intro to compiler design

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Compiler Construction

1. IntroductionProf. O. NierstraszFall Semester 2008


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Oscar Nierstrasz


LecturerProf. Oscar [email protected]. 14/103Tel. 031 631.4618

Assistant Toon VerwaestLectures IWI 003, Wednesdays @ 10h15-12h00Exercises IWI 003, Wednesdays @ 12h00-13h00

WWW www.iam.unibe.ch/~scg/Teaching/CC/

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Roadmap

> Overview> Front end> Back end> Multi-pass compilers

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Roadmap


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Textbook

> Andrew W. Appel, Modern compiler implementationin Java(Second edition), Cambridge University Press,New York, NY, USA, 2002, with Jens Palsberg.

Thanks to Jens Palsberg and Tony Hoskingfor their kind permission to reuse and adaptthe CS132 and CS502 lecture notes.

http://www.cs.ucla.edu/~palsberg/http://www.cs.purdue.edu/homes/hosking/

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Other recommended sources

> Compilers: Principles, Techniques, andTools, Aho, Sethi and Ullman http://dragonbook.stanford.edu/

> Parsing Techniques, Grune and Jacobs http://www.cs.vu.nl/~dick/PT2Ed.html

> Advanced Compiler Design andImplementation, Muchnik

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Schedule

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1 17-Sep-08 Introduction

2 24-Sep-08 Lexical Analysis

3 1-Oct-08 Parsing

4 8-Oct-08 Parsing in Practice

5 15-Oct-08 Semantic Analysis

6 22-Oct-08 Intermediate Representation

7 29-Oct-08 Code Generation

8 5-Nov-08 Introduction to SSA [Marcus Denker]

9 12-Nov-08 Optimization [Marcus Denker]

10 19-Nov-08 The PyPy tool chain [Toon Verwaest]

11 26-Nov-08 PEGs, Packrats and Executable Grammars

12 3-Dec-08 Domain Specific Languages [Lukas Renggli]

13 10-Dec-08 Program Transformation

14 17-Dec-08 Final Exam


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Compilers, Interpreters

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PS Introduction

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What is a compiler?

a program that translates an executable

program in one language into an

executableprogram in another language

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What is an interpreter?

a program that reads an

executableprogram and produces

the results of running that program

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Why do we care?

artificialintelligence

greedy algorithmslearning algorithms

algorithms

graph algorithmsunion-finddynamic programming

theoryDFAs for scanningparser generatorslattice theory for analysis

systems

allocation and naminglocalitysynchronization

architecture

pipeline managementhierarchy managementinstruction set use

Compiler construction

is a microcosm of

computer science

Inside a compiler, all these things come together11


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Isnt it a solved problem?

> Machines are constantly changing Changes in architecture changes in compilers new features pose new problems changing costs lead to different concerns old solutions need re-engineering

> Innovations in compilers should prompt changes inarchitecture New languages and features

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What qualities are important in a compiler?

1. Correct code 2. Output runs fast 3. Compiler runs fast 4.

Compile time proportional to program size

5. Support for separate compilation 6. Good diagnostics for syntax errors 7. Works well with the debugger 8. Good diagnostics for flow anomalies 9. Cross language calls 10.Consistent, predictable optimization

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A bit of history

> 1952: First compiler (linker/loader) written by GraceHopper for A-0 programming language

> 1957: First complete compiler for FORTRAN by JohnBackus and team

> 1960:COBOL compilers for multiple architectures> 1962: First self-hosting compiler for LISP

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A compiler was originally a program that

compiled subroutines [a link-loader].

When in 1954 the combination algebraic

compiler came into use, or rather intomisuse, the meaning of the term had already

shifted into the present one. Bauer and Eickel [1975]

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Abstract view

recognize legal (and illegal) programs generate correct code manage storage of all variables and code agree on format for object (or assembly) code

Bigstepupfromassemblerhigherlevelnotations16


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Traditionaltwopasscompiler

intermediate representation (IR) front end maps legal code into IR back end maps IR onto target machine simplify retargeting allows multiple front ends

multiple passes better code

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Afallacy!

Front-end, IR and back-end must encodeknowledge needed for all nm combinations!

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Roadmap


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Front end

recognize legal code report errors produce IR preliminary storage map shape code for the back end

Much of front end construction can be automated20


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Scanner

map characters to tokenscharacter string value for a token is a lexemeeliminate white space

x = x + y = + 21


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Parser

recognize context-free syntax guide context-sensitive analysis construct IR(s) produce meaningful error messages attempt error correction

Parser generators mechanize much of the work22


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Context-free grammars

1. := 2. := 3. | 4. := number5. | id6. := +7. | -

Context-free syntax

is specified with a

grammar, usually inBackus-Naur form

(BNF)

A grammar G = (S,N,T,P)Sis the start-symbolNis a set of non-terminal symbolsTis a set of terminal symbolsPis a set of productions P: N(NT)*

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Deriving valid sentences

Production Result

1 2 5 y7 - y2 - y4 2 - y6 + 2 - y3 + 2 - y5 x + 2 - y

Given a grammar, valid

sentences can be

derived by repeated

substitution.

