Where We Are. Incorrect Programs. Non-Context-Free Syntax. Goals of Semantic Analysis. Type Information CS412/CS413

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1 Where We Are CS412/CS413 Iroduco o Copers T Teebau Lecure 12: Sbo Tabes Februar 20, 2007 Source code (characer srea) Toke srea Absrac sa ree (AST) Decoraed AST f (b == 0) a = b; f ( b == 0 ) a = b ; f == b 0 f booea == b 0 = a b = a b vaue Leca Aass Sa Aass (Parsg) Seac Aass Errors (correc progra) CS 412/413 Sprg 2007 Iroduco o Copers 1 CS 412/413 Sprg 2007 Iroduco o Copers 2 No-Coe-Free Sa Progras ha are correc wh respec o he aguage s eca ad coe-free sacc rues a s coa oher sacc errors Leca aass ad coe-free sa aass are o powerfu eough o esure he correc usage of abes, obecs, fucos, saees, ec. No-coe-free sacc aass s kow as seac aass CS 412/413 Sprg 2007 Iroduco o Copers 3 Icorrec Progras Eape 1: eca aass does o dsgush bewee dffere abe or fuco defers ( reurs he sae oke for a defers) a; a; a = 1; b = 1; Eape 2: sa aass does o correae he decaraos wh he uses of abes he progra: a; a = 1; a = 1; Eape 3: sa aass does o correae he pes fro he decaraos wh he uses of abes: a; a; a = 1; a = 1.0; CS 412/413 Sprg 2007 Iroduco o Copers 4 Goas of Seac Aass Seac aass esures ha he progra sasfes a se of addoa rues regardg he usage of prograg cosrucs (abes, obecs, epressos, saees) Eapes of seac rues: Varabes us be decared before beg used A abe shoud o be decared upe es he sae scope I a assge saee, he abe ad he assged epresso us have he sae pe The codo of a f-saee us have pe Booea Soe caegores of rues: Seac rues regardg pes Seac rues regardg scopes CS 412/413 Sprg 2007 Iroduco o Copers 5 Tpe Iforao Tpe forao cassfes a progra s cosrucs (e.g., abes, saees, epressos, fucos) o caegores, ad poses rues o her use ( ers of hose caegores) wh he goa of avodg rue errors abes: a; eger ocao epressos: (a+1) == 2 Booea saees: a = 1.0; vod fucos: pow(, ) CS 412/413 Sprg 2007 Iroduco o Copers 6 1

2 Tpe Checkg Tpe checkg s he vadao of he se of pe rues Eapes: The pe of a abe us ach he pe fro s decarao The operads of arhec epressos (+, *, -, /) us have eger pes; he resu has eger pe The operads of coparso epressos (==,!=) us have eger or srg pes; he resu has Booea pe Tpe Checkg More eapes: For each assge saee, he pe of he updaed abe us ach he pe of he epresso beg assged For each ca saee (v 1,, v ), he pe of each acua ue v us ach he pe of he correspodg fora ue f fro he decarao of fuco The pe of he reur vaue us ach he reur pe fro he decarao of he fuco Tpe checkg: e wo ecures. CS 412/413 Sprg 2007 Iroduco o Copers 7 CS 412/413 Sprg 2007 Iroduco o Copers 8 Scope Iforao Scope forao characerzes he decarao of defers ad he poros of he progra where use of each defer s aowed Eape defers: abes, fucos, obecs, abes Leca scope s a eua rego he progra Saee bock Fora ue s Obec bod Fuco or ehod bod Modue bod Whoe progra (upe odues) Scope of a defer: he eca scope whch s vad Scope Iforao Scope of abes saee bocks: { a; scope of abe a { b; scope of abe b I C: Scope of fe sac abes: curre fe Scope of eera abes: whoe progra Scope of auoac abes, fora paraeers, ad fuco sac abes: he fuco CS 412/413 Sprg 2007 Iroduco o Copers 9 CS 412/413 Sprg 2007 Iroduco o Copers 10 Scope of fora ues of fucos/ehods: facora( ) { Scope of abes: vod f() { goo ; : a =1; goo ; Scope Iforao scope of fora paraeer scope of abe Scope Iforao Scope of obec feds ad ehods: cass A { prvae ; pubc vod g() { =1; cass B eeds A { pubc h() { g(); scope of fed scope of ehod g CS 412/413 Sprg 2007 Iroduco o Copers 11 CS 412/413 Sprg 2007 Iroduco o Copers 12 2

