东南大学 编译原理 课件 Cp5.ppt

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1、Chapter5Syntax-DirectedTranslationZhaiYuqingZhouXiaoyuApproachestoImplementSyntax-DirectedTranslationSemanticStaticSemanticDynamicSemanticE.g.Annotatedparsetreefor3*5+4E.val=19E.val=15+T.val=4F.val=3F.val=4T.val=3*F.val=5digit.lexval=4digit.lexval=3digit.lexval=5T.val=15BasicIde

2、a(1)Guidedbycontext-freegrammar(Translatingwhileorafterparsing)Attachingattributestothegrammarsymbolsrepresentingtheprogramconstruction.Theattributesrepresentanythingwechoose:astring,anumber,atype,amemorylocation,etc.BasicIdea(2)Thedependencybetweentheattributesofrelevantnodesins

3、yntaxtree.Thevalueofanattributeataparsetreenodeiscomputedbya“semanticrule”associatedwiththeproductionusedatthatnode.BasicIdea(3)Evaluationofthesemanticrulesmaygeneratecode,saveinformationinasymboltable,issueerrormessages,orperformanyotheractivities.AssociatingSemanticRuleswithPro

4、ductionsSyntax-directedDefinition.TranslationSchemes.Syntax-directeddefinitionsHigh-levelspecificationsfortranslations.Hideimplementationdetails.NoneedtospecifyexplicitlytheorderinwhichtranslationtakesplaceEE1+E2{E.val=E1.val+E2.val}TranslationSchemeIndicatetheorderinwhichsemant

5、icrulesaretobeevaluatedAllowsomeimplementationdetailstobeshown.ConceptualViewofSyntax-DirectedTranslation(1)InputstringParsetreeDependencygraphEvaluationorderforsemanticrulesConceptualViewofSyntax-DirectedTranslation(2)Specialcasesofsyntax-directeddefinitionscanbeimplementedinasi

6、nglepassbyevaluatingsemanticrulesduringparsing,withoutexplicitlyconstructingaparsetreeoragraphshowingdependenciesbetweenattributes.Syntax-directedDefinitionAgeneralizationofacontext-freegrammarinwhicheachgrammarsymbolhasanassociatedsetofattributes.TypesofAttributeSynthesizedAttri

7、buteThevalueofasynthesizedattributeatanodeiscomputedfromthevaluesofattributesatthechildrenofthatnodeintheparsetree.InheritedAttributeThevalueofaninheritedattributeiscomputedfromthevaluesofattributesatthesiblingsandparentofthatnode.AnnotatedParseTreeAparsetreeshowingthevaluesofatt

8、ributesateachnodeTheprocessofcomputingth