To recognize a valid

sentence in some

CFG, we reverse thisprocess and build up a

parse.

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Parse trees

A parse can be represented by a

tree called a parseor syntaxtree.

Obviously, this contains a lotof unnecessary information

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Abstract syntax trees

So, compilers often use an abstractsyntaxtree(AST).

ASTs are often

used as an IR.

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Roadmap


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Back end

translate IR into target machine code choose instructions for each IR operation decide what to keep in registers at each point ensure conformance with system interfaces

Automation has been less successful here

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Instruction selection

produce compact, fast code use available addressing modes pattern matching problem

ad hoc techniques tree pattern matching string pattern matching dynamic programming

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Register allocation

have value in a register when used limited resources changes instruction choices can move loads and stores optimal allocation is difficult

Modern allocators often use an analogy to graph coloring30


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Roadmap


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Traditional three-pass compiler

analyzes and changes IR goal is to reduce runtime must preserve values

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Optimizer (middle end)

Modern optimizers are usually built as a set of passes

constant propagation and folding code motion reduction of operator strength common sub-expression elimination redundant store elimination dead code elimination

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The MiniJava compiler

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Compiler phases

Lex Break source file into individual words, or tokensParse

Analyse the phrase structure of program Parsing Actions Build a piece of abstract syntax treefor each phrase Semantic Analysis

Determine what each phrase means, relate uses of variables to their definitions,check types of expressions, request translation of each phrase

Frame LayoutPlace variables, function parameters, etc., into activation records (stack frames)in a machine-dependent way

TranslateProduce intermediate representation trees(IR trees), a notation that is not tiedto any particular source language or target machine

CanonicalizeHoist side effects out of expressions, and clean up conditional branches, forconvenience of later phases

Instruction SelectionGroup IR-tree nodes into clumps that correspond to actions of target-machineinstructions

Control Flow AnalysisAnalyse sequence of instructions into control flow graphshowing all possibleflows of control program might follow when it runs

Data Flow AnalysisGather information about flow of data through variables of program; e.g.,

liveness analysiscalculates places where each variable holds a still-needed(live) value

Register AllocationChoose registers for variables and temporary values; variables notsimultaneously live can share same register

Code Emission Replace temporary names in each machine instruction with registers 35


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Astraight-lineprogramminglanguage(no loops or conditionals):

Stm Stm ; Stm CompoundStmStm id := Exp AssignStm Stm print ( ExpList ) PrintStmExp id IdExp Exp num NumExp Exp Exp Binop Exp OpExp Exp ( Stm , Exp ) EseqExpExpList Exp , ExpList PairExpListExpList Exp LastExpListBinop + PlusBinop - MinusBinop TimesBinop / Div

a := 5 + 3; b := (print(a,a1),10a); print(b)prints 8 780

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Tree representation

a := 5 + 3; b := (print(a,a1),10

a); print(b)

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Java classes for trees

abstract class Stm {}class CompoundStm extends Stm {

Stm stm1, stm2;CompoundStm(Stm s1, Stm s2){stm1=s1; stm2=s2;}

}class AssignStm extends Stm {

String id; Exp exp;AssignStm(String i, Exp e) {id=i; exp=e;}

}class PrintStm extends Stm {

ExpList exps;PrintStm(ExpList e) {exps=e;}

}abstract class Exp {}class IdExp extends Exp {

String id;IdExp(String i) {id=i;}

}

class NumExp extends Exp {int num;NumExp(int n) {num=n;}

}class OpExp extends Exp {

Exp left, right; int oper;final static int Plus=1,Minus=2,Times=3,Div=4;OpExp(Exp l, int o, Exp r) {left=l; oper=o; right=r;}

}class EseqExp extends Exp {

Stm stm; Exp exp;EseqExp(Stm s, Exp e) {stm=s; exp=e;}

}abstract class ExpList {}class PairExpList extends ExpList {

Exp head; ExpList tail;public PairExpList(Exp h, ExpList t) {head=h; tail=t;}

}class LastExpList extends ExpList {

Exp head; public LastExpList(Exp h) {head=h;}

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What you should know!

What is the difference between a compiler and aninterpreter?

What are important qualities of compilers? Why are compilers commonly split into multiple passes? What are the typical responsibilities of the different parts

of a modern compiler? How are context-free grammars specified? What is abstract about an abstract syntax tree? What is intermediate representation and what is it for? Why is optimization a separate activity?

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Can you answer these questions?

Is Java compiled or interpreted? What about Smalltalk?Ruby? PHP? Are you sure?

What are the key differences between modern compilersand compilers written in the 1970s?

Why is it hard for compilers to generate good errormessages?

What is context-free about a context-free grammar?

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License

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