3 Seac Rues for Scopes Ma rues regardg scopes: Rue 1: Use a defer o f defed ecosg scope Rue 2: Do o decare defers of he sae kd wh deca aes ore ha oce he sae eca scope Ca decare defers wh he sae ae wh deca or overappg eca scopes f he are of dffere kds cass X { X; vod X( X) { X: for(;;) break X; X( X) { X; goo X; { X; X: X = 1; No Recoeded! CS 412/413 Sprg 2007 Iroduco o Copers 13 Sbo Tabes Seac checks refer o properes of defers he progra -- her scope or pe Need a evroe o sore he forao abou defers = sbo abe Each er he sbo abe coas he ae of a defer addoa forao: s kd, s pe, f s cosa, NAME p KIND fu TYPE boo boo ATTRIBUTES eer auo cos cos CS 412/413 Sprg 2007 Iroduco o Copers 14 Scope Iforao Eape How o represe scope forao he sbo abe? Idea: There s a herarch of scopes he progra Use a sar herarch of sbo abes Oe sbo abe for each scope Each sbo abe coas he sbos decared ha eca scope ; vod f( ) {, ; {, ; ; { ; : ; g( ) { boo ; ; fuc f sab Goba sab f fu vod g fu ab fuc g sab boo CS 412/413 Sprg 2007 Iroduco o Copers 15 CS 412/413 Sprg 2007 Iroduco o Copers 16 Idefers Wh Sae Nae The herarchca srucure of sbo abes auoaca soves he probe of resovg ae cosos (defers wh he sae ae ad overappg scopes) To fd he decarao of a defer ha s acve a a progra po: Sar fro he curre scope Go up he herarch u ou fd a defer wh he sae ae ; vod f( ) {, ; {, ; = 1; { ; : = 2; g( ) { boo ; = 3; Eape Goba sab f fu vod g fu ab = 1 = 2 boo = 3 CS 412/413 Sprg 2007 Iroduco o Copers 17 CS 412/413 Sprg 2007 Iroduco o Copers 18 3

4 ; Cachg Seac Errors vod f( ) {, ; {, ; = 1; { ; : = 2; g( ) { boo ; = 3; f g fu vod fu ab = 1 = 2 Error! boo = 3 Sbo Tabe Operaos Three operaos Creae a ew ep sbo abe wh a gve pare abe Iser a ew defer a sbo abe (or error) Lookup a defer a sbo abe (or error) Cao bud sbo abes durg eca aass herarch of scopes ecoded he sa Bud he sbo abes: Whe parsg, usg he seac acos Afer he AST s cosruced CS 412/413 Sprg 2007 Iroduco o Copers 19 CS 412/413 Sprg 2007 Iroduco o Copers 20 Arra Ipeeao Spe peeao = arra Oe er per sbo Sca he arra for ookup, copare ae a each er Ls Ipeeao Dac srucure = s Oe ce per er he abe Ca grow daca durg copao p fu boo boo Dsadvaage: abe has fed sze eed o kow advace he uber of eres fuc boo Dsadvaage: effce for e sbo abes eed o sca haf he s o average p Var boo CS 412/413 Sprg 2007 Iroduco o Copers 21 CS 412/413 Sprg 2007 Iroduco o Copers 22 Hash Tabe Ipeeao Effce peeao = hash abe I s a arra of ss (buckes) Uses a hashg fuco o ap he sbo ae o he correspodg bucke: hashfuc : srg Good hash fuco = eve dsrbuo he buckes fuc hashfuc( ) = 0, hashfuc( ) = 3 p boo Forward Refereces Forward refereces = use a defer wh he scope of s decarao, bu before s decared A coper phase ha uses he forao fro he sbo abe us be perfored afer he abe s cosruced Cao pe-check ad bud sbo abe a he sae e Eape: cass A { () { reur (); () { reur 1; CS 412/413 Sprg 2007 Iroduco o Copers 23 CS 412/413 Sprg 2007 Iroduco o Copers 24 4

5 Suar Seac checks esure he correc usage of abes, obecs, epressos, saees, fucos, ad abes he progra Scope seac checks esure ha defers are correc used wh he scope of her decarao Tpe seac checks esures he pe cossec of ous cosrucs he progra Sbo abes: a daa srucure for sorg forao abou sbos he progra Used seac aass ad subseque coper sages Ne e: pe-checkg CS 412/413 Sprg 2007 Iroduco o Copers 25 5

Abstract Syntax Trees. AST Data Structure. Visitor Interface. Accept methods. Visitor Methodology for AST Traversal CS412/CS413

Abstract Syntax Trees. AST Data Structure. Visitor Interface. Accept methods. Visitor Methodology for AST Traversal CS412/CS413 Abstract Syta Trees CS412/CS413 Itroductio to Copilers Ti Teitelbau Lecture 12: Visitors; Sybol Tables February 18, 2005 Separate AST costructio fro seatic checkig phase Traverse the AST ad perfor seatic