a = a + 1; } Given a reasonably sensible assembly language a hand- compilation might be: LDA #3 STA 1 LDA 1 ADD a, #1 STA 1

17. 410/510 17 of 20 & an Instant Compiler could look like … Switch( source_code_construct ) { case INT_DEC: print( “LDA #”, INT.value) print(“STA 1”) break case INT_ADD: print(“LDA 1”) print(“ADD a,#”, ADD.value) print(“STA 1”) break } /* end switch */

18. 410/510 18 of 20 The Problems …. Not efficient, (LDA #4; STA 1) Only works for 1 variable Only works at one location in memory –(usually let assembler deal with symbolic addresses) Only has 2 programming constructs! Not even slightly portable: – 1 instruction set & 1 source language

19. 410/510 19 of 20 More problems… No error reporting –type checking? Assumes: –Program is correct –Recognition of programming language constructs int a = 3  INT_DEC –Access to values INT.value, ADD.value –1:1 relationship between integers and memory locations

20. 410/510 20 of 20 Solutions We can View compilers as a solution to all of these problems E.g. –Only compile correct programs to object code –Recognise all constructs in the language –Improve the efficiency of code Execution speed Memory usage –Meaningful error messages to the user –Cope with different target architectures

21. 410/510 21 of 20 Why are compilers called compilers? In early compilers one of the main tasks was connecting object program to –standard library functions, I/O devices collecting information from different sources(e.g. libraries) –OS and processor dependent This is now performed by ‘linkers’ Compile – ‘construct by collecting from different sources’