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Introduction to Compiler Construction
David Notkin Autumn 2008 Source Program [Higher-Level Programming Language] Compiler Target Program [Lower-Level Language/ Architecture] CSE
“Compiler”: from the web
- The Oxford English Dictionary (OED) indicates that the first usage of the term is circa 1330, referring to one who collects and puts together materials - They also note a usage “Diuerse translatours and compilaris” from Scotland in 1549
- Most dictionaries give the above definition as well as the computing-based definition (which the OED dates to 1953) - A program that translates programs written in a high-level programming language into equivalent programs in a lower- level language
- Wikipedia credits Grace Hopper with the first compiler (for a language called A-0) in 1952, and John Backus’ IBM team with the first complete compiler (for FORTRAN) in 1957 Trivia: In what year was I born? CSE401 Au08 2
A world with no compilers
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Assembly/machine language coding
- …is slow, error-prone, tedious, not portable, …
- The size (roughly, lines of code) of a high-level language program relative to its assembly language equivalent is approximately linear – but that may well be a factor of 10 or even 100 - Microsoft Vista is something like 50 million lines of source code (50 MLOC) - Printed double-sided something like triple the height of the Allen Center - Something like 20 person-years just to retype
- Q: Why is harder to build a program 10 times larger? CSE401 Au08 4
Ergo: we need compilers
- And to have compilers, somebody has to build compilers - At least every time there is a need to program in a new <programming language, architecture> pair - Roughly how many pl’s and how many ISA’s? Cross product?
- Unless the compilers could be generated automatically – and parts can (a bit more on this later in the course) Trivia: In what year did I first write a program? CSE401 Au08^ In what language? On what architecture? 5
But why might you care?
- Crass reasons: jobs
- Class reasons: grade in 401
- Cool reasons: loveliest blending of theory and practice in computer science & engineering
- Cruel reasons: we all had to learn it
- Practice reasons: more experience with software design, modifying software written by others, etc.
- Practical reasons: the techniques are widely used outside of conventional compilers
- Super-practical reasons: lays foundation for understanding or even researching really cool stuff like JIT (just-in-time) compilers, compiling for multicore, building interpreters, scripting languages, (de)serializing data for distribution, and more… CSE401 Au08 6
Better understand…
- Compile-time vs. run-time
- Interactions among
- language features
- implementation efficiency
- compiler complexity
- architectural features CSE401 Au08 7
Compiling (or related) Turing Awards
- 1966 Alan Perlis
- 1972 Edsger Dijkstra
- 1976 Michael Rabin and Dana Scott
- 1977 John Backus
- 1978 Bob Floyd
- 1979 Bob Iverson
- 1980 Tony Hoare
- 1984 Niklaus Wirth
- 1987 John Cocke
- 2001 Ole-Johan Dahl and Kristen Nygaard
- 2003 Alan Kay
- 2005 Peter Naur
- 2006 Fran Allen CSE401 Au08 8
Lexical analysis (scanning, lexing)
Source Program (^) scan; Analyze: parse Representation^ Intermediate t 6 : = Fa c. Co mp u t e Fa c ( t h i s , t 3 ) ; Scan (lexical analysis) Token Stream Character Stream 28 characters not counting whitespace name=t6,assign,name=Fac,period, name=ComputeFac,lparen,name=this, comma,name=t3,rparen,semicolon (11 tokens) CSE401 Au08 13
Syntactic analysis
name=^ name=t6,assign,name=ComputeFac,lparen,nameFac,period=this,, comma,name=t3,rparen,semicolon Assignment statement Lefthand side Identifier: t Righthand side invocation^ Method Method name QualifiedName Identifier: Fac Identifer ComputeFac: Parameter List Identifier: this Identifier: t Analyze: scan; parse Abstract syntax tree CSE401 Au08 14 statement^ Assign… Lefthand side Identifier : t Righthand side invocation^ Method Method name Qualified… Identifier: Fac Identifer ComputeFac: Parameter List Identifier: this Identifier : t
Semantic analysis
syntax tree
which identifiers
are associated with
which declarations
issue
data structure
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Code generation (backend)
Target Program Generate (back end) Annotated abstract syntax tree Intermediate Language Intermediate code generation Annotated abstract syntax tree Target code generation Target Program CSE401 Au08 16
Optimization
- Takes place at various (and multiple) places during code generation - Might optimize the intermediate language code - Might optimize the target code - Might optimize during execution of the program
- Q: Is it better to have an optimizing compiler or to hand-optimize code? CSE401 Au08 17
Quotations about optimization
- Michael Jackson
- Rule 1: Don't do it.
- Rule 2 (for experts only): Don't do it yet.
- Bill Wulf
- More computing sins are committed in the name of efficiency (without necessarily achieving it) than for any other single reason – including blind stupidity.
- Don Knuth
- We should forget about small efficiencies, say about 97% of the time: premature optimization is the root of all evil. CSE401 Au08 18
Questions?
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Lexing: reprise
- Read in characters
- Clump into tokens
- Strip out whitespace and comments
- Tokens are specified using regular expressions Ident ::= Letter AlphaNum* Integer ::= Digit+ AlphaNum ::= Letter | Digit Letter ::= 'a' | … | 'z' | 'A' | … | 'Z' Digit ::= '0' | … | '9'
- Q: regular expressions are equivalent to something you’ve previously learned about… what is it? CSE401 Au08 20
Example: source
Sample (extended) MiniJava program: Factorial.java // Computes 10! and prints it out class Factorial { public static void main(String[] a) { System.out.println( new Fac().ComputeFac(10)); } } class Fac { // the recursive helper function public int ComputeFac(int num) { int numAux; if (num < 1) numAux = 1; else numAux = num * this.ComputeFac(num-1); return numAux; } } CSE401 Au08 25 Example: intermediate representation Int Fac.ComputeFac(? this, int num) { int t1, numAux, t8, t3, t7, t2, t6, t0; t0 := 1; t1 := num < t0; ifnonzero t1 goto L0; t2 := 1; t3 := num - t2; t6 := Fac.ComputeFac(this, t3); t7 := num * t6; numAux := t7; goto L2; label L0; t8 := 1; numAux := t label L2; return numAux }* CSE401 Au08 26
Questions?
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Don’t forget
- Survey (before Friday)
- Readings (on calendar)
- Visit office hours (on calendar)
- Ask questions CSE401 Au08 28
