Compilers Structure of a Compiler Alex Aiken Intro to Compilers - - PowerPoint PPT Presentation

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Jan 26, 2024 291 likes •470 views

Compilers Structure of a Compiler Alex Aiken Intro to Compilers 1. Lexical Analysis 2. Parsing 3. Semantic Analysis 4. Optimization 5. Code Generation Alex Aiken Intro to Compilers First step: recognize words. Smallest unit above

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Alex Aiken

Compilers

Structure of a Compiler

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Alex Aiken

Intro to Compilers

1. Lexical Analysis
2. Parsing
3. Semantic Analysis
4. Optimization
5. Code Generation

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Alex Aiken

Intro to Compilers

First step: recognize words.

– Smallest unit above letters This is a sentence.

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Alex Aiken

Intro to Compilers ist his ase nte nce

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Alex Aiken

Intro to Compilers

Lexical analysis divides program text into “words” or

“tokens” if x == y then z = 1; else z = 2;

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Alex Aiken

Intro to Compilers

Once words are understood, the next step is to understand

sentence structure

Parsing = Diagramming Sentences

– The diagram is a tree

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Intro to Compilers This line is a longer sentence verb article noun article adjective noun subject

bject

sentence

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Intro to Compilers if x == y then z = 1; else z = 2; if-then-else x y z 1 z 2 == assign relation assign predicate else-stmt then-stmt

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Intro to Compilers

Once sentence structure is understood, we can try to

understand “meaning” – This is hard!

Compilers perform limited semantic analysis to catch

inconsistencies

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Alex Aiken

Intro to Compilers

Example:

Jack said Jerry left his assignment at home.

Even worse:

Jack said Jack left his assignment at home?

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Alex Aiken

Intro to Compilers

Programming languages

define strict rules to avoid such ambiguities { int Jack = 3; { int Jack = 4; cout << Jack; } }

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Intro to Compilers

Compilers perform many semantic checks besides

variable bindings

Example:

Jack left her homework at home.

A “type mismatch” between her and Jack; we know

they are different people

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Intro to Compilers

Optimization has no strong counterpart in English

– But a little bit like editing

Automatically modify programs so that they

– Run faster – Use less memory

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Intro to Compilers X = Y * 0 is the same as X = 0

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Intro to Compilers

Produces assembly code (usually)
A translation into another language

– Analogous to human translation

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Alex Aiken

Intro to Compilers

The overall structure of almost every compiler

adheres to our outline

The proportions have changed since FORTRAN