Chapter_1(new) - Compiler Construction 1 Definition A...

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Unformatted text preview: Compiler Construction 1 Definition A compiler is an executable program that can read a program in one high-level language and translate it into an equivalent executable program in machine language. program in high-level language Compiler executable program in machine language input Executable program in machine language output 2 Textbook: Compiler Construction Principles and Practice authored by Kenneth C. Louden Reference book: Lex & yacc by John R. Levine, Tony Mason & Doug Brown O'Reilly & Associates, Inc. 3 Web Site a 4 Grading Homework (25%) - Programming (lex, yacc, semantic actions) - Hand-written Assignments (3) Midterm Exam (25%) Final Exam (25%) Final Project (25%) 5 Prerequisites Data Structures Discrete Mathematics Programming Languages Computer Architectures Assembly Languages Finite Automata (helpful) 6 Chapter 1 Introduction 7 Source program Compiler Target program 8 The progression of programming languages: Machine language c7 06 0000 0002 Assembly language mov x 2 Highlevel language x = 2 *The first compiler was developed by the team at IBM led by John Backus between 1954 and 1957. 9 Why do we need to learn compilers? (1) for new platforms (2) for new languages language extensions & improvement specification languages 4th generation languages (3) foundation of parallelizing compilers & related tools 10 (4) theories learned are applicable to other fields e.g., silicon compiler, prototyping tools, database languages, text formatter, FSM (Finite State Machine) translator, query interpreter, command interpreter, interface programs, etc. (5) for improving capabilities of existing compiler/interpreter 11 Silicon compiler A silicon compiler is a software system that takes a user's specifications and automatically generates an integrated circuit (IC). The process is sometimes referred to as hardware compilation. Source language: conventional programming language Variables Represents not the location but logical signals (0 or 1) or groups of signals in a switching circuit. Output : circuit design in an appropriate language 12 Programs Related to Compilers Interpreters Assemblers Linkers Loaders Preprocessors Editors Debuggers Profilers Project Managers source program preprocessor modified source program compiler target assembly program assembler relocatable machine code linker/loader target machine code Library files 13 Definitions of (translationrelated) Languages Source language Target language Implementation language 14 Translator A program, written in the implementation language, that takes sentences (strings) in the source language and outputs equivalent sentences (strings) in the target language. e.g. preprocessor, pretty printer, fortran2c, pascal2c (high to high) assembler (low to lower) disassembler (lower to low) compiler (high to low) 15 Category of compilers 1. Self-compiling Compiler Source and implementation languages are the same. 2. Self-resident Compiler Implementation and object languages are the same. 3. Cross compiler A compiler that runs on one machine and produces object code for another machine. 16 Interpreter Def. An interpreter performs the operations implied by the source program. Interpretation system lowest level Source low program middle input high Interpreter output 17 A hybrid compiler Source program Translator Intermediate program Input Virtual Machine Output 18 What are the differences between "Interpreter" and "compiler"? portability execution speed with/without object code debugging capability with/without optimization 19 The AnalysisSynthesis Model of Compilation There are two parts to compilation: analysis & synthesis. During analysis, the operations implied by the source program are determined and recorded in a hierarchical structure called a tree. During synthesis, the operations involved in producing translated code. 20 The Frontend and Backend Model of Compilation Source Intermediate Target Front End Back End Code Code Code 21 Target code optimizer 22 Preprocessor (or Character handler ) throw away the comments compress multiple blank characters include files (include nested files) perform macro expansions (nested macro expansion) a macro facility is a text replacement capability (two aspects: definition & use). a macro statement will be expanded into a set of programming language statements or other macro. compiler option (conditional compilation) (These jobs may be conducted by lexical analyzer.) 23 Scanner (Lexical Analyzer) To identify lexical ( ) structure Input: a stream of chars; Output: a stream of tokens. A scanner may also enter identifiers into the symbol table and enter literals into literal table. (literals include numeric constants such as 3.1415926535 and quoted strings such as "Hello, world!"). 24 An Example: a[index] = 4 + 2 ; (1) Output of the Scanner : a ===> identifier [ ===> left bracket index ===> identifier ] ===> right bracket = ===> assignment 1 ===> number + ===> plus sign 1 ===> number ; ===> semicolon 25 How tokens (string of chars) are formed from underlying character set? Usually specified (described) by sequence of regular expression. Lexical structures are analyzed via finite state automata. But it has the lookahead requirement. (To recognize a token the scanner may need to look more characters ahead of the token.) 26 Parser (Syntax Analyzer) To identify syntax structure Input: a stream of tokens Output: On a logical level, some representation of a parse tree. Determine how do the tokens fit together to make up the various syntax entity of a program. **Most compilers do not generate a parse tree explicitly but rather go to intermediate code directly as syntax analysis takes place. Usually specified via context free grammar. Syntax structures are analyzed by DPDA 27 (2) Output of the parser parse tree (logical level) structure names tokens 28 Predefined contextfree grammar expression assignexpression | subscriptexpression | additiveexpression | identifier | number assignexpression expression = expression subscriptexpression expression [ expression ] additiveexpression expression + expression 29 (2)' Output of the parser Abstract Syntax Tree (AST) (condensed parse tree) = + 30 Semantic Analyzer ==> Semantic Structure What is the program supposed to do? Semantics analysis can be done during syntax analysis phase or intermediate code generator phase or the final code generator. typical static semantic features include declarations and type checking. information (attributes) gathered can be either added to the tree as annotations or entered into the symbol table. 