Compiler design Introduction
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Compilers translate programs written in high-level languages into executable machine code. They perform several phases including lexical analysis, syntax analysis, semantic analysis, code generation, and optimization. The overall goal is to generate efficient executable code from the high-level source code while checking for errors.
![Global optimizations: reorder, remove or add instructions to change the structure of
generated code
Consumes a significant fraction of the compilation time
Optimization capability varies widely
Simple optimization techniques can be very valuable
Code Generation
Map instructions in the intermediate code to specific machine instructions.
Memory management, register allocation, instruction selection, instruction scheduling,
...
Generates su�cient information to enable symbolic debugging.
Symbol Table
Records the identifiers used in the source program
Collects various associated information as attributes
Variables: type, scope, storage allocation
Procedure: number and types of arguments method of argument passing
It’s a data structure with collection of records
Di�erent fields are collected and used at di�erent phases of compilation
Error Detection, Recovery and Reporting
Each phase can encounter error
Specific types of error can be detected by specific phases
Lexical Error: int abc, 1num;
Syntax Error: total = capital + rate year;
Semantic Error: value = myarray [realIndex];
Should be able to proceed and process the rest of the program after an error detected
Should be able to link the error with the source program
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Compiler design Introduction
- 1. Introduction Why compiler? Programming problems are easier to solve in high-level languages Languages closer to the level of the problem domain, e.g., SmallTalk: OO programming JavaScript: Web pages Solutions are usually more e�cient (faster, smaller) when written in machine language Language that reflects to the cycle-by-cycle working of a processor Compilers are the bridges Tools to translate programs written in high-level languages to e�cient executable code What is a compiler? "A program that reads a program written in one language and translates it into another language." Traditionally, compilers go from high-level languages to low-level languages. Traditionally, compilers go from high-level languages to low-level languages. How to translate? https://www.slideshare.net/Amansharma1037 https://www.linkedin.com/in/includeaman
- 2. Requirement: In order to translate statements in a language, one needs to understand both the structure of the language: the way “sentences" are constructed in the language the meaning of the language: what each “sentence" stands for. Terminology: Structure ≡ Syntax Meaning ≡ Semantics Analysis-Synthesis model of compilation : Two parts Analysis Breaks up the source program into constituents Synthesis Constructs the target program Compilation Steps / Phases https://www.slideshare.net/Amansharma1037 https://www.linkedin.com/in/includeaman
- 3. Compilation Steps/Phases Lexical Analysis Phase: Generates the “tokens” in the source program Syntax Analysis Phase: Recognizes “sentences" in the program using the syntax of the language Semantic Analysis Phase: Infers information about the program using the semantics of the language Intermediate Code Generation Phase: Generates “abstract” code based on the syntactic structure of the program and the semantic information from Phase 2. Optimization Phase: Refines the generated code using a series of optimizing transformations Final Code Generation Phase: Translates the abstract intermediate code into specific machine instructions. Lexical Analysis Convert the stream of characters representing input program into a sequence of tokens Tokens are the “words" of the programming language https://www.slideshare.net/Amansharma1037 https://www.linkedin.com/in/includeaman
- 4. Lexeme The characters comprising a token For Example, the sequence of characters “static int" is recognized as two tokens, representing the two words “static" and “int" The sequence of characters “*x++" is recognized as three tokens, representing “*", “x" and “++“ Removes the white spaces Removes the comments Lexical Analysis Input: result = a + b * 10 Tokens: Syntax Analysis Uncover the structure of a sentence in the program from a stream of tokens. For instance, the phrase “x = +y", which is recognized as four tokens, representing “x", “=“ and “+" and “y", has the structure =(x,+(y)), i.e., an assignment expression, that operates on “x" and the expression “+(y)". Build a tree called a parse tree that reflects the structure of the input sentence. Syntax Analysis: Grammars Expression grammar Exp ::=Exp ‘+’ Exp | Exp ‘*’ Exp | ID | NUMBER https://www.slideshare.net/Amansharma1037 https://www.linkedin.com/in/includeaman
