Compiler Design 1

Administrivia • Lecturer:

– Kostis Sagonas (Hus 1, 352)

Compiler Design 1

• Course home page: http://user.it.uu.se/~kostis/Teaching/KT1-11

• If you want to be enrolled in the course, send mail with your name and UU account to:

Introduction to Programming Language Design and to Compilation

• Assistant:

[email protected]

– Stavros Aronis ([email protected]) – responsible for the lessons and the assignments

Compiler Design 1 (2011)

Course Structure

2

Course Literature

• Course has theoretical and practical aspects • Need both in programming languages! • Written examination = theory (4 points) • Assignments = practice (1 point)

– Electronic hand-in to the assistant before the corresponding deadline

Compiler Design 1 (2011)

3

Compiler Design 1 (2011)

4

Academic Honesty

The Compiler Project

• For assignments you are allowed to work in pairs (but no threesomes/foursomes/...) • Don’t use work from uncited sources

• A follow-up course • that will be taught by Sven-Olof Nyström • in period 3

– Including old assignments

PLAGIARISM

Compiler Design 1 (2011)

5

Compiler Design 1 (2011)

How are Languages Implemented?

Language Implementations

• Two major strategies:

• Batch compilation systems dominate

– Interpreters (older, less studied) – Compilers (newer, much more studied)

– gcc

• Some languages are primarily interpreted

• Interpreters run programs “as is”

– Java bytecode – Postscript

– Little or no preprocessing

• Some environments (e.g. Lisp) provide both

• Compilers do extensive preprocessing

Compiler Design 1 (2011)

6

– Interpreter for development – Compiler for production

7

Compiler Design 1 (2011)

8

(Short) History of High-Level Languages

FORTRAN I

• 1953 IBM develops the 701

• 1954 IBM develops the 704 • John Backus

• Till then, all programming done in assembly

– Idea: translate high-level code to assembly – Many thought this impossible • Had already failed in other projects

• Problem: Software costs exceeded hardware costs!

• 1954-7 FORTRAN I project • By 1958, >50% of all software is in FORTRAN • Cut development time dramatically

• John Backus: “Speedcoding” – An interpreter – Ran 10-20 times slower than hand-written assembly Compiler Design 1 (2011)

– (2 weeks → 2 hours)

9

Compiler Design 1 (2011)

FORTRAN I

The Structure of a Compiler

• The first compiler

1. 2. 3. 4. 5. 6.

– Produced code almost as good as hand-written – Huge impact on computer science

• Led to an enormous body of theoretical work • Modern compilers preserve the outlines of the FORTRAN I compiler

Compiler Design 1 (2011)

10

Lexical Analysis Syntax Analysis Semantic Analysis IR Optimization Code Generation Low-level Optimization The first 3, at least, can be understood by analogy to how humans comprehend English.

11

Compiler Design 1 (2011)

12

Lexical Analysis

More Lexical Analysis

• First step: recognize words.

• Lexical analysis is not trivial. Consider: ist his ase nte nce

– Smallest unit above letters

This is a sentence.

• Plus, programming languages are typically more cryptic than English: *p->f ++ = -.12345e-5

• Note the – Capital “T” (start of sentence symbol) – Blank “ ” (word separator) – Period “.” (end of sentence symbol)

Compiler Design 1 (2011)

13

Compiler Design 1 (2011)

And More Lexical Analysis

Parsing

• Lexical analyzer divides program text into “words” or “tokens” if (x == y) then z = 1; else z = 2;

• Once words are understood, the next step is to understand the sentence structure

14

• Parsing = Diagramming Sentences – The diagram is a tree

• Units: if, (, x, ==, y, ), then, z, =, 1, ;, else, z, =, 2, ;

Compiler Design 1 (2011)

15

Compiler Design 1 (2011)

16

Diagramming a Sentence (1) This

line

article

is

a

Diagramming a Sentence (2) longer

sentence

noun verb article adjective

noun

article

noun phrase noun phrase

This

line

is

a

longer

noun verb article adjective

subject

verb phrase

sentence noun

object sentence

sentence Compiler Design 1 (2011)

17

Compiler Design 1 (2011)

Parsing Programs

Semantic Analysis

• Parsing program expressions is the same • Consider: If (x == y) then z = 1; else z = 2; • Diagrammed:

• Once sentence structure is understood, we can try to understand its “meaning”

x

==

y

relation predicate

z

=

1

assignment then-stmt

z

=

18

– But meaning is too hard for compilers

• Most compilers perform limited analysis to catch inconsistencies

2

assignment • Some optimizing compilers do more analysis to improve the performance of the program

else-stmt

if-then-else Compiler Design 1 (2011)

19

Compiler Design 1 (2011)

20

Semantic Analysis in English

Semantic Analysis in Programming Languages

• Example: Jack said Jerry left his assignment at home. What does “his” refer to? Jack or Jerry?

• Programming languages define strict rules to avoid such ambiguities

• Even worse: Jack said Jack left his assignment at home? How many Jacks are there? Which one left the assignment?

• This C++ code prints “4”; the inner definition is used

Compiler Design 1 (2011)

21

{ int Jack = 3; { int Jack = 4; cout