31 (3) Output of the semantic analyzer annotated AST with subscripts from a range 32 (3) Output of the semantic analyzer (cont'd) finds the consistence of data type among `a', `index', and 2 + 4, or declares a type dismatch error if not. 33 The time ratio for scanning, parsing, and semantic processing is 30:25:45. 34 Source Code Optimizer 35 (4) Output of the Source Code Optimizer with subscripts from a range 36 Intermediate Code Generator Transform the parse tree (logical level) into an intermediate language representation, e.g., three address code: A = B op C ( op is a binary operator) Difference between intermediate code and assembly code: Specify the registers to be used for each operation in assembly code. Actually intermediate code can be represented as any internal representation such as the syntax tree. 37 15 27 index 33 temp . . . . Three address code temp = 6 a [ index ] = 6 a [ index ] = temp 12 15 27 #6 Quadruple: (in implementation) operator location1 location2 location3 a 8 33 #6 = temp a 6 (5) Output of the intermediate code generator : intermediate code (three address code, two address code, Pcode, etc.) ( logical ) = index temp 12 15 27 33 (symbol table) ( reality ) Advanced Code Optimizer Detection of undefined variables Constant folding Detection of loop invariant computation Removal of induction variables Elimination of common expression 39 Induction Variable Elimination When there are two or more induction variables in a loop we have opportunity to get rid of all but one. ..... ..... I = 1 T = 0 Remove I Repeat Repeat T = 4 * I ===> T = T + 4 X = Y [T] X = Y [T] Prod = Prod + X Prod = Prod + X I = I + 1 Until T > 76 Until I > 20 * Suppose I is not needed after the loop terminates 40 Elimination of common expression A = B + C + D E = B + C + F might be T = B + C A = T + D E = T + F 41 Code Generator 42 (6) Output of the code generator Mov R0, index // value of index > R0 Mul R0, 2 // double value in R0 Mov R1, &a // address of a > R1 Add R1, R0 // add R0 to R1 Mov *R1, 6 // constant 6 > address in R1 43 (Machinedependent) Peephole Optimizer A simple but effective technique for locally improving the target code. Examine a short sequence of target instruction (called peephole) and replacing these instruction by a shorter or faster sequence whenever possible. e.g. redundant instruction elimination flowofcontrol optimization algebraic simplification use of machine idioms 44 (7) Output of the peephole optimizer Mov R0, index // value of index > R0 Shl R0 // double value in R0 Mov &a[R0], 6 // constant 6 > address a + R0 45 Error Handling (Detection & Reporting) An important function of the compiler. Errors can be encountered by all of the phases of a compiler. The error messages should be reported to allow the programmer to determine where the errors have occurred. Once the error has been noted the compiler must modify the input to allow the latter phases can continue processing. 46 Possible errors detected in each phase of compilation process Phase Example Lexical Analyzer A token is misspelled. Syntax Analyzer A syntax entity is unable to be inferred. Semantic analyzer An operator whose operands have incompatible /Intermediate Code types. Generator Code Optimizer Certain statements can never be reached. Code Generator A compilercreated constant is too large to fit in a word of the target machine Symbol Table An identifier that has been multiply declared Management with contradictory attribute. Major Data Structures in a Compiler Token => a value The Syntax Tree => pointerbased structure The Symbol Table => hash table/an array of struct /... The Literal Table => an array of struct Intermediate Code => Quadruple (an array of struct) Temporary Files 48 Developing the first working compiler Suppose that we have a self-compiling C compiler for Sun Sparc 2. Suppose we also have an inefficient self-resident C compiler for Sun Sparc 2. How can we get an efficient self-resident C compiler for Sun Sparc 2? C Sun C C Sun C C Sun Sun dirty C Sun Sun inefficient C Sun Sun C Sun Sun efficient (inefficient) Developing the first working compiler Suppose that we have a self-compiling C compiler for Sun Sparc 2. Suppose we also have an inefficient self-resident C compiler for Sun Sparc 2. How can we get an efficient self-resident C compiler for Sun Sparc 2? C Sun C C Sun Sun dirty C Sun Sun inefficient C Sun C C Sun Sun (inefficient) C Sun Sun efficient Porting a compiler for a new machine that you have a self-compiling C compiler for Sun Sparc 2. Suppose you also have a self-resident C compiler for IBM AS400. How can we get a self-resident C compiler for Sun Sparc 2? C Sun C C Sun C C As As C Sun As C Sun As C Sun Sun cross compiler Suppose cross compiler Extending a language and developing its corresponding compiler Suppose you have both self-compiling and self-resident C compilers for Sun Sparc 2. If you want to extend the C language to become C+ with some new features. How do you get the self-compiling and self-resident C+ compilers for Sun Sparc 2? C+ Sun C C Sun Sun C+ Sun Sun C+ Sun C+ C+ Sun Sun C+ Sun Sun Improving an existing compiler Suppose you have a good self-resident C compiler for IBM AS400. Now you want to develop a enhanced version of C compiler with excellent optimizing capabilities for IBM AS400. How do you do it? C As C C As C C As As C As As C As As C As As ...
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