compiler construction - iit bombayviren/courses/2014/compiler/lecture1.pdf · compiler construction...

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Compiler Construction An Introduction

Virendra Singh

Associate Professor Computer Architecture and Dependable Systems Lab

Department of Electrical Engineering Indian Institute of Technology Bombay

http://www.ee.iitb.ac.in/~viren/ E-mail: [email protected]

A Short Course on Compiler Construction & Optimization Lecture 1 (22 May 2014)

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Use of Computers: Problem Solving

1.  Problem defini/on 2.  Algorithm design/ Algorithm specifica/on 3.  Algorithm analysis 4.  Implementa/on 5.  Tes/ng 6.  [Maintenance]

22 May 2014 Compilers@EE-IITB 2

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Running Program on Processor

Processor Performance = -‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐ Time

Program

Architecture -‐-‐> Implementa9on -‐-‐> Realiza9on

Compiler Designer Processor Designer Chip Designer

Instructions Cycles

Program Instruction Time

Cycle

(code size)

= X X

(CPI) (cycle time)

Compilers@EE-IITB 22 May 2014 3

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From Source to Executable

Compiler main() sub1() data

source program foo.c

main sub1 data

object modules foo.o

prinE scanf gets fopen exit data ...

sta9c library libc.a

Linkage Editor

main sub1 data prinE exit data

load module a.out

other

programs ...

main sub1 data prinE exit data

other ... ...

kernel

Machine memory

?

(system calls)

Loader

(Run Time)

Dynamic library case not shown

“Load 9me”


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What is a compiler?

A program that reads a program wriGen in one language and translates it into another language.

Source language Target language

Tradi/onally, compilers go from high-‐level languages to low-‐level languages.

22 May 2014

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Compilers •  Common compila/on tasks

–  Language transla/on –  Error checking and report –  Performance improvement

•  Fundamental compila/on principles ü The compiler must preserve the meaning of source program

ü The compiler must improve the source program in some discernible way

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Compilers Evolution

•  In the beginning, there was machine language – Ugly – wri/ng code, debugging –  Then came textual assembly – s/ll used on DSPs

– High-‐level languages – Fortran, Pascal, C, C++ – Machine structures became too complex and soYware management too difficult to con/nue with low-‐level languages


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Why are Compilers Important? •  Computer architecture

–  Build processors that soYware can be automa/cally mapped to efficiently

–  Exploi/ng hardware features •  CAD tools

–  Behavioral synthesis / C-‐to-‐gates tools are hardware compilers

–  Use program analysis/op/miza/on to generate cheaper hardware

•  SoYware developers –  How do I create a compiler? –  How does it map my code to the hardware



Compiler Architecture

Front End – language specific

Back End – machine specific

Source Language

Target Language

Intermediate Language

In more detail:

•  Separa/on of Concerns •  Retarge/ng

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Scanner (lexical

analysis)

Parser (syntax

analysis)

Code Optimizer

Semantic Analysis

(IC generator)

Code Generator

Symbol Table

Source language

tokens Syntactic structure


Target language


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Translation of an assignment

Translation of an assignment statement

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Lexical Analysis •  Character stream è token stream

–  Recognize “words” of a language •  Theore/cal problem: specify and recognize paGerns in strings –  Scanner as a prac/cal applica/on –  Regular expression, finite automata –  Tools that automa/cally generate scanners are commonly used

index := start + step * 20 Input: index := start + step * 20 After scanning:

identifier operator number


Syntactical Analysis •  Token stream è syntax tree

–  Recognize “sentences” of a language

•  Grammars and parsers –  CFG

•  Parsers can be automa/cally generated

–  Top-‐down and boGom-‐up parsing •  Predic/ve parsing •  Driven process of compiler front-‐ends

After scanning: index := start + step * 20

After parsing:

index

Assign

Exp ID :=

Num ID

ID

+ Exp

*

start

step 20

Exp

Exp Exp


Semantic Analysis •  The seman/c analyzer uses the syntax tree and the informa/on in

the symbol table to check the source program for seman/c consistency with the language defini/on.

•  Gathers type informa/on and saves it in either the syntax tree or the symbol table, for subsequent use during intermediate-‐code genera/on.

•  An important part of seman/c analysis is type checking, where the compiler checks that each operator has matching operands. Ø  For example, many programming language defini/ons require an array index

to be an integer; the compiler must report an error if a floa/ng-‐point number is used to index an array.

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Semantic Analysis •  The language specifica/on may permit some type conversions

called coercions. –  For example, a binary arithme/c operator may be applied to either a pair of

integers or to a pair of floa/ng-‐point numbers. If the operator is applied to a floa/ng-‐point number and an integer, the compiler may convert or coerce the integer into a floa/ng-‐point number.

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Semantic Analysis •  Understand/annotate meaning of the program –  Syntax-‐directed transla/on –  Check seman/c errors

•  Inconsistent variable defini/ons and uses • Type systems

–  Collect knowledge of the input program • Symbol tables • Scopes



Scanner (lexical

analysis)

Parser (syntax

analysis)

Code Optimizer

Semantic Analysis

(IC generator)

Code Generator

Symbol Table

Source language

tokens Syntactic structure


Target language


22 May 2014


Intermediate Code Generation •  Representa/on of the input program

–  Internal to the compiler –  Encode knowledge collected during compila/on – Varied forms and levels

• Typically a compiler use more than one kind of IR

– Desired proper/es • Easy to produce, manipulate, and translate into the target code

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IR scheme


•  front end produces IR

•  optimizer transforms IR to more efficient program

•  back end transforms IR to target code

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Kinds of IR •  Abstract syntax trees (AST) •  Linear operator form of tree (e.g., posfix nota/on)

•  Directed acyclic graphs (DAG) •  Control flow graphs (CFG) •  Program dependence graphs (PDG) •  Sta/c single assignment form (SSA) •  3-‐address code •  Hybrid combina/ons


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Categories of IR •  Structural

–  graphically oriented (trees, DAGs) –  nodes and edges tend to be large –  heavily used on source-‐to-‐source translators

•  Linear –  pseudo-‐code for abstract machine –  large varia/on in level of abstrac/on –  simple, compact data structures –  easier to rearrange

•  Hybrid –  combina/on of graphs and linear code (e.g. CFGs) –  aGempt to achieve best of both worlds


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Important IR properties •  Ease of genera/on •  Ease of manipula/on •  Cost of manipula/on •  Level of abstrac/on •  Freedom of expression (!) •  Size of typical procedure •  Original or deriva/ve


Subtle design decisions in the IR can have far-reaching effects on the speed and effectiveness of the compiler! è Degree of exposed detail can be crucial

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Thank You


compiler construction - iit bombayviren/courses/2014/compiler/lecture1.pdf · compiler construction...

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