Some Thoughts on Grad School. Undergraduate Compilers Review and Intro to MJC. Structure of a Typical Compiler. Lexing and Parsing

Transcription

1 Undergrdute Compilers Review nd Intro to MJC Announcements Miling list is in full swing Tody Some thoughts on grd school Finish prsing Semntic nlysis Visitor pttern for bstrct syntx trees Some Thoughts on Grd School Gol lern how to lern subject in depth lern how to orgnize project, execute it, nd write bout it Iterte through the following: red the bckground mteril try some exmples sk lots of questions repet You will hve too much to do! lern to prioritize it is not possible to red ALL of the bckground mteril spend 2 hours of dedicted time EACH dy on ech clss/project wht grde you get is not the point hve fun nd lern ton! CS553 Lecture Undergrdute Compilers Review 2 CS553 Lecture Undergrdute Compilers Review 3 Structure of Typicl Compiler Lexing nd Prsing Anlysis chrcter strem lexicl nlysis tokens words syntctic nlysis AST sentences semntic nlysis nnotted AST interpreter Synthesis IR code genertion IR optimiztion IR code genertion trget lnguge Lexing theoreticl tool: regulr expressions recognizing substrings insted of strings so need longest mtch nd rule priority implementtion tools: flex, lex, SbleCC, etc. generte code tht implements deterministic finite utomt tht recognizes the specified tokens Prsing theoreticl tool: context free grmmrs recognizing whole progrm of tokens implementtion tools: bison, ycc, SbleCC, etc. generte LALR(1) or bottom-up prser tht uses shift-reduce prsing to recognize the progrm nd uses syntx-directed trnsltion to generte n AST CS553 Lecture Undergrdute Compilers Review 4 CS553 Lecture Undergrdute Compilers Review 5 1

2 Syntctic Anlysis (Prsing) Impose structure on token strem Limited to syntctic structure ( high-level) Prsers re usully utomticlly generted from grmmrs (e.g., ycc, bison, cup, jvcc), which use shift-reduce prsing An implicit prse tree occurs during prsing s grmmer rules re mtched Output of prsing is usully represented with n bstrct syntx tree (AST) for Exmple for i = 1 to 10 do [i] = x * 5 i 1 10 sg rr i tms x 5 Bottom-Up Prsing: Shift-Reduce Grmmer (1) S -> E (2) E -> E T (3) E -> T (4) T -> id b c S -> E -> E T -> E id -> E T id -> E id id -> T id id -> id id id Rightmost derivtion: expnd rightmost non-terminls first SbleCC, ycc, nd bison generte shift-reduce prsers: LALR(1): look-hed, left-to-right, rightmost derivtion in reverse, 1 symbol lookhed LALR is prsing tble construction method, smller tbles thn cnonicl LR Reference: Brbr Ryder s 198:515 lecture notes CS553 Lecture Undergrdute Compilers Review 6 CS553 Lecture Undergrdute Compilers Review 7 Syntx-directed Trnsltion: AST Construction exmple Grmmer with production rules S: E $$ = $1 E: E T $$ = new node(, $1, $3) T $$ = $1 T: $$ = new lef( id, $1) Implicit prse tree for bc E T Reference: Brbr Ryder s 198:515 lecture notes E S E T T b c AST for bc CS553 Lecture Undergrdute Compilers Review 8 b c Shift-Reduce Prsing Exmple (precedence problem) $ Stck Input Action b * c shift (1) S -> E (2) E -> E T (3) E -> E * T (4) E -> T (5) T -> id CS553 Lecture Undergrdute Compilers Review 9 2

