1. 1 Crafting a Compiler with C Chapter 1 Introduction Teacher : Dr. Lawrence Y. Deng contact: Lawrence@mail.sju.edu.tw Grading: Attendance 10%, Midterm exam. 30%, Homework 20%, Final exam. + Team project 40%Lawrence@mail.sju.edu.tw Textbook: “Crafting a compiler with C” C. N. Fischer and R. J. LeBlanc, Jr.1991, The Benjamin/Cummings Publishing Company Reference “Compilers Principles, Techniques, and Tools”,A. V. Aho, R. Sethi, J. D. Ullman, 2006 2th, Addison Weslay

2. 2 Outlines 1.1 Overview and History 1.2 What Do Compilers Do? 1.3 The Structure of a Compiler 1.4 The Syntax and Semantics of Programming Languages 1.5 Compiler Design and Programming Language Design 1.6 Compiler Classifications 1.7 Influences on Computer Design

3. 3 Overview and History Compilers are fundamental to modern computing. They act as translators, transforming human-oriented programming languages into computer-oriented machine languages. Programming Language (Source) Compiler Machine Language (Target)

4. 4 Compilers are fundamental to modern computing: Natural Language Processing – 資訊檢索、機器翻譯、智慧型介面 ( 介面設計 ) 、寫 作輔助、語音辨識與合成、 OCR – 網頁的生成、檢索、擷取、多媒體性、及多語言性 – 手語、行為偵測、網路監控、遊戲對奕 – 內容管理

5. 5 Reference Technologies Finite State Machine Network Data Classification Web Content Structure/Content/Usage Mining

6. 6 Overview and History (Cont’d) The first real compiler –FORTRAN compilers of the late 1950s, IBM –18 person-years to build Compiler technology is more broadly applicable and has been employed in rather unexpected areas. –Text-formatting languages, like nroff and troff; preprocessor packages like eqn, tbl, pic –Silicon compiler for the creation of VLSI circuits –Command languages of OS –Query languages of Database systems efficient? (compared with assembly program) –not bad, but much easier to write –high-level languages are feasible. 18 man-year, ad hoc structure Today, we can build a simple compiler in a few month. Crafting an efficient and reliable compiler is still challenging.

7. 7 1.2 What Do Compilers Do? Compilers may be distinguished according to the kind of target code they generate: –Pure Machine Code –Augmented Machine Code –Virtual Machine Code JVM, P-code

8. 8 What Do Compilers Do? (Cont’d) Another way that compilers differ from one another is in the format of the target machine code they generate –Assembly Language Format –Relocatable Binary Format A linkage step is required –Memory-Image (Load-and-Go) Format

9. 9 Another kind of language processor, called an interpreter, differs from a compiler in that it executes programs without explicitly performing a translation What Do Compilers Do? (Cont’d) Source Program Encoding Output Interpreter Data

10. 10 1.3 The Structure of a Compiler Any compiler must perform two major tasks –Analysis of the source program –Synthesis of a machine-language program

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12. 12 The Structure of a Compiler (Cont’d) ScannerParser Semantic Routines Code Generator Optimizer Source Program (Character Stream) TokensSyntactic Structure Intermediate Representation Target Machine Code Symbol and Attribute Tables (Used by all Phases of The Compiler) The structure of a Syntax-Directed Compiler

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14. 14 the structure of a compiler source program scanner parser semantic routine optimizer code generator target code symbol table a:=b*2+0 syntax trees id:=id*int+int 1. type are correct load b mul 2 add 0 sta a load b shL 1 sta a oo1F 2b4A 309F

15. 15 The Structure of a Compiler (Cont’d) Scanner –The scanner begins the analysis of the source program by reading the input, character by character, and grouping characters into individual words and symbols (tokens) –The tokens are encoded and then are fed to the parser for syntactic analysis –For details, see the bottom of page 8. Scanner generators

16. 16 The Structure of a Compiler (Cont’d) Parser –Given a formal syntax specification (typically as a context-free [CFG] grammar), the parse reads tokens and groups them into units as specified by the productions of the CFG being used. –While parsing, the parser verifies correct syntax, and if a syntax error is found, it issues a suitable diagnostic. –As syntactic structure is recognized, the parser either calls corresponding semantic routines directly or builds a syntax tree.

17. 17 Parser: identify syntactic structure - Syntax is specified by grammars,e.g., IfStmt==if ( Exp ) then Stmt Exp==  … - Parsers can be generated from grammars. grammar yacc or llgen parser - Error-repair, e.g., ")" is missing if ( a > 3 then - Parsers may build a syntax tree or it may call semantic routines directly.

18. 18 The Structure of a Compiler (Cont’d) Semantic Routines –Perform two functions Check the static semantics of each construct Do the actual translation –The heart of a compiler Optimizer –The IR code generated by the semantic routines is analyzed and transformed into functionally equivalent but improved IR code. –This phase can be very complex and slow –Peephole optimization

19. 19 Semantic routines - Check that variables are defined, that types are correct,  … , etc. Ex. x := x + true - Generate IR (3-addr code), e.g., ADD A, B, C - hand-coded - associated with grammar rules - formalized as attribute grammars (AG)

20. 20 peephole optimization: –simple and effective –Ex 1. STORE R1, A LOAD A, R1 –Ex 2.MUL R1, #1 –Ex 3.ADD R1, #0 –These innocent code can be actually generated by a naive compiler.

21. 21 The Structure of a Compiler (Cont’d) One-pass compiler –No optimization is required –To merge code generation with semantic routines and eliminate the use of an IR Compiler writing tools –Compiler generators or compiler-compilers E.g. scanner and parser generators

22. 22 1.4 Compiler Design and Programming Language Design An interesting aspect is how programming language design and compiler design influence one another. Programming languages that are easy to compiler have many advantages –See the 2 nd paragraph of page 16.

23. 23 1.5 Compiler Design and Programming Language Design (Cont’d) Languages such as Snobol and APL are usually considered noncompilable What attributes must be found in a programming language to allow compilation? –Can the scope and binding of each identifier reference be determined before execution begins –Can the type of object be determined before execution begins? –Can existing program text be changed or added to during execution?

24. 24 1.6 Compiler Classifications Diagnostic compilers Report and repair compile-time errors. - Add run-time checks, e.g., array subscripts. - should be used in real world. - vs. production compiler Optimizing compilers - for production use - 'optimal' is suspicious because 1. theoretically undecidable 2. practically infeasible - Perform a lot of transformations with unknown effects. Ex. place data in registers ›fast access ›slow procedure call Retargetable compiler Localize machine dependence. - difficult to implement - less efficient object code