II. Language Processing ystem skeletal source program preprocessor source program compiler target object assembly program assembler relocatable machin

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1 CP Mathematical Foundations of C Dr.. Rodger ection: The tructure of a Compiler 1.1 What is a Compiler I. Translator Deænition: program in translator program in language! for! language X X Y Examples: ource Object Language Language Name Example High Level High Level preprocessor ratfor! f77 Assembly Machine assembler as High Level Machine compiler f77 cc pc Any executes interpretor BAIC often immediately c shell apl lisp æ Preprocessor For i=1 to n do stmts end for i=1 While ié=n do stmts i=i+1 end while 1

2 II. Language Processing ystem skeletal source program preprocessor source program compiler target object assembly program assembler relocatable machine code loaderlink-editor absolute machine code III. Compiler program in program in high level! compiler! machine language X for X language Y 2

3 1.2 TRUCTURE OF A COMPILER General Overview ç ç ç çç ç çç ymbol Table Management l ll l ll l l ource Code Lexical Analysis tokens yntax Analysis parse trees Intermediate Code Generation l ll l l intermediate code @ Handling Object Program Figure 1: 3

4 1.3 PHAE OF COMPILATION Lexical Analysis canner a. Purpose: Read the same program character by character grouping them into atomic units called ëtokens." b. Tokens: æ depend on language and compiler writer æ Examples: reserved words if for operators +; ; é; = constants punctuation g ë identiæers sb ch æ treated as a pair: token.type and token.value í token type is a mnemonic integer í some tokens have no value c. Example if x é= 0x=y+z when put through lexical analyzer produces: token type value if id 23 ëx" é= 27 int constant id 23 ëx" = assgnment 4 id 23 ëy" + 34 id 23 ëz" 4

5 d. How does one build a lexical analyzer æ from scratch æ lex e. Preview of Lex æ idea: tokens described by regular expressions æ basic syntax: regular expression action æ basic semantics: if match regular expression then do action. æ Example: ëif" ëë ë0-9ë+ return25; return28; return22; f. Remarks Besides returning token types and values the lexical analyzer might a print error messages b insert identiæers in the symbol table yntax Analysis Parsing a. Purpose: Accepts the sequence of tokens generated by the lexical analyzer checks whether the program is syntactically correct and generates a parse tree. b. yntax: formally described by a context free grammar. 5

6 c. Parse Tree if xé=0x=y+z statement if-statement ç P A PPP ç ççç ç A if condition hhhhhhhhhhhhhhhh statement P C PPPPP!!! relation! C expression relop expression L L assg. stmt Z ç ççç ææ Z lhs = rhs id é= constant id expr D H HHH D expr + expr C C id id Figure 2 is the parse tree for this statement. d. How does one build a parser Figure 2: Parse tree æ from scratch æ using a parser generator such as yacc Intermediate Code Generator a. Purpose: Traverse the parse tree producing simple intermediate code. b. Three-Address Code: Instructions: 1. id := id op id 2. goto label 3. if condition goto label 6

7 Example: if xé=0 x = x + z if xé=0 goto L1 goto L2 L1: x:=y+z L2: Intermediate Code Generation a. Purpose: Transform the intermediate code into ëbetter" code. b. Examples 1 Rearrangement ofcode if xé=0 goto L1 if xé0 goto L2 goto L2! x = y + z L1: x=y+z L2: L2: 2 Redundancy Elimination a=w+x+y b=x+y+z T1=x+y! a=w+t1 b=t1+z 3 trength Reduction x 2! x æ x expensive! cheap operator operator 4 Frequency Reduction for i=1; ién; i=i+1 f T1 = sqrt26 x = sqrt26! for i=1; ién; i=i+1 f g x=t1 g 7

8 c. Remarks: 1 Main criteria for optimization is speed Code Generation a. Purpose: Transform intermediate code to machine code assembler b. Example: a=b+c mov add mov b R1 c R1 R1 a c. Remarks 1 completely machine dependent whereas other phases are not 2 ëregister allocation" is the most diæcult task æ idea - use registers fast access to avoid memory use slow access æ problem - only a ænite number of registers during intermediate code phase one assumes an inænite number 1.4 ymbol Table a. Purpose: record information about various objects in the source program b. Examples æ procedure - no. and type of arguments æ simple variable - type æ array - type size c. Use - information is required during æ parsing æ code generation 8

9 1.5 Error Handler a. Errors - all errors should be æ detected æ detected correctly æ detected as soon as possible æ reported at the appropriate place and in a helpful manner b. Purpose æ report errors æ ëerror recovery" - proceed with processing c. Note: Errors can occur in each phase æ misspelled token æ wrong syntax æ improper procedure call æ statements that cannot be reached 9

Sardar Vallabhbhai Patel Institute of Technology (SVIT), Vasad M.C.A. Department COSMOS LECTURE SERIES ( ) (ODD) Code Optimization

Sardar Vallabhbhai Patel Institute of Technology (SVIT), Vasad M.C.A. Department COSMOS LECTURE SERIES (2018-19) (ODD) Code Optimization Prof. Jonita Roman Date: 30/06/2018 Time: 9:45 to 10:45 Venue: MCA