3 Using SbleCC to specify grmmr nd generte AST Productions cst_stm -> stm = cst_exp -> New stm(cst_exp.exp) cst_exp -> exp = plus_rule cst_exp t_plus cst_term -> New exp.plus(cst_exp.exp, cst_term.exp) term_rule cst_term -> cst_term.exp cst_term -> exp = t_id -> New exp.id(t_id) minijv.scc excerpts Productions cst_progrm -> progrm = cst_min_clss cst_clss_decl* -> New progrm(cst_min_clss.min_clss,[cst_clss_decl.clss_decl]) cst_exp_list -> exp* = mny_rule cst_exp cst_exp_rest* -> [cst_exp.exp, cst_exp_rest.exp] empty_rule -> [] cst_exp_rest -> exp* = t_comm cst_exp -> [cst_exp.exp] Abstrct Syntx Tree progrm = min_clss [clss_decls]:clss_decl* exp = cll exp t_id [rgs]:exp* Abstrct Syntx Tree stm = exp exp = plus [l_exp]:exp [r_exp]:exp id t_id CS553 Lecture Undergrdute Compilers Review 10 CS553 Lecture Undergrdute Compilers Review 11 Exmple Abstrct Syntx Tree MJC Semntic Anlysis clss Fctoril public sttic void min(string[] ) System.out.println(new Fc().ComputeFc(10)) clss Fc public int ComputeFc(int num) int num_ux if (num < 1) num_ux = 1 else num_ux = num * (this.computefc(num-1)) return num_ux Determine whether source is meningful Check for semntic errors Check for type errors Gther type informtion for subsequent stges Relte vrible uses to their declrtions Some semntic nlysis tkes plce during prsing Exmple errors (from C) function1 = x = 570 hello, world! sclr[i] CS553 Lecture Undergrdute Compilers Review 12 CS553 Lecture Undergrdute Compilers Review 13 3

4 Compiler Dt Structures Using the Visitor Pttern for semntic nlysis Symbol Tbles Compile-time dt structure Holds nmes, type informtion, nd scope informtion for vribles Scopes A nme spce e.g., In Pscl, ech procedure cretes new scope e.g., In C, ech set of curly brces defines new scope Cn crete seprte symbol tble for ech scope Using Symbol Tbles For ech vrible declrtion: Check for symbol tble entry Add new entry (prsing) dd type info (semntic nlysis) For ech vrible use: Check symbol tble entry (semntic nlysis) public clss DepthFirstAdpter extends AnlysisAdpter public void inaplusexp(aplusexp node) defultin(node) public void outaplusexp(aplusexp node) defultout(node) public void cseaplusexp(aplusexp node) inaplusexp(node) if(node.getlexp()!= null) node.getlexp().pply(this) if(node.getrexp()!= null) node.getrexp().pply(this) outaplusexp(node) public finl clss APlusExp extends PExp public void pply(switch sw) ((Anlysis) sw).cseaplusexp(this) CS553 Lecture Undergrdute Compilers Review 14 CS553 Lecture Undergrdute Compilers Review 15 Symbol Tble in the MiniJv Compiler Concepts Compiltion stges Scnning, prsing, semntic nlysis, intermedite code genertion, optimiztion, code genertion Prsing generting n AST shift-reduce prsing Semntic Anlysis symbol tbles using visitors over the AST CS553 Lecture Undergrdute Compilers Review 16 CS553 Lecture Undergrdute Compilers Review 17 4

5 Next Time Reding skim Ch 2-6 in Appel focus on 2.1, 2.2, 3.1, 3.3 except prser genertion, Ch 4, 5.2, Ch 6 skip 3.2 except for FOLLOW description, 3.5, 5.1 skim Ch 7-9, 12 focus on 7.1, 7.3, 8.1, 8.2, 9.3, 12 skip 9.2 Lecture Finish Undergrd Compilers Review Prsing Terms (Definitely know these terms) Lexicl Anlysis longest mtch nd rule priority regulr expressions tokens CFG (Context-free Grmmer) production rule terminl non-terminl FOLLOW(X): the set of terminls tht cn immeditely follow X Syntx-directed trnsltion inherited ttributes synthesized ttributes CS553 Lecture Undergrdute Compilers Review 18 CS553 Lecture Undergrdute Compilers Review 19 Prsing Terms cont Top-down prsing LL(1): left-to-right reding of tokens, leftmost derivtion, 1 symbol look-hed Predictive prser: n efficient non-bcktrcking top-down prser tht cn hndle LL(1) More generlly recursive descent prsing my involve bcktrcking Bottom-up Prsing LR(1): left-to-right reding of tokens, rightmost derivtion in reverse, 1 symbol lookhed Shift-reduce prsers: for exmple, bison, ycc, nd SbleCC generted prsers Methods for producing n LR prsing tble SLR, simple LR Cnonicl LR, most powerful LALR(1) BNF (Bckus-Nur Form) nd EBNF (Extended BNF): equivlent to CFGs CS553 Lecture Undergrdute Compilers Review 20 5