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Chapter 1: Introduction to Compiling (Cont.)

Chapter 1: Introduction to Compiling (Cont.). Phase 3. Semantic Analysis. :=. :=. position. +. position. +. initial. *. initial. *. rate. 60. rate. inttoreal. 60. Find More Complicated Semantic Errors and Support Code Generation Parse Tree Is Augmented With Semantic Actions.

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Chapter 1: Introduction to Compiling (Cont.)

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  1. Chapter 1: Introduction to Compiling (Cont.)

  2. Phase 3. Semantic Analysis := := position + position + initial * initial * rate 60 rate inttoreal 60 • Find More Complicated Semantic Errors and Support Code Generation • Parse Tree Is Augmented With Semantic Actions Compressed Tree Conversion Action

  3. Phase 3. Semantic Analysis • Most Important Activity in This Phase: • Type Checking - Legality of Operands • Many Different Situations: Real := int + char ; A[int] := A[real] + int ; while char <> int do …. Etc.

  4. Supporting Phases/ Activities for Analysis • Symbol Table Creation / Maintenance • Contains Info (storage, type, scope, args) on Each “Meaningful” Token, Typically Identifiers • Data Structure Created / Initialized During Lexical Analysis • Utilized / Updated During Later Analysis & Synthesis • Error Handling • Detection of Different Errors Which Correspond to All Phases • What Kinds of Errors Are Found During the Analysis Phase? • What Happens When an Error Is Found?

  5. The Many Phases of a Compiler Source Program 5 1 2 6 Code Optimizer Lexical Analyzer Code Generator Syntax Analyzer 3 Semantic Analyzer Error Handler Symbol-table Manager 4 Intermediate Code Generator Target Program 1, 2, 3 : Analysis - Our Focus 4, 5, 6 : Synthesis

  6. The Synthesis Task For Compilation • Intermediate Code Generation • Abstract Machine Version of Code - Independent of Architecture • Easy to Produce and Do Final, Machine Dependent Code Generation • Code Optimization • Find More Efficient Ways to Execute Code • Replace Code With More Optimal Statements • 2-approaches: High-level Language & “Peephole” Optimization • Final Code Generation • Generate Relocatable Machine Dependent Code

  7. Reviewing the Entire Process intermediate code generator lexical analyzer syntax analyzer semantic analyzer := + id1 id2l * id3 60 := + id1 id2l * id3 inttoreal 60 position := initial + rate * 60 id1 := id2 + id3 * 60 Symbol Table Errors position .... initial …. rate….

  8. Reviewing the Entire Process intermediate code generator code optimizer final code generator Errors Symbol Table position .... initial …. rate…. temp1 := inttoreal(60) temp2 := id3 * temp1 temp3 := id2 + temp2 id1 := temp3 3 address code temp1 := id3 * 60.0 id1 := id2 + temp1 MOVF id3, R2 MULF #60.0, R2 MOVF id2, R1 ADDF R1, R2 MOVF R1, id1

  9. Assemblers • Assembly code: names are used for instructions, and names are used for memory addresses. • Two-pass Assembly: • First Pass: all identifiers are assigned to memory addresses (0-offset)e.g. substitute 0 for a, and 4 for b • Second Pass: produce relocatable machine code: MOV a, R1 ADD #2, R1 MOV R1, b 0001 01 00 00000000 * 0011 01 10 00000010 0010 01 00 00000100 * relocation bit

  10. Loaders and Link-Editors • Loader: taking relocatable machine code, altering the addresses and placing the altered instructionsinto memory. • Link-editor: taking many (relocatable) machine code programs (with cross-references) and produce a single file. • Need to keep track of correspondence between variable names and corresponding addresses in each piece of code.

  11. Compiler Cousins:PreprocessorsProvide Input to Compilers 1. Macro Processing #define in C: does text substitution before compiling #define X 3 #define Y A*B+C #define Z getchar()

  12. 2. File Inclusion defs.h main.c ////// ////// ////// #include “defs.h” …---…---…--- …---…---…--- …---…---…--- ////// ////// ////// …---…---…--- …---…---…--- …---…---…--- #include in C - bring in another file before compiling

  13. 3. Rational Preprocessors • Augment “Old” Languages With Modern Constructs • Add Macros for If - Then, While, Etc. • #Define Can Make C Code More Pascal-like #define begin { #define end } #define then

  14. 4. Language Extensions for a Database System EQUEL - Database query language embedded in a programming language. C ## Retrieve (DN=Department.Dnum) where ## Department.Dname = ‘Research’ is Preprocessed into: ingres_system(“Retr…..Research’”,____,____); a procedure call in a programming language.

  15. The Grouping of Phases Front End : Analysis + Intermediate Code Generation vs. Back End : Code Generation + Optimization Number of Passes: A pass: requires r/w intermediate files Fewer passes: more efficiency. However: fewer passes require more sophisticated memory management and compiler phase interaction. Tradeoffs ……..

  16. Compiler Construction Tools Parser Generators : Produce Syntax Analyzers Scanner Generators : Produce Lexical Analyzers <= Lex (Flex) Syntax-directed Translation Engines : Generate Intermediate Code <= Yacc (Bison) Automatic Code Generators : Generate Actual Code Data-Flow Engines : Support Optimization

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