May 31, May 31, 2016May 31, 2016May 31, 2016 Azusa, CA Sheldon X. Liang Ph. D. Computer Science at Azusa Pacific University Azusa Pacific University, Azusa, CA 91702, Tel: (800) Department of Computer Science, CS400 Compiler Construction

May 31, Azusa Pacific University, Azusa, CA 91702, Tel: (800) Department of Computer Science, Administrative info  Instructor  Name: Sheldon X. Liang   Office: WC 204  Hours: to set up appointment CS400 Compiler Construction

May 31, CS400 Compiler Construction Azusa Pacific University, Azusa, CA 91702, Tel: (800) Department of Computer Science, Administrative info  Course webpage  cs-linux.cs.apu.edu/~sliang  contains: lecture notes & other handouts howeworks & manuals policies, grades useful links

May 31, CS400 Compiler Construction Azusa Pacific University, Azusa, CA 91702, Tel: (800) Department of Computer Science, What is a compiler  A program that reads a program written in some language and translates it into a program written in some other language Modula-2 to C Java to bytecodes Ada to C++  How was the first compiler created?

May 31, CS400 Compiler Construction Azusa Pacific University, Azusa, CA 91702, Tel: (800) Department of Computer Science, Why study compilers?  Typical front-end technology: Grammars e.g. human-computer interaction => HCI Regular expressions e.g. limited rules to represent unlimited expressions Parsers e.g. grasp meanings from information stream Syntax-directed e.g. guide to “speak” in right way

May 31, CS400 Compiler Construction Azusa Pacific University, Azusa, CA 91702, Tel: (800) Department of Computer Science, Why study compilers?  Technology found use outside compilers: Used in tools that find bugs in software e.g. human-computer interaction => HCI Used in tools that find security holes in existing code e.g. limited rules to represent unlimited expressions Applied to a wide range of problems e.g. in software design and software development  We learn something not just for something Competence of problem-solving Solve new problems we will encounter in the future

May 31, CS400 Compiler Construction Azusa Pacific University, Azusa, CA 91702, Tel: (800) Department of Computer Science, Why study compilers?  Application of a wide range of theoretical techniques Data Structures Theory of Computation Algorithms Computer Architecture  Good SW engineering experience  Better understanding of programming languages

May 31, CS400 Compiler Construction Azusa Pacific University, Azusa, CA 91702, Tel: (800) Department of Computer Science, Features of compilers  Correctness preserve the meaning of the code check syntactic mistakes alert potential problems  Speed of target code  Cooperation with debugger  Support for separate compilation  Good error reporting / handling

May 31, CS400 Compiler Construction Azusa Pacific University, Azusa, CA 91702, Tel: (800) Department of Computer Science, Compiler structure  Use intermediate representation why? source code target code Front EndBack End IR

May 31, CS400 Compiler Construction Azusa Pacific University, Azusa, CA 91702, Tel: (800) Department of Computer Science, Compiler structure  Front end  Recognize legal/ illegal programs  Generate IR (for further process)  The process can be automated !!!  Back end  Translate IR into target code instruction selection register allocation instruction scheduling

May 31, CS400 Compiler Construction Azusa Pacific University, Azusa, CA 91702, Tel: (800) Department of Computer Science, Compiler structure

May 31, CS400 Compiler Construction Azusa Pacific University, Azusa, CA 91702, Tel: (800) Department of Computer Science, Compiler structure  Optimization  goals improve running time of generated code improve space, power consumption, etc.  how? perform a number of transformations on the IR multiple passes  Important: preserve meaning of code what you think and what you get

May 31, CS400 Compiler Construction Azusa Pacific University, Azusa, CA 91702, Tel: (800) Department of Computer Science, The Front End  Scanning (aka lexical analysis)  recognize “words” (tokens) key words, variables etc.  Parsing (aka syntax analysis)  check syntax if - then not if - else  Semantic analysis  examine meaning (e.g. type checking) duplicate declaration

May 31, CS400 Compiler Construction Azusa Pacific University, Azusa, CA 91702, Tel: (800) Department of Computer Science, Compiler: structure and process Scanning… Parsing… Checking… IR

