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Overview of Compilation The Compiler Front End

Overview of Compilation The Compiler Front End. Module 02.1 COP4020 – Programming Language Concepts Dr. Manuel E. Bermudez. Definition: A translator is an algorithm that converts source programs into equivalent target programs.

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Overview of Compilation The Compiler Front End

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  1. Overview of CompilationThe Compiler Front End Module 02.1COP4020 – Programming Language Concepts Dr. Manuel E. Bermudez

  2. Definition: A translator is an algorithm that converts source programs into equivalent target programs. Definition: A compiler is a translator whose target language is at a “lower” level than its source language. Target Source Translator Overview of translation

  3. When is one language’s level “lower” than another’s? Definition: An interpreter is an algorithm that simulates the execution of programs written in a given source language. input Source Interpreter output Overview of translation

  4. Definition: An implementationof a programming language consists of a translator (or compiler) for that language, and an interpreter for the corresponding target language. Overview of translation input Source Target Compiler Interpreter output

  5. A source program may be translated an arbitrary number of times before the target program is generated. Overview of translation Source Translator1 Translator2 ... TranslatorN Target

  6. Each translation is a phase. Not to be confused with a pass, i.e., a disk dump. Divide a compiler into phases: Use a formal model of computation, Do it efficiently. Overview of translation

  7. Usual division into phases: Two major phases, many possibilities for subdivision. Phase 1: Analysis (determine correctness) Phase 2: Synthesis (produce target code) Another criterion: Phase 1: Syntax (form). Phase 2: Semantics (meaning). Overview of translation

  8. Group character sequences in the source. Form logical atomic units called tokens. Examples of tokens: Identifiers, keywords, integers, strings, punctuation marks, “white spaces”, end-of-line characters, comments, etc. PHASE 1: Scanning (Lexical analysis). Scanner (Lexical analysis) Source Sequence of Tokens

  9. Proceeds sequentially. First character usually determines the token. A preliminary classification of tokens is made. Example: ‘program’ and ‘Ex’ are classified as Identifier. Lexical rules must be provided. “_” allowed in identifiers ? Comments cross line boundaries ? Must deal with end-of-line and end-of-file characters. PHASE 1: Scanning (Lexical analysis).

  10. Remove unwanted tokens (spaces, comments). Recognize keywords. Merge/simplify tokens. Prepare token list for next phase (parser). Sequence of Tokens Screener Sequence of Tokens PHASE 1: Screening (post-process)

  11. Is the token sequence syntactically correct ? Group the tokens into the correct syntactic structures. Expressions, statements, procedures, functions, modules. Use “re-write” rules (a.k.a. BNF). Build a “syntax tree”, bottom-up, as the rules are used. Use a stack of trees. PHASE 2: Parsing (Syntax Analysis)

  12. FIRST 2 PHASES OF COMPILATION: PHASE 1: Scanning, Screening (a.k.a. Lexical Analysis) From characters to tokens. Proceeds sequentially. PHASE 2: Parsing (Syntax Analysis) From tokens to a tree. Post-order tree traversal. Summary

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