- 5. Assign ::= ID ‘=‘ Exp Syntax Tree Input: result = a + b * 10 Semantic Analysis Concerned with the semantic (meaning) of the program Performs type checking Operator operand compitability Intermediate Code Generation Translate each hierarchical structure decorated as tree into intermediate code A program translated for an abstract machine Properties of intermediate codes Should be easy to generate Should be easy to translate Intermediate code hides many machine-level details, but has instruction-level mapping to many assembly languages Main motivation: portability One commonly used form is “Three-address Code” Code Optimization Apply a series of transformations to improve the time and space e�ciency of the generated code. Peephole optimizations: generate new instructions by combining/expanding on a small number of consecutive instructions. https://www.slideshare.net/Amansharma1037 https://www.linkedin.com/in/includeaman
- 6. Global optimizations: reorder, remove or add instructions to change the structure of generated code Consumes a significant fraction of the compilation time Optimization capability varies widely Simple optimization techniques can be very valuable Code Generation Map instructions in the intermediate code to specific machine instructions. Memory management, register allocation, instruction selection, instruction scheduling, ... Generates su�cient information to enable symbolic debugging. Symbol Table Records the identifiers used in the source program Collects various associated information as attributes Variables: type, scope, storage allocation Procedure: number and types of arguments method of argument passing It’s a data structure with collection of records Di�erent fields are collected and used at di�erent phases of compilation Error Detection, Recovery and Reporting Each phase can encounter error Specific types of error can be detected by specific phases Lexical Error: int abc, 1num; Syntax Error: total = capital + rate year; Semantic Error: value = myarray [realIndex]; Should be able to proceed and process the rest of the program after an error detected Should be able to link the error with the source program https://www.slideshare.net/Amansharma1037 https://www.linkedin.com/in/includeaman
- 7. Translation of a statement https://www.slideshare.net/Amansharma1037 https://www.linkedin.com/in/includeaman
- 11. Syntax Analyzer versus Lexical Analyzer Both of them do the similiar thing ; But the lexical analyzer deals with simple non-recursive constructs of the language. The syntax analyzer deals with recursive constructs of the language. The lexical analyzer simplifies the job of the syntax analyzer. The lexical analyzer recognizes the smallest meaningful units (tokens) in a source program. The syntax analyzer works on the smallest meaningful units (tokens) in a source program to recognize meaningful structures in our programming language. Cousins of the Compiler Preprocessor Macro preprocessing : Define and use shorthand for longer constructs File inclusion :Include header files “Rational” Preprocessors :Augment older languages with modern flow-of-control or data-structures Language Extension:Add capabilities to a language Equel: query language embedded in C Assemblers https://www.slideshare.net/Amansharma1037 https://www.linkedin.com/in/includeaman
- 12. Two-Pass Assembly Simplest form of assembler First pass All the identifiers are stored in a symbol table Storage is allocated Second pass Translates each operand code in the machine language https://www.slideshare.net/Amansharma1037 https://www.linkedin.com/in/includeaman
- 13. Loaders and Link-Editors Loader Converts the relocatable machine code into absolute machine code Map the relocatable address Place altered instructions and data in memory Linker Makes a single program from several files of relocatable machine code Several files of relocatable codes Library files Grouping of Phases Front End and Back End with Front end consisting of phases that depend iupon source language and are independent of target language. Passes : Several phases of compilers with similiar function are grouped in Passes. often Passes generate an explicit output file In each pass whole input file is processed. Issues Driving Compiler Design Correctness Speed (runtime and compile time) https://www.slideshare.net/Amansharma1037 https://www.linkedin.com/in/includeaman
- 14. Degrees of optimization Multiple passes Space Feedback to user Debugging Other Applications In addition to the development of a compiler, the techniques used in compiler design can be applicable to many problems in computer science. Techniques used in a lexical analyzer can be used in text editors, information retrieval system, and pattern recognition programs. Techniques used in a parser can be used in a query processing system such as SQL. Many software having a complex front-end may need techniques used in compiler design. A symbolic equation solver which takes an equation as input.That program should parse the given input equation. Most of the techniques used in compiler design can be used in Natural Language Processing (NLP) systems. https://www.slideshare.net/Amansharma1037 https://www.linkedin.com/in/includeaman