Compiler Construction: Two-pass Compiler, Cheat Sheet of Compiler Construction

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Compiler

Construction

Lecture 2

Two-pass Compiler

Front End Back End source code IR (^) machine code errors

Two-pass Compiler

• Back end maps IR into target machine code
• Admits multiple front ends & multiple passes

Two-pass Compiler

• Front end is O(n) or O(n log n)
• Back end is NP-Complete (NPC)

The Front-End

Modules

• Scanner
• Parser scanner parser source code tokens IR errors

Scanner

scanner parser source code tokens IR errors

Scanner

• Example x = x + y becomes < id , x > < assign , = > < id , x > < op , + > < id , y > token type word < id , x >

Scanner

• we call the pair “<token type, word>” a “token”
• typical tokens: number , identifier , +, - , new , while , if

Parser

• Recognizes context-free syntax and reports errors
• Guides context-sensitive (“semantic”) analysis
• Builds IR for source program

Context-Free Grammars

• Context-free syntax is specified with a grammar G= ( S,N,T,P )
• S is the start symbol
• N is a set of non-terminal symbols
• T is set of terminal symbols or words
• P is a set of productions or rewrite rules

The Front End

• For this CFG

S = goal

T = { number, id, +, - }

N = { goal , expr , term , op }

P = { 1, 2, 3, 4, 5, 6, 7}

Context-Free Grammars

• Given a CFG, we can derive sentences by repeated substitution
• Consider the sentence (expression) x + 2 – y

The Front End

• To recognize a valid sentence in some CFG, we reverse this process and build up a parse
• A parse can be represented by a tree: parse tree or syntax tree

Parse

Production Result goal 1 expr 2 expr op term 5 expr op y 7 expr – y 2 expr op term – y 4 expr op 2 – y 6 expr + 2 – y 3 term + 2 – y 5 x + 2^ –^ y^