May 31, CS400 Compiler Construction Azusa Pacific University, Azusa, CA 91702, Tel: (800) Department of Computer Science, Compiler tool: lexical analysis Scanner   Its job ：  recognize words (tokens) e.g. x = 1 becomes ID equal Int  collect identifier information e.g. ID corresponds to x and its type  Ignore white space and comments  report errors  Good news :~)  the process can be automated

May 31, CS400 Compiler Construction Azusa Pacific University, Azusa, CA 91702, Tel: (800) Department of Computer Science, Compiler tool: syntax analysis Parser   Its job ：  Check & verify syntax based on rules e.g. “ID equal Int” makes up an expression coming soon: how context-free grammars specify syntax  Report errors  Build IR often a syntax tree  Good news :~)  the process can be automated

May 31, CS400 Compiler Construction Azusa Pacific University, Azusa, CA 91702, Tel: (800) Department of Computer Science, Compiler tool: semantic analysis checker   Its job ：  Check the meaning of the program e.g. x = y; are x, y declared properly? e.g. x = y; is y defined before being used? e.g. x = y; are theirs types compatible?  Meaning may depend on context  Report errors (less effectively)  Report warnings (more effectively)

May 31, CS400 Compiler Construction Azusa Pacific University, Azusa, CA 91702, Tel: (800) Department of Computer Science, Compiler result: intermediate IRs   Intermediate Representations ：  Graphical e.g. parse tree, DAG (directed acyclic graph)  Linear e.g. three address code (one operator): x+y*z ==> t 1 = y*z / t 2 = x+t 1  Hybrid e.g. linear for blocks of straight-line code, a graph to connect blocks  Low-level or high-level machine-dependent or machine-independent

May 31, CS400 Compiler Construction Azusa Pacific University, Azusa, CA 91702, Tel: (800) Department of Computer Science, Compiler result: intermediate IRs   Intermediate Representations ：  Graphical e.g. parse tree, DAG (directed acyclic graph)  Linear e.g. three address code (one operator): x+y*z ==> t 1 = y*z / t 2 = x+t 1  Hybrid e.g. linear for blocks of straight-line code, a graph to connect blocks  Low-level or high-level machine-dependent or machine-independent

May 31, CS400 Compiler Construction Azusa Pacific University, Azusa, CA 91702, Tel: (800) Department of Computer Science, Compiler process: scanning Scanning   Lexical analysis ：  Main goal: recognize words  How? by recognizing patterns e.g. an ID is a sequence of letters or digits that starts with a letter  Lexical patterns form a regular language  Regular languages are described using regular expressions (REs)  Can we create an automatic RE recognizer? Yes! (Hold that thought)

May 31, CS400 Compiler Construction Azusa Pacific University, Azusa, CA 91702, Tel: (800) Department of Computer Science, Compiler process: scanning Scanning   Definition: regular expression (over alphabet  )   is an RE denoting {  }  If , then  is an RE denoting {  }  If r and s are Res, then (r) => RE denoting L(r) r | s => RE denoting L(r)  L(s) rs => RE denoting L(r)L(s) r* => RE denoting the Kleene closure of L(r)  Property: REs are closed under many operations  This allows us to build complex REs

May 31, CS400 Compiler Construction Azusa Pacific University, Azusa, CA 91702, Tel: (800) Department of Computer Science, Compiler process: scanning Scanning   Definition: Deterministic Finite Automaton(DFA)  A 5-tuple ( , S, , s 0, F) where  is the alphabet S is he set of states  is the transition function (S  S ) s 0 is the starting state F is the set of final states (F  S)  Notation:  Use a transition diagram to describe a DFA  DFAs are equivalent to REs  Hey! We just came up with a recognizer!

May 31, CS400 Compiler Construction Azusa Pacific University, Azusa, CA 91702, Tel: (800) Department of Computer Science, Compiler process: scanning Scanning   Goal: automate the process  Idea:  Start with an RE  Build a DFA  How? We can build a non-deterministic finite automaton (Thompson’s construction) Convert that to a deterministic one (subset construction) Minimize the DFA (Hopcroft’s algorithm)  Implement it  Existing scanner generator: flex

Thank you very much! Questions? May 31, Azusa Pacific University, Azusa, CA 91702, Tel: (800) Department of Computer Science, CS400 Compiler Construction Introduction to Compiler