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Lecture 01 - Introduction THEORY OF COMPILATION EranYahav 1 Who? EranYahav Taub 734 Tel: 8294318 [email protected] Monday 13:30-14:30 http://www.cs.tecnion.ac.il/~yahave TAs: • Adi Sosnovich • Maya Arbel • Guy Hefetz 2 What is a Compiler? “A compiler is a computer program that transforms source code written in a programming language (source language) into another language (target language). The most common reason for wanting to transform source code is to create an executable program.” --Wikipedia 3 What is a Compiler? source language C C++ Pascal Java target language IA32 IA64 SPARC txt exe C C++ Executable Pascal Java code Postscript Source TeX text Perl JavaScript Python Ruby Java Bytecode … Prolog Lisp Scheme ML OCaml Compiler 4 What is a Compiler? Compiler txt exe Source Executable text code int a, b; a = 2; b = a*2 + 1; MOV R1,2 SAL R1 INC R1 MOV R2,R1 5 Anatomy of a Compiler Compiler txt Source text int a, b; a = 2; b = a*2 + 1; exe Frontend Semantic Backend (analysis) Representation (synthesis) Executable code MOV R1,2 SAL R1 INC R1 MOV R2,R1 6 SET R1,2 STORE #0,R1 SHIFT R1,1 STORE #1,R1 ADD R1,1 STORE #2,R1 Modularity txt Source Language 1 txt Source Language 1 txt Source Language 1 int a, b; a = 2; b = a*2 + 1; Frontend Backend SL1 TL1 Frontend SL2 Semantic Representation Backend TL2 Frontend Backend SL3 TL3 exe Executable target 1 exe Executable target 1 exe Executable target 1 MOV R1,2 SAL R1 INC R1 MOV R2,R1 7 Anatomy of a Compiler Compiler txt Source text int a, b; a = 2; b = a*2 + 1; exe Frontend Semantic Backend (analysis) Representation (synthesis) Lexical Analysis Syntax Analysis Parsing Semantic Analysis Intermediate Representation (IR) Code Generation Executable code MOV R1,2 SAL R1 INC R1 MOV R2,R1 8 Interpreter Interpreter txt Source text int a, b; a = 2; b = a*2 + 1; Frontend Semantic Execution (analysis) Representation Engine Output Input 9 Compiler vs. Interpreter txt Source text exe Frontend Semantic Backend (analysis) Representation (synthesis) Frontend Semantic Execution (analysis) Representation Engine Executable code txt Source text Input Output 10 Compiler vs. Interpreter 3 b = a*2 + 1; Frontend Semantic Backend (analysis) Representation (synthesis) MOV R1,8(ebp) SAL R1 INC R1 MOV R2,R1 7 b = a*2 + 1; Frontend Semantic Execution (analysis) Representation Engine 3 7 11 Just-in-time Compiler (Java example) txt Java Source txt Java source to Java bytecode compiler Java Java Virtual Machine Output Bytecode Input Just-in-time compilation: bytecode interpreter (in the JVM) compiles program fragments during interpretation to avoid expensive re-interpretation. 12 Why should you care? Every person in this class will build a parser some day Or wish she knew how to build one… Useful techniques and algorithms Lexical analysis / parsing Semantic representation … Register allocation Understand programming languages better Understand internals of compilers Understand (some) details of target architectures 13 Why should you care? Compiler Useful formalisms Source Programming Languages Software Engineering Regular expressions Context-free grammars Attribute grammars Data structures Algorithms Target Runtime environment Garbage collection Architecture 14 Why should you care? 15 Course Overview Compiler txt Source text Lexical Analysis Syntax Analysis Parsing Semantic Analysis Inter. Rep. (IR) Code exe Gen. Executable code 16 Journey inside a compiler Token Stream txt x = b*b – 4*a*c <ID,”x”> <EQ> <ID,”b”> <MULT> <ID,”b”> <MINUS> <INT,4> <MULT> <ID,”a”> <MULT> <ID,”c”> Lexical Analysis Syntax Analysis Sem. Analysis Inter. Rep. Code Gen. 17 Journey inside a compiler <ID,”x”> <EQ> <ID,”b”> <MULT> <ID,”b”> <MINUS> <INT,4> <MULT> <ID,”a”> <MULT> <ID,”c”> expression expression MINUS expression Syntax Tree term MULT factor term term term factor ID MULT factor term MULT ID ‘b’ ‘b’ ID factor factor ID ID ‘a’ ‘c’ ‘4’ Lexical Analysis Syntax Analysis Sem. Analysis Inter. Rep. Code Gen. 18 Journey inside a compiler Abstract Syntax Tree MINUS MULT ‘b’ MULT ‘b’ MULT ‘4’ Lexical Analysis Syntax Analysis ‘c’ ‘a’ Sem. Analysis Inter. Rep. Code Gen. 19 Journey inside a compiler MINUS MULT type: int ‘b’ loc: sp+16 type: int loc: R1 Annotated Abstract Syntax Tree type: int loc: R1 ‘b’ MULT type: int loc: sp+16 MULT type: int loc: const ‘4’ Lexical Analysis Syntax Analysis type: int loc: R2 type: int loc: R2 ‘c’ type: int loc: sp+24 type: int ‘a’ loc: sp+8 Sem. Analysis Inter. Rep. Code Gen. 20 Journey inside a compiler type: int loc: R1 MINUS MULT type: int loc: sp+16 ‘b’ type: int loc: R1 R2 = 4*a R1=b*b R2= R2*c R1=R1-R2 type: int MULT loc: R2 type: int ‘b’ loc: sp+16 type: int loc: const Intermediate Representation MULT type: int loc: R2 ‘c’ type: int loc: sp+24 type: int ‘a’ loc: sp+8 ‘4’ Lexical Analysis Syntax Analysis Sem. Analysis Inter. Rep. Code Gen. 21 Journey inside a compiler type: int loc: R1 MINUS MULT type: int loc: sp+16 ‘b’ type: int loc: R1 R2 = 4*a R1=b*b R2= R2*c R1=R1-R2 type: int MULT loc: R2 type: int ‘b’ loc: sp+16 type: int loc: const Intermediate Representation MULT type: int loc: R2 ‘c’ type: int loc: sp+24 MOV R2,(sp+8) SAL R2,2 MOV R1,(sp+16) MUL R1,(sp+16) MUL R2,(sp+24) SUB R1,R2 type: int ‘a’ loc: sp+8 ‘4’ Lexical Analysis Syntax Analysis Sem. Analysis Inter. Rep. Code Gen. Assembly Code 22 Error Checking In every stage… Lexical analysis: illegal tokens Syntax analysis: illegal syntax Semantic analysis: incompatible types, undefined variables, … Every phase tries to recover and proceed with compilation (why?) Divergence is a challenge 23 Errors in lexical analysis txt pi = 3.141.562 Illegal token txt pi = 3oranges Illegal token txt pi = oranges3 <ID,”pi”>, <EQ>, <ID,”oranges3”> 24 Error detection: type checking MULT txt MULT x = 4*a*”oranges” type: int loc: const ‘4’ type: int loc: R2 type: int loc: R2 “oranges” type: string loc: const type: int ‘a’ loc: sp+8 25 The Real Anatomy of a Compiler txt Source text Process text input characters Lexical Analysis tokens Syntax Analysis AST Sem. Analysis Annotated AST Intermediate code generation IR Intermediate code optimization Code generation IR Symbolic Instructions Target code optimization SI Machine code generation MI Write executable output exe Executable code 26 Optimizations “Optimal code” is out of reach many problems are undecidable or too expensive (NP-complete) Use approximation and/or heuristics Must preserve correctness, should (mostly) improve code Many optimization heuristics Loop optimizations: hoisting, unrolling, … Peephole optimizations Constant propagation Leverage compile-time information to save work at runtime (precomputation) Dead code elimination Majority of compilation time is spent in the optimization phase 27 Machine code generation Register allocation Optimal register assignment is NP-Complete In practice, known heuristics perform well assign variables to memory locations Instruction selection Convert IR to actual machine instructions Modern architectures Multicores Challenging memory hierarchies 28 Compiler Construction Toolset Lexical analysis generators lex Parser generators yacc Syntax-directed translators Dataflow analysis engines 29 Summary Compiler is a program that translates code from source language to target language Compilers play a critical role Bridge from programming languages to the machine Many useful techniques and algorithms Many useful tools (e.g., lexer/parser generators) Compiler constructed from modular phases Reusable Different front/back ends 30 Coming up next Lexical analysis 31